A tree-on-a-chip: Design and analysis of MEMS-based superheated loop heat pipes exploiting nanoporous silicon membranes

Abstract

This paper reports the design, fabrication and analysis of a plant-inspired, MEMS- based superheated loop heat pipe (SHLHP) that would exploit nanoporous membranes to allow for operation with large capillary pressures and superheated liquid. The operating principles of SHLHPs differ from conventional designs in 1) the un-coupling of the working fluid from its saturation curve to eliminate limitations associated with temperature head and sub-cooling conditions and 2) the possibility of maintaining sub-saturation throughout the device to eliminate film condensation and improve the condenser thermal conductivity. Nanoporous silicon membranes integrated with DRIE channels are fabricated and characterized. The ability of the membrane to hold liquid under tension is tested by equilibrating water-filled device with various relative humidity and observing the cavitation events within individual voids underneath the membrane. Silicon membranes with desired functionality are further incorporated with patterned glass substrates to form prototype MEMS-based SHLHPs.