Journal of Engineering Physics and Thermophysics, Vol. 92, No. 6, November, 2019 ADSORPTION OF CO 2 AND ETHANOL BY A SPHERICAL ACTIVATED CARBON IN A HEAT PUMP K. Uddin, a,b A. Pal, a K. Thu, a,c and B. B. Saha a,d UDC 622.323 A promising adsorbent representing a phenol resin activated with potassium hydroxide, which can be used in innovative next-generation adsorption cooling and heating pump systems, is proposed. Keywords: activated carbon, adsorbent, carbon dioxide, ethanol, heat pump, phenol resin, uptake. Introduction. After the imposition of international restrictions on the production and use of refrigerants causing a depletion of the ozone potential and a global warming, the efforts of researchers worldwide to find a system alternative to a heat pump were intensified. The demand for thermal comfort was also increased due to the necessity of safeguarding against the adverse environmental effect caused by the additional consumption of electric energy. An adsorption heat-pump system has been developed as a suitable alternative to a conventional vapor-compression system. An adsorption heat pump works on the basis of natural adsorption and desorption effects. Adsorption takes place at low temperatures, whereas desorption is realized at high temperatures. An adsorption heat-pump system has many advantages over a vapor-compression system, because it practically does not consume electric energy, can operate on the basis of natural refrigerants (CO 2 , water, ethanol, methanol), and is free of vibrations and noise [1]. Moreover, an adsorption heat-pump system can be easily driven by low- intensity thermal energy available abundantly in major parts of the world, e.g., solar energy or low-grade waste heat of temperature below 100 o C. The performance of the adsorbents used in an adsorption heat-pump system is primarily governed by their surface area, the volume and size of the pores in them, and the size of the granules in an adsorbent powder. The main hindrance to the widespread use of this environment-friendly technology is the poor performance of an adsorption heat-pump system and its bulkiness, which is explained by the limited sorption capacity of an adsorbent and the low rate of heat transfer in the adsorber and desorber reactors of such a system. Therefore, the selection of innovative adsorbent–refrigerant pairs possessing a high adsorption uptake and a rapid kinetics is a hot research problem. Different approaches to the improvement of the performance of an adsorption heat-pump system can be found in the open literature. In [2, 3] a single-stage, two-bed adsorption chiller operating on the basis of a silica gel–water mixture, which can be energized by a heat source with a temperature below 85 o C, is described. In another endeavor, the authors of these works investigated multibed adsorption chillers for the purpose of increasing the efficiency of such an apparatus and smoothening the temperature of the delivered chilled water [4–6]. To use effectively a heat source with a temperature below 70 o C, multistage and multibed approaches were taken by many authors [7–11]. Different adsorbent– refrigerant pairs, such as activated carbon (AC)–ammonia, AC–methanol, AC–R134a, silica gel–water, and zeolite–water, were investigated for the purpose of determining the applicability of them in adsorption systems. The use of carbon dioxide (CO 2 ) as a refrigerant became popular due to its negligibly small impact on the environment and high operating pressure. An adsorption heat pump using CO 2 provides two solutions: 1) a decrease in the geometry of the apparatus and 2) a decrease in the impact of it on the environment, which contributes positively to the commercialization of the system. The key parameters of an adsorption heat-pump system operating on the basis of CO 2 are the rate of adsorption of CO 2 and the amount of the CO 2 adsorbed. Ethanol is another popular refrigerant having a relatively high vapor pressure compared to that of water. The latent heat of vaporization of ethanol is about 838 J/g. Moreover, its normal boiling point (78 o C) and low melting point (–115 o C) are advantageous for low-temperature refrigerators. 0062-0125/19/9206-1575 ©2019 Springer Science+Business Media, LLC 1575 a International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan; email: uddin.kutub.md.360@m.kyushu-u.ac.jp; b Faculty of Physics, Jagannath University, Dhaka-1100, Bangladesh; c Green Asia Education Center, Kyushu University, Kasuga-koen 6-1, Kasuga-shi, Fukuoka 816-8580; email: kyaw.thu.813@m.kyushu-u.ac.jp; d Mechanical Engineering Department, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan; email: saha.baran.bidyut.213@m.kyushu-u.ac.jp. Published in Inzhenerno-Fizicheskii Zhurnal, Vol. 92, No. 6, pp. 2623–2629, November–December, 2019. Original article submitted 17.01.2019. DOI 10.1007/s10891-019-02076-5