Onset of choking

Flow through the pipe is under viscous, laminar conditions (see Example 2.6 for typical assessment). From Equation (2.17), the onset of choked flow would require a pressure ... 

It has been found in practice that choking does not always occur immediately bubbles form, but that the onset of choked flow may be delayed until the mean throat pressure has fallen to a fraction, r p, of the vapour pressure at the valve inlet ... 

The onset of cavitation for a globe valve occurs with the onset of choking, as was noted in Section 7.5.2. Hence it will be predicted when W = Wchokr-Cavitation in a rotary valve occurs before choking, when the throat pressure equals the vapour pressure at valve inlet temperature, and equation (7.11) applies. This is of precisely the same form as equation (7.19), but with K replaced by and set to unity. This similarity of form enables us to repeat the development set out in Section 8.3 to determine the flow at choking. Thus we reach the following equation for cavitating flow, IV,., ... 

The derivation of this equation in Section 9.3 implies that it will be valid when the valve pressure ratio is high. The validity of equation (9.21) at low pressure ratios may be tested against direct data presented in the Fisher Control Valve Handbook for the low valve pressure ratios associated with the onset of choking. Tlie Fisher data are in the form of a graph of Ap/pi(= 1 - PiIp ) versus CJ ( = CyC see Appendix 3) at the onset of choking, which may be converted into a relationship between (pi/p du>kt) versus under the assumption that the data refer to the passage of air, which is a diatomic gas, with y = 1.4. The critical throat pressure ratio, Pk/p, for a diatomic gas is 0.5283 (equation (9.4)), which condition may be inserted into equation (9.21) to allow us to plot the variation of pi P ch, c ) with and compare the result with the direct data. See Figure 9.3. 

Figure 9.3 Valve pressure ratio at the onset of choking versus squared friction coefficient comparison of equation (9.21) with Fisher direct data.

Figure 9.9 Worked example transient behaviour of the calculated valve pressure ratio, pj/pi, and the valve pressure ratio at the onset of choking, (P2/P1...

The onset of choking is predicted from equation (9.45) when... 

Meanwhile the FUGSE predicts the onset of choked flow in the valve when the two terms on the right-hand side of equation (A4.4) ate equal ... 

Inhalation of vapors of lower chloroformates result in coughing, choking, and respiratory distress, and, with some chloroformates like methyl chloroformate, inhalation can be fatal as a result of the onset of pulmonary edema, which may not appear for several hours after exposure (55). Table 5 gives the acute toxicides of some chloroformates (55—57). 

A 0.70 specific gravity gas is expanded through a choke. Upstream conditions are 3000 psia and 150°F. What is the lowest pressure to which the gas can be expanded prior to onset of hydrate formation What is the temperature at this pressure ... 

Ghlorine is a gas with intermediate water solubility, thereby causing injury to both the upper and lower airways. Exposure to chlorine gas results in rapid onset of upper airway and pulmonary symptoms including choking, gasping, stridor, wheezing, shortness of breath, and respiratory compromise. Eye irritation and the development of a chemical conjunctivitis may also occur. 

A. Pulmonary aspiration usually causes Immediate onset of coughing, gagging, or choking. This may progress within minutes or hours to tachypnea, gmnting, wheezing, and severe chemical pneumonitis. Death may ensue from secondary bacterial infection and other respiratory complications. 

In gas systems, the flow becomes choked when the exit velocity through the orifice plate reaches sonic velocity. The mass flow rate is essentially independent of downstream conditions but can be increased by increasing the upstream pressure or decreasing the temperature. For an ideal gas and isentropic flow, the pressure ratio to calculate the onset of sonic conditions depends on the ratio of the specific heats, g, and is often known as the isentropic expansion factor ... 

In this lecture we characterize the effect of absence of unconstrained thermodynamic equilibrium and onset of a metastable state on the adiabatic flow of a mixture of liquid and its vapor through a convergent-divergent nozzle. We study steady-state flows and emphasize the relations that are present when the flow is choked. In such cases, there exists a cross-section in which the flow is critical and in which the adiabatic wave of small amplitude is stationary. More precisely, the relaxation process which results from the lack of equilibrium causes the system to be dispersive. In such circumstances, the critical velocity is equal to the frozen speed of sound, a corresponding to... 

The use of phosgene gas by both sides continued for the rest of the war and caused the most fatalities from chemical warfare agents. Because of its lower water solubility compared with chlorine, phosgene was found to be more effective in producing a late onset of pulmonary oedema at lower concentrations. It was therefore more toxic than chlorine. It also caused immediate incapacitation due to its short latency upper respiratory tract actions ( irritant or choking ). 

Panic disorder is characterized by the repeated and often unpredictable occurrence of panic attacks. According to the Diagnostic and Statistical Manual of Mental Disorders, panic attacks have an abrupt onset, reach their peak in 10 minutes, and are accompanied by at least 4 of 13 listed symptoms, which include shortness of breath, increased heart rate, chest pain, dizziness, choking sensations, numbness or tingling, hot/cold flashes, sweating, trembling, and nausea. Victims of these episodes feel an intense fear that can be better characterized as terror, often of losing control of their body and/or... 

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