The Critical Capture Velocity of Coal Ash Particles Oblique Impact on a Stainless Steel Surface

In this paper, the rebound characteristics of coal ash particles impacting on a stainless steel surface are studied experimentally with the background of ash deposition on the heating surface of the boiler. The impact processes of coal ash particles with different incident angles were recorded by high-speed digital camera technology. The evolution of the normal restitution coefficient with incident normal velocity was obtained. Three different static contact theories are used to establish the equations of motion to predict the critical capture velocity of particles. The results show that the normal restitution coefficient first increases and then decreases with the increase of incident normal velocity. The critical capture velocity of particles under the three models was predicted. It is found that the prediction results of the Brach and Dunn (BD) model for the critical capture velocity are close to the experimental results. Taking the particle of size 23 μm as an example, the maximum critical capture velocity predicted by BD model is 1.0611 m/s at 0° incident angle. The minimum value is 0.7940 m/s when the incident angle is 45°.The critical capture velocity of particles decreases with the increase of incident angle and with the increase of particle diameter.

A Study on Improvement Capture Velocity for Increasing Inhalation Efficiency of Hood in Local Ventilation System

This study was numerically and experimentally investigated on improvement capture velocity for increasing inhalation efficiency of hood in local ventilation system. The inhalation efficiency of hood was studied to improve by increasing inhalation force of the hood that attached the new device named “Gas-Guide-Device (GGD)”. Also, harmful material that couldn’t inhale in hood was removed by increasing capture velocity at the edge of hood. For the numerical study, computational fluid dynamic (CFD) was used to predict the improvement of flow velocity with attached GGD in hood. To verify the numerical result, the flow velocity was experimentally measured using a hot-wire type anemometer. As a result of the numerical and experimental study for improving the effect of the GGD on the inhalation efficiency of the hood, it was verified that the capture velocity around the hood inlet was relatively higher for the hood with the GGD than for the one without it.