Transient, Laminar, Combined Free and Forced Convection in a Duct

1962 ◽  
Vol 84 (2) ◽  
pp. 141-148 ◽  
Author(s):  
S. L. Zeiberg ◽  
W. K. Mueller
Keyword(s):  
Steady State ◽  
Forced Convection ◽  
Wall Temperature ◽  
Axial Direction ◽  
Transient Heating ◽  
Fully Developed Flow ◽  
Fluid Properties ◽  
Free And Forced Convection ◽  
Approach To Steady State ◽  
Rayleigh Numbers

Transient, laminar, combined free and forced convection in a duct is analyzed under the assumptions of constant fluid properties, and fully developed flow. The transient heating is taken to be a result of wall temperature variations; the wall temperatures vary linearly with the axial co-ordinate of the duct (this is shown to be the only permissible axial dependence, other than no wall temperature variation in the axial direction). Numerical results show that for certain combinations of the Prandtl and Rayleigh numbers, an oscillatory approach to steady state exists. This phenomenon can induce a large reduction of the Nusselt number (compared to steady state) during the transient period.

Transient Natural Convection Experiments in Shallow Enclosures

1982 ◽  
Vol 104 (3) ◽  
pp. 533-538 ◽  
Author(s):  
R. Yewell ◽  
D. Poulikakos ◽  
A. Bejan
Keyword(s):  
Steady State ◽  
Natural Convection ◽  
Theoretical Prediction ◽  
Thermal Stratification ◽  
Wave Motion ◽  
The Core ◽  
Transient Natural Convection ◽  
Aspect Ratios ◽  
Approach To Steady State ◽  
Rayleigh Numbers

This paper reports experimental observations on transient natural convection in enclosures at high Rayleigh numbers (1.28×109, 1.49×109) and low aspect ratios (0.0625, 0.112). The phenomenon consists of the establishment of thin intrusion layers along the horizontal adiabatic surfaces; in time, the intrusion layers exchange heat with the isothermal core of the cavity, leading to the thermal stratification of the core. The approach to steady state is gradual, contrary to the theoretical prediction of Brunt-Vaisala wave motion (Patterson and Imberger [6]). The measured durations of the observed transients agree very well with theoretical estimates.

Thermal Modeling of a Claw-Pole Electrical Generator: Steady-State Computation and Identification of Free and Forced Convection Coefficients

2014 ◽  
Vol 50 (1) ◽  
pp. 279-287 ◽  
Author(s):  
Olivier Maloberti ◽  
Anthony Gimeno ◽  
Alejandro Ospina ◽  
Guy Friedrich ◽  
Khadija El Kadri Benkara ◽  
...  
Keyword(s):  
Steady State ◽  
Forced Convection ◽  
Thermal Modeling ◽  
Free And Forced Convection ◽  
Electrical Generator

Fully developed forced convection analysis of magneto-hydrodynamic nano fluid through annular sector duct

2021 ◽  
pp. 095440622110071
Author(s):  
Farhan Ahmed
Keyword(s):  
Friction Factor ◽  
Forced Convection ◽  
Axial Direction ◽  
Nano Particles ◽  
Convection Flow ◽  
Fully Developed Flow ◽  
Electrically Conducting ◽  
Nano Fluid ◽  
Annular Sector ◽  
Transfer Flow

During this study, we have investigated the effect of magnetic field on heat transfer flow of an electrically conducting magneto-hydrodynamic, ( MHD) nano fluid through annular sector duct. The problem is formulated under the assumption of fully developed flow by ignoring the deviation of velocity components in the axial direction only; and simulated with the help of semi implicit method for pressure linked equations revised, ( SIMPLER). The effect of Hartman number, M, on fully developed forced convection flow has been determined for different values of Copper nano particles contribution in base fluid, ϕ, apex angle, β and ratio of radii, Ȓ. With increase in the value of M, a prominent effect has been observed on friction factor, fRe. Furthermore, the influence of nano particles contribution on friction factor, fRe, has been dominated, when we increase the value of M.

On the Conjugate Problem of Laminar Combined Free and Forced Convection through Vertical Non-Circular Ducts

1972 ◽  
Vol 94 (1) ◽  
pp. 52-56 ◽  
Author(s):  
M. Iqbal ◽  
B. D. Aggarwala ◽  
A. K. Khatry
Keyword(s):  
Heat Conduction ◽  
Laminar Flow ◽  
Forced Convection ◽  
Small Variation ◽  
Conjugate Problem ◽  
Momentum Equation ◽  
Variational Technique ◽  
Fluid Properties ◽  
Free And Forced Convection ◽  
Axial Heat

The present analysis deals with the conjugate problem of combined free and forced convection through vertical non-circular ducts. The equations coupling heat conduction in the walls with the convection inside the fluid are solved to establish the influence of peripheral wall conduction, using variational technique. Fully developed laminar flow with uniform axial heat input and constant fluid properties, except for the small variation of density in the buoyancy term of the momentum equation, is assumed. The problem has been solved in a generalized way and the results have been presented for rectangular ducts. It is found that large values of the free convection effects and/or of the conduction parameter tend to minimize the asymmetries in circumferential wall temperature.

