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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,
Boiling Outside Tubes and Tube Bundles
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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,
Boiling Outside Tubes and 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, 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:
W X Y Z
V Vapor injection, effect of on boiling heat transfer in tube bundles,
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Boiling Outside Tubes and Tube Bundles

DOI 10.1615/hedhme.a.000195

2.7 BOILING AND EVAPORATION
2.7.5 Boiling outside tubes and tube bundles

J. G. Collier and G. F. Hewitt

A. Boiling outside single tubes in cross flow

(a) Flow patterns

This section deals with the case where the flow past the tube or cylinder is by forced rather than by natural convection. This latter situation is dealt with in Section 192. Photographs presented by Vliet and Leppert (1962a) show very clearly the flow patterns that occur when nearly saturated water flows upward across a uniformly heated cylindrical tube. At moderate heat fluxes, typically around 20% of the critical heat flux, a vapor cavity forms in the cylinder’s wake. Initially this cavity is not continuous along the length of the cylinder, but as the heat flux is increased, the increase in the length of the cavity in the direction of flow results in the formation of a very uniform vapor sheet. An increase of velocity from 0.4 to 1.5 m/s or of tube diameter from 0.254 mm to 4.8 mm also results in a large stable vapor cavity behind the cylinder. Under these circumstances the only liquid reaching the top half of the cylinder is that which is supplied between the vapor bubbles and the heater surface as the bubbles enter the cavity wake near the horizontal diameter. For low heat fluxes, more liquid is supplied than evaporated and the excess is removed by entrainment in the cavity. The critical heat flux is reached when the liquid supplied in this manner becomes insufficient to cool the upper half of the cylinder.

In a parallel study, Vliet and Leppert (1962b) extended their work to include the effect of subcooled water flowing across the heated rod. For low subcoolings (< 16 °C), the flow pattern observed was similar to that for water at the saturation temperature. For greater subcoolings there is insufficient vapor to form a cavity in the wake of the cylinder because of the rapid condensation.

(b) Boiling heat transfer at heat fluxes lower than the critical heat flux

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