Advanced Hot Reservoir Variable Conductance Heat Pipes for Planetary Landers

Kuan-Lin Lee[1], Calin Tarau[2] , Andy Lutz[3] and William G. Anderson[4]
Advanced Cooling Technologies ,Inc, Lancaster, PA, 17601

and

Cho-Ning Huang[5], Chirag Kharangate[6] and Yasuhiro Kamotani[7]
Case Western Reserve University, Cleveland, OH, 44106

The next generation of Lunar rovers and landers requires variable thermal links to maintain payload temperatures nearly constant over wide sink temperature fluctuations.  It has been demonstrated on earth that a hot reservoir variable conductance heat pipe (VCHP) can provide a much tighter passive thermal control capability compared to a conventional VCHP with a cold-biased reservoir. However, previous ISS test results revealed that the fluid management of a hot reservoir VCHP needs to be improved to ensure its long-term reliability. Under an STTR Phase I program, Advanced Cooling Technologies, Inc. in collaboration with Case Western Reserve University performed fundamental research to understand the complex transport phenomena within a hot reservoir VCHP. A novel loop VCHP configuration was developed during the program. This loop design allows a net flow to be induced and circulate along the NCG tubing system, which will continuously remove the excessive working fluid from the reservoir (i.e. purging) in a much faster rate compared to diffusion alone. Two potential mechanisms to induce net transport flow were identified:

1. By momentum transfer from  vapor to NCG through shearing in the condenser/front region. It was called “DC” mechanism.
2. By filtering the pulses (via a tesla/check valve) generated in the heat pipe section of VCHP loop. It was called “AC” mechanism.

Although these two mechanisms are independent, the AC mechanism can be further added/superimposed on the top of the DC mechanism to achieve a higher flow rate. This paper presents the work performed in Phase I to prove the existence of momentum transfer flow (“DC flow) and its effectiveness on VCHP purging. The work includes theoretical analysis, numerical modeling, prototype development and experimental demonstration.

Nomenclature

AC            =   fluctuating component of the flow within a loop VCHP
DC           =    constant component of the flow within a loop VCHP
D              =    diffusion coefficient
LNCG       =    length of NCG tube
RNCG        =    internal radius of NCG tube
U              =    average induced flow velocity
µ               =    viscosity of NCG
ψ               =    vapor concentration in the reservoir
Δp             =    pressure difference between inlet and outlet of NCG tube

I.      Introduction

NASA’s plans to further expand human and robotic presence in space automatically involve significant challenges. Spacecraft architectures will need to handle unprecedented thermal environments in deep space. In addition, there is a need to extend the duration of the missions in both cold and hot environments, including cis-lunar and planetary surface excursions. The heat rejection turn–down ratio of the increased thermal loads in the above-mentioned conditions is crucial for minimizing the usage of vehicle resources (e.g. power). Therefore, future exploration activities will need thermal management systems that can provide higher reliability and performance, and, at the same time, with reduced power and mass. To meet these requirements, passive thermal management concepts that offer large turn-down ratios are highly encouraged. As an example, the anchor node network (which is a lander that includes a seismometer, a laser reflector, and a probe for measuring heat flow from the Moon’s interior) has a Warm Electronics Box (WEB) and a battery, both of which must be maintained in a fairly narrow temperature range.  A variable thermal link between the WEB and radiator is required.  During the day, the thermal link must transfer heat from the WEB electronics to the radiator as efficiently as possible, with minimum thermal resistance, to minimize the radiator size.  On the other hand, the thermal link must be as ineffective as possible (provide as high thermal resistance as possible) during the Lunar night.  This will keep the electronics and battery warm with minimal power, even with the very low temperature (100 K) heat sink.  At this time, heat must be shared between the electronics and battery, to keep the battery warm. Moreover, since the cold lunar night is very long (14 days) minimizing or even eliminating the survival power is highly desired. This can be done with a passive variable thermal link between the WEB and the Radiator. This variable thermal link can be a hot reservoir variable conductance heat pipe (VCHP).

Figure 1. (a) Analytical thermal control predictions for two VCHP hot and cold reservoir configuration with five different working fluids: Methanol, Toluene, Pentane, Ammonia and Propylene3 (b) VCHP with an integrated hot reservoir for ISS test

It was already demonstrated both analytically and experimentally[1],[2],[3] that hot reservoir VCHPs would offer tight passive thermal control as opposed to the traditional cold biased reservoir VCHPs that, for the same tightness of thermal control need reservoir heating. Figure 1 shows analytical thermal control predictions for two VCHP hot (Configuration 1) and cold (Configuration 2) reservoir designs with five different working fluids: Methanol, Toluene, Pentane, Ammonia and Propylene. As seen, the hot reservoir configuration shows a much narrower vapor temperature band compared to the cold reservoir configuration, as sink temperature sweeps vary between -90℃ and 40℃.

The hot reservoir VCHP was tested on ISS in 2017 as part of the Advanced Passive Thermal experiment (APTx) project[4]. While the ground testing was a success, the microgravity testing failed. The pipe showed higher than admissible temperatures that tripped the safety thermostats. The explanation of the failure is as follows: during startup, the absence of natural convection in the reservoir delayed the non-condensable gas (NCG) heating compared to the vapor heating which is much more effective because of the metallic (copper) path of the incoming heat. The consequence was that vapor pressure increased faster than NCG pressure (because of poor heating) and the resulted pressure wave pushed vapor into the reservoir (where colder NCG was present), where part of it condensed. As a result, the NCG was displaced out in the condenser increasing vapor temperature considerably. The next step was the attempt to remove vapor from the reservoir by applying heat to the reservoir, which is referred to as the “purging process”. It was found that the rate of purging was very low. The slow purging rate became a show stopper for the experiment.

Based on the ISS test results, it was concluded that fluid management within the reservoir and the NCG tube (typically non-wicked) of VCHPs is the key area to be improved. Advanced features/solutions that can (1) prevent working fluid condensing inside a reservoir and (2) remove working fluid from the reservoir efficiently are needed to support foreseeable long-term warm reservoir VCHP space operations. Under this STTR program, Advanced Cooling Technologies, Inc (ACT) in collaboration with Case Western Reserve University (CWRU) perform a detailed and fundamental study to understand complex transport phenomena of multi-species within a hot reservoir VCHP.  A novel “Loop hot reservoir VCHP” configuration resulted from this study, which can potentially enhance VCHP’s reliability in both ground and microgravity operations.

[1] R&D Engineer III, Advanced Cooling Technologies, Inc., 1046 New Holland Ave., Lancaster, PA 17601
[2] Principal Engineer, Advanced Cooling Technologies, Inc., 1046 New Holland Ave., Lancaster, PA 17601
[3] R&D Engineer II, Advanced Cooling Technologies, Inc., 1046 New Holland Ave., Lancaster, PA 17601
[4] Chief Engineer, Advanced Cooling Technologies, Inc., 1046 New Holland Ave., Lancaster, PA 17601
[5] Graduate Student, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106
[6] Assistant Professor, Case Western Reserve University,10900 Euclid Ave., Cleveland, OH 44106
[7] Professor, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106

II.      Loop Hot Reservoir VCHP Configuration

 

Figure 2. Regular VCHP with integrated warm reservoir (Green: NCG rich gas; Yellow: Vapor rich gas)

 

As depicted in Figure 2, a regular hot reservoir VCHP uses only one internal NCG tube connecting the reservoir with the condenser. A loop hot reservoir VCHP concept is illustrated in Figure 3. This novel configuration consists of a hot reservoir VCHP and two NCG tubes. One tube (internal) coming out from the NCG reservoir goes into the heat pipe section from the evaporator end. A second tube externally connects the end of the condenser with the reservoir. This loop configuration would allow a secondary (the vapor flow is considered as “primary”) fluid flow to be induced and move along the loop in the favorable direction (reservoir-internal tube-condenser) for purging (indicated with the black arrows). The mechanism to induce the secondary flow (i.e. transport flow) is as follows,

Figure 3. Loop Hot Reservoir VCHP (Green: NCG rich gas; Yellow: Vapor rich gas)

  1. A strong vapor flow (i.e. primary flow) is generated in the heat pipe section due to evaporation and condensation of the working fluid.
  2. The primary flow will carry momentum in axial direction. As the vapor passes by the end of the internal NCG tube, some of the momentum will be transferred to the NCG stream through the shear between two species as well as a low static pressure point is created at the end (entrance) of the NCG tube.
  3. Both the momentum transfer from vapor flow to NCG at the interaction region (shown in Figure 2) as well as the low-pressure point would induce a flow of NCG in a preferential direction.

Compared to the primary flow (vapor) velocity, the secondary flow (mostly NCG) is relatively weak but it would still be beneficial for VCHP purging in the following aspects,

  1. During startup, this flow will condition the VCHP by transporting NCG-vapor mixture from the reservoir to the condenser via the internal NCG tube. This reduces the vapor concentration (NCG humidity) in the reservoir by bringing dryer NCG from the condenser via the external tube.
  2. This secondary flow exists all the time as long as vapor flow exists within the heat pipe section. Therefore, the vapor concentration within the reservoir can be maintained at low (design) values all the time.
  3. Based on the above-described mechanism, heating of the reservoir (to encourage purging) may be eliminated.
  4. This convective-based purging will be significantly more effective than the diffusion-based purging. Diffusion is basically governed by concentration gradient between reservoir and condenser, so the rate of purging will decay as the concentration gradient decreases. But the convection-based purging rate is all thermally driven for as long as power/heat is transferred by the VCHP.

