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2.2 Air 139 Table 2.3 Local loss factors ξ Local resistance ξ Entering an opening: 0.5 Leaving an opening: 1.0 Widening: σ =Ao/A1 Ao small section A1 large section d2 ε = [(d1 + d2 + d3 + d4)/4]/dH d1 d2 d3 d4 dH Fig. 2.5 Relative roughness Re 1000 0:036 ‡ 9:6 105Re ‡ Δξ 1000 <Re 3000 1:28 105 Re1:223 ‡ Δξ Re >3000 0:21 Re0:012 ‡ Δξ with σ 0.5: Δξ ˆ 0:78 1:56σ with σ > 0.5: Δξ ˆ 0:48 0:96σ Narrowing: σ =Ao/A1 Ao small section A1 large section Re 1000 0:98 Re0:03 ‡ A 1000 <Re 3000 10:59 Re0:37 ‡ A Re >3000 0:57 Re0:01 ‡ A where A ˆ 0:0373 σ2 0:067 σ Leak: 2.85 Angle or curve: kRe0ξgk0 where ξg ˆ 0:885 bo width inlet channel … dH † 0 b1 width of channel after the curve refers to the inlet channel fo friction factor in inlet channel 0:86 b1 b0 and Relative roughness ε 3000 Re< 40 000 Re > 40 000 kRe0 k0= dH … † 0 kRe0 k0= dH … † 0 0 45fo 1 1.1 1 0–0.001 45fo 1 1.0 1 +0.5 × 103a > 0.001 45fo 1 1.1 1


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