Local pressure

Introduction and Commercial Application Section 8.0 considered the dynamic behaviour in the reservoir, away from the influence of the wells. However, when the fluid flow comes under the influence of the pressure drop near the wellbore, the displacement may be altered by the local pressure distribution, giving rise to coning or cusping. These effects may encourage the production of unwanted fluids (e.g. water or gas instead of oil), and must be understood so that their negative input can be minimised. 

Here, P is the bulk pressure, which is the same in both phases, and p is the local pressure, which varies across the interface. 

In summary, it has become quite clear that contact between two surfaces is limited to a small fraction of the apparent area, and, as one consequence of this, rather high local temperatures can develop during rubbing. Another consequence, discussed in more detail later, is that there are also rather high local pressures. Finally, there is direct evidence [7,8] that the two surfaces do not remain intact when sliding past each other. Microscopic examination of the track left by the slider shows gouges and irregular pits left in the softer metal... 

As two surfaces are brought together, the pressure is extremely large at the initial few points of contact, and deformation immediately occurs to allow more and more to develop. This plastic flow continues until there is a total area of contact such that the local pressure has fallen to a characteristic yield pressure of the softer material. 

The coefficient of friction between two unlubricated solids is generally in the range of 0.5-1.0, and it has therefore been a matter of considerable interest that very low values, around 0.03, pertain to objects sliding on ice or snow. The first explanation, proposed by Reynolds in 1901, was that the local pressure caused melting, so that a thin film of water was present. Qualitatively, this explanation is supported by the observation that the coefficient of friction rises rapidly as the remperarure falls, especially below about -10°C, if the sliding speed is small. Moreover, there is little doubt that formation of a water film is actually involved [3,4]. 

The mechanism of boundary lubrication may then be pictured as follows. At the unusually prominent asperities, the local pressure exceeds the yield pressure... 

It is difficult to determine exactly the areas of localized pressure reductions inside the pump, although much research has been focused on this field. It is easy, however, to measure the total fluid pressure (static plus dynamic) at some convenient point, such as pump inlet flange, and adjust it in reference to the pump centerline location. By testing, it is possible to determine the point when the pump loses performance appreciably, such as 3% head drop, and to define the NPSH at that point, which is referred to as a required NPSH (NPSHR). The available NPSH (NPSHA) indicates how much suction head... 

Most often, the Mach number is calculated using the speed of sound evaluated at the local pressure and temperature. When M = 1, the flow is critical or sonic and the velocity equals the local speed of sound. For subsonic flowM < 1 while supersonic flows have M > 1. Compressibility effects are important when the Mach number exceeds 0.1 to 0.2. A common error is to assume that compressibihty effects are always negligible when the Mach number is small. The proper assessment of whether compressibihty is important should be based on relative density changes, not on Mach number. 

Vessel Codes Other Than ASME Different design and construction rules are used in other countries. Chemical engineers concerned with pressure vessels outside the United States must become familiar with local pressure-vessel laws and regulations. Boilers and Pressure Vessels, an international survey of design and approval requirements published by the British Standards Institution, May-lands Avenue, Hemel Hempstead, Hertfordshire, England, in 1975, gives pertinent information for 76 political jurisdic tions. 

The bubbling action of the bed produces local pressure fluctua-... 

Cavitation may be defined as the instantaneous formation and collapse of vapor bubbles in a liquid subject to rapid, intense localized pressure changes. Cavitation damage refers to the deterioration of a material resulting from its exposure to a cavitating fluid. 

For jointing large bus sections it may be advisable to use pressure plates to avoid excessive local pressure. 

High pressure Low/no flow - chlorine gas supply line for bleaching line A (linked from 5.2) High temperature (linked from 4.3) High pressure - chlorine railcar (linked to 1.5) Potential damage to the vaporizer if isolated from the relief valve on the chlorine railcar (linked to 4.9) Local pressure indication ... 

This combustion product is diluted with air entering through holes on the liner to make the temperature appropriate for blade material and to have enough volume-flow in the dilution zone. Air is jet-penetrated mainly because of converging clearances and creates high local pressure. 