III.      Concept Feasibility Study – Numerical and Theoretical Analysis

A.   Diffusion-based Purging Model

Figure 4. Computational domain of purging model

 

To study the purging process of a hot reservoir VCHP, a CFD-based model was developed and by CWRU. The computational domain is shown in Figure 4. For simplicity, an axisymmetric model was considered where a thin NCG pipe is connected to a cylindrical reservoir at the center. This is a simplified version of the heat pipe internal tube, condenser and reservoir sections. The NCG pipe is cooled at the other end, which induces the condensation of the vapor. It is assumed that a uniform mixture of vapor and NCG exists before the cooling. After the start of cooling, the concentration of the vapor decreases gradually starting from the cooling section. Eventually, by diffusion process, the vapor concentration of the whole system is reduced to the value dictated by the cooling section temperature.

The vapor concentration (ψ) is determined by solving the diffusion equation.

Formula 1

The diffusion coefficient, D, changes with the temperature and pressure within the system.

      Formula 2         

where D = D0 at T0 = 273 K (0°C) and P0 = 1 atm (101 kPa).   Except for the condenser, all other walls are assumed to be insulated. A mixture of water vapor and helium (NCG) is considered in the present analysis. Before the cooling starts, the mixture everywhere is assumed to be 50% water vapor and 50% helium at a temperature of 30°C. After time = 0, the cooling wall temperature is set at 10°C.  For this mixture, D0 is estimated to be equal to 2 × 10-5 m2/s. The mixture temperature changes from 30°C to 10°C in the process. The variation of vapor concentration within the reservoir is shown in Figure 5.

Figure 5. Variation of vapor concentration within the reservoir with time for (a) various length of NCG tubes (ID 1.2 mm) and (b) various NCG tube diameters

Figure 5(a) shows how the values of ψmax change with time for several values of NCG pipe lengths. As the figure shows, diffusion (or purging) is a very slow process due to the fact that the mass transfer rate through the thin NCG pipe is limited. Although the total purging time depends on how we define the acceptable value of  ψmax, the purging will take several days if the pipe length is longer than about 10 cm.  The effect of the pipe diameter on the purging process is shown in Figure 5(b). As seen in the figure, a diameter of 2.8 mm reduces the purging time to around 15 hours. The analysis results demonstrated that the purging by diffusion may take tens of hours or even days, which matches ACT’s past testing experience.

B.    Numerical Study of Hot Reservoir VCHP Loop

Another numerical model is developed by CWRU to study the interaction between vapor and NCG within a hot reservoir VCHP and verify the momentum inducing the flow mechanism described in the previous section. The computational domain is shown schematically in Figure 5. In this study the working fluid is acetone and the NCG is helium. The working temperatures are: 50, 60, 70, 80°C. It is assumed that the heat pipe operates in a gravity-assisted mode, so there is no wick structure. The pipe wall is made of aluminum. The relevant dimensions of the loop VCHP are summarized in Table 1. The amount of NCG is arbitrary determined such that the vapor-NCG interface is located halfway in the condenser section at 50°C. The interface moves more into the condenser section with an increase in operating temperature. The cooling is assumed to be done by forced convection cooling with a specified heat transfer coefficient. The heat transfer coefficient is specified such that the heat input is nearly equal to 30W at 50°C with the ambient temperature equal to 20°C. Since the phenomena in the evaporator are not the focus in the present study, it is assumed that the evaporator simply generates enough vapor to balance the amount of condensation in steady-state, so that the vapor flow is analyzed only in the adiabatic and condenser sections. The total pipe length (heat pipe and loop) is assumed to be 1 m. Since the NCG pipe is long and thin and the flow through the pipe is expected to be on the order of mm/s, the flow in the pipe can be assumed to be fully developed. Therefore, instead of analyzing the pipe flow in detail, the known pressure drop-velocity relation for fully-developed pipe flow is used. The relation can be written as

     Formula 3

The computed pressure difference (∆P) within a heat pipe with an internal NCG tube is about 0.1 Pa. Even though the pressure difference is small, it is enough to generate appreciable flow. For example, 0.1 Pa of pressure difference can induce around 3.4 mm/s of flow (calculated based on Equation (3)).

Figure 6. Schematic of VCHP loop

Table 1. Dimensions of hot reservoir VCHP Loop for numerical study

Figure 7. (a) Average velocity through the NCG pipe vs. NCG pipe outlet location. (b) Average velocity through the NCG pipe vs. heat input

The dependence of the velocity on the NCG pipe outlet location is shown in Figure 7 (a). The velocity increases as LNCG becomes smaller. This happens because as the NCG pipe recedes (LNCG becomes smaller), the friction effect on the vapor flow in the heat pipe decreases so that the stagnation pressure (or the pressure in the NCG region) increases. For the condition of Figure 7 (a), the maximum velocity through the NCG pipe is about 4 mm/s. Figure 7 (b) shows how the velocity changes with Q while keeping Tsat constant. Q is changed from 8.9 to 41.5 W by changing the heat transfer coefficient for the cooling from 44 to 435 Wm-2∙K-1. The pipe flow velocity increases almost linearly with Q.

Figure 8. (a) Induced flow velocity vs. temperature with constant Q (b) Induced flow velocity and Q vs. temperature with constant heat transfer coefficient for cooling

The effect of working temperature on the average NCG flow velocity is also numerically investigated. The relation between working temperature and induced NCG flow velocity when Q is fixed at 31W is presented in  Figure 8(a). This figure shows that the velocity decreases with temperature.  This occurs because as the vapor temperature increases, vapor density increases as well, which results in a decelerating vapor flow (for fixed Q), and therefore, the shearing effect on NCG decreases. To be noted is the fact that, in this case, the front goes away from the NCG tube which, according to modeling results, would increase the pressure difference. However, vapor velocity decrease dominates. Next, the combination effects of Q and the interface location with constant cooling rate is studied, which is shown in Figure 8 (b).  As shown above, the effect of Q on the velocity is opposite to that of the interface location: increasing Q increases average flow velocity but moving the vapor front further away from the NCG tube end decreases the flow velocity.

Axial velocity profile along the cross-section A-A (aligned with the NCG pipe outlet) is presented in Figure 9. Since the NCG flow coming out from the internal tube is very small compared to the primary vapor velocity (~0.25 cm/s), it is very difficult to observe in the figure that there is a non-zero velocity near the center core (r = 0). In summary, utilizing this loop based VCHP concept, it is possible to obtain a sufficiently large velocity through the external pipe so that the purging can be accomplished within several minutes, which represents a significant improvement compared to the diffusion-based purging process discussed above. It is also found through simulation that multiple design parameters will affect the induced flow velocity, including

  • Figure 9. Velocity distribution across A-A section (induced flow velocity in the center is around 3 mm/s)

    Internal NCG tube end location and vapor front location.

  • Heat input.
  • Vapor temperature.
  • Annular space between heat pipe and NCG tube.
  • Gravity level and orientation of the pipe.

IV.      Concept Feasibility Study – Experimental Validation

A.   Experimental apparatus

Figure 10. Schematic of experimental apparatus for Loop VCHP concept feasibility demonstration

In parallel to the mathematical study, an experimental demonstration was conducted by ACT to prove the existence of the momentum transport flow within a VCHP Loop.  The schematic experimental system is shown in Figure 10 and the actual test setup is shown in Figure 11. The test apparatus consists of a VCHP with a non-integrated reservoir and an external NCG tube connecting between the condenser and the reservoir. The structural material is stainless steel. Working fluid and NCG are acetone and helium. The heat pipe section is in a slight gravity-aid orientation (< 5°) and there is no wick structure inserted within the adiabatic and condenser sections for liquid return. According to the findings from numerical analysis (Figure 8(a)), the internal NCG tube length was adjusted so it ends in the adiabatic section before the condenser to obtain a higher induced flow velocity. Temperatures at various locations along the heat pipe and the loop are measured by 26 TCs. The key dimensions of the test setup are summarized in Table 2.

Figure 11. Experimental apparatus of the VCHP loop concept demonstration

Table 2. Dimensions of the component of the VCHP Loop experimental apparatus

Measuring the secondary flow induced by the primary vapor flow, a gas flow transducer (Omega FMA 1702A) is mounted in the line of the external NCG loop. This flow meter has no moving parts and uses thermal-based technique to measure gas flow rate (hot wire anemometry). The measurement range of this flow meter is 0 to 10 cc/min. A very important fact is that this flow meter measures flow in only one direction. It allows however reverse flow but it reports “zero” flow rate in the DAQ system.

