Parametric study of a silica gel water adsorption refrigeration cycle - The influence of thermal capacitance and heat exchanger UA-values on cooling capacity, power density, and COP

The influence of heat exchanger UA-values (adsorber/ desorber, evaporator, and condenser) is investigated for an adsorption chiller, with consideration given to the thermal capacitance of the adsorber/desorber by means of a lumped parameter cycle simulation model developed by the authors and co-workers for the single-stage silica gel-water adsorption chiller. The closed-cycle-type chiller, for use in air conditioning, is driven by low-grade waste heat (85 degrees C [185 degrees F]) and cooled by water at 31 degrees C (88 degrees F) and operates on relatively short cycle times (420 seconds adsorption/desorption; 30 second adsorber/desorber sensible cooling and heating). The results showed cycle performance to be considerably affected by the thermal capacitance and UA-value of the adsorber/desorber, which is attributed to the severe sensible cooling/heating requirements resulting from batched cycle operation. The model is also sensitive to the evaporator UA-value-but to a lesser extent. The condenser UA-value is the least sensitive parameter due To the working pair adsorption behavior in the temperature range defined for desorption and condensation.