Study On Seawater Desalination Unit Combined With Solar Air Collector

With the fast development of economy and the growth of population, the demand of fresh water for human is growing rapidly. At the same time, the damages of the environment such as water pollution, losses of water and soil, and desertification of land make many countries and regions to face water crisis. To solve the shortage of fresh water is a major challenge that mankind faces at present. Solar desalination is one of the effective methods to solve the fresh water shortage of the mankind.In this paper, a solar desalination unit is designed based on humidification-dehumidification cycle by using hot air which comes from a solar air collector. Hot air is the heat source, which transfers the energy to seawater, at the same time water molecule will be taken out of the seawater. Then the hot air becomes humidified, the humid air is introduced to the condenser by an air pump and dehumidified, with distilled water collected in a tank. The latent heat from condenser is used to preheat the saline water and the feed saline water's temperature is increasing, which is helping for improving the evaporation and the thermal efficiency of the system.This paper includes four works as following:1. A new type of solar desalination unit is designed by direct mixing of seawater with hot air which comes from a solar air collector. Four methods is designed to evaporate the seawater, such as using hot air contact with water at the surface and inside of the water, spraying distillation and heating the water by electricity. The result showing that using hot air contact with water at the inside of the water is the best method.2. A type of distillation unit is designed by using hot air contact with water at the inside of the water. By using experimental test, it shows that that the temperature and flow rate of the inlet air, the temperature and initial mass of seawater are the most important parameters affecting the evaporation. The maximum evaporation is about 1.72kg/h. A solar desalination unit is constructed by using hairdryer to simulate solar collector, selecting two type of condenser which is made of coil pipe and fins pipe. It's found that the condenser made of fins pipe is the best choice. The thermal efficiency of the system approaches 40%.3. A real prototype system test combined with solar collector is conducted. The results show that the thermal efficiency of the solar air collector is very low, which leads to a lack of energy that the collector input to the distillation, which has brought the water production rate and the system's thermal efficiency is much lower than the simulation result that using hairdryer. A desalination unit is designed combining with a solar air collector and an electric heater which is used to simulate solar water collector, test results showed that increasing the water temperature can greatly enhance the water production rate and the thermal efficiency.The experimental results show that the water production rate and thermal efficiency of the system combined with solar air collector and seawater desalination unit is too low, , it is necessary to add solar water collector, concentrated collector and so on to raise the temperature of the air or the water, then to improve the operating temperature of the system.