The purpose of this paper is to demonstrate the importance of the use of the exergy analysis in the optimization of the geometry of a periodic-flow regenerator. The optimum geometry of the regenerator is determined using the unit cost of exergy of the warm air delivered as the objective function. The running cost is determined using different unit costs for the pressure component of exergy E˙ΔP and the thermal component of exergy E˙ΔT, which are evaluated separately. The ratio of the two unit costs has been calculated for an air-conditioning application in which the regenerator is used. A mathematical model of condensation, evaporation, thermal conductivity and heat transfer is presented for calculating the fluid and matrix temperatures effect on the regenerator performance. The governing differential equations have been formulated in terms of the characteristic dimensionless groups (Πt,Λt, and Zt).

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