Preparation of Active Carbons for Adsorption Cooling System
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Preparation of Active Carbons for Adsorption Cooling System BRONISLAW BUCZEK∗, ELIZA KLIMOWSKA AND ELZBIETA VOGT AGH – University of Science and Technology, Faculty of Fuels and Energy, 30-059 Cracow, Poland [email protected]
Abstract. Among the gas–solid adsorption processes the active carbon methanol adsorption seems to be interesting for use in thermodynamic systems such as heat pumps and cooling systems. The porous structure of active carbon modified by successive removal of external layers from a particle surface as produced by abrasion in spouted bed, next by demineralization and oxidation was evaluated on the basis of nitrogen adsorption data and those for methanol. The aim of this study was to test the improvement of texture and nature of surface of active carbon for adsorption refrigeration system. Keywords: adsorption, refrigeration, active carbon-methanol pair
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Introduction
Adsorption processes have been proposed for heat management as a consistent alternative to vapor compression systems. Gas adsorption phenomenon is strictly correlated to energy transfer and transformation because they are regulated by temperature and pressure. Taking into account these properties and combining endothermic desorption with exothermic adsorption processes in closed cycles, it is possible to realize several attracted features for both heat pump and heat transformers applications (Critoph, 1989). Adsorption systems show some advantages: the adsorbent is not submitted to any change of volume during the sorption processes, as in solid absorption; it does not need a rectifying column as in liquid absorption. Moreover, adsorption techniques allow large amounts of refrigerant liquid to be cycled. In the design of adsorption refrigeration/heat pump systems, the characteristics of both adsorbent— adsorbate (refrigerant) pairs and adsorption cycles play an important role in various kinds of applications. A number of suitable adsorbents can be used to sorb refrigerants from the air with the simultaneous release of energy. At present two pairs dominate in refrigeration ∗ To
whom correspondence should be addressed.
systems: zeolite–water and active carbon–methanol. Methanol is easily desorbed from active carbon when it is heated and can evaporate at a temperature largely below 273 K. In adsorption cooling system as important as choice of adsorbate is appropriate choice of adsorbent. Recently we can observe increasing interest porous structure of carbon adsorbent which work effective in cycles adsorption—desorption. The adsorption depends on the surface area and pore size distribution, which in turn arises due to the nature of the raw material and the method of activation used. The adsorbent should not only have a high surface area, but should also be able to provide a high packing density. It seems that the carbon - methanol pairs appears to be a most promising medium for the heat storage systems (Buczek et al., 2003). The effective work presented systems depends on: adsorption capacity, heat of adsorption, rate of adsorpt
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