Characterization of evaporation and boiling from sintered powder wicks fed by capillary action

The thermal resistance to heat transfer into the evaporator section of heat pipes and vapor chambers plays a dominant role in governing their overall performance. It is therefore critical to quantify this resistance for commonly used sintered copper powder wick surfaces, both under evaporation and b...

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Bibliographic Details
Published in:International journal of heat and mass transfer 2010-09, Vol.53 (19), p.4204-4215
Main Authors: Weibel, Justin A., Garimella, Suresh V., North, Mark T.
Format: Article
Language:English
Subjects:
Applied sciences
Boiling
Design. Technologies. Operation analysis. Testing
Devices using thermal energy
Electronics
Energy
Energy. Thermal use of fuels
Evaporation
Exact sciences and technology
Heat pipe
Heat pipes
Heat transfer
Integrated circuits
Microstructured surfaces
Particle size
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Sintered powder wick
Sintering
Thermal resistance
Vapor chamber
Wicks
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Summary:The thermal resistance to heat transfer into the evaporator section of heat pipes and vapor chambers plays a dominant role in governing their overall performance. It is therefore critical to quantify this resistance for commonly used sintered copper powder wick surfaces, both under evaporation and boiling conditions. The objective of the current study is to measure the dependence of thermal resistance on the thickness and particle size of such surfaces. A novel test facility is developed which feeds the test fluid, water, to the wick by capillary action. This simulates the feeding mechanism within an actual heat pipe, referred to as wicked evaporation or boiling. Experiments with multiple samples, with thicknesses ranging from 600 to 1200 μm and particle sizes from 45 to 355 μm, demonstrate that for a given wick thickness, an optimum particle size exists which maximizes the boiling heat transfer coefficient. The tests also show that monoporous sintered wicks are able to support local heat fluxes of greater than 500 W cm −2 without the occurrence of dryout. Additionally, in situ visualization of the wick surfaces during evaporation and boiling allows the thermal performance to be correlated with the observed regimes. It is seen that nucleate boiling from the wick substrate leads to substantially increased performance as compared to evaporation from the liquid free surface at the top of the wick layer. The sharp reduction in overall thermal resistance upon transition to a boiling regime is primarily attributable to the conductive resistance through the saturated wick material being bypassed.
ISSN:0017-9310
1879-2189
DOI:10.1016/j.ijheatmasstransfer.2010.05.043