Experimental System of Solar Adsorption Refrigeration with Concentrated Collector

With the ozone-depletion problem of traditional vapor compressed refrigeration growing more serious, substituting traditional refrigeration with green technology has become a hot topic in recent years. Among those green technologies, the solar adsorption refrigeration has attracted much of the attention of researchers. Driven by low-grade thermal energy, the adsorption refrigeration system has the advantages of being environmentally friendly, small, and flexible. This adsorption system can also be driven with non-solar energy, for instance by waste heat discharged from thermal equipment or by engine exhaust gases from vehicles, as mentioned by Hu et al.¹

In an adsorption cooling system, the adsorption bed is the key component. Its work directly affects the performance of the whole system. Therefore, the design of the adsorption bed is the most important issue as pointed out by Sutuki.² A decade ago, the flat bed was mostly used in the adsorption cooling system.^3,4,5 Without any solar concentrating device, the flat bed temperature was usually low and hence the COP of the system was unsatisfactory. In contrast, the tubular adsorption bed improved the COP. It was reported that the COP could reach 0.21 in sub-Sahara region by Hadj Ammar et al.⁶ Furthermore, Wang et al.⁷ developed a spiral plate adsorber that was distinguished by the characteristic of continuous heat regeneration. The novel design of the adsorption bed shortened the cycle time of the system. Abu-Hamdeh et al.⁸ reported their study on the solar adsorption refrigeration system with a parabolic trough collector. Their test results showed the COP of the system varied from 0.18 to 0.20. El Fadar et al.⁹ studied an adsorption refrigeration system that was coupled with a heat pipe and powered by parabolic trough collector, which showed an optimum COP of 0.18.

To enhance the heat transfer of the tubular bed, some finned tube adsorbers were considered and the effect of the enhancement was examined. An innovative bed that took the form of the shell and tube heat exchanger was presented by Restuccia et al.¹⁰. The internal finned tube was coated with a zeolite layer so that the contact transfer resistance of heat/mass between the metal surface and the adsorbent material could be reduced. The system produced an output of 30-60 W/kg of specific cooling power in the cycling time of 15-20 s. Al Mers et al.¹¹demonstrated that the enhanced adsorber with 5-6 fins could significantly reduce the heat loss of the adsorber to ambiance and thereby improving the COP by 45%. The effect of a finned tube adsorber on the performance of the solar driven system was also studied by Louajari et al.¹². Using activated carbon-ammonia as the working pair, they showed that the cycling mass transfer in the adsorber with fins was greater than the one without fins.

In the current study, we experimentally studied an improved solar adsorption refrigeration system, in which a solar tracking parabolic trough collector was applied and an internal cooling tunnel was deployed. With the SAPO-34/ZSM-5 zeolite and the water vapor as the working pair, the system showed interesting characteristics in terms of thermodynamics and refrigeration. The experimental methodology as well as the typical test results will be presented and discussed in this report.