An Experimental Study on the Multi-stage Direct Contact Membrane Distillation

Abstract

In this study, multi-stage direct contact membrane distillation (DCMD) experiments were conducted to examine the effect of feed temperature, feed and permeate circulating flow rates on permeate flux. Flat-sheet membrane modules with adjustable stages from 1-stage to 3-stage were employed to investigate the effect of module stage on performance, and a commercially available polytetrafluoroethylene/ polypropylene (PTFE/PP) membrane was used in the module. The net type spacer-filled PP channels of membrane modules were applied to change the flow characteristics and promote regions of turbulence. The experimental results for total water vapor flux were 0.4 kg/h, 0.68 kg/h and 0.88 kg/h, and the permeate fluxes were 40.1 kg/m2h, 34.2 kg/m2h, and 29.2 kg/m2h at 1-stage, 2-stage, and 3-stage, respectively, with inlet feed temperature of 70℃, and the flow rate of 1.5 l/m were constant. With this experiment, as the inlet feed temperature, feed and permeate flow rates increased, the permeate flux also increased. The inlet feed temperature on the permeate flux was found to be a key factor when compared to the flow rate. In addition, the number of stages is a key parameter for performance in multi-stage module design and system size.