In some cases, such as an air restrictor, it may be useful to describe a flow obstacle by its thermodynamic behaviour instead of some geometric data.

In such case, the
obstacle element, that will be placed into the manifold as a connection between two nodes (i.e. volume, environment, valve area), should previously be placed on a flow bench, where the user should measure, the given "inlet" gas state (pressure, temperature) being constant, for several "outlet" pressures (always lower than the inlet pressure) the mass flow rate across the obstacle and its outlet temperature.