FAN AND BLOWER CALCULATIONS Table 34. Loss Coefficients, Air Duct Fittings Machinery's Handbook, 31st Edition
2812
K (upstream)
K (downstream)
Fitting Type
Geometry
0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 40° 80°
0.64 0.36 0.16 0.04
A upstream A downstream ------------- =
Sudden Expansion
0.32 0.25 0.16 0.06
A downstream A upstream ------------- =
Sudden Contraction
0.012 0.032 0.07 0.55
Gradual Contraction
Included Angle
120° 1.25 1.5 1.75 2.25 2.5 2.75 1.25 1.5 1.75 2 2.25 2.5 2.75 2
0.39 0.32 0.27 0.26
90° Elbow
r / d =
0.22 0.26 0.275 0.195 0.16 0.135 0.13 0.11 0.13 1.2
45° Elbow
r / d =
Two Piece Three Piece
Straight Miter
0.34 Compressibility factor is the ratio of total pressure that would be developed with an incompressible fluid to the total pressure developed with a compressible gas. When fan total pressure is less than 12 in.w.g., the compressibility factor can be assumed to be equal to 1 (incompressible flow). Power output is the product of capacity, total pressure, and compressibility factor. Total efficiency is the ratio of power output to power input. Static efficiency is the product of total efficiency and the ratio of static pressure to total pressure. These values can be calculated using the following equations. Fan efficiency grades have been established to classify fan performance. P o K p Qp t = where P o is output power imparted to the gas, K p is compressibility factor, and p t is fan total pressure. η t
P o P B = ---
where P B is power supplied to the driver. η t Q CFM p t in. w.g. ( ) 6356 P B = -------------------
Q CFM p s (in w.g.) 6356 P B = -------------------
η s
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