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Fixed Beds
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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
Vacuum equipment, operational problems of, Vacuum operation, of reboilers, Valle, A, Valves: Vaned bends, single-phase flow and pressure drop in, Vapor blanketing, as mechanism of critical heat flux, Vapor injection, effect of on boiling heat transfer in tube bundles, Vapor-liquid disengagement, in kettle reboilers, Vapor-liquid separation, for evaporators, Vapor mixtures, condensation of, Vapor pressure, Vapor recompression, in evaporation, Vaporization, choice of evaporator type for, Vaporizer, double bundle, constructional features, Vapors, saturation properties of, Vapors, properties of superheated, Vasiliev, L, Vassilicos, J C, Velocity defect law: Velocity distribution: Velocity fluctuations, in turbulent pipe flow, Velocity ratio (slip ratio): Venting of condensers Vertical condensers: Vertical cylindrical fired heater, Vertical pipes: Vertical surfaces: Vertical thermosiphon reboilers: Vessels of non-circular cross section, design to ASME VIII code, Vessels of rectangular cross section, EN13445 guidance for, Vetere method, for enthalpy of vaporisation, Vibrated beds, heat transfer to, Vibration: Vinyl acetate: Vinyl benzene: Vinyl chloride: Virial equation: Virk equation for maximum drag reduction, Visco-elastic fluids, flow of, Viscometric functions (non-Newtonian flow), methods of determining, Viscosity: Viscosity number (Vi), Viscous dissipation, influence on heat transfer in non-Newtonian flows, Viscous heat generation, in scraped sauce heat exchangers, Viscous sublayer, in duct flow, Void fraction, Voidage, in fixed beds, definition,
Fixed Beds
Volumetric heat transfer coefficient, Volumetric mass transfer coefficient, von Karman friction factor equation for fully rough surface, von Karman velocity defect law, Vortex flow, in helical coils of rectangular cross section, Vortex flow model, for twisted tube heat exchangers, Vortex shedding:
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V Voidage, in fixed beds, definition,
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Fixed Beds

DOI 10.1615/hedhme.a.000147

2.2.5 Fixed beds

P. J. Heggs

The structural properties of fixed beds have been extensively reviewed by Haughey and Beveridge (1969). Two categories of fixed bed exist: regular and random packed. Regular packings provide complete control of bed voidage and surface area, but assembly is expensive. Regular packings are used, however, in thermal regenerators, checkerwork in high-temperature stoves in the glass and steel industries, and metallic matrix arrangements in the Ljungstrom rotary regenerators used in the power generation industry. In all these situations the pressure drop across the fixed bed must be small.

Random packings are found in a wide range of industrial operations: adsorption, catalysis, combustion, filtration, separation, and solid-fluid contacting in general. They are formed by the haphazard positioning of particles to provide a bed and the average bed properties are largely dependent on the mode of assembly (Debbas and Rumpf, 1966). The geometrical shape of fixed beds is normally cylindrical with the flow of the fluid parallel to the axis of the cylinder, however radial flow through annular beds is also used, when low pressure drop restrictions are specified. Only an infinitely sized bed is wholly random, but this is closely approached when the ratios of the container diameter (D) or diameters (Di and D0) and container length L to the particle diameter (d) are greater than 10 (Ridgway and Tarbuck, 1967). Random beds are simple in design, assembly is cheap, and construction is rugged.

Fixed beds are normally characterized by the specific surface area of the bed SB and the mean fractional voidage of the bed, εm. The latter is defined as the free volume of the bed divided by the volume of the bed, that is,

\[\label{eq1} \varepsilon_{m}=\dfrac{bed\;volume - packing\;volume}{bed\;volume}\tag{1}\]

and the specific surface area of the bed is strictly dependent on the value of the mean bed voidage, εm. The specific surface area of the particles S is defined as the surface area of the particles divided by the volume of the particles. For a sphere,

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