Rotameter

Rotameter

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  FLUID DYNAMICS Submitted To: Dr. Syed Mohsin Ali Kazmi Submitted By : Muhammad Jawad Qasim 2018-CH-257
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  ROTAMETER
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  INTRODUCTION • A rotameteris a device that measures the volumetric flow rate of fluid in a closed tube. It belongs to a class of meters called variable area meters, which measure flow rate by allowing the cross-sectional area the fluid travels through to vary, causing a measurable effect.
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  CONSTRUCTION A rotameter ismade up of a tapered tube and a float inside it . The glass tapered tube has a scale on the surface or a scale is placed adjacent to it, according to purpose Tapered tube : The tapered tube is placed vertically in the flow channel with a conical shape inside . The quantity measured is defined by the height of float going up . Glass tubes are used for both liquid and gas measurement . Metallic tubes are used where the process fluid with high temperature and pressure. Float : Stainless steal floats are commonly used, there are different types of metals from lead to aluminium used as floats . A float material, shapes are also varied according to applications considering density . Spherical shape floats are used for small flows .
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  PRINCIPLE • “The buoyantforce exerted on an immersed object is equal to the weight of liquid displaced by that object.”
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  WORKING • Fluid entersfrom the bottom of the tapered tube. • Now the float experience two forces in opposite direction, darg force upward and gravitational force downward. • Fluid flow moves the float upward against gravity .At some point, the flowing area reaches a point where the pressure - induced force on the floating body exactly matches the weight of the float . The float will find equilibrium when the area around float generates enough drag equal to weight – buoyancy. • As the float weight and gravity are constant, the distance float displaced upward is proportional to the flow velocity of the fluid passing through the tapered tube .
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  PRESSURE DROP • Thepressure drop arises from the conversion of pressure energy and from frictional losses which are accounted for in the coefficient of discharge. • The pressure difference over the float -∆𝑃, is given by: −∆𝑃 = 𝑉 𝑓 𝜌 𝑓−𝜌 𝑔 𝐴 𝑓 • This equation shows the pressure difference across the float is equal to its weight in the fluid divided by its maximum cross sectional area.
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  COEFFICIENT OF DISCHARGE
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  MEASURING PRINCIPLE OFROTAMETER • However, the difference in this application is that the value inside the radicand is constant since the pressure difference will remain constant and the fluid density will likely remain constant as well. • Thus, k will change in proportion to Q. The only variable within k relevant to float position is the flowing area between the float and the tube walls. 𝑄 =𝐾 𝑃1−𝑃2 𝜌
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  REFERENCES • Rotameter –Wikipedia • How does a variable area flow meter work? | Omega Engineering • Working of Rotameter / Variable area flowmeter - Field Instrumentation / Flow Measurement - Industrial Automation, PLC Programming, scada & Pid Control System