The use of factorial design in the analysis of air-gap membrane distillation data

A complete set of experimental data on air-gap membrane distillation (AGMD) is analyzed using the methods of factorial design (FD). A two-level and three-level FD were applied to investigate the influence of the main operating parameters on permeation flux of water. The data involves a study of the effects of salt concentration (at pre-set conditions of different input parameters such as feed temperature, coolant temperature, feed flow rate) on permeate flux for four inorganic salts (MgCl₂, NaCl, Na₂CO₃ and Na₂SO₄) using three commercial membranes in an air gap distillation unit. The objective is to gain an idea about the effects of the involved factors and their interactions. The factorial models have been obtained and validated by analysis of variance. Membrane pore diameter (membrane porosity) is found to be the most influential factor. Interaction terms are found to be insignificant. The predicted responses were compared with the experimental ones. In general, the predicted values were in reasonable agreement with the experimental data, thus confirming the prediction ability of the models. When salt type is treated as a third factor (factor C) besides salt concentration (A) and membrane porosity (B) some binary and ternary interactions were found significant for some salts.