B.    Thermal Control Capability Demonstration

Figure 12. (a) VCHP test loop operation at 80 W with step change in sink temperature (b) Instantaneous heat pipe temperatures of VCHP test loop at 75 °C hot sink temperature and -10 °C cold sink temperature

A thermal control testing is performed to assess/verify that adding an external NCG loop to hot reservoir VCHPs will not compromise the thermal control capability of the VCHP. Figure 12(a) shows the operation of the VCHP loop at 80 W. At t = 2200 seconds, sink temperature is suddenly decreased from 75 °C to -10 °C. As the figure shows, the variation of evaporator temperature is less than 10 °C. Instantaneous temperature profiles\ of the heat pipe at steady state before and after a decrease of sink temperature are shown in Figure 12(b). It can be observed that the vapor NCG front is located beyond the end of the condenser during the hot sink temperature mode before the step change. Then, the vapor NCG-front moves to reduce the active condenser length after the sink temperature drops. The new front is located at end of the adiabatic section. Based on these test results, it is reasonable to state that adding an external NCG loop to a hot reservoir VCHP has minimal impact on its thermal control capability.

C.   Flow Measurements

Figure 13 shows the temperature evolution of the Loop VCHP and the corresponding flow rate measured by the flow meter. For this test, an amount of 6 ml of acetone was charged.

  • As the vapor/NCG is established within the condenser (shown as a purple line merging with the light blue line), an oscillating flow is observed.
  • The amplitude of oscillations is at around 1.5 sccm before the valve connecting heat pipe and loop is closed.
  • Immediately after closing the valve (t =8200 sec), the amplitude dramatically increases.
  • As mentioned above, the flow meter cannot detect the flow in the opposite direction. All the “zero” values observed in this plot indicate that a reverse flow is passing the flow meter.

Figure 13. Temperature of VCHP Loop vs. secondary flow rate

Flow test results reveal that the flow within the current Loop VCHP is a pulsating flow.  One of the probable causes of these pulses is the puddle formation in the evaporator. Since the heat pipe is slightly tilted, the excess working fluid liquid will accumulate at the bottom of evaporator and form a puddle. The expansion and collapse of bubbles might generate pressure waves. Another hypothesis of the origin of these pressure waves is the liquid slug forming in the condenser. Both phenomenon (puddle and slug formation within a heat pipe) are gravity-dependent and related to wick design. In microgravity, puddles and slugs might not form within a wicked heat pipe (either sintered powder or screen). However, liquid bodies and slugs could form within a grooved heat pipe in microgravity. Further investigation/assessements are needed for future space and planetary applications. This pressure wave generated from the heat pipe section propagates through the NCG tubes. The response of flow in the NCG tube will change depending on the status of the valve

  • If the valve is open, the pressure wave will propagate through both sides of NCG tube (external and internal) and partially cancel each other. The amplitude of the pulses is small.
  • If the valve is closed, pressure wave will propagate through only one side of NCG tube (internal) and the flow meter will experience a higher amplitude of oscillation.

Based on this finding, two potential mechanisms associated with Loop VCHP configuration to induce/enhance a net flow for purging are identified:

  • Flow induced by the momentum generated in the NCG tube through pressure variation (original mechanism). This mechanism is called “DC” mechanism.
  • Flow induced by filtering (via a Tesla or a check valve) the pulse generated within the heat pipe section. This mechanism is called “AC” mechanism.

Note that the DC and AC mechanisms are independent in this context, meaning that they can be superimposed to induce a higher net mass flow rate within a loop VCHP.

D.   Momentum Transfer Flow (DC Mechanism) Identification

Figure 14. Momentum transport induced flow rate increases as the heat input increases

The flow induced by DC mechanism is embedded within the total flow with pulses. In order to detect the flow, it is necessary to minimize the amplitude of the pulses. This is done by inserting a layer of screen mesh into the evaporator section and minimizing fluid inventory to avoid puddle formation in the evaporator. Test results are shown in Figure 14. The red line represents the heat input to the evaporator and the blue line represents the induced net flow rate. With a 2 ml of working fluid inventory, pulse amplitude is minimized to be within the resolution of the flow meter. A clear relationship between the induced flow rate and the heat input can be identified. The flow rate of induced flow increases as the heat input increases. With 72W of heat input, the net flow velocity being induced is 0.8 cm/min (0.13 mm/s). All the evidence points to the same conclusion: there is a net flow induced by the momentum transfer from the vapor to NCG within the Loop VCHP. The existence of DC flow is successfully proven.

V.      Prototype Development and Performance Demonstration

Figure 15. (a) Hot Reservoir VCHP Loop prototype (b) testing system

A hot Reservoir VCHP loop prototype is then developed for concept demonstration, which is shown in Figure 15(a). This VCHP prototype has an integrated reservoir similar to the VCHPs previously developed under another NASA Phase II program. This prototype consists of several parts, including reservoir, condenser, internal NCG tube, heat pipe adiabatic section and the external NCG tube. These parts are joined by Swagelok fittings, so they can be exchangeable. The working fluid is acetone and NCG is helium. No wick structure is inserted within the heat pipe adiabatic and condenser sections. liquid return is simply achieved by gravity. Similar to the loop VCHP experimental setup, a layer of screen is inserted into the evaporator to avoid puddle formation. There are two fill tubes in this prototype: one fill tube attached to the end of the condenser is for working fluid and NCG charging; another fill tube welded on the top of the reservoir is used for the purging test only. The experimental system for VCHP prototype testing is shown in Figure 15(b). Heating to the evaporator is provided by a heater block from the bottom of the evaporator. The cooling of the condenser is provided by a chiller block. The instrumentation includes 25 T-type TCs and the flow meter to measure the induced flow rate through the NCG loop. Two DAQ systems (one for temperature and one for flow meter) are simultaneously operating to collect both temperature and flow data.

Figure 16. Purging performance of Hot Reservoir VCHP Loop

The purging performance of this prototype was tested and the result are shown in Figure 16. At t=t0, heat input incrementally increases from 110W to 140W. At t=t1, 0.3 ml of acetone, which is 12% of the working fluid inventory is directly injected into the reservoir. Immediately, payload temperatures increase and condenser temperatures decrease, meaning that the vapor front is pushed towards the adiabatic section decreasing the active length of the condenser. Monitoring payload temperature decaying rate between t2 and t3 it can be observed that the average dropping rate is around -4°C in 3000 seconds. The corresponding induced flow rate measured by the flow meter is around 0.16 ml/min. Compared to a regular hot reservoir VCHP without a loop, the purging speed of this prototype is 6.7 times faster. This test results conclude that new loop configuration and the induced flow concept does improve the purge rate and reliability of VCHP.

Still, there is significant room for improvement. ACT and CWRU team believe that an even higher induced flow can be achieved by design optimization and implementation of other features (e.g. pulse filtering devices and nozzles etc.). Figure 17 below shows how effective the purging process would be if a transport flow can be induced within the Loop VCHP. This calculation assumes that an NCG reservoir volume of 100 c.c. contains 50% of vapor initially and the internal NCG tube (with 0.18”ID) has a length of 50 cm. Purging by diffusion will take roughly 24 hours to reduce vapor concentration within the reservoir from 50% to 35%. If a 0.5 mm/s of transport flow can be induced within the loop VCHP, it will only take 6 hours to achieve the same level of concentration reduction (from 50% to 35%). If a 20 mm/s flow velocity within a VCHP loop can be achieved (through superimposing DC and AC mechanisms discussed above), purging time can be significantly reduced to less than 10 mins. To achieve a higher flow rate in the loop VCHP, the ACT-CWRU team plans to (1) systematically study the momentum induced flow and identify influential design parameters (2) develop features that can amplify the momentum induced flow and (3) develop pules filtering devices to obtain a net flow from pulses.

VI.      Conclusion

Figure 17. Convection-based purging rate vs. diffusion-based purging rate

Under this STTR Phase I, ACT and CWRU performed a fundamental investigation to understand the complex transport phenomena within a hot reservoir VCHP. In order to address the slow purging problem of a hot reservoir VCHP, a novel loop configuration is developed that uses an external NCG tube connecting the reservoir and the condenser to create a closed flow path for NCG to replenish the reservoir. With the loop configuration, the momentum of vapor within the heat pipe section will generate a pressure difference that can induce a net NCG flow in a favorable direction for reservoir purging (i.e. removal of vapor from the reservoir). Modeling results demonstrate the possibility of flow generation through momentum transport/transfer in a Loop hot reservoir VCHP. A Loop VCHP experiment is performed and the following key findings are identified:

  • Thermal control capability of hot reservoir VCHP is not affected by adding a loop.
  • Flow within a hot reservoir VCHP loop is pulsating.
  • The momentum transfer based induced flow is successfully identified using an accurate gas flow meter.

In addition, two independent mechanisms that can induce a net flow are identified:

  1. By the momentum transfer from the vapor to NCG through shearing. This mechanism is called “DC” mechanism .
  2. By filtering the pulses generated within Loop VCHP, using a fluid diode (e.g. Tesla valve). This mechanism is called “AC” mechanism.

