Mehdi Bahiraei, Seyed Mostafa Hosseinalipour and Morteza Hangi
The purpose of this paper is to attempt to investigate the particle migration effects on nanofluid heat transfer considering Brownian and thermophoretic forces. It also tries to…
Abstract
Purpose
The purpose of this paper is to attempt to investigate the particle migration effects on nanofluid heat transfer considering Brownian and thermophoretic forces. It also tries to develop a model for prediction of the convective heat transfer coefficient.
Design/methodology/approach
A modified form of the single-phase approach was used in which an equation for mass conservation of particles, proposed by Buongiorno, has been added to the other conservation equations. Due to the importance of temperature in particle migration, temperature-dependent properties were applied. In addition, neural network was used to predict the convective heat transfer coefficient.
Findings
At greater volume fractions, the effect of wall heat flux change was more significant on nanofluid heat transfer coefficient, whereas this effect decreased at higher Reynolds numbers. The average convective heat transfer coefficient raised by increasing the Reynolds number and volume fraction. Considering the particle migration effects, higher heat transfer coefficient was obtained and also the concentration at the tube center was higher in comparison with the wall vicinity. Furthermore, the proposed neural network model predicted the heat transfer coefficient with great accuracy.
Originality/value
A review of the literature shows that in the single-phase approach, uniform concentration distribution has been used and the effects of particle migration have not been considered. In this study, nanofluid heat transfer was simulated by adding an equation to the conservation equations to consider particle migration. The effects of Brownian and thermophoretic forces have been considered in the energy equation. Moreover, a model is proposed for prediction of convective heat transfer coefficient.
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Sumit Kumar Mehta, Sukumar Pati, Shahid Ahmed, Prangan Bhattacharyya and Jishnu Jyoti Bordoloi
The purpose of this study is to analyze the thermal, hydraulic and entropy generation characteristics for laminar flow of water through a ribbed-wavy channel with the top wall as…
Abstract
Purpose
The purpose of this study is to analyze the thermal, hydraulic and entropy generation characteristics for laminar flow of water through a ribbed-wavy channel with the top wall as wavy and bottom wall as flat with ribs of three different geometries, namely, triangular, rectangular and semi-circular.
Design/methodology/approach
The finite element method-based numerical solver has been adopted to solve the governing transport equations.
Findings
A critical value of Reynolds number (Recri) is found beyond which, the average Nusselt number for the wavy or ribbed-wavy channel is more than that for a parallel plate channel and the value of Recri decreases with the increase in a number of ribs and for any given number of ribs, it is minimum for rectangular ribs. The performance factor (PF) sharply decreases with Reynolds number (Re) up to Re = 50 for all types of ribbed-wavy channels. For Re > 50, the change in PF with Re is gradual and decreases for all the ribbed cases and for the sinusoidal channel, it increases beyond Re = 100. The magnitude of PF strongly depends on the shape and number of ribs and Re. The relative magnitude of total entropy generation for different ribbed channels varies with Re and the number of ribs.
Practical implications
The findings of the present study are useful to design the economic heat exchanging devices.
Originality/value
The effects of shape and the number of ribs on the heat transfer performance and entropy generation have been investigated for the first time for the laminar flow regime. Also, the effects of shape and number of ribs on the flow and temperature fields and entropy generation have been investigated in detail.
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Alireza Rahimi, Pouria Azarikhah, Abbas Kasaeipoor, Emad Hasani Malekshah and Lioua Kolsi
This paper aims to investigate the natural convection fluid flow and heat transfer in a finned/multi-pipe cavity.
Abstract
Purpose
This paper aims to investigate the natural convection fluid flow and heat transfer in a finned/multi-pipe cavity.
Design/methodology/approach
The cavity is filled with the CuO-water nanofluid. The Koo–Kleinstreuer–Li model is used to estimate the dynamic viscosity and consider Brownian motion. On the other hand, the effect of the shapes of nanoparticles on the thermal conductivity and related heat transfer rate is presented.
Findings
In the present investigation, the governing parameters are Rayleigh number, CuO nanoparticle concentration in pure water and the thermal arrangements of internal active fins and solid bodies. Impacts of these parameters on the nanofluid flow, heat transfer rate, total/local entropy generation and heatlines are presented. It is concluded that adding nanoparticles to the pure fluid has a significant positive influence on the heat transfer performance. In addition, the average Nusselt number and total entropy generation have direct a relationship with the Rayleigh number. The thermal arrangement of the internal bodies and fins is a good controlling tool to determine the desired magnitude of heat transfer rate.
Originality/value
The originality of this paper is to use the lattice Boltzmann method in simulating the nanofluid flow and heat transfer within a cavity included with internal active bodies and fins.