scholarly journals Enhancement of Turbulent Convective Heat Transfer using a Microparticle Multiphase Flow

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1282
Author(s):  
Tao Wang ◽  
Zengliang Gao ◽  
Weiya Jin
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Volume Fraction ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Better Than

The turbulent heat transfer enhancement of microfluid as a heat transfer medium in a tube was investigated. Within the Reynolds number ranging from 7000 to 23,000, heat transfer, friction loss and thermal performance characteristics of graphite, Al2O3 and CuO microfluid with the particle volume fraction of 0.25%–1.0% and particle size of 5 μm have been respectively tested. The results showed that the thermal performance of microfluids was better than water. In addition, the graphite microfluid had the best turbulent convective heat transfer effect among several microfluids. To further investigate the effect of graphite particle size on thermal performance, the heat transfer characteristics of the graphite microfluid with the size of 1 μm was also tested. The results showed that the thermal performance of the particle size of 1 μm was better than that of 5 μm. Within the investigated range, the maximum value of the thermal performance of graphite microfluid was found at a 1.0% volume fraction, a Reynolds number around 7500 and a size of 1 μm. In addition, the simulation results showed that the increase of equivalent thermal conductivity of the microfluid and the turbulent kinetic energy near the tube wall, by adding the microparticles, caused the enhancement of heat transfer; therefore, the microfluid can be potentially used to enhance turbulent convective heat transfer.

scholarly journals Convective Heat Transfer of Al2O3 and CuO Nanofluids Using Various Mixtures of Water-Ethylene Glycol as Base Fluids

2017 ◽  
Vol 7 (2) ◽  
pp. 1496-1503
Author(s):  
K. Boukerma ◽  
M. Kadja
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Ethylene Glycol ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Volume Fraction ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Volume Fractions

In this work, a numerical study has been performed on the convective heat transfer of Al2O3/Water-Ethylene Glycol (EG) and CuO/(W-EG) nanofluids flowing through a circular tube with circumferentially non-uniform heating (constant heat flux) under the laminar flow condition. We focus on the study of the effect of EG-water mixtures as base fluids with mass concentration ranging from 0% up to 100% ethylene glycol on forced convection. The effect on the flow and the convective heat transfer behavior of nanoparticle types, their volume fractions (φ=1-5%) and Reynolds number are also investigated. The results obtained show that the highest values of the average heat transfer coefficient is observed between 40% and 50% of EG concentration. The average Nusselt number increases with the increase in EG concentration in the base fluid, and the increase in the Reynolds number and volume fraction. For concentrations of EG above 60%, and for all volume fractions, the increase of thermal performance of nanofluids became inversely proportional to the increase of Reynolds number. In addition, CuO/(W-EG) nanofluids show the best thermal performance compared with Al2O3/ (W-EG) nanofluids.

Augmented Heat Transfer in a Rectangular Channel With Permeable Ribs Mounted on the Wall

1994 ◽  
Vol 116 (4) ◽  
pp. 912-920 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Area Ratio ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Open Area ◽  
Number Range ◽  
Solid Type

Turbulent heat transfer and friction in a rectangular channel with perforated ribs arranged on one of the principal walls are investigated experimentally. The effects of rib open-area ratio, rib pitch-to-height ratio, rib height-to-channel hydraulic diameter ratio, and flow Reynolds number are examined. To facilitate comparison, measurements for conventional solid-type ribs are also conducted. Laser holographic interferometry is employed to determine the rib permeability and measure the heat transfer coefficients of the ribbed wall. Results show that ribs with appropriately high open-area ratio at high Reynolds number range are permeable, and the critical Reynolds number of initiation of flow permeability decreases with increasing rib open-area ratio. By examining the local heat transfer coefficient distributions, it is found that permeable ribbed geometry has an advantage of obviating the possibility of hot spots. In addition, the permeable ribbed geometry provides a higher thermal performance than the solid-type ribbed one, and the best thermal performance occurs when the rib open-area ratio is 0.44. Compact heat transfer and friction correlations are also developed for channels with permeable ribs.

