Laminar Forced Convection Heat Transfer in the Combined Entry Region of Non-Circular Ducts

2004 ◽  
Vol 126 (1) ◽  
pp. 54-61 ◽  
Author(s):  
Y. S. Muzychka ◽  
M. M. Yovanovich
Keyword(s):  
Circular Tube ◽  
Convection Heat Transfer ◽  
Numerical Data ◽  
Asymptotic Results ◽  
Cross Sectional ◽  
Fully Developed Flow ◽  
Nusselt Numbers ◽  
Proposed Model ◽  
Laminar Forced Convection ◽  
Plate Channel

A new model for predicting Nusselt numbers in the combined entrance region of non-circular ducts and channels is developed. This model predicts both local and average Nusselt numbers and is valid for both isothermal and isoflux boundary conditions. The model is developed using the asymptotic results for convection from a flat plate, thermally developing flows in non-circular ducts, and fully developed flow in non-circular ducts. Through the use of a novel characteristic length scale, the square root of cross-sectional area, the effect of duct shape on Nusselt number is minimized. Comparisons are made with several existing models for the circular tube and parallel plate channel and with numerical data for several non-circular ducts. Agreement between the proposed model and numerical data is within ±15percent or better for most duct shapes.

Transient Laminar Mixed Convective Heat Transfer in a Vertical Flat Duct

1991 ◽  
Vol 113 (2) ◽  
pp. 384-390 ◽  
Author(s):  
T. F. Lin ◽  
C. P. Yin ◽  
W. M. Yan
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Convection Heat Transfer ◽  
Unsteady Heat Transfer ◽  
Fully Developed Flow ◽  
Nusselt Numbers ◽  
Time Variations ◽  
Mixed Convection Heat Transfer ◽  
Asymmetric Heating ◽  
Insignificant Correlation

Unsteady laminar aiding and opposing mixed convection heat transfer in a vertical flat duct is numerically investigated for an initially fully developed flow. Results indicate that unsteady heat transfer characteristics in the flow are principally determined by wall-to-fluid heat capacity ratios. Effects of the buoyancy and degree of asymmetric heating or cooling are rather insignificant. Correlation equations for the time variations of local Nusselt numbers with wall-to-fluid heat capacity ratios are proposed.

Heat Transfer in Internally Finned Tubes

1976 ◽  
Vol 98 (2) ◽  
pp. 257-261 ◽  
Author(s):  
J. H. Masliyah ◽  
K. Nandakumar
Keyword(s):  
Heat Transfer ◽  
Circular Tube ◽  
Uniform Heat Flux ◽  
Heat Transfer Characteristics ◽  
Fully Developed Flow ◽  
Maximum Heat ◽  
Finned Tubes ◽  
Maximum Heat Transfer ◽  
Internal Fins ◽  
Laminar Forced Convection

Heat transfer characteristics for a laminar forced convection fully developed flow in an internally finned circular tube with axially uniform heat flux with peripherally uniform temperature are obtained using a finite element method. For a given fin geometry, the Nusselt number based on inside tube diameter was higher than that for a smooth tube. Also, it was found that for maximum heat transfer there exists an optimum fin number for a given fin configuration. The internal fins are of triangular shape.

scholarly journals Laminar forced convection at low Péclet number

1972 ◽  
Vol 6 (1) ◽  
pp. 83-94 ◽  
Author(s):  
A.S. Jones
Keyword(s):  
Forced Convection ◽  
Peclet Number ◽  
Asymptotic Form ◽  
Circular Tube ◽  
Physical Parameters ◽  
Heat Sources ◽  
Temperature Changes ◽  
Péclet Number ◽  
Nusselt Numbers ◽  
Laminar Forced Convection

This work is concerned with the forced convection of heat in a circular tube. The fluid flow is assumed to be laminar Poiseuille flow, and the physical parameters; viscosity, density, conductivity; are assumed to be independent of temperature changes. Viscous dissipation terms are also ignored, and there are no heat sources in the fluid. The problem is treated for the case of a step change in the wall temperature, and the eigenvalues have been obtained as an expansion in powers of the Péclet number for the smaller values, and in an asymptotic form for the larger values. The temperature distribution in the fluid in the neighbourhood of the temperature jump has been calculated for two values of the Péclet number, as have the Nusselt numbers.

Heat Transfer for Laminar Flow in Ducts With Arbitrary Time Variations in Wall Temperature

1960 ◽  
Vol 27 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Robert Siegel
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Wall Temperature ◽  
Fluid Velocity ◽  
Convection Heat Transfer ◽  
Arbitrary Time ◽  
Time Variations ◽  
Time Required ◽  
Laminar Forced Convection ◽  
Plate Channel

An analysis is made for laminar forced-convection heat transfer in a circular tube or a parallel plate channel whose walls may undergo arbitrary time variations in temperature. The time-varying process can begin from an already established steady-state situation with heat transfer taking place, or the fluid and walls can be initially at the same uniform temperature. The fluid velocity distribution is fully developed and unchanging with time. At any instant during the transient the wall temperature is spatially uniform, that is, all portions of the wall simultaneously undergo the same temperature-time variation. The greater part of the analysis is concerned with the response to a step change in wall temperature, and the time required to reach steady state is given for this type of transient. Then the results are generalized to apply for arbitrary variations with time.