These two mechanisms are independent, so they can be superimposed to induce a higher flow rate for purging.  A proof-of-concept prototype that has an integrated evaporator and reservoir design similar to the hardward tested at ISS is developed. The thermal control capability and momentum induced flow of the prototype are experimentally demonstrated. The reliability of the prototype is also tested, which shows a 6.7 times of purging rate improvement compared to regular hot reservoir VCHP without loop and induced flow. If a 20 mm/s flow velocity within a VCHP loop can be achieved (through superimposing DC and AC mechanisms discussed above), purging time can be significantly reduced to less than 10 mins.

Acknowledgments

This project is sponsored by NASA Marshall Space Flight Center (MSFC) under an STTR Phase I program (Contract# 80NSSC18P2155). We would like to thank the program manager, Brian O’Connor and Dr. Jeff Farmer for their supports and valuable inputs during the program. Special appreciation goes to Philip Texter and Chris Jarmoski who have provided significant technical contributions to the program.

References

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[2] Tarau C., Schwendeman C. L., Anderson W.G., Cornell P.A. and Schifer N.A., “Variable Conductance Heat Pipe Operated with Stirling Convertor”, in IECEC, 2013
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Bradley Richard et al., 49th International Conference on Environmental Systems (ICES), Boston, Massachusetts, July 7-11 2019

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24 Hour Consumable-based Cooling System for Venus Lander

Kuan-Lin Lee and Calin Tarau, 49th International Conference on Environmental Systems (ICES), Boston, Massachusetts, July 7-11 2019

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Thermal Control of Lunar and Mars Rovers/Landers Using Hybrid Heat Pipes

Mohammed T. Ababneh et al, Journal of Thermophysics and Heat Transfer, Vol. 33(3), July 2019

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Mohammed T. Ababneh et al., 49th International Conference on Environmental Systems (ICES), Boston, Massachusetts, July 7-11 2019

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Performance Evaluation of a Loop Thermosyphon Based Heat-Sink for High Power SiC-based Converter Applications

Sayan Acharya, et al., IEEE: Transactions on Components, Packaging and Manufacturing Technology, June 17 2019, 1-1

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Bradley Richard, et al., Semi-Therm, San Jose, CA, March 18 – 22 2019

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Fangyu Cao and Jianjian Wang, 4th Thermal & Fluids Engineering Conference, Las Vegas, NV, April 14-17 2019

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Advances in Lightweight Heat Sinks

Mohammad Reza Shaeri and Richard Bonner, 4th Thermal & Fluids Engineering Conference, Las Vegas, NV, April 14-17 2019

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A Nonlocal Peridynamics Modeling Approach for Corrosion Damage and Crack Propagation

Srujan Rokkam, et al., Theoretical and Applied Fracture Mechanics, 101, 2019, 373–387 (2019)

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Vortex dynamics and heat transfer of longitudinal vortex generators in a rectangular channel

Zhaoqing Ke, et al., International Journal of Heat and Mass Transfer, 132, 875-885 (2019)

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Meshless Peridynamics Method for Modeling Corrosion Crack Propagation

Srujan Rokkam, et al., 6th International Crack Paths Conference, Verona, Italy, September 19-21 2018

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Bio-inspired self-agitator for convective heat transfer enhancement

Zheng Li et al., Applied Physical Letters 113, 113703 (2018)

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Corrosion testing of metals in contact with calcium chloride hexahydrate used for thermal energy storage

S. J. Ren et al., Materials and Corrosion, Volume 68, Issue 10, July 2017

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Fangyu Cao et al., Proceedings of the 16th International Heat Transfer Conference, Bejing, China, August 10-15, 2018

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Loop Heat Pipe Wick Fabrication via Additive Manufacturing

Bradley Richard et al., 48th International Conference on Environmental Systems, Albuquerque, New Mexico, July 8-12, 2018

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Design Analysis and Performance testing of a Novel Passive Thermal Management System for Future Exploration Missions

Angel R. Alvarez-Hernandez et al., International Conference on Environmental Systems, Albuquerque, NM July 8-12, 2018

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High-Heat-Flux (> 50 W/cm2) Hybrid Constant Conductance Heat Pipes

Mohammed T. Ababneh et al. International Conference on Environmental Systems, Albuquerque, NM, July 8-12, 2018

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Demonstration of Copper-Water Heat Pipes Embedded in High Conductivity (HiK™) Plates in the Advanced Passive Thermal eXperiment (APTx) on the International Space Station (ISS)

Mohammed T. Ababneh et al., International Conference on Environmental Systems, Albuquerque, NM July 8-12, 2018

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Advanced Passive Thermal eXperiment (APTx) for Warm-Reservoir Hybrid-Wick Variable Conductance Heat Pipes on the International Space Station (ISS),”

Calin Tarau, et al., International Conference on Environmental Systems (ICES 2018), Albuquerque, NM July 8-12, 2018

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Apparatus for Characterizing Hot Surface Ignition of Aviation Fuels

Andrew Slippey et al., AIAA Propulsion and Energy Forum, (AIAA 2018-4708), Cincinnati, OH, July 9-12, 2018

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Titanium Water Heat Pipe Radiators for Space Fission System Thermal Management

Kuan-Lin Lee, et al., 19th International Heat Pipe Conference, Pisa, Italy, June 10-14, 2018

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Copper-Water and Hybrid Aluminum-Ammonia Heat Pipes for Spacecraft Thermal Control Applications

Mohammed Ababneh, et al., 19th International Heat Pipe Conference, Pisa, Italy, June 10-14, 2018

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Loop Heat Pipe Wick Fabrication via Additive Manufacturing

Bradley Richard, et al., 19th International Heat Pipe Conference, Pisa, Italy, June 10-14, 2018

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Meshless Computational tools for Fatigue Damage and Failure Modeling

Srujan Rokkam et al., ITHERM 2018 (17th Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems), San Diego, CA, May 29 – June 1

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Thermal Management Technologies for Embedded Cooling Applications

Andy Slippey et al., ITHERM 2018 (17th Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems), San Diego, CA, May 29 – June 1

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Experimental Investigation of Gravity-Driven Two-Phase Cooling for Power Electronics Applications

Devin Pellicone, PCIM 2018, Nuremberg, Germany, June 5-7, 2018.

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Experimental, Numerical and Analytic Study of Unconstrained Melting in a Vertical Cylinder with a Focus on Mushy Region Effects

Chunjian Pan,⇑, Joshua Charles, Natasha Vermaak, Carlos Romero, Sudhakar Neti, Energy Research Center, Lehigh University, Bethlehem, PA 18015, USA Ying Zheng, Chien-Hua Chen, Richard Bonner III, Advanced Cooling Technologies, Inc., Lancaster, PA 17601, USA International Journal of Heat and Mass Transfer, Accepted 2 April 2018

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A Non-Thermal Gliding Arc Plasma Reformer for Syngas Production

Howard Pearlman, 3rd Thermal and Fluids Engineering Conference (TFEC), Fort Lauderdale, FL, March 4-7, 2018

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An Innovative Volatile Organic Compound Incinerator

Joel Crawmer et al., International Thermal Treatment Technologies (IT3), Houston, TX, March 6-8 2018

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Developing High-Temperature Water-Repellent Glass Fibers Through Atomic Layer Deposition

Mohammad Reza Shaeri et al., 3rd Thermal and Fluids Engineering Conference (TFEC), Fort Lauderdale, FL, March 4-7, 2018.

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Dropwise Condensation on Hydrophobic Microporous Powder and the Transition to Intrapowder Droplet Removal

Sean Hoenig and Richard W. Bonner, III, 3rd Thermal and Fluids Engineering Conference (TFEC), Fort Lauderdale, FL, March 4-7, 2018.

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The Key Role of Pumping Power in Active Cooling Systems

Mohammed Reza Shaeri, 3rd Thermal and Fluids Engineering Conference (TFEC), Fort Lauderdale, FL, March 4-7, 2018.

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Nucleating agent enhanced thermal desalination at the triple point

Fangyu Cao et al., 3rd Thermal and Fluids Engineering Conference (TFEC), Fort Lauderdale, FL, March 4-7, 2018

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Titanium Water Heat Pipes for Space Fission Power Cooling

Kuan-Lin Lee et al. ANS NETS 2018 – Nuclear and Emerging Technologies for Space Las Vegas, NV, February 26 – March 1, 2018

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Dropwise Condensation on Superhydrophobic Microporous Wick Structures

Sean Hoenig, Richard Bonner, Ph.D., ASME doi:10.1115/1.4038854 History: Received April 28, 2017; Revised December 06, 2017

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A Peridynamics-FEM Approach for Crack Path Prediction in Fiber-Reinforced Composites

Srujan Rokkam et al., 2018 AIAA SciTech Forum, Kissimmee, FL, January 8-12, 2018.

