Solidified expanded natural graphite (ENG) has good heat and mass transfer characteristics and has recently been utilized as a matrix for heat and mass transfer performance intensification in adsorption refrigeration and air conditioning equipment. In order to gain an overall understanding of the heat and mass transfer process in solidified expanded natural graphite, the anisotropic thermal conductivities and permeabilities are investigated in two types of solidified block, i.e. discs of solidified expanded natural graphite (DSENG) and plates of solidified expanded natural graphite (PSENG), in which the heat conductive and mass transfer directions are parallel and perpendicular, respectively, to the pressing direction producing blocks. An unexpected phenomenon is found in the research, which is that the thermal conductivity sometimes decreases while the density of the solidified ENG increases, this only occurring for the heat conductive direction perpendicular to the pressing direction. Results also show that the direction has larger thermal conductivity also has a better permeability; the phenomena of anisotropic thermal conductivities are strongly dependent on density. The reasons are analyzed in the paper, and they are mainly related with the distribution of micro layers inside the samples.

Our experiments show that active carbon fiber (ACF) might be a good substitute for activated carbon (AC) as the refrigeration capacity Qf and adsorption time of ACF are three times more and 1/5 ∼ 1/10 of those of normal activated carbon (AC), respectively. The COP for ACF-methanol could be 10 percent ∼ 20 percent higher than that of AC-methanol. Thus ACF-methanol might be a good adsorption refrigeration pair for constructing adsorption refrigerators, especially those for household applications.

Adsorption refrigeration and heat pump systems have been considered as very important means for the efficient use of low grade thermal energy in the temperature range of 60–150°C. Sorption systems are merely heat exchanger based thermodynamic systems, and therefore a good design to optimize heat and mass transfer with reaction or sorption processes is very important for high performance of the systems. Studies on heat and mass transfer enhancement in adsorption beds have been done extensively. Notable techniques is whereby the adsorbent bed is fitted with finned heat exchanger embedded with adsorbent particles, or the adsorbent particles may be compressed and solidified and then coupled with finned tube or plate heat exchangers. The use of expanded graphite seems to be an effective method to improve both heat and mass transfer in the reaction bed. Studies have also shows the need to enhance the heat transfer in adsorption bed to match with the heat transfer of thermal fluids. Use of heat pipes and good thermal loop design could yield higher thermal performances of a sorption system, when coupled with adsorption beds to provide heating and cooling to the beds. A novel design with passive evaporation, known as rising film evaporation coupled with a gravity heat pipe was introduced for high cooling output. It has also been shown that heat and mass recovery in the internal sorption systems is critical, and novel arrangement of thermal fluid and refrigerant may result in high performance sorption systems. Based upon the above researches, various sorption systems have been developed, and high efficient performances have been reached. Typical sorption systems include (1) A silica gel-water adsorption water chillier with a COP about 0.55 when powered with 80°C hot water, (2) A CaCl2-ammonia adsorption refrigerator with a COP over 0.3 at −20 °C when powered with 120 °C water vapor, which has a specific cooling power about 600 W/kg-adsorbent. The above mentioned systems have shown that solid sorption systems have become market potential products, and low grade thermal energy, which is usually considered as waste heat, could be utilized to provide high grade cooling. This paper gives details of high efficient solid sorption systems recently developed, their heat transfer design, thermodynamic system coupling, and performance test results. Some examples of low grade thermal powered cooling systems are also presented.

in Wiley InterScience (www.interscience.wiley.com).The conceptual design of an innovative multimode, multisalt and multieffect solid-gas chemisorption refrigeration system with evaporation and resorption processes is presented. In the proposed system, both the evaporation heat of the refrigerant during adsorption process and the reaction heat of the low-temperature salt during resorption process are employed to provide useful cooling. The reaction heat of the high-temperature salt is recovered for the regeneration process of the middle temperature salt. The presented system has the distinct advantage of larger cooling capacity per unit of heat input in comparison with other types of sorption refrigeration systems, based exclusively on evaporation or resorption. To identify the expected COP of the proposed system, two groups of working pairs containing metal chlorides and ammonia were analyzed. The ideal coefficient of performance (COP) can be improved by more than 59 to 169% if compared to the COP obtained with other kinds of cycle. When the sensible heats of the reactant, the refrigerant and the metallic part of the reactors are considered in the calculation of the COP, this figure can reach values between 0.91 and 1.80, according to the salts employed and the mass ratio between the metallic part of the reactor and the salt.

Properties, such as thermal conductivity and permeability, are important for the heat and mass transfer performance in sorption refrigeration. This Technical Brief investigates the thermal conductivity and permeability of eight types of chlorides, which are consolidated with expanded natural graphite (ENG) for the heat transfer intensification.