Research Of Composite Adsorbent Permeability Characteristics And Mass Transfer Enhancement

As an energy saving and environment benign refrigeration method, adsorption refrigeration has been widely used in solar energy, geothermal energy and recycling of low-grade heat. It has made a great contribution to relieve the tension of electricity supply, to reduce fossil fuel consumption, to improve environment. The core of adsorption refrigeration, namely adsorption working pairs, directly affects the choice of adsorption refrigeration machine’s design parameters and operation mode. Chemical adsorption has larger adsorption amount than physical adsorption, and can achieve higher COP and SCP. But there are many problems in the process of chemical adsorption, including expansion, agglomeration, poor heat transfer and gas permeability. Recently, composite/compound adsorbent has become research hot pot.The purpose of this thesis were exploring the permeability characteristic of composite adsorbent, solving synergistic enhancement problem of heat and mass transfer, acquiring adsorbent preparation process which had superior mass transfer performance without affecting heat conduction, and analyzing the influence of various factors on permeability. Based on this, a test platform suitable for testing of adsorbent permeability has been constructed according to Ergun model. A five factors and five levels orthogonal table was built combined with the principle of orthogonal experiment. At last, the mechanism of ammonia adsorption’s effect on mass transfer performance and the principle of how to control a certain amount of ammonia adsorption were discussed. The samples optimized by orthogonal experiment have been tested under different amount of ammonia adsorption. Influence of sample’s residual water content on permeability test after activation has been considered. Details are as follows:(1) Based on the Darcy law and Ergun model, a system suitable for nitrogen and ammonia permeability test was designed and built. The system has four parts: constant temperature water bath system, constant pressure gas supply system, testing system and ammonia treatment system. Each part was constructed with related equipment, all of them were elaborate to ensure high precision of experiment results. There are many differences about the dimension of permeability test subject at home and abroad, so the influence of two different dimension of subject on permeability has been analyzed. Considering the anisotropy of permeability, the influence of relationship between test direction and pressing direction on test result has been analyzed. Permeability of calcium chloride/graphite adsorbent under different density was tested, the empirical formula was acquired.(2) Based on the pore forming mechanism of carbonization and activation, wood powder was used for the preparation of adsorbent. According to the principle of orthogonal experiment, a table considering ratio of CaCl2 to wood powder, ratio of CaCl2 to graphite, temperature, time and particle mesh has been designed. These specimens were prepared fully under the guidance of orthogonal experiment. After that, the test results were analyzed by the statistical analysis software SPSS. Factors whether had a significant impact on permeability test results or not have been studied. The marginal mean values of the five factors have been estimated, the effect of each factor’s level on permeability has been analyzed. According to these, the preparation method of adsorbent with the best permeability characteristic was acquired. Finally, the orthogonal experiment results were verified, samples selected by orthogonal experiment have been tested under different curing density and were compared with the traditional calcium chloride/graphite composite adsorbents.(3) The influence of different ammonia adsorption capacity on permeability characteristic has been analyzed theoretically, so does the method to test the permeability in this case. In order to simplify the work, temperature has been considered as the main index of different adsorption amount when using the small dimension subject. The sample together with calcium chloride/graphite composite adsorbent has been tested, and the feasibility of carbonization and activation as the method to improve mass transfer characteristic has been verified. At last, the influence of different residual amount of water after the sample being dried and the residual amount of water under different density on permeability have been analyzed.