Heat exchangers are widely used for efficient heat transfer from one medium to another. Nanofluids are potential coolants, which can provide excellent thermal performance in heat exchangers. This paper presents the thermodynamic second law analysis of a helical coil heat exchanger using three different types of nanofluids (e.g. CuO/water, Al2O3/water and ZnO/water). Heat transfer coefficient and entropy generation rate of helical coil heat exchanger were analytically investigated considering the nanofluid volume fractions and volume flow rates in the range of 1-4% and 3-6 L/min, respectively. During the analyses, the entropy generation rate was expressed in terms of four parameters: particle volume concentration, heat exchanger duty parameter, coil to tube diameter ratio and Dean number. Amongst the three nanofluids, CuO/water nanofluid, the heat transfer enhancement and reduction of entropy generation rate were obtained about 7.14% and 6.14% respectively. Furthermore, heat transfer coefficient was improved with the increasing of nanoparticles volume concentration and volume flow rate, while entropy generation rate went down. (C) 2013 Elsevier Ltd. All rights reserved.