Experimental And Simulation Study On Solar Humidification Desalination Unit With Grading Regeneration Technology

Seawater desalination is an important means to solve the problem of water shortages today, conventional desalination techniques consume a lot of valuable fossil fuels, which have a tremendous impact on the environment, its negative effects has aroused people’s attention. Solar desalination technology can balance the energy and water demands, it’s an important developmental direction of desalination industry.The previous research of desalination process was reviewed. According to the basic principles of grading regeneration and humidification desalination technology, a new desalination method was developed to solve the existing problems in the humidification desalination unit. A mathematical model of the process was established to obtain the characteristic curve and optimal parameters. Specific tasks accomplished include the followings:(1) A new solar desalination unit using humidification dehumidification technology was developed, and the performance of the distillation was investigated. The effects of parameters on humidification desalination process were analyzed. The study shows that closed air circulation can decrease the heat loss; when the air speed less than0.5m/s, the spraying water temperature is below70℃, the output moist air is almost saturation.(2) The features of wet film humidifier were investigated by experimental and theoretical analysis. The experimental data showed that the output moist air temperature of humidifier is related to water to air ratio and the spraying water temperature; the dimensionless temperature Θ increased with water vapor increases; the dimensionless temperature Θ had a linear relationship to the spraying water temperature. The experimental model of dimensionless temperature Θ was fitted and compared with the simulation results.(3) The performance of the distillation was researched under natural conditions, the performance impact of grading regeneration was analyzed, and the thermal performance and quality of freshwater were evaluated. The test showed that the optimal pre-condenser flow rate was2:7, the ratio of heat recovery could reach35%-45%, the measured freshwater yield was6.53kg/(m2·d), increased by29.6%compared to single stage distillation.(4) A mathematical model of the humidification desalination process has been established to predict the temperature field at the wet film and the performance of the distillation. The correlation and error were analyzed by comparing the simulation and experimental results. The results indicated that the mathematical model was highly correlated to the experimental data, the optimal wet film thickness was200-300mm, the effect of wet film thickness was more significant than height; the optimal water to air ratio is0.75, and the optimal cooling water mass flow rate of pre-condenser was1.0to1.5times of air flow rate; the production of second stage was about25% of first stage.