An Experimental Study on Buoyancy Induced Convective Heat Transfer in a Square Cavity using Multi-Walled Carbon Nanotube (MWCNT)/Water Nanofluid
01 Sep 2016-Vol. 745, Iss: 3, pp 032033
TL;DR: In this paper, a square enclosure of dimensions (40 × 40 × 200) mm is used as test section and MWCNT/Water nanofluid with volume fractions 0.1%, 0.3%, 1% and 2% and Rayleigh numbers ranging from 7 × 105 to 1 × 107 are studied.
Abstract: In recent times, convective heat transfer using nanofluid has been a active field of study. However experimental studies pertaining to buoyancy induced convective heat transfer using various nanofluid is relatively scarce. In present study, a square enclosure of dimensions (40 × 40 × 200) mm is used as test section. Initially, Al2 O3 /Water nanofluid with volume fractions 0.3%, 1% and 2% and Rayleigh numbers ranging from 7 × 105 to 1 × 107 are studied. These results are then compared with Ho's[1] experimental data. Nusselt number is calculated based on the thermo-physical properties that are measured in-house for the given conditions. Further, MWCNT/Water nanofluid with volume fractions 0.1%, 0.3% and 0.5% is formulated and are studied for various Rayleigh numbers. Comparison of Al2O3 /Water and MWCNT/Water nanofluid have been made for different volume fractions and for various range of Rayleigh numbers. It is observed that MWCNT/Water nanofluid when compared with Al2 O3 /Water nanofluid yields higher values of the Nusselt number for a given volume fractions. All the existing experimental studies using particle based nanofluid concluded a deterioration in natural convective heat transfer. This study for the first time demonstrates an enhancement in natural convection using MWCNT/Water nanofluid. Such enhancement cannot be simply explained based only on the relative changes in the thermophysical properties. Other factors such as percolation network in MWCNT/Water nanofluid which increases the heat transfer pathway between two walls and the role of slip mechanisms might be the possible reasons for the enhancement.
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TL;DR: In this paper, the authors present a comprehensive and up-to-date review of carbon nanotubes (CNTs) being applied in various heat transfer (convective and boiling) and mass transfer systems such as heat exchangers and separators.
Abstract: The pursuit of superior working fluids for heat and mass transfer systems in the industry is on the rise, inspired by not only to maximize revenue but also to accommodate heat dissipation or chemical separation under extreme conditions The addition of a small amount of nanoparticle, a product called nanofluid, has been initiated over the last decade In particular, researchers have employed carbon nanotubes (CNTs) into conventional fluids as their preferred nanoparticles due to the merits of having a remarkable thermal conductivity compared to other nanoparticles Here, we present a comprehensive and up to date review of this incredible fluid being applied in various heat transfer (convective and boiling) and mass transfer systems such as heat exchangers and separators Other critical parameters associated with the practicality of the CNT nanofluids such as pumping power and efficiency are also discussed We surveyed a remarkable range of results of some of the heat and mass transfer studies that strongly depend on the inherent CNT nanofluid characteristics and operating conditions such as CNT treatment, size, concentration, Reynolds number, and so on A major conclusion that can be drawn from this review is the significantly higher heat transfer coefficient at lower pressure drop or pumping power of the CNT nanofluid compared to other nanofluids, which implied better thermal performance of the heat transfer system Besides that, the concentration of CNT is the influential factor to achieve optimum boiling heat transfer while the mass transfer performance of the CNT nanofluid is moderately good against other nanofluids Additionally, CNT treatment using covalent functionalization is crucial for the overall stability and performance of the CNT nanofluid However, several issues that inhibit their widespread use such as possible corrosion-erosion in systems, lack of risk assessments, and high cost of CNT nanofluid must be thoroughly addressed in future studies
91 citations
TL;DR: In this paper, an experimental study on the convective heat transfer of nanofluids was conducted in a vertical rectangular enclosure with one heating and one cooling wall. And the results showed that the high nanoparticle concentrations of nanoparticles exhibit higher heat transfer coefficient as compared to the pure thermal oil.
