Abstract
The objective of this study is to assess the hydrothermal performance of a non-Newtonian hybrid nanofluid with temperature-dependent thermal conductivity and viscosity compared with a Newtonian hybrid nanofluid with constant thermophysical properties. A counter-current double-pipe mini-channel heat exchanger is studied to analyze the effects of the hybrid nanofluid. The nanofluid is employed as the coolant in the tube side, while the hot water flows in the annulus side. Two different nanoparticles including tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic-coated carbon nanotubes are used to prepare the water-based hybrid nanofluid. The results demonstrated that the non-Newtonian hybrid nanofluid always has a higher heat transfer rate, overall heat transfer coefficient, and effectiveness than those of the Newtonian hybrid nanofluid, while the opposite is true for the pressure drop, pumping power, and performance evaluation criterion. Supposing that the Fe3O4-carbon nanotube/water hybrid nanofluid is a Newtonian fluid with constant thermal conductivity and viscosity, there leads to large error in the computation of pressure drop (1.5–9.71%), pumping power (1.5–9.71%), and performance evaluation criterion (18.24–19.60%), whereas the errors in the computation of heat transfer rate, overall heat transfer coefficient, and effectiveness are not considerable (less than 2.91%).
Highlights
Double-pipe heat exchangers have been widely employed in various applications to exchange heat between two fluids called as heat transfer fluids [1, 2]
CNT/water hybrid nanofluid flowing inside a double-pipe heat exchanger are evaluated and compared with those obtained by regarding the hybrid nanofluid as a Newtonian fluid with constant thermal conductivity and viscosity
The results show that there is no specific pattern on the relationship between the difference in the heat transfer rate of the Newtonian and non-Newtonian nanofluids and the magnetite concentration
Summary
Double-pipe heat exchangers have been widely employed in various applications to exchange heat between two fluids called as heat transfer fluids [1, 2]. Scientists and researchers around the world have revealed that the heat exchanger performance can be considerably enhanced by improving the thermal conductivity of working fluids [3, 4]. This goal can be achieved through the use of nanofluids, which are prepared by suspending nanoparticles with sizes typically of 1-100 nm in conventional heat transfer fluids such as water, oil, and ethylene glycol [5,6,7,8]. This term was first suggested by Choi [9] in 1995, and it has since gained in popularity [10,11,12,13,14,15,16,17]
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