How to convert between standard cubic meters per hour and working condition cubic meters per hour?
Thread Content
As the title says. The range of the on-site gas flow meter is XX-XXX standard cubic feet per hour. How can this be converted to the range applicable under actual operating conditions on site?
This post was last edited by ylb913 on 2018-6-21 at 20:26. The phrase “convert to the range corresponding to the actual operating conditions on site” is incorrect; it should be “convert to the flow rate corresponding to the actual operating conditions on site”. This comes from PV=nRT. It is particularly important to note that the P here refers to absolute pressure, not gauge pressure ； T is 273+t. Derivation: n remains the same, and R is also a constant. As a result, nR takes on a constant (equal) value under different operating conditions, since nR = PV/T = P1V1/T1 = P0V0/T0. Thus, we have P1V1/T1 = P0V0/T0, where 1 represents the actual operating conditions and 0 represents the standard conditions. Under the specified operating conditions, P0=1 and T=273; therefore, P1V1/T1=1*V0/273. Then what is V0? It is the flow rate displayed on the instrument (flow rate at standard conditions) ； What is required is V1 (the flow rate under actual operating conditions). V1=V0*(1/P1)*(T1/273). It is easy to understand that the higher the pressure, the lower the flow rate, and the higher the temperature, the greater the flow rate. The above calculations are kept as simple as possible: for temperature conversion, 273.15 is replaced by 273 ； Pressure conversion: one standard atmosphere, one industrial atmosphere, and 0.1 MPa are all considered equivalent to one standard atmosphere.
The standard state refers to a pressure of one atmosphere (101.325 KPa) and a temperature of 0 degrees. Because under standard conditions, the density of a gas is a constant, and this density multiplied by the volume at standard conditions gives the mass flow rate; therefore, the volumetric flow rate under standard conditions is equivalent to the mass flow rate. Therefore, when selecting a gas mass flow meter or gas mass flow controller, it is necessary to confirm whether the flow rate range corresponds to the standard volumetric flow rate under standard conditions (that is, the mass flow rate). If it is the flow rate under operating conditions, it must be converted to the standard-condition volume flow rate using the following formula. Without considering the compression factor, the conversion formula between the gas flow rate under standard conditions and the flow rate under actual operating conditions is: Q_standard = Q_actual * [(P_gauge + 0.1)/0.1] * [273.15/(273.15 + T_actual)]
I usually just go by: whatever the stated value is, that’s what it actually is. . . .
At that time, density under operating conditions * volumetric flow rate / density under standard conditions = flow rate under standard conditions; it can be calculated simply in this way. For temperature and pressure compensation, it is calculated using the formula: Q under standard conditions = Q under operating conditions * [((P gauge + 0.1) / 0.1)] * [273.15 / (273.15 + T under operating conditions)]
1. Industries with different standard conditions vary; generally, pressure is set at one standard atmosphere (101.325 KPa), but the temperature can be either 0°C (273.15 K) or 20°C (293.15 K)； 2. In the formula, “P gauge + 0.1” is incorrect; it should be the absolute pressure value, meaning that 0.1 represents the local atmospheric pressure.