Muối ăn: một loại gia vị phổ biến trong chế biến thức ăn, gồm chủ yếu là chất vô cơ có công thức hóa học là NaCl, một phần KCl và các khoáng chất khác. Muối ăn có thể được khai thác từ biển, hoặc đôi khi từ mỏ muối. | 24 Desalination Trends and Technologies Fig. 2. Principles of DCMD T1 T2 Tp TD temperatures at both sides of the membrane and temperatures of feed and distillate respectively pF pD water vapor partial pressure at the feed and distillate sides respectively Membranes and modules The porous and hydrophobic MD membranes are not selective and their pores are filled only by the gas phase. This creates a vapour gap between the feed and the produced distillate what is necessary for MD process operation. However during the MD a part of the membrane pores may be wetted that decreases a thickness of vapour gap inside the membrane wall Gryta Barancewicz 2010 . Therefore the properties of membrane material and membrane porous structure are important for MD process performance Bonyadi Chung 2009 Khayet et al. 2006 . Membrane for MD process should be highly porous hydrophobic exhibit a desirable thermal stability and chemical resistance to feed solution El-Bourawi et al. Gryta et al. 2009 . These requirements are mostly fulfilled by the membranes prepared from polymers with a low value of the surface energy such as polytetrafluoroethylene PTFE polypropylene PP or poly vinylidene fluoride PVDF El Fray Gryta 2008 Gryta 2008 Li Sirkar 2004 Teoh et al. 2008 Tomaszewska 1996 . Apart from the hydrophobic character of the membrane material also the liquid surface tension pores diameter and the hydraulic pressure decide about the possibility of the liquid penetration into the pores. This relation is described by the Laplace - Young Kelvin law equation Schneider et al. 1988 AP . Pf - Pd .-4 Bd c e 2 where AP is liquid entry pressure LEP B is the pore geometry coefficient B 1 for cylindrical pores d is the surface tension of the liquid is the liquid contact angle dP is the diameter of the pores PF and PD are the hydraulic pressure on the feed and distillate side respectively. Water and the solutions of inorganic compounds have high surface tension d 72x10-3 N m however when the .
