Droplet-gas interactions

Liu H, Rangel RH, Lavernia EJ. Modeling of droplet-gas interactions in spray atomization of Ta-2.5W alloy. Mater Sci Eng 1995 A191 171-184. 

The Enhanced-TAB Model (E-TAB) has been developed by Taimer in 1997 [7] and reflects a cascade of droplet breakups, in which the breakup condition is determined by the Taylor droplet oscillator dynamics (this method is further described in the next section). The droplet size is reduced in a continuous manner, until the product droplets reach a stable condition. The model maintains the droplet deformation dynamics of the TAB model [5]. According to this approach, the droplet distortion is described by a forced damped harmonic oscillator, in which the forcing term corresponds to the aerodynamic droplet-gas interaction, the restoring force is due to surface tension, while damping is attributed to the liquid s viscosity. 

In the CAB model the breakup condition is determined by means of the drop deformation dynamics of the standard Taylor analogy breakup model [5] (cf. TAB model above). In this approach, the drop distortion is described by a forced, damped, harmonic oscillator in which the forcing term is given by the aerodynamic droplet-gas interaction, the damping is due to the liquid viscosity and the restoring force is supplied by the surface tension. More specifically, the drop distortion is described by the deformation parameter, y = Ixjr, where x denotes the largest radial distortion from the spherical equilibrium surface, and r is the drop radius. The deformation equation in terms of the normalized distortion parameter, y, as provided in Eq. 9.29 is... 

The aim of this numerical study is to analyze the effects of the grouping/clustering of droplets in sprays on the heat transfer. In this study an Euler-Lagrangian algorithm is used to simulate the droplet-gas interactions. The droplets are assumed spherical with a radius smaller than the smallest length scale of the turbulence and a density much larger than that of the ambient gas. The heat transfer of individual droplets is characterized by the Nusselt number, which is defined by the... 

In the gas/liquid spray form of nebulizer, a stream of gas interacts with a stream of liquid. Depending on the relative velocity of the two streams and their relative orientation, the liquid flow is broken down into a spray of droplets, as in the common hair sprays. 

Nucleation a process by which a gas interacts and combines with droplets. See homogeneous nucleation. 

Depending on the scrubber design, the scrubbing liquid is sprayed into the gas stream before the gas encounters the Venturi throat, or in the throat, or upwards against the gas flow in the throat. The scrubbing liquid is then atomized into small droplets by the turbulence in the throat, and droplet-particle interaction is increased. Some designs use supplemental hydraulically or pneumatically atomized sprays to augment... 

The fundamental issues to be addressed in the process modeling include spray enthalpy, gas consumption, spray mass distribution, microstructure of solidified droplets, and droplet-substrate interactions. The effects of atomization gas chemistry, alloy composition and operation conditions on the resultant droplet properties are also to be investigated in the process modeling. 

Mass spectrometry Medium Unclear — need more data pM to mM No Up to 0-5 Days 0.5 wk (individually) Up to 2 pg/cpd < 2/well Interaction in the condensed droplet/gas phase... 

Nebulizers are used to introduce analyte solutions as an aerosol spray into a mass spectrometer. For use with plasma torches, it is necessary to produce a fine spray and to remove as much solvent as possible before the aerosol reaches the flame of the torch. Various designs of nebulizer are available, but most work on the principle of interacting gas and liquid streams or the use of ultrasonic devices to cause droplet formation. For nebulization applications in thermospray, APCI, and electrospray, see Chapters 8 and 11. 

Droplet Dispersion. The primary feature of the dispersed flow regime is that the spray contains generally spherical droplets. In most practical sprays, the volume fraction of the Hquid droplets in the dispersed region is relatively small compared with the continuous gas phase. Depending on the gas-phase conditions, Hquid droplets can encounter acceleration, deceleration, coUision, coalescence, evaporation, and secondary breakup during thein evolution. Through droplet and gas-phase interaction, turbulence plays a significant role in the redistribution of droplets and spray characteristics. 

Electrostatic Precipitation—the electrical charging of the liquid droplets may come about by the interaction of the gas and liquid streams. Not much known of this action. 

Condensed phase interactions can be divided roughly into two further categories chemical and physical. The latter involves all purely physical processes such as condensation of species of low volatility onto the surfaces of aerosol particles, adsorption, and absorption into liquid cloud and rainwater. Here, the interactions may be quite complex. For example, cloud droplets require a CCN, which in many instances is a particle of sulfate produced from SO2 and gas-particle conversion. If this particle is strongly acidic (as is often the case) HNO3 will not deposit on the aerosol particle rather, it will be dissolved in liquid water in clouds and rain. Thus, even though HNO3 is not very soluble in... 

The vapor-layer model developed in Section IV.A.2 is based on the continuum assumption of the vapor flow. This assumption, however, needs to be modified by considering the kinetic slip at the boundary when the Knudsen number of the vapor is larger than 0.01 (Bird, 1976). With the assumption that the thickness of the vapor layer is much smaller than the radius of the droplet, the reduced continuity and momentum equations for incompressible vapor flows in the symmetrical coordinates ( ,2) are given as Eqs. (43) and (47). When the Knudsen number of the vapor flow is between 0.01 and 0.1, the flow is in the slip regime. In this regime, the flow can still be considered as a continuum at several mean free paths distance from the boundary, but an effective slip velocity needs to be used to describe the molecular interaction between the gas molecules and the boundary. Based on the simple kinetic analysis of vapor molecules near the interface (Harvie and Fletcher, 2001c), the boundary conditions of the vapor flow at the solid surface can be given by... 

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