Test Reports

Heat Pipe Test Report for Copper Water Sintered Powder Metal Wick Heat Pipes

The following tests were conducted to determine the performance of copper sintered powder metal wick heat pipes filled with deionized water as the working fluid. The operational range for a water filled heat pipe is designed to be from 5oC to 150oC. Various pipe diameters and pipe lengths were tested under the given heat loads and orientations. The test orientations include +90o, +60o, +30o (gravity assist), 0o (horizontal), -30o, -60o, -90o (against gravity). In the test apparatus, the length for the evaporator and the condenser was 50mm for all pipe diameters and pipe lengths. The coolant was circuited in between the constant water bath and the condenser heat exchanger. The coolant inlet temperature to the condenser heat exchanger was set at 35oC. Multiple temperatures were measured in the evaporator and condenser. Using the temperature data & given heat loads, the corresponding thermal conductivity can be calculated if the heat pipe is considered as a solid rod. The corresponding thermal conductivity can also be used in model heat pipe in the thermal modeling software; CFD or finite element. From the test reports we can see that the pipe’s adiabatic length and orientation affect the heat pipe performance the most.

Heat Pipe Test Report for Copper Methanol Sintered Powder Metal Wick Heat Pipes

The following tests were conducted to determine the performance of copper sintered powder metal wick heat pipes filed with methanol alcohol as the working fluid. The operational range for a methanol filled heat pipe is designed to be from -20oC to +80oC. Various pipe diameters and pipe lengths were tested under the given heat loads and orientations. The test orientations include +90o, +60o, +30o (gravity assist), 0o (horizontal), -30o , -60o, -90o (against gravity). In the test apparatus, the length for the evaporator and the condenser was 50mm for all pipe diameters and pipe lengths. The coolant was circuited in between the constant water bath and the condenser heat exchanger. The coolant inlet temperature to the condenser heat exchanger was set at -10oC. Multiple temperatures were measured in the evaporator and condenser. Using the temperature data & given heat loads, the corresponding thermal conductivity can be calculated if the heat pipe is considered as a solid rod. The corresponding thermal conductivity can also be used in model heat pipe in the thermal modeling software; CFD or finite element.  Since the surface tense of methanol is quite low, the methanol heat pipe does not perform well at the against gravity orientation.

Heat Pipe Test Report on Effect of Coolant Temperature

In theory, when a heat pipe operates at a higher temperature the performance is higher. In this test set up, the coolant temperature pumped to the condenser heat exchanger varied from 5oC to 70oC. The test results demonstrate that the calculated thermal conductivity of a copper water sintered powder metal wick heat pipe is 5 times higher at 70oC coolant to 5oC coolant.

Heat Pipe Test Report on Effect of Flattening

There are four operating limits in a heat pipe; boiling, sonic, entrainment, and capillary.  In some real world applications, heat pipe needs to be flattened.  When heat pipe is flattened, the internal vapor passage will be reduced; making the sonic limit the deciding factor.  In this test set up, the 6mm x 300mm round copper water sintered wick heat pipe was tested. This same pipe was then flattened to 3.5mm thick and retested. Lastly, the same pipe was flattened to 2.5mm and tested again. Our test results show that when the pipe is flattened to 3.5mm, no reduction in performance is visible. However, at 2.5mm thickness, the performance was reduced significantly.

Heat Pipe Test Report on Effect of Bending

A test was set up for understanding the bend that affects heat pipe performance. In this set up, a 6mm x 300mm round copper water sintered wick heat pipe was tested. The same pipe was then formed to a 30o bend and retested. Next the same pipe was formed and tested at 60o, 90o, 120o, 150o and 180o bends. The test results show that a heat pipe’s performance is not affected by the bend angle when bending up to 180o provided the bend radius is at least 3 times the pipe diameter. However, A shape radius bend may crack the wick inside and degrade the heat pipe’s performance.

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