Optimization of 3d Branching Networks of Microchannels for Microelectronic Device Cooling

The aim of this work is to present a methodology to develop cost-effective thermal management solutions for microelectronic devices, capable of removing maximum amount of heat and delivering maximally uniform surface temperature distributions. The topological and geometrical characteristics of multiple-story threedimensional branching networks of microchannels were developed using multi-objective optimization. The design variables which will be subject to optimization in this analysis are the geometric parameters of the microchannel network, i.e. the number of network floors in a 3D network, the amount of branching levels per floor, the connectivity of the cooling channels, their crosssectional areas and lengths. A conjugate heat transfer analysis software package (CHETSOLP) and an automatic 3D microchannel network generator (3DBNGEN) were developed and coupled with a multi-objective particle-swarm optimization (MOPSO) algorithm with a goal of creating a design tool for 3D networks of optimized coolant flow channels. Numerical algorithms in the conjugate heat transfer solution package include a quasi-1D thermo-fluid solver (COOLNET) and a 3D steady heat diffusion solver, which were validated against results from high-fidelity Navier-Stokes equations solver and analytical solutions for basic fluid dynamics test cases. The conjugate heat transfer solution is achieved by simultaneous prediction of the quasi-1D internal flow-field in the microchannel network and 3D internal temperature field in the solid substrate [1]. Minimization of the pumping power requirement and maximization of total heat removal subject to temperature uniformity (at the heated surface) were the objectives. Pareto-optimal solutions demonstrate that thermal loads of up to 400 W/cm2 can be managed with 3D multifloor microchannel networks, with pumping power requirements that are up to 50% lower with respect to pumping power requirements in currently used highperformance cooling technologies, such as jet impingement and hybrid impingement-microchannel flow. INTRODUCTION The development of higher performance technologies in the computer and electronics industries is constrained by the ability of cooling systems to deliver adequate thermal management solutions. The heat dissipation of commercial microprocessors has delineated an exponential increase over the past decade and up to 10 times larger heat fluxes, with respect to current devices, are expected in next-generation microelectronics [2]. The thermal load produced by a conventional computer chip is currently of the order of 150 W/cm2, which can be handled with traditional cooling mechanisms implementing a combination of heat sinks and fans. However, as the power density of microchips rises, the need for more sophisticated thermal management solutions, capable of managing high-order heat fluxes and producing uniformly cooled surfaces, becomes indisputable. Effective cooling solutions employing coolants have been developed to address the issue described above. One of the most compelling new techniques is microchannel heat sinks. The heat transfer coefficients derived from fluid flow trough microscopic channels are of great magnitude. Nevertheless, this scheme tends to need increased power supply for pumping the coolant fluid and high temperature gradients along fluid flow direction, causing a counterproductive effect: non-uniform cooling of the heat source. Microchannel heat sinks have been investigated both experimentally and numerically [2-7]. Bowers and Mudawar [5] achieved up to 3,000 W/cm2 of heat