Effective orifice area

S = Specific gravity at flowing temperature versus water at 15°C fi= Viscosity of fluid at flowing temperature, centipoises or mPa-s A = Effective orifice area, mm from the manufacturer s literature). 

Sizing methods for pilot-operated pressure relief valves are in accordance with the accepted formulas described above, utilizing the appropriate discharge coefficients and effective orifice areas as recommended by the valve manufacturer. The following points should be noted ... 

After the value of R is determined (in Appendix G), the factor Kv is obtained from the graph in Appendix G. Factor Kv is applied to correct the preliminary required discharge area. If the corrected area exceeds the chosen effective orifice area, the above calculations should be repeated using the next larger effective orifice size, as the required effective orifice area of the valve selected cannot be less than the calculated required effective area. 

In this section, we will describe the techniques that may be used for calculating the required effective orifice area for an SRV application on two-phase flow based on the work done by the Design Institute for Emergency Relief... 

From API Std. 526 we would select an H orifice relief valve with effective orifice area 0.785 in. A size 2H3 carbon steel relief valve will allow a set pressure up to 740 psig in the expected range of operation temperature. In practice, however, we would have to consider two-phase flow due to entrainment of boiling liquid with the vapor and might select a larger orifice size after more detailed design. 

The pressure drop allowed through the inlet and discharge lines is unlimited as long as the capacity of the line is adequate for the relief requirements. That is, at the required flow rate the vessel pressure must not exceed the maximum allowable accumulated pressure. In sizing a safety disc, it is usually assumed that the entrance loss at the nozzle is the governing restriction insofar as capacity is concerned. Thus the effective orifice area is considerably larger than the effective orifice area of a safety valve of the same pipe size. Consequently,... 

In vitro pressure drop, flow rate, and regurgitation data were in most cases obtained directly from their respective articles. From these data the valve areas (VA) (i.e. effective orifice area) were calculated from the following formula ... 

When prelimitwy PRV sizes are calculated for various relief cases, select the largest one as the required PRV orifice area. From Manufacturer s catalog or API 26, we will be able to select which relief valve to use, and what arc its inlet and outlet nozzle sizes. In general, PRV is designated with a letter 1o indicate its size. Commonly used PRV and its effective orifice area arc as follows ... 

Pressure Drop Effective Orifice Area and Performance Index Regurgitation Flow Patterns and Turbulent Shear Stresses Percutaneous Valves Implications for Thrombus Deposition Durability Wear Fatigue Mineralization... 

TABLE 77.1 Effective Orifice Areas of Different Prosthetic Aortic Valve Designs... 

In addition to valve velocity, the manufacturer can furnish the effective flow area of the valve. This area is determined by measuring the pressure drop across the valve with a known flow rate and then calculating an equivalent orifice area that provides the same pressure drop. Valves with larger effective flow areas have less pressure drop and better efficiencies. The effects of the seat area, the lift area, and the flow paths are automati-... 

A= effective discharge area, in square inches (from manufacturers standard orifice areas). 

Ap = Final column inside net area, ft, or in. a = Surface area of an orifice, in. a = Effective interfacial area for contacting gas and liquid phases, ft /ft. Because this is very difficult to evaluate, it is usually retained as a part of the coefficient such as Kca or Kj a a = Area of transfer surface per unit of tower volume in water cooling towers, ft /ft, or, termed contact area... 

The former observation is concerned with the effective electrode area. In the early part of drop life, its size is similar to that of the capillary orifice. A significant part of the drop is thus not in contact with the solution, a fact which qualitatively explains the lower observed currents. Also, close to the capillary surface, the diffusion process will be restricted, the so-called shielding effect. This is particularly pertinent with modern polarographic equipment where mechanical drop timers are often used in conjunction with short drop times. These problems have been discussed recently [59]. The following modification was proposed... 

Thus, the rate of outflow is expressible as a first-order kinetic process with a rate coefficient that is a function of pressure, temperature, molecular weight, and the orifice area to reactor volume ratio. The effective area exit... 

Orifice area See effective discharge area (Figure 3.5). API has determined standard orifice areas from D to T, each with a corresponding orifice size (in2 or cm2) (See Section 4.2.3). 

After determining the required orifice area necessary to flow the required capacity, the appropriate valve size and style may be selected. It should have a nominal effective area equal to or greater than the calculated required effective area. API effective areas and coefficient of discharge for different manufacturers can be found in their respective catalogues or in their comprehensive sizing software. ... 

The effective orifice size and effective coefficient of discharge specified in the API Standards are assumed values used for initial selection of an SRV size from configurations specified in API 526, independent of an individual valve manufacturer s design. In most cases, the actual area and the rated coefficient of discharge for an API-lettered orifice valve are designed so that the actual certified capacity meets or exceeds the capacity calculated using the methods presented in API 520. 

When an SRV is sized for viscous liquid service, it is suggested that it would be sized first as for a non-viscous type application in order to obtain a preliminary required effective discharge area (A). From the manufacturer s standard effective orifice sizes, select the next larger orifice size and calculate the Reynolds number, Re, per the following formula ... 

A = Effective discharge area (in2, from manufacturers standard orifice... 

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