Nozzles fluid dynamics

Toma, T., Yoshino, K. and Morioka, S. Fluctuation characteristics of bubbly liquid flow in converging-diverging nozzle. Fluid Dynamic Research 2 (1988) 217-228. 

Flow through chokes and nozzles is a special case of fluid dynamics. For incompressible fluids the problem can be handled by mass conservation and Bernoulli s equation. Bernoulli s equation is solved for the pressure drop across the choke, assuming that the velocity of approach and the vertical displacement are negligible. The velocity term is replaced by the volumetric flow rate times the area at the choke throat to yield... 

For the delivery of atomization gas, different types of nozzles have been employed, such as straight, converging, and converging-diverging nozzles. Two major types of atomizers, i.e., free-fall and close-coupled atomizers, have been used, in which gas flows may be subsonic, sonic, or supersonic, depending on process parameters and gas nozzle designs. In sonic or supersonic flows, the mass flow rate of atomization gas can be calculated with the following equation based on the compressible fluid dynamics ... 

Problem understanding In many cases, experiments can provide only reliable integral values. In the case of twin screw extruders, for example, these are the shaft torque and the pressure and the temperature at the extrusion nozzle. Computational fluid dynamics, however, provide local information about pressure, velocity, and temperature within the overall computational domain. The calculation of gradients provides additional information about the shear rate or the heat transfer coefficients. 

It is shown in specialized texts on fluid dynamics that a convergent-diveigent nozzle is needed to accelerate a gas from subsonic to supersonic conditions, since gas acceleration in the subsonic regime requires the flow area to diminish with speed, while gas acceleration from sonic to supersonic speeds requires the flow area to expand with speed. The subsonic, convergent part of the nozzle is linked to the supersonic, divergent part of the nozzle by a duct of constant flow area, known as the throat, which is kept very short in practice in order to avoid frictional losses. The throat is the only section of the nozzle in which sonic flow can occur, and it is impossible for the throat to support any speed greater than sonic. The above remarks apply to all polytropic... 

L. Huang, K. Kumar, A.S. Mujumdar, A comparative study of a spray dryer with rotary disc atomizer and pressure nozzle using computational fluid dynamic simulations, Chemical Engineering and Processing, 45 (2006) 461-470. 

In this Chapter, the theoretical models for non-equilibrium chemical kinetics in multi-component reacting gas flows are proposed on the basis of three approaches of the kinetic theory. In the frame of the one-temperature approximation the chemical kinetics in thermal equilibrium flows or deviating weakly from thermal equilibrium is studied. The coupling of chemical kinetics and fluid dynamics equations is considered in the Euler and Navier-Stokes approximations. Chemical kinetics in vibrationaUy non-equilibrium flows is considered on the basis of the state-to-state and multi-temperature approaches. Different models for vibrational-chemical coupling in the flows of multi-component mixtures are derived. The influence of non-equilibrium distributions on reaction rates in the flows behind shock waves and in nozzle expansion is demonstrated. 

Advantages of a new burner concept were developed for the FlammaTec Flex Burner in the years 2006 and 2007. The Flex Burner utilizes two (2) fully separate gas inlets and gas flows into the burner which would be controlled and measured independently. The burner tip was optimized utilizing computational fluid dynamic modeling to minimize turbulence at the burner tip. The burner nozzle was also designed to be fully adjustable. Hence, the new burner design offered some technological advanti es. 

The specific burner nozzle dimensions are measured and modeled using computation fluid dynamic models to minimize flame turbulence as shown in Figure 3. 

The concept of spray etching adds another dimension to the fluid dynamics. The surface of the panel is never really free of a liquid film. The top side of a panel has the etch liquid held up between dehvery by the sprays and removal by flow off the edges. This flow is influenced by the number, flow, and pattern of the nozzles, the interaction of the flow between the sprays, the motion of the panels, and the effects of rollers and other contacting and shadowing objects. Even the bottom side retains fluid by surface tension and is influenced by the amount of hquid moving under the direction of the nozzles. The end result is complicate flow patterns that are the result of testing and optimization by the machine manufacturers. 

Fixed Spray Array. This is a system of spray tubes containing multiple nozzles connected transversely across the conveyor to a header pipe on one or both sides. The spray nozzles are placed into the tubes in a pattern designed to optimize the effect. Care must be taken to install and orient the nozzles properly for designed effect. Mechanical intervention to selectively activate (or deactivate) portions of the design to effect the fluid dynamics of particular patterns shonld be included. 

The simulation results show that the velocity of the air injected via the nozzle has a strong influence on the fluid dynamics of the whole granulator. 

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