Numerical Re-examination of Chilton–Colburn Analogy for Variable Thermophysical Fluid Properties

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Rajan Kumar ◽  
Shripad P. Mahulikar
Keyword(s):  
Heat Transfer ◽  
Energy Transport ◽  
Momentum Transport ◽  
Flow Friction ◽  
Steep Temperature Gradient ◽  
Fluid Properties ◽  
Conservation Of Momentum ◽  
Energy Equations ◽  
Fanning Friction Factor

The Chilton–Colburn analogy is very helpful for evaluating the heat transfer in internal forced flows. The Chilton–Colburn analogy between the Chilton–Colburn j-factor for heat transfer, jH (St·Pr2/3) and the Fanning friction factor (cf) is popularly considered to hold when St·Pr2/3 equals to cf/2, for constant fluid properties. The physical fluid properties, namely, viscosity and thermal conductivity, are generally a function of temperature for microconvective water flow due to a quite steep temperature gradient. Therefore, in present investigation, the validity of Chilton–Colburn analogy between St·Pr2/3 and cf is re-examined for laminar microconvective flow with variable thermophysical fluid properties. It is observed that the Chilton–Colburn analogy is valid only for that portion of the flow regime, where St·Pr2/3 decreases with decreasing cf. The validity of Chilton–Colburn analogy is also verified by the inverse dependence of Reynolds number (Re) with cf. Two modified nondimensional parameters “ΠSμ and ΠSk” are emerged from the nondimensional form of 2D, steady-state, incompressible, pure continuum-based, laminar conservation of momentum and energy equations, respectively. These modified nondimensional parameters show the significance of variable fluid properties in momentum transport and energy transport. Additionally, the role of ΠSμ and ΠSk in flow friction is also investigated. The higher values of ΠSμ and ΠSk indicate the stronger influence on microconvection due to large variations in fluid properties.

Venus: Energy Transport and Winds

2013 ◽  
Author(s):  
Andrew P. Ingersoll
Keyword(s):  
Energy Transport ◽  
Equilibrium Temperature ◽  
Blackbody Radiation ◽  
Hydrostatic Equilibrium ◽  
Momentum Transport ◽  
Lapse Rate ◽  
Temperature Structure ◽  
Hadley Cells ◽  
Equilibrium Emission

This chapter examines the modern-day climate of Venus, focusing on the role of winds in energy transfer. It first explains how radiation and convection influence the temperature structure of Venus's atmosphere before discussing other basic physical processes such as Hadley cells and the accompanying winds. It also considers gases in hydrostatic equilibrium, adiabatic lapse rate and stability, the flux and intensity of electromagnetic radiation, blackbody radiation and the Planck function, blackbodies in the solar system, radiative transfer, optically thick atmosphere, radiative-convective equilibrium, emission of radiation to space, equilibrium temperature, energy transport by fluid motions and eddies, eddy momentum transport, and the phenomenon of superrotation.

Interaction of Heat Transfer by Conduction, Convection, and Radiation in a Radiating Fluid

1963 ◽  
Vol 85 (4) ◽  
pp. 318-328 ◽  
Author(s):  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Energy Transport ◽  
Relative Role ◽  
Heat Transfer Characteristics ◽  
Temperature Variations ◽  
System Parameters ◽  
Heating And Cooling ◽  
Finite Distance ◽  
Parallel Surfaces

Consideration is given to the interaction of conduction, convection, and radiation in a fully developed laminar flow. The flat duct consists of two diffuse, nonblack, isothermal parallel surfaces a finite distance apart; the fluid between them emits and absorbs thermal radiation. The problem is formulated in terms of a nonlinear integro-differential equation, and the solution is obtained by a method employed by Barbier. Numerical examples show the influence of the system parameters such as the optical thicknesses, the ratio which determines the relative role of energy transport by conduction to that by radiation, the emissivity of the duct walls as well as the differences between heating and cooling on the temperature variations across the duct and on the heat-transfer characteristics. Two methods for obtaining approximate temperature distributions for optically transparent and opaque radiating media are outlined and the results discussed.

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

scholarly journals Experimental analysis and ANN prediction on performances of finned oval-tube heat exchanger under different air inlet angles with limited experimental data

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 968-980
Author(s):  
Xueping Du ◽  
Zhijie Chen ◽  
Qi Meng ◽  
Yang Song
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Correlation Equation ◽  
Tube Heat Exchanger ◽  
Flow Friction ◽  
Air Inlet ◽  
Comparison Results ◽  
Wide Range ◽  
Oval Tube

Abstract A high accuracy of experimental correlations on the heat transfer and flow friction is always expected to calculate the unknown cases according to the limited experimental data from a heat exchanger experiment. However, certain errors will occur during the data processing by the traditional methods to obtain the experimental correlations for the heat transfer and friction. A dimensionless experimental correlation equation including angles is proposed to make the correlation have a wide range of applicability. Then, the artificial neural networks (ANNs) are used to predict the heat transfer and flow friction performances of a finned oval-tube heat exchanger under four different air inlet angles with limited experimental data. The comparison results of ANN prediction with experimental correlations show that the errors from the ANN prediction are smaller than those from the classical correlations. The data of the four air inlet angles fitted separately have higher precisions than those fitted together. It is demonstrated that the ANN approach is more useful than experimental correlations to predict the heat transfer and flow resistance characteristics for unknown cases of heat exchangers. The results can provide theoretical support for the application of the ANN used in the finned oval-tube heat exchanger performance prediction.

Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces

1998 ◽  
Vol 120 (3) ◽  
pp. 641-653 ◽  
Author(s):  
G. F. Naterer ◽  
W. Hendradjit ◽  
K. J. Ahn ◽  
J. E. S. Venart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Inclined Surfaces ◽  
Wide Range ◽  
Model Predictions ◽  
Microlayer Evaporation ◽  
Near Wall

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

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