Duct, turn-around

Streamlines for turbulent flow in an axi-symmetric turn-around duct. (Reproduced with permission of Fluid Dynamics International)... 

Tape plastic over any windows in the room. Use duct tape around the windows and doors and make an unbroken seal. Use the tape over any vents into the room and seal any electrical outlets or other openings. Sink and toilet drain traps should have water in them (you can use the sink and toilet as you normally would). Push a wet towel up against the crack between the door and the floor to seal it. If it is necessary to drink water, drink the stored water, not water from the tap. Turn on the radio. Keep a telephone close at hand, but don t use it unless there is a serious emergency. 

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%. 

Example 10.7 An air duct of 2- by 2-ft square cross section turns a bend of radius 4 ft to the center line of the duct. If the measured pressure difference between the inside and outside walls of the bend is 1 in of water, estimate the rate of air flow in the duct. Assume standard sea-level conditions in the duct, and assume ideal flow around the bend. 

Wrap 5 turns of detonating cord around the propane bottle, on the centerline. Cover this with several layers of tightly wrapped duct tape. Leave a 12-inch tail of det cord exposed on one end. 

Low-durometer EPDM seals can be used to seal round ductwork into foundation walls. However, it is important that equal force be maintained around the ducts as the seals are tightened. The seals should be tightened in a clockwise direction, and no bolt should receive more than two turns, rather than the standard four, during each successive pass. 

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