Steam divided into saturated steam and superheated steam, in general, manufacturers will give saturated vortex flowmeter, superheated steam mass flow rate range table for user selection, in order to determine the diameter size.
For superheated steam to compensate the temperature and pressure, in the true sense of saturated steam temperature or pressure compensation, according to temperature and pressure when measuring density check table to ensure the required quality traffic.
Due to the condition changes, when actual measurements of saturated steam and superheated steam may deviate from the original state of design, makes the usually by steam temperature and pressure to calculate its density change, the relationship between affect measurement accuracy.
There are two kinds of steam existence form, one is superheated steam, the other is a saturated steam.
For manufacturers in the customer's selection of vortex flowmeters order stage, will give you the flow range of saturated steam and superheated steam table to help the user selection, main is to help the customer determine the size of the diameter, the second press for temperature compensation if there is a request to confirm.
Generally speaking, if in the measurement of the medium is the superheated steam temperature and pressure compensation are needed, which is referred to as 'temperature compensation.
For ZhiZheng sense of saturated steam, only need to compensate the temperature or pressure is ok, at the same time, according to the measurement of temperature and pressure through the calculation of density table to get the required quality and flow rate.
Actual measurement in the process, due to the change of working condition and unstable, saturated steam and superheated steam may deviate from the original design, makes the usually by steam temperature and pressure to calculate its density change, the relationship between affect measurement accuracy.
This article is aimed at this kind of situation to analysis and explanation.
Superheated steam in the vortex flow computing devices according to the density of superheated steam temperature and pressure look-up table to calculate the mass flow rate, but when the superheated steam after long distance transmission, or due to improper measures of pipeline insulation, often because of the temperature to reduce the heat loss from overheating state into the critical saturation state, and even some steam condense into droplets by a phase change, then become wet saturated steam (
Wet saturated steam after the vortex flow meter
installed in the pressure reducing valve, wet saturated steam suddenly significantly reduced pressure, fluid of adiabatic expansion, the droplets evaporate part, absorb heat of vaporization from the liquid and vapor phases at the same time, the lower the temperature of liquid, if the temperature is lower much or evaporates before humidity is higher, can make the temperature down to rapid and new pressure of the saturated temperature, establish a new equilibrium, steam is still the saturated steam at this moment, if the pressure to reduce a lot or evaporates before humidity is low, due to water evaporation and the lower the temperature is still higher than new pressure after the corresponding saturation temperature, the steam into superheated steam.
The output of the vortex flowmeter with only through the measuring tube is directly proportional to the fluid velocity, when moisture saturated steam, water droplets on the influence of vortex street flowmeter output negligible, so you can think of vortex street flowmeter output entirely by various steam dry wet full part (
Caused, and the density of dry part according to pressure or temperature compensation pinpointed.
Steam metering part if the two sides agreed by steam when clearing fees, condensed water not to collect fees, the phase transition to measure the impact of small, can be ignored.
If also in accordance with the steam condensed water fee, the vortex street flowmeter measurement results on the low side.
After the occurrence of the evaporation, the former had no effect on compensation, just dry part of the increase in steam, dry degree increases accordingly, the latter is wet saturated steam into superheated steam, then the impact on the meter points the following three conditions: (
When the design has been given the steam into overheating, or difficult to determine what is the status, or sometimes is overheating sometimes is saturated state, so the temperature pressure compensation, the above phase change not influence the result of the measurement.
Design according to the saturated steam, and USES the pressure compensation, the above phase transition will lead to smaller error, namely the superheated steam temperature with saturated steam temperature difference caused by density difference of corresponding compensation error.
Design according to the saturated steam, but USES the temperature compensation, the superheated steam temperature as saturation temperature check density table, generally can cause larger error.
Solve the above problem has the following three ways: (
Will always steam flow meter installed in front of the pressure reducing valve, due to the steam without decompression, there is no phase change problem, so install before the pressure reducing valve, flow meter according to the compensation method for saturated steam processing, can guarantee the measurement accuracy.
If the flowmeter can only be installed behind the pressure reducing valve, can be added 1 pressure transmitter, temperature pressure compensation.
If better stability of the pressure reducing valve, flow meter can be upstream pressure value as a constant value is set to display instrument, temperature and pressure compensation.
Voltage compensation installation diagram: (
Instrument science and technology in this paper by embellish release, if you encounter any problems in the process of using the instrument, can call our domestic sales service hotline: 0517 -
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