Development of an Electroosmotic Pump-Driven Micro LiBr Absorption Heat Pump System for Controlling Microclimate in Protective Clothing: Feasibility Review and Role of the Pump

Abstract

In this study, the feasibility of using a micro LiBr/water-based absorption heat pump system embedded in protective clothing used in hazardous environments is explored and the characteristics of various microelectromechanical-system-based components are reviewed. The pump is identified as a key part of optimizing the performance of the system. An electroosmotic (EO) micro pump is suggested due to its higher flow rate together with many other advantages. A fabrication process of the EO micro pump was developed and various prototypes of the EO pump were fabricated using standard microfabrication technology. Experiments were conducted to study the performance of the EO micro pump. The results show that a thinner pump offers a higher pressure capacity but a lower flow rate. Higher electric field strength results in an enhanced pressure capacity and flow rate. The flow rate increases at higher temperatures. The effect of the ionic concentration on pumping performance is weak even if the flow rate and pressure capacity are enhanced to some extent. Ethanol was also explored, and it was found that both the flow rate and the pressure are lower when water is used as the working liquid. The information from these results is valuable for use in the subsequent design of the overall micro heat pump system. A thermodynamic analysis using the EO pump information shows that the energy density of the micro heat pump system can be as high as 2.6 W/g and is feasible for use in protective clothing aiming at a total cooling load of about 300 W. The EO pump has been found to contribute about 45% of the total mass of the micro heat pump system.