Simulation and optimization of a novel solar-powered adsorption refrigeration module

摘要

A mathematical model has been developed to simulate and optimize the performance of a solar-powered adsorption refrigeration module with the solid adsorption pair of domestic type of charcoal and methanol. The module is composed of a modified glass tube having a circular generator (sorption bed) at one end and a combined evaporator and condenser at the other end. The charcoal is mixed with small pieces of blackened steel to enhance the heat transfer in the sorption bed. Simple arrangement of plane reflectors is used to heat the generator. The angles of inclination of the reflectors are chosen according to optical and thermal analysis to receive maximum solar energy at noontime. The model accounts for transient heat and mass transfer inside the bed of the module. After an experimental validation based on the results of previous tests of this module, the effects of design and climatic conditions on the module performance all year round are discussed and optimized. It is found by virtue of using the proposed reflector arrangement, solar energy input to the system increases especially in cold climate. This increase ranges from 10% for hot climate to 30% for cold climate. The effects of using steel additives inside the sorption bed and using glass shell over the bed are investigated. It is found that the percentage increase in desorped methanol ranges from 3% in the hottest month to about 19% in the coldest month as a result of using a mass of steel pieces equal about 33% of the mass of the charcoal, (M_(st)/M_(ch) = 0.33). These improvements increase to 7% and 43% in the hottest and coldest months respectively when glass shell is used over the bed. Generally, the improvements are more pronounced in cold months than hot ones. The ratio (M_(st)/M_(ch) inside the sorption bed is optimized and found to be 0.75. Comparison between the model results for the steel additives ratio (M_(st)/M_(ch) = 0.33 and results obtained with the optimum ratio shows that, the yearly average ice production increases from 0.23 to 0.25 kg/day, the yearly average bed efficiency increases from 55.2% to 58.5%, and the yearly average net COP increases from 0.146 to 0.1558. The effect of climatic conditions on the module performance all year round is also investigated. It is found that, about 28% of the cooling energy is lost due to climate effect in hot months and this ratio reaches 17.5% in cold months.