I would like to know the minimum parameters required for predicting the pressure drop across an orifice plate. Steam flow rates can be measured by using orifice plates. The f l is the square root of the ratio of valve pressure drop to the pressure drop from the inlet pressure to the pressure at the vena contracta. May 11, 2015 i am in need of a formula to calculate mass flow rate of liquids through a known orifice size and known pressure secondary pressure. Compressible flow pressure drop calculation pipelines. I need to do this for multiple liquids and i know the specific gravity for each liquid. I did not understand what it is that you are asking. An orifice meter is a conduit and a restriction to create a pressure drop. Flow through orifice plates in compressible fluid service at high pressure drop nov 08 2010 01. Flow through orifice plates in compressible fluid service. 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. Pressure drop online calculator for mobile and pdaelement of pipe. Compressible flow through an orifice cfd online discussion. Nozzles and orifices are often used to deliberately reduce pressure, restrict flow or to measure flow rate.
Discharge coefficients for compressible flow through smalldiameter. Fm 308 flow measurement by venturi and orifice meter objectives. How do i calculate the pressure drop of air across an. Venturi meter and orifice meter are the commonly used flow meters for measuring massvolumetric flow rate or velocity of the flowing fluid. K, is tabulated or plotted in books for different orifice shapes. When there is no flow, there is no differential pressure. The pressure drop caused by friction of laminar flow does not depend of the roughness of pipe. Design guide for multistage restriction orifices ros. Subscript 1 denotes conditions at pipe inlet and 2 denotes at pipe outlet.
Nozzles and diffusers and converging diverging nozzles 2. Orifice flow meters are used to determine a liquid or gas flow rate by measuring the differential pressure p 1p 2 across the orifice plate. Modeling choked flow through an orifice applied flow technology. History of orifice flow measurement across the orifice figure 2 increases when the rate of flow increases. The pressure drop is measured using a differential pressure sensor, and when calibrated, this pressure drop becomes a measure of flow rate. Do the pressure drop remains same if we devide the total hole area to n number of holes. Pressure drop control using multiple orifice system in. Since the pressure at 1 will be higher than the pressure at 2 for flow moving from 1 to 2, the pressure difference as defined will be a positive quantity. I used total pressure, total temperature for the inlet of the plenum and fixed pressure at the outlet of the pipe. One dimensional isentropic flow compressible pipe flow. A nozzle, venturi or thin sharp edged orifice can be used as the flow restriction. 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.
Usually extremes are considered like adiabatic and isothermal flow. How i can calculate the temperature after a stage of orifice plate in which we drop pressure from p1 to p2. Small bore orifice flow meter calculation for gas flow. Large diameter orifice flow meter calculation for gas flow. To calculate the flowrate of a fluid passing through an orifice plate, enter the parameters below. Consider gas flowing in a duct which varies in size. Pressure drop evaluation along pipelines petrowiki. The present cfd data showed that the orifice systems, which have been applied to incompressible flow regime to date, could not be used for the high operating pressure ratio flows. An orifice meter is a device used for measuring the rate of fluid flow. Pressure drop in pipe fittings and valves equivalent length. How i can calculate the temperature after a stage of orifice.
Compressible flow in pipe, adiabatic, isothermal flow, specific volume, pressure drop in compressible flow, exact relation between pressure and specific volume is required, but it is not easily determined in each specific problem. The differential pressure is proportional to the square root of the velocity. For long lines, you can break up the line into segments that each have a pressure drop that keeps the change in density to. Orifice plate sizing calculator pressure drop, pipe. In order to use any of these devices for measurement it is necessary to empirically calibrate them. By measuring the difference in fluid pressure across tappings upstream and downstream of. Since the pressure drop and the flow rate are quite high 3 bar.
Flow of compressible fluid like vapors and gases in a pipe. By using a mechanical energy balance, compressible fluid flow in unchoked. When a flowing fluid at a given pressure and temperature passes through a. Venturis also require much less straight pipe upstream. Pdf discharge coefficients for compressible flow through small. Pressure drop along pipe length fluid flow hydraulic and. The table given below gives the discharge of air through an orifice in cu. Softwarefactory norbert schmitz am moenchhof 7a 67105 schifferstadt germany tel. An orifice plate is a device used for measuring flow rate, for reducing pressure or for restricting. 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. Fm 308 flow measurement by venturi and orifice meter.
On the flow of a compressible fluid through orifices by d. I am in need of a formula to calculate mass flow rate of liquids through a known orifice size and known pressuresecondary pressure. Cunningham 1951 first drew attention to the fact that choked flow will not occur across a standard, thin, squareedged orifice. This pressure drop would not be affected by the roughness of the pipe attached to it. Orifice flow rate measurement meters are typically less expensive to install and manufacture than the other commonly used differential pressure flow rate meters. We assume that the thickness of the plate is small in comparison to the pipe diameter. For the piping that is carrying flow to the orifice plate, you want a maximum gas or vapor velocity of approximately 200300 fts, and a maximum liquid velocity of approximately 10 fts, because higher velocities lead to too much pressure drop per foot of pipe, meaning that too much energy is lost. American gas association, aga gas measurement manual, american. If the pressure drop due to the flow of a gas through a.
