This white paper provides an overview of orifice meter technology, its advantages and. Student solutions manual to accompany engineering fluid mechanics, 7 th edition clayton t. Switch between metric and imperial units in one click. Orifice meters with supercritical compressible flow, rg cunningham asme, july 1951 perrys chemical engineering handbook 7th edn rh perry, dw green flow measurement engineering handbook, 3rd edn rw miller note. In this paper, we developed a onedimensional compressible flow model to study the behavior of various diaphragmless drivers numerically. Friends, does anyone have any suggestions or rulesofthumb from their experience when sizing restriction orifices in compressible flow. When a flowing fluid at a given pressure and temperature passes through a restriction such as the throat of a convergentdivergent nozzle or a valve in a pipe into a lower pressure. Modeling choked flow through an orifice applied flow technology.
The current industrial standard iec 6053421 for sizing valves requires a series of flow tests to be completed which define three parameters of internal geometry. The compressible fluid flow rate is measured by differential pressure flow meter 8 25 psid with 0. Orifice flow calculation data sheet calculating an orifice diameter it is difficult to accurately calculate the flow of a gas or liquid through a tiny orifice due to the effect of the leading edge of the orifice. Effect of compressibility on the discharge coefficient of orifices and.
Orifice plate fluid mechanics mechanical engineering. Supercritical ratio control system utilizing a sonic flow. Hence, for achieving choked flow for the present work the length of the orifice plate l was assumed d. The calculation of compressible flow through orifice plates at high dp critical flow appears to be carried out incorrectly in most instances. International organization of standards measurement of fluid flow by means of pressure differential devices inserted in circular crosssection conduits running full. Investigation of flow through multistage restricting orifices.
A little downstream of the orifice the flow reaches. No such minimum value of y is provided for a square edge orifice indicating the limitations in using the crane method to evaluate choked flow through an orifice. Modeling a flow meter with compressible flow pipeflo professional has certain limitations concerning the use of compressible fluids in a piping network. Flow through orifice plates in compressible fluid service at. As the flow approaches the critical regime local sonic condition, measurements diverge from the theoretical result. Aft modeling choked flow through orifice fluid dynamics. For such flows, a correction factor in the form of a discharge coefficient is required to. Orifice meters, sometimes referred to as orifice fittings, satisfy most flow measurement applications and are the most common flow meter type in use today. In this chapter, the heat transfer between supercritical fluid flows and solid walls and that between compressible flows and solid walls is described. In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the pressure drop, computations using the massaveraged implicit navierstokes equations were applied to the axisymmetric pipe flows with the operating pressure ratio from 1. Improved method for determining flow rates in venturis, orifices and flow nozzles involving total pressure and static pressure measurements. Pressure drop control using multiple orifice system in. This is a worstcase condition and would probably only last a very short time. Lets go on to apply the knowledge of entropy to the flow of compressible fluids starting with isentropic flow.
Compressible flow in a tube 1 supercritical helium. The discharge coefficient of a simple plate orifice, for instance, is greatly dependent on the amount of jet contraction, and this may be influenced by changes in downstream pressure even under criticalflow conditions. The orifice flow meter has the advantages of compact size and weight. Oct 23, 2012 restriction orifice sizing for compressible flow posted in industrial professionals. Cunningham, transactions of the asme, july latexman chemical 29 apr 19 14. The concentric orifice plate flow meter has a sharp squareedged concentric bore that provides an almost pure line contact between the plate and the fluid, with negligible friction drag at the boundary.
The orifice, nozzle and venturi flow rate meters use the bernoulli equation to calculate fluid flow rate using pressure difference through obstructions in the flow sponsored links in a flow metering device based on the bernoulli equation the downstream pressure after an obstruction will be lower than the upstream pressure before. Experimental parametric equation for the prediction of. Orifice ports are accurately machin ed f or precision measur ements. Petrochemical company reduces risk of lost production. References for small bore orifice for gas flow calculation top of page american society of mechanical engineers asme. In this case we will consider the flow to be adiabatic also, that is, with no heat transfer. The orifice meter, sometimes also called a head loss flow meter, is chosen most frequently because of its long history of use in many applications, versatility. This purpose is accomplished in, essentially, two steps. Flow measurement free download as powerpoint presentation.
A wide range of unsteady compressible flow phenonema exist and these are covered in the works of glass and sislian 1994 and kentfield. Orifice inlet densities ranged from 111 kgm 3 to 630 kgm 3. The manufacturers should be contacted for detailed information. If the fluid is a liquid, a different type of limiting condition also known as choked flow occurs when the venturi effect acting on the liquid flow through the restriction causes a decrease of the liquid pressure beyond the restriction to below that of the liquids vapor pressure at the prevailing liquid temperature. The study of compressible flow is relevant to highspeed aircraft, jet engines, rocket motors, highspeed entry into a planetary atmosphere, gas. The overall pressure loss in the pipe due to an orifice plate is lower than the measured pressure, typically by a factor of application. The calculation of the valve size required to control a reservoir condition is a function of the valves internal geometry. Heat transfer of supercritical fluid flows and compressible.
