Exergy analysis of an isothermal heat pump dryer

We determine the energy efficiency benefit obtainable from an isothermal plate-type heat pump dryer employing contact heat transfer, by developing a numerical simulation to compare such a system with a conventional heat pump dryer. The model presented combines a comprehensive heat pump model with a detailed air-flow model, which solves the mass, momentum and energy balances within the drier ducts. We assess the accuracy of an idealised model used in a previous analysis. Although the performance of the idealised model is sensitive to system temperature variations, this does not lead to significant error under typical heat pump drying conditions. We employ exergy analysis to examine the benefit associated with contact heat pump drying. Isothermal drying is found to reduce irreversibility occurring within the refrigerant cycle by roughly the same amount as that occurring in heat transfer from the condenser to the product.