gas “standard state”(Industry abbreviation)“Standard condition”The corresponding volume unit symbol is Nm³The flow unit is Nm³/h）It is designed to unify gas volume measurement and eliminate the influence of temperature and pressure on gas volumeStandardization reference conditionsDue to the strong volume of gas “Temperature pressure dependence”——When the temperature rises, the distance between gas molecules increases and the volume expands. When the pressure rises, molecules are compressed and the volume shrinks, so it is necessary to pass through“Standard condition”Converting the gas volume under actual operating conditions to the volume under uniform conditions is necessary to achieve flow comparison, measurement, and trade settlement in different scenarios.

1、 The core definition of standard conditions: a unified temperature and pressure benchmark

The essence of standard conditions is to set the volume of gas “Fixed temperature（T₀）And pressure（P₀）Benchmark”The volume of any gas under this reference (i.e“standard volume”，Nm³）All have comparability.

However, it should be noted that different countries/Due to differences in historical habits or application scenarios, there are temperature and pressure regulations for benchmark conditions in the industry

Two mainstream systemsIn practical use, specific standards need to be clearly defined to avoid confusion.

IIComparison of two mainstream standard condition systems

*Note: Chinese National Standards（GB/T 20727-2006）Clearly stipulate that the standard conditions for gas flow measurement are 101.325 kPaThe0℃, withISOConsistent universal system.*

threeThe core function of standard conditions is to solve the problem of gas volume Incompatibility

Gas's“Actual volume”(such as operating condition volume, symbol)m³）Will vary with the temperature on site（T）And pressure（P）Real time changes, direct comparison is meaningless. The core value of the standard condition is throughTemperature pressure conversionUnify the volume under different operating conditions to standard conditions, achieving “Fair measurement”and“Comparable data”.

For example:

·1m ³ of airWorking conditions（25℃、0.8MPa）Below, the molecules are highly compressed, resulting in a larger actual mass;

·1m ³ of airStandard condition（0℃、101.325kPa）Below, the molecular spacing is large, but the actual mass is small;

·If converted to standard conditions: under the above working conditions1m ³ of air, corresponding to a standard volume of approximately7.8 Nm³(Calculated based on the ideal gas state equation).

Clearly, only through“Standard condition volume（Nm³）”Only then can it accurately reflect the gasThe actual quantity of mass or substanceThis is also the annotation of traffic units “Nm³/h”The core reason——It represents“Volume of gas in standard state per hour”Essentially, it is correct“mass flow rate”Indirect measurement.

fourStandard condition and The correlation between "working conditions" and "ideal gas state equation"

Standard condition volume（Nm³）Compared to the actual working condition volume（m³）The core basis for conversion isIdeal gas state equation(Neglecting the volume and interaction forces of gas molecules, acceptable errors in industry):

fiveKey precautions

1. Clarify the standard system to avoid confusionDifferent industries may adopt different temperature and pressure standards (such asIf the difference between 20 ℃ and 0 ℃ is not clearly defined, it may lead to measurement errors (for example, the volume of the 20 ℃ standard condition is approximately 7% higher than that of the 0 ℃ standard condition). In practical applications, industry standards such as GB/T 20727 for industrial use and GB/T 19204 for gas use should be given priority.

2. Nm ³ "does not represent" quality ", but can indirectly reflect qualityThe relationship between standard volume and mass needs to be combined with gas density (under standard conditions, the air density is about)1.293 kg/Nm³， Natural gas is approximately 0.7~0.8 kg/Nm ³, which means "mass=standard condition volume x standard condition density".

3. Only applicable to gases, not applicable to liquidsThe volume of liquid is minimally affected by temperature and pressure, so there is no need for it The concept of "standard condition" can be directly measured in m ³ or L.

Overall, the standard situation（Nm³/h）It's gas metering“universal language”——By fixing the temperature and pressure benchmark, the influence of operating conditions on volume is eliminated, ensuring the accuracy, comparability, and fairness of gas flow data in different scenarios.