Accuracy analysis of vortex flowmeter in measuring steam flow rate

Uncertainty in measurement of superheated steam flow

There is a one-to-one correspondence between the temperature and pressure of saturated steam, and there is only one independent parameter between the two.Saturated steam is easy to condense. If there is heat loss in the process of transmission, droplets or liquid mist will form in the steam, resulting in a decrease in temperature and pressure.Steam containing droplets or mist is called wet steam.Strictly speaking, saturated steam more or less contains droplets or fog, so different states cannot be described by the same gas state equation.The content of droplet or mist in saturated steam reflects the quality of steam.Dryness of steam is the percentage of dry steam per unit volume of saturated steam.It is difficult to accurately measure the flow rate of saturated steam. Generally, the flow rate of two-phase fluid cannot be accurately detected by the flowmeter. The steam pressure fluctuation will cause the change of the specific volume of the steam, and the measurement value of the flow rate will generate additional errors.Therefore, in the measurement of saturated steam, it is necessary to keep the steam breaking degree stable at the measuring point and take compensation measures when necessary.

No matter adopt what kind of flow measurement of saturated steam flow, under the condition of steam pressure fluctuation, pressure compensation measures must be taken, this is because the flow equation, the working conditions with the design conditions, the steam volume than reading will produce error, error of the size and the pressure of work and design deviation is related to the size of the actual pressure is greater than design pressure will appear negative error, otherwise there will be a positive error.The dryness of steam is an important condition for the accurate measurement of steam flow.the on-line steam dryness measuring instrument is being developed and applied to the steam flow metering and compensation system, which will further improve the accuracy of measurement.