In this article, distilled water and CuO particles with volume fraction of 1%, 2% and 4% are numerically studied. The steady state flow regime is considered laminar with Reynolds number of 100, and nano particles diameters are assumed 20 nm and 80 nm. The hydraulic diameter and the length of equilateral triangular channel are 8 mm and 1000-mm, respectively. The problem is solved for two different boundary conditions; firstly, constant heat flux for all sides as a validation approach; and secondly, constant heat flux for two sides and constant temperature for one side (hot plate). Convective heat transfer coefficient, Nusselt number, pressure loss through the channel, velocity distribution in cross section and temperature distribution on walls are investigated in detail. The fluid flow is supposed to be one-phase flow. It can be observed that nano-fluid leads to a remarkable enhancement on heat transfer coefficient. Furthermore, CuO particles increase pressure loss through the channel and velocity distribution in fully developed cross section of channel, as well. The computations reveal that the size of nano-particles has no significant influence on heat transfer properties. Besides, the study shows a good agreement between provided outcomes and experimental data available in the literature. (C) 2016 Elsevier B.V. All rights reserved.