Boiling peak flux

Because the bubble population increases with heat flux, a point of peak flux may be reached in nucleate boiling where the outgoing bubbles jam the path of the incoming liquid. This phenomenon can be analyzed by the criterion of a Hemholtz instability (Zuber, 1958) and thus serves to predict the incipience of the boiling crisis (to be discussed in Sec. 2.4.4). Another hydrodynamic aspect of the boiling crisis, the incipience of stable film boiling, may be analyzed from the criterion for a Taylor instability (Zuber, 1961). 

Elkassabgi, Y., and J. H. Licnhard, 1988, The Peak Pool Boiling Heat Fluxes from Horizontal Cylinders in Subcooled Liquids, Trans. ASME, J. Heat Transfer /70 479—496. (2)... 

Lienhard, J. H., and V. K. Dhir, 1973b, Extended Hydrodynamic Theory of the Peak and Minimum Pool-Boiling Heat Fluxes, NASA CR-2270, UCLA, Los Angeles, CA. (2)... 

Lienhard, J. H., and K. B. Keeling, Jr., 1970, An Induced Convection Effect upon the Peak Boiling Heat Flux, Trans ASME, J. Heat Transfer 92. (5)... 

Sun and Lienhard (34] have presented a relation for the peak boiling heat flux on horizontal cylinders which is in good agreement with experimental data. The relation is... 

J. H. Lienhard and V. K. Dhir, Hydrodynamic Prediction of Peak Pool Boiling Heat Fluxes from Finite Bodies. Journal of Heat Transfer 95 (1973), pp. 152 158. 

K. H. Sun and J. H. Lienhard, The Peak Pbol Boiling Heat Flux on Horizontal Cylinders, Int. J. Heat Mass Transfer (13) 1425-1439,1970. 

The experimental data plotted in Figs. 1 through 6 represent the highest values reported and show the broad superheat range typical of nucleate boiling, which is often due to different nucleation conditions. For comparison, the heat flow density (the peak flux of natural convection pool boiling on a horizontal plate as given by Kutateladze)... 

Rohsenow and Griffith propose a correlation for peak flux represented by equation (1). Their correlation is based upon considerable experimental data for the boiling of organic liquids and water ... 

Lienhard, J.H., Dhir, V.K., and D.M. Riherd. 1973. Peak pool boiling heat flux measurements on finite horizontal flat plates. /. Heat Trans. 95 477-482. 

Question by J. A. Clark, University of Michigan I believe the Forster—Zuber correlation is for the maximum heat flux points. How is this correlation justified for application to the nucleate-boiling data Did you correlate the peak flux data with any of the existing correlations ... 

Answer by Author It is our understanding that the Forster—Zuber correlation applies also to the entire nucleate-boiling curve. No correlation was attempted with the peak flux data since our peak flux data are slightly lower than a true peak, and we were not primarily concerned with locating this point. 

Figure 8 shows that increasing the heat flux at constant mass velocity causes the peak in wall temperature to increase and to move towards lower enthalpy or steam quality values. The increase in peak temperature is thus due not only to a higher heat flux, which demands a higher temperature difference across the vapor film at the wall, but to a lower flow velocity in the tube as the peaks move into regions of reduced quality. The latter effect of lower flow velocity is probably the dominant factor in giving fast burn-out its characteristically rapid and often destructive temperature rise, for, as stated earlier, fast burn-out is usually observed at conditions of subcooled or low quality boiling. 

Point C in Figure 15.14 is termed the critical heat flux or maximum boiling flux or peak boiling flux as bubbles coalesce on the surface creating a vapor blanket. Critical heat flux occurs because insufficient liquid is able to reach the heat transfer surface due to the rate at which vapor is leaving. Beyond Point D, the surface is dry and entirely blanketed by vapor and heat is transferred by conduction and radiation. 

A heat-flux DSC trace of the boiling of water is shown in Figure 3.12. The shape of the peak differs from that of fusion in that there is a broad leading edge. 

The peak heat flux for nucleate pool boiling is indicated as point a in Fig. 9-3 and by a dashed line in Fig. 9-8. Zuber [7] has developed an analytical expression for the peak heat flux in nucleate boiling by considering the stability requirements of the interface between the vapor film and liquid. This relation... 

Calculate the peak heat flux for boiling water at atmospheric pressure on a horizontal cylinder of 1.25-cm OD. Use the L.ienhard relation. 

Estimate the peak heat flux for boiling water at normal atmospheric pressure. 

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