Traditional flowmeters are mature products, however, recently there have been flowmeters designed on the basis of electromagnetic principles in the market. Therefore, choosing a satisfactory flow meter is not a trivial matter, but should be considered according to the requirements of specific metering tasks. The manufacturer should state that the accuracy and repeatability of the convection mouse meter must pass actual rigorous tests and checks according to flow measurement standards with known accuracy. For an overview and recent developments in flow meters, see Harrison (1980), Pedersen and Saxtorph (1989).
1. Type of flowmeter
Two types of flow meters have been developed in parallel:
Volume flow meter: Indicates the volume of passing fluid, such as a domestic water meter.
Velocity flowmeter : Indicates the amount of fluid passing through fa) in units of time.
The indication of most flowmeters can be converted to another mode of indication, but the accuracy may be lost.
2.4.2 Flowmeter star principle
For the main coating industry, the meter that pays special attention to the flow rate can be divided into two categories:
mechanical
Type: differential pressure device (orifice plate)
Positive Displacement (Gear Pump) Turbine Flow Meter.
Hydraulic Shock Flow Meter
Features: The pressure drop through the flowmeter is obvious. Abrasive flow meters require frequent calibration when measuring abrasive fluids. Dynamometer
The range is limited, so several flowmeters are needed to cover the flow range.
No barrier (see table 2. 2)
Type: Volume: Electromagnetic, Ultrasonic
Mass: fluid momentum (complementary)
Reasoning formula (volume flow intensity + density)
Features: There is no pressure loss and flow pattern change through the flow meter. Insensitive to particles in the fluid.
Table 2.2 Features of barrier-free flow meters
| form | principle | advantage | shortcoming |
| Electromagnetic | According to Faraday's law, the fluid generates 4 induced voltages in the conduction (fluid) through the magnetic field In a dual-pipe system, the sound wave pulse travels through the pipe and meets the liquid flow, and the elapsed time of the two wave pulses is proportional to the velocity of the flow T The measuring part (U-shaped tube, 2 f-line tubes) is forced to vibrate soup, and the measured phase displacement ratio is thousand mass flow rate. | No moving parts, can be used for clean or polluted fluids and has nothing to do with viscosity and density, pipe diameter: 2~2000mm, dynamic range: 20 | Electrode contaminated fluid. Zero drift, only applicable to conductive fluids. Pipe diameter: 3~50mm |
| ultrasound | It is suitable for clean or polluted fluid and has nothing to do with the nature of the liquid. There are a variety of sensor materials, with a diameter of 4~2400mm. Dynamic range 30. | ||
| momentum compensation | Suitable for clean or contaminated fluids. Independent of fluid viscosity and density, dynamic range: 15 |
3. Velocity measurement accuracy
．Values for precision and repeatability are stated by the manufacturer and are difficult to improve.
．Calibration is required for almost all types of flow meters (minimum sampling frequency).
．There is no uniform specification and verification method (international standard) among suppliers of barrier-free flowmeters.
．The accuracy of all flowmeters is affected by disturbances such as changes in the flow rate of the fluid being measured, inlet vortices, and air bubbles.
．A long straight pipe is installed upstream of the flowmeter so that the fluid can flow in a straight line and the interference of the vortex can be completely avoided.
4. Measurement of two-phase fluid velocity
2.4.4 Measurement of two-phase fluid velocity
-. The side position of the phase fluid flow rate is very difficult, and the error value of the measurement accuracy of 10%~50% is not uncommon. We therefore recommend not to perform two-phase measurements, but to measure the flows of the different phases separately before mixing.
