Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.
Small amount of additives like e.g. surfactants can significantly suppress friction in turbulent flow of water. However the drag reduction is accompanied by a considerable decrease of heat transfer. Both drag reduction and good heat transfer are desired properties of systems employed in district heating systems. We investigated therefore the drag reduction properties of some surfactant mixtures with sodium salicylate. This contribution presents the results of drag reduction by three cationic surfactants. There was also investigated heat transfer effectiveness in these surfactants, particularly heat transfer behind singularities which were a valve and a tube bend. The singularities have negligible effect on heat transfer in water alone. They influence heat transfer coefficient only in the imminent part of the tube. The heat transfer enhancement is rather small.