Testing a simple Lee's disc method for estimating throuh-plane thermal conductivity of polymeric ion-exchange membranes

Abstract

Thermal conductivity of a material is a critical parameter for using it in non-isothermal applications. The new emphasis on using ion-exchange membranes as thermoelectric materials makes necessary to study the relation between thermal and structure properties. Here, through-plane thermal conductivity of different polymeric ion-exchange membranes was measured by a rapid experimental method using a simple Lee's Disc apparatus. Membranes with different structures and thicknesses in the interval 25–700 micrometers were analysed with the aim of testing the feasibility of the method in this kind of samples. Thermal conductivity of the investigated membranes was found to vary from as low as 0.03 up to as high as 0.41 W K−1m−1, depending on the type of membrane. Membranes with reinforcement in their structure presented lower values of the through-plane thermal conductivity. Although the thermal conductivity mainly depended on the composition of the membrane matrix, larger thermal resistances were estimated, in general, for membranes with higher density and thickness. No significant influence of the membrane ion-exchange capacity was observed for homogeneous and reinforced membranes, but a positive correlation was observed for heterogeneous membranes. The results obtained for homogeneous Nafion membranes were compared with values given in the literature for these same membranes, finding a good agreement. A thickness-dependent thermal conductivity was estimated for these membranes, suggesting that a size effect may play an important role in this kind of membranes. Despite its simplicity, the method allows to make a good estimation for the value of the through-plane thermal conductivity of polymeric ion-exchange membranes.