Investigation of mass transport in porous media for desalination purposes

Shortage of fresh water resources is a major problem that human has been faced, especially in some remote mountains and islands where were lack of electricity. Solar desalination technology is an effective method to satisfy the need for drinkable water resources in some regions which are far away from cities or short of power, like islands and villages near the sea. In order to have a progress in developing this technology there are some critical issues should be focused on, like the materials should be inexpensive, the technology should be easy-to-applied, and devices should be able to run without too much maintenance and keep the stable supply of fresh water for local resident. Nevertheless, there’s a big barrier in front of us, how to avoid the accumulation of salt on the device so that the fresh water production rate is not affected by it during the working process. In this passage, a type of solar passive distiller with several stages is discussed. This technology helps solving the challenge mentioned before very well (stable and better performance with salt rejection at the same time) by optimizing the configuration. Here to make it clear why the salt accumulation is not happened in this device, which means the mass transport here is more effective than the pure diffusion phenomenon, an integrated theory is given. In this paper, between the boundary of the saline and the air the Marangoni effect is considered for the reason of the concentration differences and thus the surface tension. Just as expected, the simulation results showed that the salt rejection ability of this device is good enough to cope with the clogging during the whole desalination process. In addition, the same device with different configurations (like thickness) will have different salt rejection performances, also the concentration gradient between two sides of the layer can cause the change of the effect. Thus, this study can be an inspiration on how to optimize the performance of the solar passive desalination device by changing the structure so that this technology can be broadly adopted in rural areas with hard access with fresh water resources in a dependable way.