In this study, overall heat transfer coefficient for a rotating cavity type heat exchanger has been investigated. The heat exchanger mainly consisted of a rotating cylindrical cavity with axially throughflow. The cylindrical cavity was rotated in a stationary housing. An axial througflow of cold water was supplied in the cavity through a pipe rotating with cavity. The cold water left the cavity via an identical pipe. Hot water flowed between rotating cylindrical cavity and stationary housing. Experiments were conducted to obtain the effects of cold water flow rate, hot water now rate, and rotational speed on overall heat transfer coefficient. (C) 1999 Elsevier Science Ltd.