# Gas Flow Rate

Published: | Updated: August 16, 2019

## Definition - What does Gas Flow Rate mean?

A gas flow rate is the volume of gas that passes a particular point in a particular period of time.

Gas flow rate calculations are used extensively in the disciplines of chemical engineering and process engineering. Flow rate calculations through pipes are often challenging because pipes can vary in diameter along their length. The same basic calculations can be applied to any kind of gas.

## Corrosionpedia explains Gas Flow Rate

Gases are compressible and change volume when placed under pressure, are heated or are cooled. A volume of gas under one set of pressure and temperature conditions is not equivalent to the same gas under different conditions. References are made to "actual" flow rate through a meter and "standard" or "base" flow rate through a meter with units such as actual cubic meters per hour (acm/h), thousand standard cubic meters per hour (kscm/h), linear feet per minute (LFM) or million standard cubic feet per day (MSCFD).

Gas flow rate can be directly measured, independent of pressure and temperature effects, with thermal mass flow meters, Coriolis mass flow meters or mass flow controllers. The measurements are related to the material's density. The density of gases depends greatly upon pressure, temperature and to a lesser extent, composition.

When the upstream pressure is greater than or equal to twice the downstream pressure, the gas flow rate can be calculated with the formula:

816 x P1

QG = CV ------------------

√ (S.G. x T)

where:

QG = gas flow in cubic feet per hour

CV = the coefficient of flow

P1 = the upstream (inlet) pressure in psia

S.G. = the specific gravity of the medium

T = the absolute temperature in °R (i.e., °F + 460)

Gas flow rate is important, for example, in welding a uniform flow of gas is needed to shield the molten metal by blanketing it properly to avoid atmospheric contamination, which can lead to increased levels of oxidation or even porosity of the finished weld.

Gas flow rates can vary and it is important to select the correct flow rate for each application, as this can improve efficiency and ensure a quality weld. It also varies according to the type of application — for example, manual welding typically requires a lower flow rate than mechanized or automated welding systems.