Nozzles flow measurement

Flow nozzles are commonly used in the measurement of steam and other high velocity fluids where erosion can occur. Nozzle flow coefficients are insensitive to small contour changes and reasonable accuracy can be maintained for long periods under difficult measurement conditions that would create unacceptable errors using an orifice installation. 

When testing to estabhsh the thermodynamic performance of a steam turbine, the ASME Performance Test Code 6 should be followed as closely as possible. The effec t of deviations from code procedure should be carefully evaluated. The flow measurement is particularly critical, and Performance Test Code 19 gives details of flow nozzles and orifices. The test requirements should be carefully studied when the piping is designed to ensure that a meaningful test can be conducted. 

Nozzle arrangements for various applications vary considerably. For subcritical flow measurement at the outlet end, where nozzle differential pressure p is less than the barometric pressure, flow should be measured with impact tubes and manometers as shown in Figure 20-3. 

Flow itnbalance, double-flow centrifugals, 144 Flow measurement, 345 Flow meters, 431 Flow nozzle, 431 Flow terminology conventions, 21... 

The absolute, barometric pressure is not normally required in ventilation measurements. The air density determination is based on barometric pressure, but other applications are sufficiently rare. On the other hand, the measurement of pressure difference is a frequent requirement, as so many other quantities are based on pressure difference. In mass flow or volume flow measurement using orifice, nozzle, and venturi, the measured quantity is the pressure difference. Also, velocity measurement with the Pitot-static tube is basically a pressure difference measurement. Other applications for pressure difference measurement are the determination of the performance of fans and air and gas supply and e. -haust devices, the measurement of ductwork tightness or building envelope leakage rate, as well as different types of ventilation control applications. 

Flow Rate. The values for volumetric or mass flow rate measurement are often determined by measuring pressure difference across an orifice, nozzle, or venturi tube. Other flow measurement techniques include positive displacement meters, turbine flowmeters, and airflow-measuring hoods. 

A link between laminar and turbulent lifted flames has been demonstrated based on the observation of a continuous transition from laminar to turbulent lifted flames, as shown in Figure 4.3.13 [56]. The flame attached to the nozzle lifted off in the laminar regime, experienced the transition by the jet breakup characteristics, and became turbulent lifted flames as the nozzle flow became turbulent. Subsequently, the liftoff height increased linearly and finally blowout (BO) occurred. This continuous transition suggested that tribrachial flames observed in laminar lifted flames could play an important role in the stabilization of turbulent lifted flames. Recent measurements supported the existence of tribrachial structure at turbulent lifted edges [57], with the OH zone indicating that the diffusion reaction zone is surrounded by the rich and lean reaction zones. 

The mass flow rate under adiabatic conditions is always somewhat greater than that under isothermal conditions, but the difference is normally <20%. In fact, for long piping systems (L/D > 1000), the difference is usually less than 5% (see, e.g., Holland, 1973). The flow of compressible (as well as incompressible) fluids through nozzles and orifices will be considered in the following chapter on flow-measuring devices. 

The axial velocity profiles, calculated on the basis of Tollmien similarity and experimental measurement in Yang and Kcaims (1980) were integrated across the jet cross-section at different elevations to obtain the total jet flow across the respective jet cross-sections. The total jet flows at different jet cross-sections are compared with the original jet nozzle flow, as shown in Fig. 31. Up to about 50% of the original jet flow can be entrained from the emulsion phase at the lower part of the jet close to the jet nozzle. This distance can extend up to about 4 times the nozzle diameter. The gas is then expelled from the jet along the jet height. 

ASME, Flow Measurement by Means of Standardized Nozzles and Orifice Plates, of Information on Instruments and Apparatus, ASME Power Test Codes, American Society of Mechanical Engineers, New York, 1940, p. 45. 

Most, if not all, solutions of the nozzle expansion problem have used equilibrium composition chamber conditions as the initial condition for nozzle solution. The feature is common to all of the nozzle flow solutions that is, the equilibrium composition expansion, frozen composition expansion, Bray freezing model, and kinetic rate solutions have all invoked the assumption of equilibrium composition at the beginning of the expansion process. While the failure to obtain equilibrium composition predicted performance, in terms of experimental characteristic velocities, has suggested a departure from equilibrium in the combustion chamber, only recently have non-equilibrium compositions been measured directly (31). 

The equivalent aerodynamic diameter of dry powder or aerosol particles can be measured using aerodynamic sizing in nozzle flow. This measures the transit times between two focussed laser beams in accelerated air flow seeded with particles. 

Flow rate is typically measured in gallons per minute (gpm) or gallons per hour (gph). A variety of devices can be used to accomplish flow measurement. Common examples of flow measurement devices are orifice plates, venturi nozzles, nutating disc meters, turbine flow meters, oval gear meters, rotameters, pitot tubes, weir and flume, and flow transmitters. Figure 7-4 shows a few examples of flow-measurement devices. 

Mullen C, Smith MA. (2005) Temperature dependence and kinetic isotope effects for the OH + HBr reaction and H/D isotopic variants at low temperatures (53-135 K) measured using a pulsed supersonic Laval nozzle flow reactor. J. Phys. Chem. A 109 3893-3902. 

The discharge coefficient is in general determined experimentally by the valve manufacturer for a fixed nominal lift. It corresponds to the average value of the ratio from mass flows measured and calculated with the nozzle flow model [1]. At least... 

The REAL nozzle flow model was validated with measurements performed on a high-pressure nozzle with nitrogen at a test facility of BASF. The measurements were conducted at inlet pressures of up to 1000 bar [15]. In addition, the calculations agree very accurately with the values in DIN EN ISO 9300 [13], based on many measurements on nozzles performed worldwide at pressures below 200 bar. Moreover, Beune [6] has intensively studied the flow behavior through high-pressure safety valves by numerical simulations with ANSYS CFX. He underlined the precision of the real gas nozzle flow model. In addition, he verified experimentally for a certain valve type that the discharge coefficient of the safety valve in combination with the REAL nozzle flow model can be regarded as constant as is presently stated in EN-ISO 4126-7. 

The three most extensively used types of flow-metering devices are the thin-plate square-edged oriflce, the flow nozzle, and the venturi tube. They are differential-head instruments and require secondaiy elements for measimement of the differential pressure produced by the primary element. The Supplement to ASME Power Test Codes Instruments and Apparatus, describes construction of the above primary flow-measuring elements and their installation as well as installation of the secondary elements. The method of flow measimement, the equations for flow computation, and the limitations and accimacy of measurements are discussed. Diagrams and tables showing the necessary flow coefficients as a function of Reynolds number and diameter ratio are included in the standards. Diagrams of the expansion factor for compressible fluids are given. 

---