Siphon Discharge Rate Calculator

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Siphon Discharge Rate Calculator

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Fluids Flow Design and Engineering

Siphon Discharge Rate Equations and Calculator

A siphon is a bent or curved tube that carries fluid from a fluid surface at a high elevation to another fluid surface at a lower elevation. Normally, it would not seem difficult to have a fluid flow to a lower elevation. However, the fluid seems to flow “uphill” in a portion of a siphon. Figure 1 illustrates a siphon.

Starting a siphon requires the tube to be completely filled with liquid. Then, since the fluid weight is greater in the longer arm than in the shorter arm, the fluid in the longer arm “falls” out of the siphon, “pulling” more liquid into the shorter arm and over the bend.

Operation of a siphon is essentially independent of atmospheric pressure. The theoretical discharge is the same as predicted by the Torricelli equation. A correction for discharge is necessary, but little data is available on typical values of C_d. Therefore, siphons should be tested and calibrated in place.

Preview Siphon Discharge Rate Calculator

Eq. 1,
V = C_d · A_v = C_d · A ( 2 · g · h )^0.5

Where

V = volumetric flow rate, ft³/sec, m³/s
A = area of siphon discharge, ft², m²
h = height difference of liquid, ft, m
g = gravitational acceleration, 32.2 ft/s², (9.81 m/s²)
C_d = Approximate Orifice Coefficients for Turbulent Water, see Table 1

Figure 1 Siphon Configuration

Table 1 Approximate Orifice Coefficients for Turbulent Water

Illustration	Description	C_d
A	sharp-edged	0.62
B	round-edged	0.98
C	short tube* (fluid separates from walls)	0.61
D	sharp tube (no separation)	0.82
E	short tube with rounded entrance	0.97
F	reentrant tube, length less than one-half of pipe diameter	0.54
G r	eentrant tube, length 2 to 3 pipe diameters	0.72
H	Borda	0.51
(none)	smooth, well-tapered nozzle	0.98

*A short tube has a length less than approximately 3 diameters.

Illustrations for Table 1

Source:

Civil Engineering Reference Manual, Fourteenth Edition
Michael R. Lindeburg, PE