Enhancement of solar desalination by humidification-dehumidification technique

摘要

This paper presents experiments for increasing the fresh water yield from water desalination by humidification-dehumidification technique (HDT). The scheme of this system is to increase the humidification rate by increasing the surface area for the purpose of efficient contact between water and air, which can be accomplished by misting the saline water within the air stream, thus the rate of fresh water production increases. A parabolic trough was used to heat the saline water. It appeared that it takes three hours to raise 251 of water from 35 to 70℃, this time was insufficient to fulfill the continuous saline water feed to the humidification-dehumidification (HD) unit, and thus electric heater was used to raise the temperature of the saline water to the desired degree. The results of HD unit showed that water production depends on both saline water temperature and droplet size. The maximum attainable water production was 31.7 1/d/m~2 of solar water heater at 85℃. For this experiment, the humidity of carrier air was 93% after the humidification step and 81% after the condensation. By comparing the amount of water corresponding respectively to humidity of 93% and 81%, it is clear that the air with volumetric flow rate of 0.11 m~3/s and humidity of 93% should carry 12.36 kg_w/h and the theoretical yield of fresh water will be 2.86 kg_w/h, which is in agreement with the data obtained experimentally. Moreover, the condenser efficiency is 23%, and additional condensation steps are necessary to increase the yield of fresh water from HD unit. The energy consumption of such unit is 45.3 kWh/m3, which could be obtained if we involve photovoltaic cell.