Fired Heater Learning Center

Return Bend Equivalent Length Calculator

Equivalent Length Of Return Bends & Elbows: Method used in WinHeat Software

The equivalent length of a return bend may be obtained from the following curves based on Maxwell table and corrected using the Reynolds number correction factor.

Lequiv = FactNre*Lrb
FactNre = Reynolds number correction
Lrb = Equivalent length of return bend, ft
Return Bend Equivalent Length
Reynolds Correction

G = Mass velocity, lb/sec-ft2
Di = Inside tube diameter, in
Visc = Viscosity, cp
Equivalent Length Of Return Bends & Elbows: Alternate Method

DescriptionVelocity HeadsEquivalent Length, Tube Dia
Long Radius 90° Elbow0.3016.5
Short Radius 90° Elbow0.5027.5
Long Radius 180° Return0.5027.5
Short Radius 180° Return0.7541.25
Velocity Head1.0055

Calulations based on above data:

Friction Loss:
Dp = 0.00517/di*G2*Vlm*F*Lequiv
Dp = Pressure drop, psi
di = Inside diameter of tube, in
G = Mass velocity of fluid, lb/sec-ft2
Vlm = Log mean specific volume correction
F = Fanning friction factor
Lequiv = Equivalent length of pipe run, ft
Vlm = (V2-V1)/ln(V2/V1)
For single phase flow,
V1 = Specific volume at start of run, ft3/lb
V2 = Specific volume at end of run, ft3/lb

Pressure Drop with Alternate Fitting Equivalent Length Methods Calculator
Coil Data
Pipe schedule: Nominal pipe dia, in:
Pipe straight length, ft:
Fitting type: Number of fittings:
Process Data
Mass vel., lb/sec-ft2: Viscosity, cp:
Spec. vol. at start, ft3/lb: Spec. vol. at end, ft3/lb:
Friction factor, Fanning: Inside diameter, in:
Maxwell equiv fitting lgth, ft: Alternate equiv fitting lgth, ft:
Maxwell total lgth, ft: Alternate total lgth, ft:
Maxwell pressure drop, psi: Alternate pressure drop, psi:


The formulas and correlations presented herein are all in the public domain and are to be used only as a learning tool. Note that any product, process, or technology in this document may be the subject of other intellectual property rights reserved by sponsors or contributors to this site. This publication is provided as is, without any warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of fitness for a particular purpose, or non-infringement.

The formulas, correlations, and methods presented herein should not be considered as being recommended by or used by the sponsors of this site. The purpose of this site is educational and the methods may or may not be suitable for actual design of equipment. Only a fired heater design engineer is qualified to decide if a calculation or procedure is correct for an application.