American gas association, aga gas measurement manual, american. An orifice meter is a device used for measuring the rate of fluid flow. The present invention provides a method and device for ascertaining flow rate of a fluid based on measured values of the upstream fluid totalpressure and staticpressure measured downstream the entrance of a flow constricting member, such as an orifice plate, a flow nozzle or a venturi. Calculation of flow through nozzles and orifices neutrium. In view of the acknowledged difficulty in metering unsteady flows, this is a most valuable property, and it is thought that critical flow meters are very suitable for measuring the output of reciprocating compressors, free piston gasifiers and other plant delivering gas at high pressure. Isentropic exponent applicable for compressible orifice measurement meter piping and header velocity fps maximum, minimum, normal. Nozzles and orifices are often used to deliberately reduce pressure, restrict flow or to measure flow rate. The flow does act as a compressible fluid of low speed of sound and exhibits shock structure. Download limit exceeded you have exceeded your daily download allowance. An orifice plate is a device used for measuring flow rate, for reducing pressure or for restricting. This is because gases are compressible, and with traditional technologies dporifice, turbine, rotary, diaphragm, process pressure, temperature, and fundamentals of coriolis meters for gas measurement tom obanion, micro motion, inc.
Pdf discharge coefficients for compressible flow through small. Modeling a flow meter with compressible flow engineered. Driver performance is optimized by accelerating the barrier element before breaching to minimize the opening time of the. Singlephase and twophase flow through thin and thick. First, the physical fundamentals of supercritical fluids and compressible flows are explained. When a flowing fluid at a given pressure and temperature passes through a restriction such as the throat of a convergentdivergent nozzle or a valve in a pipe into a lower pressure environment the fluid. Article information, pdf download for criticalflow nozzle meter and its. The orifice flow meter, flow nozzle meter, and venturi meter are three commonly used types of differential pressure meter for pipe flow measurement.
Select a subscription plan and enable the full service. The parameter that becomes choked or limited is the velocity. Because of the distance from the orifice, exact location is not critical, but. Cunningham in his paper orifice meters with supercritical compressible flow, ref.
The parameter that becomes choked or limited is the fluid velocity. The limits of the darcy weisbach equation pertaining to compressible fluids are covered on page 18 of the method of solution for pipeflo and elsewhere in this knowledge base. Choked flow is a fluid dynamic condition associated with the venturi effect. For a wellformed convergent nozzle, the experimental maximum flow ratio is essentially identical with the theoretical criticalpressure ratio. The beta or diameter ratios of concentric orifice plates range from 0. Us5365795a improved method for determining flow rates in. The flow of supercritical carbon dioxide through short orifices was measured. This technique, referred to as insitu calibration, is something like proving a linear meter. By using a mechanical energy balance, compressible fluid flow in unchoked conditions may.
Consider gas flowing in a duct which varies in size. However, if meters are misapplied to applications and are subject to erosion or corrosion or over pressurization of the. Isentropic exponent applicable for compressible orifice measurement meter piping and header velocity fps maximum, minimum, normal prover velocity fps maximum, minimum, normal. However, the conventional singlehole orifice flow meter suffers from higher pressure drop due to lower discharge coefficient. Us5403089a method and apparatus for metering and mixing. It uses bernoullis principle which states that there is a relationship between the pressure of the fluid and the velocity of the fluid. Compressible flow equations for fuel orifices revision 3. Method to simulate critical flow of hydrogen through convergentdivergent. Criticalflow nozzle meter and its application to the. Criticalflow nozzle meter and its application to the measurement of. An orifice plate is a thin plate with a hole in it, which is usually placed in a pipe. Pdf this paper presents a study of the compressibleflow behavior of light gases. Most modern browsers have builtin pdf readers if you have problems opening this file in your browser, check your browsers or computer systems settings. While all flows are compressible, flows are usually treated as being incompressible when the mach number is less than 0.
