Particle loss in a critical orifice

Particle deposition in different regions of a critical orifice assembly was studied numerically and experimentally. The investigated orifice is an O’Keefe E-9 (O’Keefe Control Co.) orifice whose diameter is 0.231 mm and critical flow rate is 0.455 slpm. The orifice assembly has an inlet tube (inner diameter=10.4mm,length=90mm) and outlet tube (inner diameter=6.2mm,length=60mm). In the numerical study, axisymmetric, laminar flow field of the orifice assembly was obtained first by solving the Navier–Stokes equations. The diffusion loss of nanoparticles was then calculated by solving the convection–diffusion equation. Inertial impaction and interception loss of 2–10μm particles was calculated by tracing particle trajectories in the flow field. In the experimental study, monodisperse NaCl (20–800 nm in aerodynamic diameter) and fluorescein-containing oleic acid (2–10μm in aerodynamic diameter) particles were used to test particle loss in both diffusion- and inertial impaction-dominated regimes. The numerical results were compared with the experimental data and good agreement was obtained with the maximum deviation smaller than 10.4%.