Analysis and improvement of the efficiency of NH3-NaSCN single effect absorption cooling system

Abstract

This work aims at reinforcing simultaneously the coefficient of performance (COP) and the exergetic coefficient of performance (ECOP), in order to improve the operation of an absorption chiller to be used in tropical areas. It uses a new method based on the determination of variable one-line matrix that allows to find the NH3 mass fraction of NH3-NaSCN solution on each branch of the system.This matrix is obtained by substitution between the empirical formulae of NH3 and NH3-NaSCN from two different approaches, with the aim of making the current model more simple and less complex than those commonly used by other researchers. The approach developed is a direct digital method, easy to implement and allowing to find and understand some hidden functions of the black boxes of several energy simulation softwares, such as the Engineering Solver Equation (EES). The modeling of the system is carried out in Matlab to predict the temperatures and mass flows that can upgrade the system. The purpose is to contribute to the improvement and commissioning of an absorption chiller operating at thermal comfort temperatures in two cities in Cameroon: Douala and Yaoundé. The results show that the temperatures in the generator, condenser and absorber for which the COP and ECOP are maximum are respectively [92°C; 100°C]; 35°C, and [35°C; 40.8°C], and those of the mass flow rates of the refrigerant leaving the generator and condenser are respectively [0.44 kg/s; 0.86 kg/s] and 0.98 kg/s. The evaporator does not show these remarks. The simulation results can be used for thermodynamic optimisation of the cooling capacity (CC) and reduction of electrical energy consumption of the current system.