High Temperature Heat Pipes
High temperature heat pipes are typically defined as heat pipes that operate between 400 and 1100°C. However, the fluid properties vary too much across this wide temperature range for any one fluid. Three fluids are typically used to cover this range; Cesium, Potassium, and Sodium. The operating range for each fluid is shown below:
- Cesium 300 to 600°C (572 to 1,112°F)
- Potassium 400 to 1000°C (752 to 1,832°F)
- Sodium 500 to 1100°C (932 to 2,012°F)
Materials of construction are typically Alloy 600 for Cesium, Potassium, and Sodium. ACT also manufactures a Haynes 230/Sodium heat pipe for extended operation near 1100°C because of the significantly higher creep strength. Austenitic stainless steels can be used for applications that are at the lower end of the temperature range.
Typical applications for high temperature heat pipes include the following:
- Heat Engine Receivers (Steam, Stirling, Brayton, Rankine)
- Solar Thermal
- Heat exchangers
- Hypersonic wing leading edges
- Waste heat recovery
- Nuclear power
- Thermoelectric Generators
- Isothermalizing furnace elements
High temperature heat pipes can be used to build custom heat transfer devices for both high power throughput and precise temperature uniformity. Power throughput in the 1 to 100 kW range is typical. Precision heat treating and materials processing furnaces are capable of extraordinarily precise temperature set points and isothermality. Set point accuracy, stability, and isothermality of ± 0.1°C is common with a single heated zone, using an off-the-shelf temperature controller. Because of the inherent temperature uniformity and stability of heat pipes, they are an integral component in nearly all of the most precise temperature calibration instruments in the primary calibration laboratories around the world (See ACT’s Temperature Calibration and Control Products). This technology can also be applied to research, commercial, and industrial applications for processes such as annealing, sintering, crystal growing, brazing, and controlled diffusion.