• Constant friction method
• Constant velocity method
• Gradual velocity reduction method
• Pressure recovery method
• Balanced pressure loss method
The design methods are normally a combination of one or more of the above methods.
TABLE 9.9 Recommended Air Velocities to Ensure An Economic Minimum Of Noise Production
• Balanced pressure loss method. This is a method which is used to improve the performance of a preliminary design of a duct system and reduce the number of control dampers.
Apart from the energy constraints due to the friction losses, the main reason for limiting the air velocities in ducts is to reduce noise production. Some recommended air velocities are given in Table 9.9.
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