The equivalent low-dissipation combined cycle system and optimal analyses of a class of thermally driven heat pumps

The performance characteristics, operation, and design strategies of a class of thermally driven heat pumps are investigated due to their important roles in the efficient utilization of low-grade thermal energy. In order to establish a more generic thermodynamic model of thermally driven heat pumps mainly including absorption, adsorption, and ejector heat pumps, low-dissipation assumption is adopted. Accordingly, the associated dissipation parameters accounting for the specific information on the irreversibilities in each heat-transfer process are introduced rather than specifying heat-transfer law. Based on the proposed model, the theoretical results of the coefficient of performance and heat load are derived with regard to two key parameters denoting the size ratio of the two involved subsystems and the matching deviation from reversible limit. The performance characteristics and the optimally operating regions of the whole system are determined and the differences between thermally driven heat pump and refrigerator are highlighted. The proposed model and obtained results further develop the low-dissipation model and may provide a useful description for the operation and design of practical thermally driven heat pumps.