Turbine flowmeter

Turbine flowmeters are probably the most common example where pulse inputs are used. Another example is a watt-hour meter. Basically any measurement device that invowes a rotational element can be interfaced via pulses. 

A turbine flowmeter consists of a straight flow tube containing a turbine which is free to rotate on a shaft supported by one or more bearings and located on the centerline of the tube. Means are provided for magnetic detection of the rotational speed, which is proportional to the volumetric flow rate. Its use is generally restric ted to clean, noncorrosive fluids. Additional information on construction, operation, range, and accuracy can be obtained from Holzbock (Instruments for Measurement and Control, 2d ed., Reinhold, New York, 1962, pp. 155-162). For performance characteristics of these meters with liquids, see Shafer,y. Basic Eng., 84,471-485 (December 1962) or May, Chem. Eng., 78(5), 105-108 (1971) and for the effect of density and Reynolds number when used in gas flowmetering, see Lee and Evans, y. Basic Eng., 82, 1043-1057 (December 1965). 

Flow Rate. The values for volumetric or mass flow rate measurement are often determined by measuring pressure difference across an orifice, nozzle, or venturi tube. Other flow measurement techniques include positive displacement meters, turbine flowmeters, and airflow-measuring hoods. 

Turbine flowmeters, liquid meters 271 Turbines, flat-bladed 295... 

Any combination of flowmeter and suitable specific gravity (density) meter (Section 6.6) can in theory be employed to produce a mass rate of flow. However, these so-called indirect meters have a limited range and accuracy and require careful and frequent calibration and maintenance. An instrument based on the turbine flowmeter (Volume 1, Section 6.3.9) and acoustic density meter (Section 6.6.1) has been employed with good results<8) (see Fig. 6.5). 

In electronic Btu sensors, the flow sensor is usually a high-accuracy turbine flowmeter, and the temperature difference is usually detected by RTD transmitters which provide high repeatability and wide turndown. Their total error usually does not exceed 0.5% of full scale. 

The liquid turbine meter is one of the most accurate meters having the highest rangeability, and can handle practically any pressure and extremely high and low temperatures. Their capacities are listed in Table 3.92, and their installation is illustrated in Figure 3.93. Turbine flowmeters in gas service are similar but designed for higher velocity and lower torque. 

The liquid-nitrogen flow rate was measured with a turbine flowmeter. The total pressure of the jet exhaust Ptj was measured at an orifice in the model plenum chamber by a Precision Pressure Balance transducer. The total temperature of the CO2 exhaust was measured by a thermocouple in the line leading into the vacuum chamber. This thermocouple was downstream of the pressure-regulating valve and therefore measured the total temperature of the CO2 after the expansion to near the jet total pressure. The total temperature and the total pressure of the jet were used in a one-dimensional isentropic flow equation for choked nozzles to calculate the mass flow of CO2. The specific heat ratio used was that corresponding to the total temperature and pressure of the jet. 

Classic flow rate measurement tools are mass flowmeter, electromagnetic flowmeter, rotameter, and turbine flowmeter, their measurement ranges being normally larger than 10 m /s (0.1 mL/s). But in microscale flows, the range of flow rate is usually 10-10 m /s, in other words 10 pL/s— 1 iiL/s. In nanoscale flows, the flow rate is from 10 to lOm /s (IpL/s IfL/s). So the measurement and calibration methods will be different for micro- or nanoscale flows, compared to classic macroscale flows. 

Turi>o-Bar, Insertion turbine flowmeter, EMCO Flowmeters... 

Fluid-power flowmeters are used in low-velocity, moderately viscous flows. In addition to industrial control applications, turbine flowmeters (Fig. 18.10(a)) are sometime used as speed indicators for ships or boats. Paddle wheel flowmeters (Fig. 18.10(b)) are used both in closed- and open-flow applications such as liquid flow in flumes. Since a fluid-power gear motor (Fig. 18.10(c)) is a constant volume device, motor shaft speed is always a direct indication of fluid flow rate. 

FIGURE 18.10 Fluid power flowmeters (a) turbine flowmeter, (b) paddlewheelflowmeter,(c) gear motor flowmeter. 

RP31.1 Specification, Installation, and Calibration of Turbine Flowmeters. 

Among the indirect volume flowmeters, turbine flowmeters are the most important. They measure the speed of the flowing medium from the speed of an impeller, or rotor. There are devices arranged in an axial or radial direction to the flow. Turbine flowmeters can be used for liquids, gases, and vapors. 

There exist gas turbine flowmeters for flows up to 4500 m h [4]. Linearity is 1% over a flow range of 20 1 [4]. Rangeabilities can be as much as 100 1. If one wants total volumes using flowmeters, for example for accounting purposes that require high accuracy, then the instantaneous measurement must be integrated with time. This can be accomplished with pneumatic or electrical counters. 

It will be shown that there is a direct correlation between the water and liquid-hydrogen calibrations on one turbine flowmeter within 2 and on the orifice within 5. ... 

As a true volume flow measurement technique, the turbine flowmeter is an outstanding device having excellent repeatability. To achieve this excellence, it must, however, be used correctly. All too frequently, the turbine flowmeter is misapplied either by using it outside of its specified flow range or in two-phase fluid applications. 

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