The noise and quiet in stainless steel ventilation duct affect the liner of sound absorption duct. The decibel of pipe length per foot is measured directly. The loudspeaker is used as the sound source for rectangular pipes with and without linings of various shapes, sizes and frequencies. The relationship between attenuation and pipeline cross-section size and absorption coefficient is closer to Sivian's theoretical formula than other formulas that have been proposed. The measurement is also carried out through the noise connected to the 5000 CFM capacity fan system. It turned out that the noise was caused by the . Caused by. Compared with the negligible noise generated by fan blades, air with and without linings can produce friction speeds of up to 1500 feet per minute on the inner wall of pipes. By introducing a special baffle structure, the effects of static pressure and air resistance flow system were tested. For lined and non-lined pipes, the absorption friction resistance is the same.
Wheel heat exchangers can be used when air ducts are used side by side with external air ducts. Half of the wheel is in one tube and half is in another. When the wheel rotates, the part of the wheel in the heating tube heats the porous wheel structure. The hub part in the cooling pipe removes heat from the porous hub structure. Wheels can also be treated with desiccants so that water can flow from one stream to another.
The wheels are not fully sealed, and the volume of the wheels themselves leaks from one pipe to another. Therefore, applications requiring zero-transfer (cross-contamination) between streams cannot use wheels. Wheels need side-by-side and pipes of the same size, which limits the freedom of packaging required by many applications. Last but not least, wheels are active moving machines with motors, belts, pulleys, bearings and so on, requiring highly skilled maintenance personnel to keep the wheels turning.