Pressurization transient

It should be emphasized at this point that the speed of response is cnti-cal. The pressure transient pressure should not fall to less than 50% of the difference in pressure between the standby pump start pressure and the low oil pressure trip pressure. This is normally achievable with good design practice and the use of a switch and direct wiring. There is some tendency to use a transmitter and control through a remote computer. The latter arrangement is difficult to check on a shop test and normally is too slow to meet the requirement. An accumulator can be added and must be used if the requirement cannot be met. This additional hardware contributes to higher initial cost and possible reliability problems in the future. The direct switch method is therefore highly recommended. 

Accumulators can be used to help stabilize the lube system against pressure transients such as that from the turbine power operator during a large correction. For a sizing rule of thumb, the system pressure should not vary by more than 10%, while the turbine servo travels full stroke in a one second interval. The role of accumulators for pump switching was covered earlier in the section on Startup Control. 

A vapor poeket on the exchanger s low-pressure side can create a cushion that may greatly diminish the pressure transient s intensity. A transient analysis may not be required if sufficient low-pressure side vapor exists (although tube rupture should still be considered as a viable relief scenario). However, if the low-pressure fluid is liquid from a separator that has a small amount of vapor from flashing across a level control valve, the vapor pocket may collapse after the pressure has exceeded the fluid s bubble point. The bubble point will be at the separator pressure. Transient analysis will prediet a gradually inereasing pressure until the pressure reaches the bubble point. Then, the pressure will increase rapidly. For this ease, a transient analysis should be considered. 

Velocity flame stoppers have been used for feeding waste fuel gas to furnace burners when the gas can become flammable due to contamination with air. They have also been used for feeding waste or depleted air streams to furnaces when the air streams can become contaminated with flammable gases (Howard 1982). It should be noted that a furnace pressure transient may render this device ineffective and consideration should be given to providing an upstream detonation flame arrester. In this arrangement a demand will only be placed on the detonation flame arrester when the velocity flame stopper fails. Therefore, detonation flame arrester maintenance should be minimal. 

During the third phase, the motor chamber continues to fill with propellant combustion products until the steady-state pressure has been reached. The chamber-pressure transient during this phase is described by... 

Igniter(s) design, 21-24 pyrotechnic, 23-24 rocket exhaust, 21-23 aft end, 23, 28 heat end, 21-23 Ignition approaches kinetic, 9 thermodynamic, 9 chamber-pressure transient, 7-8 delay time, 20, 24-25 hot-wire, 11-12 hypergolic, 24 pressure transients, 29-30 theory... 

Figure 9. Bubble radius and pressure transients of the water vapor inside the bubbles. The first maximum in pressure at 650 ps marks the collapse of the bubbles. The following modulations are only expected for oscillatory bubble motion.

Ehlig-Economides, C. "Use of the Pressure Derivative for Diagnosing Pressure-Transient Behavior," J. Petr. Technol.. October 1988, 1280-1282. 

The interpretation of these coverage-dependent effects involves such ideas as island formation, mixed domains of CO and 0, the mobility of CO and 0 and the adsorption of CO on oxygen-covered regions (1,18,26, 27). A deeper understanding of the roles of these processes comes from isothermal experiments involving pressure transients. 

Throughout this section on pressure transients we have emphasized electron spectroscopy as a procedure for directly detecting surface species, and, with difficult calibration, their concentration. It is important to keep in mind that the detection limit for these is about 0.01 of a monolayer. Using flash desorption as a complementary technique this limit can be extended to 0.001 monolayer in certain cases. The fact remains that extremely labile chemisorbed species may be present in kinetically important but undetectable concentrations. Since residence times as short as 2 x 10 - seconds can be determined, molecular beam techniques, as described below, afford an alternative but indirect method of measuring the properties of these very reactive species. 

Although the curves in Figures 13-15 were developed for transient loads defined by total applied forces and inpulses, we could as easily have developed them by initially specifying an applied pressure transient loading, with its accompanying specific impulse, plus a loaded area. So, the concept certainly applies to simple structures under blast loading. The inportant inferences to be drawn from the simple- analyses are that structures respond primarily to peak overpressure if their vibration periods are much shorter than the blast duration, while they respond primarily to specific impulse if their vibration periods are much longer than the blast duration. 

For blast resistant design, the most significant feature of an explosion is the sudden release of energy to the atmosphere which results in a pressure transient, or blast wave. The blast wave propagates outward in all directions from the source at supersonic or sonic speed. The magnitude and shape of the blast wave depends on the nature of the energy release and on the distance from the explosion epicenter. The characteristic shapes of blast waves are shown in Figure 3.1. 

