The pressure along the meter is obtained using the 11 pressure taps at the locations shown on the diagram. The eccentric or more costly segmental orifice is used for more difficult fluids. The inlet diameter equals d 26 mm and the throat diameter d 16 mm. Inserttype venturi flow meter installation and operation. Meters should have at least 10 pipe diameters of smooth, clean, straight pipe upstream and downstream for accurate readings. To find the coefficient of discharge for venturi meter. By employing the continuity equation and bernoullis principle, the volumetric flow rate through the orifice meter can be calculated as described previously for venturi meter. Each has built in excel formulas to calculate unknowns like the pipe flow. Bengtson orifice and venturi pipe flow meters for liquid. Schematic diagram of orifice plate the orifice flow meter consists of a 20mm bore tube with an orifice of 12mm. 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. This pressure is set by contract, by governmental law or as an agreement of the measurement by the two parties. The expanding section of venturi meter returns the flow. It works on the basic principle of bernoullis equation.
Excel templates can be downloaded to make venturi meter and orifice flow meter calculations in u. It uses the same principle as a venturi nozzle, namely bernoullis principle which states that there is a. One of the disadvantages of orifice meters is the large irreversible pressure loss across the orifice, which results in substantial pumping costs in case of large diameter pipes. In simple language, this is defined as the sum of pressure energy, kinetic energy per unit volume and potential energy per unit volume equal in the same. Venturi meter presents a costlier method to measure the rate flow of fluid through the pipe. An orifice meter is a conduit and a restriction to create a pressure drop. The concentric orifice plate flow meter reduces the pressure by forcing the fluid through a thin plated circular opening. Use excel formulas for orifice, venturi meter and ideal. If a pump forces the liquid through a tube connected to a system consisting of a venturi to increase the liquid speed the diameter decreases, a short piece of tube with a small hole in it, and last a venturi that decreases speed so the pipe gets wider again, the gas will be sucked in through the small hole because of changes in pressure. This is evident in a turbine flow meter, where the impact force of the water on the blades sets the rotor in motion. It has no projections into the fluid, no sharp corners and no sudden changes in contour.
The principle of the method of measurement is based on the installation of a venturi tube into a pipeline in which a fluid is running full. Fm 308 flow measurement by venturi and orifice meter. However this meter is relatively complex to construct and hence expensive. For these reasons it is widely used, particularly for large volume liquid and gas flows.
Due to the smooth transition to the throat and gradual transition back to full pipe diameter, the head loss through a venturi meter is quite low and the discharge coefficient is quite high. Energy losses through venturi, orifice, and rotameter. Calibration of an orifice plate flowmeter mechanical engineering department king saud university riyadh submitted by. The venturi meter has a converging conical inlet, a cylindrical throat and a diverging recovery cone. A venturi tube is a device which consists of a convergent inlet connected to a cylindrical throat which is in turn connected to a conical expanding section called the divergent exit. Determine that the meter is installed with the arrow on the nameplate and on the meter body pointing in the direction of the flow. Both are used to measure the flow rate of gases and liquids. Venturi flow meter installation and operation manual. Most modern browsers have builtin pdf readers if you have problems opening this file in your browser, check your browsers or computer systems settings. Venturi tube has a smooth entry as well as a smooth exit. Venturi meter and orifice meter are the commonly used flow meters for measuring massvolumetric flow rate or velocity of the flowing fluid an orifice plate is a device used for measuring flow rate.
This is a typical turndown ratio for a orifice plate. Unlike the orifice meter, the fluid jet after passing through the restriction throat of venturi expands to a large area gradually. To find the coefficient of discharge for orifice meter. Venturi meters are costly and used only when absolutely necessary.
As the flow area in a pipe decreases, the flow velocity that is accompanied by a decrease in pressure. Venturi meter is a device or component which is used for measuring the rate of flow of liquid through pipes. When the venturi meter is inclined, the potential head changes. The orifice meter, the nozzle meter, and the venturi meter are the most common devices used to measure the instantaneous flowrate. Laboratory experiment on venturi meter and orifice meter. Venturi meter a cross section of the brass venturi meter tested is shown in figure 3. The water flow rate can be adjusted using the valves on the hydraulics bench. Each of these meters operates on the similar principle. A venturi can also be used to mix a liquid with a gas. Tr 12 kgs 3 kgs 4 normally expressed as turndown ratio of 4. Excel formulas use the ideal gas law to calculate the density of a gas for known gas molecular weight, temperature and pressure. Energy losses through venturi, orifice, and rotameter flowmeters. For a venturi meter, the discharge coefficient is typically. Flow meter performance, validation and compliance to 40.
