A Microboiler: Waste Heat To Power Scavenging System

This paper presents the detailed fabrication and baseline operational characterization of a miniature device capable of recovering waste heat for power: Waste heat to power is the process of scavenging heat from a large process as a result of mechanical inefficiencies and using that heat to generate useful power. To address this waste heat to power recovery approach, a MEMS based microboiler has been investigated in this work which is capable of capturing waste heat. The microboiler consists of a micro fabricated boilerplate and a steamdome. The boilerplate has been designed with capillary channels capable of driving fluid flow from the surrounding reservoirs to the heated surface, thus eliminating the need of an electrically powered flow pump. The working fluid undergoes phase change inside the enclosed central steamdome attached atop the boilerplate. This pressurized vapor can be made available to another MEMS device such as PZT membrane capable of generating mechanical or electrical power. In this way, the discarded heat from the larger process can be utilized to generate power output.In contrast to the previous work, a thick acrylic steamdome has been replaced with a thin glass steamdome to minimize premature condensation of vapor due to heat loss via large mass. The tests were performed on the microboiler with the input powers of 1.8 W and 2.7 W and the comparisons of the results were carried out using a simulation model. The average temperatures at the top of the boilerplate were 106 degrees C and 144 degrees C for the power inputs of 1.8 W and 2.7 W respectively. The available powers at the top of the boilerplate via heat conduction were 1.14 W and 1.72 W for the power inputs of 1.8 W and 2.7 W for the supplied powers of 1.8 W and 2.7 W respectively. With these known available power throughputs and the heat of vaporization of the future working fluid, the calculated maximum mass flow rates were 13.6 mg/s and 9.12 mg/s, respectively.