Dynamic overpressure

Such dynamic overpressure systems (sic.) with traps experiencing cyclic fill-drain periods was proposed by Leonard (1993) and invokes intermittent breaching of the seal and subsequent annealing due to petroleum column loss, progressive burial and diagenetic cementation. 

Holm, G. M. 1996. The Central Graben a dynamic overpressure system. In Glennie, K. Hurst, A. (eds) NWEurope s Hydrocarbon Industry. Geological Society, London, 107-122. 

Other pressure quanities in blast modeling are the reflected pressure and the dynamic pressure. The reflected pressure is the pressure on a structure perpendicular to the shock wave and is at least a factor of 2 greater than the side-on overpressure. Another quantity is the dynamic overpressure—it is determined by multiplying the density of the air times the square of the velocity divided by 2. 

The most corroded areas of the original feed water distributing system are the welds in the T-junction (see Figure 4.66). Due to dynamic effects of the feed water flow, with local dynamic overpressures of 20-30 kPa or local dynamic forces of up... 

Tertiary blast injury - injuries due to the blast wind The blast wind (dynamic overpressure) results from the motion of the combustion products of the explosion. Resultant injuries vary from total disruption to amputation and devastating injuries from impact of the displaced body on the envirorunent. 

Dynamic explosion detectors use a piezoresistive pressure sensor installed behind the large-area, gas-tight, welded membrane. To ensure optimum pressure transference from the membrane to the active sensor element, the space between the membrane and the sensor is filled with a special, highly elastic oil. The construc tion is such that the dynamic explosion detec tor can withstand overpressures of 10 bar without any damage or effect on its setup characteristic. The operational range is adjustable between 0 and 5 bar abs. Dynamic explo-... 

Volume of vessel (free volume V) Shape of vessel (area and aspect ratio) Type of dust cloud distribution (ISO method/pneumatic-loading method) Dust explosihility characteristics Maximum explosion overpressure P ax Maximum explosion constant K ax Minimum ignition temperature MIT Type of explosion suppressant and its suppression efficiency Type of HRD suppressors number and free volume of HRD suppressors and the outlet diameter and valve opening time Suppressant charge and propelling agent pressure Fittings elbow and/or stub pipe and type of nozzle Type of explosion detector(s) dynamic or threshold pressure, UV or IR radiation, effective system activation overpressure Hardware deployment location of HRD suppressor(s) on vessel... 

Making a detailed estimate of the full loading of an object by a blast wave is only possible by use of multidimensional gas-dynamic codes such as BLAST (Van den Berg 1990). However, if the problem is sufficiently simplified, analytic methods may do as well. For such methods, it is sufficient to describe the blast wave somewhere in the field in terms of the side-on peak overpressure and the positive-phase duration. Blast models used for vapor cloud explosion blast modeling (Section 4.3) give the distribution of these blast parameters in the explosion s vicinity. 

The solid lines in Figure 4.5 represent extrapolations of experimental data to full-scale vessel bursts on the basis of dimensional arguments. Attendant overpressures were computed by the similarity solution for the gas dynamics generated by steady flames according to Kuhl et al. (1973). Overpressure effects in the environment were determined assuming acoustic decay. The dimensional arguments used to scale up the turbulent flame speed, based on an expression by Damkohler (1940), are, however, questionable. 

Table 6.10 presents some damage effects. It may give the impression that damage is related only to a blast wave s peak overpressure, but this is not the case. For certain types of structures, impulse and dynamic pressure (wind force), rather than overpressure, determine the extent of damage. Table 6.10 was prepared for blast waves of nuclear explosions, and generally provides conservative predictions for other types of explosions. More information on the damage caused by blast waves can be found in Appendix B. 

Other properties of tlie blast wave are tlie shock velocity, wliich is tlie rate or speed of tlie blast wave as it travels tluough tlie air, tlie particle velocity (or peak wind velocity), tlie peak dynamic pressure, and tlie peak rejected overpressure. 

Off-the-shelf catalogue sales of micro reactors have just started [15]. With an increasing number of commercial products, quality control will become more important. Brandner et al. describe quality control for micro heat exchangers/reactors at the Forschungszentrum Karlsruhe [23]. All manufacturing steps are accompanied by quality control and documentation. Leak rates (down to 10 mbar 1 s for He) and overpressure resistance (up to 1000 bar at ambient temperature) are measured. Under standardized conditions, the mean hydraulic diameter is determined. Dynamic tests supplement this quality control. 

