Experimental investigation of temperature polarisation by capturing the temperature profile development over DCMD membranes
Hiras Ahamed Hijaz, Masoumeh Zargar, Abdellah Shafieian, Amir Razmjou, Mehdi Khiadani
Abstract
Temperature polarisation (TP) is a major drawback limiting the global acceptance of membrane distillation (MD) technology. TP is typically quantified using a dimensionless index known as Temperature Polarisation Coefficient (TPC). TPC has significant limitations, whereby it cannot be used to compare different MD configurations or design conditions, nor to analyse the TP phenomenon along the membrane. In this research, the temperature profile over and along a lengthy DCMD membrane has been measured under various operational conditions, where its impact on TP has been explored for the first time. A specialised DCMD membrane cell was manufactured to capture temperature profiles, both along and over the membrane surfaces, using miniature thermocouples. The effects of flow rate and feed temperature were investigated on the temperature profiles. The results showed that the extent of TP was not constant along the membrane, and that the temperature profile was not symmetrical across the feed and permeate side, predominantly due to the effects of the inlet and outlet on the flow. The TPC value calculated using the conventional method was not able to accurately reflect the TP phenomenon along the membrane, indicating TPC to be an ineffective tool to study TP along the membrane.