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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
F-correction method: F-factor charts and equations for various heat exchanger configurations, F-factor method: F-type shells: Fabrication: Failure modes of heat exchangers, Falling films, direct contact heat transfer in, Falling film evaporator: Fanno flow, Fans in air-cooled heat exchangers: Fatigue as failure mode of a heat exchanger Fatigue life, of expansion bellows, Fawcett, R Fedor's method, for critical temperature, Fenghour, A Ferritic stainless steels, as material of construction, Fick's law for diffusion, Film boiling: Film model, condenser design by Film temperature, definition of for turbulent flow over flat plate, Films in heat exchangers, Filmwise condensation: Fincotherm, heat transfer medium, Finite-difference equations: Finite difference methods: Finite-element methods: Fins (see also Extended surfaces): Fire-tube boiler, Fired heaters, Fires, room, radiation interaction phenomena in, Firsova, E V, Fixed beds: Fixed tubesheet, shell-and-tube exchangers: Flanges, mechanical design of in heat exchangers, Flash evaporation Flat absorber of thermal radiation, Flat heads: Flat plate: Flat reflector of thermal radiation, Floating head designs for shell-and-tube heat exchangers: Flooded type evaporator, in refrigeration, Flooding phenomena: Flow distribution: Flow-induced vibration, Flow regimes: Flow stream analysis method for segmentally baffled shell and tube heat exchangers, Flue gases, fouling by, Fluid elastic instability as source of flow-induced vibration, Fluid flow, lost work in, Fluid mechanics, Eulerian formulation for, Fluid-to-particle heat transfer in fluidized beds, Fluidized bed dryer: Fluidized bed gravity conveyors, Fluidized beds: Fluids: Fluorine: Fluorobenzene: Fluoroethane (Refrigerant 161): Fluoromethane (Refrigerant 41): Fluted tubes: Flux method, for modeling radiation in furnaces, Flux relationships in heat exchangers, Fogging in condensation Food processing, fouling of heat exchangers in, Forced flow reboilers: Formaldehyde: Formamide: Formic acid: Forster and Zuber correlation for nucleate boiling, Fouling, Foam systems, heat transfer in, Four phase flows, examples, Fourier law for conduction Fourier number (Fo): Frames for plate heat exchangers, France, guide to national practice for mechanical design, Free convection: Free-fall velocity, of particles, Free-stream turbulence, effect on flow over cylinders, Freeze protection of air-cooled heat exchangers, Freezing, of condensate in condensers Fresnel relations in reflection of radiation, Fretting corrosion, Friction factor: Friction multipliers in gas-liquid flow: Friction velocity, definition, Friedel correlation for frictional pressure gradient in straight channels, Froude number: Fuels, properties of, Fuller, R K, Furan: Furfural: Furnaces: Fusion welding, of tubes into tubesheets in shell-and-tube heat exchangers,

