Principle analysis of various types of flowmeters
(1) Principles of mechanics: Instruments belonging to such principles have differential pressure and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; direct mass type using Newton's second law; The target type of the momentum principle; the turbine type using the angular momentum theorem; the vortex type using the principle of fluid oscillation, the vortex type; the pitot tube type using the total static pressure difference; the volumetric type, the enthalpy, the trough type, and the like.
(2) Electrical principle: The instruments used for such principles are electromagnetic, differential capacitive, inductive, strain resistant, etc.
(3) Acoustic principle: Ultrasonic type, acoustic type (shock wave type), etc. are used for flow measurement using the acoustic principle.
(4) Thermal principle: The heat, direct thermal, indirect calorimetry, etc., which measure the flow using the thermal principle.
(5) Optical principle: laser type, photoelectric type, etc. are instruments belonging to such principles.
(6) Originally based on physical principles: nuclear magnetic resonance, nuclear radiation, etc. are instruments of this type.
(7) Other principles: Marking principle (trace principle, NMR principle), related principles, etc.
Second, gas turbine flowmeter measurement characteristics
1. Gas turbine flowmeter is one of the main types of flowmeters. Its working principle is: the gas entering the gas turbine flowmeter is accelerated by the fluid, and the accelerated gas acts on the blades of the turbine through the inlet passage. The impulse causes the turbine of the flow meter to rotate in the flow path, and within a certain flow range, the number of revolutions of the turbine is proportional to the volume of the gas flowing therethrough. By mechanical or electromagnetic induction, the number of revolutions f of the turbine can be obtained, so that the flow rate Q of the gas flowing through the flow meter can be obtained.
2. Gas turbine flowmeters are widely used in the measurement of gas flow or total gas volume, and are widely used in natural gas flow measurement at home and abroad. The theoretical research and practical experience of gas turbine flowmeters are very mature, and there are corresponding international standards. Countries also have corresponding national standards. China also adopts international standards. In Europe and the United States, gas turbine flow meters are the most important gas flow meters, and the Netherlands alone uses more than 2,600 gas turbine meters on natural gas pipelines.
Steam vortex flowmeter measurement requirements
Keywords: steam vortex flowmeter, saturated steam vortex flowmeter, superheated steam vortex flowmeter
What should I pay attention to when measuring vortex flowmeter? What is the best way to measure steam installation by vortex flowmeter? Can vortex flowmeters be used for steam metering? The vortex flowmeters are evaluated for their measurement performance under single-phase flow conditions. There is currently no single-phase flowmeter for measuring the system variation of two-phase flow. However, the two-phase flow exists objectively, and its influence on flow measurement is unavoidable. Despite the difficulties, people are still trying to study the mechanism of its influence on flow measurement, and take corresponding countermeasures to improve the accuracy of flow measurement.
First, steam flow measurement difficulties
During long-distance transportation, dry steam will partially condense due to heat loss, resulting in reduced steam dryness and become wet steam. The gas-liquid two-phase flow structure in the horizontal pipe is related to the gas-liquid two-phase volume ratio and the flow velocity. In the steam pipe, since the volume ratio of the condensed water in the wet steam is small, the drain pipe drawn from the bottom of the horizontal pipe is made. , can receive a good hydrophobic effect. When the flow rate is particularly high, it will also behave as a circular flow, that is, there is a liquid film on the pipe wall, and the central part of the pipe is a gas core with droplets. Due to the influence of gravity during horizontal flow, the lower liquid film is higher than the upper pipe. The thickness of the wall, in the vertical ascending pipeline, the basic structure of the gas-liquid two-phase flow has a fine bubble flow structure, a bullet-like flow structure, a block flow structure, a ring-shaped flow structure with fibers, and an annular flow structure.