Near fields of annular slotted hoods measured via 2D-PIV

In order to improve the effectiveness of a local exhaust ventilation system, an attempt is the changed hood geometry by adding a plate. The near fields of a simple exhaust and the annular slotted hoods with different slot widths are measured by a 2D-particle image velocimetry (PIV) system. The time-averaged velocity fields show that the slotted-hood designs enhance the capture velocities beyond half a diameter (0.5D) downstream the hood. The relative velocity increase coefficient (IC) along the hypothetical boundaries in the near fields was proposed to compared with the simple exhaust and determine the effect of slot width on the capture velocity enhancement, the IC for different slot widths is approximately 109%-130%. To predict the velocity at downstream of the hood for a given slot width and velocity, a unimodal-skewed distribution model was developed with a correlation coefficient of approximately 94%. Regarding turbulence statistics, the influence of the plate only involves the near hood region. The higher-order statistics also show no obvious differences between slotted hoods with different slot widths. In general, this study not only motivates us to design and improve the performance of LEV systems for forced advection problems by adding a baffle plate, but also provides benchmark flow data for a follow-up numerical simulation study.