Viscous Dissipation Effects on Combined Free and Forced Convection Through Vertical Circular Tubes

1970 ◽  
Vol 37 (4) ◽  
pp. 931-935 ◽  
Author(s):  
M. Iqbal ◽  
B. D. Aggarwala ◽  
M. S. Rokerya
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Viscous Dissipation ◽  
Transfer Rate ◽  
Circular Duct ◽  
Circular Tubes ◽  
Nusselt Numbers ◽  
Fluid Properties ◽  
Flow Phenomena ◽  
Free And Forced Convection

The effect of viscous dissipation on the flow phenomena and heat transfer rate in a vertical circular duct is analyzed for combined free and forced convection. All fluid properties are considered constant, except variation of density in the buoyancy term. It is noted that effect of viscous dissipation is to reduce the temperature differences in the system which in turn counteract the buoyancy effects. Therefore the viscous dissipation reduces the flow velocity near the wall and increases it near the tube center. Viscous dissipation effects reduce the Nusselt numbers. The reduction in Nusselt numbers is about six percent at the high values of the buoyancy rate (Rayleigh number = 1000) and the dissipation effect Eckert number/Reynolds number = 0.0005 was used in the present study.

Analysis of Transient Laminar Forced Convection of Nanofluids in Circular Channels

2012 ◽  
Author(s):  
İsmail Ozan Sert ◽  
Nilay Sezer-Uzol ◽  
Sadik Kakac
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Numerical Analysis ◽  
Forced Convection ◽  
Wall Temperature ◽  
Particle Diameter ◽  
Wall Heat Flux ◽  
Transient And Steady State

In this study, forced convection heat transfer characteristics of nanofluids are investigated by numerical analysis of incompressible transient laminar flow in a circular duct under step change in wall temperature and wall heat flux. The thermal responses of the system are obtained by solving energy equation under both transient and steady-state conditions for hydrodynamically fully developed flow. In the analyses, temperature dependent thermo-physical properties are also considered. In the numerical analysis, Al2O3/water nanofluid is assumed as a homogenous single-phase fluid. For the effective thermal conductivity of nanofluids, Hamilton-Crosser model is used together with a model for Brownian motion in the analysis which takes the effects of temperature and the particle diameter into account. Temperature distributions across the tube for a step jump of wall temperature and also wall heat flux are obtained for various times during the transient calculations at a given location for a constant value of Peclet number and a particle diameter. Variations of thermal conductivity in turn, heat transfer enhancement is obtained at various times as a function of nanoparticle volume fractions, at a given nanoparticle diameter and Peclet number. The results are given under transient and steady-state conditions; steady-state conditions are obtained at larger times and enhancements are found by comparison to the base fluid heat transfer coefficient under the same conditions.

Combined Free and Forced Convection Through Vertical Rectangular Channels With Unequal Heating From Sides

1971 ◽  
Vol 38 (4) ◽  
pp. 829-833 ◽  
Author(s):  
M. Iqbal ◽  
B. D. Aggarwala
Keyword(s):  
Forced Convection ◽  
Unit Length ◽  
Heat Fluxes ◽  
The Body ◽  
Short Side ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
Rectangular Channels ◽  
Fluid Properties ◽  
Free And Forced Convection

Fully developed laminar combined free and forced convection through vertical rectangular channels is studied. Uniform heat input per unit length is considered. All fluid properties are considered invariant with temperature except for the variation of density in the body-force term of the equation of motion. Broad sides of the duct are assumed at uniform temperature. The short sides have been treated for adiabatic condition; or under nonzero finite and even unequal heat fluxes. An exact solution of the problem has been presented. Nusselt numbers have been evaluated and their variation with respect to aspect ratios, buoyancy parameter, and short side heat fluxes have been studied.

Combined Free and Forced Convection of Water Between Horizontal Concentric Cylinders

1983 ◽  
Vol 105 (3) ◽  
pp. 498-504 ◽  
Author(s):  
T. Hung Nguyen ◽  
P. Vasseur ◽  
L. Robillard ◽  
B. Chandra Shekar
Keyword(s):  
Finite Difference Methods ◽  
Axial Flow ◽  
Axial Direction ◽  
Boussinesq Approximation ◽  
Characteristic Parameters ◽  
Governing System ◽  
Concentric Cylinders ◽  
Free And Forced Convection ◽  
Laminar Convection ◽  
Rayleigh Numbers

This paper presents a theoretical study of combined free and forced laminar convection of a mass of water confined between two horizontal concentric cylinders with constant surface temperatures and subject to an externally-imposed constant pressure gradient along the axial direction. The governing system of differential equations is solved, within the Boussinesq approximation, by perturbation and finite difference methods, and the solutions are obtained in terms of the various characteristic parameters of the problem. Essentially, it is found that the flow pattern and the wall shear stress in the axial direction are significantly affected by the Prandtl and the Rayleigh numbers. Thus, the axial flow shows a tendency to develop in two or even three jets, depending on the Rayleigh number. The occurrence of the inversion of density, for water at 4°C, was found to modify completely the convective, or secondary flow, but to have little effect on the main, or axial, flow.

On Unsteady Heat Transfer of Combined Free and Forced Convection in Circular Tubes

1963 ◽  
Vol 30 (2) ◽  
pp. 257-262 ◽  
Author(s):  
L. N. Tao
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Wall Temperature ◽  
Time Variation ◽  
Circular Tube ◽  
Unsteady Heat Transfer ◽  
Transient Problem ◽  
Axial Temperature ◽  
Free And Forced Convection ◽  
Transfer Problems

The unsteady heat-transfer problems of combined free and forced convection of a fully developed laminar flow of a heat-generating fluid in a circular tube with constant axial temperature gradient at the wall are investigated. The general solution with arbitrary time-dependent pressure gradient, heat generation, and wall temperature is established by the application of the “generalized Duhamel’s theorem.” Two specific cases are then studied. The results indicate that this type of transient problem has a time-variation of an oscillatory type with decaying amplitude. This time-variation is different from that of forced convection or of combined free and forced convection with constant axial wall temperature.

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