Vapor-Venting, Micromachined Heat Exchanger for Electronics Cooling

Abstract

The increasing complexity of modern integrated circuits and need for high-heat flux removal with low junction temperatures motivates research in a wide variety of cooling and refrigeration technologies. Two-phase liquid cooling is especially attractive due to high efficiency and low thermal resistances. While two-phase microfluidic cooling offers important benefits in required flow rate and pump size, there are substantial challenges related to flow stability and effective superheating. This work investigates the use of hydrophobic membrane to locally vent the vapor phase in microfluidic heat exchangers. Previous work has demonstrated selective venting of gas in microstructures and we extend this concept to two-phase heat exchangers. This paper details the design, fabrication and preliminary testing of the novel heat exchanger. Proof-of-concept of the device, carried out using an isothermal air-water mixture, found the air-mass venting efficiency exceeding 95%. Two-phase, thermal operation of the heat exchanger found the pressure-drop to be smaller compared to a two-phase, non-venting model. The paper also includes a discussion of design challenges such as membrane leakage and optical inaccessibility. The favorable results demonstrated in this first-generation, vapor-venting, micromachined, heat exchanger motivates further study of this and other novel microstructures aimed at mitigating the negative effects of phase-change. With continued research and optimization, we believe two-phase cooling is a viable solution for high heat flux generating electronics.

Design and Modeling of Membrane-Based Evaporative Cooling Devices for Thermal Management of High Heat Fluxes

“…As shown in Eqn. (17), Π2 was obtained by normalizing with σρlhfg/μ evaluated for water at 25 °C. The rationale behind using this figure of merit is that the capillary budget scales with σ and the viscous loss scales with μl(ρlhfg) -1 given a heat removal rate.…”

“…To address these issues in flow boiling, previous studies have investigated into techniques such as dynamic active flow control [11], integrating microstructures [12], flow re-entrance [13], inlet restriction [14] and phase separation [15][16][17]. Particularly, in phase separation approaches, liquid is actively pumped into microchannels covered by a hydrophobic nanoporous membrane and vapor is vented through the pores.…”

Altering Bubble Dynamics via In Situ Vapor Extraction

“…The application of vapor extraction to heat sinks was first introduced by Apreotesi et al [3] using a fractal-like branching microchannel flow network and by David et al [4] for several microscale configurations. The latter group extended these studies by employing a computational fluid dynamic analysis (Fang,et al [5]).…”

Volume of Fluid Simulation of Boiling Two-Phase Flow in a Vapor-Venting Microchannel

“…Continuing increases in component density and reductions in VLSI chip dimensions demand the development of high-performance and low-profile thermal packaging solutions. According to the International Technology Roadmap for Semiconductors high performance microprocessors require heat removal rates exceeding 200W with a thermal resistance of up to 0.1 K/W (David et al, 2007). Conventional cooling techniques based on fans and heat pipes do not scale well with diminished device dimensions.…”

“…The core technological challenge of the vapor-venting heat exchanger lies in achieving phase separation that is reliable and leakage free for the liquid phase. The first experimental realiziation of this approach was provide by David et al (2007). The design, as illustrated in Fig.1, incorporates a pair of parallel liquid and vapor silicon microchannels sandwiching a porous, hydrophobic membrane inbetween.…”