Surface energy liquid-vapor

A case can be made for the usefulness of surface tension as a concept even in the case of a normal liquid-vapor interface. A discussion of this appears in papers by Brown [33] and Gurney [34]. The informal practice of using surface tension and surface free energy interchangeably will be followed in this text. 

The specialty class of polyols includes poly(butadiene) and polycarbonate polyols. The poly(butadiene) polyols most commonly used in urethane adhesives have functionalities from 1.8 to 2.3 and contain the three isomers (x, y and z) shown in Table 2. Newer variants of poly(butadiene) polyols include a 90% 1,2 product, as well as hydrogenated versions, which produce a saturated hydrocarbon chain [28]. Poly(butadiene) polyols have an all-hydrocarbon backbone, producing a relatively low surface energy material, outstanding moisture resistance, and low vapor transmission values. Aromatic polycarbonate polyols are solids at room temperature. Aliphatic polycarbonate polyols are viscous liquids and are used to obtain adhesion to polar substrates, yet these polyols have better hydrolysis properties than do most polyesters. 

A capillary system is said to be in a steady-state equilibrium position when the capillary forces are equal to the hydrostatic pressure force (Levich 1962). The heating of the capillary walls leads to a disturbance of the equilibrium and to a displacement of the meniscus, causing the liquid-vapor interface location to change as compared to an unheated wall. This process causes pressure differences due to capillarity and the hydrostatic pressures exiting the flow, which in turn causes the meniscus to return to the initial position. In order to realize the above-mentioned process in a continuous manner it is necessary to carry out continual heat transfer from the capillary walls to the liquid. In this case the position of the interface surface is invariable and the fluid flow is stationary. From the thermodynamical point of view the process in a heated capillary is similar to a process in a heat engine, which transforms heat into mechanical energy. 

Maa (M2) developed a procedure for calculating the liquid surface temperature as a function of the time each liquid element is in contact with the vapor. He assumed that the latent heat of vaporization is transferred from the interior of the liquid to the interface by pure conduction. Consequently, the sole source of energy for vaporization is the sensible heat made available by a change in the liquid temperature. If exposure time is short, only the liquid near the surface will undergo a temperature change. The heat transfer within the liquid is modeled by... 

Eleat transfer occurs not only within the solid surface, droplet and vapor phases, but also at the liquid-solid and solid-vapor interface. Thus, the energy-balance equations for all phases and interfaces are solved to determine the heat-transfer rate and evaporation rate. 

Typically a BLEVE occurs after a metal container has been overheated above 538 °C (1,000 °F). The metal may not be able to withstand the internal stress and therefore failure occurs. The contained liquid space of the vessel normally acts as a heat absorber, so the wetted portions of the container are usually not at risk, only the surfaces of internal vapor spaces. Most BLEVEs occur when containers are less than 1/2 to 1/3 full of liquids. The liquid vaporization expansion energy is such that container pieces have been thrown as far as 0.8 km (1/2 mile) from the rupture and fatalities from such incidents have occurred up to 244 meters (800 ft.) away. Fireballs may occur at the time of rupture, that are several meters in diameter, resulting in intense heat exposure to nearby personnel. Fatalities due to burns from such incidents have occurred to personnel as much as 76 meters (250 Ft.) away from the point of rupture. 

Specific surface energy or surface tension of a solid Specific free energy of an interface between UC and U vapor Specific energy or tension of a liquid-solid interface Surface tension of a solid in a foreign vapor Surface tension of a grain boundary... 

Weber and Newman do the averaging by using a capillary framework. They assume that the two transport modes (diffusive for a vapor-equilibrated membrane and hydraulic for a liquid-equilibrated one) are assumed to occur in parallel and are switched between in a continuous fashion using the fraction of channels that are expanded by the liquid water. Their model is macroscopic but takes into account microscopic effects such as the channel-size distribution and the surface energy of the pores. Furthermore, they showed excellent agreement with experimental data from various sources and different operating conditions for values of the net water flux per proton flux through the membrane. 

At the critical temperature, Tc, and critical pressure, Pc, a liquid and its vapor are identical, and the surface tension, y, and total surface energy, as in the case of the energy of vaporization, must be zero (Birdi, 1997). At temperatures below the boiling point, which is 2/3 Tc, the total surface energy and the energy of evaporation are nearly constant. The variation in surface tension, y, with temperature is given in Figure A.l for different liquids. 

This is defined as the surface free energy per unit area projected onto the low index facet plane. The use of the projected free energy allows a direct analogy with the thermodynamics of a liquid-vapor system. See, e.g., Williams et al. for a clear discussion. 

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