NUCLEATE BOILING. THE REGION OF ISOLATED BUBBLES AND THE SIMILARITY WITH NATURAL CONVECTION

Journal Article · Tue Jan 01 00:00:00 EST 1963 · Intern. J. Heat Mass Transfer

DOI:https://doi.org/10.1016/0017-9310(63)90029-2· OSTI ID:4707105

Zuber, N

Experimental data indicate that nucleate boiling consists of two regions, (a) the region of isolated bubbies and (b) the region of interference. The vapor removal pattern, the flow pattern, and the mechanisms of heat transfer in the two regions are discussed and analyzed. A criterion for the change from one region to another is presented. In the regime of isolated bubbles, bubbles do not interfere with each other and at any particular point vapor is produced intermittently. Jakob's description of the naturai flow circulation in nucleate pool boiling from a horizontal surface is similar to Malkus' and Townsend's description of the flow regime in turbulent natural convection from a horizontal surface. In both cases the heat transfer is caused by the up-draught'' induced circulation. lt is shown that the same equations which predict the heat-transfer coefficient and the average turbulent velocity fluctuation in natural turbulent convection from a horizontal surface can be used in the regime of isolated bubbles if the vapor void coefficient, i.e., the vapor hold-up is taken into accourt in evaluating the mean density of the fluid. Equations relating the vapor void coefficient to the heat-transfer coefficient or to the bubble population density and liquid superheat tempernture are presented. It is shown that an upper limit exists for the heat-transfer mechanism induced by the updraught'' circulation. Equations predicting the limiting value of the heat- transfer coefficient and of the heat flux density in the regime of isolated bubbles are presented aiso. All these results, predicted by the analysis, are shown to be in qualitative and quantitative agreement with experimental data presently available. In the region of interference, bubbles interfere with each other to form continuous vapor coiumns and patches. Vapor is continuously produced by vaporization of a pulsating micro-layer (proposed and described by Moore and Mesler) at the base of a vapor column or of a vapor patch. In this regime the dominant heat-transfer mechanism is, most probably, the latent heat transport process (formulated by Gaertner) and the latent heat transport associated with the large bursts of vapor caused by collapsing vapor patches. The results of the analysis indicate that a particular regime of nucleate pool boiling (a two-phase problem) can be analyzed as a turbulent natural convection problem (a single-phase problem). Applications of similar considerations to other aspects of the two-phase flow appear therefore promising. The important effect of the two-phase flow patterns on the mechanism of heat transfer and on the coefficient of heat transfer for a two-phase mixture is demonstrated again, emphasized and discussed. (auth)

• Research Organization: General Electric Co., Schenectady, N.Y.
• NSA Number: NSA-17-012429
• OSTI ID: 4707105
• Journal Information: Intern. J. Heat Mass Transfer, Vol. Vol: 6; Other Information: Orig. Receipt Date: 31-DEC-63
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ENGINEERING AND EQUIPMENT
ANALOG SYSTEMS
BOILING
BUBBLES
CONFIGURATION
CONVECTION
DENSITY
EFFICIENCY
EQUATIONS
EVAPORATION
FILMS
FLOW MODELS
FLUID FLOW
HEAT TRANSFER
HEATING
JACOB CORRELATION
LIQUIDS
MATHEMATICS
MIXING
NUCLEATE BOILING
PERFORMANCE
POOL BOILING
STANDARDS
SUPERHEATING
SURFACE TENSION
SURFACES
TEMPERATURE
THERMODYNAMICS
TURBULENCE
VAPORS
VELOCITY
VIBRATIONS
VOID FRACTION
ZONES