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Abstract
In this work, a mathematical model has been developed for vacuum membrane distillation incorporating molecular diffusion–Knudsen diffusion–Poiseuille flow and validated with the experimental data. The feed-side membrane surface temperature used in mathematical model was estimated by computational fluid dynamics modeling. The effects of different operating parameters such as feed flow rate, feed bulk temperature, inlet concentration, and permeate-side pressure on water flux and salt rejection have been studied using PTFE membrane. It has been shown that with variation in feed flow rate from 0.5 to 2 lpm, the permeate flux increased from 20.1 to 25.6 kg/m2 h. Similarly, with increase in feed bulk temperature from 40 to 60°C, the permeate flux increased from 2.10 to 26.6 kg/m2 h. The permeate flux showed the variation from 17.8 to 19.5 kg/m2 h on decreasing permeate pressure from 7 to 5.5 kPa. No significant effect of feed salt concentration was observed on permeate flux. More than 99% rejection was obtained at the feed salt concentration of 40,000 ppm of NaCl. Few runs were also carried out by taking multi-ion feed (Ca++, Mg++, Na+, K+, Cl−, , Fe++,
, F−) equivalent to that in ground water; in which case also more than 99% rejection was obtained.