Vaporizing droplet streams

Nonequilibrium Distillation Effects in Vaporizing Droplet Streams... 

The vaporized glycerine stream passes through the entrainment separator [10] and condenses on the internal U-tube condenser [9]. Droplets of material entrained with the vapor stream impinge on the entrainment separator and flow back to the heated wall through centrifugal force of the rotating assembly. Distillate flows out the distillate outlet [11] and noncondensables flow out through the vacuum outlet [13]. 

In a concentric-tube nebulizer, the sample solution is drawn through the inner capillary by the vacuum created when the argon gas stream flows over the end (nozzle) at high linear velocity. As the solution is drawn out, the edges of the liquid forming a film over the end of the inner capillary are blown away as a spray of droplets and solvent vapor. This aerosol may pass through spray and desolvation chambers before reaching the plasma flame. 

Liquid fuel is injected through a pressure-atomizing or an air-blast nozzle. This spray is sheared by air streams into laminae and droplets that vaporize and bum. Because the atomization process is so important for subsequent mixing and burning, fuel-injector design is as critical as fuel properties. Figure 5 is a schematic of the processes occurring in a typical combustor. 

Condensation Scrubbing The collection efficiency of scrubbing can be increased by the simultaneous condensation of water vapor from the gas stream. Water-vapor condensation assists in particle removal by two entirely different mechanisms. One is the deposition of particles on cold-water droplets or other surfaces as the result of... 

At the central platform, water and hydrocarbon liquids are first removed in knockout drums. Then saturated natural gas, free of any liquid droplets, enters the twin expanders. The gas is cooled below its dewpoint, allowing heavy hydrocarbon components and water vapor to condense in the discharge stream. Turboexpanders were chosen for two main reasons They are more compact than competing methods of controlling the dewpoint and their operating costs are typically lower than those of many alternatives. 

To obtain a low flash zone pressure, the number of plates in the upper section of the vacuum pipe still is reduced to the minimum necessary to provide adequate heat transfer for condensing the distillate with the pumparound streams. A section of plates is included just above the flash zone. Here the vapors rising from the flash zone are contacted with reflux from the product drawoff plate. This part of the tower, called the wash section, serves to remove droplets of pitch entrained in the flash zone and also provides a moderate amount of fractionation. The flash zone operates at an absolute pressure of 60-90 mm Hg. 

A thermospray system is shown schematically in Figure 4.6. This consists of a heated capillary through which the LC eluate flows, with the temperature of this capillary being carefully controlled to bring about around 95% vaporization of the liquid. The vapour so produced acts as a nebulizing gas and aids the break-up of the liquid stream into droplets. 

Two-phase flows are classified by the void (bubble) distributions. Basic modes of void distribution are bubbles suspended in the liquid stream liquid droplets suspended in the vapor stream and liquid and vapor existing intermittently. The typical combinations of these modes as they develop in flow channels are called flow patterns. The various flow patterns exert different effects on the hydrodynamic conditions near the heated wall thus they produce different frictional pressure drops and different modes of heat transfer and boiling crises. Significant progress has been made in determining flow-pattern transition and modeling. 

The Water Cycle. The evaporation of water from land and water surfaces, the transpiration from plants, and the condensation and subsequent precipitation of rain cause a cycle of transportation and redistribution of water, a continuous circulation process known as the hydrologic cycle or water cycle (see Fig. 86). The sun evaporates fresh water from the seas and oceans, leaving impurities and dissolved solids behind when the water vapor cools down, it condenses to form clouds of small droplets that are carried across the surface of the earth as the clouds are moved inland by the wind and are further cooled, larger droplets are formed, and eventually the droplets fall as rain or snow. Some of the rainwater runs into natural underground water reservoirs, but most flows, in streams and rivers, back to the seas and oceans, evaporating as it travels. 

Horizontal blowdown drum/catch tank This type of drum, shown in Fig. 23-49, combines both the vapor-liquid separation and holdup functions in one vessel. Horizontal arums are commonly used where space is plentiful. The two-phase mixture usually enters at one end, and the vapor exits at the other end. To overcome reentrainment of liquid droplets, due to high inlet velocities, various devices and piping arrangements are used to provide a more uniform distribution of vapor-liquid mixtures into the separator, as shown in Fig. 23-50. For two-phase streams with very high vapor flow rates, inlets may be provided at each end, with the vapor outlet at the center of the drum, thus minimizing vapor velocities at the inlet and aiding vapor-liquid separation. 

There are a variety of nozzles that can be provided to hoses and monitors. They are capable of projecting a solid, spray or fog stream of water depending on the requirements and at varying flow rates. Straight stream nozzles have a greater reach and penetration, while fog and water sprays will absorb more heat because the water droplets absorb more heat due to greater surface area availability. Fog and water spray nozzles are sometimes used to assist in the dispersion of vapor releases. 

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