Research on the chemical adsorption precursor state of CaCl_2-NH_3 for adsorption refrigeration

摘要

As a type of chemical adsorption working pair, the physical adsorption occurs first for CaCl_2-NH_3 because the effective reaction distance for van der Waals force is longer than that for chemical reaction force, and this physical adsorption state is named the precursor state of chemical adsorption. In order to get the different precursor states of GaCl_2-NH_3, the different distances between NH_3 gas and Ca~(2+) are realized by the control of different phenomena of swelling and agglomeration in the process of adsorption. When the serious swelling exists while the agglomeration does not exist in the process of adsorption, experimental results show that the activated energy consumed by adsorption reaction increases for the reason of longer distance between Ca~(2+) and NH_3, and at the same time the performance attenuation occurs in the repeated adsorption cycles. When the agglomeration occurs in the process of adsorption, the activated energy for the transition from precursor state to chemical adsorption decreases because the distance between NH_3 gas and Ca~(2+) is shortened by the limited expansion space of adsorbent, and at the same time the performance attenuation does not occur. The adsorption refrigeration isobars are researched by the precursor state of chemical adsorption; results also show that the precursor state is a key factor for isobaric adsorption performance while the distribution of Ca~(2+) does not influence the permeation of NH_3 gas in adsorbent.