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G-type shells in shell-and-tube heat exchangers: Gaddis, E S, Galerkin method, for heat conduction finite-element calculations, Galileo number, Gas-liquid flows: Gas-liquid-solid interfaces, fouling at, Gas-solid interfaces, fouling at, Gas tungsten arc welding, Gaseous fuels, properties of, Gases: Gaskets: Gauss-Seidel method, for solution of implicit equations, Geometric optics models for radiative heat transfer from surfaces, geothermal brines, fouling of heat exchangers by, Germany, Federal Republic of, mechanical design of heat exchangers in: Gersten, K, Girth flanges, in shell-and-tube heat exchangers, Glass production, furnaces and kilns for, Glycerol (glycerine): Gn (heat generation number), Gnielinski, V
Forced Convection in Ducts Helically Coiled Tubes of Circular Cross Sections
Gnielinski correlation, for heat transfer in tube banks, Gomez-Thodas method, for vapour pressure, Goodness factor, as a basis for comparison of plate fin heat exchanger surfaces, Goody narrow band model for gas radiation properties, Gorenflo correlation, for nucleate boiling, Gowenlock, R, Graetz number: Granular products, moving, heat transfer to, Graphite, density of, Grashof number Gravitational acceleration, effect in pool boiling, Gravity conveyor: Gregorig effect in enhancement of condensation, Grid baffles: Grid selection, for finite difference method, Griffin, J M, Groeneveld correlation for postdryout heat transfer, Groeneveld and Delorme correlation for postdryout heat transfer, Gross plastic deformation Group contribution parameters tables, Guerrieri and Talty correlations for forced convective heat transfer in two-phase flow, Gungor and Winterton correlation, for forced convective boiling, Gylys, J,

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HEDH
A B C D E F G
G-type shells in shell-and-tube heat exchangers: Gaddis, E S, Galerkin method, for heat conduction finite-element calculations, Galileo number, Gas-liquid flows: Gas-liquid-solid interfaces, fouling at, Gas-solid interfaces, fouling at, Gas tungsten arc welding, Gaseous fuels, properties of, Gases: Gaskets: Gauss-Seidel method, for solution of implicit equations, Geometric optics models for radiative heat transfer from surfaces, geothermal brines, fouling of heat exchangers by, Germany, Federal Republic of, mechanical design of heat exchangers in: Gersten, K, Girth flanges, in shell-and-tube heat exchangers, Glass production, furnaces and kilns for, Glycerol (glycerine): Gn (heat generation number), Gnielinski, V
Forced Convection in Ducts Helically Coiled Tubes of Circular Cross Sections
Gnielinski correlation, for heat transfer in tube banks, Gomez-Thodas method, for vapour pressure, Goodness factor, as a basis for comparison of plate fin heat exchanger surfaces, Goody narrow band model for gas radiation properties, Gorenflo correlation, for nucleate boiling, Gowenlock, R, Graetz number: Granular products, moving, heat transfer to, Graphite, density of, Grashof number Gravitational acceleration, effect in pool boiling, Gravity conveyor: Gregorig effect in enhancement of condensation, Grid baffles: Grid selection, for finite difference method, Griffin, J M, Groeneveld correlation for postdryout heat transfer, Groeneveld and Delorme correlation for postdryout heat transfer, Gross plastic deformation Group contribution parameters tables, Guerrieri and Talty correlations for forced convective heat transfer in two-phase flow, Gungor and Winterton correlation, for forced convective boiling, Gylys, J,
H I J K L M N O P Q R S T U V W X Y Z
G Gnielinski, V
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Forced Convection in Ducts

DOI 10.1615/hedhme.a.000168

2.5.1 Forced convection in ducts

Volker Gnielinski

A. Introduction

When fluids flow at very low velocities, all the individual particles are flowing in parallel lines. This type of flow is called laminar flow. If a fluid stream enters a duct with a uniform velocity a velocity profile develops as the fluid moves down the tube, with the velocity at the duct wall being zero. At a sufficient distance downstream from the inlet, the velocity pattern becomes fixed. The shape of the velocity distribution curve is parabolic for flow in a tube or between parallel plates.

If the velocity of the fluid is gradually increased, there will be a point at which the fluid no longer flows in parallel lines, but by a series of eddies that result in a complete mixing of all parts of the flow except those immediately adjacent to the wall. This type of flow is called turbulent flow. The Reynolds number at which the flow changes from laminar to turbulent is the "critical Reynolds number" Re, where Re = u ρ d /η where u is the fluid average velocity, ρ its density, η its viscosity and d the channel equivalent diameter. The value of the critical Reynolds number in round tubes is between 2,100 and 2,300. In long rectangular ducts and annular spaces, the transition from laminar to turbulent flow also starts at a Reynolds number of 2,100 when the hydraulic diameter of the duct is used as the characteristic geometric dimension in calculating the Reynolds number.

At Reynolds numbers greater than 104, the flow is fully turbulent. Between the lower and upper limits lies the zone of transition from laminar to turbulent flow. These limits are affected by the type of entry, initial disturbances in the fluid, roughness, and so on.

If the duct wall is at a temperature different from that of the fluid, heat will be transferred and a temperature profile will develop in the fluid. At a sufficient distance from the beginning of heating or cooling, the temperature profile becomes fully developed and therefore the heat transfer coefficient is constant. The rate of heat transfer is always greater in turbulent flow.

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