Differential pressure calculation

Step 7 Calculate the differential in Ae One PRT eontrol objeetive is to maintain the differential pressure between the regenerator and the reaetor stripper. At the time of the breaker opening, it is assumed that the reaetor stripper pressure will not vary. Therefore, to keep the differential pressure eonstant, the regenerator pressure needs to also remain eonstant. Eor the expander, this means that must remain eonstant. To keep P eonstant, the mass flow before and after the breaker opening must remain eonstant (Equations 7-7 and 7-8). This implies that whatever mass flow is redueed on the inlet valve must be rerouted over the bypass valve. 

If the system differential pressure requirements are low, sometimes a fan can be used. A fan is limited to a maximum of about 65 inches of water (just over 2psi) in vacuum service or 77 inches of water in pressure service (just under 3psi). To estimate fan horsepower use the equations found in Chapter 6 in the section entitled Horsepower Calculation. In lieu of manufacturer s data use an adiabatic efficiency of 50% for initial work. 

Calculate the volumetric efficiency using Equation 3.5. Use. 05 for L because of the high differential pressure ... 

A sizing constant of 1.2 can be used to make a reasonable approximation of many commercial sizes. The constant, c, varied from 1.11 to 1.27 for a number of the frames investigated. With the displaced size approximated, the delivered volume can be calculated. Use Equation 4.10 and an assumed volumetric efficiency of. 90. This is arbitrary, as the actual volumetric efficiency varies from. 95 to. 75 or lower for the higher differential pressure applications. Once a slip speed has been determined. Equation 4.9 can be used to complete the calculation. The tip speed should stay near 125 fps. 

Surface measurements on the mud can be used to estimate the mudcake characteristics. If the formation pressure is known, the differential pressure can be calculated, and a chart similar to Figures 4-293a and b can be plotted. 

Pressure balance deals with the hydraulics of catalyst circulation in the reactor/regenerator circuit. The pressure balance starts with the static pressures and differential pressures that are measured. The various pressure increases and decreases in the circuit are then calculated. The object is to ... 

Sulphuric acid of density 1300 kg/m3 is flowing through a pipe of 50 mm, internal diameter. A thin-lipped orifice, 10 mm in diameter is fitted in the pipe and the differential pressure shown on a mercury manometer is 0.1 m. Assuming that the leads to the manometer are filled with the acid, calculate (a) the mass flow rate of acid and (b) the approximate drop in pressure caused by the orifice in kN/m2. The coefficient of discharge of the orifice may be taken as 0.61, the density of mercury as 13.550 kg/m3 and the density of the water as OHIO kg/m ... 

In operation the tube sheets are subjected to the differential pressure between shell and tube sides. The design of tube sheets as pressure-vessel components is covered by BS 5500 and is discussed in Chapter 13. Design formulae for calculating tube sheet thicknesses are also given in the TEMA standards. 

The phenomenon of critical flow is well known for the case of single-phase compressible flow through nozzles or orifices. When the differential pressure over the restriction is increased beyond a certain critical value, the mass flow rate ceases to increase. At that point it has reached its maximum possible value, called the critical flow rate, and the flow is characterized by the attainment of the critical state of the fluid at the throat of the restriction. This state is readily calculable for an isen-tropic expansion from gas dynamics. Since a two-phase gas-liquid mixture is a compressible fluid, a similar phenomenon may be expected to occur for such flows. In fact, two-phase critical flows have been observed, but they are more complicated than single-phase flows because of the liquid flashing as the pressure decreases along the flow path. The phase change may cause the flow pattern transition, and departure from phase equilibrium can be anticipated when the expansion is rapid. Interest in critical two-phase flow arises from the importance of predicting dis-... 

Air Flow Rate Into System. The flow rate into the system is calculated based on the flow rate out of the system and an assumed expansion factor (o). The flow rate of exhaust air coming out of the system corrected to 20°C (Vi) is based on the differential pressure across the bidirectional probe and the average temperature in the stack ... 

Two principal types of fabric are adaptable to filter use woven fabrics, which are used in shaker and reverse-flow filters and felts, which are used in reverse-pulse filters. The felts made from synthetic fibers are needle felts (i.e., felted on a needle loom) and are normally reinforced with a woven insert. The physical properties and air permeabilities of some typical woven and felt filter fabrics are presented in Tables 17-6 and 17-7. The air permeability of a filter fabric is defined as the flow rate of air in cubic feet per minute (at 70°F, 1 atm) that will pass through 1 ft2 of clean fabric under an applied differential pressure of Vt in water. The resistance coefficient KF of the clean fabric is defined by the equation in Table 17-6, which may be used to calculate the value of KF from the air permeability. If Ap, is taken as 0.5 in water, t as 0.0181 cP (the viscosity of air at 70°F and 1 atm), and Vj as the air permeability, then //, = 27.8/air permeability. 

Differential vaporization calculations of two types interest petroleum engineers. In both cases differential vaporization is at constant temperature, and the composition of the initial liquid is known. In the first case, initial conditions and final pressure are given and the number of moles to be vaporized is calculated. In the second case, the initial conditions and the number of moles, to bevalorized arc given and the final pressure is calculated. Either case requires a trial-and-error solution. 

Differential Vaporization—Calculation Procedure, Final Pressure Known... 

The error in differential vaporization calculations caused by variable Kj can be minimized by making the calculations illustrated by Examples 12-8 and 12-9 in stepwise manner. Select relatively small changes in pressure, obtain values of Kj at the average pressure, then calculate the resulting nLf and xjf by trial and error. These values of nLf and xjf then are used as njj and Xj for the next calculation over another small change in pressure. 

Equations 1 and 3 are solved at the same time by using an appropriate numerical algorithm for simultaneous first-order differential equations. Calculation of the term pgq may require an iteration within the integration routine, depending on the number of flow restrictions in series and the flow regime that is encountered. For two restrictions in series, pgq depends upon the pressures Pc, Pi and PQ. 

The flow coefficient is constant for the system based mainly on the construction characteristics of the pipe and type of fluid flowing through the pipe. The flow coefficient in each equation contains the appropriate units to balance the equation and provide the proper units for the resulting mass flow rate. The area of the pipe and differential pressure are used to calculate volumetric flow rate. As stated above, this volumetric flow rate is converted to mass flow rate by compensating for system temperature or pressure. 

For the precise measurement of gas flow (steam) at varying pressures and temperatures, it is necessary to determine the density, which is pressure and temperature dependent, and from this value to calculate the actual flow. The use of a computer is essential to measure flow with changing pressure or temperature. Figure 10 illustrates an example of a computer specifically designed for the measurement of gas flow. The computer is designed to accept input signals from commonly used differential pressure detectors, or from density or pressure plus temperature sensors, and to provide an output which is proportional to the actual rate of flow. The computer has an accuracy better than +0.1% at flow rates of 10% to 100%. 

As previously discussed, flow rate is proportional to the square root of the differential pressure. The extractor is used to electronically calculate the square root of the differential pressure and provide an output proportional to system flow. The constants are determined by selection of the appropriate electronic components. 

The extractor is used to electronically calculate the square root of the differential pressure and to provide an output proportional to system flow. 

Virtually all normalization programs will calculate the normalized permeate flow, normalized salt rejection and/or passage, and differential pressure (some programs normalize it, some do not). Some programs also include net driving pressure as an output as well as the following outputs ... 

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