Mass flow rate control system for time-dependent laminar and turbulent flow investigations

Most experimental flow investigations are carried out under imposed steady-state flow conditions. The major reason for this is that there is a lack of experimental facilities to impose well-controlled time-dependent inlet and outlet conditions on flows. There is apparently no equipment available to supply, in a well-controlled manner, the mass flow rate for time-dependent internal flow investigations. The work described in this paper remedies this situation. It introduces the basic ideas for a mass flow rate control system for time-dependent laminar and turbulent flow investigations. A first unit was built for controlled mass flow rate variations in the range of 0–217.8 g min⁻¹ under atmospheric conditions corresponding to 0–180 l min⁻¹. With this first unit the authors demonstrate that the basic ideas put forward in the paper can be used to build mass flow rate control units for experimental fluid mechanics studies. The flow rate can be simply controlled by a voltage input. The system was designed to work up to frequencies of 125 Hz.