Flow characteristics of turbine flowmeter

Turbine flowmeters are generally composed of two parts: a sensor and a display, and can also be made into an integral type. Turbine flowmeters, positive displacement flowmeters, and Coriolis mass flowmeters are called the three types of repeatability in flowmeters. As one of the top ten types of flowmeters, their products have developed into a multi-variety, multi-series mass production scale. When the flow rate is greater than the initial flow value, as the flow rate increases, the turbine flowmeter's turbine rotation angular velocity will also increase. Within the measurement range, the resistance torque T produced by the fluid will become the main factor affecting the characteristics of the flowmeter. Relatively speaking, the mechanical resistance torque generated by the friction of bearings and other mechanical transmission parts is relatively small. In the following discussion, assuming that the mechanical resistance torque is 0, the instrument coefficient: K=B - C[T/ρQ2 ] (1) In the formula: Q——The flow rate of the fluid in the pipe; B, C——Constants. Since the mechanism and effect of fluid resistance are different under different flow states, the laminar flow state and turbulent flow state will be discussed separately. To distinguish between laminar flow state and turbulent flow state, the concept of Reynolds number (Re) must be introduced Re=4Q/πdν (2) In the formula: Q——the flow rate of the fluid in the pipe; d——the diameter of the pipe; ν——the fluid in the pipe kinematic viscosity. Usually Re ≥ 2320 is the basis for judging that the flow in the pipe changes from a laminar flow state to a turbulent flow state. In laminar flow state, fluid flow resistance torque T is proportional to fluid dynamic viscosity (also known as viscosity) μ and fluid flow Q, that is, T=C1μQ. In the formula, C1 is a constant, which can be substituted into formula (1): if the viscosity changes, the instrument coefficient K also changes accordingly; if the viscosity remains unchanged. Then K will increase with the increase of flow. When the turbine flowmeter is in the turbulent flow state, the fluid flow resistance torque T is proportional to the fluid density and Q2. At this time, the influence of fluid viscosity can be calculated. That is, T=C2ρQ2. In the formula, C2 is a constant. Substituting it into formula (1), it can be seen that in the state of turbulent flow, the meter coefficient K is only related to the structural parameters of the meter itself, but has nothing to do with parameters such as flow rate Q and fluid viscosity μ. Approximately constant. Only in this state, the instrument coefficient K really shows the nature of a constant. The range where the instrument coefficient K is constant is the high-quality measurement range of the turbine flowmeter.

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