To determine the coefficient of discharge of the orifice meter 1. I have read about pressure recovery for both meters and found that there is always a permanent pressurehead loss dependent on the area ratio for orifice while for venturi, fluid slows down in a cone with smaller angle where kinetic energy is converted back to. Venturi meterconstruction, working, equation, application. Install meter in the pipe line so that the flow directional arrow agrees with the direction of the. What is the difference between venturimeter and orificemeter. It is mainly used for robust applications as it is known for its durability and is very economical.
An orifice meter is basically a type of flow meter used to measure the rate of flow of liquid or gas, especially steam, using the differential pressure measurement principle. Pdf experimental investigation of the installation. Discharge coefficient performance of venturi, standard. Select the orifice by either pressure drop or by flow. This also work on the same principle as that of venturimeter. Flow measurement with orifice,venturi and rotameter engi. Various forms of construction of a venturi meter are employed, depending on size, but all are. A schematic of the venturi meter is shown on the diagram at the end of the procedure. This is considered by many users to be the standard or classical venturi meter.
So this type of flow meter experiences lesser pressure drop as compared to that of the orifice. The pressure at the entrance to the meter is gauge and it is undesirable that the pressure should at any point, fall below absolute. The venturi flow meter obtains a pressure differential by constricting the flow area and therefore increasing the velocity at the constriction, which creates a lower pressure according to bernoullis theorem. The proper method of installing a halmi venturi meter 2 caution. The venturi meter is a piping component and should be handled with th e same safety precautions. Unit operations of chemical engineering by mccabe and smith. The inlet section is a standard asme longradius nozzle with a throat diameter dv of 0. In general a orifice plates has turndown ratio between 3.
However, the same principle can be exploited with only minimal pressure loss with the use of a venturi meter. Venturi meter flow is measured using the differential pressure principle differential pressure integrated with time, so that it is used to any engineering parameters like flow rate. The throat length of these meters is equal to the throat diameter. Comprehensive teaching package as optional attachments.
It consists of flat circular plate which has a circular hole, in concentric with the pipe. Venturi meter and orifice meter are the commonly used flow meters for measuring massvolumetric flow rate or velocity of the flowing fluid. The proper method of installing a venturi meter 2 caution. Venturi meter vs orifice meter student cheresources. Gaskets are provided to seal both sides of the plate. There are many different meters used to measure fluid flow.
Energy losses are less in a venturi meter whereas energy losses. Screwed brass venturi vbs use the tables on pages 2 and 3 for sizing a threaded orifice. The following figure shows the venturi meter with uniform cylindrical section before converging entrance, a throat and divergent outlet. I have this misconception about pressure drop of venturi meter and orifice meter. This article contains three example excel templates that can be downloaded. The turndown ratio tr for an orifice meter with maximum flow of 12 kgs and a minimum flow of 3 kgs can be calculated as. If wear was not a problem the orifice remained the meter of choice. As the name implies, it consists of an orifice plate which is the basic. To define the quantity of gas measured, the base pressure must be defined. Use the tables on page 4 and 5 for sizing a flanged, carbon steel orifice. It is a cheaper device as compared to venturimeter. Flow measurement in pipes and ducts ced engineering. Fm 308 flow measurement by venturi and orifice meter objectives.
A small drain or vent hole is drilled in a standard orifice to vent gas or drain liquid. Orifice flow meter s are ideal for measuring air and gas flows in combustion systems. What are some industrial uses of venturi and orifice. The expansibility factor is applied to the flow equation in the same way as the discharge coefficient. Orifice meter presents a cheaper method to measure the rate of flow through the pipe. The tables show the air flow in scfh in hundreds and the corresponding pressure drop in inches of water column. Orifice meter the venturi meter described earlier is a reliable flowmeasuring device. As we learned in the impact jet lab, the speed of a moving jet of water is proportional to the waters velocity. The ratio of the orifice plate bore divided by the inside pipe diameter. For orifice meter cross sectional area to orifice meter s2 1. The reading of manometer h m is employed to get h, as discussed before.
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