Transient dynamic response of solar diffusion driven desalination

Abstract

The dynamic response for the solar diffusion driven desalination (DDD) process has been investigated. The heat and mass transfer within the direct contact evaporator is analyzed by one-dimensional conservation equations. The heat and mass transport models account for the transient variations within the packed bed due to time varying inlet water and air temperatures and humidity. The conservation equations are solved numerically using a finite difference scheme to predict water, air/vapor mixture and packed bed temperatures and humidity ratio within the evaporator and the condenser. The system dynamic response for the packed bed materials, wettability, and liquid hold-up, sudden increase–decrease in the inlet water temperature is investigated. It is found that the response time for the outlet water to reach the steady state temperature in the evaporator is shorter for lower liquid hold-ups. The response time is not sensitive to the packing material. Higher wettability does not affect the response time, but it does result in improved heat transfer with a higher exit air temperature and lower exit water temperature. The steady state temperature in the evaporator is not dependent on the heat capacity of the packing material, and liquid hold up. A delayed operating mode for the solar DDD is introduced to enhance the fresh water production rate. It is found that increasing the initial saline water temperature and decreasing the initial water volume in the seawater tank results in a higher fresh water production rate.