The hot-wire sensor or constant temperature anemometer (CTA) is a widely used research tool for local velocity measurement. The CTA supplies a heating current to maintain a constant sensor temperature. By instantaneously measuring the change in heat transfer from the sensor, the CTA is able to quantify the fluid velocity, including turbulent fluctuations on the sensor surface. Better understanding of the velocity distributions in membrane modules and channels could provide critical information on optimisation of spacer and module design. This study examines the incorporation of CTA technology into membrane channels to precisely measure local values of flow. Repeatability tests indicated a standard deviation up to 10 % when different sensors were used; neither ageing nor fouling was observed during long-term trials. Estimation of the liquid velocity was carried out for the CTA placed in different positions in the membrane module. These results revealed the potentials and limitations of this type of miniaturised sensor in such an environment. The use of CTA to detect and assess bubble characteristics in a spiral wound membrane module is also reported. These results indicate the potential of this technique for submerged membrane applications using air sparging. (c) 2006 Elsevier B.V. All rights reserved.