Comparison among three adsorption pairs for using as the working substances in a multi-bed adsorption heat pump

A comparison among three adsorption pairs (activated carbon-methanol, silica gel-water and 13X molecular sieves-water) for using as the working substances in a four-bed adsorption heat pump is presented. A solid-side resistance model considering a finite mass flow-rate of heating/cooling fluid was adopted. The result shows that, for small mass flowrates of the heating/cooling fluid, assuming a constant temperature for the heating/cooling fluid might give rise to an over-predication of the system performance. For the adsorption heat pump, there exists an optimum mode operating time (T) which corresponds to a maximum specific cooling power. For operations at the maximum specific cooling power (tau = 3-6 min) and with regeneration temperatures in the range 80-120 degrees C, among the three adsorption pairs, the activated carbon-methanol pair leads to the highest specific cooling power, COP value and second-law efficiency. For the silica gel-water pair, the temperature rise resulting from adsorption heat significantly downgrades the system performance. This causes its corresponding specific cooling power, COP value and second-law efficiency to be lower than those for the activated carbon-methanol pair. The 13X molecular sieves-water pair possesses the smallest cyclic variation of adsorbate content, thus it yields the lowest specific cooling power, COP value and second-law efficiency. (c) 2007 Elsevier Ltd. All rights reserved.