As the wave front moves forward, the reflected overpressure on the face of the structure drops rapidly to the side-on overpressure, plus an added drag force due to the wind (dynamic) pressure. At the same time, the air pressure wave bends or "diffracts" around the structure, so that the structure is eventually engulfed by the blast, and approximately the same pressure is exerted on the sides and the roof. The front face, however, is still subjected to wind pressure, although the back face is shielded from it. 

Because these loads are usually suddenly applied, and because they last from fractions of a millisecond to at most seconds, the response of or damage to loaded structures or objects is almost always dynamic. So, usually structural response or damage is dependent not only on the amplitude (peak overpressure) of the applied blast loading, the loaded area and the structural strength but also on the mass or inertia of the structure, and either the duration of the transient pressure loading or the applied specific impulse. 

Pressure detection shall be used for closed enclosure applications. Threshold detectors provide an electric signal when a preset overpressure is exceeded. Dynamic detectors provide an electric signal to the control and indicating equipment (CIE). Typically they have both rate-of-rise and pressure threshold triggering points that can be configured specifically to the application conditions. Although this type of detector minimizes spurious activation of the isolation system (due to pressure fluctuations other than explosion pressure rise), care shall be taken to set up such detectors to meet appropriate detection response criteria for the particular application and protected enclosure geometry. 

For a building with a flat roof (pitch less than 10°) it is normally assumed that reflection does not occur when the blast wave travels horizontally. Consequently, the roof will experience the side-on overpressure combined with the dynamic wind pressure, the same as the side walls. The dynamic wind force on the roof acts in the opposite direction to the overpressure (upward). Also, consideration should be given to variation of the blast wave with distance and time as it travels across a roof element. The resulting roof loading, as shown in Figure 3.8, depends on the ratio of blast wave length to the span of the roof element and on its orientation relative to the direction of the blast wave. The effective peak overpressure for the roof elements are calculated using Equation 3.11 similar to the side wall. 

This blast effect is due to air movement as the blast wave propagates through the atmosphere. The velocity of the air particles, and hence the wind pressure, depends on the peak overpressure of the blast wave. Baker 1983 and Hvf 5-/300 provide data to compute this blast effect for shock waves. In the low overpressure range with normal atmospheric conditions, the peak dynamic pressure can be calculated using the following empirical formula from Afewmark I956 ... 

Most blast door manufacturers opt to perform static load tests on prototype assemblies of low-range blast doors to demonstrate that the assembly will resist the blast overpressure specified. Static tests should be accepted only if the dynamic structural response and dynamic load factors have been considered and the door, frame, and restraining hardware are manufactured using the same materials, dimensions, and tolerances as those in the prototype static test. 

Information gained from simulations can reveal key insights that explain gaps or contradictions in information. The time line is a useful tool in this development. For incidents of unexpected chemical reactions, it is common to attempt a lab scale simulation of the conditions involved in the exotherm or explosion. Many chemical processes can be modeled and duplicated dynamically by computer algorithms. Accelerated rate calorimeters (ARC) have proven to he highly useful tools for studying exothermic or overpressure runaway reactions. 

If.equation (6.2) is used, then comparison with dynamic simulation131 suggested that Leung s method would increasingly oversize at absolute overpressures above 50%. Provided the rate of temperature rise due to the runaway continues to increase at high overpressures, the arithmetic mean (equation 6.2) overestimates the true average q. 

A proper sizing criteria Is to determine the liquid volume that could be dumped before the ESD system shuts in the relief valve source of overpressure. Thus, a dynamic liquid holdup determines the size of the relief drum. It will generally be smaller with the liquid holdup sizing criteria than a comparable horizontal API sized vessel. 

The first step of the assessment is screening for the energy potential of a sample of a reaction mass, where a reaction has to be assessed, or of a sample of a substance, where the thermal stability has to be assessed. This may be obtained from a dynamic DSC experiment on samples of the reaction mass taken before, during, and after the reaction. Obviously, when the thermal stability of a sample has to be assessed, this is reduced to a representative sample of the reacting mass. If there is no significant energy potential, such as if the adiabatic temperature rise is less than 50 K and there is no overpressure, the study can be stopped at this stage. 

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