Performance and optimization analysis of a constructal T-shaped fin subject to variable thermal conductivity and convective heat transfer coefficient

2010 ◽  
Vol 53 (1-3) ◽  
pp. 254-267 ◽  
Author(s):  
B. Kundu ◽  
D. Bhanja
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Variable Thermal Conductivity ◽  
Optimization Analysis

Investigations on Transient Natural Convection in Boron Nitride-Mineral Oil Nanofluid Systems

2012 ◽  
Author(s):  
Shijo Thomas ◽  
C. B. Sobhan ◽  
Jaime Taha-Tijerina ◽  
T. N. Narayanan ◽  
P. M. Ajayan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Boron Nitride ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Mineral Oil

Nanofluids are suspensions or colloids produced by dispersing nanoparticles in base fluids like water, oil or organic fluids, so as to improve their thermo-physical properties. Investigations reported in recent times have shown that the addition of nanoparticles significantly influence the thermophysical properties, such as the thermal conductivity, viscosity, specific heat and density of base fluids. The convective heat transfer coefficient also has shown anomalous variations, compared to those encountered in the base fluids. By careful selection of the parameters such as the concentration and the particle size, it has been possible to produce nanofluids with various properties engineered depending on the requirement. A mineral oil–boron nitride nanofluid system, where an increased thermal conductivity and a reduced electrical conductivity has been observed, is investigated in the present work to evaluate its heat transfer performance under natural convection. The modified mineral oil is produced by chemically dispersing boron nitride nanoparticles utilizing a one step method to obtain a stable suspension. The mineral oil based nanofluid is investigated under transient free convection heat transfer, by observing the temperature-time response of a lumped parameter system. The experimental study is used to estimate the time-dependent convective heat transfer coefficient. Comparisons are made with the base fluid, so that the enhancement in the heat transfer coefficient under natural convection situation can be estimated.

A numerical prediction and potential control of typical icing process on automobile windshield under nocturnal radiative cooling and subfreezing conditions

2019 ◽  
Vol 234 (5) ◽  
pp. 1480-1496
Author(s):  
Xuzhi Du ◽  
Zhigang Yang ◽  
Zheyan Jin ◽  
Yuyu Zhu ◽  
Zhiwei Zhou
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Relative Humidity ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Cloud Amount ◽  
Potential Control

In this work, a simplified mathematical model, concerned with transient heat conduction as well as convective and radiative heat transfer, was developed to predict the variations of temperature and supercooling of the windshield during practical nocturnal cooling processes of a car. Final supercooling [Formula: see text] was introduced as an indicator to evaluate the probability of occurrence of frosting. Following that, the Taguchi statistical method was used to conduct a parameter sensitivity analysis and then figure out the potential control strategies for frosting suppression. The results showed that relative humidity had the most significant influence on the distribution of supercooling during the nocturnal cooling period, whereas the initial temperature as well as the thickness and thermal conductivity of the windshield played a minor role in it. An increase in relative humidity resulted in a significant increase in [Formula: see text], which might be expected to trigger an earlier initiation of frosting. The emissivity of the windshield, concerned with the nocturnal radiation potential, showed a considerable effect on the response of [Formula: see text], whereas the influence of the total opaque cloud amount appeared to be largely limited. In addition, through a potential control of the thermal conductivity of the windshield, [Formula: see text] just exhibited a very limited decline, thus contributing little to frosting mitigation. However, with a moderate potential control of the internal convective heat transfer coefficient, the frosting behavior might be effectively suppressed under a severe condition that favored the occurrence of icing. Besides, by introducing a combined control of the emissivity of the windshield and the internal convective heat transfer coefficient, [Formula: see text] could be well reduced to a value below zero even as the relative humidity increased up to 90%, which was supposed to prevent the occurrence of frosting under a far severer condition.

Numerical Study of Natural Convection Around an Isolated Horizontal Cylinder and Determination of Critical Radius Effect With a Variable Heat Transfer Coefficient

2009 ◽  
Author(s):  
S¸. O¨zgu¨r Atayılmaz ◽  
Hakan Demir ◽  
O¨zden Agra
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Critical Radius ◽  
Convective Heat Transfer Coefficient ◽  
Horizontal Cylinder ◽  
Insulation Thickness

