Flash atomization

Whether flashing will occur and thus provide energy for flash atomization... 

The experimental data permit the extension of cold-flow work resulting in the desired high temperature, oil penetration correlations. The additional information on particle sizes, velocities, and spray stability was used to confirm and revise our present understanding of the flashing/ atomization/vaporization phenomena occurring in the ACR. 

Apparatus. The experiments were performed in a pilot plant consisting of a 1-ft. diameter, 15-ft. high AST reactor and its accessories. A schematic flow sheet of the pilot plant is shown in Figure 1. Details of the reactor and the auxiliary equipment were described earlier (1,9). Flashing atomization at 160°-220°C. and 400-1000 p.s.i.g., through small-orifice stainless steel atomizing nozzles was used in all tests described. 

Abstract A bquid droplet may go through shape oscillation if it is forced out of its equilibrium spherical shape, while gas bubbles undergo both shape and volume oscillations because they are compressible. This can happen when droplets and bubbles are exposed to an external flow or an external force. Liquid droplet oscillation is observed during the atomization process when a liquid ligament is first separated from a larger mass or when two droplets are collided. Droplet oscillations may change the rate of heat and mass transport. Bubble oscillations are important in cavitation problems, effervescent atomizers and flash atomization where large number of bubbles oscillate and interact with each other. This chapter provides the basic theory for the oscillation of liquid droplet and gas bubbles. 

Gas bubbles are relevant to various aspects of the atomization and sprays. In flashing process or flash atomization, bubbles are formed inside the liquid which significantly alter the atomization process (see Chap. 10). Also in effervescent atomizers, high-pressure air is injected inside a liquid and disperses as small bubbles. In addition, bubbles are formed in cavitating nozzles, which significantly alter the atomization process. Gas bubbles go through volume oscillations in addition to shape oscillation discussed in the previous section. In this section, dynamic evolution and stability of a spherical bubble undergoing volume oscillation is discussed. 

Abstract This chapter discusses flashing in spray nozzles. Different physical aspects involved in flashing such as phase change, bubble nucleation, bubble growth, internal two-phase flow and flash atomization are discussed. The effect of flashing on droplet size and velocity are also discussed. 

Keywords Boiling evaporation Bubble growth Droplet size Flashing Flash atomization Jet breakup Nucleation... 

When the jet is released into the ambient medium, a combination of hydrodynamic instabilities and thermal non-equilibrium conditions in the flow expands the jet. Violent and explosive characteristics of the jet cause its break-up into smaller droplets. This process is referred to as flash atomization. 

A model for flash atomization is proposed by Razzaghi [7]. In this model, each droplet is assumed to form a nucleate bubble inside. This bubble grows bursting the drop. The secondary droplets each go through the same process forming the spray. The process is also referred to as microexplosion in drops (Fig. 10.6). 

Witlox proposed a transitional model for the flash atomization as depicted in Fig. 10.12 and 10.13. For Fig. 10.12 the following correlations where proposed to find the degrees of superheat at which points A and C occur ... 

The pilot scale plant was used to perform spray experiments with an excess of CO2. There is a continuous flow of CO2. The liquid which shall be atomized is added cyclic with a piston pump. Therefore, it is assumed that the flow regime in and upstream the nozzle is a two phase flow consisting of a compressed gas phase and a gas-enriched liquid phase. This flow regime equals to the flow regime of a flash atomization with internal flashing. The optically transparent capillary with an inner diameter of 1 x 10 m is assembled to the pilot scale plant to analyze the flow regime and to verify these assumptions. 

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