40 citations
TL;DR: In this article, the effect of particle mass ratios of hybrid nanofluids on the thermal properties of deionized water (DIW)-based γ-Al2O3 and MWCNT hybrid nanoparticles was investigated.
Abstract: The hybridization of nanoparticles is a concept employed for the improvement of the thermal properties of nanofluids. Presently, there is a scarcity of studies in the open literature concerning the influence of particle mass ratios of hybrid nanofluids on the thermal properties. Thus, this paper investigated the effect of temperatures (15–55 °C) and particle mass ratios (90:10, 80:20, 60:40, 40:60, and 20:80) on the viscosity and electrical conductivity of deionized water (DIW)-based γ-Al2O3 and MWCNT hybrid nanofluids. A two-process strategy was deployed to prepare the hybrid nanofluids at a volume concentration of 0.1%. The hybrid nanofluids were characterized for their morphology using a transmission electron microscope. Hybrid nanofluid stability was monitored using UV visible spectrophotometer, viscosity, and visual inspection methods. The prepared nanofluids were observed to be stable with relatively constant viscosity and absorbance values. At 55 °C, maximum enhancements of 442.9% and 26.3%, and 288.0% and 19.3% were recorded for the electrical conductivity and viscosity of Al2O3–MWCNT/DIW nanofluids at particle mass ratios of 90:10 and 20:80, respectively, in relation to DIW. Temperature increase was observed to significantly reduce the viscosity of hybrid nanofluids while the particle mass ratio considerably and positively impacted the electrical conductivity. The relatively low viscosity of the hybrid nanofluids coupled with its reduction under increasing temperature and its insignificance increase as the particle mass ratio of the Al2O3 nanoparticles increased to make them viable coolants for engineering applications. New correlations were proposed to accurately estimate the viscosity and electrical conductivity of the hybrid nanofluids.
28 citations
TL;DR: In this paper, a numerical simulation of 2D, steady and laminar free convection in rectangular cavities with different aspect ratios filled with water-based nanofluid is presented.
12 citations
TL;DR: In this paper, a multiple relaxation times lattice Boltzmann method (MRT-LBM) has been used to investigate the natural convection behavior of nanofluids in an enclosure.
Abstract: Purpose
The purpose of this paper is to investigate the natural convection behavior of nanofluids in an enclosure. The enclosure is a 3D capsule with curved boundaries filled with TiO2-water nanofluid.
Design/methodology/approach
In this paper, a multiple relaxation times lattice Boltzmann method (MRT-LBM) has been used. Two-component LBM has been conducted to consider the interaction forces between nanoparticles and the base fluid.
Findings
Results show that the enhanced Nusselt number (Nu*) increases with the increase in volume fraction of nanoparticles (ϕ) and Ra number and decrease of nanoparticle size (λ). Additionally, the findings indicate that increasing volume fraction beyond a certain value decreases Nu*.
Originality/value
This paper presents a MRT model of lattice Boltzmann in a 3D curved enclosure. A correlation is also presented based on the current results for Nu* depending on Ra number, volume fraction and size of nanoparticles. Furthermore, a comparison for the convergence rate and accuracy of this model and the SIMPLE algorithm is presented.
4 citations
References
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2,546 citations
TL;DR: In this article, an apparently paradoxical behaviour of heat transfer deterioration was observed in nano-fluid and its dependence on parameters such as particle concentration, material of the particles and geometry of the containing cavity have been investigated.
Abstract: Fluids with nano size solid particles suspended in them have been given the name nano-fluid which in recent studies have shown tremendous promise as heat transfer fluids. However, before suggesting such fluids for applications a thorough knowledge of physical mechanism of heat transfer in such fluids is wanted. The present study deals with one such aspect of natural convection of nano fluids inside horizontal cylinder heated from one end and cooled from the other. An apparently paradoxical behaviour of heat transfer deterioration was observed in the experimental study. Nature of this deterioration and its dependence on parameters such as particle concentration, material of the particles and geometry of the containing cavity have been investigated. The fluid shows characters distinct from that of common slurries.
906 citations
TL;DR: In this article, the authors considered the forced convection flow of water and ethylene glycol inside a uniformly heated tube that is submitted to a constant and uniform heat flux at the wall.
648 citations