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Vapor chambers with hydrophobic and biphilic evaporators in moderate to high heat flux applications

Mohammad Reza Shaeri, Daniel Attinger, Richard W. Bonner III, Applied Thermal Engineering, Volume 130(5), Pages 83-92, February 2018

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Model-Based Dynamic Control of Active Thermal Management System

ASME 2017 International Mechanical Engineering Congress and Exposition IMECE 2017 - 71918, November 3-9, 2017 Tampa, FL. Nathan Van Velson, Srujan Rokkam, Quang Truong, Bryan Rasmussen

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Efficient optimization of a longitudinal finned heat pipe structure for a latent thermal energy storage system

Sean Hoenig et al., Energy Conversion and Management, 153, pp. 93-105, 2017.

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The Electroneutrality Constraint in Nonlocal Models

Eitan Lees, Srujan Rokkam, Sachin Shanbhag, and Max Gunzburger. Journal of Chemical Physics 147, 124102 (2017)

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Heat Pipe Embedded Thermoelectric Generator for Diesel Generator Set Waste Heat Recovery

James Schmidt and Mohammed Ababneh. 14th International Energy Conversion Engineering Conference, AIAA Propulsion and Energy Forum, (AIAA 2016-4605)

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Efficient Modeling of Phase Change Material Solidification with Multidimensional Fins

C. Pan et al., International Journal of Heat and Mass Transfer, Vol. 115, Part A, pp. 897-909, December 2017.

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Integrated Vapor Chamber Heat Spreader for Power Module Applications

Clayton Hose et al., InterPACK 2017, San Francisco, CA, August 29 – September 1, 2017

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Heat transfer and pressure drop in laterally perforated-finned heat sinks across different flow regimes

Mohammad Reza Shaeri, Richard Bonner Advanced Cooling Technologies, Inc., Lancaster, PA 17601, United States , Available online 24 August 2017

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Feasibility Study of a Vapor Chamber with a Hydrophobic Evaporator Substrate in High Heat Flux Applications

Mohammad Reza Shaeria et al., International Communications in Heat and Mass Transfer, Vol. 86, pp. 199–205, 2017.

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Effect of Perforation Size to Perforation Spacing on Heat Transfer in Laterally Perforated-Finned Heat Sinks

Mohammed Reza Shaeri, and Richard W. Bonner III, ASME 2017 Summer Heat Transfer Conference (HT2017), July 9-14, 2017, Bellevue, Washington, USA

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Two-Phase Heat Exchanger with Thermal Storage Capability for Space Thermal Control System

Two-Phase Heat Exchanger with Thermal Storage Capability for Space Thermal Control System, Kuan-Lin Lee, et al. 47th International Conference on Environmental Systems (ICES 2017), July 16-20, 2017, Charleston, South Carolina

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Advanced Passive Thermal Experiment for Hybrid Variable Conductance Heat Pipes and HiK™ Plates on the International Space Station

Advanced Passive Thermal Experiment for Hybrid Variable Conductance Heat Pipes and HiK™ Plates on the International Space Station, Mohammed T. Ababneh, et al. 47th International Conference on Environmental Systems (ICES 2017), July 16-20, 2017, Charleston, South Carolina

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LHP Wick Fabrication via Additive Manufacturing

LHP Wick Fabrication via Additive Manufacturing. Bradley Richard, et al. 47th International Conference on Environmental Systems (ICES 2017), July 16-20, 2017, Charleston, South Carolina

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High Temperature Water Heat Pipes for Kilopower System

Derek Beard et al., IECEC – AIAA Propulsion and Energy Forum and Exposition (AIAA Propulsion and Energy 2017), July 10-12, Atlanta, Georgia

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Sodium Heat Pipes for Space and Surface Fission Power

Derek Beard, Calin Tarau, and William G. Anderson, IECEC – AIAA Propulsion and Energy Forum and Exposition (AIAA Propulsion and Energy 2017), July 10-12, Atlanta, Georgia

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Laminar Forced Convection Heat Transfer From Laterally Perforated-Finned Heat Sinks

Mohammad Reza Shaeri and Richard W. Bonner III, Applied Thermal Engineering, Volume 116, pp. 406-418, April 2017.

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An Innovative Volatile Organic Compound Incinerator

Joel Crawmer et al., 10th U. S. National Combustion Meeting, College Park, MD, April 23-26, 2017

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A Swiss Roll Style Combustion Reactor for Non-Catalytic Reforming

Ryan Zelinsky et al., 10th U. S. National Combustion Meeting, College Park, MD, April 23-26, 2017

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Thermal Resistance Network Model for Heat Pipe-PCM Based Cool Storage System

Sean Hoenig et al., 2nd Thermal and Fluid Engineering Conference (TFEC2017), Las Vegas, NV, April 2-5 2017.

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Development of Low Cost Radiator for Surface Fission Power

Calin Tarau et al., International Energy Conversion Engineering Conference (IECEC), Salt Lake City, UT, July 25-27, 2016

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Generation of amorphous carbon models using liquid quench method: A reactive molecular dynamics study.

Raghavan Ranganathan, Srujan Rokkam, Tapan Desai, Pawel Keblinski Carbon, Volume 113, March 2017, Pages 87–99

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Self-Venting Arterial Heat Pipes for Spacecraft Applications

Derek Beard, William G. Anderson, and Calin Tarau, International Energy Conversion Engineering Conference (IECEC), Salt Lake City, UT, July 25-27, 2016

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Hybrid Heat Pipes for Lunar and Martian Surface and High Heat Flux Space Applications

Mohammed T. Ababneh et al., International Conference on Environmental Systems (ICES) 2016, Vienna. Austria, July 11-14, 2016

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Development of a Pumped Two-phase System for Spacecraft Thermal Control

Michael C. Ellis and Richard C. Kurwitz, International Conference on Environmental Systems (ICES) 2016, Vienna. Austria, July 11-14, 2016

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Vapor Chamber with Phase Change Material-Based Wick Structure

James Yun, Calin Tarau, and Nathan Van Velson, International Conference on Environmental Systems (ICES) 2016, Vienna. Austria, July 11-14, 2016

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A Novel Closed System, Pressure Controlled Heat Pipe Design for High Stability Isothermal Furnace Liner Applications

Taylor Maxwell et al., 13th International Symposium on Temperature and Thermal Measurements in Industry and Science (TEMPMEKO 2016), Zakopane, Poland, June 26 – July 1, 2016

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Thermal Enhancements for Separable Thermal Mechanical Interfaces

James Schmidt et al., AIAA Thermophysics Conference, Washington, D.C., June 13-17, 2016

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The Design of a Split Loop Thermosyphon Heat Exchanger for Use in HVAC Applications

Daniel Reist et al., Joint 18th International Heat Pipe Conference and 12th International Heat Pipe Symposium, Jeju, Korea, June 12-16, 2016

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Hot Reservoir Stainless-Methanol Variable Conductance Heat Pipes for Constant Evaporator Temperature in Varying Ambient Conditions

Jens Weyant et al., Joint 18th International Heat Pipe Conference and 12th International Heat Pipe Symposium, Jeju, Korea, June 12-16, 2016

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Hybrid Variable and Constant Conductance Heat Pipes for Lunar and Martian Environments and High Heat Flux Space Applications

Mohammed T. Ababneh et al., Joint 18th International Heat Pipe Conference and 12th International Heat Pipe Symposium, Jeju, Korea, June 12-16, 2016

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Self-Venting Arterial Heat Pipes for Spacecraft Applications

William G. Anderson et al., Joint 18th International Heat Pipe Conference and 12th International Heat Pipe Symposium, Jeju, Korea, June 12-16, 2016

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Performance Life Testing of a Nanoscale Coating for Erosion and Corrosion Protection in Copper Microchannel Coolers

Nathan Van Velson and Matt Flannery, IEEE ITherm Conference, May 31-June 3, 2016, Las Vegas, NV

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Heat Pipes used as Heat Flux Transformers and for Remote Heat Rejection

Devin Pellicone and Jens Weyant, PCIM Europe 2016, Nuremberg, Germany, May 10-12, 2016

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Enhanced Filmwise Condensation with Thin Porous Coating

Ying Zheng, Chien-Hua Chen, Howard Pearlman, Richard Bonner, First Pacific Rim Thermal Engineering Conference, PRTEC, March 13-17, 2016, Hawaii's Big Island, USA.

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Optimized Alkali Metal Backup Cooling System Tested with a Stirling Convertor

Calin Tarau, Nuclear and Emerging Technologies for Space (NETS) 2016, Huntsville, AL, February 22-25, 2016.

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Status of the Development of Low Cost Radiator for Surface Fission Power II

Calin Tarau, Nuclear and Emerging Technologies for Space (NETS) 2016, Huntsville, AL, February 22-25, 2016.

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Passivation and Stabilization of Aluminum Nanoparticles for Energetic Materials

Matthew Flannery, Journal of Nanomaterials, vol. 2015, Received 17 June 2015; Accepted 13 October 2015

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Modeling high-temperature diffusion of gases in micro and mesoporous amorphous carbon

Raghavan Ranganathan, Srujan Rokkam, Tapan Desai, Pawel Keblinski, Peter Cross, and Richard Burnes, The Journal of Chemical Physics 143, 084701 (2015).

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Optimized Heat Pipe Backup Cooling System Tested with a Stirling Convertor

Carl L. Schwendeman, Calin Tarau, Nicholas A. Schifer, John Polak, and William G. Anderson, 13th International Energy Conversion Engineering Conference (IECEC), Orlando, FL, CA, July 27-29, 2015.

