E+H mass flow meter’s
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I have a question regarding mass flow meters: there is an E+H mass flow meter in use on site for measuring the volumetric flow rate of gases, with a designed range of 0–5 NM3/h and a minimum flow rate of 0.2 NM3/h. The upper and lower measurement limits for the on-site flow meter are set at 0–5 M3/h; subsequently, through the DCS system, the flow rate measured by the mass flow meter is converted into standard cubic flow rate using the ideal gas equation. The gas pressure before the flow meter is 0.33 Mpa to 0.35 Mpa, and the temperature is essentially the ambient temperature, fluctuating between -5°C and 15°C throughout the day. A pneumatic control valve is installed after the flow meter to regulate the flow rate. Why, when the valve is opened to 0.1%–3% at different times, does the flow rate displayed on the computer always remain at 0.28 NM3/h? Is it due to the effect of temperature changes? Also, with the valve set to automatic mode and the desired flow rate fixed at a certain value, why is the valve opening larger at night and smaller during the day? Sometimes, during the day, the valve opening value may keep decreasing, but the flow rate remains constant. One final question: if the pressure difference before and after the valve remains constant, and the valve opening remains unchanged, will the mass flow rate and volume flow rate of the gas passing through the valve change?
The reason why the flowmeter reading remains unchanged may not be entirely due to temperature changes, but rather the result of a combination of other factors. First, it is necessary to confirm whether the flow meter is accurately calibrated and whether the minimum flow limit (0.2 NM3/H) is appropriate for the current operating conditions. When the actual flow rate approaches or falls below this minimum flow rate, the flow meter may be unable to measure accurately, resulting in a fixed displayed value. As for the issue of changes in valve opening, this is usually related to the load, fluctuations in system pressure, and control strategies. Daytime and nighttime temperatures, as well as other uses of the system, can cause changes in system pressure, which in turn affects the valve opening degree. If the system pressure is high, the valve needs to be opened further to maintain the same flow rate ； Conversely, it needs to be opened wider. When the pressure difference before and after the valve as well as the valve opening remain constant, theoretically, if no external factors (such as temperature or pressure) change, the mass flow rate and volume flow rate of the gas will not change. However, in practice, slight changes in environmental and equipment conditions can lead to variations in the actual flow rate. It is recommended to perform regular calibration and maintenance of the flow meter, while also monitoring and recording detailed data on flow rate, pressure, and temperature, in order to more accurately identify issues and make necessary adjustments. .
It might not be professional, just mentioning it. Why is the mass flow meter reporting flow rate under operating conditions? Shouldn’t it directly output the mass? A mass flow meter can measure the density in real time and then calculate the mass flow rate. I didn’t look into it in detail, but I think it might be putting us off from using it effectively. Thinking too much. ?
A mass flow meter directly measures the mass flow rate. Since the density of the gas under standard conditions is known, isn’t it possible to determine the volume flow rate under standard conditions directly?