Cavitation corrosion occurs when a surface is exposed to pressure changes and high-velocity flows. Under pressure conditions, bubbles form on the surface. Implosion of the bubbles causes local pressure changes sufficiently large to flake off microscopic portions of metal from the surface. The resulting surface roughness acts to promote further bubble formation, thus increasing the rate of corrosion. 

V.ilve too [iitemai f.iilijf d Operation High Nj pressure at HF cylinders, HF vaporizer vessel rupture - HF released to atmosphere Local pressure indication on N, line PRV-3 nt V- i / nutlcl 11 If N - line relic valwh lot, vapori/cr relief valve should not lift. 

Valve cin vil loo tai [iiloni-il valve failure Operation No Ny pressure to HF cylinder - no HF flow Lo vaporizer, B-l wing Local pressure indication on N2 line None tv ... 

If severe, same as valve closed too far Local pressure indication on Nj line, if severe ... 

Airflows are determined basically by a steady-state calculation for each time step. At each time step, first, pressures at external nodes are calculated on the basis of the wind pressure coefficients and the actual wind speed and direction. Then, for all conductances, the local pressures at each side of the link are calculated. At internal links, this pressure is dependent on the (unknown) zone pressure p and the aerostatic pressure variation due to the height of the link with respect to the zone reference height. At external links, this pressure is dependent on the external node pressure and the aerostatic pressure variation due to the height of the link with respect to the stack reference height. For the aerostatic pressure, the air density is determined considering the temperature, the humidity, and (if relevant) the contaminant concentrations in the zone or in the outside air, respectively. From this, the pressure differences across each conductance can be calculated, and from this the mass airflow tor each conductance /. 

Here v is the space- and time-dependent velocity field, p is the density of the fluid, p is the local pressure, v is the kinematic viscosity, and / is some arbitrary body-force acting on each small element of the fluid (gravitation, for example). 

Estimates of pressures inside the cloud vary widely. Gugan (1978) calculated that the forces required to produce damage effects observed, such as the bending of steel, would have required local pressures of up to 5-10 bar. 

Cavitation is the term to used to describe the formation of bubbles in liquid flow when the local pressure falls to around vapor pressure. Two effects are experienced in the pump a reduction in flow rate (accompanied. 

Vaporous cavitation can remove protective films, such as oxides, from metals and so initiate corrosion . In addition, the very high local pressures and temperatures associated with the final stage of cavity collapse can induce chemical reactions that would not normally occur. Thus certain additives are damaged by cavitation and their decomposition products can be corrosive. 

The boiling of water results in the continuous absorption of heat energy until a point is reached, for any particular pressure, at which the liquid (water) changes into a gas (steam). This boiling point or (heat) saturation temperature occurs when the water vapor pressure is equal to the local pressure. 

Formation of vapor bubbles in rapidly flowing or turbulent water causing risk of pumping failure and erosion and/or corrosion. Due to an increase in velocity at the pump head resulting in a localized pressure reduction and the subsequent collapse of the vapor into voids or cavities. Where FW temperatures are high (over perhaps 195-205 °F) the pump velocity can reduce FW vapor pressure below that corresponding to the temperature of the liquid and cavitation can occur accompanied by some noise. Warning of severe pump cavitation is often indicated by a heavy noise. 

The data of ONB in trapezoidal micro-channels of results reported by Lee et al. (2004) and prediction of Eq. (6.10) with various different values of r x- the experimental data points in Fig. 6.5, the saturation temperature is corresponding to the local pressure at each of the ONB locations. The local pressure is estimated by assuming a linear pressure distribution in the channel between the inlet and exit ones. The system pressure may vary from case to case. For Fig. 6.5 an average system pressure of 161.7 kPa over various different cases of this study was employed. As for the wall temperature, it is assumed that the channel wall temperature is uniform as the channel is relatively short and the wall material, silicon, has relatively good thermal conductivity. The figure indi-... 

The flow patterns (expansion of the bubbly, slug and annular regions of flow) affect the local pressure drop, as well as the pressure oscillations in micro-channels (Kandlikar et al. 2001 Wu and Cheng 2003a,b, 2004 Qu and Mudawar 2003 Hetsroni et al. 2005 Lee and Mudawar 2005a). 

This is the local pressure gradient. It is assumed to vary slowly in the z-direction. The pressure at position z is... 

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