Overview of various flow meters

Thread Content

This post was last edited by Wake up on 2011-4-7 15:09 •Orifice flow meters• Orifice flow meters are a type of flow measurement instrument that is widely used, accounting for about 70% of all flow measurement instruments. It consists of a throttling device and a differential pressure gauge. When the fluid filling the circular tube flows through the throttling element (such as an orifice plate), the flow stream narrows locally at the orifice plate; as a result of the increased flow velocity and decreased static pressure, a pressure difference is generated before and after the orifice plate, and this pressure difference is proportional to the square of the flow rate. •Rotary flow meter • A rotary flow meter is a type of variable-area flow meter suitable for measuring low flow rates. •A differential pressure flow meter measures the flow rate by detecting changes in differential pressure, with the throttling area remaining constant. In contrast, a rotameter maintains a constant pressure difference and uses changes in the throttling area to reflect the flow rate; hence it is known as a flow measurement method with a constant pressure difference and variable throttling area. •Electromagnetic flowmeter • An electromagnetic flowmeter measures flow rate based on the principle of Faraday’s law of electromagnetic induction. • When a conductive fluid flows through a measuring tube surrounded by a magnetic field, an induced electromotive force E is generated in a direction perpendicular to both the flow velocity and the magnetic field, and this force is proportional to the average flow velocity V. This induced electromotive force is detected by a pair of electrodes located on the wall of the flowmeter, and the flow rate can be determined through calculations. (Keep the right hand flat, with the thumb perpendicular to the other four fingers, and all of them lying in the same plane as the palm.) Place the right hand in a magnetic field; if the magnetic field lines enter the palm perpendicularly (when the magnetic field lines are straight, this means the palm is facing the N pole), and if the thumb points in the direction in which the wire moves, then the direction indicated by the four fingers is the direction of the induced current in the wire. In electromagnetism, the right-hand rule is primarily used to determine directions that are independent of force. ) • Mass flow meter • A mass flow meter is a new type of flow measurement instrument that can be used to directly measure the mass flow rate, density, and temperature of a medium. •Turbine flow meter: • A turbine flow meter is a type of velocity-type flow meter that utilizes the fact that the angular velocity of the impeller placed in the fluid is proportional to the flow velocity of the fluid; by measuring the rotation speed of the impeller, it is possible to determine the volume flow rate. As the fluid passes through the turbine flow transmitter, it drives the turbine to rotate; the highly magnetic turbine blades periodically pass over the magnets, causing periodic changes in the magnetic resistance of the magnetic circuit. As a result, the magnetic flux in the coil also changes periodically, which generates an alternating electrical signal in the coil. The frequency of this signal is proportional to the speed of turbine rotation, and thus proportional to the flow rate. But note that when the turbine starts rotating, there is a minimum flow rate required to overcome the frictional torque in the bearings; if the flow rate is below this value, the instrument will not produce any output. •Differential intelligent flow meter: As the medium flows through the measuring tube, its kinetic energy together with the pressure difference created by the flow-blocking elements results in forces acting on a pair of force-sensitive elements; the magnitude of these forces is proportional to the square of the medium’s flow velocity. F=CDAPU2/2 • F——The force acting on the element under stress; CD——The drag coefficient of the object; AP——The axial projection area of the element under stress on the measuring tube; P: The density of the medium under the given conditions; U——The average flow velocity of the medium within the measuring tube.