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

• Data on air gap membrane distillation is analyzed using factorial designs.
• Two-level and three-level factorial designs are applied.
• Effects of porosity on permeate flux are greater than those of salt concentration.
• Effect of salt concentration on permeate flux: MgCl2 > NaCl > Na2SO4 > Na2CO3
• Factorial design is able to predict the permeation rate quite satisfactorily

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.