What do you need to pay attention to when using vortex flowmeters for steam metering?
　　
Steam is divided into saturated steam and superheated steam. In general, vortex flowmeter manufacturers will provide a table of saturated, superheated steam mass flow rates for user selection in order to determine the size of the caliber. For the superheated steam to be temperature and pressure compensation, the electromagnetic flowmeter needs only temperature or pressure compensation for the true sense of saturated steam. During the measurement, check the density table according to the temperature pressure to obtain the required mass flow. In actual measurement, due to the change of operating conditions, both saturated steam and superheated steam may deviate from the original design state, which makes the relationship between the steam temperature pressure and its density generally changed, which affects the measurement accuracy.
　　
Superheated steam
　　
In the flow calculation device, the mass flow rate can be obtained based on the temperature and pressure of the superheated steam, and the density can be obtained by looking up the table. However, when the superheated steam is transported over a long distance, or because the pipe insulation measures are improper, the heat loss temperature is often decreased from The overheated state enters the critical saturation state, and even part of the steam condensation changes into a water droplet, and it becomes a wet saturated steam (saturated steam).
　　
The output of the vortex flowmeter is only proportional to the flow velocity of the fluid flowing through the measuring tube. When the saturated steam is measured, the influence of the water drop on the output of the vortex flowmeter is negligible. Therefore, it can be considered that the output of the vortex flowmeter is completely controlled by the It is caused by the saturation of the dry (saturated) portion of the steam, and the density of the dry portion can be accurately detected based on pressure compensation or temperature compensation. If the two parties agreed to settle the cost of the dry part of the steam and the condensate does not charge for steam metering, the effect of the phase change on the measurement is negligible and can be ignored. If the condensate is also charged as steam, the measurement result of the vortex flowmeter is low.
　　
2. Wet saturated steam
　　
When the vortex flowmeter is installed in the pressure reducing valve, the wet saturated steam suddenly decompresses, the fluid appears adiabatic expansion, the water droplets evaporate partially, and the vaporization heat is absorbed from the liquid phase and the vapor phase, so that the vapor-liquid phase temperature is reduced. If the temperature does not decrease much or the humidity before the evaporation is high, the temperature will rapidly decrease to the saturation temperature corresponding to the new pressure and a new equilibrium will be established. At this time, the steam is still saturated steam if the pressure is reduced much or before the evaporation. When the humidity is low, the steam becomes superheated steam because the water droplet evaporates and the temperature is still lower than the saturation temperature corresponding to the new pressure.
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