|
As the increase of global population compound with the rapid economic growthin mant developing countries, the demand for fresh water in those areas hasresen to a record level. Therefore, seeking a good clean water resource hasbecome an important domestic as well as worldwide issue. It is believed thesea water desalination may be the ultimate way to provide enough fresh water.Among many desalination methods, membrane distillation method is chosen as the interesting method in my study to investigate its performance in separatingthe fresh water from brine water.Membrane distillation is a process in which two solutions at different temperatures are separated by a microporous membrane. Because temperaturedifference which causes a corresponding vapor pressure difference across themembrane provides the driving force of the membrane distillation process. Thevapor evaporates through a porous membrane, and condenses on a coolant surfaceat the other side of the membrane. This paper is focused on air-gap membrane distillation (AGMD). A single stageAGMD facility is set up to investigate the transfer process, and the obtained data is confirmed by the theory of heat and mass transfers. Various kinds ofmembrane are used to examine the relationship between the permeate flux andmany other important parameters such as feed and cooling temperatures,membrane pore size, porosity etc. Finally, the scanning electron microscopy(SEM) is used to observe and analyze the detailed structure of membrane andthe crystallized salt on the membrane surface.The obtained experimental results show that the permeate flux increases exponentially with an increase in hot side temperature and is only slightly affected by the increase in salt concentration, and it*s hardly changed with the coolant flow rate. As the temperature difference between the feed solution and cooling flow increases, the effect due to polarization become obvious. The crystallized salts are found ( under SEM ) to block the membrane pores and result in the reduce of permeate flux or even the damage of membrane structure.
|