Micro and macro scale electrohydrodynamic enhancement of thin-film evaporation

Evaporation of thin liquid films has long been recognized as one of the most effective methods of heat removal. As a result, techniques that employ this mechanism have potential for use in many practical applications such as electronic cooling, heat pipes, and process heat exchangers. Demand for high-power density electronics, along with the associated requirements including temperature uniformity and the limitation on maximum temperature, will require the development of new methods of heat removal for these devices. The electrohydrodynamic (EHD) technique offers a promising alternative for the uniform distribution of temperature and the removal of heat at high power levels. These factors directly affect the performance, cost, and reliability of such devices.; An experimental investigation was undertaken to study the feasibility of applying the EHD technique for heat transfer enhancement of thin-film evaporation. Macro-scale experiments were conducted on several heat transfer surfaces in both horizontal and vertical orientations and the mechanisms involved in heat transfer enhancement were clarified. For the various heat transfer surface/electrode geometries tested, enhancement factors ranging from 25% to 390% were obtained.; The novel concept of EHD-enhanced source level cooling utilizing MEMS and thin-film evaporation was then introduced. The device was designed and fabricated using VLSI fabrication technology. This technology allowed the integration of an active cooling device, a micropump, and temperature sensors into a single chip, greatly facilitating the manufacturing process, increasing the cooling capacity, and improving the thermal management of future high-power density electronics. The results indicate a maximum cooling capacity of 65 W/cm2 and a corresponding pumping head of 250 Pa. This unique microcooling device has high commercialization potential and can pave the way for practical utilization of thin-film evaporation in microelectronics cooling and many other applications.; An analytical model was also developed to predict the heat transfer and flow characteristics of EHD-enhanced thin-film evaporation. The model predicts film thickness, local and average heat transfer coefficients, dryout areas, and velocity profile. The agreement between the model and the experimental data is satisfactory and the trends of data support the contention that the model provides a realistic treatment of the flow and heat transfer. Both the analytical model developed in this study and the experimental results will facilitate the design of new microcooling devices capable of operating at high power levels.