Sauter droplet diameter

The Sauter droplet diameter dy is therefore dependent on the physical properties of the relevant mixture ... 

Figure 7-9. Sauter droplet diameter d as function of (a) specific flow rate of the dispersed phase up (b) relative column load uc/uQpj (c) mean acetone concentration in water for mass transfer direction C D [11-14]...

Thep and q denote the integral exponents of D in the respective summations, and thereby expHcitiy define the diameter that is being used. and are the number and representative diameter of sampled drops in each size class i For example, the arithmetic mean diameter, is a simple average based on the diameters of all the individual droplets in the spray sample. The volume mean diameter, D q, is the diameter of a droplet whose volume, if multiphed by the total number of droplets, equals the total volume of the sample. The Sauter mean diameter, is the diameter of a droplet whose ratio of volume-to-surface area is equal to that of the entire sample. This diameter is frequendy used because it permits quick estimation of the total Hquid surface area available for a particular industrial process or combustion system. Typical values of pressure swid atomizers range from 50 to 100 p.m. 

Droplet Size Corrections. The majority of correlations found in the Hterature deal with mean droplet diameters. A useflil equation for Sauter... 

Sauter mean, as in dSM, Sauter mean diameter subcooled condition superheated condition transition boiling, or Taylor bubble crossflow due to droplet deposition a group of thermodynamic similitude... 

Ligament diameter depends mainly on the film thickness, and thus thinner liquid films break down into smaller droplets. Rizk and Lefebvre 9X observed SMD oc ts0A, where SMD is the Sauter mean diameter of droplets. York et al.[255 and Dombrowski and... 

Recently, Knoll and Sojka[263] developed a semi-empirical correlation for the calculation of the Sauter mean diameter of the droplets after primary breakup of flat-sheets in twin-fluid atomization of high-viscosity liquids ... 

Recently, Razumovskid441 studied the shape of drops, and satellite droplets formed by forced capillary breakup of a liquid jet. On the basis of an instability analysis, Teng et al.[442] derived a simple equation for the prediction of droplet size from the breakup of cylindrical liquid jets at low-velocities. The equation correlates droplet size to a modified Ohnesorge number, and is applicable to both liquid-in-liquid, and liquid-in-gas jets of Newtonian or non-Newtonian fluids. Yamane et al.[439] measured Sauter mean diameter, and air-entrainment characteristics of non-evaporating unsteady dense sprays by means of an image analysis technique which uses an instantaneous shadow picture of the spray and amount of injected fuel. Influences of injection pressure and ambient gas density on the Sauter mean diameter and air entrainment were investigated parametrically. An empirical equation for the Sauter mean diameter was proposed based on a dimensionless analysis of the experimental results. It was indicated that the Sauter mean diameter decreases with an increase in injection pressure and a decrease in ambient gas density. It was also shown that the air-entrainment characteristics can be predicted from the quasi-steady jet theory. 

The observed flame features indicated that changing the atomization gas (normal or preheated air) to steam has a dramatic effect on the entire spray characteristics, including the near-nozzle exit region. Results were obtained for the droplet Sauter mean diameter (D32), number density, and velocity as a function of the radial position (from the burner centerline) with steam as the atomization fluid, under burning conditions, and are shown in Figs. 16.3 and 16.4, respectively, at axial positions of z = 10 mm, 20, 30, 40, 50, and 60 mm downstream of the nozzle exit. Results are also included for preheated and normal air at z = 10 and 50 mm to determine the effect of enthalpy associated with the preheated air on fuel atomization in near and far regions of the nozzle exit. Smaller droplet sizes were obtained with steam than with both air cases, near to the nozzle exit at all radial positions see Fig. 16.3. Droplet mean size with steam at z = 10 mm on the central axis of the spray was found to be about 58 /xm as compared to 81 pm with preheated air and 96 pm with normal unheated air. Near the spray boundary the mean droplet sizes were 42, 53, and 73 pm for steam, preheated air, and normal air, respectively. The enthalpy associated with preheated air, therefore, provides smaller droplet sizes as compared to the normal (unheated) air case near the nozzle exit. Smallest droplet mean size (with steam) is attributed to decreased viscosity of the fuel and increased viscosity of the gas. 

In all these tasks, the achievable (as narrow as possible) droplet size distribution represents the most important target quantity. It is often described merely by the mean droplet size, the so-called Sauter mean diameter J32 (Ref. 19), which is defined as the sum of all droplet volumes divided by their surfaces. Mechanisms of droplet formation are ... 

Whereas few actual values of n for sprays from various fuel injectors are reported, it is usually possible to obtain a fairly reliable estimate of x. This is so because x is uniquely related to various mean droplet diameters solely in terms of n, and data for Sauter mean diameter are rather frequently reported. Sauter mean diameter (SMD) is that diameter representative of the surface area per unit volume which is characteristic of the actual spray. 

The Reynolds number of gas flow, Rea, exhibits a medium influence on the Sauter mean diameter of the droplets, both before and after the impingement while the liquid to gas mass flow rate ratio, mL/m. affects the same amount very weakly. 

The Sauter mean diameters of the spray droplets, D32, both before and after the impingement can be correlated and predicted with Eq. (5.6), which gives reasonable and acceptable fitting of the experimental data. 

According to Assumption (4) above, the specific interface area calculated from the Sauter mean diameter of spray droplets, a, is kept constant. Thus, the integral amount of S02 absorbed within the residence time of the gas and droplets in the effective volume of the reactor, t, can be obtained as... 

Sauter mean diameters of spray droplets with various concentrations of Ca(OH)2 (atomizing... 

The gas-film mass transfer coefficient, kG, was determined based on the Sauter mean diameter of spray droplets. The results show essentially no influence of initial concentration of SOz on kG, suggesting that the process is controlled by diffusion through gas film and that the method proposed for the determination of kG is feasible ... 

Sauter Mean Diameter The diameter of a droplet whose ratio of volume to surface area is equal to that of the complete spray sample. 

The Sauter mean diameter has been found to be the most useful of the above definitions for characterizing the spray produced by a nozzle. It is a good indicator of a spray s performance in complex interactions with a droplet s surface and volume. Applications include spray drying, evaporative cooling, dry scrubbing, gas quenching, and gas absorption (Stavis, 1991). 

The primary aerosol droplets also become slightly smaller as the sample uptake rate is decreased. However, the Sauter mean diameter is not as sensitive to changes in sample uptake rate as it is to the nebulizer gas flow rate. For example, when the uptake rate was decreased from 1.0 to 0.6 mL/min, the Z>3 2 value decreased by only 4% (10.9 to 10.5 at a nebulizer gas flow rate of 0.8 L/min) [5]. 

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