If the reynolds number 2320, you have turbulent flow. The values of upstream pressure,pipe size and orifice diameter is enogh to predict the pressure drop. A venturi meter is more efficient, but usually more expensive and less accurate unless calibrated in a laboratory than an orifice plate. Values of y as a function of the pressure drop ratio defined as the pressure differential divided. Jobson by making certain basic assumptions, the author has determined a theoretical expression for the contraction coefficient, c, appropriate to an orifice when transmitting a compressible fluid, either. Lets go on to apply the knowledge of entropy to the flow of compressible fluids starting with isentropic flow. All gases flow from upstream higher pressure sources to downstream lower. When the velocity increases, the pressure decreases and vice versa. Several of the assumptions are listed and discussed. The orifice interval did not strongly affect the total pressure drop, but the orifice area ratio more than 2. Compressible gas flow generally represents a flow that the downstream density is less than 90% of the upstream density. Accepting this makes our hydraulic pressure drop calculations in piping much easier to understand. The various types of fluid flow are dis cussed, and the euler equations are developed. Formulas for flow rate through orifice physics forums.
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. In this case we will consider the flow to be adiabatic also, that is, with no heat transfer. The effect of a rounded plate is a matter of detail and will not be considered here. The diagram below indicates steam flow rate lb s hr through orifices ranging diameter 2 to 12 and 2 300 psig steam line pressure downstream pressure equals atmospheric pressure. Compressible gas flow calculators for pressure drop, pipe. Unlike liquids, gases are compressible, and the change in the conditions of the fluid as it moves down the pipe must be considered in these calculations. To find the coefficient of discharge for orifice meter. A flow rate of 150 usgpm through a 3 globe valve with a c v of 105 us units would result in a pressure drop of 2. Choked flow is a fluid dynamic condition associated with the venturi effect. How i can calculate the temperature after a stage of. Flow and pressure drop of highly viscous fluids in small aperture orifices a thesis presented to the academic faculty by lalit kumar bohra in partial fulfillment of the requirements for the degree. Consider an orifice plate placed in a pipe flow as shown in fig.
Hi i have an orifice on a sea water discharge line in order to reduce the pressure to the one present in a downstream common discharge. Jun 11, 2007 pressure drop for compressible fluids gas posted in industrial professionals. The parameter that becomes choked or limited is the fluid velocity. A controversy was found in the literature between hasegawa1 and dagan2 papers. On the flow of a compressible fluid through orifices. Flow through orifice plates in compressible fluid service at.
Practical for larger tube diameters and for dirty fluid. Orifice plates are small and inexpensive but do not recover the pressure drop as well as a venturi, nozzle, or venturinozzle does. A fluid passing though an orifice constriction will experience a drop in pressure across the orifice. Introduction to compressible flow mechanical engineering. These values were about 47% larger than the literature values from perrys handbook. Why does compressible flow never choke in a thinplate orifice. Pressure drop for compressible fluids gas industrial. I am investigating the effects of sound waves on the flow through an orifice.
Calculation of flow through nozzles and orifices neutrium. Orifice flow meters are used to determine a liquid or gas flow rate by measuring the differential pressure p 1 p 2 across the orifice plate. The discharge coefficient for knifeedge orifices correlates very well with a dimensionless pressure drop for the entire range of diameters, gases, pressures and. There are practical considerations involved in sizing an orifice plate and the associated piping. How do i calculate the pressure drop of air across an orifice. Discharge of air through an orifice equation engineers edge. To find the coefficient of discharge for venturi meter. Design guide for multistage restriction orifices ros plates with 1 hole and n 3 holes technical report march 2016 with 4,255 reads how we measure reads. Orifice flow meters are generally less expensive to install and manufacture than the other commonly used differential pressure flow meters.
For compressible flow, break up the line into segments short enough such that the pressure drop is less than 10% of the inlet pressure to each segment. There is an irregular motion of fluid particles in directions transverse to the direction of the main flow. If the piping were galvanized steel with a roughness of 0. Multi hole orifice pressure drop pipelines, piping and. Fluid flow table of contents hydraulic and pneumatic knowledge. Based on the magnitude of pressure drop, flow rate can be calculated. Pressure drop for compressible fluids gas posted in industrial professionals. Two phase pressure drop the calculation of pressure drop in twophase flow is very complex and is based on empirical relationships to take into account the phase changes that occur because of pressure and temperature changes along the flow, the relative velocities of the phases, and complex effects of elevation changes.
This article provides calculation methods for correlating design, flow rate and pressure loss as a fluid passes through a nozzle or orifice. Subscript 1 denotes conditions at pipe inlet and 2 denotes. In hasegawa paper, measurements of the pressure drop across orifices for laminar flow were done in an aperture diameter as small as 8 microns. The pressure drop calculation formula for the pipe is explained in more detail below. Orifice plate pressure drop calculator is used for flow rate measuring in pipe systems. Orifice sizing principles chemical engineering now. The basic equation for calculating the pressure drop through an orifice or venturi is the bernoulli equation. This tool calculates flow of a single phase compressible fluid through a pipe for a given pressure drop. Throttles flow regulators, an obstruction in a duct that controls pressure drop. The diagram below indicates steam flow rate lb s hr through orifices ranging diameter 2 to 12 and 2 300 psig steam line pressure. An orifice meter is an easy method to measure singlephase, continuous flow rates in large pipes and is relatively inexpensive. The flow is fed from a plenum through the orifice into a pipe. As a starting point, i need to set up a flow with certain pressure drop across the orifice. Compressible fluid flow through an orifice by herschel nathaniel waller, jr.
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