Bubble superheated liquid

In this section, the phenomenon of BLEVE is discussed according to theories proposed by Reid (1976), Board (1975), and Venart (1990). Reid (1979, 1980) based a theory about the BLEVE mechanism on the phenomenon of superheated liquids. When heat is transferred to a liquid, the temperature of the liquid rises. When the boiling point is reached, the liquid starts to form vapor bubbles at active sites. These active sites occur at interfaces with solids, including vessel walls. 

Thermodynamic and mechanical equilibrium on a curved vapor-liquid interface requires a certain degree of superheat in order to maintain a given curvature. Characteristics of homogeneous and heterogeneous nucleation can be estimated in the frame of classical theory of kinetics of nucleation (Volmer and Weber 1926 Earkas 1927 Becker and Doring 1935 Zel dovich 1943). The vapor temperature in the bubble Ts.b can be computed from equations (Bankoff and Flaute 1957 Cole 1974 Blander and Katz 1975 Li and Cheng 2004) for homogeneous nucleation in superheated liquids... 

These studies consider the dynamics of a single bubble that grows in infinity space, which is filled by superheated liquid. Under these conditions the bubble expansion depends on inertia forces or on intensity of heat transfer. In the case when inertia forces are dominant the bubble radius grows linearly in time (Carey 1992) ... 

Figure 2.8 Bubble growth in one-component superheated liquid. (From Scriven, 1959. Copyright 1959 by Elsevier Science Ltd, Kidlington, UK. Reprinted with permission.)...

Figure 2.9 Representation of pressure-temperature relationship that exists during the growth period of a spherical bubble in a superheated liquid of infinite extent. (From Dwyer, 1976. Copyright 1976 by American Nuclear Society, LaGrange Park, IL. Reprinted with permission.)...

The thickness, s, and average velocity, V, of the bubble layer are approximately constant along the flow direction before DNB. The layer thickness includes the thin layer of superheated liquid in contact with the wall and is considered a homogenized inside layer. 

Dergarabedian, P, 1960, Observations on Bubble Growth in Various Superheated Liquids, J. Fluid Mech. 9 39-48. (6)... 

Our "superheated liquid-film concept" stands on the thermodynamic basis of (1) equilibrium shifts due to reactive separation under boiling and refluxing conditions and (2) irreversible processes of heat flows through the catalyst layer as well as bubble formation from the catalyst surface. 

As far as the Prigogine-type coupling between heat- and mass flow is operative from the catalytic active sites to the vigorously generating bubbles, the adsorbed products will be readily taken out and a large amount of vacant sites will be generated stationarily. Therefore, the restriction of equilibrium conversion (AG < 0) even becomes removable as a consequence of AG < AG by adopting the superheated liquid-film catalysis. 

Let us consider a superheated liquid which has attained the limit of superheat and a vapor embryo forms in equilibrium with the liquid. The bubble radius is ro, the pressure in the bulk liquid is Pq, and the temperature is Tq. Assume the liquid is pure. 

The vapor embryo, or bubble, is in unstable equilibrium and will either collapse or grow. We are only interested in those that follow the latter path. The chemical criteria of equilibrium between the bubble and liquid state that the temperature and chemical potential of the material in the bubble are equal to those in the superheated liquid, i.e.. 

In Fig. 12, we show the computed values of bubble radius for superheated liquid propane at two pressure levels 1 and 5 atm. Consider the inertial rate first. At 1 atm, liquid superheated propane attains the limit of superheat at about 328 K, where the vapor pressure is —18.9 atm. With Eq. (12), Tinertiai 52f m, where t is in seconds. At 5 atm, the driving force [Eyp(To) - Eq] is less than that at 1 atm, but the difference is slight. Thus, the 1 and 5 atm radii are shown as a single line in Fig. 12. 

The basic reason why superheated liquids can exist is that the nucleation step requires that a vapor embryo bubble of a minimum size must be achieved. Vapor embryos less than the critical size are unstable and tend... 

Eberhart, J. G., Kremsner, W., and Blander, M. (1975). Metastability of superheated liquids AD753S61, bubble nucleation in hydrocarbons and their mixtures. J. Colloid Interface Sci. 50(2), 369. 

Prosperetti, A., and Plesset, M. S. (1978). Vapour-bubble growth in a superheated liquid. J. Fluid Mech. 85, 349. 

Clausius-Clapeyron equation, and to obtain a theoretical expression for a vapor bubble growing in a superheated liquid. The equation (F5, F6) is a second-order differential equation which is so complex as to be of limited usefulness without serious modification. Fortunately, the equation becomes enormously simpler if the inertia of the liquid can be ignored during bubble growth. Forster and Zuber give a careful discussion of the physical requirements for neglecting inertia of the liquid. These are that either the bubble must be very small or the temperature of the bubble... 

The temperature of a bubble growing in a superheated liquid changes with the bubble size. If liquid inertia is negligible, the Forster-Zuber derivation gives the expression... 

The rate of appearance of nuclei in a superheated liquid determines the rate of macroscopic bubble formation and therefore must be of importance for nucleate boiling. This rate is found from a knowledge of the free-energy change necessary to form a nucleus. This is found by differentiation of Eq. (44), d AF)/dR = 0, which leads to R — R0, and... 

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