Choked orifice

The geometry of the present opposed-flow burner is identical to the one designed by Puri and coworkers (see [18] for example). The burner consists of two opposing ducts with 20-millimeter diameter separated by 15 mm. The exhaust is extracted by a vacuum pump though a water-cooled annulus mounted around the bottom duct and a guard co-flow of nitrogen is issued from an annulus around the top duct. Experiments were performed with methane (99% purity) and premixed air introduced from the bottom duct and air admitted from the top duct. The flow rates were monitored using choked orifice meters. 

A fixed fuel-flow system is a simple set-up that is operated to maintain a constant fuel-flow rate. The fuel-rich gas flows out from the gas generator through a choked orifice that is attached at its aft-end. The mass generahon rate of the fuel-rich gas is therefore independent of the pressure in the ramburner. When a projectQe operated by a fixed-flow ducted rocket flies at a constant supersonic speed and at constant altitude, the airflow rate through the air-intake remains constant. Since the gas generahon rate in the gas generator is kept constant, the air-to-fuel raho also remains constant. Ophmized combustion performance is thereby obtained. This class of ducted rocket is termed a fixed fuel-flow ducted rocket . 

The tests were run in multipurpose rocket test cells. An overall schematic of the ACR gas-yield test equipment is given in Figure 4. The full-scale equipment was manufactured from uncooled 304 stainless steel. A water-cooled burner was used to supply the cracking steam to the ACR test piece at commercial-scale flow rates, pressures, and temperature. The burner was mated to the ACR venturi test piece through a choked orifice and a diameter transition section. The reactor venturi consisted... 

So, when q, > q t (low subcooling, flashing before the choke print), use the compressible solution, Eq. (26-95) with q p = q,. Otherwise (for high subcooling, no flashing before the choke point), use the hquid orifice equation, Eq. (26-94). 

Discharge Coefficients and Gas Discharge A compressible fluid, upon discharge from an orifice, accelerates from the puncture point and the cross-sec tional area contracts until it forms a minimum at the vena contracta, If flow is choked, the mass flux G, can be found at the vena contrac ta, since it is a maximum at that point, The mass flux at the orifice is related to the mass flux at the vena contracta by the discharge coefficient, which is the area contraction ratio (A at the vena contracta to Ay at the orifice) ... 

Critical and Subcritical Flow - The maximum vapor flow through a restriction, such as the nozzle or orifice of a pressure relief valve, will occur when conditions are such that the velocity through the smallest cross-sectional flow area equals the speed of sound in that vapor. This condition is referred to as "critical flow" or "choked flow . 

The flow of a compressible fluid through an orifice is limited by critical flow. Critical flow is also referred to as choked flow, sonic flow, or Mach 1. It can occur at a restriction in a line such as a relief valve orifice or a choke, where piping goes from a small branch into a larger header, where pipe size increases, or at the vent tip. The maximum flow occurs at... 

Chokes are used to control flow where there is a large pressure drop. They can either be adjustable, where the opening size can be varied manually as shown Figure 15-14 and 15-15 or have a fixed size orifice. Due to the erosive nature of the fluid flow through a choke, they are constructed so beans, discs, and seats can be easily replaced. 

To prevent foreign matter from damaging components and choking valves or atomizer orifices, filters must be incorporated into the handling system. There are usually two stages of filtration. The first provides protection for pumps and fire valves which handle oil at temperatures below those required at the oil-burning equipment. Second-stage... 

Methane is to be fed to a reactor at a rate of 101bm/min. The methane is available in a pipeline at 20 psia, 70°F, but the pressure in the reactor fluctuates between 2 and 10 psia. To control the flow rate, you want to install an orifice plate that will choke the flow at the desired flow rate. What should the diameter of the orifice be ... 

A choked flow takes place when the pressure ratio p2/Pi of gas through an orifice is very small. In the choked flow, the gas speed beyond the orifice is close to the sound velocity, and a change of p2 does not modify the flow rate. This regime finds application in the production of molecular beams. 

For sharp-edged orifices with Reynolds numbers greater than 30,000 (and not choked), a constant discharge coefficient C0 of 0.61 is indicated. However, for choked flows the discharge coefficient increases as the downstream pressure decreases.9 For these flows and for situations where C0 is uncertain, a conservative value of 1.0 is recommended. 

Also note that the computed choked pressures differ for each case, with a substantial difference between the orifice and the adiabatic/isothermal cases. A choking design based on an orifice calculation might not be choked in reality because of high downstream pressures. 

Search with values of Pi until G is maximized. The choke pressure, PcU is the value of Pi that produces a maximum value of mass flux Gmax. The discharge rate w is given from the mass flux, a discharge coefficient CD, and the orifice cross-sectional area A as... 

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