Thermophysical Problem Researches On Solar Desalination Based On Humidification-dehumidification Process

With the environment getting worse in the world,water scarcity in the developing world,indicates a pressing need to develop decentralized small-scale desalination technologies which use solar energy.Humidification-dehumidification(HDH)desalination to get potable fresh water is an important way to solve the above problem.Wide ranges of research on this subject have been done worldwide.Many exploratory studies have been done on this project focus on the new type of solar HDH desalination device's internal energy flow law and heat and mass transfer during operating.In this paper,a typical ideal single-effect closed-air open-water(CAOW)water-heated solar HDH process is proposed and analyzed using the first and second-laws of thermodynamics to minimum work requirement for individual processes.The ideal operation process of solar HDH desalination driven by solar collector is theoretical proposed.Based on the detailed analysis above,the potential maximum gained output ratio(GOR)and minimum work requirement is varying with humidify temperature,environment temperature,concentration ratio and salinity.To reduce energy consumption,the multi-stage type is a promising technology used in the humidification-dehumidification desalination system.Two types of multi-stage desalination system(regenerative and traditional multi-stage desalination)were proposed and studied relatively separately.The pinch analysis models of regenerative and traditional multi-stage desalination were established and numerically analyzed.In order to match the solar HDH desalination,light tracing method has been used to analyze the transmissivity Fresnel concentrator performance with circular cross section.The maximum thickness l and minimum thickness d were determined by geometric calculation.Optical simulation software is used to analyze the performance of concentrators.Tracking error sensitive and axial direction incidence angle influence were studied.The paper has presented a tubular body vacuum tube as the receiver of concentrating solar system.Improved the light collection efficiency of the dish paraboloid condenser and decreased the tracking precise to system which reduces engineering cost and operating cost.The optics and heat transfer theory can be performance analysis shows that the geometric concentrating ratio change principle along with the geometries.To strengthen the water vapor evaporation process.This paper performed experimental tests on the mass transfer coefficient of HDH solar desalination device filled with hollow plastic ball as a packed bed and compared with the mass transfer coefficients of other material packed beds.We introduce the structure and operation of the test device and present the relationship of the mass transfer coefficient changing with different operating parameters.The experimental result indicates that this hollow plastic ball has a relatively high evaporation mass transfer coefficient due to the relatively high wet surface and interior porous water storage material.Experimental results are presented for verifying the theoretical analysis.A novel three-stage multi-effect solar desalination based on humidification-dehumidification process is experimental investigated.The main objective of this work is to study the thermophysical problem of vapor in the process of evaporation and condensation.The fresh water production of the device can reach 182.47 kg/h and the Performance ratio(PR)can reach 2.65,because it recycles and reutilizes latent heat and the residual heat in the brine.A mathematical model based on mass and energy balances in each component of the unit is developed.A serious of experiments were conducted and compared with the simulation results to validate the developed models.In order to use the heat-island effect of ascending air,study the two different superimposed units based on conventional finned condenser and direct spray-cooling type of condenser.Further reducing heat transfer losses between solar system and desalination system.This study demonstrates a multi-stage humidification-dehumidification(HDH)solar desalination system heated directly by a cylindrical Fresnel lens concentrator.In this novel system,the solar receiver and the evaporator of the system are a whole in which the black fillers in seawater directly absorb the concentrated solar lights to heat the seawater film to produce the evaporation.Using three-stage isothermal tandem heating mode,the variation of the fresh water yield rate and the absorber temperature with time were measured experimentally and were compared with theoretical calculations.The experimental results show that the maximum yield of the unit is about 3.4 kg/h,the maximum gained output ratio(GOR)is about 2.1,when the average intensity of solar radiation is about 867 W/m~2.