Experimental investigations and model calculations of power consumption and heat transfer coefficients from a vessel wall to mixed liquid for ribbon impellers operating in a laminar regime are discussed in the paper. On the basis of the obtained results, the heat transfer efficiency of particular impellers was calculated and geometrical dimensions of the most efficient ribbon impeller were determined. The most efficient appeared to be an impeller with a diameter of d/D = 0.94 and ribbon pitch p/d = 0.25. (c) 2005 Elsevier Ltd. All rights reserved.