A flat heat pipe was used to study the effects of an advanced working fluid previously shown to improve the thermal performance of phase change heat transfer devices through surface augmentation of the wick. Surface structures were created by the working fluid through chemical oxidation reactions and solubility forced deposits. The modular heat pipe apparatus allowed water and the advanced working fluid to be compared in the same device. A clear viewing cover plate allowed for visual observation of the evaporating section of the heat pipe. The setup was first tested for repeatability with water and produced three sets of thermal resistance values within 5%. The advanced working fluid decreased thermal resistance by approximately 20% and nearly tripled the capillary limit. The advanced working fluid was also tested at larger angles and was able to maintain normal operation due to the additional capillarity of the fluid deposits. This work also provides insight into the design of fluids for other wick geometries by examining the effect of increasing the concentration of the fluid and how the fluid deposits on the surface. The results indicate that concentration of the fluid was over the amount necessary for the evaporative surface area of the grooved wick.

While heat pipes are a widely used and highly efficient means of spreading heat or transferring it from one location to another, there are some fluid-casing combinations which cannot be used due to material incompatibilities. These incompatibilities generally result in the generation of non-condensable gases such as the hydrogen gas produced when water is used with aluminum devices. Some attempts at using inhibitors in aqueous solution are found in literature but a method for screening which inhibitors to use that can also predict and assess the performance of different concentrations is not available. Using a thermodynamic approach, principles of corrosion engineering have been applied to the specific application of phase change heat transfer devices. Experimental data from previous tests has been used to show the E-pH diagrams match the reported NCG generation observed experimentally. Using thermodynamic equilibrium diagrams and measurements of heat pipe fluid E and pH can be a valuable tool when investigating passivating fluids for previously incompatible fluid-casing combinations. (C) 2016 Elsevier Ltd. All rights reserved.

Rising power densities of electronics has called for more advanced cooling solutions. In harsh environment electronics, thermal management is especially challenging due to reliability and geometric constraints. Heat pipes and other two phase cooling methods are promising passive thermal management technologies. This work explores a designer working fluid for use in phase change heat transfer devices. Different fluids are tested in a flat grooved heat pipe. The surface augmentation created by using these fluids is studied with microscopic imaging and elemental analysis. The performance results show enhancements over water and the surface characterization confirms previous chemical analysis, lending insight into the optimization process for these fluids.

Frozen startup of phase change heat transfer devices is a complex problem that can have a large impact on heat transfer systems. A patented novel working fluid developed at UCLA comprised of an inorganic aqueous solution (IAS) was investigated for potential effects on the freeze/thaw capabilities in phase change heat transfer devices by examining the melting process of droplets. Preliminary visual tests were conducted to gain insight into any physical processes that surface augmentation created by this fluid may have on the freezing and melting process. These tests demonstrated significant differences in liquid spreading, the melting process, and the melting rate of droplets on surfaces pre-treated with IAS. Contact angle measurements exhibited enhanced wetting properties. SEM images of frozen droplets showed that liquid freezes in the small capillary wick formed by the initial evaporation of IAS. Video of melting droplets showed a significant increase in melting rate when the surface was first treated with IAS due to superior liquid spreading.

A novel replacement for traditional wedgelocks used to mount PCB boards to cold plates is presented. This project began as part of a DARPA design competition to develop a field reversible thermal connector that could be repeatedly assembled and disassembled without the use of tools while providing constant thermal resistance. The team from UCLA was tasked with designing a new device to meet these constraints. The design meets the DARPA goals and significantly reduces the thermal resistance between the electrical board and the heat sink. The device consists of opposing aluminum wedges, driven by thermally actuated Nitinol springs, which slide against one another to provide the requisite locking force to hold a board in place and decrease contact resistance between the interfaces. These smart material springs push the wedges towards the outside of the device, elevating the upper surface and locking the board in place on the cold plate. The design increases the contact area between the components and decreases the thermal resistance relative to current devices. Experimental results have shown that the UCLA team has addressed the chief design problems posed by the REVCON program. Nitinol has been shown to be an effective material for use as a thermally actuated spring capable of repeatedly engaging and disengaging without the use of tools. The wedge locking force increases with rising temperature, enhancing its thermal performance. The UCLA design has been shown to out-perform similar sized current state of the art wedgelock designs in terms of thermal resistance. Reductions in thermal resistance of 30%-45% have been demonstrated and shown to be repeatable. Our prototype design increases the interfacial contact area which has a dramatic impact on performance. This means that higher power density electronics can be utilized or that more real estate will be made available on current computer boards in order to maintain current performance. Further, the use of thermally actuated leaf springs removes the need for mechanical force for installation allowing for less installation time.