Effect of temperature difference between channel walls on the heat transfer characteristics of nanoscale-confined gas

The evaporation of isolated drops (2.1−3.0 mm diameter) of nonazeotropic n-pentane/n-hexane mixtures in the medium of water was observed under pressures of 0.11−0.46 MPa and temperature differences up to 27 K. The mole fractions of n-pentane, x, in the mixtures were set at 0.9, 0.5, 0.1, and 0, to be completed by the condition x = 1 set in a preceding work (Shimaoka and Mori, 1990). Experimental results are presented in terms of the instantaneous rise velocity of, and an expression of instantaneous heat transfer to, each drop evaporating and thereby transforming into a liquid/vapor two-phase bubble and finally into a vapor bubble. The dependencies of the heat transfer characteristics on the pressure, the temperature difference, and x are discussed.

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Modeling Study on Heat Transfer in Marangoni Dropwise Condensation for Ethanol-Water Mixture Vapors

Energies ◽

10.3390/en13246726 ◽

2020 ◽

Vol 13 (24) ◽

pp. 6726

Author(s):

Jinshi Wang ◽

Ziqiang Ma ◽

Yong Li ◽

Weiqi Liu ◽

Gen Li

Keyword(s):

Heat Transfer ◽

Surface Temperature ◽

Temperature Difference ◽

Diffusion Layer ◽

Water Mixture ◽

Dropwise Condensation ◽

Heat Transfer Characteristics ◽

Vapor Diffusion ◽

Transfer Characteristics ◽

Condensate Layer

In this paper, a model was developed to predict the heat transfer characteristics of Marangoni dropwise condensation. In accordance with the feature of Marangoni condensation, condensation was treated as dropwise condensation of mixture vapors. The condensation space was divided into two parts: the vapor diffusion layer and the condensate layer. For the condensate layer, the classical heat transfer calculation method of dropwise condensation was imitated to obtain the heat transfer characteristics. For the vapor diffusion layer, the heat transfer characteristics were achieved by solving the conservation equations. These heat transfer characteristics were coupled through the conjunct boundary, which was the vapor-liquid interface. The model was applied to the condensation of water-ethanol mixture vapors. A comparison with the existing experimental data showed that the developed model could basically reflect the influences of vapor-to-surface temperature difference, vapor concentration, vapor pressure, and vapor velocity on heat transfer characteristic of Marangoni condensation. Results showed that some differences existed between the calculation results and experimental results, but the prediction deviation of the model could be acceptable in the range of vapor-to-surface temperature difference where the condensation heat transfer coefficients reached peak values.

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The Effect of Temperature Dependent Electrical Conductivity on the MHD Natural Convection of Al2O3–Water Nanofluid in a Rectangular Enclosure

ASME 2014 12th International Conference on Nanochannels, Microchannels and Minichannels ◽

10.1115/icnmm2014-21758 ◽

2014 ◽

Author(s):

Ali Mohammad Asadian ◽

Omid Abouali ◽

Mahmoud Yaghoubi ◽

Goodarz Ahmadi

Keyword(s):

Magnetic Field ◽

Heat Transfer ◽

Electrical Conductivity ◽

Natural Convection ◽

Effect Of Temperature ◽

Fluid Viscosity ◽

Heat Transfer Characteristics ◽

Volume Fractions ◽

Transfer Characteristics ◽

Flow And Heat Transfer

The present paper is concerned with the study of flow and heat transfer characteristics in the steady state free convective flow of Al2O3-waternanofluids in a square enclosure in the presence of magnetic field. Attention is given to the temperature variation of the electrical conductivity and its effect on the electromagnetic force induced by the motion of the nanofluid. A new experimental correlation recently presented in the literature was used for this aim. In all the earlier studies in this area the electrical conductivity variation of nanofluid with temperature was neglected. The fluid viscosity and thermal conductivity are assumed to vary as a function of temperature and this variation is modeled using the available experimental correlations. The governing differential equations are solved numerically using finite element method. The features of fluid flow and heat transfer characteristics are analyzed for various strengths of the magnetic field and different nanoparticle volume fractions. The results show that when the inclusion of the variation of the electrical conductivity with temperature in the numerical model noticeably affects the natural convection heat transfer in the studied rectangular cavity. The variations of Nusselt number for natural convection of Al2O3-water nanofluid with nanoparticle volume fractions are presented at various Rayleigh and Hartmann numbers.

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Inaccuracy of Heat Transfer Characteristics of a Metal Duct Neglecting Heat Radiation Effect in Ambient Air

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.516-517.322 ◽

2012 ◽

Vol 516-517 ◽

pp. 322-327 ◽

Cited By ~ 1

Author(s):

King Leung Wong ◽

Wen Lih Chen ◽

Yung Chin Chiu

Keyword(s):

Heat Transfer ◽

Temperature Difference ◽

Radiation Effect ◽

Ambient Air ◽

Heat Radiation ◽

Heat Transfer Characteristics ◽

Circular Duct ◽

Transfer Characteristics ◽

Internal Fluid ◽

Fluid Convection

A heat radiation equation contains 4th exponential order of temperature which makes mathematics analysis complicated and time-consumption. Most heat transfer experts and scholars believe, based on their own experiences, that the heat radiation effect can be ignored in situations of small temperature difference between duct surfaces and surroundings. This paper studies in detail for complete heat transfer characteristics of a circular duct with heat radiation effect taken into account. It is found that, in some practical conditions, the heat radiation effect can not be ignored especially in cases of lower ambient convection heat coefficients and larger surface emissivities, as well as the smaller the duct size and/or the greater the duct conductivity and/or internal fluid convection coefficients, even though the temperature-difference between inner and outer fluid-temperatures of duct is low to 1 °C. It is found that the conventional LMTD method (ignoring heat radiation) cannot be applied to calculate the total heat transfer rate of a single-duct heat exchanger located in ambient air, such as condenser and evaporator.

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