Investigation of Microboiler for Discarded Thermal Scavenging

Abstract

This paper presents detailed fabrication and operational characterization of a MEMS based microboiler designed to scavenge waste thermal energy from sources like transportation or industry. Microboiler operation is based on capillary action that drives the working fluid from surrounding reservoirs to the surface that is heated by the waste thermal energy. As a result of phase change from liquid to vapor, pressure is created inside the enclosed central steamdome. This pressurized vapor can be made available to another MEMS device (PZT membranes, thermoelectric, etc.) to produce useful power output. In contrast to previous work, the new miniature microboiler design has undergone several modifications that improve operating efficiency. Capillary channels that were designed in linear fashion have been upgraded to a radial layout. This modification facilitated boiler enhancements in capillary flow, operating pressure, and rate of mass transfer. Capillary channels are formed from the silicon substrate with 50 μm widths and 100 μm depths. Power inputs of 2W, 3W and 4W are utilized to characterize performance. Maximum energy absorption via phase change of working fluid was 1.6 mW given a source temperature of 128 °C. The maximum steady state operating pressure achieved during testing was 3.65 kPa.

Experimental and computational investigation of a MEMS-based boiler for waste heat recovery

“…These values showed improvement versus boilers presented in prior efforts where a larger dimension acrylic steamdome was utilized [28,30]. The use of a thin glass wafer as a steamdome eliminated a significant heat sink effect previously encountered.…”

“…The glass was preferred as a material of fabrication because of its insulating properties. The glass also represented significant mass reduction as compared to prior work [28,30]. This reduced the steamdome thermal impact as part of boiler operation.…”

“…Capillary channels themselves were designed based on prior experimental work [28][29][30] as well as expectations from open channel models [29,31]. Two components were brought together to form the boiler.…”