User:El sjaako/sandbox

Gas flow, as we use it, can be expressed in: - Volume (f.i. l/min) - Standardized or Normalized flow (f.i nlpm or slpm) - Real Mass flow (f.i. Gr/min or Kg/hr) Relation between Volume flow and Real mass flow:

$$\mbox{Volume (f.i. l/min)}\cdot\mbox{Actual density (f.i. gr/l)}= \mbox{Real Mass flow (f.i. Gr/min)}$$

Relation between Normalized flow and Real mass flow:

$$ \mbox{Normalized flow (f.i nlpm)} \cdot \mbox{Normalized Density (f.i. gr/l at }0^\circ{C/1013.25)}= \mbox {Real Mass (f.i. Gr/min)}$$ Relation between Volume and Normalized flow To calculate Volume flow (f.i. l/min) to Normalized flow (f.i nlpm) you need to apply the Law of Boyle/Gay-Lussac

Volume and Real Mass are easy, but what about Standardized or Normalized? Standardized or Normalized means “Referred to predefined conditions”. In case of gas it means predefined Pressure and Temperature, because those are variables that relate Mass to Volume. The relation between Volume, Pressure and Temperature for gasses is defined in the Law of Boyle/Gay-Lussac. There is a lot of confusion around these values. S or N in front of a unit are two different items with a difference of 7.2 %. Compressor manufacturers specify their capacity in M3/hr on the inlet of the compressor. So this is close to Standardized values.

Below some additional information

Standardized or Normalized conditions:

Sierra measures Mass flow not Volumetric flow. The best and most logical way to define mass flow units is Kg per time unit, however in the gas industry we often translate a volume to certain standard conditions. These standard conditions are not always the same and can if interpreted wrong create big errors.

For instance, if we have a vessel of 1 m3 filled with air at 100°C and 10 Bar, what would the volume be if we keep the same amount of air molecules (=Mass) under the conditions of 1013,25 mBar (abs) and 0ºCelsius ? (referred to as “normal” like in nm3/hr), (we assume Pamb to be 1013,25 mBar)

And what under the conditions of 1013,25 mbar (abs) and 21,1 Degrees Celsius ? (referred to as “standard” as in SLPM)

Mass flow can be calculated with the law of Boyle/Gay-Luzac.

$$Mass=\frac {273.15+Tref}{273.15+Tact}\cdot {\frac{Pamb+Pg}{1013.25}}\cdot \mbox{Actual (Volume, flow or speed)}$$

The formula to calculate from Mass to Actual is as follows

$$Actual=\frac{273.15+Tact}{273.15+Tref}\cdot{\frac{1013.25}{Pamb+Pg}}\cdot \mbox{Mass (Volume, flow or speed)}$$ In which:
 * Tact = Actual proces temp (C)
 * Tref = Reference Temp (Normal=0°C, Standard=21,1°C
 * Pamb = Absolute atmospheric pressure (mBar)
 * Pg= Process pressure (mBar gauge)

(The answer is 7,957 m3 at 0°C and 8,572 at 21,1°C)

In Europe we mostly use “Normal”, referred to 0°C but at other places “Normal” can be used to mean 21,1ºC so it always need to be defined so there is no confusion.