**ABSTRACT**

In this study, thermo-physical and geometrical parameters affecting entropy generation of nanofluid turbulent flow such as the volume fraction, Reynolds number and diameter of the channel and micro-channel with circular cross section under constant flux are examined analytically. Water is used as a base fluid of nanofluid with nanoparticles of Ag, Cu, CuO and TiO2. The study is conducted for Reynolds numbers of 20000, 40000 and 100000, volume fractions of 0, 0.01, 0.02, 0.03 and 0.04, channel diameters of 2, 4, 6 and 8 cm and micro-channel diameters of 20, 40, 60 and 80 micrometers. Based on the results, the most of the generated entropy in channel is due to heat transfer, and also, with increasing the diameter of the channel, Bejan number increases. The contribution of entropy generation due to heat transfer in the micro-channel is very poor and the major contribution of entropy generation is due to friction. The maximum amount of entropy generation in channel belongs to nanofluids with Ag, Cu, CuO and TiO2 nanoparticles, respectively, while in the micro-channel this behavior is reversed; and the minimum entropy generation happens in nanofluids with Ag, Cu, CuO and TiO2 nanoparticles, respectively. In channel and micro-channel, for all nanofluids except for the water-TiO2, with increasing volume fraction of nanoparticles, the entropy generation decreases. In channel and micro-channel, the total entropy generation increases as Reynolds number augments.

**KEYWORDS**

PAPER SUBMITTED: 2015-11-12

PAPER REVISED: 2015-12-26

PAPER ACCEPTED: 2016-03-27

PUBLISHED ONLINE: 2016-04-09

**THERMAL SCIENCE** YEAR

**2016**, VOLUME

**20**, ISSUE

**Issue 6**, PAGES [2037 - 2050]

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