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Status of the Low-Cost Radiator for Fission Power Thermal Control

Taylor Maxwell, Calin Tarau, William G. Anderson, Scott Garner, Matthew Wrosch, and Maxwell H. Briggs, 13th International Energy Conversion Engineering Conference (IECEC), Orlando, FL, CA, July 27-29, 2015.

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Water-Titanium Heat Pipes for Spacecraft Fission Power

Rebecca Hay and William G. Anderson, 13th International Energy Conversion Engineering Conference (IECEC), Orlando, FL, CA, July 27-29, 2015.

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Two-Phase Thermal Switch for Spacecraft Passive Thermal Management

Nathan Van Velson, Calin Tarau, and William G. Anderson, 45th International Conference on Environmental Systems (IECS), Bellevue, WA, July 12-16, 2015.

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Multiple Loop Heat Pipe Radiator for Variable Heat Rejection in Future Spacecraft

Nathan Van Velson, Calin Tarau, Mike DeChristopher, and William G. Anderson, 45th International Conference on Environmental Systems (IECS), Bellevue, WA, July 12-16, 2015.

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Hybrid Heat Pipes for Planetary Surface and High Heat Flux Applications

Mohammed T. Ababneh, Calin Tarau, and William G. Anderson, 45th International Conference on Environmental Systems (IECS), Bellevue, WA, July 12-16, 2015.

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Experimental Investigation on the Thermal and Hydraulic Performance of Alumina–Water Nanofluids in Single-Phase Liquid-Cooled Cold Plates

Ehsan Yakhshi-Tafti, Sanjida Tamanna and Howard Pearlman, Journal of Heat Transfer, Vol. 137, July 1, 2015

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A “Swiss-Roll” Fuel Reformer: Experiments and Modeling

Chien-Hua Chen, Bradley Richard, Ying Zheng, Howard Pearlman, Shrey Trivedi, Srusti Koli, Andrew Lawson, and Paul Ronney, “A “Swiss-Roll” Fuel Reformer: Experiments and Modeling,” 9th U. S. National Combustion Meeting, Cincinnati, OH, May 17-20, 2015.

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Effect of Porous Coating on Condensation Heat Transfer

Ying Zheng, Chien-hua Chen, Howard Pearlman, Matt Flannery and Richard Bonner. 9th International Conference on Boiling and Condensation Heat Transfer, April 26-30, 2015, Boulder, Colorado.

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High Temperature Water-Titanium Heat Pipes for Spacecraft Fission Power

Rebecca Hay and William G. Anderson, Nuclear and Emerging Technologies for Space (NETS-2015), Albuquerque, NM, February 23-26, 2015.

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Nanoscale Coating for Microchannel Cooler Protection in High Powered Laser Diodes

Tapan Desai, Matthew Flannery, Nathan Van Velson, and Philip Griffin, “Nanoscale Coating for Microchannel Cooler Protection in High Powered Laser Diodes,” Semiconductor Thermal Measurement and Management Symposium (SEMI-THERM 2015), San Jose, CA, March 16-19, 2015.

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Fuel-Flexible Hybrid Solar Coal Gasification Reactor

M. Flannery et al., "Fuel-Flexible Hybrid Solar Coal Gasification Reactor," 2014 Pittsburgh Coal Conference, Pittsburgh, PA, October 6 - 9, 2014.

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Heat Pipe Embedded Carbon Fiber Reinforced Polymer Composite Enclosures for Avionics Thermal Management

Andrew Slippey, Michael C. Ellis, Bruce Conway, and Hyo Chang Yun. SAE 2014 Aerospace Systems and Technology Conference, Cincinnati, OH, September 23-25, 2014.

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Passive Thermal Management for Avionics in High Temperature Environments

Michael C. Ellis, William G. Anderson, and Jared R. Montgomery. SAE 2014 Aerospace Systems and Technology Conference, Cincinnati, OH, September 23-25, 2014.

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Passivation of Aluminum Nanoparticles by Plasma-Enhanced Chemical Vapor Deposition for Energetic Nanomaterials

T. Desai et al., ACS Applied Materials and Interfaces Journal, 2014, 6 (10), pp. 7942–7947, DOI: 10.1021/am5012707

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Thermal Modeling and Experimental Validation for High Thermal Conductivity Heat Pipe Thermal Ground Planes

Ababneh, Mohammed T., Shakti Chauhan, Pramod Chamarthy, and Frank M. Gerner. "Thermal Modeling and Experimental Validation for High Thermal Conductivity Heat Pipe Thermal Ground Planes." Journal of Heat Transfer 136, no. 11 (2014): 112901.

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Launch Vehicle Avionics Passive Thermal Management

W. G. Anderson et al., “Launch Vehicle Avionics Passive Thermal Management,” 44th International Conference on Environmental Systems (ICES 2014), Tucson, AZ, July 13-17, 2014.

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Low Cost Radiator for Fission Power Thermal Control

Taylor Maxwell et al, 12th International Energy Conversion Engineering Conference (IECEC), Cleveland, OH, July 28-30, 2014.

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Flow Boiling Heat Transfer Enhancement in Subcooled and Saturated Refrigerants in Minichannel Heat Sinks

E. Yakhshi-Tafti et al., ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting and 12th International Conference on Nanochannels, Microchannels, and Minichannels, August 3-7, 2014, Chicago, IL.

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Thermal-Fluid Modeling for High Thermal Conductivity Heat Pipe Thermal Ground Planes

M. T. Ababneh et al., published in the AIAA Journal of Thermophysics and Heat Transfer, Vol. 28, No. 2, pp. 270-278, April 2014.

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Thermoelectric Performance Model Development and Validation for a Selection and Design Tool

Thomas Nunnally, Devin Pellicone, Nathan Van Velson, James Schmidt, Tapan Desai, 2014 IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), Orlando, FL, May 27-30, 2014.

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High Heat Flux Heat Pipes Embedded in Metal Core Printed Circuit Boards for LED Thermal Management

Dan Pounds, Richard W. Bonner III, 2014 IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), Orlando, FL, May 27-30, 2014

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Enhancing Thermal Performance in Embedded Computing for Ruggedized Military and Avionics Applications

Darren Campo, Jens Weyant, Bryan Muzyka, 2014 IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), Orlando, FL, May 27-30, 2014.

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A Corrosion and Erosion Protection Coating for Complex Microchannel Coolers used in High Power Laser Diodes

Tapan G. Desai, Matthew Flannery, Angie Fan, Jens Weyant, Henry Eppich, Keith Lang, Richard Chin, and Aland Chin, 2014 IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), Orlando, FL, May 27-30, 2014

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The Thermal Conductivity of Clustered Nanocolloids

T. Desai et al., APL Materials, 2, 066102 (2014); doi: 10.1063/1.4880975. 21 May 2014;

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Diffuse interface modeling of void growth in irradiated materials. Mathematical, thermodynamic and atomistic perspectives

Anter El-Azab Karim Ahmed, Srujan Rokkam, Thomas Hochrainer, Published in Current Opinion in Solid State and Materials Science (COSSMS), Vol. 18, pg. 90-98, 2014.

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Effect of Crosslink Formation on Heat Conduction in Amorphous Polymers

Gota Kikugawa, Tapan G. Desai, et al., Journal of Applied Physics 114, published online July 16, 2013

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Variable Conductance Heat Pipe Cooling of Stirling Convertor and General Purpose Heat Source

Calin Tarau, et al.,11th International Energy Conversion Engineering Conference (IECEC), San Jose, CA, July 15-17, 2013.

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High Temperature Heat Pipes for Space Fission Power

Kara L. Walker, et al.,11th International Energy Conversion Engineering Conference (IECEC), San Jose, CA, July 15-17, 2013.

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Variable Conductance Heat Pipe Radiator for Lunar Fission Power Systems

William G. Anderson, et al., 11th International Energy Conversion Engineering Conference (IECEC), San Jose, CA, July 15-17, 2013.

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Ammonia and Propylene Loop Heat Pipes with Thermal Control Valves – Thermal/Vacuum and Freeze/Thaw Testing

Kara Walker, et al., 43rd International Conference on Environmental Systems (ICES 2013), Vail, CO, July 14-18, 2013.

