The correct selection method and suggestion of steam flowmeter

 many different kinds of flowmeter selection, flow meter, but the measurement of steam flow meter products is relatively small, commonly used steam flowmeter are mainly orifice, V cone, vortex street, bend, power, industrial flow meter as many as more than 60 varieties, so, for history is not yet, any range, any one for any fluid flow state and any conditions of use are using flow meter, each flow meter has its particular applicability, has its limits.If the flow meter is not selected properly, the flow must be measured incorrectly.But flow measurement is a complex technology, and flow meter variety, even for a certain application, the selection of a suitable flow meter will become a very technical work, need to make a final choice before carefully and in-depth consideration and weighing many factors related to the measurement problem.

Five main factors: characteristics of the measured flow, production process, installation conditions, maintenance requirements, and characteristics of the flow meter.For steam measurement, the above five factors should also be considered.Here, the characteristics of flow meter, installation conditions, maintenance requirements and the selection of flow meter should pay attention to several issues.

At present, the main instruments for measuring steam flow are vortex flowmeter, differential pressure flowmeter (orifice plate, average velocity tube, bent pipe), diverging rotor flowmeter, bulbar flowmeter, float flowmeter, etc. The vortex flowmeter, orifice plate flowmeter and elbow flowmeter are mainly discussed here.

2.1 vortex street flowmeter for steam measurement: integrated temperature compensation or integrated pressure compensation vortex street flowmeter can be used to measure the flow rate of saturated steam, and integrated temperature and pressure compensation vortex street flowmeter can be used to measure the flow rate of superheated steam.

Vortex flowmeter is a new type of flowmeter developed successfully based on karman vortex flowmeter principle.It is reported that the proportion of vortex flowmeter used in Japan, Europe and the United States and other developed countries has increased substantially, and it has been widely used in various fields.It has the following characteristics:

(1) simple and firm structure, no moving parts, long-term operation is very reliable;

(2) maintenance is very convenient, low installation costs;

(3) the sensor does not directly contact the medium, stable performance, long life;

(4) the output is directly proportional to the flow of the pulse signal, no zero drift, high precision, and convenient with the computer network;

(5) the measuring range is wide, with a range ratio of 1:10

6 pressure loss is small, low operating costs, more energy saving significance;

7 within a certain Reynolds number range, the output signal frequency is not affected by the physical properties and components of the fluid, the meter coefficient is only related to the shape and size of the vortex body, the measurement of fluid volume flow without compensation, replacement accessories without re-calibration of the meter's coefficient;

8, a wide range of applications, gas, liquid flow can be measured;

9) the approval period is 2-4 years.

At the same time, the vortex flow meter also has the following limitations:

(1) vortex street flowmeter is a kind of velocity flowmeter, the stability of vortex separation is affected by the velocity of flow, so it has certain requirements on the straight pipe section, generally the first 10D, 5D;

(2) when measuring the liquid, the upper limit of velocity compression damage and gas corrosion phenomenon is limited, generally 0.5-8m/s;

(3) to measure the gas, the upper velocity is limited by the compressibility of the medium, and the lower velocity is limited by the Reynolds number and the sensitivity of the sensor. The steam is 8-25m/s.

(4) stress vortex street flowmeter is more sensitive to vibration, so in the larger vibration of the pipeline installation flow timing, the pipeline must have a certain shock absorption measures;

(5) the stress vortex flowmeter adopts piezoelectric crystal as the detection sensor, so it is limited by temperature, generally -40-+300℃.