Enthalpy and exergy transfers of high pressure switching expansion reduction

The energy balance, air internal energy, enthalpy and exergy transfers of high pressure switching expansion reduction (SER) are comparatively analyzed in this paper to give a better understanding about the exergy analysis and its difference between energy conversion analyses for the pneumatics. In SER, the exergy transfer efficiency is much lower than the enthalpy efficiency. The enthalpy efficiency is primarily related to the initial pressure of supply tanks, and the exergy efficiency is primarily related to the pressure reduction ratios. Heat transfers increase the internal energy, enthalpy and exergy of air; the influence on exergy is relatively small. The total enthalpy in SER decreases as the air temperature decreases in the expansion process of the air. And exergy loss is primarily related to the irreversible process of isenthalpic throttling but not energy conversion. Based on the analyses, to improve the exergy efficiency of the pneumatics, the pressure reduction without power output should be avoided.