Ohnesorge number liquid

To determine if a droplet experiences spreading or splashing when it impinges onto a liquid film on a solid surface, the correlation between the Weber number and Ohnesorge number derived by Walzel[398] may be used ... 

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 addition, the Ohnesorge number describes the influence of the viscosity of the liquid. 

The first term is essentially the reciprocal of the Weber number and the second term is a function of the Ohnesorge number. Equation 13 may be invalid for airblast atomizers operating at high pressures, >1 MPa (>10 atm), or with high viscosity liquids. 

An infinitely long cylindrical Newtonian liquid jet, is disturbed with a spatially harmonic surface displacement of a cosine shape R = a — Cocoskz, where k = Ina/X, and a is determined such that the volume of the jet is kept constant when the initial amplitude is changed. Therefore, a = (1 — Co/2) - The dynamics of this jet due to capillary forces was investigated for various values of initial disturbance wave number k, and initial amplitude i o> and of the jet Ohnesorge number, Oh. 

The shortcoming of the Weber number is that it does not consider the effects from the viscosity of the fluid. Therefore the Weber number is not adequate to describe the release of droplets from highly viscous liquids which are known to be challenging to dispense. To account for the liquid viscosity in droplet formation, the appropriate nondimensional number is the Ohnesorge number which represents the ratio of internal viscosity dissipation to the surface tension energy [15]. The Ohnesorge number may be written in terms of the Reynolds and Weber numbers ... 

To account for the liquid viscosity in droplet formation, the appropriate nondimensional number is the Ohnesorge number which represents the ratio of internal viscosity dissipation to the surface tension energy. The Ohnesorge number may be written in terms of the square root of the... 

Droplet dispensing is the procedure of ejecting single droplets or small jets out of a nozzle of a dispensing apparatus. Here we only consider liquid droplet dispensing into a gaseous environment. Dimensionless numbers like the Reynolds, the Weber and the Ohnesorge numbers are well suited to describe the droplet formation qualitatively. 

To better understand the origin of the oscillations of the shear-thinning droplets and the equivalent Ohnesorge number, the spatial distribution of the viscosity is analyzed. Figure 17.22 shows the magnitude of the velocity field together with the orientation of the velocity vectors in this plane scaled by the magnitude and Fig. 17.23 shows the shear rate distribution and the liquid dynamic viscosity. 

For steady injection of a liquid through a single nozzle with circular orifice into a quiescent gas (air), the mechanisms of jet breakup are typically classified into four primary regimes (Fig. 3 2)[4°][41][22°][227] according to the relative importance of inertial, surface tension, viscous, and aerodynamic forces. The most commonly quoted criteria for the classification are perhaps those proposed by Ohnesorge)40] Each regime is characterized by the magnitudes of the Reynolds number ReL and a dimensionless number Z ... 

The Weber number becomes important at conditions of high relative velocity between the injected liquid and surrounding gas. Other dimensionless parameters, such as the Ohnesorge ((We)1 2/Re), Euler (AP/ p V2 ), and Taylor (Re/ We) numbers, have also been used to correlate spray characteristics. These parameters, however, are not used as often as the Reynolds and Weber numbers. 

Orzechowski derived two more correlations, one for kerosene 24.7.x, and the other for a water-glycerin mixture 24.7.xi. The correlations are said to be a functirm of film thickness, Weber number and Ohnesorge s number. The effect of film thickness and Weber number remains unchanged on both liquids. The difference arises in Ohnesorge s number, where the exponent is slightly lower for kerosene. Figure 24.46 shows a comparison of the two equations, using t = 0.1 nun. 

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