In the present work, the laminar forced convection heat transfer characteristics of using the Eicosane-inwater Nano-PCM emulsion as the phase change nanofluid in a circular tube heated with constant heat flux have been investigated experimentally. A circular oxygen-free copper tube, for which the inner and outer diameters are 3.4 mm and 4.0 mm, respectively, is fabricated with an iso-flux heated section of length 40 cm. Forced convection heat transfer experiments have been performed for the horizontal tube using the pure water, the water-based phase change nanofluids containing various mass fractions of Nano-PCM particles (omega(pcm) = 1, 2, 5, and 10 wt%) as the coolant under the following operating conditions: the volume flow rate (Q) over dot = 12.5-180 cm(3)/min, the heating power applied at the outer wall of the tube q(o) = 20, 30, 40, 50, 60 W, with the inlet fluid temperature T-in near 27 degrees C. Experimental results show that when the flow rate and the heat flux are in an appropriate range, the tube wall temperature along the iso-flux heated section can be effectively suppressed with increasing mass fraction of the Nano-PCM particles in the water based phase change nanofluid compared with that of the pure water. Meanwhile, a penalty of pressure drop increase of using the phase change nanofluids to replace the pure water in the tube was found to greatly uplift with the mass fraction of Nano-PCM particles. (C) 2017 Elsevier Ltd. All rights reserved.