Restriction orifice sizing for compressible flow industrial. Small bore orifice flow meter calculation for gas flow. It uses the same principle as a venturi nozzle, namely bernoullis principle which says that there is a relationship between the pressure of the fluid and the velocity of the fluid. Flow measurement engineering handbook, third edition. These are devices that have applications in flow measurement. The flow rate signal is then sent to the ratio controller 10, not shown. The flow at which depth of the channel is greater than critical depth, velocity of flow is less than critical velocity and slope of the channel is also less than the critical slope is known as subcritical flow. The core flow experienced the expected behavior in its transition from subcritical to supercritical pressure, namely, a reduction in surface tension. Each orifice plate has model number and orifice diameter stamped on tab for easy identification and selection. Model 5 720 calibrated orifice flow meters are desig ned for measurin g flows of air or g ases at pressures up to 100 psig and temperatures to 700 of. Discharge coefficients for compressible flow through smalldiameter orifices and convergent nozzles article pdf available in chemical engineering science 467. The channel is called as deep channel for subcritical flow. The discharge coefficient in incompressible flow, using deionized di water as the working fluid, rises and peaks at a critical reynolds number, 200.
This flow condition is often encountered on gas plants, compressor stations and pipelines where orifice plates are commonly used as a cheap and convenient way to regulate blowdown and pressurising rates. In supercritical compressible flow, as will be explained more fully below, the point of minimum area lies very close to the back side of orifice plate. Difference between compressible and incompressible fluids. Orifice plate sizing calculator pipe flow calculations.
All three use a constriction in the flow path like an orifice plate to cause a pressure drop across the meter that can be measured and correlated with flow rate. An orifice is an obstruction meter used to determine the flow rate of a fluid. Compressible gas flow university of texas at austin. The key difference between compressible and incompressible fluids is that the compressible fluids occur in reality whereas the incompressible fluids is a concept developed for ease of calculations fluids are either gases or liquids that take the shape of the container. Would be happy to provide more data and details if desired. This is true for compressible and noncompressible fluids. T he influence of the coaxial flow, as discussed by davis and chehroudi 61 is to accelerate the liquid breakup process for subcritical jets and to enhance mixing for supercritical turbulent jets. Compressible flow is the branch of fluid mechanics that deals with flows having significant changes in fluid density. There is no time dependent shift in the calibration factor due to the lack of moving or wearing parts. The maximum velocity and minimum static pressure occurs.
When a fluid whether liquid or gaseous passes through the orifice, its pressure builds up slightly upstream of the orifice. For any valve designed to have a unique control characteristic would require a manufacturer to first. All matter is composed of exceedingly tiny particles called molecules. It uses the same principle as a venturi nozzle, namely bernoullis principle which states that there is a relationship between the pressure of the fluid and the velocity of the fluid. Y has a minimum value corresponding to choked flow. An orifice meter is a conduit and a restriction to create a pressure drop. Sub critical flow is also called as slow or tranquil flow. This article provides calculation methods for correlating design, flow rate and pressure loss as a fluid passes through a nozzle or orifice. According to principles set forth herein, this parameter allows simplification of flow rate determinations. A new theory for the compressible flow through an orifice is presented which provides a significant advance over the approach currently employed. Both the pressure and temperatu re profiles along the flatplate indicate a circular core of high pressure and temperature, falling off to lower values away. As the flow approaches the critical regime local sonic condition, measurements diverge from the theoretical result due to the nononedimensionality of the flow.
Definition of critical, subcritical and supercritical flow. An orifice plate is a device used for measuring the volumetric flow rate. On the compressible flow through an orifice journal of. Either a volumetric or mass flow rate may be inferred with an orifice meter depending on the calculation associated with the orifice plate. Orifice plates are most commonly used to measure flow rates in pipes, when the fluid is singlephase rather than being a mixture of gases and liquids, or of liquids and solids and wellmixed, the flow is continuous rather than pulsating, the fluid. Coriolis flowmeters are well known for their long term stability. Modeling choked flow through an orifice applied flow. Bengtson orifice and venturi pipe flow meters for liquid.
In round numbers at ambient temperature the compressibility affects volume by 0. The subsonic and criticalflow regions for 16 orifice and nozzle flow. I need to place an ro in a nitrogen inerting line to a tank in the event a regulator fails. The present invention is directed to methods and apparatus for effectively proportionating a mixture of compressible and noncompressible fluids and in particular, the present invention is directed to apparatus and methods for forming a coating composition mixture containing a substantially accurate proportionated amount of at least one supercritical fluid used as a viscosity reduction diluent. Measurement of fluid flow using small bore precision orifice meters. Through rigorous testing, you could develop a unique cd for each of your orifice meters. The parameter that becomes choked or limited is the velocity or the mass flow rate. Stresses on an infinitesimal volume of a viscous fluid. When a flowing fluid at a given pressure and temperature passes through a constriction such as the throat of a convergentdivergent nozzle or a valve in a pipe into a lower pressure environment the fluid. Improved method for determining flow rates in venturis. Measurements of the flow of supercritical carbon dioxide. In fluid dynamics, the compressibility of a fluid is a very important factor.
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