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Industry Information
Glass tube rotor flowmeter principle and structure
2012-2-29 13:54:19

转子流量计是以浮子在垂直锥管中随流量变化而升降,改变它们之间的流通面积而进行测量体积的体积流量仪表,也称转子流量计。 Glass tube rotor flow meter Rotary flow meter is a volume flow meter that measures the volume by changing the flow rate of the float in the vertical cone tube and changing the flow area between them. It is also called a rotameter. Float flowmeters are more suitable for small diameters and low flow rates. They can also be used for medium diameters. For ordinary full-flow floats, they cannot be used for large diameters. For glass tube float flowmeters, the maximum can be DN100; metal tubes can be DN150. . The flow range is generally 10: 1; the float meter can be used to measure liquid, gas and steam. According to its application classification, it can be divided into: ordinary type, jacket insulation type, explosion-proof type, corrosion-resistant type and blow-flow type.
The glass tube rotor flowmeter is generally used as an intuitive flow indicator or a field indicator with low measurement accuracy. It can be used in power, chemical, petrochemical, metallurgical and other process industries and sewage treatment utilities.
Principle and structure of glass tube float flowmeter The flow detection element of glass tube rotor flowmeter is composed of a vertically tapered tube that expands from bottom to top and a float group that moves up and down along the axis of the cone tube. The working principle is shown in Figure 1. When the measured fluid passes from the bottom to the ring gap 3 formed by the cone 1 and the float 2, a differential pressure is generated at the upper and lower ends of the float to form a rising force of the float. When the floating force is greater than the immersion fluid When the weight of the float rises, the float rises, the area of the annulus increases, the flow velocity of the fluid at the annulus immediately decreases, the differential pressure at the upper and lower ends of the float decreases, and the rising force acting on the float also decreases until the rising force is equal to immersion in the fluid. When the weight of the float is medium, the float is stable at a certain height. The height of the float in the cone has a corresponding relationship with the flow rate. The basic equation of volume flow Q is (1) when the float is a non-solid core hollow structure (load adjustment amount), then the float flow meter
(2) In the formula, α——the flow coefficient of the instrument varies with the shape of the float; ε——the gas expansion coefficient when the measured fluid is a gas, which is usually ignored due to the small correction amount of this coefficient, and has been verified by verification. It is included in the flow coefficient, ε = 1 if it is a liquid; △ F——circulation annular area, m2; g—local acceleration of gravity, m / s2; Vf—volume of the rotor, if it is an extension, it should also be included, m3; ρf—the density of the rotor material, kg / m3; ρ——the density of the measured fluid, such as the density of the gas on the upstream cross section of the float, kg / m3; Ff——the working diameter (maximum diameter) of the rotor Cross-sectional area, m2; Gf——mass of rotor, kg. The relationship between the circulation ring area and the height of the float is shown in equation (3). When the structural design has been determined, d and β are constant. There is a quadratic term of h in the formula. Generally, this nonlinear relationship cannot be ignored. Only when the cone angle is very small can it be regarded as approximately linear. m2 (3) where d——the maximum diameter of the rotor (that is, working diameter), m; h——the height of the rotor from the cone diameter equal to the maximum diameter of the rotor, m; β——the cone angle of the cone; a, b --constant. The typical structure of a 15-40mm transparent cone-shaped tube float meter is shown in Figure 2. The most commonly used transparent conical tube 4 is made of borosilicate glass, and it is customarily referred to as a glass tube float flow meter. The flow indexing is directly engraved on the outer wall of the cone tube 4, and an indexing scale is also installed beside the cone tube. The inner cavity of the cone tube has two types: a smooth surface of the cone and a rib (or plane) with a guide. The rotor moves freely in the cone tube, or moves under the guidance of the ribs of the cone tube, and the instrument with a smooth inner surface of a larger mouth is also guided by a guide rod. Glass tube float flow meter right-angle installation method Typical structure of metal tube float flow meter, usually suitable for instruments with a diameter of 15-40mm or more. The cone tube 5 and the float 4 constitute a flow detection element. There is an extension of the guide rod 3 in the sleeve, and the displacement of the float is transmitted to the conversion part outside the sleeve through a magnetic steel coupling method. The conversion part has two types: local indication and remote signal output. In addition to the right-angle installation structure, there is a straight-through structure with the inlet and outlet center lines concentric with the tapered tube, which is usually used for instruments with a diameter of less than 10-15mm.
