Thermodynamic optimization of heat-driven refrigerators in the transient regime

The present work introduces a transient endoreversible model of a heat-driv en refrigeration plant, which is driven by a fuel-burning heater The model consists of a combustion chamber with negligible heat loss to the ambient, a refrigerator with three finite-size heat exchangers, namely, the evaporat or between the refrigeration load and refrigerant, the condenser between th e refrigerant and the ambient, and the generator between the combustion cha mber and the refrigerant, and finally the refrigerated space. The total the rmal conductance of the three heat exchangers is fixed. A thermodynamic opt imization of the absorption cycle is then performed, reporting the operatin g conditions for minimum time to reach a prescribed cold-space temperature, thus maximum refrigeration rate, specifically the optimal mass fuel flow r ate and the optimal way of allocating the thermal conductance inventory. Ha lf of the total supply of thermal conductance has to be divided equally bet ween the generator and evaporator and the other half allocated to the conde nser for optimal operation. A narrow range of fuel flow rates lead to the m inimum time to achieve a prescribed cold-space temperature, thus stressing the importance of the transient analysis. Appropriate dimensionless groups were identified and the generalized results are reported in dimensionless c harts.