Modeling Transient/Steady-State Convection From Isoflux Vertical Plates

2012 ◽  
Author(s):  
Mehran Ahmadi ◽  
Majid Bahrami
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Analytical Model ◽  
Vertical Plate ◽  
Convection Heat Transfer ◽  
Constant Property ◽  
Nusselt Numbers ◽  
Proposed Model ◽  
Transient And Steady State ◽  
State Average

A new compact analytical model is developed to predict transient heat convection from isoflux vertical plates into a constant property surrounding region. The proposed model is based on a blending of the two asymptotes corresponding to transient diffusion into a half-space and the steady-state convection heat transfer from an isoflux vertical plate. A compact relation for transient and steady-state average Nusselt numbers is proposed. The proposed model is successfully verified with existing experimental data of Goldstein and Eckert. The maximum difference between the proposed compact analytical model and the experimental data is less than 6%.

Numerical investigation of nanofluids heat transfer in a channel consisting of rectangular cavities by lattice Boltzmann method

2018 ◽  
Vol 29 (11) ◽  
pp. 1850108 ◽  
Author(s):  
Pouria Ranjbar ◽  
Rasul Mohebbi ◽  
Hanif Heidari
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Numerical Code ◽  
Nusselt Numbers ◽  
Maximum Value ◽  
Laminar Forced Convection ◽  
Boltzmann Method ◽  
Plate Channel

In this study, lattice Boltzmann method (LBM) simulation is performed to investigate laminar forced convection of nanofluids in a horizontal parallel-plate channel with three rectangular cavities. Two cavities are considered as located on the top wall of the channel and one on the bottom wall. The effects of the Reynolds number (100–400), the cavity aspect ratio (AR = 0.25, 0.5), the various distances of the cavities from each other ([Formula: see text]) at different solid volume fractions of nanofluids ([Formula: see text]) on the velocity and the temperature profiles of the nanofluids are studied. In addition, the flow patterns, i.e. the deflection and re-circulation zone inside the cavities, and the local and averaged Nusselt numbers on the channel walls are calculated. The results obtained are used to ascertain the validity of the written numerical code, which points to the excellent agreement across the results. The results show that, as the solid volume fraction of nanofluids is enhanced, the transfer of heat to working fluids increases significantly. Further, the results show that the maximum value of the averaged Nusselt number in the channel is obtained at [Formula: see text] for AR = 0.5 and [Formula: see text] for AR = 0.25. The interval [0.1224, 0.1304] is the best position for the second cavity. It is concluded that the results of this paper are very useful for designing optimized heat exchangers.

Laminar Non-Newtonian Fluid Flow in Noncircular Ducts and Microchannels

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
Y. S. Muzychka ◽  
J. Edge
Keyword(s):  
Fluid Flow ◽  
Newtonian Fluid ◽  
Circular Tube ◽  
Characteristic Length ◽  
Current Model ◽  
Rectangular Duct ◽  
Cross Sectional ◽  
Circular Annulus ◽  
Proposed Model ◽  
Power Law Fluids

Non-Newtonian fluid flow in noncircular ducts and microchannels is examined. A simple model is proposed for power law fluids based on the Rabinowitsch–Mooney formulation. By means of a new characteristic length scale, the square root of the cross-sectional area, it is shown that dimensionless wall shear stress can be made a weak function of duct shape. The proposed model is based on the solution for the rectangular duct and has an accuracy of ±10% or better. The current model eliminates the need for tabulated data or equations for several common shapes found in handbooks, namely, circular tube, elliptic tube, parallel channel, rectangular duct, isosceles triangular duct, circular annulus, and polygonal ducts.

scholarly journals Unsteady mixed convection in a porous media filled lid-driven cavity heated by a semi-circular heaters

2015 ◽  
Vol 19 (5) ◽  
pp. 1761-1768 ◽  
Author(s):  
M.M. Rahman ◽  
Hakan Öztop ◽  
R. Saidur ◽  
S. Mekhilef ◽  
Khaled Al-Salem
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Computational Study ◽  
Convection Heat Transfer ◽  
Darcy Number ◽  
Dimensionless Time ◽  
Cross Sectional ◽  
Driven Cavity ◽  
Nusselt Numbers ◽  
Unsteady Mixed Convection

A computational study has been performed on natural convection heat transfer and fluid flow in a porous media filled enclosure with semi-circular heaters by using finite element method. The ceiling of the cavity moves with a constant velocity and it is insulated. Temperature of vertical walls is lower than that of heaters. Results are presented via streamlines, isotherms, average Nusselt numbers and cross sectional velocity for different governing parameters such as Richardson number, Darcy number and dimensionless time. It is observed that both circulation of the flow and heat transfer is strongly affected with time increment and Darcy number inside the cavity.

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