The present work reports on the use of ultrasound assisted emulsion polymerization for the synthesis of polyaniline (PANI) nanoparticles. The study of heat transfer characteristics of PANI based nanofluids at different loading (0-1.2 wt%) of PANI nanoparticles in water (reference fluid) was performed at fixed Reynolds number. The heat transfer coefficient enhancement was also studied at two different Reynolds numbers by keeping loading of PANI in the range of 0.2-1.2 wt%. The heat transfer performance of PANI nanofluid was studied in a copper tube under constant heat flux conditions. The results showed that the heat transfer coefficient increases with an increase in the colloidal PANI concentration and Reynolds number. For 0.2 wt% PANI nanofluids, 33% increment in heat transfer coefficient was observed while it was 63% for 1.2 wt% addition of PANI nanoparticles. (C) 2015 Elsevier B.V. All rights reserved.