- Thursday, January 1, 2009
- Solar Energy Refrigeration by Liquid-Solid Adsorption Technique
The design, construction and operation of a solid adsorption solar cooler are presented in this work. Granular activated carbon-methanol as the adsorbent /adsorbate pair was used. The System has three important components: collector/adsorber, condenser and evaporator.
A flat plate type collector made of stainless steel with effective exposed area of 0.95m² was used. Two types of condensers were tested, the first one was a helical copper tube immersed in water tank and the other one was a finned stainless steel tube.
Solar radiation was simulated using an electrical heater regulated by a solid state relay and potentiometer. The experimental work was focused on optimizing the suitable amount of activated carbon/methanol pairs, the influence of regenerator temperature, and the influence of solar flux on the performance of the system.
It was found that regenerator temperature greater than 100 °C was necessary to release methanol from the activated carbon.
The operating pressure was also found to be an important parameter to achieve cooling effect; the system pressure must be less than 20kPa absolute.
As the adsorbent bed is the heart of such system, and its characteristics directly affected the performance of the system, the experimental work showed that the adsorbent bed which was used in this study didn't achieve the best results expected, therefore another adsorbent bed with hollow tubes generator was suggested, it was found that in this type of generator is easier to control the leakage and the pressure inside the system.
The type of the condenser and its length was found to be important parameters that affect the performance of the used system. The condenser length should be as short as possible, however, the condenser tube should be straight pipe with fins and without any curvatures to prevent pressure drop in the system.
In most cases, the water temperature of 10 °C was obtained using the system for air-conditioning, food and vaccines preservation, and for producing chilled water. The obtained temperature was effected directly by the heat flux applied and the heating period. The optimum heating period was found to be at least 5 hours, while the cooling period was more than 10 hours.
In a Lab scale setup solar cooler, it was found that the evaporator volume has a significant effect on the performance of such system; the evaporator volume should not be much larger than the maximum methanol volume charged in the system. The maximum methanol adsorption capacity of the used activated carbon was found to be 0.26 kg methanol / kg activated carbon.