Inlet nozzle

Flow Nozzles. A flow nozzle is a constriction having an eUiptical or nearly eUiptical inlet section that blends into a cylindrical throat section as shown in Figure 8. Nozzle pressure differential is normally measured between taps located 1 pipe diameter upstream and 0.5 pipe diameters downstream of the nozzle inlet face. A nozzle has the approximate discharge coefficient of an equivalent venturi and the pressure drop of an equivalent orifice plate although venturi nozzles, which add a diffuser cone to proprietary nozzle shapes, are available to provide better pressure recovery. 

Flow Nozzles A simple form of flow nozzle is shown in Fig. 10-17. It consists essentially of a short cylinder with a flared approach section. The approach cross section is preferably elliptical in shape but may be conical. Recommended contours for long-radius flow nozzles are given in ASME PTC, op. cit., p. 13. In general, the length of the straight portion of the throat is about one-h f throat diameter, the upstream pressure tap is located about one pipe diameter from the nozzle inlet face, and the downstream pressure tap about one-half pipe diameter from the inlet face. For subsonic flow, the pressures at points 2 and 3 will be practically identical. If a conical inlet is preferred, the inlet and throat geometry specified for a Herschel-type venturi meter can be used, omitting the expansion section. 

Turbine inlet temperature (first stage nozzle inlet temperature)... 

P = beta ratio orifice diameter to pipe diameter (or nozzle inlet diameter) e = (epsilon) emissivity value... 

A common dimensionless number used to characterize the bubble formation from orifices through a gas chamber is the capacitance number defined as Nc — 4VcgpilnDoPs. For the bubble-formation system with inlet gas provided by nozzle tubes connected to an air compressor, the volume of the gas chamber is negligible, and thus, the dimensionless capacitance number is close to zero. The gas-flow rate through the nozzle would be near constant. For bubble formation under the constant flow rate condition, an increasing flow rate significantly increases the frequency of bubble formation. The initial bubble size also increases with an increase in the flow rate. Experimental results are shown in Fig. 6. Three different nozzle-inlet velocities are used in the air-water experiments. It is clearly seen that at all velocities used for nozzle air injection, bubbles rise in a zigzag path and a spiral motion of the bubbles prevails in air-water experiments. The simulation results on bubble formation and rise behavior conducted in this study closely resemble the experimental results. 

It is necessary first to define the region or control volume for which the momentum equation is to be written. In this example, it is convenient to select the fluid within the nozzle as that control volume. The control volume is defined by drawing a control surface over the inner surface of the nozzle and across the flow section at the nozzle inlet and the outlet. In this way, the nozzle itself is excluded from the control volume and external forces acting on the body of the nozzle, such as atmospheric pressure, are not involved in the momentum equation. This interior control surface is shown in Figure 1.9(a). 

Calculations relating to the sizing of the exchanger nozzle inlets and outlets are presented in Appendix H.12. 

Kf = Correction coefficient depending mainly on the pressure drop due to the type of nozzle inlet, something that is ignored in the API A = SV orifice area (cm2)... 

The capacity of a nozzle depends on the pressure difference across the nozzle s orifice. This pressure difference is usually a function of the liquid pressure at the nozzle inlet and the atmosphere. However, if the nozzle is to discharge into a volume that is greater than atmospheric pressure, this must be taken into account and the pressure difference adjusted accordingly. 

Consider an air-standard cycle for representing the turbojet power plant shown in Fig. 8.13. The temperature and pressure of the air entering the compressor are 1 bar and 30°C. The pressure ratio in the compressor is 6,5, and the temperature at the turbine inlet is l,I00°C. If expansion in the nozzle is isentropic and if the nozzle exhausts at 1 bar. what is the pressure at the nozzle inlet (turbine exhaust) and what is the velocity of the air leaving the nozzle ... 

Exauple 13 A high-velocity nozzle is designed to operate with steam at 700 kPa and 300°C. At the nozzle inlet the velocity is 30 m s 1. Calculate values of the ratio A/A (where A, is the cross-sectional area of the nozzle inlet) for the sections where the pressure is 600,500,400,300, and 200 kPa. Assume that the nozzle operates isentropi-cally. 

Compute the total pumping head. The total head, expressed in feet of water, equals static head + friction head + required nozzle head = 10 + 35 + 8(0.434) = 48.5 ft of water (145.0 kPa). A pump having a total head of at least 50 ft of water (15.2 m) would be chosen for this spray pond. If future expansion of the pond is anticipated, compute the probable total head required at a future date and choose a pump to deliver that head. Until the pond is expanded, the pump would operate with a throttled discharge. Normal nozzle inlet pressures range from about 6 to 10 lb/in2 (41.4 to 69.0 kPa). Higher pressures should not be used, because there will be excessive spray loss and rapid wear of the nozzles. 

The stabilizing effect of a slightly protruding inlet pipe has been confirmed by Reddy et al. (Rl), who obtained better results with a converging nozzle inlet (Fig. 28b) than with a straight pipe. These workers consider... 

Nozzles, Inlets and Outlets Three principles must be kept in mind in designing inlets and outlets. 

Membranes should be continued out through all nozzles (inlets and outlets) and over the exterior flange, so that the membrane has no discontinuity. 

This qua) itati ve picture was verified experimentally by blocking part of the nozzle inlet. The pattern of the deposit showed that for po < po min the panicle paths crossed between the nozzle inlet and the target (Fig. 4.15a), whereas for po > pomin crossing did not occur. 

Now from equation (14.40), the kinetic energy at nozzle inlet is ... 

Since there is no inlet velocity, the stagnation values of temperature, pressure etc. are unchanged from the basic values. Treating air as a perfect gas with a compressibility factor of unity, we may use the characteristic gas equation to calculate the specific volume at nozzle inlet as... 

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