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)
