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Round duct support rings are spaced, often at three diameters, or as require at up to about 50 ft centers (14 m). At this spacing the main support rings are designed for the sum of suction pressure stresses & support bending moments. Round ductwork allowable compressive stress is = 662 /(d/t) +339 * Fy (tubular steel structures, chapter 2).
For the limiting case of a very wide duct, i.e. a slot of width b, where b ≫ a, and a is the water depth, then D H = 4a. For a fully filled duct or pipe whose cross-section is a convex regular polygon , the hydraulic diameter is equivalent to the diameter D {\displaystyle D} of a circle inscribed within the wetted perimeter .
Round duct is made using a continuous spiral forming machine which can make round duct in nearly any diameter when using the right forming die and to any length to suit, but the most common stock sizes range evenly from 4" to 24" (10-60 cm) with 6"-12" (15-30 cm) being most commonly used. Stock pipe is usually sold in 10' (300 cm) joints.
The viscous friction causes the flow properties to change along the duct. The frictional effect is modeled as a shear stress at the wall acting on the fluid with uniform properties over any cross section of the duct. For a flow with an upstream Mach number greater than 1.0 in a sufficiently long duct, deceleration occurs and the flow can become ...
Turning vanes inside of large ductwork Turning vane close-up. HVAC turning vanes are sheet metal devices inside of mechanical ductwork used to smoothly direct air inside a duct where there is a change in direction, by reducing resistance and turbulence.
The ductwork airtightness level is the airflow rate through ductwork leakages divided by the ductwork area. It is recommended to test at least 10% and 10 m 2 of the duct surface including all duct types and a variety of sizes and components. The ductwork surface area is estimated according to EN 14239. [11]
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Clay tiles are usually about 2 feet (0.61 m) long, available in various sizes and shapes, and are installed in new construction as the chimney is built. A refractory cement is used between each tile. Metal liners may be stainless steel, aluminum, or galvanized iron and may be flexible or rigid pipes.