3.7 Head loss due to Transitions and Fittings (Local loss)
Whenever flow velocity changes direction or magnitude in a conduit (e.g., at fittings, bends, and other appurtenances) added turbulence is induced. The energy associated with that turbulence is eventually dissipated into heat that produces a minor head loss, or local (or form) loss. The local (minor) loss associated with a particular fitting can be evaluated by
where V = mean velocity in the conduit (m/s, ft/s)
K = loss coefficient for the particular fitting involved.
The table given below provides the loss coefficients (K) for various transitions and fittings.
Table 3-3: Typical Minor Loss Coefficients
Type of form loss | K | ||
Expansion | Sudden | D1 < D2 |
|
Gradual | D1/D2 = 0.8 | 0.03 | |
D1/D2 = 0.5 | 0.08 | ||
D1/D2 = 0.2 | 0.13 | ||
Contraction | Sudden | D1 > D2 |
|
Gradual | D2/D1 = 0.8 | 0.05 | |
D2/D1 = 0.5 | 0.065 | ||
D2/D1 = 0.2 | 0.08 | ||
Pipe entrance | Square-edge | 0.5 | |
Rounded | 0.25 | ||
Projecting | 0.8 | ||
Pipe exit | Submerged pipe to still water | 1.0 | |
Tee | Flow through run | 0.6 | |
Flow through side outlet | 1.8 | ||
Orifice | (Pipe diameter /orifice diameter) | D/d = 4 | 4.8 |
D/d = 2 | 1.0 | ||
D/d = 1.33 | 0.24 | ||
Venturi (long-tube) | (Pipe diameter /throat diameter) | D/d = 3 | 1.1 |
D/d = 2 | 0.5 | ||
D/d = 1.33 | 0.2 | ||
Bend | 90o miter bend with vanes | 0.2 | |
90o miter bend without vanes | 1.1 | ||
45o miter bend | 0.2 | ||
Type of form loss (continued) | K | ||
Bend | 45o smooth bend: (bend radius /pipe diameter) | r/D = 1 | 0.37 |
r/D = 2 | 0.22 | ||
r/D = 4 | 0.2 | ||
90o smooth bend | r/D = 1 | 0.5 | |
r/D = 2 | 0.3 | ||
r/D = 4 | 0.25 | ||
Closed return bend | 2.2 | ||
Sluice | Submerged port in wall | 0.8 | |
As conduit contraction | 0.5 | ||
Without top submergence | 0.2 | ||
Valve | Globe valve, fully open | 10 | |
Angel valve, fully open | 5.0 | ||
Swing check valve, fully open | 2.5 | ||
Gate valve, fully open | 0.2 | ||
Gate valve, half open | 5.6 | ||
Butterfly valve, fully open | 1.2 | ||
Ball valve, fully open | 0.1 | ||
Source: Nicklow and Boulos (2005)
