Subcooling mechanics

An adequate explanation of the linearity has not yet been found, although it would seem to have something simple yet basic to say about the burn-out mechanism. It will be seen in the following sections that it enables a very effective burn-out correlation to be derived. It is also considered that a plot of burn-out flux against inlet subcooling, as in Figs. 17 and 19, is the best... 

G3. Grace, T. M., The mechanism of burnout in initially subcooled forced convection systems, TID-19845 (1963). 

Figure 2.38 Effect of liquid subcooling on peak heat flux, for heaters of various sizes in isopropanol. (From Elkssabgi and Lienhard, 1988. Copyright 1988 by American Society of Mechanical Engineers, New York. Reprinted with permission.)... 

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). 

Judd (1989) interpreted experimental results of Ibrahim and Judd (1985), in which the bubble period first increased and then decreased as subcooling varied over the range 0 < (7 t - Tm) < 15°C (27°F), by means of a comprehensive model incorporating the contributions of nucleate boiling, natural convection, and microlayer evaporation components. The mechanism responsible for the nucleation of bubbles at exactly the frequency required at each level of subcooling is the subject of their continuing research. 

Figure 4.10 Thermocapillarity mechanism of subcooled boiling. (From Brown, 1967. Reprinted with permission of Massachusetts Institute of Technology, Cambridge, M A.)...

W-3 CHF correlation. The insight into CHF mechanism obtained from visual observations and from macroscopic analyses of the individual effect of p, G, and X revealed that the local p-G-X effects are coupled in affecting the flow pattern and thence the CHF. The system pressure determines the saturation temperature and its associated thermal properties. Coupled with local enthalpy, it provides the local subcooling for bubble condensation or the latent heat (Hfg) for bubble formation. The saturation properties (viscosity and surface tension) affect the bubble size, bubble buoyancy, and the local void fraction distribution in a flow pattern. The local enthalpy couples with mass flux at a certain pressure determines the void slip ratio and coolant mixing. They, in turn, affect the bubble-layer thickness in a low-enthalpy bubbly flow or the liquid droplet entrainment in a high-enthalpy annular flow. 

A CHF model for subcooled flow boiling with low quality, based on a critical bubbly layer mechanism, was presented by Weisman and Pei (1983), Ying and Weisman (1986), Lin and Weisman (1990), and Lin et al. [1989], These have been described in Section 5.3.2.2. 

Dean, R A., R. S. Dougall, and L. S. Tong, 1971, Effect of Vapor Injection on Critical Heat Flux in a Subcooled R-l 13 (Freon) Flow, Proc. Int. Symp. on Two-Phase Flow Systems, Haifa, Israel. (6) Deane, C. W., and W. M. Rohsenow, 1969, Mechanism and Behavior of Nucleate Boiling Heat Transfer to the Alkali Liquid Metals, USAEC Rep. DSR 76303-65, Massachusetts Institute of Technology, Cambridge, MA Also in 1970, Liquid Metal Heat Transfer and Fluid Dynamics J. C. Chen and A. A. Bishop, Eds., ASME Winter Annual Meeting, New York. (4)... 

Ivey, H. J., and D. J. Morris, 1962, On the Relevance of the Vapor Liquid Exchange Mechanism for Subcooled Boiling Heat Transfer at Higher Pressure, Rep. AEEW-R-137, UK Atomic Energy Authority, Winfrith, England. (2)... 

If a subcooled (below the boiling point) liquid at point A is expanded isothermally, it will boil at point B ordinarily. However, if the liquid is of good purity and its container is not contaminated, it is easy to proceed along the line toward C. Such a liquid is then under tension that is, an external, mechanical pulling force is being resisted by the liquid. Numerous investigators have demonstrated the existence of liquids in... 

Mechanics of subcooling. As the condensed steam flow out of the radiator is restricted, the surface area of the radiator, available to cool the hot water, increases. Hence, the water temperature leaving the radiator decreases. To summarize, the effect of restricting the condensate flow from a radiator or condenser is to... 

---