CFD analysis on natural convective heat transfer of Al2O3-gear oil nanolubricant used in HEMM

2017 ◽  
Vol 69 (5) ◽  
pp. 673-677
Author(s):  
Ankit Kotia ◽  
Subrata Kumar Ghosh
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Volume Fraction ◽  
Transfer Performance ◽  
Left Wall ◽  
Content Type ◽  
Gear Oil

Purpose The present work aims to numerically investigate the natural convective heat transfer performance of aluminium oxide (Al2O3)-gear oil nanolubricant used in heavy earth moving machinery (HEMM). Design/methodology/approach Viscosity, density and thermal conductivity of nanolubricants have been experimentally determined. The numerical simulation has been performed by using computational fluid dynamics (CFD) for a cylinder cavity which resembles shape of automatic transmission system of HEMM. The left wall temperature has been maintained at 293 to 313 K, and right wall is at a constant temperature of 283 K. Due to absence of any experimental study on natural convective heat transfer performance of Al2O3-gear oil nanolubricant, initially CFD model has been tested for accuracy by comparing experimental, and CFD results for Al2O3-water nanofluid has been available in open literature. Findings It has been observed that Nusselt number increases with increase in Rayleigh number, but it decreases with increasing particle volume fraction. The gear oil-based nanolubricant is expected to have the better thermal performance in HEMM at higher temperature. Practical implications The numerical analysis will help to predict the thermal performance of nanolubricant. The outcome may help the designers, researchers and manufacturers of HEMM. Originality/value Most of the previous studies have been limited with base fluid as water, ethylene glycol, etc. in the field of nanofluid. CFD study for thermal performance of Al2O3-gear oil nanolubricant is essential before the experimental work. This work is the preliminary stage of application of, nanolubricant for heat transfer.

scholarly journals Astray State-Laminar Forced Convective Heat Transfer of Al2O3 – H2O Nanofluid through 3D-Rectangular Cross- Sectional Duct

2019 ◽  
Vol 8 (2S3) ◽  
pp. 899-907
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Friction Factor ◽  
Convective Heat ◽  
Flow Rate ◽  
Base Fluid ◽  
Volume Fraction ◽  
Phase Model ◽  
Forced Convective Heat Transfer

A Steady state-laminar forced convective heat transfer has been simulated by Computational Fluid Dynamics (CFD) with a Single Phase Model (SPM), Multi Phase model & Diameter effects and also determined the effects of nanoparticles concentration and nanofluid flow rate through 3D rectangular duct under certain boundary condition (constant heat flux). The nanofluid contains Alumina nanoparticles of size 60nm diameter used for MPM which is mixed with base fluid (water) with volume fraction of 0% ≤ ȼ ≤ 5% and Reynolds number (Re) ranges from 250 ≤ Re ≤ 1000. ANSYS 18.0 has been used for simulation. Three cases of analysis have been carried out in which the thermal conductivity (k) and dynamic viscosity (µ) of nanofluids are determined using two sets of theoretical models and one set of experimental k & µ data from literature respectively. The nanoparticles which stay more dispersed in the base fluid due to increase in Reynolds number which improves HTC and also decreases the friction factor accordingly. Particular attention has been paid to the variation of heat transfer characteristics when the modeling approach is switched from SPM to MPM. It is revealed that higher heat transfer rates are observed in MPM. The results shows that the friction factor decreases and Nusselt number (Nu) increases when there is an increase in the flow rate and also increase in the volume concentration of the nanofluid, while the pressure drop increases only slightly. The increase in HTC is one of the most important aims for industry and researchers.

Effect of Volume Fraction of Nanoparticles to the Convective Heat Transfer of Nanofluids

2011 ◽  
Vol 464 ◽  
pp. 528-531 ◽  
Author(s):  
Zhi Yong Ling ◽  
Tao Zou ◽  
Jian Ning Ding ◽  
Guang Gui Cheng ◽  
Peng Fei Fu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Volume Fraction ◽  
Small Difference ◽  
Numerical Study ◽  
Convective Heat Transfer Coefficient ◽  
Full Development ◽  
Significant Difference

A numerical study on the convective heat transfer characteristics of Cu-water nanofluid under the laminar flow condition was performed. The results show that the convective heat transfer coefficient increases with the increase of the volume fraction of the nanoparticles and the Reynolds number. There is a significant difference between the numerical simulation result and the result calculated from the Shah equation in the entrance region, but a small difference in full development areas. The numerical results agree well with that obtained from the Xuan equation when the Reynolds number and the volume fraction of the nanoparticles are small, but the errors between them increase as the increase of the Reynolds number and the volume fraction of nanoparticles.