Index

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A B C D E F
F-correction method: F-factor charts and equations for various heat exchanger configurations, F-factor method: F-type shells: Fabrication: Failure modes of heat exchangers, Falling films, direct contact heat transfer in, Falling film evaporator: Fanno flow, Fans in air-cooled heat exchangers: Fatigue as failure mode of a heat exchanger Fatigue life, of expansion bellows, Fawcett, R Fedor's method, for critical temperature, Fenghour, A Ferritic stainless steels, as material of construction, Fick's law for diffusion, Film boiling: Film model, condenser design by Film temperature, definition of for turbulent flow over flat plate, Films in heat exchangers, Filmwise condensation: Fincotherm, heat transfer medium, Finite-difference equations: Finite difference methods: Finite-element methods: Fins (see also Extended surfaces): Fire-tube boiler, Fired heaters, Fires, room, radiation interaction phenomena in, Firsova, E V, Fixed beds: Fixed tubesheet, shell-and-tube exchangers: Flanges, mechanical design of in heat exchangers, Flash evaporation Flat absorber of thermal radiation, Flat heads: Flat plate: Flat reflector of thermal radiation, Floating head designs for shell-and-tube heat exchangers: Flooded type evaporator, in refrigeration, Flooding phenomena: Flow distribution: Flow-induced vibration, Flow regimes: Flow stream analysis method for segmentally baffled shell and tube heat exchangers, Flue gases, fouling by, Fluid elastic instability as source of flow-induced vibration, Fluid flow, lost work in, Fluid mechanics, Eulerian formulation for, Fluid-to-particle heat transfer in fluidized beds, Fluidized bed dryer: Fluidized bed gravity conveyors, Fluidized beds: Fluids: Fluorine: Fluorobenzene: Fluoroethane (Refrigerant 161): Fluoromethane (Refrigerant 41): Fluted tubes: Flux method, for modeling radiation in furnaces, Flux relationships in heat exchangers, Fogging in condensation Food processing, fouling of heat exchangers in, Forced flow reboilers: Formaldehyde: Formamide: Formic acid: Forster and Zuber correlation for nucleate boiling, Fouling, Foam systems, heat transfer in, Four phase flows, examples, Fourier law for conduction Fourier number (Fo): Frames for plate heat exchangers, France, guide to national practice for mechanical design, Free convection: Free-fall velocity, of particles, Free-stream turbulence, effect on flow over cylinders, Freeze protection of air-cooled heat exchangers, Freezing, of condensate in condensers Fresnel relations in reflection of radiation, Fretting corrosion, Friction factor: Friction multipliers in gas-liquid flow: Friction velocity, definition, Friedel correlation for frictional pressure gradient in straight channels, Froude number: Fuels, properties of, Fuller, R K, Furan: Furfural: Furnaces: Fusion welding, of tubes into tubesheets in shell-and-tube heat exchangers,
G H I J K L M N O P Q R S T U V W X Y Z

Free Convection in Layers and Enclosures

DOI 10.1615/hedhme.a.000175

2.5 SINGLE-PHASE CONVECTIVE HEAT TRANSFER
2.5.8 Free convection in layers and enclosures

Natural convection occurs in enclosures as a result of gradients in density, which are in turn due to variations in temperature or concentration. The rate of heat transfer is usually characterized by a Nusselt number as a function of a Rayleigh number, the Prandtl number, the geometry, and the boundary and initial conditions. The Nusselt and Rayleigh numbers are ordinarily based on the external temperature difference and the dimension of the enclosure in the direction of heat transfer, with some exceptions as noted below. The other variables in these groups are defined as in Section 174.

Catton (1978) provides a recent, comprehensive, and interpretive review of natural convection in enclosures. Ostrach (1972 and 1975) discusses cylindrical and rectangular enclosures in somewhat greater detail. Koschmieder (1974) has reviewed Bénard-type convection and Buchberg et al. (1976) applications of natural convection in solar collectors. Churchill and Ozoe (n.d.) have utilized theoretical and experimental results for asymptotic conditions to develop correlating equations for heat transfer in rectangular and cylindrical enclosures for a wide range of conditions with special attention to the effect of the angles of inclination and rotation.

In this section a description of the fluid motion is provided and correlations are recommended for heat transfer for conditions of primary practical importance. Referral to the references cited herein and in the above reviews is suggested for derivations and further details.

Experimental results for natural convection in enclosures are generally less accurate than for forced convection owing to difficulty in repressing and evaluating the heat fluxes through and along the nonisothermal walls. As a consequence, discrepancies between various sets of data are not completely resolved. Also, the time scale of experiments, particularly with liquids, is sometimes insufficient to attain the true stationary state.

Theoretical results are limited in accuracy and scope owing to the inherent three dimensionality of the velocity and temperature fields in all enclosures with two or three finite dimensions. This three dimensionality affects the transitions from one mode of circulation to another. If one or the other aspect ratio is near unity, the three dimensionality affects the rates of circulation and heat transfer significantly. Even so, the many two- dimensional and the few three-dimensional solutions provide a useful basis for the interpretation, correlation, and extrapolation of the experimental values.

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