Sauter mean droplet diameter

A visualization study of fuel atomization using a pulsed laser holography/photography technique indicates that basic spray formation processes are the same for both a coal-derived synthetic fuel (SRC-II) and comparable petroleum fuels (No. 2 and No. 6 grade). Measurements were made on both pressure swirl and air assisted atomizers in a cold spray facility having well controlled fuel temperature. Quality of the sprays formed with SRC-II was between that of the No. 2 and No. 6 fuel sprays and was consistent with measured fuel viscosity. Sauter mean droplet diameter (SMD) was found to correlate with fuel viscosity, atomization pressure, and fuel flow rate. For all three fuels, a smaller SMD could be obtained with the air assisted than with the pressure swirl atomizer. 

Bennington and Kerekes [17] developed the following empirical correlation for the Sauter mean droplet diameter generated by a splash plate atomizer used in large boilers. 

Coulaloglott and Tavlaiides compiled a tabulation of published correlations of drop size in agitated liquid sterns, but all the expressions were for the period after steady state had been attained with regard to drop size andjnass transfer. In contrast, the correlation by Skelland and Lee is for the Sauter mean droplet diameter dj2 when about 50% of the possible mass transfer has occurred—a significantly different condition. For agitation with a centrally locked six-fiat-blade tutbine with radial baffles they obtained... 

When passing the emulsion several (n) times through the valve, orifice, or nozzle, this has to he multiphed by the number of passes n. With the specific disruption energy v. the Sauter mean droplet diameter can he calculated in case of well-defined flow conditions by the following process functions ... 

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

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. 

Industrial liquid-liquid extraction most often involves processing two immiscible or partially miscible liquids in the form of a dispersion of droplets of one liquid (the dispersed phase) suspended in the other liquid (the continuous phase). The dispersion will exhibit a distribution of drop diameters d, often characterized by the volume to surface area average diameter or Sauter mean drop diameter. The term emulsion generally refers to a liquid-liquid dispersion with a dispersed-phase mean drop diameter on the order of 1 pm or less. 

Sauter mean drop diameter A method used to characterize the average drop size in a population of droplets in immiscible liquid-liquid dispersions. It is related to the volume fraction of the dispersed phase, <1> and the interfacial area, a. It is also known as the volume-to-area average drop diameter ... 

A gas having a density of 13 kg/m and a d5Tiamic viscosity of 0.006 cp flows through a pipe of 30 cm internal diameter at 6.7 m/s. Entrained in this gas is a liquid hydrocarbon having a density of 930 kg/m . A two-phase flow map indicates mist-annular flow. The interfacial tension (or IFT ) = 20 dynes/cm. Compute the Sauter-mean and volume-mean droplet diameters. 

An important measure of the droplet size distribution in spray appHca-tions is the Sauter mean diameter 32 = (d )/(d ). This measure is so important because during evaporative drying the mass transfer happens at the interface of the droplets and the surrounding air. To enhance the evaporation of a population of droplets, one has to maximize the active surface areas and minimize the internal volumes. The DSMC simulations showed that the Sauter mean diameter is a very nontrivial function of the axial and radial position in the spray. Figure 16 shows that at a given axial position, with increasing distance from the central axis the mean droplet diameter first increases, then decreases, and finally increases again. Exactly, the same trends... 

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. 

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. 

In order to estimate the specific surface area of the dispersed organic droplets, the mean droplet size (Sauter diameter 32) has to be determined, which can be calculated according to the Okufi equation (Eq. 5) ... 

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 ... 

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