Dehumidification efficiency model for solar thermal regeneration system

Solar liquid desiccant air-conditioning system has attracted many attentions because of low-energy consumption, and solar liquid regenerator is one of important units in that system.A novel solar liquid regenerator designed by the author is the solar air-pretreatment solution grading collector/regenerator.The proposed liquid regeneration system needs a packed bed dehumidifier, and the prediction of outlet parameters of air in that dehumidifier must be considered for the design of the novel solar liquid regeneration system.A structured packing dehumidifier was designed and the systemic experiments were made at Southeast University in Nanjing, China in 2009.The structured packing dehumidifier has the size of 0.5 m (width) × 0.5 m(height)×0.3 m (length) with cross-flow mode.In order to increase flow rate of desiccant solution, instead of injecting directly strong solution into the interior of packed bed, a circulation solution pump was used for supplying solution for the dehumidifier.At the same time, a water-cooled heat exchanger was used to cool circulating solution in advance to control inlet temperature of solution.The experiments were performed under varying conditions including varying flow rates of air and solution and their inlet parameters.However, because of single structure of the experimental unit and limited variation range of experimental parameters, a method of numerical stimulation was used in this paper to study the effects of the inlet parameters of solution and air and the structure parameters of packing on the humidity effectiveness and the isenthalpic effectiveness.The previously experimental data were used to validate numerical model.For this purpose, several assumptions in physics were made, which were followed by the models of cross-flow dehumidification.The numerical simulation showed that as the concentration of LiCl solution increased from 0.29 to 0.34 kg/kg, the humidity effectiveness was increased by 2.6%~4.7% and the isenthalpic effectiveness was reduced by 20%~30%.As the inlet temperature of solution rose from 15 to 25 ℃, the humidity effectiveness went up, especially when the liquid-gas ratio was less than 1.0.As for isenthalpic effectiveness, the solution inlet temperature had large impact on it and when the inlet temperature of solution was less than that of air, the isenthalpic effectiveness was negative.As the air humidity ratio at the inlet dropped from 12.3 to 9.6 g/kg, the humidity effectiveness was increased by 2%~10% and the isenthalpic effectiveness was increased by about 0.3.The higher inlet temperature of airflow yields the lower humidity effectiveness, and when the liquid-gas ratio is low, the effect of air's inlet temperature on humidity effectiveness is high.The effect of air's inlet temperature on isenthalpic effectiveness is similar to solution's inlet temperature, which shows when the inlet temperature of air is higher than that of solution, the isenthalpic effectiveness is negative and otherwise it is positive.As the product of area per unit volume and length of air flow channel increased from 110 to 180, the humidity effectiveness was increased by about 0.1, however, the isenthalpic effectiveness was basically unchanged.Therefore, the humidity effectiveness increases with the increasing of the inlet temperature, the concentration of solution, the area per unit volume as well as the length of air flow channel, and decreases with the increase in humidity ratio and air temperature at the inlet.The isenthalpic effectiveness is affected dramatically by inlet temperatures of air and solution.Structure parameters of packing have little effect on the isenthalpic effectiveness.Moreover, with the increasing of the liquid-gas ratio, the humidity effectiveness increases and the isenthalpic effectiveness decreases.Finally, 2 equations about humidity effectiveness and isenthalpic effectiveness were obtained by applying a nonlinear regression to rearrange numerical simulation results, which provide the theoretical basis for the modeling of solar air-pretreatment solution grading collector/regenerator.