Phase 1 During phase 1, the increased thoracoabdominal pressure transiently increases venous return, thereby raising BP and reflexly lowering heart rate. Phase 2 During phase 2, the sustained rise in intrathoracic pressure reduces venous return VR and so BP falls until a compensatory tachycardia restores it. Phase 3 The release of pressure in phase 3 creates a large empty venous reservoir, causing BP to fall. Show that the heart rate remains elevated. Phase 4 The last phase shows how the raised heart rate then initially leads to a raised BP as venous return is restored. This is followed by a reflex bradycardia before both parameters eventually return to normal. 

Anderson and Armstrong (1977) summarize a number of other studies carried out at the Argonne National Laboratory and elsewhere in which there was contact between R-22 and water (or R-22 and mineral oil) (see Henry et ai, 1974, 1976 Board et al., 1974). In these studies, pressure transients were measured. Anderson and Armstrong have summarized these data in Fig. 11. Note that for water temperatures below about 350 K, the pressure rise upon contact is small. Above a water temperature of about 350 K, which corresponds to a calculated interface temperature of... 

K, there is a significant increase in pressure and values of 30 bar (or higher) were recorded. Assuming that the water-R-22 interface temperature had to attain the superheat-limit value before an explosion occurred, these data are in remarkable agreement with in Table XVI. Also shown in Fig. 11 is the vapor pressure of R-22 calculated for the interface temperature between the water and the saturated R-22 (232 K). Essentially all measured pressures fall below this curve, and this suggests that the maximum pressure transient corresponds to the vapor pressure determined in this manner. (Another limit could be chosen as the critical pressure of R-22, 50 bars, but this value significantly exceeds any measured pressure.)... 

One assumes that and are constant and that the burning rate is expressed by Eq. (3.68) during the pressure transient in the rocket motor Eq. (14.6) is then represented byhl... 

If the pressure in a rocket motor changes during the time interval x, the pressure transient is considered to represent a steady-state combustion when x > x and a non-steady-state combustion when x < x. ... 

To protect the HPRT outlet casing integrity and mechanical seals from possible downstream back pressure transients a relief valve installed in the HPRT outlet piping circuit should be considered (see Figure C.1). 

Succinylcholine increases intraocular pressure transiently. It can also cause muscle pain, which may be due to fasciculation and uncoordinated muscle contraction. The prior administration of a competitive blocking agent may prevent both fasciculation and pain. 

Fig. 12.85. Pressure transient obtained during the sequence of increasing overpotentials q = -0.45 V and -0.60 V. (Reprinted from Z. Minevski, dissertation, Texas A M University, 1995.)...

The derivative of the pressure with respect to the density is usually referred to as the square of the speed of sound, vbich however is very misleading for two-phase problems and for single phase fluids in an elastic pipe. The velocity c, should rather be taken as the speed of propagation of large scale pressure transients in the pipeline. 

In order to characterize the adsorbed species in the zeolite pores during the reaction, IR spectra of the catalyst on stream were recorded (time resolution 30 sec. for the first 5 minutes, 5 min. afterwards) after introducing the carrier gas stream containing the reactants (pressure transient response). The concentrations of the adsorbed species were derived from the integrated areas of the ring vibrations of the aromatic molecules (for details see ref. [13]). Simultaneously, samples of the effluent gas stream were collected into the 16 loops of the multiport valve and subsequently analyzed by means of gas chromatography. 

Table XV provides a summary of the coal moisture, steam feed rate and exit gas pressure transient response runs showing the time required to reach the given condition. It provides a rough estimate for the values of the bifurcation points for these runs. Thus, the bifurcation point for the coal moisture step change runs lies between 30.08 and 31.05 wt % moisture. For the steam feed rate changes, it lies between -2.25% and -2.50%, and for the exit gas pressure, it is bracketed by the 3.14 MPa (31 atm) and 3.24 MPa (32 atm) values.

Changing the exit gas pressure also gave three multiple steady state responses in which the same set of operating parameters produced different reactor profiles. Finally, a rough estimate for the location of the bifurcation points was given for the coal moisture, steam feed rate, and exit gas pressure transient response runs. 

The first method, shown in Figure 3.12(A), places a valve in the condensate hne and directly backs up the liquid into the condenser as needed. The second method places a control valve in a vapor hne, added to bypass the condenser and go directly into the accumulation tank (see Figure 3.12(B)). Although somewhat counterintuitive, the vapor bypass valve must open as pressure drops, in order to raise the pressure at the accumulation tank and force hquid condensate back into the condenser to restore the energy balance. Care must be taken that the surface of the liquid in the tank is not disturbed, as undesirable pressure transients can develop with the hot vapor in contact with the sub-cooled liquid. Another concern with both of these condensate methods is the venting of process inerts as they build up over time. Valve position is the best indication of this pending problem. 

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