ABSTRACT
An understanding of flow measurement requires basic
knowledge of the physical properties of air, such as tem-
perature, pressure, density, specific gravity, viscosity,
sonic conductivity, and compressibility. The density of
air changes with changes in temperature and pressure.
Because of this, airflow rate is usually defined at
“standard” conditions, i.e., 20C temperature and 101.3 kPa pressure. Mass flow depends on volume and
air density. The Ideal Gas Law provides a relationship
between pressure, temperature, and density. Methods are
available to correct for compressibility due to high velocity
flows.
