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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.
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