40 CIRCULAR 7 4 0, V. S. DEPARTMENT OF AGRICULTURE 



V. 



..J. 



Lateral 



Figure 11. — Ducts that are streamlined with easy curves around turns avoid 

 resistance to air flow from eddies and turbulence. A, Deflector vane installed 

 to throw part of the flow into a vertical duct. 



is greatest in parts where the velocity is high and where the air changes 

 velocity- or direction. Air flows like water, and abrupt changes induce 

 turbulence and eddies that increase the resistance (fig. 11). Abrupt 

 changes in the area of ducts and unrounded turns should be avoided. 



Even in rounded turns 

 the flow of air is accel- 

 erated by curved split- 

 ters (fig. 12) that aid 

 the air in making the 

 turn with a more equal 

 velocity over the en- 

 tire face of the duct, 

 Thus dividing the air 

 stream at turns pre- 

 vents piling up pres- 

 sure against the out- 

 side face of the turn 

 and reduces turbu- 

 lence. 



The inside of the 

 ducts should be free of 

 obstructions and as 

 smooth as possible. 

 Where obstructions, such as posts or girders (fig. 13), cannot be 

 avoided, it is worth while to ease the flow around them by installing 

 air splitters to give a streamline effect. This is particularly true 

 at points where the velocity is high. Large ducts are preferable, 



Figtjee 12. — Section of air duct with lateral, show- 

 ing splitters for preventing excessive air turbu- 

 lence in the bend. (Not drawn to scale.) 



