Many small-scale energy systems require effective miniaturized pumps and expanders. These devices are responsible for conveying a working fluid through various components to execute a cycle that may result in power production, heat pumping, or refrigeration. As an example, a pump is required for pressurizing the working fluid in Rankine power cycles. Miniaturized pumps could also cycle a heat transfer fluid through a cooling loop for heat rejection purposes. On the other hand, expanders are necessary for any cycle employing a working fluid to generate power. Specific examples include microturbines, miniaturized piston-based machines, and roots-type expanders. (more…)

Heat-actuated heat pumps are cooling systems requiring no electricity for operation. Rather, a heat source is used, avoiding the need for batteries. This consideration is critical for portable applications because on a weight basis, a stored liquid fuel has anywhere from 35 to 300 times the energy content of batteries, depending on the battery technology considered. Thus, although the simple solution of combining an electric motor, a battery package, and a vapor compression refrigerator may sound appealing, it actually suffers a severe volume and weight disadvantage when compared with a heat-actuated system. (more…)