Advantages and disadvantages of glass tube rotor flowmeters Rotor flowmeters are used for small pipe diameters and low flow rates. The diameter of commonly used instruments is below 40-50mm, and the minimum diameter is 1.5-4mm. It is suitable for measuring low flow rate and small flow rate. Taking liquid as an example, the nominal pipe diameter of full-scale flow rate of glass tube float flowmeter with a diameter of less than 10mm, the flow rate is only between 0.2-0.6m / s, even lower than 0.1m / s; metal The tube float flowmeter and the glass tube float flowmeter with a diameter greater than 15mm are slightly higher, and the flow rate is between 0.5-1.5m / s. Glass tube rotor flowmeter Rotor flowmeter can be used for lower Reynolds number. Use a float with insensitive shape. As long as the Reynolds number at the circulation gap is greater than 40 or 500, the flow coefficient of the Reynolds number will remain constant, that is, the fluid viscosity will not change. Affects the flow coefficient. This value is far lower than the minimum Reynolds number of the standard orifice plate and other differential pressure instrument 104-105 requirements. Most rotor flowmeters do not have upstream straight pipe requirements, or the upstream straight pipe requirements are not high. Glass tube float flowmeter Float flowmeter has a wide flow range, generally 10: 1, the lowest is 5: 1, and the highest is 25: 1. The output of the flow detection element is close to linear. Low pressure loss. The glass tube rotor flowmeter has a simple structure and a low price. As long as the flow indicator is convenient to use at the scene, the disadvantage is that there is a risk of fragility of the glass tube, especially the non-guided structure float for gas. The metal tube float flow meter has no risk of cone tube breakage. Compared with the glass tube float flowmeter, the operating temperature and pressure range is wide. Glass tube rotor flowmeters Most structures of the rotor flowmeter can only be used for bottom-up vertical flow pipeline installation. Vertical glass tube rotor flowmeter Rotor flowmeter applications are limited to small and medium diameters. Ordinary full-flow float meters cannot be used for large tube diameters. The maximum diameter of glass tube rotor flowmeters is 100mm, and that of metal tube rotor flowmeters is 150mm, which is larger. The pipe diameter can only be used with split type instruments. When the fluid used is different from the factory calibration fluid, the flow indication value should be corrected. Rotary flowmeters for liquids are usually calibrated with water, and gases are calibrated with air. If the density and viscosity of the fluid used are different, the flow rate should deviate from the original graduation value and conversion correction should be made.
Classification of vertical glass tube rotor flowmeter:
Often, stereotyped products and special instruments can be classified from different angles, such as: According to the material of the conical tube, it is divided into transparent conical tube and metal conical tube. According to the presence or absence of remote transmission signal output, it is divided into local indication type and remote transmission signal output type, and the latter is divided into electric remote transmission and air remote transmission. Divided into liquid, gas and steam according to the tested fluid. According to the volume of the measured fluid passing through the float flowmeter, it is divided into full flow type and split flow type.
Glass tube float flow meter application overview:
转子流量计作为直观流动指示或测量精确度要求不高的现场指示仪表,占浮子流量计应用的90%以上,被广泛地用在电力、石化、化工、冶金、医药等流程工业和污水处理等公用事业。 Glass tube rotor flowmeter Rotary flowmeter, as an intuitive flow indicator or a field indicator with low measurement accuracy requirements, accounts for more than 90% of the application of float flowmeters. Utilities such as industry and wastewater treatment. Some application sites only need to monitor the flow rate not exceeding or not lower than a certain value. For example, the increase of the cable inert protective gas flow indicates that a new leak point has occurred. Circulating cooling and culture tank and other places such as water or air flow reduction and cut-off alarm can choose glass tube float flowmeter with upper or lower limit flow alarm.
The environmental protection atmospheric sampling and process industry online monitoring and analysis instruments continuously sample, and the sampling flow monitoring is also the bulk service object of the float flowmeter. As the measurement of liquid level, density and other parameters in the process industry, constant flow measurement and control auxiliary instruments are widely used and also occupy a considerable share. Remote transmission metal rotor flow meters with signal output are often used as flow control detection instruments or pipeline mixing ratios in the process industry, such as controlling the ratio of raw water and chemical solution in the water supply process.
Glass tube rotor flowmeter installation and use precautions Most of the instrument installation direction The rotor flowmeter must be installed vertically on the vibration-free pipe, there should be no obvious tilt, the fluid flows from the bottom to the top of the meter. The angle between the centerline of the rotor flowmeter and the plumb line generally does not exceed 5 degrees, and the high-precision (above 1.5) meter θ≤20 °. If θ = 12 °, there will be 1% additional error. There is no strict requirement for the length of the upstream straight pipe section, but there are also manufacturers that require the length of (2-5) D, which is actually not necessary.
转子流量计的校验和标定转子流量计的校验和标定液体常用标准表法、容积法和称量法;气体常用钟罩法,小流量用皂膜法。 Glass tube rotor flowmeter calibration and calibration Rotor flowmeter calibration and calibration liquids are commonly used in standard meter method, volume method and weighing method; gas bell method is commonly used, small flow using soap film method. The bulk products of some foreign manufacturers have achieved dry calibration, that is, controlling the size of the conical tube and the weight of the rotor, and indirectly determining the flow value to reduce costs. Only high-precision instruments are calibrated in real flow. There are also some domestic manufacturers that strictly control the inner diameter and taper of the starting point of the conical tube and the size of the float. The actual flow verification only serves to check the quality of the inner surface of the conical tube. Gauges, tapered tubes and floats from these manufacturers have been interchanged and do not need to be replaced in sets. Rotameters are calibrated with a standard meter method, which is a high-efficiency method that has been applied by various manufacturers. Some manufacturers make a standard meter of a certain flow range into several sections of glass tube rotor flowmeters with a small taper, extend the length of the standard meter, increase the accuracy of the standard meter, and make the calibration and calibration work achieve high accuracy and high efficiency.