Experimental application of particle imaging to fluid velocity analysis in building drainage systems

Previous research into the hydraulic and pneumatic conditions in the pipework associated with building drainage waste and ventilation (DWV) systems has been interpreted as suggesting that the flow regime within the vertical stack consists of an annular water flow entraining a central air core with an associated pressure drop. However, previous evidence had suggested that a significant proportion of the water was found in the air core by Pink[1] and Wyly and Eaton[2]. A new model has recently been proposed by Campbell & MacLeod[3] which suggests that the airflow entrainment is due to the distribution of work between the water annulus and the droplets falling in the central air core. This paper describes the investigation of the velocity profile of mixed phase fluid flow in building DWV systems utilising the Particle Tracking Velocimetry (PTV) flow measurement technique previously established by Campbell[4]. PTV is a non-intrusive optical flow measurement technique that supplies an instantaneous sample of velocity throughout a two dimensional plane in the flow field. The results of the PTV investigation support the assumption that water droplets exist in the air core and have a velocity greater than that of the water annulus.