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Intermediate Temperature Heat Pipe Life Tests and Analyses

W. G. Anderson, et al., 43rd International Conference on Environmental Systems (ICES 2013), Vail, CO, July 14-18, 2013

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Correlation for dropwise condensation heat transfer: Water, organic fluids, and inclination

Richard W. Bonner III, International Journal of Heat and Mass Transfer, Volume 61, June 2013, Pages 245-253

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A Non-Catalytic Fuel-Flexible Reformer

Chien-Hua Chen, et al., 8th U. S. National Combustion Meeting, hosted by the University of Utah, May 19-22, 2013

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Planar vapor chamber with hybrid evaporator wicks for the thermal management of high-heat-flux and high-power optoelectronic devices

P. Dussinger et al., International Journal of Heat and Mass Transfer, Volume 60, pp. 163–169, May 2013.

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Variable Conductance Thermal Management System for Balloon Payloads

Calin Tarau and William G. Anderson, 20th AIAA Lighter-Than-Air Systems Technology Conference, Daytona Beach, FL, March, 25-28, 2013

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Preliminary First Principle Based Electro-thermal Coupled Solver for Silicon Carbide Power Devices

Angie Fan et al., 29th IEEE SEMI-THERM Symposium, San Jose, CA, March 17-21, 2013

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Variable Conductance Heat Pipe Radiator Trade Study for Lunar Fission Power Systems

William G. Anderson, Bryan J. Muzyka, and John R. Hartenstine, Nuclear and Emerging Technologies for Space (NETS-2013), Albuquerque, NM, February 25-28, 2013.

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Alkali Metal Backup Cooling for Stirling Systems – Experimental Results

Carl Schwendeman, Calin Tarau, William G. Anderson, and Peggy A. Cornell, Nuclear and Emerging Technologies for Space (NETS-2013), Albuquerque, NM, February 25-28, 2013.

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Alkali Metal Heat Pipes for Space Fission Power

Kara L. Walker, Calin Tarau, and William G. Anderson, Nuclear and Emerging Technologies for Space (NETS-2013), Albuquerque, NM, February 25-28, 2013.

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Syngas Production by Thermochemical Conversion of CO2 and H2O Using a High-Temperature Heat Pipe Based Reactor

H. Pearlman and Chien-Hua Chen, SPIE Solar Hydrogen and Nanotechnology VII, Proceedings of SPIE Vol. 8469 San Diego, CA, August 12-14, 2012.

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Diode Heat Pipes for Venus Landers

Calin Tarau et al., 9th Intersociety Energy and Conversion Engineering Conference (IECEC), San Diego, CA, July 31 - August 3, 2012.

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Long-Lived Venus Lander Thermal Management System Design

Rebecca Hay et al., 9th Intersociety Energy and Conversion Engineering Conference (IECEC), Atlanta, GA, July 30 July-August 1, 2012.

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Variable Conductance Heat Pipes for Variable Thermal Links

W. G. Anderson et al., 42nd International Conference on Environmental Systems (ICES 2012), San Diego, CA, July 15-19, 2012.

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Pressure Controlled Heat Pipe Applications

W. G. Anderson et al., 16th International Heat Pipe Conference, Lyon, France, May 20-24, 2012.

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The Effect of Device Level Modeling on System-Level Thermal Predictions

Jens Weyant, et al., ITherm, San Diego, CA, May 30, 2012,

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Integration of a Phase Change Material for Junction-Level Cooling in GaN Devices

Daniel Piedra, et al., Semitherm, San Jose, CA, March 2012

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An Innovative Passive Cooling Method for High Performance Light-emitting Diodes

Angie Fan, et al., Semitherm, San Jose, CA, March 2012

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Ultra High Temperature Isothermal Furnace Liners (IFLs) For Copper Freeze Point Cells

Peter Dussinger and John Tavener, 9th International Temperature Symposium, Anaheim, CA, March 2012

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High Heat Flux, High Power, Low Resistance, Low CTE Two-Phase Thermal Ground Planes for Direct Die Attach Applications

Peter Dussinger, et al., GOMACTech 2012, Las Vegas, NV, March 2012

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Passive Control of a Loop Heat Pipe with Thermal Control Valve for Lunar Lander Application

K. L. Walker et al., 42nd International Conference on Environmental Systems (ICES 2012), San Diego, CA, July 15-19, 2012.

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A Computational Model of a Phase Change Material Heat Exchanger in a Vapor Compression System with a Large Pulsed Heat Load

G. Troszak and X. Tang, Proceedings of the ASME 2012 Summer Heat Transfer Conference, Puerto Rico, July 8-12, 2012.

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2-D Simulation of Hot Electron-Phonon Interactions in a Submicron Gallium Nitride Device Using Hydrodynamic Transport Approach

Angie Fan et al., ASME 2012 Summer Heat Transfer Conference, Puerto Rico, USA , July 8-12, 2012

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Novel Junction Level Cooling in Pulsed GaN Devices

Tapan G. Desai, et al., ITherm, San Diego, CA, May 30, 2012,

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Intermediate Temperature Heat Pipe Life Tests

W. G. Anderson, et al., 16th International Heat Pipe Conference, Lyon, France, May 20-24, 2012.

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Passivation Coatings for Micro-channel Coolers

Richard W. Bonner III, Jens Weyant, Evan Fleming, Kevin Lu, Daniel Reist, APEC 2012, Orlando FL, February 1, 2012

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Pressure Controlled Heat Pipe Solar Receiver for Regolith Oxygen Production with Multiple Reactors

John Hartenstine, et al., 9th Intersociety Energy and Conversion Engineering Conference (IECEC), San Diego, CA, July 31 - August 3, 2011

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Thermal Management System for Long-Lived Venus Landers

Calin Tarau, et al., 9th Intersociety Energy and Conversion Engineering Conference (IECEC), San Diego, CA, July 31 - August 3, 2011

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Pressure Controlled Heat Pipes

William Anderson, et al., 41st International Conference on Environmental Systems, Portland, OR, July 17-21, 2011

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Variable Conductance Heat Pipe for a Lunar Variable Thermal Link

Chris Peters, et al., 41st International Conference on Environmental Systems, Portland, OR, July 17-21, 2011

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Two-Phase Heat Sinks with Microporous Coating

T. Semenic and S. M. You, 9th International Conference on Nanochannels, Microchannels, and Minichannels, Edmonton, CA, June 19-22, 2011

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Die Level Thermal Storage for Improved Cooling of Pulsed Devices

Richard Bonner III, et al., Semitherm, San Jose, CA., March 2011

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A 2-D Numerical Study of Microscale Phase Change Material Thermal Storage for GaN Transistor Thermal Management

Xudong Tang, et al., Semitherm, San Jose, CA, March 2011

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Dynamic Response of Phenolic Resin and Its Carbon-nanotube Composites to Shock Wave Loading

Arman, et. al., Journal of Applied Physics, 109, 013503 (2011)

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Loop Heat Pipe with Thermal Control Valve for Variable Thermal Conductance Link of Lunar Landers and Rovers

Loop Heat Pipe with Thermal Control Valve for Variable Thermal Conductance Link of Lunar Landers and Rovers, J. R. Hartenstine et al., 49th AIAA Aerospace Sciences Meeting, Orlando, FL, January 4-7, 2011.

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Electronics Cooling Using High Temperature Loop Heat Pipes with Multiple Condensers

William G. Anderson, et al., SAE Power Systems Conference, Ft. Worth, TX, November 2010

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Development of Heat Pipe Loop Technology for Military Vehicle Electronics Cooling

Xudong Tang et al., NDIA Ground Vehicle Systems Engineering and Technology Symposium, Dearborn, Michigan, August 2010

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Dropwise Condensation Life Testing of Self Assembled Monolayers

Richard Bonner III, IHTC14, Washington, DC, August 2010

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Heat and Mass Transfer in a Permeable Fabric system Under Hot Air Jet Impingement,

Sangsoo Lee et. al., International Heat Transfer Conference (IHTC14), Washington, DC, August, 2010

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Variable Thermal Conductance Link for Lunar Landers and Rovers

William G Anderson et. al., IECEC, Nashville, Tennessee, July, 2010

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Sodium Variable Conductance Heat Pipe for Radioisotope Stirling Systems – Design and Experimental Results

Calin Tarau and William G Anderson, IECEC, Nashville, Tennessee, July, 2010

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Sodium Variable Conductance Heat Pipe with Carbon-Carbon Radiator for Radioisotope Stirling Systems

Calin Tarau and William G. Anderson, 15th International Heat Pipe Conference, Clemson, SC, April 2010

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Low-Temperature, Dual Pressure Controlled Heat Pipes for Oxygen Production from Lunar Regolith

Kara Walker et al., 15th International Heat Pipe Conference, Clemson, South Carolina, April, 2010

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Intermediate Temperature Fluids for Heat Pipes and Loop Heat Pipes

William G. Anderson, John R. Hartenstine, David B. Sarraf, and Calin Tarau, Advanced Cooling Technologies, Inc., Pennsylvania, 15th International Heat Pipe Conference (15th IHPC) Clemson, USA, April 25-30, 2010.

