Pressure of condensation

The tendency is greatest, however, where pressures are close to atmospheric and "superheat" relative to atmosphere is least. Pipestill atmospheric towers and cat unit fractionators tend to fall in this category. Some operators consider that the likelihood is great that calculated condensation (dew) will coalesce to droplets which will gravitate (rain) when the partial pressure of condensibles at the dew point exceeds 1/3 atmosphere. With this factor and environmental protection in mind, some plants have diverted such releases into closed systems. Generally, however, this has not been of sufficient concern, and such releases have been treated as though they were all vapor. 

Vapor pressure of condensable vapor, pounds per square inch absolute (or other absolute units)... 

L = temperature of condensate film, °F p = vapor pressure of condensate at L, psia or atm... 

R ardless of the chemistry, there are some physical constraints on aerosol-gas interactions. Particles must be close to or at equilibrium with respect to the surrounding vapor to exist in air for any substantial period. Thus, the partial pressure of condensed species on particles must be less than or equal to the saturation vapor pressure at atmospheric temperature for stability. As shown later in this chapter, the requirement of low vapor pressure is particularly important to the stability of organic aerosols. 

The sensitivity diagram of cycle efficiency versus condenser pressure demonstrates that decreasing the condenser pressure decreases the condenser temperature. This drops the average temperature at which heat is removed to the surroundings and thus raises the cycle efficiency. Operating pressures of condensers have decreased over the years to 5kPa (0.75 psia) today. 

As the butane liquid level in the condenser increased, the area of the exchanger exposed to the condensing vapors would decrease. Let s assume that the tower s reboiler duty was constant. The vapor flow rate to the condenser would then be constant. To condense the same flow rate of vapor, with a shrinking exchanger surface area, the pressure of condensation must increase. The tower pressure would also go up, as the condenser pressure rose. 

As the hot-vapor bypass valve opens, the condensate level in the shell side of the condenser increases to produce cooler, subcooled liquid. This reduces the surface area of the condenser exposed to the saturated vapor. To condense this vapor, with a smaller heat-transfer area, the pressure of condensation must increase. This, in turn, raises the tower pressure. This then is how opening the hot bypass pressure-control valve increases the tower pressure. 

We can consider an equivalently idealized situation for condensation if we assume that the pressure of condensable species in the gas is large compared to their saturation vapor pressure relative to the substrate on which condensation takes place. It follows from Equation (3) that... 

F Pressure associated with initial sorption Fq Vapor pressure of condensed sorbate at T r Intermolecular distance R Gas constant... 

The rates and relative importance of condensation and intramodal coagulation depend upon the number concentration and size of nanoparticles, the partial pressures of condensable gases, and the accommodation coefficients of the gases onto the particles... 

MP/PIA] Imperatori, P., Piacente, V., Vapour pressure of condensed HgSe... 

The vapor pressures of condensed substances can be calculated from the values of log Af on the basis of the equilibrium reaction for evaporation. 

C = capture coefficient k = Boltzmann constant, ergs/°K M = molecular weight, g/mole n/m = fraction of molecules with energy greater than j Pe = pressure in the chamber, mm Hg Po = pressure in front of standard leaks, mm Hg Pi = vapor pressure of condensate at mm Hg P = universal gas constant, ergs/mole-°K S =s pumping speed, liters/cm -sec Te= temperature of chamber, °K Tff= temperature of the gas, °K To = temperature of the standard leaks, °K... 

This plasticization phenomena can be observed in some glassy polymers exposed to high pressures of condensable gases, such as CO2. Moreover, a pressure dependence of permeability occurs for glassy polymers prior to plasticization, whereas rubbery materials tend to have essentially pressure-independent permeabilities. The decrease in permeability of component A with increasing partial pressure of either component A or B prior to the onset of plasticization (70) shown in Figure 21 (71) is characteristic of glassy polymers. 

Condensable = 0.6758 mole fraction Noncondensable (gas) = 0.3242 mole fraction Molecular weight of vapor and gas = 52 (from simulation) Molecular weight on noncondensable gas (nitrogen) = 28 Calculated molecular weight of condensable vapor = 63.5 Calculated partial pressure of condensable vapor = 440.1 kPaA Specific volume of condensable vapor (R T/MW/P) = 0.099 m /kg P = saturation bubble point pressure = 485.8 kPaA Po = relieving pressure = 651.3 kPaA Pgg = noncondensable gas partial pressure... 

---