Differences between mass flow rate and volume flow rate for the flow of a certain medium
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In a differential pressure flow meter, the flow rate is proportional to the square root of the differential pressure; therefore, the measured differential pressure must be taken to the power of one half in order to obtain the corresponding flow rate. The result obtained in this way represents the mass flow rate. What meaning does the number obtained without taking the square root have? Is it the volumetric flow rate figure?
The output of the flow transmitter is proportional to the square root of the input differential pressure; if the relationship between the secondary instrument and flow rate is linear, then the transmitter’s output must be taken to the power of one half. The method is: first convert the differential pressure to a percentage, take its square root to obtain the flow percentage, and then convert it into an output current. If a flow transmitter has a differential pressure range of 0–10 KPa, it corresponds to a flow rate of 0–50 t/h. When the differential pressure is 5 KPa, the output current is as follows: 1. Convert 5 KPa to a percentage: 5/10 * 100% = 50%. 2. Convert this percentage value into a flow rate percentage by taking the square root: √50% = 70.71%. 3. Convert this flow rate percentage into an output current: (20 – 4) * 70.71% + 4 = 15.31 mA. 4. The corresponding flow rate is 70.71% * 50 = 35.355 t/h. For a flow rate of 25 t/h, the differential pressure should be: 50% squared = 25%, and 25% * 10 = 2.5 KPa; the same method can be applied to other values as well. The square root of 25% equals 50%; the square root of 50% equals 70%; the square of 70% equals 50%. If square roots are not used, is the resulting value the volumetric flow rate?
The relationship between volumetric flow rate and mass flow rate is determined by the density of the medium, and it has nothing to do with taking square roots.
The poster said, “So it is necessary to take its square root, and the resulting value corresponds to its mass flow rate.” What meaning does the number obtained without taking the square root have? Is it the volumetric flow rate figure? ” Taking the square root yields the flow rate value, but whether this value represents volumetric flow rate or mass flow rate depends on the choices made during the design of the throttling device. If the square root is not taken, the differential pressure value is displayed; if a linear calculation is performed, this figure has no meaning. It can’t be a volume figure. To determine the mass flow rate using a differential pressure flow meter, in addition to measuring the differential pressure to obtain the volume flow rate, it is also necessary to perform compensation calculations for temperature and pressure in order to determine the density of the fluid; this density is then multiplied by the volume flow rate to get the mass flow rate.
The relationship between mass flow rate and volume flow rate is determined by the density of the medium. It has nothing to do with the others
Taking the square root of the percentage value on the differential pressure transmitter and then multiplying it by the maximum flow rate gives its mass flow rate; simply multiplying the percentage value on the transmitter by the maximum flow rate gives its volume flow rate. Is this understanding correct?