Manufacturing Turnkey Thermal Solutions for the Medical Industry

Manufacturing Turnkey Thermal Solutions for the Medical Industry

Hamilton storage partners with Advanced Cooling TechnologiesHamilton Storage, an affiliate entity of Hamilton Company, an industry leader in the design and manufacture of liquid handling, process measurement, robotics and storage solutions, has developed an array of automated sample storage and management systems used in pharmaceutical and bio-medical applications worldwide.

Cold storage is a critical part of sample management and storage, therefore Hamilton invested in a unique large-scale cooling system in their early product

Hamilton Storage

Figure 1: Hamilton Storage Bios at Inselspital, Bern University Hospital. Source article.

iterations. Hamilton Storage built the first-generation thermal management systems for these large cold storage units; however, in order to push the next generation of the product to new abilities, they were in need of a thermal partner that could help optimize their existing design.

In the hopes of improving on the original product concept, Hamilton Storage contacted ACT looking for an improved evaporator design for their sub-zero vapor compression system that both enhanced thermal performance and manufacturability.

ACT Solution:

Utilizing decades of experience in designing two-phase cooling products, ACT developed a multiple-pass copper tube and aluminum base evaporator assembly. The assembly consists of several independent flow circuits for redundancy and 90-degree bends that maximize the cooling coverage area of the storage container. Each circuit consists of over 100 feet of continuous copper tubing with no fittings or braze joints to maximize the system reliability. The aluminum base parts were extruded to reduce cost and create modularity for future design iterations. The result was a nearly 50% increase in cooling contact area with the cold storage cabinet while maintaining high reliability and an economic design. For more information on ACT’s custom thermal solutions for the medical industry click here.

ACT Manufactures cold storage solution with enhanced evaporator design for Hamilton Storage

Figure 2: ACT’s enhanced evaporator design for cold storage

Detailed look at the cold storage side panels by ACT

Figure 3: Detailed look at a side panel of ACT’s enhanced evaporator design for cold storage

High Heat Flux Loop Thermosyphon for Laboratory Measurement Systems

High Heat Flux Loop Thermosyphon for Medical Devices

High Heat Flux Loop Thermosyphon for Medical Devices

High performance laboratory measurement systems must be accurate, precise and reliable.  With these requirements comes increased importance in thermal management.  ACT recently assisted a multi-national corporation that produces such high precision instruments to replace an outdated and inefficient thermal management system with a more advanced and reliable one.

The analytical device had a very high heat load (kW level) that required a large chiller to cool two areas containing heat generating components. Because an in-house air system was required for the installation of the analytical device, and the customer wanted to use that air supply to cool the heat-generating components and eliminate the need for a chiller.

ACT designed a custom thermal solution for an analytical device like this one.

Through a design study conducted by its thermal engineering experts, ACT developed a solution met all of the customer’s requirements. ACT replaced the chiller with two loop thermosyphons, one for each of the heat generating areas, that was able to more efficiently utilize the air supply as the ultimate heat sink.  The flexibility of the loop thermosyphon technology enabled the evaporator design to be  unique to each heat generating area. The highest heat flux area had a heat flux of approximately 80W/cm2 during operation.  ACT’s solution was successfully tested to over 100 W/cm2.  Further, ACT designed an evaporator with minichannels which improved the performance by reducing the heat flux seen by the thermosyphon working fluid. With this loop thermosyphon solution,  the temperature at the heat sources was maintained to within 5% of the chiller solution, without of course, the need for a chiller.

The custom thermal solution designed by ACT provided the customer higher reliability, reduced maintenance, reduced power, reduced noise, and a reduced space requirement.

ACT can custom design a solution for your thermal challenge.  The thermal experts at ACT are experienced in design studies, prototyping, and manufacturing large-scale solutions for any challenge, and at any stage of your project.  Contact us today to discuss your application.

Passive and Quiet Cooling Solutions for Medical Equipment

Sophisticated Medical Imaging machines provide detailed three-dimensional (3D) images of internal organs.  One method of achieving these images is by taking “2D image slices” and rotating the imaging equipment about the body.  The imaging devices are themselves a series of slices containing sensors which must have the same temperature to provide the same image quality.

The problem facing the product development engineers at a leading medical device company was how to quadruple the number of sensors per slice, while still maintaining a highly uniform temperature across the imaging equipment. In the earlier version of the product, it was quite easy to transfer a small amount of heat over a short distance from the inner sensors to the outer edge, where a liquid cooling system ultimately dissipated the heat. However, with so many more sensors the temperature gradient from the inner sensors to the outer ones became unacceptably high. Extending the liquid cooling inward was considered but ultimately deemed impractical because of the complexity and risks of having tubing and manifolding within the slice.

Heat pipes were considered a very good option to regulate medical equipment temperature because of their ability of transferring heat without consuming power and making noise. But the customer’s engineers had some concerns: Could heat pipes provide a uniform temperature across the many sensors, and just as critically, perform reliably under the very high rotational speed?  That’s where ACT entered the picture.  Working as a team with our customer’s engineers, ACT first developed a simulation model to evaluate the performances of various heat pipe designs under high speed rotations, and then built and tested several prototypes to confirm the predicted temperature gradient (less than 2°C). As the high performance imaging machine went into production ACT manufacturing ramped up effectively and continues to meet the customer’s quality and delivery requirements

C.T.E. Matched Vapor Chambers

Figure 1. C.T.E. matched vapor chamber allows direct bonding of LED, eliminating a thermal interface. The vapor chamber acts as a thermal transformer, spreading the heat so that it can be removed by air cooling.

