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Flow Measurement

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Flow Measurement

  1. 1. Om Pratap Singh
  2. 2. <ul><li>Volumetric Flowmeters </li></ul><ul><ul><li>Orifice </li></ul></ul><ul><ul><li>Rotameter </li></ul></ul><ul><ul><li>Magnetic Flowmeter </li></ul></ul><ul><li>Mass Flowmeters </li></ul><ul><ul><li>Coriollis Mass Flowmeter </li></ul></ul>
  3. 3. Basic Equations: a.) Continuity: mass in = mass out b.) Bernoulli’s Eqn. Total pressure is constant throughout i.e. ½ ρ V 2 + P =constant For a fluid flowing in a horizontal pipe. m 1 =m 2 & m = ρ AV .’. ρ 1 A 1 V 1 = ρ 2 A 2 V2 For incompressible fluids ρ 1 = ρ 2 Thus A 1 V 1 = A 2 V 2
  4. 5. P 1 P 2 d D D/2 D P 1 P 2 Vena contracta
  5. 7. <ul><li>A rotameter consists of a tapered tube as shown, typically made of glass, with a float inside that is pushed up by flow and pulled down by gravity. </li></ul><ul><li>At a higher flow rate more area (between the float and the tube) is needed to accommodate the flow, so the float rises. </li></ul><ul><li>The float is shaped so that it rotates axially as the fluid passes. This allows you to tell if the float is stuck since it will only rotate if it is free. </li></ul><ul><li>Note :-The &quot;float&quot; does not actually float in the fluid: it has to have a higher density than the fluid, otherwise it will float to the top even if there is no flow. </li></ul>
  6. 8. <ul><li>What is a Magnetic Flow Meter? A magnetic flow meter (mag flowmeter) is a volumetric flow meter which does not have any moving parts and is ideal for wastewater applications or any dirty liquid which is conductive or water based. Magnetic flowmeters will generally not work with hydrocarbons, distilled water and many non-aqueous solutions). Magnetic flowmeters are also ideal for applications where low pressure drop and low maintenance are required. Principle of Operation <>The operation of a magnetic flowmeter or mag meter is based upon Faraday's Law, which states that the voltage induced across any conductor as it moves at right angles through a magnetic field is proportional to the velocity of that conductor. Faraday's Formula: E is proportional to V x B x D where: E = The voltage generated in a conductor V = The velocity of the conductor B = The magnetic field strength D = The length of the conductor To apply this principle to flow measurement with a magnetic flowmeter, it is necessary first to state that the fluid being measured must be electrically conductive for the Faraday principle to apply. As applied to the design of magnetic flowmeters, Faraday's Law indicates that signal voltage (E) is dependent on the average liquid velocity (V) the magnetic field strength (B) and the length of the conductor (D) (which in this instance is the distance between the electrodes).In the case of wafer-style magnetic flowmeters, a magnetic field is established throughout the entire cross-section of the flow tube (Figure 1). If this magnetic field is considered as the measuring element of the magnetic flowmeter, it can be seen that the measuring element is exposed to the hydraulic conditions throughout the entire cross-section of the flowmeter. With insertion-style flowmeters, the magnetic field radiates outward from the inserted probe (Figure 2). </li></ul>
  7. 9. Magnetic flowmeters will generally not work with hydrocarbons,distilled water and many non-aqueous solutions.
  8. 10. <ul><li>A mass flow meter , also known as an inertial flow meter or a coriolis flow meter , is a device that measures mass flow rate of a fluid traveling through a tube. The mass flow rate is the mass of the fluid traveling past a fixed point per unit time. </li></ul><ul><li>The mass flow meter does not measure the volume per unit time (e.g., cubic meters per second) passing through the device; it measures the mass per unit time (e.g., kilograms per second) flowing through the device. Volumetric flow rate is the mass flow rate divided by the fluid density. If the density is constant, then the relationship is simple. If the fluid has varying density, then the relationship is not simple. The density of the fluid may change with temperature, pressure, or composition, for example. The fluid may also be a combination of phases such as a fluid with entrained bubbles. </li></ul><ul><li>In a typical mass flow meter the fluid is contained in a smooth tube, with no moving parts that would need to be cleaned and maintained, and that would impede the flow. </li></ul>
  9. 11. <ul><li>Coriollis Force – These are generated in oscillating systems when a liquid or a gas moves away from or towards an axis of oscillation. </li></ul><ul><li>A Coriollis force measuring system </li></ul><ul><li>is of symmetrical design as shown. </li></ul><ul><li>The tubes can be one or two. </li></ul><ul><li>When no fluid is flowing, the vibration of tubes </li></ul><ul><li> is symmetrical. </li></ul><ul><li>During mass flow, the two vibrations are out </li></ul><ul><li> of sync which is directly proportional to the </li></ul><ul><li> mass Flow rate. </li></ul><ul><li>This Distortion is picked up by sensor. The </li></ul><ul><li>oscillating characteristic of the measuring tube </li></ul><ul><li>are dependent on temperature, so it is also </li></ul><ul><li>continuously measured. </li></ul>
  10. 12. <ul><li>Mass Flow rate = K u -I u ω 2 *t </li></ul><ul><li>Ku= The temperature dependent stiffness of tube. </li></ul><ul><li>K = a shape-dependent factor of tube. </li></ul><ul><li>D = the width, </li></ul><ul><li>Τ= the time lag, </li></ul><ul><li>ω =the vibration frequency </li></ul><ul><li>Iu =the inertia of the tube. </li></ul>2Kd 2
  11. 13. <ul><li>Thanking You </li></ul>