DILLEMA ABOUT INFLUENCE OF SPLITTER VANES ON HYDRAULIC CHARACTERISTIC AT RECTANGULAR RADIUS ELBOW

Abstract

Elbows are fittings in rectangular ducts which change the direction of the air stream without changing the air quantity or average velocity. When there is a change in direction in a duct then duct walls must absorb the sudden impact of the air in order to redirect the airflow to the desired direction. Splitter vanes assist the airflow in making a smoother and more gradual change in direction, thus transferring less impact and less force to the duct walls. While the splitter vane surfaces do add a small amount of friction, the amount of energy loss due to friction from the vanes is very little compared to the energy loss resulting from the airflow taking an abrupt change in direction. Splitter vanes in rectangular elbow are perhaps one of the greatest sources of conflict between the state that splitter vanes can cause the ductwork to become less efficient by increasing the pressure drop in the system and contrary that the obtaining a uniformity of the airflow into the rectangular ducts give better efficiency and lower pressure drop. This paper presents results of experimental and numerical research of hydraulic characteristic at rectangular radius elbow without and with splitter radial vanes at different relative position in the domain of elbow. The results are presented through the loss coefficient of elbows which is function of the elbow radius, duct dimensions, angle of turn and Reynolds number. The numerical results of fluid flow domain are comparatively used for presenting the influence of splitter vane on uniformity of discharge distribution in the space of the elbow and on uniformity of fluid flow velocity profile. The results show that the splitter vanes are proven very valuable for reducing pressure losses and increasing system efficiencies. Designers should add or remove turning vanes from the design with aim to specify fittings with the highest possible efficiency and to increase system efficiency at every available opportunity.