Abstract
The entropy generation based on the second law of thermodynamics is investigated for turbulent forced convection flow of ZrO2-water nanofluid through a square pipe with constant wall heat flux. Effects of different particle concentrations, inlet conditions and particle sizes on entropy generation of ZrO2-water nanofluid are studied. Contributions from frictional and thermal entropy generations are investigated, and the optimal working condition is analyzed. The results show that the optimal volume concentration of nanoparticles to minimize the entropy generation increases when the Reynolds number decreases. It was also found that the thermal entropy generation increases with the increase of nanoparticle size whereas the frictional entropy generation decreases. Finally, the entropy generation of ZrO2-water was compared with that from other nanofluids (including Al2O3, SiO2 and CuO nanoparticles in water). The results showed that the SiO2 provided the highest entropy generation.
Highlights
The idea of using nanoparticles in fluids is not quite new
The ZrO2-water nanofluid is used for studying the effect of variations in nanoparticle concentration, Reynolds number, and nanoparticle diameter
It is seen that the thermal entropy generation is dominant compared with the frictional entropy generation in this case
Summary
The idea of using nanoparticles in fluids is not quite new. About one hundred years ago Maxwell [1] found that the thermal conductivity of a suspension of nanoparticles increased compared to that of the base fluid. Choi [2] for a suspension of nanoparticles in base fluids. Nanoparticles could be silica, polymers, metal dioxides, metals and carbon nanotubes. Water and ethylene glycol are the common base fluids. In many cases the nanofluids have higher thermal conductivity compared to that of the base fluid; the nanofluids have more desirable heat transfer properties. Nowadays many researchers are studying the potential use of nanofluids in a variety of engineering equipment to improve the energy efficiency and to enhance the system’s thermal performance. Solar collectors [3], car radiators, chillers, boilers, cooling and heating systems in buildings, and micro-channel and heat pipes are just a few examples [4,5,6,7,8,9,10,11,12,13,14,15]
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