Spray angle

The Reynolds number is sufficient as a parameter for describing the internal flow characteristics, such as discharge coefficient, air core ratio, and spray angle at the atomizer exit. 

Some concerns directly related to a tomizer operation include inadequate mixing of Hquid and gas, incomplete droplet evaporation, hydrodynamic instabiHty, formation of nonuniform sprays, uneven deposition of Hquid particles on soHd surfaces, and drifting of small droplets. Other possible problems include difficulty in achieving ignition, poor combustion efficiency, and incorrect rates of evaporation, chemical reaction, solidification, or deposition. Atomizers must also provide the desired spray angle and pattern, penetration, concentration, and particle size distribution. In certain appHcations, they must handle high viscosity or non-Newtonian fluids, or provide extremely fine sprays for rapid cooling. 

Because of the complexity of designs and performance characteristics, it is difficult to select the optimum atomizer for a given appHcation. The best approach is to consult and work with atomizer manufacturers. Their technical staffs are familiar with diverse appHcations and can provide valuable assistance. However, they will usually require the foUowing information properties of the Hquid to be atomized, eg, density, viscosity, and surface tension operating conditions, such as flow rate, pressure, and temperature range required mean droplet size and size distribution desired spray pattern spray angle requirement ambient environment flow field velocity requirements dimensional restrictions flow rate tolerance material to be used for atomizer constmction cost and safety considerations. 

Spray Angle A shift to a smaller-angle nozzle gives slightly larger drops for a given type of nozzle because of the reduced tendency of the sheet to thin. Dietrich [Pi oc. 1st Jnt. Conf. Liq. Atomization Spray Systems, Tokyo, (1978)] shows the following ... 

In calculating the impact point of spray, one should recognize that the spray angle closes in as the spray moves away from the nozzle. This is caused by loss of momentum of the spray to the gas. 

Power plants in both peaking and standby modes aehieved 30,000 hours between major overhauls. It was during these operations that the deposit problem on the turbine nozzles beeame apparent. Also, deposits developed on the fuel nozzles, a situation that eould eause deviation in the fuel spray angle and related eombustion problems. Therefore, both turbine and fuel nozzles needed frequent eleaning. 

Spray nozzle type plays an important role in the success of agrochemical application. For broadcast applications to soil, flat fan nozzles should be used. Newer spray tips such as the DG TeeJet, XR TeeJet, Turbo TeeJet and similar nozzles supplied by Lechler and Hardy have provided acceptable results in a number of studies. For a given nozzle type, the lower the application pressure, the larger is the spray droplet size and the less potential for spray drift. Similarly, the closer the boom is positioned to the soil surface, the less is the potential for spray drift." Most applications are made with spray tips having 80° or 110° spray angles and boom heights of about 50 cm above the soil surface. 

Pressure Atomization Plain- Orifice 25-250 Diesel engines, Jet engine afterburners, Ramjets Simple, Rugged, Cheap Narrow spray angle, Solid spray cone... 

Simplex 20-200 Gas turbines, Industrial furnaces Simple, Cheap, Wide spray angle High supply pressure, Varying spray angle with pressure differential and ambient gas density... 

Duplex 20-200 Gas turbine combustors Simple, Cheap, Wide spray angle, Good atomization over a wide range of liquid flow rates Narrowing spray angle with increasing liquid flow rate... 

Dual- Orifice 20-200 A variety of aircraft and industrial gas turbines Good atomization, Turndown ratio 50 1, Relatively constant spray angle Poor atomization in transition range, Complexity in design, Susceptibility of small passages to blockage... 

Two-Fluid Atomization Air-Blast Plain-Jet 15-130 [79]-[82] Industrial gas turbines Simple, cheap, good atomization Narrow spray angle. Atomizing performance inferior to prefilming air-blast type... 

Pre- filming 25-140 [83]-[86] Wide range of aircraft and industrial gas turbines Good atomization especially at high ambient pressures. Wide spray angle Poor atomization at low air velocities... 

In fan spray atomization, the effects of process parameters on the mean droplet size are similar to those in pressure-swirl atomization. In general, the mean droplet size increases with an increase in liquid viscosity, surface tension, and/or liquid sheet thickness and length. It decreases with increasing liquid velocity, liquid density, gas density, spray angle, and/or relative velocity between liquid and surrounding air. 

Generally, the mean droplet size is proportional to liquid surface tension, and inversely proportional to liquid density and vibration frequency. The proportional power index is —1/3 for the surface tension, about -1/3 for the liquid density, and -2/3 for the vibration frequency. The mean droplet size may be influenced by two additional parameters, i.e., liquid viscosity and flow rate. As expected, increasing liquid viscosity, and/or flow rate leads to an increase in the mean droplet size,[13°h482] while the spray becomes more polydisperse at high flow rates.[482] The spray angle is also affected by the liquid flow rate, vibration frequency and amplitude. Moreover, the spray shape is greatly influenced by the direction of liquid flow (upwards, downwards, or horizontally).[482]... 

Rumpf H. Agglomeration. Krepper W, ed. NY (Publ.) Interscience, 1962 374. Schaefer T, Worts O. Control of fluidized bed granulation I effects of spray angle, nozzle height and starting materials on granule size and size distribution. Arch Pharm Chem Sci Ed 1977 5 51-60. 

During this phase, the solvent evaporates, and the diameter of the drop increases. The energy required to form a drop is the product of the surface tension and the new surface area. About 0.1 cal/g is needed to subdivide 1 g of water into l-(xm droplets. The air pressure required to atomize the binder liquid is set by means of a pressure regulator. The spray pattern and spray angle are adjusted by adjusting the air cap. 

Schaefer, T. and O. Worts, Control of Fluidized Bed Granulation, I. Effects of Spray Angle, Nozzle Height and Starting Materials on Granule Size and Size Distribution, Arch. Pharm. Chemi. Sci., Ed. 5, 1977, pp.51-60. 

The experiments on the PGSS of PEG were performed in a laboratory-scale plant with sample sizes of about 200-400 g powder, and in a small pilot plant with sample sizes of 1-3 kg powder. Depending on the nozzles (orifices 0.4 / 0.5 /1.0 mm, spraying angles 30° and 90°), the kind of PEG (MW 1500/4000/8000/35000) and on pressure (100-250 bar) and temperature (45-70°C) three classes of particles were obtained fibres, spheres and sponges as presented in Figure 9.8-17. 

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