scholarly journals FRACTAL-STRUCTURAL ANALYSIS OF CONVECTION HEAT TRANSFER IN A TURBULENT MEDIUM

2020 ◽  
Vol 17 (2) ◽  
pp. 61-68
Author(s):  
A.Zh. Turmukhambetov ◽  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Structural Analysis ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Convective Heat Exchange ◽  
Spherical Body ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat

The features of convective heat transfer of bodies in a turbulent environment are considered. The results of experimental research by one of the authors are discussed. Experimental data show that the heat transfer of a spherical body is affected by natural convection, the thermo-physical properties of the medium, the tightness of the flow, the turbulent flow regime, etc. Due to these factors, the formula for calculating convective heat transfer, which includes many experimental constants, becomes cumbersome and inconvenient for practical application. The paper presents the results of applying fractal-structural analysis methods to describe experimental data on convective heat exchange of badly streamlined (cylinder and sphere) bodies in a channel. Quantitative relations are obtained that link the intensity of turbulent heat transfer with the criteria for the degree of self-organization.

Convective Heat Transfer in the Impingement Region of a Buoyant Plume

1987 ◽  
Vol 109 (1) ◽  
pp. 120-124 ◽  
Author(s):  
R. L. Alpert
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Rates ◽  
Order Of Magnitude

Fires of hazardous scale generate turbulent plumes within which convective heat transfer to surfaces can be important. Relatively little work has been done on developing reliable convective heat transfer correlations applicable to such large-scale flows. The present study, confined to heat transfer rates within the plume impingement region on a ceiling, achieves plume Reynolds numbers an order of magnitude beyond those of previous work by performing laboratory-scale experiments at elevated ambient pressures. Flow disturbances which normally cause scatter in plume heat transfer data are reduced as a consequence of this technique. It is shown that impingement zone Nusselt number depends on the 0.61 power of plume Reynolds numbers in the range of 104 to 105. This result is between the 1/2 power dependence expected for strain rate control (forced jet impingement) and the 2/3 power expected for buoyancy control of turbulent heat transfer rates.

An Semi-Empirical Model of Turbulent Convective Heat Transfer to Fluids at Supercritical Pressure

2008 ◽  
Author(s):  
J. Derek Jackson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Critical Pressure ◽  
Supercritical Pressure ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Governing Equations ◽  
Semi Empirical

Recently, there has been a renewed interest in heat transfer to fluids at supercritical pressure because of the consideration now being given to the Supercritical Pressure Water-cooled Reactor (SPWR). This will supply high temperature ‘steam’ to turbines at pressures well above the critical value. The particular feature of fluids at pressures just above the critical pressure which makes them of special interest is that as they change from being liquid-like to gaseous the transition occurs in a continuous manner over a narrow band of temperature without the discontinuous behaviour encountered when phase occurs in fluids at sub-critical pressure. However, when heat takes place within fluids at supercritical pressure, extreme non-uniformities of physical and transport properties can be present. The governing equations for flow and convective heat transfer have to be written in a form which takes account of the temperature dependence of the properties. They are complicated, highly non-linear and strongly inter-dependent. The proportionality between heat flux and temperature difference found in constant property forced convection no longer exists. Also, the effectiveness of heat transfer can be very sensitive to imposed heat flux. Particular problems arise due to the non-uniformity of density by virtue of the fluid being caused to accelerate where the bulk density is falling or as a consequence of the flow field and turbulence being modified by the influence of buoyancy. Severe impairment on heat transfer can be encountered due to such effects. The requirements for achieving similarity and the approach to the correlation of data on heat transfer to fluids at supercritical pressure are matters that need to be carefully considered and soundly based. This necessitates representing the general form of the governing equations and the boundary conditions in non-dimensional form to identify the parameters that are involved. In this paper, an extended model of turbulent heat transfer to fluids at supercritical pressure is presented which utilises a semi-empirical multiplier to account for the combined effects of flow acceleration and buoyancy.

Experimental Model of Temperature-Driven Nanofluid

2006 ◽  
Vol 129 (6) ◽  
pp. 697-704 ◽  
Author(s):  
A. G. Agwu Nnanna
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Small Volume ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Isothermal Condition ◽  
Carrier Fluid ◽  
Small Volume Fraction ◽  
The Impact

This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm Al2O3–H2O nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, 0.2⩽ϕ⩽2% the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction ϕ>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for Nuϕ as a function of ϕ and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

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