Abstract
‡In this paper, a heat-actuated cooling system based on an expander/compressor heat pump cycle is introduced. It combines a Rankine-type power cycle with a refrigeration cycle. By exploiting the higher stored energy density of liquid hydrocarbons over batteries, this heat pump cycle has a large performance advantage (size, weight, and portability) over battery powered vapor compression systems. The work output from the power cycle is used to drive the refrigeration cycle. The same working fluid is used throughout to reduce system complexity. Furthermore, the design of the components has been accomplished using microtechnology-based structures to enhance heat transfer and to reduce system weight and volume. A computational model was developed to estimate system performance for a set of given components and operating conditions. According to preliminary experimental results on the expander/compressor, reasonable isentropic efficiencies for the expander and compressor were used in the model to determine the COP of the heat-actuated heat pump system. For the desired cooling load of 150 Watts, both the baseline cycle and a heat recovery cycle were studied. Results show that system performance is significantly affected by incorporating heat recovery, especially when the working fluid is superheated. The COP of this latter cycle increases with superheat. However, the COP of the system without heat recovery decreases with increasing superheat. To optimize performance, some parametric studies have also been performed to investigate the effects of operating conditions of each heat pump component. Results show that the COP of the heat-actuated heat pump can attain a value of 1.3 with 100 o C superheat over a saturation temperature of 116 o C. This is a very attractive coefficient of performance for a heat-actuated system.
Published Version
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