Nước cất thông thương được chia thành 3 loại: nước cất 1 lần (qua chưng cất 1 lần), nước cất 2 lần (nước cất 1 lần được chưng cất thêm lần 2). nước cất 3 lần (nước cất 2 lần được chưng cất thêm lần 3). Ngoài ra, nước cất còn được phân loại theo thành phần lý hóa (như TDS, độ dẫn điện,.) | DOE Method for Optimizing Desalination Systems 269 T5 M5 w5 Fig. 12. Humidifier Accordingly mass and energy balance equations in the humidifier are defined as m aha5 m v5hv5 m w3hf3 m aha6 m v6hv6 m b4hf4 21 m v6 m b4 m v5 m w3 22 M5 h6 -h5 Ka V h3 - h6 - h4 - h5 lnh h4 - h5 23 In the above equation KaV the humidifier characteristic could be determined by the following imperial equation Nafey et al. 2004 KaV f Mw i Mw IM5J 24 where A and n are constant value for a kind of packing material see Table 7 . Humidity ratio is characterized as a function of atmospheric pressure steam partial pressure and dry bulb temperature. nr. . w vn n ma P - Pvn Relative humidity is also defined as follow p 2 . n P- gn 25 26 270 Desalination Trends and Technologies n A Type of Packing A B C D E F G H I Table 7. Constant value of n and A used in Frass 1989 Fig. 13. Condenser dehumidifier The energy and mass balance equations for the condenser which is shown in Fig. 13 are defined as m a ha6 m v6 hv6 rhw1 hf1 ma ha7 m v7 hv7 rhd hf7 m w2 hf2 27 md mv6 - mv5 mw1 111 w2 mw3 Mw 28 Qc Mw Cpw T2 - T1 Ucond AcondLMTD 29 LMTD is condenser s logarithmic average temperature difference which is described by DOE Method for Optimizing Desalination Systems 271 LMTD T - T2 - T - Tị In T - T2 T7 - t1 30 Enthalpy and humidity ratio for saturation can be obtained from the following relationship. h T3 - T2 T - 31 W T3 10-6 T2 10-4 T 10-3 - 32 Heating input energy at the flat-plat solar collector is calculated by Qu FrAc I Ta-UL Ti - Ta 33 These equations have been solved simultaneously to find the plant performance. Details of numerical procedure and validation could be found in the work by Farsad et al. 2010 . 5. Results and discussions The adopted mathematical formulation and numerical procedure could determine the .
