Transient Characteristics of a Single-Effect Absorption Refrigeration Cycle

This paper deals with a lumped-parameter dynamic simulation of a single-effect LiBr-H2O absorption chiller. In many studies the thermodynamic properties of LiBr-H2O solution were taken from some approximate relations causing the results to be somewhat inaccurate. These relations were used to solve simultaneous differential equations involving the continuity of species constituting the LiBr-H2O solution, momentum equations, and energy balances. To diminish the effect of these approximate relations on the results, in this study the thermodynamic properties were taken from the EES software. By making a link between EES and MATLAB softwares, the simultaneous differential equations were solved in MATLAB environment and this process was continued until the convergence criterion was satisfied. Moreover, this study considers the effect of quality on the concentration of solution at the exits of generator and absorber. This effect was ignored in the previous works. In other words, the concentrations of solution at the generator and absorber were not assumed to be equal to the corresponding concentration at the exit of those components in this model. Furthermore, a transient analysis of exergy is accomplished. As time passes, both the coefficient of performance and exergetic efficiency decrease, approaching the steady-state values. The results deduced from the dynamic simulation are compared with those in steady-state condition. The comparison shows that the transient simulation predictions are in close agreement with steady-state results.