Vapor transfer

A 40-nietcr elevated vapor transfer line in a petroleum refinery suddenly ruptures. It is estimated that 375 g/s of a hazardous gas is being emitted. If the emission from the mpture is brought under control 2 minutes later, estimate the concentration 1000 meters downwind and 100 meters displaced from centerline eonditions 5 minutes later. The wind velocity is 4.0 m/s and the stability category is D. 

Chemical vapor deposition may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapor phase. It belongs to the class of vapor-transfer processes which is atomistic in nature, that is the deposition species are atoms or molecules or a combination ofthese. Beside CVD, they include various physical-vapor-deposition processes (PVD) such as evaporation, sputtering, molecular-beam epitaxy, and ion plating. 

Kayserilioglu, B. S., Bakir, U., Yilmaz, L. Akkas, N. (2003). Use of xylan, an agricultural by-product, in wheat gluten based biodegradable films mechanical, solubility and water vapor transfer rate properties. Bioresource Technology, Vol. 87, 3, (May 2003), pp. (239-246), ISSN 0960-8524... 

K Ito, S-I Kaga, Y Takeya. Studies on hard gelatin capsules I. Water vapor transfer between capsules and powders. Chem Pharm Bull 17 1134—1137, 1969. 

Figure 29 Reciprocal of resistance (conductance) for water vapor transfer through semistopper closures dependence on pressure. (From Ref. 5.)... 

The approaches used for preparation of inorganic nanomaterials can be divided into two broad categories solution-phase colloidal synthesis and gas-phase synthesis. Metal and semiconductor nanoparticles are usually synthesized via solution-phase colloidal techniques,4,913 whereas high-temperature gas-phase processes like chemical vapor deposition (CVD), pulsed laser deposition (PLD), and vapor transfer are widely used for synthesis of high-quality semiconductor nanowires and carbon nanotubes.6,7 Such division reflects only the current research bias, as promising routes to metallic nanoparticles are also available based on vapor condensation14 and colloidal syntheses of high-quality semiconductor nanowires.15... 

Values for the average vapor-transfer coefficient from the gas phase to the airway epithelium can also be estimated from heat-transfer data in straight, curved, or bifurcating cylindrical tubes by using the analogy between heat transfer and mass transfer. Such an approach has been used by Yeh to predict the diffusional deposition of small particles in the conducting airways. 

The rate of flow of electrons from such a charged particle depends on the availability of an accessible site for this transfer. Although it is known that lattice defects provide such sites and that conduction band electrons can trickle down through solid dislocation levels reduction sites for electron accumulation are usually provided by metallization of the semiconductor particle. This can be achieved through photo-platinization or by a number of vapor transfer techniques and the principles relevant to hydrogen evolution on such platinized surfaces have been delineated by Heller The existence of such sites will thus control whether single or multiple electron transfer events can actually take place under steady state illumination. 

Dissolved oxygen and other gases can be removed from the solvent by the freeze-pump-thaw (FPT) method, or by the expansion of gases above the solvent into an evacuated container on the vacuum line. It is customary to freeze-pump-thaw the solvents before vapor transfer from the storage container to the vacuum electrochemical cell. Such FPT cycles should be done as soon as the solvent is brought into contact with the drying agent. The FPT method involves three basic steps (i.e., one cycle), which are often repeated ... 

Figure A2.1.1 A representation of a vapor-pressure-evaluating system. Region A includes the sample and its environment. Region B is a vapor transfer path to the sensor region, C, which includes the sensor and its environment. TA and Tc are the temperatures in regions A and C, respectively.

The sensitivity of the sample or the sensor to vapor transfer must also be considered. Here, the quantity of material represented by the sample or by the sensor is important. Vapor pressure is established by the presence of a particular number of molecules in a defined volume of space. The transfer of water molecules into the vapor phase may cause a measurable change in the gravimetric water contents of the sample and sensor. It is necessary that the sample water content (or the initial sample weight) be known. It may also be necessary to... 

Theoretically this is possible, and — 150-atm. tension has been demonstrated experimentally on water in Berthelot (3) tubes. However, negative pressures in Town-end s experiments with dilute solution were less than 1 atm. and it is felt that more basic research on liquid tensions is necessary before schemes A and B of Table I can be considered for solutions as concentrated as sea water. Townend measured only equilibrium and had no need for rapid vapor transfer. 

A subtle aspect of stability analysis of freeze-dried products in vials with rubber stoppers is the tendency for water vapor to be transferred from the stopper to the solid during storage. Representative data for residual moisture as a function of time at different temperatures are shown in Figure 11. As expected, the residual moisture level increases more rapidly at higher temperature, but the plateau level is independent of temperature as equilibrium is established between the freeze-dried solid and the stopper. The extent to which this is observed depends on several factors. First, the nature of the rubber stopper formulation affects the diffusivity of water in the rubber. Second, the processing of the stopper can affect the level of residual moisture present. It is not uncommon for extended drying of the stopper to be necessary to minimize residual moisture. Finally, the mass of the freeze-dried solid determines the extent to which the percent residual moisture is affected by water vapor transfer from the stopper, where large cakes may be relatively unaffected by the small amount of water vapor that is... 

Figure 11 Changes in residual moisture during storage of freeze-dried solids due to water vapor transfer from the stopper at different storage temperatures 5°C (diamonds), 25°C (squares), and 40°C (triangles).

Regardless of the chemical vapor transfer mode, CVG uses a gas-liquid separator to separate the chemical vapor from the liquid reagents prior to its introduction into the atomizer. There are several designs of gas-liquid separators, but they can be classified into three basic types hydrostatic separators, forced outlet separators, and membrane separators. A detailed description of gas-liquid separators will be found in specialized monographs.32... 

Membrane distillation involves partially evaporating a solution through a microporous membrane that is vapor-permeable but liquid-repellent. The membrane has no permselectivity, but provides a stable liquid-gas-liquid interface for vapor transfer. As shown in Fig. 28, the membrane separates a heated feed solution from a cooler product solution. Since the vapor pressure of solvent in the feed solution is higher than that in the product solution, solvent... 

Heat and vapor transfer in a wetted-wall tower. Ind. Eng. Chem., 33 436-442. 

Active through systemic acropetal and basipetal movement and by vapor transfer... 

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