Differential pressure development

The degree of reaction, R, in the axial compressor is defined as the ratio of the static differential pressure in the rotor to the static differential pressure developed across the stage. 

The orifice, the venturi, and the nozzle are instruments for the measurement of duct or pipe flow rate. A constriction, throttling the flow, is placed in the duct, and the resulting differential pressure developed across the constriction is measured. It is the difference in the geometric shape that characterizes the three devices see Fig. 12.22. 

If specified, the maximum discharge pressure shall be increased by the additional differential pressure developed during one or more of the following operating circumstances ... 

The additional differential pressure developed at trip speed is normally a momentary excursion to be absorbed by the hydrotest margin. 

The loading for a bed consists of dead load, liquid load and live load. The dead load consists of the weight of the supports and the media it supports, i.e. catalyst, packing, inert balls, sand, clay, etc. The live load consists of the delta P, differential pressure, developed by the restriction of the bed to downward flow. Typically there is some amount of fouling that occurs in beds that cause a buildup... 

AP = Differential pressure developed by the compressor, psig MW = Molecular weight, Ib/mole i = Initial condition f = Final condition... 

It is desirable to have additional axial-load control on the multistage compressor. A balance piston, also refeired to as the balance drum, can be located at the discharge end (see Figure 5-46). The balance piston consists of a rotating element that has a specified diameter and an extended rim for sealing. The area adjacent to the balance piston (opposite the last stage location) is vented, normally to suction pressure. The differential pressure across the balance piston acts on the balance piston area to develop a thrust force opposite that generated by the impellers. The pressure on the... 

In the following we apply the dynamic method of air curtain design (see Fig. 7.92). The basic dependency is illustrated for a one-sided air curtain that is supplied at angle a and developed on the plane surface XOY. Since the jet of the air curtain is bent by the effect of differential pressure from outside and inside (P ) the building, the jet of the air curtain flows to the opposite side of the aperture and splits into two parts. After the division, one part of the jet flows along the outer surface of the enclosure and the other one enters the room at an angle (i to the plane surface of the aperture. We isolate the... 

Rupture discs are also used below relief valves to protect them from corrosion due to ves.sel fluids. The rupture disc bursts first and the relief valve immediately opens. The relief valve reseals, limiting flow when the pressure declines. When this configuration is used, it is necessary to monitor the pressure in the space between the rupture disk and the relief valve, either with a pressure indicator or a high pressure switch. Othei-wise, if a pinhole leak develops in the rupture disk, the pressure would equalize on both sides, and the rupture disk would not rupture at its set pressure because it works on differential pressure. 

Velocity pressure is a measure of the velocity pressure in the fan outlet It is indicated by a differential reading of an impact tube facing the direction of air flow in the fan outlet and by a static reading normal to air flow in the fan outlet. It is a measure of the kinetic energy per unit volume of gas, existing at the fan ouflet. Also see Table 12-15.The portion of the pressure developed by a fan due to the air or gas velocity is termed velocity pressure. 

Foam created in the foam generator is fed directly to the inlet of the test unit in the test cell, and the pressure drop developed by its flow through the test unit is measured by means of a differential pressure transducer, not shown in the figure, connected between inlet and outlet, and provided with by-pass and isolation valves for protection against accidental overloading. 

Pressure nozzles are somewhat inflexible since large ranges of flowrate require excessive variations in differential pressure. For example, for an atomiser operating satisfactorily at 275 kN/m2, a pressure differential of 17.25 MN/m2 is required to increase the flowrate to ten times its initial value. These limitations, inherent in all pressure-type nozzles, have been overcome in swirl spray nozzles by the development of spill, duplex, multi-orifice, and variable port atomisers, in which ratios of maximum to minimum outputs in excess of 50 can be easily achieved(34). 

Heat exchangers should include differential pressure monitoring or utilize a heat transfer medium of equal or better quality to avoid problems if leaks develop. 

A centrifugal pump develops the same feet of head, regardless of the density of the liquid pumped, as long as the flow is constant. This statement is valid as long as the viscosity of the liquid is below 40 cp or 200 SSU (Saybolt Seconds Universal). But, as process operators or engineers, we are not interested in feet of head. We are interested only in pressure. Differential pressure is related to differential feet of head as follows ... 

Pressure is measured extensively in the chemical processing industries and a wide variety of pressure measuring methods has been developed. Some of these have already been discussed in Volume 1, Section 6.2.2, viz. the manometer (which is an example of a gravity-balance type of meter), the Bourdon gauge (an example of an elastic transducer) and mention is made of the common first element in most pressure signal transmission systems—the differential pressure (DP) cell (Volume 1, Section 6.2.3). The latter also frequently forms part of a pneumatic transmission system and further discussion of this can be found in Section 6.3.4. 

Elbow taps develop relatively low differential pressures. For this reason, they cannot be used for measurement of low-velocity streams. Typically, water flowing at an average velocity of 1.5 m/s (5 ft/s) through a short-radius elbow with a centerline radius equal to the pipe diameter develops about 2.5 kPa (10 in. H20) water differential pressure. This is approximately the minimum full-scale pressure drop that is needed for reliable measurement. If the elbow is installed with 25 diameter upstream and 10 diameter downstream straight pipe runs, the measurement error will be under 10% FS over a 3 1 range. 

Use of piezoelectric gages in closed bomb tests of solid proplnts) 55)H.Rumpff, Explosivst 1957, 43-5 [Differential pressure measurements on burning of proplnts, using an oval-shaped bomb developed in 1953-55 by Rumpff previously used bombs for this purpose were of Krupp-Schmitz (1913), Liebes-sart (1921), Thring (1927), Rumpff (1930) ... 

During the past few years four methods have been developed for the study of the kinetics of oxide film formation, all being semicontinuous in nature. The polarimetric method has been adapted by Lustman and Mehl (14) for the measurement of the oxidation of copper. A spectro-photometric method has been applied by Waber, Sturdy, Wise, and Tipton (15) to the study of the oxidation of tantalum while a differential pressure method has been developed by Campbell and Thomas (16) for a study of the oxidation of a series of metals and alloys at elevated temperatures. We have chosen to use a sensitive weight gain method (17,18) in which a quartz microbalance is placed directly in the vacuum system. 

Van der Linden, Wassink and Theusink, have recently reported on a novel technique for mechanically extracting water though the use of a pressure differential across fabrics which is on the order of 0.5 atmospheres (6). The pressure differential is developed by either throttling high pressure steam (6 atm.) or compressed air through a one-mil wide nozzle (Machnozzle). Steam is usually employed since the nozzle operates isoenthaipically,... 

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