Duct Airflow Measurement by Tracer Gas – Development of a New Portable Device for convenient HVAC Auditing

The development of a new device for the injection of tracer gas is discussed with the objective of practical application in the field of HVAC airflow measurements. The uniform tracer gas dispersion for very short distances, when measuring airflow by the constant emission method is of great interest. This new injection device has a compact tubular shape, with magnetic fixation to be easy to apply to duct walls. After a preliminary study with an initial prototype already tested, further detailed experiments had been carried out, culminating in a second prototype. This paper presents the CFD study for new tracer gas injection device. This work shows that the major potential for tracer gas dispersion is the injection by two rows of sonic micro jets, oriented near perpendicular to the main flow. A parametric study is necessary for optimisation and best injection angle. Preliminary conclusions show that 90 to 70 degree angle relative to the main airflow direction, in the flow separation region, are one of the best strategies.