In this work, process side heat transfer coefficients were determined through the use of a heat flux sensor and compared to those using conventional thermocouples and heat balance technique. A local heat fluxmeter was mounted on the inner wall of a rounded bottom vessel equipped with an atypical helical ribbon impeller supported by two vertical arms. A detailed analysis of the variations of instantaneous heat flux with impeller positions is also presented. It is shown that the heat flux sensor is able to monitor the thermal boundary layer thickness and its renewal with the impeller rotation. (c) 2005 Elsevier B.V. All rights reserved.