Working Principle of Flow Measurement , Application, Installation , Advantage disadvantage , Technical specification, comparison with others
The operation of a Coriolis flow meter is based on the mechanics of motion. The Coriolis force happens when a mass moves in a rotating inertial frame. The rotation is created by vibrating two opposing tubes on the flow meter. When a fluid flows through the opposed vibrating tubes, the tubes twist due to the Coriolis force. The twisting alternates with the vibration and creates two phase-shifted sinusoidal wave forms on coils mounted to the tubes. The amount of shift is proportional to the mass flow rate. In addition, the frequency of vibration is proportional to the fluid density.
Vortex flow meters utilize a bluff body or cylinder mounted in a pipe spool that creates alternating vortices behind the cylinder. The frequency of the alternating vortex is proportional to the fluid velocity. Vortex flow meters have no moving parts to maintain or repair, and the signal is read electronically and simply converted to a flow rate. Vortex meters work well with most clean fluids and have similar application ranges to DP flow meters.
A turbine flowmeter unit is constructed of a multiple-bladed rotor installed with a pipe in a perpendicular direction to the fluid flow. As the liquid flows through the blades, the rotor rotates. The rotational speed of the rotor is correlated to the flow rate of the liquid. The speed of the rotor can be sensed by various mechanisms such as magnetic pick-up, photoelectric cell, or gears. A tachometer can also be attached to the turbine for measuring its rotational speed which in turn helps in determining the liquid flow rate.
Orifice plates are one of the oldest DP flow meter technologies and were first documented in Roman times. The first U.S. patent for the orifice plate was awarded to T.R. Weymouth in 1916. Orifice plates have remained popular because of their simplicity and the inherent scalability and repeatability of the flow through a sharp-edged orifice bore. Orifice plate pressure-based flow elements in existence, the most common is the orifice plate. This is simply a metal plate with a hole in the middle for fluid to flow through. Orifice plates are typically sandwiched between two flanges of a pipe joint, allowing for easy installation and removal:
The thermal mass meter measures gas flow based on the concept of convective heat transfer. The flow meters are available in either inline flow bodies or insertion-style. In either case, the meter’s probe inserts into a gas stream of a pipe, stack or duct. Toward the tip of the meter’s probe are two sensors. These sensors are resistance temperature detectors (RTDs) or resistance thermometers and measure temperature. The RTDs consist of durable reference-grade platinum windings clad in a protective 316 SS or Hastelloy C sheath.One of the RTDs is heated by an integrated circuit and functions as the flow sensor.
Magnetic flow meters operate on Faraday’s Law of Electromagnetic Induction. Electrodes mounted on opposite sides of the flow meter body measure a voltage generated by the flow of a conductive liquid in a magnetic field. The voltage generated is proportional to the flow rate. The magnetic flow meter uses a full-sized pipe spool that is lined with one of several types of inert plastic materials. This makes the magnetic flow meter ideal for use in applications with dirty fluids, sewage, or slurries.
Ultrasonic flow meters calculate the flow rate by utilizing the speed of sound through a fluid created by transducers mounted to the pipe wall. There are two types of ultrasonic meters: Doppler and Time-of-Flight. The Doppler ultrasonic meter requires particles in the fluid to reflect sound waves back to the pipe wall transducers. The difference in frequency between the sent and reflected wave is proportional to fluid velocity. The Time-of-Flight ultrasonic meter requires a clean fluid and works by using opposing transducers mounted to transmit/receive sound waves at an angle across the pipe.
Positive Displacement flow meters are the only flow measuring technology to directly measure the volume of fluid that passes though the flow meter. It achieves this by trapping pockets of fluid between rotating components housed within a high precision chamber. This can be compared to repeatedly filling a beaker with fluid and pouring the contents downstream while counting the number of times the beaker is filled.
A Rotameter is a form of Variable area flow meter which has a simplistic operation one of the oldest and mature principles in flow measurement with its simple design: a float rises inside a conically shaped glass tube as the flow increases and its position on a scale can be read off as the flow rate. Since this measuring method is purely mechanic, it as simple as it is reliable. As fluid flows upward through the tube, a pressure differential develops across the plummet. This pressure differential, acting on the effective area of the plummet body, develops an upward force (F = PA)