MEMS-BASED PHASE CHANGE FOR HEAT TRANSFER WITH THERMOELECTRIC DEVICES AND ENERGY HARVESTING

The investigation of a capillary-based heat exchanger is presented for potential integration with thermoelectric devices and thermal energy harvesting. The exchanger is a microfabricated device, designed to promote phase change of low boiling-point working fluids and enhance heat transfer from thermoelectric devices as a result. Several heat exchanger designs are studied and compared in these experiments. All designs rely on capillary channels to pump working fluid from surrounding reservoirs out across a heated exchanger surface. First, a baseline silicon device is fabricated using standard RIE techniques to produce silicon capillary channels. Channel widths of 100 mu m are studied with varying heights. In addition to this base silicon device, SU-8 is used to further vary channel height. Heat exchangers are characterized based on operating temperature and heat input using 3M (TM) HFE 7200 working fluid. Maximum mass transfer rate recorded is 5.50 mg/s for Si channels operating above the boiling point of the working fluid. By contrast, SU-8 channels are shown to be more effective at temperatures below the boiling point. Maximum mass transfer rate is 2.29 mg/s for SU-8 based channels operating at these reduced temperatures.