Flow capacity calculation

If the superimposed back pressure is less than the calculated critical flow pressure, the capacity of a conventional PR valve in vapor service is unaffected and back pressure is not a factor. However, builtup back pressure on a conventional pressure relief valve will affect its flow capacity and operating characteristics, and should not exceed 100% of its set pressure. If total back pressure (superimposed plus built-up) is greater than the calculated critical flow pressure, the capacity of a conventional PR valve in vapor service is affected, and total back pressure is incorporated into the sizing procedure. Any back pressure reduces the capacity of a conventional PR valve in liquid service, and... 

Air Flow - The capacity of a multijet flare to induce air flow must be calculated, to make sure that it is adequate to meet the maximum air flow requirement for smokeless combustion. (W, of Equation 4 below must be > W, of Equation 5). The term air flow capacity refers to the primary air flow rate which will be induced around each jet, and may be estimated from the following equation ... 

The method includes the mass unit vent flow capacity per unit area. G. This allows using any applicable vent capacity calculation method. The method incorporates the equilibrium rate model (ERM) for vent flow capacity when friction is negligible. Additionally, a coiTection factor is used for longer vent lines of constant diameter and with negligible static head change. ... 

As a general guide for the average system, if the actual system pressure requirement is known for one flow capacity, the system can be calculated assuming the pressure varies as the square of the volume. The curve is parabolic going through the origin of a pressure-volume plot. 

Most of the relief sizing equations given in Chapters 6-8 yield the two-phase required relief rate, W. The two-phase mass flow capacity per unit area, G, is then needed in order to obtain the required relief area. Chapter 9 contains important background information about two-phase flow, and calculation methods for G. Some system types are special cases involving highly viscous (laminar) flow, solids and/or... 

G, (expressed as- kg/m2s), is the average two-phase flow capacity per unit cross-sectional area of the vent-line. Methods for calculating G are given in Chapter... 

The logic given in Figure 5.1 can be used to check that this section is the correct one for relief system sizing for any particular case. As explained in Chapter 5, the required relief rate, W, should first be calculated using the methods described in this Chapter. A two-phase mass flow capacity per unit area, G, should then be calculated using the methods described in Chapter 9 (or Chapter 10 in special cases). The required relief flow area can then be calculated using equation (5.1). 

The two-phase mass flow capacity per unit cross-sectional area, G, can be calculated using any applicable method for non-flashing two-phase flow (see Chapter 9). In order to minimise the relief size obtained, G should be evaluated at the maximum accumulated pressure, irrespective of the relief pressure. 

The relief sizing methods detailed in Chapters 6-8 (and most methods in Annexes 4 and 5) yield an average two-phase required relief rate, W. In order to calculate the required relief flow area, A, using equation (5.1), the two-phase mass flow capacity per unit cross-sectional area of the relief system, G, is needed. This Chapter is concerned with methods for the, calculation of G. 

The capacity of the relief system can be obtained from a two-phase flow calculation for nozzle flow. If the flow is not choked, then the Omega method (see Annex 8) or suitable computer code must be used to calculate flow capacity. For choked flow a larger range of methods may be applicable, e.g. ERM for vapour pressure systems (see 9.4.2) or Tangren et al. s method for gassy systems (see 9.4.3), together with the application of a discharge coefficient. The capacity can then be obtained from ... 

In the original Boyle method1181, it was recommended that the relief system capacity be calculated on the basis of non-flashing liquid flow, and a safety factor of 3 applied to the result. The modified Boyle method1161 uses a relief system capacity calculated on the basis of two-phase flow. The modified Boyle method is therefore ... 

The calculation of the required relief rate, Wgf is described in A6.2 below, and the calculation of the single-phase relief mass flow capacity per unit area, Gg, is described in A6.3 below. ... 

The Omega method calculates the two-phase flow capacity per unit area, G, of a nozzle or pipe of constant diameter. It evaluates the homogeneous equilibrium model (see 9.4.1) for two-phase flow. The Omega method is particularly convenient, when applicable, because it does not require the use of a computer. All properties can often be evaluated at the conditions in the upstream vessel, (which are known). Most other methods to evaluate G for two-phase flow require the use of appropriate computer codes (see Annex 4). Exceptions are given in 9.4. 

The pressure at which the flow capacity of a safety valve is calculated. It is usually 10% above the set pressure to ensure the valve is fully open. 

Ref. 119. These are treatment plant unit processes, not individual digesters, that produce and use digester gas the flow capacity is 14.2 X 103 m3/d. Calculated assuming 15-d hydraulic retention time (HRT). 

Rated coefficient of discharge (API) The coefficient of discharge determined in accordance with the applicable code or regulation which is used together with the actual discharge area to calculate the rated flow capacity of an SRV (see Section 7.1). 

Obtain the Taylor-Prandtl modification of the Reynolds analogy between momentum and heat transfer and give the corresponding analogy for mass transfer. For a particular system a mass transfer coefficient of 8.71 x 10-6 m/s and a heat transfer coefficient of 2730 W/m2K were measured for similar flow conditions. Calculate the ratio of the velocity in the fluid where the laminar sub-layer terminates, to the stream velocity. Molecular diffusivity = 1.5 x 10 9 m2/s. Viscosity = 1 mN s/m2. Density = 1000 kg/m3. Thermal conductivity = 0.48 W/m K. Specific heat capacity = 4.0 kJ/kg K. 

The first gas pipeline in the erstwhile Soviet Union [3] was from Saratov to Moscow which was about 325 mm (about 13 in.) in diameter. Based on this throughput capacity, new flow capacity value for 1000 mm, 1200 mm and 1400 mm diameter pipe was calculated to be 10, 15 and 20 times this original value, respectively. The consumption of metal per unit volume of gas transported, the capital investments, and operation and maintenance expenses can be reduced by using pipelines of larger diameter. 

FIG. 19-22 Open-area factor (F ) for flow-through screen-capacity calculation. 

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