Experimental investigations and modelling of a small capacity diffusion-absorption refrigerator in dynamic mode

This paper reports on the experimental investigations in a non-steady state mode of a small capacity commercial diffusion-absorption refrigerator (DAR) and the development of a dynamic black-box model for the machine. For these investigations, the refrigerator was equipped with the appropriate metrology. Temperature time variations of the refrigerated room and of the ambient conditions were measured, monitored, and stored using a data acquisition unit connected to a computer. A standardized experimental procedure was used to determine the overall heat conductance of the refrigerated room: A value of (UA)cab = 0.554 W K−1 was found. The time evolution of the cooling capacity for different driving heat inputs to the refrigerator was investigated. Based on the experimental data, a dynamic black-box model was developed using the Matlab identification package to correlate the power input to the generator and the cooling capacity of the refrigerator. A first order transfer function with a delay was found to describe quite accurately the time evolution of the cooling capacity for all considered heat rates supplied to the generator. In a further step, regressed analytical expressions of the transfer function parameters, as a function of the generator heat supply, were incorporated into the cooling capacity function. A generalized dynamic black-box model for the DAR system was thus obtained and was then validated using the Matlab Simulink® environment. The predictions made by the model were found to be well in agreement with the experimental data. In particular, the predictions for COP under steady state conditions agreed satisfactorily with the experimental data yielding a maximum relative deviation of about 8%.