Rationale of use flanged hood in local ventilation

Purpose. The hood is a common type of local suction in industry, it is characterized by simplicity of construction and low cost. It should be noted that not always its effectiveness is quite high, and to fully capture harmful emissions may require significant amounts of exhaust air. To resolve this problem the article suggests the ways of optimizing the design of hoods. The purpose is the study of the velocity field of airflow hoods with annular ledge-screen and without it. Methodology. In this work we used mathematical modeling methods. To assess the quality of the hood air velocity values were determined at the level of the ventilated surface in the range of its receiving opening. Finding. For convenience, the results of mathematical modeling are presented in graphs. In the graphs, one can estimate the dependence of the velocity of air flow on the distance from the receiving opening of the umbrella, and the angle of taper of the width of the screen, the annular ledge. It was found that the shielding hood annular shoulder there is an abrupt change in the speed of the transition to the zone bounded by the annular shoulder and ventilated surface. The magnitude of the jump depends on the distance between the plane of the receiving opening of the umbrella and ventilated surface. Using a circular ledge-screen allows you to increase the speed of the exhaust air in the zone of the receiving opening of the umbrella. By varying the width of the annular ledge possible to widely reduce the angle at the cone apex of the canopy. Originality. With the help of the dependences obtained for the determination of air velocity at the surface of the ventilated the effect of the annular shoulder on the value of this speed. There was also established the dependence between the taper angle and area of service hood. Practical value. Using a circular ledge in the receiving hole of the canopy makes it advisable to use it for localization of harmful emissions from sources with large area in reduced height accommodate local exhausts.