Environmentally acceptable drag‐reducing surfactants for district heating and cooling

The aim of this work was to find drag‐reducing surfactants for both district heating and cooling that are environmentally more acceptable than the organic salts of quaternary ammonium compounds that so far have dominated this application. Vortex inhibition of test solutions in glass beakers has been used to screen a large number of surfactant mixtures, various electrolytes, and temperatures. For the most interesting products, the pressure drop in a test loop was measured at various flow rates and temperatures.N‐cetyl sarcosinate andN‐stearyl betaine, the latter together with Na‐dodecylbenzene sulfonate, give good drag reduction (DR) properties at 65–100 and 45–85°C, respectively. The sarcosinate is sensitive to pH changes, whereas the betaine‐sulfonate complex is more robust. Ethoxylates of oleic acid monoethanolamide show good DR properties at 0–25°C. At an increased salt concentration, a mixture of this surfactant with an ethoxylated oleyl alcohol worked well. At a still higher salt concentration, e.g., sea water, a combination ofN‐cetyl betaine and alkylbenzene sulfonate showed DR.