Boiling, pool subcooled

If the feed is subcooled, the mean temperature difference should still be based on the boiling point of the liquid, as the feed will rapidly mix with the boiling pool of liquid the quantity of heat required to bring the feed to its boiling point must be included in the total duty. 

Fig. 18. Example of the linear effect of bulk fluid subcooling on burn-out for copper and iron wires with pool boiling of water at atmospheric pressure [from Farber (FI)].

Liu Z, Winterton RHS (1991) A general correlation for saturated and subcooled flow boiling in tubes and annuli, based on a nucleate pool boiling equation. Int J Heat Mass Transfer 34 2759-2766... 

For subcooled pool boiling from vertical surface, Eq. (2-122) becomes... 

Ivey and Morris (1962) reported the ratio of subcooled critical flux to saturated critical flux of pool boiling in water, ethyl alcohol, ammonia, carbon tetrachloride, and isooctane for pressures from 4.5 to 500 psia (0.3 to 34 X 105 Pa) as... 

Elkassabgi and Lienhard (1988) provided an extensive subcooled pool boiling CHF data set of 631 observations on cylindical electric resistance heaters ranging from 0.80 to 1.54 mm (0.03 to 0.06 in.) in diameter with four liquids (isopropanol, acetone, methanol, and Freon-113) at atmospheric pressure and up to 140°C (252°F) subcooling. They normalized <7 ritsub data by Sun and Lienhard s (1970) saturated q"Tix SL prediction in terms of B,... 

It should be noted that without experimental data on the subcooled pool boiling crisis in liquid metals, the above equation cannot be verified. Another mechanism for estimating the subcooling contribution to the CHF was used for boiling with ordinary liquids (i.e., a conduction mechanism). The two mechanisms may operate simultaneously, along with the hydrodynamics and conduction-convection mechanisms (Dwyer, 1976). 

Bradficld, W. S., 1967, On the Effect of Subcooling on Wall Superheat in Pool Boiling, Trans. ASME, J. Heat Transfer 9 269-270. (4)... 

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)... 

Liu, Z., and R. H. S. Winterton, 1991, A General Correlation for Saturated and Subcooled Flow Boiling in Tubes and Annuli Based on a Nucleate Pool Boiling Equation, Int. J. Heat Mass Transfer 34(11) 2759 2766. (4)... 

Zuber, N., M. Tribus, and J. W. Westwater, 1961, The Hydrodynamics Crisis in Pool Boiling of Saturated and Subcooled Liquids, in International Developments in Heat Transfer, Part II, pp. 230-236, ASME, New York. (2)... 

When a surface is exposed to a liquid and is maintained at a temperature above the saturation temperature of the liquid, boiling may occur, and the heat flux will depend on the difference in temperature between the surface and the saturation temperature. When the heated surface is submerged below a free surface of liquid, the process is referred to as pool boiling. If the temperature of the liquid is below the saturation temperature, the process is called subcooled, or local, boiling. If the liquid is maintained at saturation temperature, the process is known as saturated, or bulk, boiling. 

Figure 5 Contribution of the various heat transfer mechanisms during subcooled pool nucleate boiling.

FIGURE 15.31 Stages in subcooled pool boiling as the surface heat flux is increased, (a) no bubble formation (natural convection heat transfer) (6) bubbles grow but do not detach (c) bubbles increase in number and some detach to condense in the bulk liquid (d) bubbles become so numerous that they coalesce to form a continuous vapor layer on the heated surface (from Hewitt et al. [13], with permission. Copyright CRC Press, Boca Raton, FL). 

FIGURE 15.37 Effect of contact angle on heat transfer coefficient in nucleate pool boiling with a constant heat flux and subcooling (from Jansen et al. [77], with permission from ASME). 

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