Nanoporous membrane device for ultra high heat flux thermal management

Abstract

High power density electronics are severely limited by current thermal management solutions which are unable to dissipate the necessary heat flux while maintaining safe junction temperatures for reliable operation. We designed, fabricated, and experimentally characterized a microfluidic device for ultra-high heat flux dissipation using evaporation from a nanoporous silicon membrane. With~100 nm diameter pores, the membrane can generate high capillary pressure even with low surface tension fluids such as pentane and R245fa. The suspended ultra-thin membrane structure facilitates efficient liquid transport with minimal viscous pressure losses. We fabricated the membrane in silicon using interference lithography and reactive ion etching and then bonded it to a high permeability silicon microchannel array to create a biporous wick which achieves high capillary pressure with enhanced permeability. The back side consisted of a thin film platinum heater and resistive temperature sensors to emulate the heat dissipation in transistors and measure the temperature, respectively. We experimentally characterized the devices in pure vaporambient conditions in an environmental chamber. Accordingly, we demonstrated heat fluxes of 665 ± 74 W/cm 2 using pentane over an area of 0.172 mm × 10 mm with a temperature rise of 28.5 ± 1.8 K from the heated substrate to ambient vapor. This heat flux, which is normalized by the evaporation area, is the highest reported to date in the pure evaporation regime, that is, without nucleate boiling. The experimental results are in good agreement with a high fidelity model which captures heat conduction in the suspended membrane structure as well as non-equilibrium and sub-continuum effects at the liquid-vapor interface. This work suggests that evaporative membrane-based approaches can be promising towards realizing an efficient, high flux thermal management strategy over large areas for high-performance electronics.

Review—The Development of Wearable Polymer-Based Sensors: Perspectives

“…Since the wearable sensors should be lightweight and simple, the low energy wireless system such as Zigbee, radiofrequency identification (RFID), and low energy Bluetooth are preferable. The power system of wearable devices can be pursued using wearable batteries, 15 supercapacitor, 155 and bio-battery/fuel cell 156 for energy storage while wearable photovoltaic 155 and kinetic energy harvester (e.g., piezoelectric, electrostatic, and electromagnetic) 157 for energy harvesting. The wearable batteries have been commercially available based on zinc air batteries for hearing aid.…”

Effect of Pore Characteristics in Polyvinylidene Fluoride/Fumed Silica Membranes on Mass Flux in Solar-Assisted Evaporation Applications

“…Desalination technologies are typically based on either thermal or membrane-based mechanisms, both of which have been reviewed extensively in the literature [2][3][4][5][6][7]. There has been a growing interest in thin-film evaporation technologies for cooling applications, electronic devices, perspiration, and more recently, for solar-assisted water desalination because they enable cost-efficient water vapor generation by utilizing solar irradiation in a relatively simple mechanism [8][9][10].…”

“…(1) an absorbed region, in which a set of attractive forces exist between the liquid and the membrane wall forming the basis of the meniscus, (2) a transition region, in which the layer of water has a high curvature, forming low thermal resistance between the wall channel and the fluid, which causes better exploitation of the latent heat of evaporation and enhances evaporation, and (3) a bulk fluid/meniscus region, in which the curvature of the interface is constant, serving as a feed for the transition region in which the capillary forces are dominant [8,10,11].…”

The role of vapor venting and liquid feeding on the dryout limit of two-layer evaporator wicks

“…Recent developments include evaporator wicks designs having a layer of screen mesh on top of the microchannels [12], lateral converging arteries that feed a thin layer of sintered particles [3], a metal foam layer supplying liquid to thin microposts [13], nano-porous membranes bonded to microchannels [14], or a combination of biporous and monoporous sintered particles [11]. These designs all focus on providing a combination of high permeability to reduce the pressure drop associated with liquid feeding, small pores that provide a high capillary pressure to drive the liquid flow, and vapor removal pathways.…”