Orifice Size - Sizing

Spray characteristics of pressure nozzles depend on the pressure and nozzle-orifice size. Pressure affects not only the spray characteristics but also the capacity. If it is desired to reduce the amount of liquid sprayed by lowering the pressure, then the spray may become coarser. To correct this, a smaller orifice would be inserted, which might then require a higher pressure to produce the desired capacity, and a spray that would be finer than desired might result. Multiple nozzles tend to overcome this inflexible charac teristic of pressure atomization, although several nozzles on a diyer complicate the chamber design and air-flow pattern and risk collision of particles, resulting in nonuniformity of spray and particle size. 

The set pressure of a conventional valve is affected by back pressure. The spring setting can be adjusted to compensate for constant back pressure. For a variable back pressure of greater than 10% of the set pressure, it is customary to go to the balanced bellows type which can generally tolerate variable back pressure of up to 40% of set pressure. Table 2 gives standard orifice sizes. 

The termination of the cone section is the apex orifice. The critical dimension is the inside diameter at the discharge point. The size of this orifice is determined by the application involved and must be large enough to permit the solids that have been classified to underflow to exit the cyclone without plugging. The normal minimum orifice size would be 10% of the cyclone diameter and can be as large as 35%. Below the apex is normally a splash skirt to help contain the underflow slurry in the case of a hydroclone. 

As normally designed, vapor flow through a typical high-lift safety reliefs valve is characterized by limiting sonic velocity and critical flow pressure conditions at the orifice (nozzle throat), and for a given orifice size and gas composition, mass flow is directly proportional to the absolute upstream pressure. 

K = Correction factor for viscous fluids, determined from Figures 15 and 16. A trial-and-error selection of orifice size is required in the determination of this factor. 

The chart given in Figure 16 can be used in the following manner in order to size a relief valve for liquid service. First, determine the area required, A, without any viscosity correction (i.e., for K = 1). Then select the next larger standard orifice size from manufacturer s literature. Determine the Reynolds number, based on the following definition ... 

Number of Valves Required - Normally a manufacturer s standard PR valve with Drifdce area equal to or larger than the calculated requirement is specified. In some cases, e.g., large reheving rates or to prevent chattering, two or more valves are necessary. Likewise, if there is an appreciable difference between the calculated orifice size and the available size, multiple PR valves are desirable to more nearly match the available area to the required orifice area. The column for "spares" indicates the requirement, if any, for spare PR valves installed on the equipment. Normally, this applies only in the case of refinery preference or local regulations, but is required in many European countries. 

Nolo that a preliminary orifice size must be determined in order to calculate Reynolds number. If the viscosity correction is significant, it may be necessary to iterate to get a final size. 

Relief valves are most often sold using the standard orifice sizes shown in Table 13-3. Once a required area is calculated from the applicable formulas, the next larger standard orifice size is specified. 

Calculate orifice size for pilot-operated relief valve. 

The viscosity of ttie liquid may reduce the velocity and capacity enough to require a larger orifice size than the usual liquid capacity equation would indicate This simplified viscosity chart and the Kj viscoscorrection factors obtainable from i( are for use m properly sizing relief valves intended for viscous liquid ser vice. Equations and graphs used m prepanng this chart reflect conservative engmeenng data on the subject... 

Since the viscosity correction factor is dependent upon the actual orifice area, direct solution is not possible and a trial orifice size must be found before Ihe Ku can be determined accurately. 

Select Ihe next larger orifice size, or an M" orifice with 360 sq in. orifice area. (This should be about 20% greater than the calculated area to allow lor reduction of capacity due to Ihe viscosity correction factor "Ku")... 

When a relief valve is sized for viscous liquid service, it is suggested that it be sized first as for nonviscous type application in order to obtain a preliminary required discharge area, A. From manufacturer s standard orifice sizes, the next larger orifice size should be used in determining the Reynold number R, from either of the following relationships ... 

After the value of R is determined, the factor Kvt is obtained from the graph. Factor Kv is applied to correct the "preliminary required discharge area. If the corrected area exceeds the chosen standard orifice area", the above calculations should be repeated using the next larger standard orifice size. 

In order to study the influence of ions on the deposition process, a reliable quantification of the ion flux and energy is imperative. This flux cannot be determined directly from the detected number of ions in an lED as measured by means of QMS, for three reasons [332]. First, the orifice size decreases during subsequent measurements due to deposition of a-Si H on the edges of the orifice. Second, due to the limited acceptance angle of the mass spectrometer system, only a fraction of the ions that arrive at the substrate is actually detected. This fraction depends on the type and number of interactions that an ion experiences while traversing... 

Standard Orifice Sizes for Flanged Steel Safety Relief Valves... 

Ghadiri, M., Cleaver, J. A. S., and Tuponogov, V. G., Influence of Distributor Orifice Size on Attrition in the Jetting Region of Fluidized Beds, Preprint Fluidization VIII, 2 799 (1995)... 

Another important application of plain-orifice atomizers is jet engine afterburner injectors. The fuel injection system typically consists of one or more circular manifolds supported by struts in a jet pipe. The fuel is supplied to the manifold by feed pipes in the support struts and sprayed into the combustion zone through the orifices in the manifold. Increasing the number of orifices and/or using a ringlike manifold may promote uniform distribution of liquid. To reduce the risk of blockage of orifices, a minimum orifice size of 0.5 mm is usually regarded as practical for kerosene-type fuels. 

Harrison and Leung1561 have shown that the frequency of formation of bubbles at an orifice (size range 1.2-25 mm) is independent of the bed depth, the flowrate of gas and the properties of the particles constituting the continuous phase, although the frequency of formation depends on the injection rate of gas, tending to a frequency of 18-21 s 1 at high flowrates. 

Primary and auxiliary sealing schematics and bills of materials including seal fluid, fluid flows, pressure, pipe and valve sizes, instrumentation, and orifice sizes. ... 

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