Experimental study for Non-adiabatic wall conditions with a 3D printed temperature-controlled aluminum critical flow venturi nozzle

This paper presents an experimental setup designed to analyse the impact of thermal boundary layer effects on the flow of Critical Flow Venturi Nozzles (CFVN). The setup utilizes a toroidal nozzle equipped with an internal heat exchanger concentrically positioned around the throat. Manufactured at PTB using aluminium via 3D printing, the nozzle boasts a throat diameter of 7.5 mm, closely adhering to ISO 9300 standards. Dimensional characterization was conducted using Coordinate Measuring Machines (CMM) at PTB. The CFVN was connected to an external temperature bath, allowing for temperature control ranging from −25 °C to 80 °C. Flow calibrations were performed against a reference standard at PTB's test facility, spanning air pressures up to 16 bar (Reynolds number ranging from 47,000 to 1,500,000). Results identified conditions for adiabatic operation closely aligned with gas properties expectations. The study presents initial calibration results comparing different heat flows from the exchanger to conventional conditions, aiming to enhance theoretical concepts for deriving nozzle discharge coefficients and reducing uncertainties outlined in ISO 9300.