Regeneration performance analysis of solar collector/regenerator with solution heat recovery

Abstract: Solar liquid desiccant air-conditioning system has attracted many attentions owing to the advantages of utilizing low grade thermal energy such as solar energy, in which the solar collector and regenerator can be designed respectively. In addition, solar collector and solution regenerator can be combined together to construct solar collector/regenerators (C/Rs) that have better performance of regeneration. Solar C/Rs are the key component of system, because the cooling capacity of system is determined mainly by the regeneration efficiency. Moreover, in order to reduce top heat losses and eliminate contamination of the solution by dust, the C/Rs can be covered with the glazing plate. An experimental study on the effect of glazing plate height of solar C/Rs indicated that the optimum glazing plate height is 0.07 m, and the performance of the optimally glazed C/R is better than an unglazed C/R for hot humid climates. Analysis based on experimental data and numerical simulation was presented, and the results show a higher inlet solution temperature can increase the performance of regeneration. So the method of preheating the inlet solution was adopted to increase the efficiency of solar C/R, and solution heat recovery device was used to preheat the inlet solution by recovering the heat from the outlet solution. However, there have not been sufficient studies on the effect of various parameters on C/R performance with solution heat recovery. In this paper, the solution heat recovery device, by recovering heat from the outlet solution to preheat the inlet solution, was adopted to increase the efficiency of solar C/R. The numerical simulation method was adopted for analyzing the effects of the glazing plate height, solution parameters, air parameters, solar radiation intensity and other factors on the regeneration efficiency of solar C/R with solution heat recovery. Several physical assumptions were made, followed by modeling of counter-flow regeneration. And the previous experimental data were used for the comparison with the numerical results to validate numerical model. In the simulation conditions, the results show: Using a heat recovery device can improve the regeneration efficiency by 93.6% equivalent to adding 0.8 m length of C/R; the higher efficiency of heat recovery device causes the higher regeneration performance; the flow rates have an optimum value, which yields a maximum rate of water evaporation and regeneration efficiency. The optimum values of flow rates of solution (or air) increased with the increase in air flow rate (or solution flow rate), and the optimum ranges of flow rates of solution and air are 8-15 and 100-150 kg/h, respectively. The optimum range of glazing plate height is 0.08-0.1 m when flow rates are in the optimum ranges; higher inlet temperature of solution or air both can increase regeneration efficiency, but the method of heating solution is much more effective than heating air; the decrease of inlet concentration of solution or relative humidity of air both can be in favor of solution regeneration; the higher solar radiation intensity yields better performance of regeneration for the solar CR with heat recovery. All these results can provide guidance for the design and performance analysis of the solar CR.