ABSTRACT
Flow rate measuring devices utilize some property of the fluid to be measured — generally, density or viscosity — as well as gas laws or fundamental thermodynamic properties of the fluid. This chapter considers various devices such as the orifice meter, venturi meter, rotameter, and mass flow meter. As with orifice meters, an empirical relationship between flow rate and pressure drop is developed by calibration. Mass flow meters should be calibrated against a primary or intermediate standard using the actual gas to be measured. Most rotameters operate in the turbulent flow regime; and for turbulent flow around the float, the drag force is proportional to this upward "pressure force", and thus proportional to the net downward forces. Rotameters are frequently built into air monitoring or other gas handling instruments to provide a quick and easy way to check flow rate.
