Sprays fluid density

It is necessary to know how the optimum drop size can be achieved. The drop size will be governed by the equipment used, particularly by the type and size of nozzle and by the conditions of pressure and liquid output under which the nozzles are operated. It will be governed also by the physical properties of the spray fluid, such as density, surface tension, and viscosity. For fan-jet nozzles, one of the commonest types of atomizing equipment used in pesticide sprays, Yeo (25) has shown that a simple expression can be used to relate the various parameters governing drop size. For static or slow-moving nozzles, this takes the form ... 

For the applications discussed in the following sections, the preceding conservation equations are supplemented by ttje ideal gas equation of state, in which Pg (not the fluid density Pf) enters. Since fj appears in each of the conservation equations, it is apparent that they are coupled to the spray equation, which therefore must also be included to obtain a complete set of integrodifferential equations describing spray combustion. 

Spray. Direct type, continuous operation. Rotary atomizer, pressure nozzle, or two-fluid nozzle. Includes combined spray-fluid bed and spray-belt dryers Suited for large capacities. Product is usually powdery, spherical, and free-flowing. High temperatures can sometimes be used with heat-sensitive materials. Products generally have low bulk density. See comments under Liquids. Pressure-nozzle atomizers subject to erosion Requires special pumping equipment to feed the atomizer. See comments under Liquids. Not applicable unless feed is pumpable Not applicable Not applicable Not applicable Not applicable... 

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. 

A high velocity of the flow, Wg, an elevated density of the fluid as well as a low viscosity of the liquid phase and a low interfacial tension between liquid and fluid represent favourable conditions for high pressure spraying. Pressurised gases evidently possess characteristics similar to those of liquids with respect to the atomisation so that the relationships which are valid for liquid/liquid spraying may lead to realistic results. In the case presented here, a modified Nukiyama-Tanasawa distribution [5] has been used to specify the maximum drop diameter in the spraying process ... 

In Figure 2, the interfacial tension of coffee oil with a high content of volatile flavours against CC>2 is depicted. Mixtures like this are of particular interest for high pressure spray extraction. At increasing density of the fluid CO2 -phase, interfacial tension is decreased by dissolution of CO2 at the interface. In this case, presence of surface active material in the liquid phase, e.g. proteins, rather seem to be of subordinate importance. With respect to foam formation these surfactants neither show their known stabilising effect as long as no polar phase such as water is added. 

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