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. The driving force in MD process (flux, water recovery) is defined by the membrane surface temperature. However, it cannot be directly measured using traditional methods (e.g. thermocouples), and 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 this approach 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: an electrical impedance method and a thermoreflectance method. The impedance approach correlates changes in properties of water and permittivity of space to changes in temperatures, while thermoreflectance techniques leverages the change in material reflectivity with temperature. Through application of these approaches it is possible to directly measure the driving force in MD, quantify membrane performance, and validate standard heat transport correlations.