Volumetric flow rate is the volume of gas being transported across a defined boundary per unit time, i.e. liters/minute, cubic feet/hour, etc. A standardized flow rate is the volume of gas transported per unit time across a boundary with the measured gas volume converted to the volume the gas will occupy at a defined pressure and temperature.
Gas is compressible and gas volume will change as the gas temperature or gas pressure changes. Compressibility of gas for a hypothetical ideal gas is defined by the ideal gas law equation of state:
- P is the absolute pressure of the gas
- V is the volume of gas
- n is the number of moles of the given gas
- R is the universal gas constant
- T is the absolute temperature of the gas
Since gas changes volume with temperature and pressure, gas flow is commonly reported as standardized flow. No single universal standardizing temperature exists, however common temperatures used are 0 centigrade and 21.1 centigrade. A standardization pressure of 760mmHg1 is universally used. For any gas flow measurement, it must be clearly stated if the gas flow measurement is volumetric flow or volumetric flow that has been standardized with the standardization temperature and pressure clearly stated.
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