Turning vanes

Poor performance can result from fan inlet eccentric or spinning dow, and discharge ductwork that does not permit development of hiU fan pressure. Sometimes inlet restrictions starve a fan and limit performance. To obtain rated performance, the air must enter the fan uniformly over the inlet area without rotation or unusual turbulence. This allows all portions of the fan wheel to do equal work. If more air is distributed to one side of the wheel, such as with an elbow on the inlet, the work performed by the lightiy loaded portions of the wheel is reduced and capacity is decreased by 5—10%. The use of an inlet box duct on a fan can reduce capacity by as much as 25% unless there are turning vanes in the duct. Use of the vanes reduces the capacity loss to around 5%. 

Although the above description has concentrated on separation from a smooth surface, separation also occurs at sharp edges. Where separation is undesirable for a process reason, it can often be eliminated by redirecting the flow using turning vanes, ie, forcing it to hug the surface. 

FIG. 12-48 Doiible-tnick dryer. (A) Air-inlet duct. (B) Air-exhaiist duct with damper. (C) Adjnstahle-pitch fan 1 to 15 hp. (D) Fan motor. (E) Fin heaters. (F) Plenum chamber. (G) Adjustable air-blast nozzles. (H) Trucks and trays. (J) Turning vanes. 

Air turning vane A vane fitted in a ductwork bend to reduce pressure loss. 

Splitters Turning vanes inserted in a fluid flow system to reduce frictional losses. 

Turning vanes Curved vanes added to ductwork elbows in an attempt to ensure streamline flow and, by so doing, reduce turbulent losses. 

Either elbows of the radius type and without turning vanes or square mitered elbows equipped with single-thickness, extended-edge turning vanes are used. 

In cases where a uniform gas flow has simply been split for purposes of conveyance, it may be necessary to include baffles, turning vanes, or other flow devices, depending upon the intended entry configuration. In some instances, model studies are recommended to determine proper performance requirements particularly when it is felt that stratification of gas flows are anticipated. 

Turning vanes may be required to ensure distribution of the airflow across the catalyst. Computer modeling (CFD) or cold flow modeling may be required to ensure the proper air distribution and the proper design of the straightening vanes. 

The flue gas enters the spray dryer and passes downward through a concentric ring of turning vanes which surround the rotary atomizers. The makeup MgO slurry is pumped to the spray dryer and passes through the internals of the rotary atomizer and is sprayed perpendicularly to the flue gas flow. The resulting intimate mixing of the flue gas and the fine MgO slurry particles results in the following primary reactions ... 

Bubble-vortex machine with adjustable blades woiks as follows. The dusty gas is fed into a cylindrical chamber 1, where the swirl 3 with blades mounted in the radial grooves of the rod, deflects the flow and gives it a rotation. Under the action occurring at the same centrifugal forces dispersed particles are moved to the sides of the unit. For adjusting the blades at the entrance and exit of each blade 3 have two tabs. With their help, the blade is in contact with a pair of eccentrics. Eccentrics are turning vanes on the inlet and outlet sections of the cylindrical chamber 1 in different directions. With this blade 3 are installed in the position corresponding to the most efficient gas purification. 

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