Dynamic Simulation of an Ammonia-water Absorption Refrigeration System

A dynamic model of a single-effect absorption refrigeration cycle with realistic thermodynamics has been developed. The thermodynamic properties are obtained from the Redlich-Kwong equation of state for ammonia/water as the refrigerant/absorbent mixture. The governing ordinary differential equations are derived from the mass, momentum and energy balances for the different components of the system. Lumped parameters are assumed, so that at any instant of time the generator, condenser, evaporator and absorber are each characterized by a single temperature, pressure and concentration. Friction factors are used to calculate pressure drops in the pipes. The transient response of the cycle to a step change in pressure rise across the pump is determined from numerical solutions of the governing equations. The dynamic responses of the mass flow rates, heat rates and the coefficient of performance are shown. The rise time seems to be about two loop circulation times.