Weibel J.A.,Purdue University |
Garimella S.V.,Purdue University |
International Journal of Heat and Mass Transfer | Year: 2010
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 1200μm and particle sizes from 45 to 355μm, 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 500Wcm-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. © 2010 Elsevier Ltd. Source
Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase I | Award Amount: 149.99K | Year: 2012
The proposed effort will seek to design and develop vacuum brazed high density folded-fin modular heat exchangers. The scalability of these heat exchangers would provide a means for fabricating large area high performance cold plates by joining via friction stir welding. Friction stir welding is a solid-state joining process that results in minimal distortion of metal characteristics. The advantages of this approach would be an increase in system performance, reliability and efficiency. From a manufacturing stand point the technology would establish the capability to facilitate future product improvement across a broad range of development programs.
Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase I | Award Amount: 79.88K | Year: 2012
To assure satisfactory cooling for future JSF upgrades, the proposed solution is a vapor compression refrigeration system packaged with both a pumped PAO cooling loop and a thermal energy storage (TES) system in a standard avionics rack for the JSF. The vapor compression system, VCS, will provide the sub-ambient cooling required as avionics power is increased. A VCS gives the highest efficiency for sub-ambient cooling. The pumped PAO loop will interface to the avionics racks. PAO is already an approved coolant for aircraft. The TES will store additional thermal capacity for the cooling system for high power transient excursions. Including this feature will increase mission capability during extreme operating conditions. The Phase 1 work effort involves a system design and subscale prototype technology emonstration.
Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase I | Award Amount: 79.68K | Year: 2012
In austere environments, erosion and corrosion seriously degrade the performance of airfoils in fan and compressor sections of gas turbine engines. To prevent damage to titanium airfoils, a powder metallurgy approach will be taken that produces a hard, erosion resistant leading edge. The leading edge should be strongly bonded to the blade body, have similar resonant characteristics (elastic modulus driven) as well as sufficiently similar to the chemistry of the blade body so as not to set up galvanic corrosion cells. The body of the blade will be fabricated using conventional powder to maintain the overall toughness of the blade in the event of large body ballistic impact. The approach that will be taken will be that of cryo-milling titanium alloy powder similar to that used in conventional blades, and using powder metallurgy techniques, such as HIP and CIP/HIP to assure that the hard, strong cryo-milled powder becomes an integral part of the leading edge of the blade. After milled and unmilled powders are placed so that the cryomilled powder will become the leading edge, consolidation will be followed by forging to obtain the proper airfoil shape.
Agency: GTR | Branch: Innovate UK | Program: | Phase: Feasibility Study | Award Amount: 112.32K | Year: 2015
Heat Pipes are vital to the thermal management of high performance silicon chips and are present in virtually every new laptop computer. Thermacore is a world leader in heat pipe technology and specialises in thermal management of high performance electronic devices such as for military applications. To protect and expand its position at the high end of the market, Thermacore Europe (TCE) and Oxford nanoSystems (ONS) have, with Brunel University (BU), identified an opportunity to improve the maximum heat flux of a heat pipe by replacing or augmenting the current internal evaporative cooling surface with a high performance nano-coating. The expected benefits including higher power, lower weight and lower cost will allow the UK to maintain its lead in this high value part of the electronics market and the partners to expand into new areas of heat and energy management.