Impact of variable fluid properties on forced convection of Fe3O4/CNT/water hybrid nanofluid in a double-pipe mini-channel heat exchanger

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%)

Numerical analysis for thermal–hydraulic characteristics and the laminar two-phase nanofluid flow inside a tube equipped with helically twisted tapes as swirl and turbulence promoters

Abstract In this study, the numerical simulation of heat transfer of Al2O3-water nanofluid in a pipe equipped with helically twisted tapes is investigated. The volume fraction of nanoparticles in this study is equal to 0, 1, 2, and 3%, and a two-phase mixture method has been used to simulate the nanofluids. The flow regime is laminar in the present study, and Reynolds numbers are Re = 250, 500, 750, and 1000. The helical twisted tapes are in three different types, single, double, and triple. The same heat flux 5000Wm-2 is applied to the walls. The simulation results showed that increasing the Re increases the Nusselt number and decreasing the friction factor. Nusselt number in case 1 and volume fraction of nanoparticles 0% for Re = 250, 500, 750 and 1000 are equal to 95.8, 57.11, 56.13 and 22.15, respectively. The average friction factor is equal to 0.18, 0.09, 0.07, and 0.05. The presence of helical twisted tapes increases the $${\text{Nu}}_{ave}$$ Nu ave . The friction factor due to secondary flows and increases the contact of the fluid and the solid surface, so that the Nusselt number in volume fraction of nanoparticles 0%, Re = 250 for case 1, case 2, case 3, and case 4 are 95.8, 46.10, 58.11, and 51.12, respectively, and the friction factor are 18.0, 29.0, 0.38 and 0.48, respectively

Numerical investigation of nanofluid mixed convection heat transfer with variable properties within a shallow lid driven cavity

This paper focuses on the study of Laminar mix convection heat transfer of water-AL2O3 and water-CuO nanofluids whit temperature and nanoparticles concentration dependent thermophyscical properties in a rectangular shallow cavity was investigated numerically. Upper movable lid of the cavity was at a lower temperature compared to the bottom wall. Simulations were performed for Grashof numbers of 104 for Richardson numbers from 0.1 to 4.5, and nanoparticle volume fraction of 0.01-0.04. The two-dimensional governing equations were discretized using a finite volume method and SIMPLE algorithm. The model prediction for very low solid volume fraction were found to be in good agreement whit earlier numerical studies for a base fluid. It is shown that under a wide range of volume fraction of nanoparticles and different Richardson number, the enhancement of heat transfer will be evaluated. The Reynolds number varies due to variation of the Richardson number. Heat transfer was elevated by increasing the concentration of nanoparticles additionally. In this paper investigated the role of nanofluid variable properties in differentially heated enclosures and found that the prediction of heat

Numerical investigation of wind velocity effects on evaporation rate of passive single-slope solar stills in Khuzestan province in Iran

Khuzestan Province is located in Iran and has average annual evaporation of over 2000 ml. It also encounters water scarcity and water salinity issues. To make proper use of the high evaporation rate in Khuzestan and help overcome the water scarcity issue, this study simulates the effects of wind velocity on the performance of passive single-slope solar stills, identifying the optimal regions for the deployment of solar stills. The wind velocities of 2.5, 7.5, 10, 12.5, 15, 17.5, and 20 m/s were incorporated. To simulate the two-dimensional steady laminar flow within the solar still, the humid air model was employed. Furthermore, the turbulence k-ε model was utilized to simulate the external flow of the solar still. The accuracy of the numerical technique was evaluated by comparing the average Nusselt number results on the water surface to different models and by comparing the production rate results to experimental data. It was observed that the numerical approach was properly accurate. The results indicate that a rise in the wind velocity decreases the freshwater production rate, with the maximum production rate reduction was occurred at a wind velocity of 15 m/s. Ramhormoz, Dehdez, and Izeh were found to be optimal regions for deploying solar stills, based on the wind velocity

THE INFLUENCE OF GRAVITY ON A MICROFLUIDIC MIXED CONVECTION BY APPLYING LATTICE BOLTZMANN METHOD

In this article the effects of gravity on the mixed convection of a microflow is studied numerically by using lattice Boltzmann method (LBM). To do this, the hydrodynamic boundary condition equations should also be modified. The cold fluid enters to the microchannel and leaves it after cooling its hot walls. Calculations are provided for a wide range of Knudsen number (Kn). The results are presented as the isotherms and streamlines, the values of slip velocity and temperature jump and the local and global profiles of velocity, temperature and Nusselt number. It is observed that LBM is able to simulate the mixed convection in a microchannel appropriately. It is claimed that the effects of buoyancy forces are important for Kn0.05 they can be ignored. Moreover, the buoyancy forces make a rotational cell in the microchannel flow which generates the negative slip velocity at Kn=0.005

Impact of ribs on flow parameters and laminar heat transfer of water–aluminum oxide nanofluid with different nanoparticle volume fractions in a three-dimensional rectangular microchannel

This article aims to study the impact of ribs on flow parameters and laminar heat transfer of water–aluminum oxide nanofluid with different nanoparticle volume fractions in a three-dimensional rectangular microchannel. To this aim, compulsory convection heat transfer of water–aluminum oxide nanofluid in a rib-roughened microchannel has been numerically studied. The results of this simulation for rib-roughened three-dimensional microchannel have been evaluated in contrast to the smooth (unribbed) three-dimensional microchannel with identical geometrical and heat–fluid boundary conditions. Numerical simulation is performed for different nanoparticle volume fractions for Reynolds numbers of 10 and 100. Cold fluid entering the microchannel is heated in order to apply constant flux to external surface of the microchannel walls and then leaves it. Given the results, the fluid has a higher heat transfer with a hot wall in surfaces with ribs rather than in smooth ones. As Reynolds number, number of ribs, and nanoparticle volume fractions increase, more temperature increase happens in fluid in exit intersection of the microchannel. By investigating Nusselt number and friction factor, it is observed that increase in nanoparticle volume fractions causes nanofluid heat transfer properties to have a higher heat transfer and friction factor compared to the base fluid used in cooling due to an increase in viscosity

Numerical simulation of convective heat transfer in a turbulant non-Newtonian nanofluid flow through a horizontal circular tube

In this paper, a numerical study on the convective heat transfer characteristics in a non-Newtonian nanofluid flow in the horizontal tube with constant heat flux is carried out using computational fluid dynamics (CFD). The primary objective is to evaluate the effect of using nanoparticles on convective heat transfer coefficient. For this purpose, non-Newtonian nanofluid containing Al2O3 and 0.5 wt.%. Aqueous solution of carboxymethyl cellulose (CMC) as a liquid single phase with two particle concentrations of 0.5 and 1.5 vol. % were used. Effect of particle concentrations on convective heat transfer coefficient was investigated in different Reynolds numbers (450