(752d) Methods for Direct Surface Temperature Measurement for Quantification of Membrane Distillation Process Performance

Membrane Distillation (MD) is a thermally driven process that can treat high salinity waters (e.g. waste brines, produced water, saline ground waters) utilizing low grade heat, providing a low-cost treatment option. The driving force in MD process is defined by the membrane surface temperature. However, traditional methods (e.g. thermocouples) cannot be used to measure the surface temperature as they can affect the bulk fluid flow, inducing turbulence and mixing. Thus, to-date most efforts to estimate the surface temperature have used thermal transport models that rely on bulk temperature and flow rate measurements. The inaccuracies from these approaches have led to high uncertainty in estimating membrane performance and translating process performance from the bench to commercial scale Herein, we present two separate approaches to measure the membrane surface temperature directly: a thermoreflectance method and an electrical impedance method. The thermoreflectance techniques leverages the change in material reflectivity with temperature, while impedance approach correlates changes in properties of water and permittivity of space to changes in temperature. These approaches make it is possible to directly measure the driving force in MD and validate standard heat transport correlations.