Natural convection heat transfer from an insulated horizontal cylinder is studied analytically and numerically. Curved surfaces such as circular cylinder which has a radius smaller than a certain critical size, adding insulation to the surface increases the heat transfer form the surface. This phenomenon occurs if the effects of the increase of the outer surface area on the heat transfer are higher than the decrease by the total thermal resistance of the insulated cylinder. The critical radius is represented as a function of thermal conductivity of the object and convective heat transfer coefficient in the textbooks on heat transfer. This is only valid if both thermal conductivity and convective heat transfer coefficient are constant. In fact, the convective heat transfer coefficient varies with outer diameter of the cylinder while thermal conductivity can be taken as constant. Therefore, a numerical and an analytical study were performed in order to investigate the effects of variable heat transfer coefficient on determining the critical radius. For this aim an isolated horizontal cylinder having different insulation thickness and a constant thermal conductivity was modeled and solved numerically using FLUENT CFD software. Also the same problem was solved analytically and numerical and analytical results were compared. The variation of the total heat transfer from cylinder surface according to insulation thickness is obtained. It is found that the standard critical radius criterion led to significant errors compared to numerical results.

An Experimental Study on the Convective Heat Transfer Behaviour of Diamond Nanofluids in Electronic Cooling Applications

2018 ◽  
Author(s):  
Farzin Mashali ◽  
Ethan M. Languri ◽  
Jim Davidson ◽  
David Kerns ◽  
Fahad Alkhaldi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Base Fluid ◽  
Convective Heat Transfer Coefficient ◽  
Cold Plate

This study presents the convective heat transfer coefficient of 0.05 wt.% diamond nanofluids containing functionalized nanodiamond dispersed in a base fluid deionized (DI) water flowing in a conduction cold plate under turbulent flow conditions, experimentally. The conduction cold plate was heated via six cartridge heaters with a constant heat transfer rate. The primary experimental study has been implemented to investigate the thermal conductivity of diamond nanofluids which showed a higher effective thermal conductivity than that of the base fluid. In addition, nanofluid was flowed in a closed system with heating at the heat exchanger and cooling via a cooling tank to keep the inlet temperature constant to explore the convection heat transfer properties of diamond nanofluids. Results indicate that the convective heat transfer coefficient and Nusselt number of diamond nanofluid are higher than that of the DI water in a same flow rate, and these properties increased with increase in Reynolds number.

Measurement of the Thermal Conductivity of a Water-Based Single-Wall Carbon Nanotube Colloidal Suspension With a Modified 3-ω Method

2009 ◽  
Author(s):  
Tae Y. Choi ◽  
Mohammad H. Maneshian ◽  
Boseon Kang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Colloidal Suspension ◽  
Convective Heat Transfer Coefficient ◽  
Model Systems ◽  
Water Based

A modified 3-ω method applied to a suspended platinum microwire was employed to measure the thermal conductivity and convective heat transfer coefficient of water-based single-walled carbon nanotubes (CNT) solution, and an expression for calculating the convective heat transfer coefficient in a free convective fluid was introduced. The measurement technique was validated for three model systems including vacuum, air, and deionized water. It is found that there is excellent agreement of these three model systems with theoretical predictions. In addition, the frequency dependence on the third harmonic response measured in deionized water reveals existence of a very low working frequency below 60 mHz. The thermal conductivity and convective heat transfer coefficient of a nanofluid (water-based single wall CNTs colloidal suspension) were determined to be 0.73±0.013 W/m·K and 14900±260 W/m2·K respectively, which corresponds to enhancement of 19.4% in thermal conductivity and 18.9% in convective heat transfer as compared to water.

Prediction of Thermal Conductivity and Convective Heat Transfer Coefficient of Nanofluids by Local Composition Theory

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
M. S. Hosseini ◽  
A. Mohebbi ◽  
S. Ghader
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Composition Theory ◽  
Local Composition

In this study, a new method based on the local composition theory has been developed to predict thermal conductivity, convective heat transfer coefficient, and viscosity of nanofluids. The nonrandom two liquid (NRTL) model is used for this purpose. The effects of temperature and particle volume concentration on thermal conductivity, convective heat transfer coefficient, and viscosity are investigated. The adjustable parameters of the NRTL model were obtained by fitting with experimental data. The results of the local composition theory are compared with the experimental data of CuO/water, Al2O3/water, TiO2/water, Cu/water, Au/water, Ni/water, TiO2/ethylene glycol, and Al/ethylene glycol (EG) nanofluids and a good agreement between the theory and the experimental data is observed. The absolute average deviation of the model for thermal conductivity was 1.51% in comparison to 42% in conventional models. This parameter for viscosity and convective heat transfer coefficient were 2.91% and 2.13%, respectively. Moreover, a new equation for calculating convective heat transfer coefficient of nanofluids is proposed and tested.

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