Pressure, average

Nonintrusive Instrumentation. Essential to quantitatively enlarging fundamental descriptions of flow patterns and flow regimes are localized nonintmsive measurements. Early investigators used time-averaged pressure traverses for holdups, and pilot tubes for velocity measurements. In the 1990s investigators use laser-Doppler and hot film anemometers, conductivity probes, and optical fibers to capture time-averaged turbulent fluctuations (39). 

One means to obtain a desired uniform distribution is to make the average pressure drop across the holes Ap large compared to the pressure variation over the length of pipe Ap. Then, the relative variation in pressure drop across the various holes will be small, and so will be the variation in flow. When the area of an individual hole is... 

FIG. 8-78 Generic depictions of average pressure at subsequent cross sections throughout a control valve, FiS selected for illustration are 0,9 and 0,63 for low and high recovery, respectively. Internal pressure in the high-recovery valve is shown as a dashed line for flashing conditions [Pg.788]

Permeability is normally determined using linear flow in the incompressible or compressible form, depending on whether a liquid or gas is used as the flowing fluid. The volumetric flowrate Q (or Q ,) is determined at several pressure drops. Q (or Q ,) is plotted versus the average pressure p . The slope of this line will yield the fluid conductivity K or, if the fluid density and viscosity are known, it provides the intrinsic permeability k. For gases, the fluid conductivity depends on pressure, so that... 

In a permeation experiment, an HERO module with a membrane area of 200 m is used to remove a nickel salt from an electroplating wastewater. TTie feed to the module has a flowrate of 5 x IQ— m /s, a nickel-salt composition of 4,(X)0 ppm and an osmotic pressure of 2.5 atm. The average pressure difference across the membrane is 28 atm. The permeate is collected at atmospheric pressure. The results of the experiment indicate that the water recovery is 80% while the solute rejection is 95%. Evaluate the transport parameters Ay and (D2u/KS). 

A filter s energy consumption, , based on average pressure loss, can be calculated as... 

Ap is average pressure loss (Pa) t is operation time (hours)... 

Over one year (8760 hours), a 1 mVs filter with an average pressure loss of 100 Pa requires 1250 kW h if the fan s efficiency is set at 70%. The energy cost is generally greater than the filter cost, and pressure loss reduction be-... 

Future costs of replacement filters and energy are calculated according to the current value method. The final result for a 1 m /s filter with average pressure loss of 200 Pa may be as shown in Table 9.3, if the calculation is based on a 10-year period. 

Mobile phases with some solvating potential, such as CO2 or ammonia, are necessary in SGC. Even though this technique is performed with ambient outlet pressure, solutes can be separated at lower temperatures than in GC because the average pressure on the column is high enough that solvation occurs. Obviously, solute retention is not constant in the column, and the local values of retention factors increase for all solutes as they near the column outlet. 

Therefore, to determine the pressure drop for inlet or average pressures other than 100 psi and at temperatures other than 60 F, multiply the values given in the table by the ratio ... 

Viscosity of the flowing fluid is constant. In general, this is not true for most real fluids. However, the effect is negligible if p at the average pressure is used. 

For the average pressure wave velocity in the pipe, compute the distance at which the amplitude falls to 1/e of its original value, the distance at which it falls at one-half of its original value (half depth) and the attenuation in dB/1,000 ft. Compute also the amplitude at surface. Bottomhole amplitude peak to peak 200 psi frequencies 0.2, 12 and 24 Hz. 

Audible sound has a frequency range of approximately 20 Hertz (Hz) to 20 kilohertz (kHz) and the pressure ranges from 20 x 10 N/M to 200 N/M. A pure tone produces the simplest type of wave form, that of a sine wave (Figure 42.1). The average pressure fluctuation is zero, and measurements are thus made in terms of the root mean square (rms) of the pressure variation. For the sine wave the rms is 0.707 times the peak value. 

Farooqi, S. 1. and Richardson, J. F. Trans. Inst. Chem. Eng. 60 (1982) 323. Horizontal flow of air and liquid (Newtonian and non-Newtonian) in a smooth pipe Part II Average pressure drop. 

Average pressure drop reduction as a function of flow rate for a series of different... 

Fig. 3.17 Average pressure drop reduction as a function of flow rate for a series of different surfaces in a micro-channel having dimensions W = 2.54 mm, H = 127 pm, and L = 50 mm. The experimental data include a series of ultrahydrophobic surfaces with a regular array of square micro-posts with d = 30 pm with a spacing between micro-posts of w = 15 pm represented by triangles (A), <7 = 30 pm and w = 30 pm represented by squares ( ), J = 30 pm and w = 60 pm represented by circles ( ), and d = 30 pm and w = 150 pm represented by diamonds ( ). Reprinted from Ou et al. (2004) with permission...

The average pressure, Pc, due to asperity contact can be obtained from Eq (5) by dehningp =FM, which gives... 

The relation between the average Fj observed and the ratio of the average chromate ion concentration to the average pressure of oxygen is... 

Figure 2.28 Experimental heat transfer results for saturated nucleate boiling of sodium from nickel disks at average pressure of 65 mm Hg. (From Marto and Rohsenow, 1966. Copyright 1966 by American Society of Mechanical Engineers, New York. Reprinted with permission.)... 

Increment number Distance from inlet (ft) Temperature at inlet to element (°K) AT (°K) Average temperature (°K) Average" pressure (psia) A Pa (psia) A/ x 103 Effluent fraction conversion... 

A surface effect (air cushion) vehicle measures 10 ft by 20 ft and weighs 6000 lbf. The air is supplied by a blower mounted on top of the vehicle, which must supply sufficient power to lift the vehicle 1 in. off the ground. Calculate the required blower capacity in scfm (standard cubic feet per minute), and the horsepower of the motor required to drive the blower if it is 80% efficient. Neglect friction, and assume that the air is an ideal gas at 80°F with properties evaluated at an average pressure. 

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