Performance, energy and economic investigation of airgap membrane distillation system: An experimental and numerical investigation

Airgap membrane distillation (AGMD) is an efficient configuration employed widely for the solar membrane distillation desalination process. In the present work, 1-D Knudsen and molecular transport (KMT) model has been developed to investigate the performance of the flat sheet PVDF membrane. A new solution algorithm for the co-current and counter-current flow regime has been designed to solve the heat and mass transfer equations iteratively for a single-stage AGMD module. The feed temperature, feed flow rate, airgap size, salinity, membrane porosity and module length were varied and compared with experimental results. The increase in feed tem-perature from 40 degrees C to 80 degrees C resulted in 10.38 times increase in flux for co-current flow and 11.05 times for counter-current flow. The maximum permeate flux at 80 degrees C was 8.668 kg/m2h and 8.871 kg/m2h for the co-current and counter-current processes, respectively. Optimizing the feed temperature, flow rate, and mem-brane length using RSM suggests 80 degrees C, 1.528 LPM and 10 m as the optimum operating condition. An AGMD module of size 0.8 m width and 10 m length under the optimum operating condition exhibited a freshwater yield of 8.73 kg/h by consuming 24.98 kWh/m3 of specific energy, and the water production cost would be around $2.25/m3.