THERMODYNAMIC MODELING OF ABSORPTION CHILLERS, HEAT PUMPS AND HEAT TRANSFORMERS

Abstract

Absorption chillers, heat pumps and heat transformers exploit thermal power input to satisfy a variety of refrigeration and heating applications, as well as for boosting the temperature of low-grade heat. Can one arrive at accurate predictions of system performance with a simple analytic irreversible thermodynamic model? How closely do present-day absorption machines operate to maximum Coefficient Of Performance (COP) conditions derived from a general thermodynamic model? The simple yet accurate thermodynamic model described in this thesis captures the key dominant physics which govern the performance of three types of absorption machines, namely, (i) external losses due to the heat and mass transfer in the generator and absorber, internal regenerator and throttling valve, (ii) internal dissipative losses (entropy generation), and (iii) external heat leaks to or from the environment and internal heat leaks between reservoirs.

Using this simple and accurate model, the author qualifies and quantifies the sources and contribution of each kind of loss, which make it possible for machine manufacturers to improve the performance of their designs. This would also highlight the various aspects to which efforts should be focused for performance enhancement. By comparing the actual performance of absorption machines with the corresponding maximum COP operation predicted by the thermodynamic model, the author has demonstrated that these heat driven machines have empirically evolved towards maximum efficiency operation.