Pressure fronts

A pressure wave propagating in air is called a blast wave because the pressure wave is followed by a strong wind. A shock wave or shock front results if the pressure front has an abrupt pressure change. A shock wave is expected from highly explosive materials, such as TNT, but it can also occur from the sudden rupture of a pressure vessel. The maximum pressure over ambient pressure is called the peak overpressure. 

For a deflagration the reaction front propagates at a speed less than the speed of sound. The pressure front moves at the speed of sound in the unreacted gas and moves away from the reaction front. One way to conceptualize the resulting pressure front is to consider the reaction front as producing a series of individual pressure fronts. These pressure fronts move away from the reaction front at the speed of sound and accumulate together in a main pressure front. The main pressure front will continue to grow in size as additional energy and pressure fronts are produced by the reaction front. 

The pressure fronts produced by detonations and deflagrations are markedly different. A detonation produces a shock front, with an abrupt pressure rise, a maximum pressure of greater than 10 atm, and total duration of typically less than 1 ms. The pressure front resulting from a deflagration is characteristically wide (many milliseconds in duration), flat (without an abrupt... 

The explosion of a dust or gas (either as a deflagration or a detonation) results in a reaction front moving outward from the ignition source preceded by a shock wave or pressure front. After the combustible material is consumed, the reaction front terminates, but the pressure wave continues its outward movement. A blast wave is composed of the pressure wave and subsequent wind. It is the blast wave that causes most of the damage. 

As described in chapter 6, detonations have a rapidly moving flame and/or pressure front. Detonation failures usually occur in pipelines or vessels with large length-to-diameter ratios. 

Hydraulic separation depends on a process called jigging, which creates a panicle siratifiealion from an alternate expansion and compaction of a bed of panicles by a pulsating fluid How. As originally developed, a baskel tilled with material was moved up and down in a lank filled with water. The more modem Baum jig process utilizes an air impulse concept in which the water is moved hy air pressure front an adjacent sealed chamber There are several refinements of the process, including the McNally Norton standard washer. 

In designing the system, the following has to be considered The explosion pressure front advances at the speed of sound, or 330 m/s (1100 ft/s), whereas the flame front propagates at about 3 m/s (10 ft/s). The detector signal trav-... 

The velocity of propagation increases with pressure, thus creating a steeply ascending pressure front, which imparts the nature of a shock wave to the pressure wave. At the onset, the velocity of propagation exceeds that of the speed of sound, but deteriorates with increasing distance, i.e. to approximately 1450 m/s. 

Some typical examples of shock properties calculated from the preceding equations are shown in Table X1V.2 for shocks traveling in N2 at STP, assuming that, in the range of shocks listed, 2c M/R = 5. It can be seen that, as the velocity of the moving surface with respect to the gas Vb decreases, the flows at the pressure front decrease toward the speed of sound (Mach 1) and the heating of the gas becomes quite small. ... 

In a detonation, a pressure front (shock wave) forms and propagates at supersonic speed, rapidly compressing and igniting the flammable mixture and giving the appearance of an instantaneous combustion. In the Vicinity of the detonation, the force of the shock wave can demolish a building or propel a bullet. The noise is the vibration of the eardrums caused by the shock wave. 

The increase in pressure and the range of the increase after a short time are symbolized by the line drawn in front of the piston. Now let the piston accelerate again and continue its motion at the new, higher rate. The new compression is imparted to the medium, some of which is already in motion, as shown in phase 2 of Fig. 11 it is moving at a faster rate, the motion of the matter is superposed and, in addition, the sonic velocity has increased in the somewhat warmer medium. Phases 3,4, etc. show that a steep pressure front is thus generated. A mathematical derivation of the relationships governing such a process would be beyond the scope of this book ). 

Under the same conditions of temperature and pressure, why does one liter of moist air weigh less than one liter of dry air In weather forecasts, an oncoming low-pressure front usually means imminent rainfall. Explain. 

Assuming the observed presence of gas near the wall of the transparent pack to be identical to the pressure front (easily verified by observing with a backlight), the overall AP can be split between the section behind the front, where foam is assumed to be present everywhere, and the section ahead of the front where only surfactant solution is present. 

Mesoscale. Phenomena occurring on scales of tens to hundreds of kilometers, such as land-sea breezes, mountain-valley winds, and migratory high- and low-pressure fronts. 

The results show clearly the swelling effect on the drying processes. The gas pressure front at the same simulation time (t = IxlO s) reaches only about 0.08m into the probe in case of swelling (Figure 2(a)) but 0.11m in case of non-swelling (Figure 3(a)). The water is thus more difficultly to... 

The energy produced in the explosion of a 20 kt weapon is distributed approximately as follows 50% pressure 35% heat 5% instantaneous radiation 10% radiation from fission products. The radiation dose at 500 m from hypocenter (the vertical point on ground below the explosion center) has been estimated to be 70 Gy at about 1.1 km it is 4 Gy. The pressure wave moves from the explosion site with the velocity of soimd. This initial short pressure front is followed by a low pressure wave leading to a rapid change in wind direction. The deaths in Hiroshima and Nagasaki resulted in 20 — 30% of the cases from primary bums, 50 — 60% from mechanical injuries and secondary bums, and only 15% from radiation injuries. The health detriment to the Japanese population is discussed in Chapter 18. 

Under conditions of constant temperature and volume, moist air exerts a lower pressure than dry air. Hence, a low-pressure front indicates that the air is moist. 

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