An experimental investigation has been carried out to study the effect of adding four different contaminants to distilled water on heat transfer under sub-cooled flow boiling conditions. Flow boiling experimental test rig has been designed and constructed to study the effect of changing the contaminant concentration and flow velocity. Lube oil, Nile river water, tap water and sea water were added at different concentrations to distilled water under sub-cooled flow boiling testing at constant bulk temperature. The effect of flow velocity was also studied for three different concentrations of 1%, 3% and 5% as compared to pure distilled water case. The heat flux applied was in the range of 100-400 kW/m(2). Flow velocities were changed from 1, 2 to 2.5 m/s at constant bulk temperature of 70 degrees C. It was found that adding any of the contaminants at all considered concentrations to distilled water impairs the heat transfer process substantially. (c) 2010 Elsevier Ltd. All rights reserved.