Experimental analysis of a transfer function for an air cooled evaporator

A transfer function to model a direct expansion air cooled evaporator, inse rted in a vapor compression refrigeration plant, is deduced by means of exp erimental analysis. For inlet air temperatures onto the evaporator and refr igerant mass flow rate variable in appropriate ranges, the evaporator dynam ic behavior is simulated by a linear model with delay. The results of trans fer function are compared with experimental data, obtained by applying both step inputs and periodic changes to the refrigerant mass flow rate. The in fluence of the hunting, typical of a thermostatic expansion valve, is also estimated experimentally and then validated by the transfer function, obtai ning a good agreement. These results could be applied to obtain a control a lgorithm for the refrigerant mass flow rate feeding the evaporator, by vary ing the speed of the compressor motor. (C) 2000 Elsevier Science Ltd. All r ights reserved.