Flow Meters

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  • Topic: Fluid dynamics, Viscosity, Fluid mechanics
  • Pages : 10 (2678 words )
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  • Published : April 14, 2013
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Sharif College of Engineering and Technology

Subject: Fluid Dynamics
Submitted by: HAFIZ M.ATEEQ UR REHMAN
Department: Chemical Engineering
Roll No. 28
Submitted to: Madam Asma Ashraf
Dated:12-04-2013

STEPS INVOLVED IN THE SELECTION FLOW METER
There are well over 20 different types of flow meters, even if we lump the various positive-displacement flow meters together as one type. Unless the process engineer knows the pros and cons of each type, it can be a daunting task to properly select one. Here are just some of the factors to consider before selecting a flow meter: • Its size and measuring range of the flow meter

• Chemical compatibility

• Process accuracy requirements• Pressure requirements

• Acceptable pressure drop

• Cleaning requirements (i.e., do you need, and does the unit offer, Clean-in-place capabilities?)

• Desired measurement units (such as volume, velocity or mass)

• Uni-directional or bi-directional measurement

• Fluid viscosity limitations

• Necessary approvals for use in hazardous areas, sanitary applications and so on (examples include Factory Mutual, Canadian Standards Assn., 3-A Standards and Accepted Practices, and Underwriters’ Laboratory approvals)

• Custody-transfer approvals

• Data-output requirements (i.e., 4–20 mA, relay, digital or simple display)

• Calibration and re-calibration requirements

• Maintenance issues

• Operating costs

• Connection styles (flanged, wafer, threaded, weld-on and so on)

MAGNETIC FLOW METER

A Magnetic flow meter 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 flow meters will generally not work with hydrocarbons, distilled water and many non-aqueous solutions). Magnetic flow meters are also ideal for applications where low pressure drop and low maintenance are required. 

WORKING PRINCIPLE
The magnetic flow meter is one of the most flexible and universally applicable flow measurement systems available. It provides completely obstruction less flow metering, is nearly insensitive to fluid properties, and is capable of measuring the harshest corrosive fluids. It installs like a conventional segment of process piping and has a pressure drop similar to an equivalent length of pipe. Magnetic flow meters are ideally suited for measuring harsh chemicals, slurries, fluids with solids in suspension, and other extremely difficult to measure fluids. Their operating principles provide flow measurement with a signal that is inherently linear to the average volumetric flow rate—regardless of fluid temperature, pressure, density, viscosity, or direction. The only limitation is that the fluid must be electrically conductive and nonmagnetic. While magnetic flow meters may be technically feasible for most fluids and offer many advantages, they are not necessarily the most cost-effective. For many clean, non-corrosive fluids other means of flow metering may be just as suitable at lower cost. Magnetic flow meter accuracy, for example, may not outweigh the advantage of a simpler device with tolerable accuracy. Where no other measurement device will work, or will not work reliably with the necessary accuracy, the magnetic flow meter is an obvious choice. Ideal fluid candidates generally fall into the categories of corrosive, viscous, or dirty fluids—particularly slurries. Magnetic flow meters are widely used in the water and waste, pulp and Paper, mining, chemical, and food industries.

APPLYING FARADAY’S LAW TO FLOW
MEASUREMENT

Faraday’s Law of Electromagnetic Induction is
The key principle applied to magnetic flow meter
Operation. Working on the same principle as the
Electrical generator, Faraday’s Law states that a
Voltage will be induced in a conductor moving
Through a magnetic field. The magnitude of the
Induced voltage is directly...
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