Study on the Performance Improvement of Single-bed Adsorption Refrigeration System Employing Activated Carbon Fiber-Ethanol Pair

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This research project aims to improve the performance of thermally powered adsorption cooling cycle by selecting new adsorbent/refrigerant pair. Adsorption capacity of adsorbent/refrigerant pair depends mainly on the porous properties (surface area, pore size and pore volume) of the adsorbent and isothermal characteristics of the adsorbent/refrigerant pair. In this paper, the porous properties of three pitch types' activated carbon fibers (ACFs) namely, ACF (A-20),ACF (A-15) and ACF (A-10) are determined from the nitrogen adsorption isotherms and compared with those of silica gels. The standard nitrogen gas adsorption/desorption measurements on the six different adsorbents at liquid nitrogen of temperature 77.3K were performed. ACFs have large surface areas and their adsorption/desorption rates are rapid due to the existence of numerous micropores in the vicinity of the fiber surface. ACF (A-20) possesses the highest surface area among all six adsorbents. Nitrogen adsorption/desorption isotherm results showed that ACF (A-20) has higher adsorption capacity in comparison with those of other two ACFs. The experimental equilibrium adsorption capacity of ethanol on ACF (A-20) is as high as 0.797 kg/kg. From the above perspectives, an intermittent adsorption refrigeration system using ACF (A-20)/ethanol pair is developed. Experiments are performed to determine the temperature and pressure profiles along with the various heat transfer rates and overall heat transfer coefficient during pre-heating and desorption processes of the reactor bed those play important roles in the cooling system performance. Experimental results show that the overall desorption heat transfer rate is as high as 1200 W/m・K.