Figure 1. C.T.E. matched vapor chamber allows direct bonding, eliminating a thermal interface. The vapor chamber acts as a thermal transformer, spreading the heat so that it can be removed by air cooling.

There are a growing number of high power  applications across industries that require highly efficient cooling solutions. Some of these products have very high localized heat fluxes, greater than 300 W/cm2, but must maintain a tight temperature range so as not to disrupt sensors or optical devices. Direct die attachment can lead to mechanical stresses at the interface if the coefficient of thermal expansion (C.T.E.) is mismatched between the die and the substrate.  The standard method to overcome this is to add an interface material, such as thermal gap pads or thermal pastes, to accommodate the mismatch.  Unfortunately the presence of this thermal interface layer increases the thermal resistance and likewise increases the temperature on the device itself.

Vapor Chambers  are an important tool in the thermal management toolbox, since they act as flux transformers, spreading the high input heat flux over the entire surface of the vapor chamber.  This allows the heat to be removed from the vapor chamber by conventional cooling methods.  Most vapor chambers are limited to an input heat flux of about 75 W/cm2, however, ACT has developed a C.T.E matched vapor chamber that allows for direct bonding of the heat source; see Figure 1.  This unique device has been demonstrated to dissipate heat fluxes as high as 700 W/cm2 and 2kW overall.  The evaporator thermal resistance of vapor chambers with this wick design is only 0.05 K-cm2/W.

The overall envelope structure is aluminum nitride with a direct bond copper exterior.  The copper on the inside of the vapor chamber ensures that the well-known water/copper performance is maintained.  In areas where the heat source is to be attached, the copper layer is removed exposing Aluminum nitride.  Aluminum nitride has a CTE of ~5.5 ppm/⁰C, which is close to many common semiconductor materials.  The devices can be directly attached to the vapor chamber, eliminating the need for a thermal interface layer.

Return to Vapor Chamber Assemblies…


LED Case Study – The Remote Sink

In many lighting applications the LED device must fit in a fixed space to accommodate a variety of customer requirements, which often do not account for thermal management considerations.  A common example is luminaire design, where the ceiling or wall fixtures are based on pre-existing designs using non-LED technologies.  These designs commonly have both restricted space for heat dissipation through conduction, and limited air flow to remove heat via convection.   In cases where there is space to remotely dissipate the heat, heat pipes can be used to transport the heat from the device to a heat sink located elsewhere.  This is called the remote sink.

Figure 1. Heat pipes transfer heat from the LED to a remote sink, with very small temperature drops.

Figure 1. Heat pipes transfer heat from the LED to a remote sink, with very small temperature drops.

The remote sink solution has a heat pipe in direct contact with the LED device at one end, which serves as the evaporator. At the other end the heat pipe is connected to the heat sink, the condenser.  A sketch of a conceptual design can be seen in Figure 1.  Here two heat pipes are in direct contact with both the LED at the bottom and heat dissipating fins at the top. A wall or other enclosure can be placed in between the LED and heat sink to separate the two.

Aluminum has a thermal conductivity of about 180 W/m K, while the thermal conductivity of copper is only 400 W/m K.  In contrast, the effective conductivity of a heat pipe can range from 10,000 to 100,000 W/m K.   This high effective thermal conductivity allows the heat sinks to be located remotely from the LED.


Figure 2. IR image and photograph of remote cooling with a heat pipe embedded radial heat sink dissipating 30 W. The temperature distribution clearly demonstrates that the heat pipe can transport heat almost isothermally, and then deliver it uniformly to the heat sink.

Figure 2.

Figure 2 shows a photograph and an infrared (IR) image of a heat pipe transporting heat to a remote sink.  The heat pipe heat sink is operating at natural convection conditions with 30 Watts of applied heat.  The heat pipe clearly demonstrates the transport of heat isothermally from the heat source to the heat sink and the even distribution of heat to the heat sink. A slight increase in temperature is measured across the heat sink (<0.5 °C), due to the sensible heating of air rising through the heat sink.

Heat pipes can efficiently transfer heat approximately 8 inches with minimal thermal gradient, and over even greater distances when the heat pipe is gravity aided.  Note that the number, size shape and location of heat pipes would be specific to the design.

Return to Photonics…


Cyclic Medical Device Cooling

A customer was developing a device for a medical application. For operation, the device needed to be applied directly to the skin and repeated use could reach uncomfortable temperature for patients. To study the device performance, FEA analysis was run at different conditions to determine where thermal conditions most needed to be addressed. Several scenarios were evaluated. In one case the device was modeled with a thermal conductivity epoxy. In another case air was modeled. The analysis concluded that the device was conduction limited and recommended either adding Phase Change Materials or a heat pipe located near the handle to significantly improve heat transfer. Product is now in the market and customer has returned to ACT for next generation thermal management concepts.

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