Design optimization of the flat plate collector for a solid absorption solar refrigerator

A study of the effects of various collector design parameters on the performance of a solar powered solid absorption refrigerator is presented. The refrigerator uses specially treated CaCl2 as absorbent and NH3 as refrigerant and operates intermittently in a diurnal cycle. The study is undertaken using version 4.0 of a simulation programme, COSSOR, developed from a transient analysis of the system. A large number of simulations was undertaken to test the performance of the refrigerator for various choices of the collector design parameters. The latter include the plate emissivity and material; absorbent pellet diameter, thermal conductivity and packing density; collector tube size, spacing and material; and number of glazing. The refrigerator performance indicators, namely total condensate yield, mass of ice produced, coefficient of performance and effective cooling, are presented for the range of values of the collector parameters of interest. Using a multiple linear regression technique, the performance indicators are correlated with the collector parameters by simple linear polynomial expressions. An objective function, suitable for selecting optimal values of the parameters, is defined, subject to specified constraints. Optimization was then carried out for the objective function. For the collector with steel tubes and steel plate, the refrigerator coefficient of performance obtained with optimal choices of tube size, spacing and plate emissivity is 0.073, representing an improvement of at least 30% with respect to the reference collector. A similar lever of improvement was obtained for a collector with aluminium tubes and plate. (C) 1997 Elsevier Science Ltd.