An Experimental Study on Buoyancy Induced Convective Heat Transfer in a Square Cavity using Multi-Walled Carbon Nanotube (MWCNT)/Water Nanofluid

Heat and mass transfer characteristics of carbon nanotube nanofluids: A review

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

An experimental study on the natural convection heat transfer in rectangular enclosure using functionalized alumina-thermal oil-based nanofluids

Abstract: The nanofluids are considered as an effective medium for thermal transport in various applications due to improved properties. Limited experimental studies are accomplished on the convective heat transfer of nanofluids. Natural convective heat transfer behavior in nanofluids is experimentally studied in a vertical rectangular enclosure (aspect ratio = 4) with one heating and one cooling wall. The fluid under investigation is a novel and highly stable functionalized alumina-thermal oil-based nanofluid. The investigations are carried out for different concentrations of nanofluids ranging from 0 to 3 wt%. The effectiveness of the natural convection heat transfer process is mainly dependent on the properties of cooling media. The measured thermophysical properties of nanofluids are used for the estimation of heat transfer characteristics with a Prandtl number range of 228–592. The heat transfer coefficient and Nusselt number are obtained at different nanoparticle concentrations. A heat flux is applied on the hot wall with a range of 1593.75–3150 W/m 2 . An improvement in the cooling performance of nanofluids is observed. The high nanoparticle concentrations of nanofluids exhibit higher heat transfer coefficient as compared to the pure thermal oil. A correlation is developed for the Nusselt number in terms of Rayleigh number (4.43 × 10 5 –2.59 × 10 6 ), nanoparticle concentration and effective thermophysical properties.

Experimental measurement of viscosity and electrical conductivity of water-based γ-Al2O3/MWCNT hybrid nanofluids with various particle mass ratios

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.

Free convection with MWCNT/water nanofluid having varying aspect ratio of MWCNT nanoparticle in thermally undulated enclosures

Abstract: The Aspect ratio of carbon nanotubes (CNTs) in cavities of different geometrical aspect ratio is one of the critical parameters of the design in thermal engineering. The present work documented a numerical simulation of 2D, steady and laminar free convection in rectangular cavities with different aspect ratios filled with water-based nanofluid. The nanoparticle considers in the present work is MWCNT with varying average diameter and length consequently varying aspect ratio. The Navier–Stokes and energy equations are solved numerically, coupling Thang et al. [43] model for calculating the effective thermal conductivity and Brenner and Condiff [44] model for determining the effective dynamic viscosity. The results are presented in the form of streamlines, isotherms, vertical velocity and Nusselt numbers. The novelty of the present study is to find the effect of MWCNT nanoparticle aspect ratio on fluid flow and heat transfer. Maximum of about 65% increment in average Nusselt number is observed at maximum aspect ratio (length/diameter) of 6 × 104 for any temperature undulation and cavity aspect ratio. Maximum MWCNT aspect ratio (or minimum diameter) is proposed for better heat transfer. A range of Rayleigh number is observed for better heat transfer for different temperature undulation value at the left wall.

3D investigation of natural convection of nanofluids in a curved boundary enclosure applying lattice Boltzmann method

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.

Convection Heat Transfer

Abstract: Fundamental Principles Laminar Boundary Layer Flow Laminar Duct Flow External Natural Convection Internal Natural Convection Transition to Turbulence Turbulent Boundary Layer Flow Turbulent Duct Flow Free Turbulent Flows Convection with Change of Phase Mass Transfer Convection in Porous Media.

Thermal transport measurements of individual multiwalled nanotubes.

Abstract: The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W/K m at room temperature, which is 2 orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. The temperature dependence of the thermal conductivity of nanotubes exhibits a peak at 320 K due to the onset of umklapp phonon scattering. The measured thermoelectric power shows linear temperature dependence with a value of 80 microV/K at room temperature.

Anomalous thermal conductivity enhancement in nanotube suspensions

Abstract: We have produced nanotube-in-oil suspensions and measured their effective thermal conductivity. The measured thermal conductivity is anomalously greater than theoretical predictions and is nonlinear with nanotube loadings. The anomalous phenomena show the fundamental limits of conventional heat conduction models for solid/liquid suspensions. We have suggested physical concepts for understanding the anomalous thermal behavior of nanotube suspensions. In comparison with other nanostructured materials dispersed in fluids, the nanotubes provide the highest thermal conductivity enhancement, opening the door to a wide range of nanotube applications.

Natural convection of nano-fluids

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.

Heat transfer behaviours of nanofluids in a uniformly heated tube

Abstract: In the present work, we consider the problem of the forced convection flow of water– γAl2O3 and ethylene glycol– γAl2O3 nanofluids inside a uniformly heated tube that is submitted to a constant and uniform heat flux at the wall. In general, it is observed that the inclusion of nanoparticles has increased considerably the heat transfer at the tube wall for both the laminar and turbulent regimes. Such improvement of heat transfer becomes more pronounced with the increase of the particle concentration. On the other hand, the presence of particles has produced adverse effects on the wall friction that also increases with the particle volume concentration. Results have also shown that the ethylene glycol– γAl2O3 mixture gives a far better heat transfer enhancement than the water– γAl2O3 mixture.