This paper deals with an experimental study on the rate of heat transfer in helical ribbon mixers and its relation with power requirement. Four ribbon impellers and eight test fluids of different consistencies and ranging from pseudoplastic non-Newtonian to highly viscous Newtonian were used in the experiment. It was found that heat transfer coefficient is a function of impeller geometry at Reynolds number less than about 0.1.Accordingly there are four correlations corresponding to the four ribbon impellers. At Reynolds number higher than 10

Heat transfer coefficient is independent of impeller geometry and a single correlation is therefore obtaind for all the four impellers. Since both the heat transfer coefficient and power consumption are functions of Reynolds number

a relation is presented between them.