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Dropwise Condensation in Vapor Chambers

Richard Bonner, 26th IEEE Semi-Therm Symposium, Santa Clara, California, February 2010

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Sodium VCHP with Carbon-Carbon Radiator for Radioisotope Stirling Systems,

Calin Tarau, et al., Space, Propulsion and Energy Sciences International Forum (SPESIF), Laurel, Maryland, February 2010

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Advanced VCS Evaporators for Lunar Lander and Lunar Habitat Thermal Control Applications

Tadej Semenic, Space, Propulsion and Energy Sciences International Forum (SPESIF), Laurel, Maryland, February 2010

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Modeling Initial Stage of Phenolic Pyrolysis: Graphitic Precursor Formation and Interfacial Effects

Tapan Desai, et al., Polymer, 52, 2010

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Slip Behavior at Ionic Solid-fluid Interfaces

Tapan Desai, NDIA Chemical Physics Letters, 501, 2010, 93-97

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Roles of Atomic Restructuring in Interfacial Phonon Transport

Seungha Shin et. al., Physical Review B, 82, 081302 (2010)

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Anisotropic Shock Response of Columnar Nanocrystalline Cu

Sheng-Nian Luo et. al., Journal of Applied Physics , 107, 123507 (2010)

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Heat Pipe Embedded Alsic Plates for High Conductivity-Low CTE Heat Spreaders

J. Weyant, ITHERM 2010, Las Vegas NV,

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Pressure Controlled Heat Pipe Solar Receiver for Oxygen Production from Lunar Regolith

John R. Hartenstine, et al., AIAA Aerospace Sciences Meeting, Orlando, Florida, January 2010

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Sodium Variable Conductance Heat Pipe for Radioisotope Stirling Systems

Calin Tarau, et al., 7th International Energy Conversion Engineering Conference, Denver Colorado, August 2009

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Loop Heat Pipe Design, Manufacturing and Testing – an Industrial Perspective

William Anderson, et al., ASME 2009 Heat Transfer Summer Conference, San Francisco, California, July 2009

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Dropwise Condensation on Surfaces with Graded Hydrophobicity

Richard Bonner, ASME 2009 Heat Transfer Summer Conference, San Francisco, California, July 2009

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Evaporators for High Temperature Lift Vapor Compression Loop for Space Applications

Tadej Semenic and Xudong Tang, ASME 2009 Heat Transfer Summer Conference, San Francisco, California, July 2009

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Variable Conductance Heat Pipe Radiators for Lunar and Martian Environments

William Anderson, et al., Space, Propulsion and Energy Sciences International Forum (SPESIF), Huntsville, Alabama, February 2009

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High Temperature Variable Conductance Heat Pipes for Radioisotope Stirling Systems

Calin Tarau, et al., Space, Propulsion and Energy Sciences International Forum (SPESIF), Huntsville, Alabama, February 2009

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Heat Pipe Solar Receiver for Oxygen Production of Lunar Regolith

John Hartenstine, et al., Space, Propulsion and Energy Sciences International Forum (SPESIF), Huntsville, Alabama, February 2009

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Variable Conductance Heat Pipe Performance after Extended Periods of Freezing

Michael Ellis and William Anderson, Space, Propulsion and Energy Sciences International Forum (SPESIF), Huntsville, Alabama, February 2009

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Loop Heat Pipe for TacSat-4

Peter Dussinger, et al., Space, Propulsion and Energy Sciences International Forum (SPESIF), Huntsville, Alabama, February 2009

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Advanced Thermal Management Technologies for High Power Automotive Equipment

Jon Zuo, et al., National Defense Industrial Association Ground Vehicle Power and Energy Workshop, Troy, Michigan, November 2008

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Vibration and Shock Tolerant Capillary Two-Phase Loop Technology for Vehicle Thermal Control

Xudong Tang and Chanwoo Park, 2008 ASME Summer Heat Transfer Conference, Jacksonville, Florida, August 2008

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NaK Variable Conductance Heat Pipe for Radioisotope Stirling Systems

Calin Tarau, et al., 6th International Energy Conversion Engineering Conference (IECEC), Cleveland, Ohio, July 2008

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Heat Pipe Cooling of Concentrating Photovoltaic (CPV) Systems

William Anderson, et al., 6th International Energy Conversion Engineering Conference (IECEC), Cleveland, Ohio, July 2008

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Startup Characteristics and Gravity Effects on a Medium/High-Lift Heat Pump Using Advanced Hybrid Loop Technology

Eric Sunada, et al., 38th SAE International Conference on Environmental Systems, San Francisco, California, June 2008

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High Temperature and High Heat Flux Thermal Management for Electronics

David Sarraf and William Anderson, IMAPS International Conference on High Temperature Electronics Conference (HiTEC 2008), Albuquerque, New Mexico, May 2008

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Heat Pipe Cooling of Concentrating Photovoltaic Cells

William Anderson, et al., 33rd IEEE Photovoltaic Specialists Conference, San Diego, California, May 2008

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Local Heat Transfer Coefficient Measurements of Flat Angles Sprays Using Thermal Test Vehicle

Richard Bonner, et al., 24th IEEE Semi-Therm Symposium, San Jose, California, March 2008

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Pressure Controlled Heat Pipe for Precise Temperature Control

David Sarraf, et al., Space Technology and Applications International Forum (STAIF), Albuquerque, New Mexico, February 2008

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Titanium Loop Heat Pipes for Space Nuclear Power Systems

John Hartenstine, et al., Space Technology and Applications International Forum (STAIF), Albuquerque, New Mexico, February 2008

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Variable Conductance Heat Pipes for Radioisotope Stirling Systems

William Anderson and Calin Tarau, Space Technology and Applications International Forum (STAIF), Albuquerque, New Mexico, February 2008

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Vapor Compression Hybrid Two-Phase Loop Technology for Lunar Surface Applications

Chanwoo Park and Eric Sunada, Space Technology and Applications International Forum (STAIF), Albuquerque, New Mexico, February 2008

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Experimental Study of Oscillating Flow Heat Transfer

Angie Fan, et al., Micro/Nanoscale Heat Transfer International Conference, Tainan, Taiwan, January 2008

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Metal Hydride Heat Storage Technology for Directed Energy Weapon Systems

Chanwoo Park, et al., 2007 ASME International Mechanical Engineering Congress & Exhibition, Seattle, Washington, November 2007

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Electronics Thermal Management Using Advanced Hybrid Two-Phase Loop Technology

Chanwoo Park, et al., 2007 ASME-JSME Thermal Engineering Summer Heat Transfer Conference, Vancouver, Canada, July 2007.

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Loop Thermosyphon Design for Cooling of Large Area, High Heat Flux Sources

John Hartenstine, et al., InterPACK 2007, Vancouver, Canada, July 2007.

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Heat Pipes for High Temperature Thermal Management

David Sarraf and William Anderson, InterPACK 2007, Vancouver, Canada, July 2007.

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Intermediate Temperature Fluids for Heat Pipes and Loop Heat Pipes

William Anderson, 2007 International Energy Conversion Engineering Conference, St. Louis, MO, June 2007.

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Intermediate Temperature Fluids Life Tests – Experiments

William Anderson, et al., 2007 International Energy Conversion Engineering Conference, St. Louis, MO, June 2007.

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Intermediate Temperature Fluids Life Tests – Theory

Calin Tarau, et al., Space Technology and Applications International Forum (STAIF), Albuquerque, NM, February 11 - 15, 2007.

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Spacecraft Thermal Management Using Advanced Hybrid Two-Phase Loop Technology

Chanwoo Park, et al., Space Technology and Applications International Forum (STAIF), Albuquerque, NM, February 11 - 15, 2007.

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Advanced Hybrid Cooling Loop Technology for High Performance Thermal Management

Chanwoo Park, et al., 2006 International Energy Conversion Engineering Conference, San Diego, CA, June 2006.

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Heat Pipe Heat Exchanger with Two Levels of Isolation for Environmental Control of Manned Spacecraft Crew Compartment

David Sarraf, 37th International Conference on Environmental Systems, Norfolk, VA, July 17-20, 2006.

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Passive Thermal Management for a Fuel Cell Reforming Process

David Sarraf, et al., 2006 International Energy Conversion Engineering Conference, San Diego, CA, June 2006.

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High Temperature Water-Titanium Heat Pipe Radiator

William Anderson, et al., 2006 International Energy Conversion Engineering Conference, San Diego, CA, June 2006.

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High Temperature Titanium-Water and Monel-Water Heat Pipes

William Anderson, et al., 2006 International Energy Conversion Engineering Conference, San Diego, CA, June 2006.

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High-Temperature Water Heat Pipes

David Sarraf and William Anderson, IMAPS International Conference on High Temperature Electronics, Santa Fe, NM, May 15 - 18, 2006

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High Performance Heat Storage and Dissipation Technology

Chanwoo Park, et al., 2005 ASME International Mechanical Engineering Congress & Exposition (IMECE), Orlando, FL, November 5 - 11, 2005.

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Design and Testing of Titanium/Cesium and Titanium/Potassium Heat Pipes

Peter Dussinger, et al., 2005 International Energy Conversion Engineering Conference (IECEC), San Francisco, CA, August 2005.

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High Temperature Lightweight Heat Pipe Panel Technology Development

Ted Stern and William Anderson, Space Nuclear Conference 2005, San Diego, CA, June 2005.

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Loop Heat Pipe Radiator Trade Study for the 300-550K Temperature Range

William Anderson and Walter Bienert, Space Technology and Applications International Forum (STAIF), Albuquerque, New Mexico, February 2005

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Hybrid Loop Thermal Bus Technology for Vehicle Thermal Management

Chanwoo Park, et al., 24th Army Science Conference, Orlando, FL, November 29 - December 2, 2004

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