Free surface vaporization

Physical Properties. Sulfur dioxide [7446-09-5] SO2, is a colorless gas with a characteristic pungent, choking odor. Its physical and thermodynamic properties ate Hsted in Table 8. Heat capacity, vapor pressure, heat of vaporization, density, surface tension, viscosity, thermal conductivity, heat of formation, and free energy of formation as functions of temperature ate available (213), as is a detailed discussion of the sulfur dioxide—water system (215). 

Finally, it is to be expected that the evaporation coefficient of a very stable compound, such as alumina, which has a large heat of sublimation resulting from the decomposition into the elements, will be low. Since the heat of evaporation must be drawn from the surface, in die case of a substance widr a low thermal conductivity such as an oxide, the resultant cooling of the surface may lead to a temperature gradient in and immediately below the surface. This will lower die evaporation rate compared to that which is calculated from the apparent, bulk, temperature of the evaporating sample as observed by optical pyromeuy, and thus lead to an apparently low free surface vaporization coefficient. This is probably die case in the evaporation of alumina in a vacuum. 

Therefore, one might ask what is meant by the terms hquid and gas. We all know what is the characteristic of a liquid. It has a free surface. However, as soon as we compress the hquid, there is no free surface and the distinction between a gas and liquid is lost. The most logical terminology would be to reserve the terms hquid and vapor for the two coexisting phases and call all other states fluid. A more common terminology is to call the fluid a hquid if its density exceeds the critical density and a gas if its density is lower. Generally speaking, in this chapter we will use the term fluid to describe both the gas and liquid phases and not make any distinction. 

In designing multiple impeller configurations, an advantage may be gained by using a self-induction impeller located near the free surface of the dispersion, and thus recycling unreacted gas from the vapor space (P3). 

Free shear flows, 77 757-760 Free sintering, 73 300 Free spectral range (FSR), 74 671-672 Free surface vaporization, 24 724-725 Free-vibration instruments, 27 745 Free-volume coefficient of self-diffusion, 23 102... 

The concept of the Galvani potential should be distinguished from that of the contact potential difference, which is widely used in physics to describe contacts of two electronic conductors. In an electrode-electrolyte system the contact potential difference Ai/l which is frequently called the Volta potential, represents the difference of electrostatic potentials between two points located in the same (vapor) phase near free surfaces of contacting electrode and electrolyte solution (see Fig. 1). Let us note that the Volta potential can be measured directly, but the Galvani potential cannot, since it represents the potential difference between points in different phases. 

The apparent velocity, t 4, is related to the fraction of area covered by liquid, t. The liquid-free surface for vapor flow is, therefore, 1 —<), with. 4, being the total surface area of the impingement pad. And the apparent velocity becomes ... 

Crystals grow from their supersaturated vapor by the addition of vapor atoms at their free surfaces. In this process, the surface is subjected to an effective pressure due to the difference in free energy between the solid and vapor. The interface moves outward toward the vapor as it acts as a sink for the incoming flux of atoms. The mechanism by which atoms leave the vapor phase and eventually become permanently incorporated in the crystal is often relatively complex, and the kinetics of the process depends upon the type of surface involved (i.e., singular, vicinal,... 

Morphology depends to a major extent upon the shapes and positions of interfaces. Every real material has at least one interface—the exterior interface which separates it from its environment. If an interface separates a material from its vapor or a vacuum, it is typically called a free surface. Interfaces that exist in materials within a condensed phase (or between condensed phases) are termed internal interfaces. 

Stefan Condition at a Free Surface. Commonly, a component (i.e., B) with a high vapor pressure is diffused into the free surface of a (3 phase. Component A has a much lower vapor pressure and does not evaporate from the surface. The Stefan condition at the free surface is then... 

Here the state with [ZA] = [Z] is taken as a standard state of the adsorbed layer thus, in the case when only one gas is adsorbed, the layer is in the standard state at the coverage 1 /2. It can be easily seen that 1 /a is the equilibrium pressure at [ZA] = [Z], i.e., at the standard state of the adsorbed substance. This value may be called desorption pressure we shall denote it as b. It is analogous to vapor pressure or dissociation pressure in monovariant systems (24). Indeed, in the case of equilibrium of liquid with its vapor, the surface from which evaporation occurs is equal to the surface for condensation the same equality is realized at the adsorption equilibrium if the fraction of the occupied surface is equal to that of the free surface. This analogy explains the applicability of the Nernst approximate formula to desorption pressure (24) ... 

For the case of sublimable secondary EM, as Belyaev indicates, variation of the aggregate state occurs at a boiling temperature which corresponds to the external pressure. Indeed, the evaporation rate from the free surface of a superheated fluid is extraordinarily high, and superheating of the fluid is practically impossible. Dilution of the vapors by reaction products diffusing from the combustion zone even lowers the temperature of the liquid surface somewhat compared with the boiling temperature. 

If a glass is held for a long period at an elevated temperature it may start to crystallize or devitrijy. Devitrification of fused quartz (silica glass) to cristabolite is slow. Nucleation is usually at a free surface and is often stimulated by contamination from alkali ions such as sodium. The rate of growth of cristabolite is increased by oxygen and water vapor. With surface contamination, devitrification of fused quartz may occur at temperatures as low as 1000 °C. However, if the surface is clean it rarely occurs below 1150 °C. 

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