Improvement of activated charcoal-ammonia adsorption heat pumping/refrigeration cycles : investigation of porosity and heat/mass transfer chacteristics

Reported in this thesis are the results of a combined theoretical and experimental study into improvements to the solid adsorption refrigeration or heat pumping cycle using the ammonia-activated charcoal pair. The three areas which have been examined are the cycle thermodynamics, the porosity characteristics of ammonia-charcoal pairs and the heat transfer through an ammonia granular charcoal packed bed. It was found through the use of advanced thermodynamic cycles utilizing multiple beds that the coefficient of performance of a refrigerator could be increased by sv 250% and the coefficient of amplification of a heat pump could be increased by co 110%. The coefficients of performance and amplification may also be increased to a lesser degree by judicious choice of the charcoal porosity characteristics. A survey of charcoal porosity characteristics revealed that the useful energy per cycle could be doubled by the correct choice of charcoal. The thermal conductivity of an ammonia granular charcoal bed was measured using a novel piece of apparatus. From the results it was decided for all practical purposes that the bed conductivity may be considered constant and equal to 0.165 W/m K. The power output of the cycle was found from modelling the dynamic desorption of a reactor using a one-dimensional finite difference model set in radial coordinates. The cycle simulations revealed that ideally the reactor should be constructed from solid charcoal shapes manufactured in such a way as to incorporate paths of enhanced conductance and be integral with the containing vessel wall