Flow through orifices

Octane/toluene/phenol equilibria, 416 Olefin production, 33,40 Orifices, flow through, 95 Osmosis, 631 equation, 631... 

The viscosity is determined by measuring the time it takes for a crude to flow through a capillary tube of a given length at a precise temperature. This is called the kinematic viscosity, expressed in mm /s. It is defined by the standards, NF T 60-100 or ASTM D 445. Viscosity can also be determined by measuring the time it takes for the oil to flow through a calibrated orifice standard ASTM D 88. It is expressed in Saybolt seconds (SSU). 

Equation 36 must be corrected for changes in the drop shape and for the effects of the inertia of Hquid flowing through the orifice, viscous drag, etc (64). As the orifice or aperture diameter is increased, d has less effect on the drop diameter and the mean drop si2e then tends to become a function only of the system properties ... 

Flow. The free flow of a powder through an orifice depends on the orifice which is standardized for the testing of the powder (14). Flow, therefore, depends not only on friction between powder particles, but also on friction between the particles and the wall of the orifice. Flow is usually expressed by the time necessary for a specific amount of powder (usually 50 g) to flow through the orifice. 

One proposed simplified theory (4) provides reasonably accurate predictions of the internal flow characteristics. In this analysis, conservation of mass as well as angular and total momentum of the Hquid is assumed. To determine the exit film velocity, size of the air core, and discharge coefficient, it is also necessary to assume that a maximum flow through the orifice is attained. 

Section 10 of this Handbook describes the use of orifice meters for flow measurement. In addition, orifices are commonly found within pipelines as flow-restric ting devices, in perforated pipe distributing and return manifolds, and in perforated plates. Incompressible flow through an orifice in a pipehne as shown in Fig. 6-18, is commonly described by the following equation for flow rate Q in terms of pressure drop across the orifice Ap, the orifice area A, the pipe cross-sectional area A, and the density p. 

In chemical process applications, one-dimensional gas flows through nozzles or orifices and in pipelines are the most important apphcations of compressible flow. Multidimensional external flows are of interest mainly in aerodynamic applications. 

FIG. 6-55 Critical cavitation number vs. diameter ratio (3. Reprinted from Thotpe, Flow regime transitions due to cavitation in the flow through an orifice, " Int. J. Multiphase Flow, i6,1023-1045. Copyright 1990, with kindper-mission from Elsevier Science, Ltd., The Boulevard, Langford Lane, Kldlington 0X5 1GB, United Kingdom. )... 

Flow is an important measurement whose calibration presents some challenges. When a flow measurement device is used in applications such as custody transfer, provision is made to pass a known flow through the meter. However, such a provision is costly and is not available for most in-process flowmeters. Without such a provision, a true cahbration of the flow element itself is not possible. For orifice meters, calibration of the flowmeter normally involves cahbration of the differential pressure transmitter, and the orifice plate is usually only inspected for deformation, abrasion, and so on. Similarly, cahbration of a magnetic flowmeter normally involves cahbration of the voltage measurement circuitry, which is analogous to calibration of the differential pressure transmitter for an orifice meter. 

The orifice-riser distributor is designed to lay the hquid carefully onto the bed, with a minimum of contact with gas during the process. It can be designed to provide a large number of liquid streams, with the limit of sufficient liquid head to provide uniform liquid flow through the orifices. The gas risers must oe designed to accommodate the expected variations in flow rate, often with a minimum of pressure drop. For veiy distribution-sensitive packings, it is necessaiy to include pour points in the vicinity of the column wall (to within 25 mm). 

For conditions approaching constant flow through the orifice, a relationship derivea by equating the buoyant force to the inertia force of the liquid [Davidson et al., Tran.s. In.stn. Chem. Engr.s., 38, 335 (I960)] (dimensionally consistent),... 

NEM for Two-Phase Ormce Discharge With flow through an orifice or nozzle, the flash is delayed, and the delay time depends on... 

In the long term, filters and strainers become clogged this is their purpose. Minerals and scale start forming on the internal pipe walls and this reduces the interior diameters on the pipe. A 4 inch pipe will eventually become a 3.5 inch pipe. This moves the pump on its curve beeause as the pipe diameter reduces, the velocity must increase to maintain flow through a smaller orifice. The Hf and Hv increase by the square of the velocity increase. 

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. 

The soft-seated spring-loaded pilot valve is so constructed as to have a long built-in blowdown. For a flowing type pilot, at the point where the pilot supply line feeds the system pressure to the pilot relief valve, it passes through a variable orifice, which is also the main valve blowdown adjustment. When the pilot opens, the flow through the supply line causes an immediate pressure drop across the orifice. By adjusting the size of the orifice and thus the amount of pressure drop across it, one can obtain any desired system blowdown (5 to 7% is typical). 

Critical and Subcritical Flow - The maximum vapor flow through a restriction, such as the nozzle or orifice of a pressure relief valve, will occur when conditions are such that the velocity through the smallest cross-sectional flow area equals the speed of sound in that vapor. This condition is referred to as "critical flow" or "choked flow . 

Chokes are used to control flow where there is a large pressure drop. They can either be adjustable, where the opening size can be varied manually as shown Figure 15-14 and 15-15 or have a fixed size orifice. Due to the erosive nature of the fluid flow through a choke, they are constructed so beans, discs, and seats can be easily replaced. 

In a later paper, Brasie (1976) gives more concrete recommendations for determining the quantity of fuel released. A leak potential can be based on the flashing potential of the full amount of liquid (gas) stored or in process. For a continuous release, a cloud size can be determined by estimating the leak rate. For a combined liquid-vapor flow through holes of very short nozzles, the leak rate (mass flow per leak orifice area) is approximately related to the operating overpressure according to ... 

In general, the sonic or critical velocity is attained for an outlet or downstream pressure equal to or less than one half the upstream or inlet absolute pressure condition of a system. The discharge through an orifice or nozzle is usually a limiting condition for the flow through the end of a pipe. The usual pressure drop equations do not hold at the sonic velocity, as in an orifice. Conditions or systems exhausting to atmosphere (or vacuum) from medium to high pressures should be examined for critical flow, otherwise the calculated pressure drop may be in error. 

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