Temperature polarization effects can considerably limit the overall performance of pervaporation modules. This study shows the measurement of temperatures in a pervaporation membrane module using ultrasonic computer tomography (U-CT). With this technique complete 2D-temperature distributions that occur in the module can be measured within seconds. Temperature distributions were also determined using computational fluid dynamics (CFD). Both temperature distributions are comparable and show that in the tubular pervaporation system studied, temperature segregation occurs. This segregation is a result of the occurring hydrodynamics in the system that is determined by mixed convection. Also, the measured water fluxes through the membrane show to be dependent of forced and natural convection.