Application of gas mass flowmeter in generator industry
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â–² Vortex flowmeter features: no moving parts, high measurement accuracy, low pressure loss detection element is not in contact with the measured fluid, the output signal is independent of the fluid temperature, pressure, density, composition, viscosity and other parameters.
The principle of vortex flowmeter: It is the principle of Karman vortex street used in fluid mechanics to measure fluid flow. A vortex generator (a non-streamlined symmetric body such as a cylinder and a triangular column) is vertically inserted into the pipe. When the fluid flows in the pipe, vortices are generated alternately on the left and right sides of the vortex generator to form a vortex array. The two rows of vortices form parallel to each other and appear alternately to the left and right with opposite directions of rotation. The frequency of vortices f (Hz) is related to the fluid's average flow velocity v (m/s) and the width of the vortex generator (m) as follows: f = St*v/d (St is the Strouhal coefficient, and the vortex Body width d is related to the fluid Reynolds number)
The use of vortex flowmeters is relatively simple and installation is relatively easy. It is divided into two types: plug-in type and pipeline type. During installation, it should be noted that the flow direction of the fluid should be the same as that indicated by the flowmeter.
â–²The disadvantages of vortex flowmeters are: small range ratio (15:1); large impact from vibration; proportionality of pipe size and price; need temperature and pressure compensation before measurement; small range is insensitive, unstable, almost unmeasurable .
2, ultrasonic flowmeter (gas)
â–² Ultrasonic Flowmeter Features: No pressure loss; Simple installation; Irrelevant to the fluid's own properties such as temperature, pressure, and viscosity; No moving parts; Can measure dirt, corrosive gases and multi-component gases.
▲ Ultrasonic Flowmeter Principle: The measurement of the propagation time of the ultrasonic wave in the forward and countercurrent directions is measured in the pipeline, and then the flow rate of the fluid is calculated. The flow rate of the fluid can be obtained from the media flow rate, the pipe diameter, and the dynamics correction of the fluid with the Reynolds number. Specifically: A pair of ultrasonic sensors are installed in the pipeline in a “Z†type, and the distance L between the two sensors is used as the propagation path of the ultrasonic waves. The forward and backward propagation times of the ultrasonic wave between the two sensors are respectively expressed as: Ts=L/(C+Vcosθ); Tn=L/(C-Vcosθ) where C is the speed of sound waves in still air, The function as a function of the nature of the gas in m/s. V is the gas medium flow rate in m/s. θ is the angle between the acoustic travel and the axis of the pipe.
▲ The use of ultrasonic flowmeter is also more convenient. The surface of the pipeline is mounted in a “Z†shape. Care should be taken to lighten the sensor mounting area and apply grease. Fasten the sensor and pipe with a fixture.
â–² Disadvantages of ultrasonic flowmeter: small range ratio (15:1); relatively cumbersome maintenance; high gas accuracy and high price; measurement requires temperature and pressure compensation;
3, rotameter (gas)
â–²Features of Rotameter: Local display, no power supply; relatively cheap price; it has two materials, commonly used glass tube flowmeter and metal tube mass flowmeter. Local display and remote display are available, and the interface has HART, standard current signal, PROFIBUS and other forms.
â–² The principle of rotameter: Rotometer is also a speed meter. It consists of two parts, one is a large, tapered tube, and the other is a rotor (also known as a float) in a conical tube. The weight of the rotor is balanced by the differential pressure ΔP produced when the fluid passes through the gap (throttle area) between the rotor and the wall of the conical tube. During operation, the fluid to be measured flows from the lower end of the conical tube and flows out from the upper end. The size F of the upward force exerted by the fluid on the rotor is always equal to the weight G of the rotor, that is, F=ΔP*A; G=V*(Ït-Ïf)g Since F=G, â–³P*A=V*(Ït -Ïf)gΔP=V*(Ït-Ïf)g/A(1) where the volume of the V-rotor; A—the maximum cross-sectional area of ​​the rotor; g—the local re-acceleration; Ït−Ïf are the material of the rotor And the density of the fluid being measured; â–³P is the pressure difference between the upper and lower fluid in the vertical direction of the rotor. As can be seen from formula (1), the pressure difference remains unchanged throughout the entire work process. When the flow rate increases, of course, the flow rate through the throttling area also increases. Only the throttling area is increased, and the flow rate is reduced to maintain the pressure difference ΔP constant. Therefore, the flow rate can be read out based on the balance position of the rotor. The equation (2) can be expressed as Q = k * h (2 â–³ P / Ïf) 1/2 (2) where k- is the meter constant; h- is the rotor floating height. Substituting equation (1) into the available Q=k*h(2gV(Ït-Ïf)/(Ïf*A))1/2
â–² The use of rotameter is convenient. Tighten the corresponding bolts when installing, but it should be noted that the direction of fluid flow must be vertical upwards.
Disadvantages of Rotameter: Smaller than 10:1 range ratio; relatively large pressure loss; easy fouling of dirt; relatively complex installation and maintenance; large impact by vibration; temperature, pressure compensation, etc.; diameter and size of the pipe are proportional, generally Below DN200.