Natural Convective Heat Transfer of Water-in-FC72 Nanoemulsion Fluids

2008 ◽  
Author(s):  
Zenghu Han ◽  
Bao Yang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Hydrodynamic Interaction ◽  
Convective Heat Transfer Coefficient ◽  
Relative Viscosity ◽  
Solid Particles ◽  
Water Loading

The use of SOLID-particles has long been a common way of increasing fluid thermal conductivity. In this paper, nanoemulsion fluids—dispersions of LIQUID-nanodroplets—are proposed. As an example, water-in-FC72 nanoemulsion fluids are developed, and their thermophysical properties and impact on natural convective heat transfer are investigated experimentally. A significant increase in thermal conductivity—up to 52% for 12vol% of water nanodroplets (or 7.1 wt%)—is observed in the fluids. The enhancement in conductivity and viscosity of the fluids is found to be nonlinear with water loading, indicating an important role of the hydrodynamic interaction and aggregation of nanodroplets. However, the relative viscosity is found to be about two times the relative conductivity if compared at the same water loading. The presence of water nanodroplets is found to systematically increase the natural convective heat transfer coefficient in these fluids, in contrast to the observation in several conventional nanofluids containing solid nanoparticles.

Thermal and Phase Change Characteristics of Self-Assembled PAO Nanoemulsion Fluids

2009 ◽  
Author(s):  
J. J. Xu ◽  
X. Liu ◽  
B. Yang ◽  
Thanh Tran
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Self Assembly ◽  
Convective Heat Transfer Coefficient ◽  
Solid Particles ◽  
Measured Temperature ◽  
Sound Waves ◽  
Conductivity Enhancement

The strategy of adding solid particles to fluids for improving thermal conductivity has been pursued for more than one century. Here, a novel concept of using liquid nanodroplets for enhancing thermal performance has been developed and demonstrated in polyalphaolefin (PAO) nanoemulsion fluids. The PAO nanoemulsion fluids are spontaneously generated by self-assembly, and are thermodynamically stable. Their thermophysical properties, including thermal conductivity and viscosity, and impact on convective heat transfer are investigated experimentally. The thermal conductivity enhancement in these fluids is found to be moderate, but increases rapidly with increasing temperature in the measured temperature range from 35 °C to 75 °C. A very remarkable increase in convective heat transfer coefficient occurs in the nanoemulsion fluids due to the explosive vaporization at the superheat limit (i.e., spinodal states). The fluid heat transfer could be augmented through the heat of vaporization (which intuitively raises the base fluid specific heat capacity) and the fluid mixing induced by the sound waves. The development of such phase-changeable nanoemulsion fluids would open a new direction for thermal fluids studies.

Thermophysical Characteristics of Self-Assembled Ethanol/Polyalphaolefin Nanoemulsion Fluids

2009 ◽  
Author(s):  
J. J. Xu ◽  
X. Liu ◽  
B. Yang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
High Speed ◽  
Convective Heat Transfer Coefficient ◽  
Solid Particles ◽  
Measured Temperature ◽  
Sound Waves ◽  
Conductivity Enhancement

The strategy of adding solid particles to fluids for improving thermal conductivity has been pursued for more than one century. Here, a novel concept of using liquid nanodroplets for enhancing thermal performance has been developed and demonstrated in polyalphaolefin nanoemulsion fluids with dispersed ethanol nanodroplets. The ethanol/polyalphaolefin nanoemulsion fluids are spontaneously generated by self-assembly, and are thermodynamically stable. Their thermophysical properties, including thermal conductivity and viscosity, and impact on convective heat transfer are investigated experimentally. The thermal conductivity enhancement in these fluids is found to be moderate, but increases rapidly with increasing temperature in the measured temperature range from 35 oC to 75 oC. A very remarkable increase in convective heat transfer coefficient occurs in the nanoemulsion fluids due to the explosive vaporization of the ethanol nanodroplets at the superheat limit (i.e., spinodal states, about 122 oC higher than the atmospheric boiling point for ethanol). The explosive liquid-vapor phase transition is monitored using high speed camera. The fluid heat transfer could be augmented through the heat of vaporization (which intuitively raises the base fluid specific heat capacity) and the fluid mixing induced by the sound waves. The development of such phase-changeable nanoemulsion fluids would open a new direction for thermal fluids studies.

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.

Numerical Study on the Surface Convective Heat Transfer of Mass Concrete Structure

2015 ◽  
Vol 723 ◽  
pp. 992-995
Author(s):  
Biao Li ◽  
Fu Guo Tong ◽  
Chang Liu ◽  
Nian Nian Xi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Flow Velocity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Convective Heat Transfer Coefficient ◽  
Concrete Surface ◽  
Mass Concrete ◽  
Air Flow Velocity

The surface convective heat transfer of mass concrete is an important element of concrete structure temperature effect analysis. Based on coupled Thermal Fluid governing differential equation and finite element method, the paper calculated and analyzed the dependence of the concrete surface convective heat transfer on the air flow velocity and the concrete thermal conductivity coefficient. Results show that the surface convective heat transfer coefficient of concrete is a quadratic polynomial function of the air flow velocity, but influenced much less by the air flow velocity when temperature gradient is dominating in heat transfer. The concrete surface convective heat transfer coefficient increases linearly with the thermal conductivity of concrete increases.

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.

Numerical Analysis on the Heat Transfer Characteristics of the Radiator in a Heating Room

2014 ◽  
Vol 501-504 ◽  
pp. 2307-2310
Author(s):  
Ye Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Outer Wall ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Important Means ◽  
Weak Influence

Natural convective heat transfer is the most important means to supply heat load for resident building to keep necessary indoor air temperature in winter. To determine the surface convective heat transfer coefficient (CHTC) of a radiator is of primary importance to evaluate the heat flow within building interiors, and thereby to affect the thermal comfort and the overall energy consumption of a building. In this paper, a turbulent k-ε model is used to numerically analyze the heat transfer characteristics of a radiator used in a heating room in Lanzhou region of China. The results indicate that the averaged Nu number of radiator surface increases with increasing outer wall thermal conductivity, decreasing outdoor temperature and decreasing radiator surface area, respectively. And the outer wall thermal conductivity has weak influence on the local Nu number of radiator surface.

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