UC Irvine

With an increasing trend towards smaller devices, advances in compact cooling systems are necessary to maintain the necessary working temperature of these devices. One of the most utilized cooling systems for compact devices is a heat pipe. Heat pipes employ a closed loop two-phase cooling mechanism in which a cooling fluid infiltrates a porous wicking media lining a small metal chamber. This cooling liquid evaporates at the end near the hot spot, allowing the vapor to travel along the open pocket of the pipe to a cool zone where the liquid condenses into the wick and flows back to the hot zone. The diameter of these heat pipes for compact electronics is generally within 0.4 - 0.8 mm with lengths of under 500 mm, depending on the electronic system. A main challenge to cooling is due to the limited volume sizes of compact devices. Heat dissipation can be improved with larger surface area contacts, however the limited device size requires optimization for addressing the heat generation of current high chip density electronics, which have increased to 300 W/cm2 for handheld devices (~10x the heat generated from the first cell phone). There are multiple directions of improvements available for heat pipe designs, involving changes to the cooling liquid, surface-area to volume ratios for the porous media, as well as surface and interfacial functionalization. The functionalizations of interest include the application of nanometer-thin films to tailor properties such as hydrophilicity, passivation, and interfacial resistance. The goal of this research is to develop an understanding of thin film coatings and the effects of surface science on optimizing heat transfer in 3D structures to create effective coatings for optimization of cooling systems. This aim has led to the exploration of PEALD coatings on porous 3D inverse opal structures in which we examine the capabilities of various oxides to improve wettability and liquid permeability for wicking applications in terms of hydrophilicity, the thermal stability, and potential coating degradation under thermal cycling. We further explore graphene surfaces and liquid behavior on these surfaces utilizing fluorescence and quantum dots to explore select area liquid motion in a microscale.