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process could lead to higher SCP and COP. Wang et al. [84] compared the performance of an adsorption system using different working pairs to identify the most suitable pair for adsorption ice making on fishing boats. The pairs compared were: 1) Activated carbon and methanol; 2) CaCl2 and ammonia; 3) compound adsorbent (80 % CaCl2 plus 20 % activated carbon) and ammonia. The pair activated carbon-methanol was that from Wang et al. [81]. In the experiment with the pair CaCl2 and ammonia, the authors measured the adsorbed mass of refrigerant at an evaporation temperature of –15 °C for different expansion ratios (void volume per filled volume of dry salt) and calculated the expected cooling capacity. The expansion ratio that produced the higher cooling capacity was 2:1. The cooling capacity was about 889 kJkg-1, and the cooling density was 185 MJm-3. The value obtained for the cooling density includes not only the volume occupied by the dry salt but also, the void volume necessary for its expansion. The compound adsorbent was tested in granular and consolidated form. The granular form presented attenuation in the adsorption performance. Based on the results of their experiments, the authors mentioned that a moderate agglomeration of the salt during the adsorption process is desirable to keep the adsorption properties stable on successive adsorption cycles, and this agglomeration was not observed with the granular compound. To promote the desired agglomeration, the authors mixed the compound with cement and produced a consolidated adsorbent. This compound presented stable adsorption performance after several adsorption phases and higher packing density. It could produce a cooling capacity of about 660 kJkg-1, and a cooling density of 254 MJm-3, when the evaporation temperature was –15 °C. Although the cooling capacity obtained with the consolidated compound was smaller than that obtained with CaCl2, the cooling density was about 38% higher. The increase in the cooling density happened because the packing density of the consolidated compound is higher than that of the CaCl2 (360 and 207 kg m-3, respectively). CaCl2 has low packing density because a high expansion space must be used inside the adsorber, as the CaCl2.8NH3 has a molar volume 4 times higher than that of the dry salt. Thus, for an application where a reduced volume is more important than a reduced mass, the consolidated compound is preferable. These authors estimated that for a 60 minutes cycle, the utilization of consolidated composite compound and CaCl2 would lead to a cooling power of about 20.3 and 14.8 kW, respectively, if they were placed in an adsorber with 0.29 m3 of useful volume. This volume was chosen to allow a comparison with the system developed by Wang et al. [81], and which had a cooling power of 2.0 kW. The same group from the previous work has achieved more progress recently with heat-powered adsorption icemakers. The new research show that split heat pipes can be successfully used in adsorption systems to heat and cool the adsorbers. This arrangement avoids the direct contact between the adsorber and the exhaust gases or the seawater. Furthermore, a significant increase of the COP and the SCP was noticed in the new system, and these results are presented in section seven of this paper. 5. ADSORPTION AIR CONDITIONERS DRIVEN BY EXHAUST GASES Air conditioning on vehicles could be another reasonable application for adsorption systems powered by exhaust gases. The vehicles more suitable for this kind of air conditioner are buses and locomotives, as adsorption systems usually still have large volume and mass. Zhang [80] studied an adsorption air conditioning system that could have the sorption beds regenerated by the exhaust gases of a bus. The adsorber consist of two concentric pipes, and the exhaust gases or the cooling air flowed through the inner pipe, to release or remove heat from the adsorbent, respectively. The adsorbent (zeolite) was placed between the inner and the outer pipe. Fins were attached to the inner pipe to increase the heat transfer between the fluids and the adsorbent, and water was used as refrigerant. The COP found was 0.38 and the SCP was 25.7 Wkg-1. The author also calculated the coefficient of waste heat cooling (WCOP), which takes into account the potential waste heat that can be recovered to produce the cooling effect, without the gas reaches the dew point. The value of WCOP found for this system was 0.31. This author suggested that the WCOP is more suitable than the COP to identify which cooling capacity could be produced from the exhaust gases of diesel engines, because in a real application, it is desirable that the gas never reaches the dew point to avoid corrosion of the adsorber. Zhang [80] assumed that in a standard bus (12.2 m long, 2.6 m wide, 3 m high, 49 seats) with a 207 kW diesel engine, cooling load around 17.6 kW, and a conventional air conditioner weighing about 300 kg, the waste heat that could be recovered from the exhaust gases would be at least 70 kW. The WCOP of 0.25 would be required to meet the cooling load demand and a SCP of about 200 Wkg-1 would be desirable to keep the bulk and cost of the equipment within the economic limits imposed by commercial applications. The system studied by this author could fit the demands of the WCOP but it was far from meeting the demand of the SCP. The low values of SCP were caused due to the low thermal conductivity of the bed (0.2 W m-1K-1) and the low wall heat transfer coefficient between the bed and the heat exchanger (25 Wm-2K-1). This system could probably be commercially applied if an adsorbent bed with enhanced heat transfer were used. Lu et al. [85] developed an air conditioner with the pair zeolite-water that could be powered by the exhaust gases of a locomotive. This system, which scheme is shown in Fig. 21, was based on a laboratory prototype developed by Jiangzhou et al. [86]. It was designed to refrigerate the driver’s cabin of a locomotive that ran in the Zhejiang province, East China. The cooling power of such a system under typical running conditions ranged from 3 to 5 kW, with a COP of 0.21. The temperature inside the cabin was between 4 and 6 °C lower than the ambient temperature, while this same cabin, without refrigeration usually had a temperature of 2 to 5 °C higher than the ambient temperature. The Fig. 22 shows the cooling power, and the inlet and outlet temperatures of the chilled water in the fan coil unit during a typical run of a locomotive from Hangzhou to Shanghai, when the average speed was between 100 and 120 km hr-1. 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