Choking limit

The lower right end of the performance curve on the figures terminates before reaching a limiting condition known as the choke limit. Extension of the performance curve would he vertical at the choke limit. Controls are usually not required for this condition hut should he considered in overall system control design. ... 

Examining the first part of the transient in more detail, we see from Figure 8.6 that the flow gradually approaches the choking limit as the valve is opened. 

While we have made allowance for a possible increase in velocity downstream of the nozzle, we should remember that the mass flow is still subject to an absolute choking limit. The mass flow under all conditions is given by combining equations (14.49) and (14.57) ... 

Fig. 8-3 ac voltage, U, in a current-limiting choke as a function of the ac flowing through it, /, for different numbers of windings, w, with and without an air gap. 

Fig. 15-7 Forced current drainage with resistor and/or choke to limit current.

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... 

Values to use for Vj, first drum volume—L, choke-tube length, and S, choke-tube flow area—will depend primarily on physical limitations and the degree of attenuation. Attenuation will be discussed later. Generally, the first drum volume may be sized according to piston displacement and volumetric efficiency considerations with a check of the physical limitations (nonacoustic method previously described) as to the choke-tube length and the pressure drop associated with the choke-tube. If the previously mentioned considerations will meet with design requirements, a further check on band-pass frequencies and the degree of attenuation are in order. 

A limitation of CVI is the necessity of interdiffusion of reactants and reaction products through relatively long, narrow, and sometimes tortuous channels. To avoid rapid deposition and choking of the entrance end of the channels, conditions are chosen to ensure deposition in the kinetically limited regime. This is a slow process which may take as much as several weeks before densification is achieved. In fact, full densification is almost impossible to obtain due to the formation of closed porosity. [ " 1... 

Equation (10-44), which applies at low pressure drops, and Eq. (10-48), which applies to critical (choked) flow, have been combined into one general universal empirical equation by Fisher Controls (1977), by using a sine function to represent the transition between the limits of these two states ... 

ACN and DCM are also known to be chemical warfare agent (CWA) simulants. ACN is a known simulant for blood CWAs, while DCM is a simulant for choking CWAs49 50. For determinations of ACN and DCM as CWA simulants, the detection limits need to be improved51. Such improvements may be possible by the application of more stable light source and detector to reduce noise in the measured signal. 

Solve the energy equation and discuss the behavior of the flame velocity in the tube. (There is a limit to the speed since the exit velocity cannot exceed the speed of sound, i.e. choked flow.)... 

Note that for most cases of interest, T is close to unity since the flowing gas mass fraction x 1. For the case of frozen flow (i.e., no heat transfer between the two phases), T would be replaced by k (or CpJC . ) in Eq. (23-106). However, the difference between the two limiting cases is small (< 10 percent) in terms of the flow capacity [Leung and Epstein, A Generalized Correlation for Two-Phase Nonflashing Homogeneous Choked Flow, Trans. ASME J. Heat Transfer 112 (May), pp. 528-530, 1990],... 

If the pressure ratio is above a critical value given below, the exiting mass flow is limited to a critical maximum value. This is sonic or choked flow ... 

It is important to calcine at the appropriate temperature to enhance the deactivation and the catalysis for the ceria-modified HM.50,51 The catalyst calcined at 300 °C had no catalytic activity. The activity for the isopropylation of naphthalene appeared over the catalyst calcined at 450 °C and reached the maximum at 550 °C. However, the activity decreased at a temperature of 700 °C. These results show that calcination at an appropriate temperature is necessary to keep the HM pores open. The selectivity for 2,6-DIPN was as high as 70% over the catalysts regardless of their calcination temperature. These phenomena show that the isopropylation proceeds inside HM pores. This selective deactivation of HM pores was limited to modification with ceria. The modification with other rare-earth metal oxides, such as lanthanum and neodymium oxides, also deactivated the external acid sites but choked the HM pore to result in low catalytic activity. The isomerization of 4,4 -DIPB was also prevented by the ceria modification of HM in the isopropylation of biphenyl.49... 

Choking is a phenomenon that occurs in high speed compressible flow (e.g. in relief systems). It occurs because, as the pressure falls along a pipe or through a nozzle, the fluid density decreases. This, means that the volumetric flow rate and, hence, the velocity increases (because the mass flow is constant). Choking occurs when the downstream pressure is reduced to the point where the velocity cannot increase any more. This effectively limits the maximum velocity and, hence, flow rate of the fluid. 

In relief systems of uniform diameter, the choke point (if choking, occurs) will be at the downstream end of the pipe. However, if the relief system comprises more than one diameter, then multiple choke points are possible and it will be necessary to determine the position of the choke point that limits the flow. This can be a complex calculation, for which there are two common cases ... 

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