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CORRELATION GUIDE / VERSION 1

Refrigerant-side single-phase friction-factor correlations

Explains website options, definitions, ranges, and reference relationships.

2026-08-24Darcy friction factorCircular tube
Distinguish available options from reference material

The current solver exposes four options; the reference table lists 15 literature correlations.

1. Options available in the current solver

Solver optionImplementation ID

2. Quick comparison of literature correlations

Ranks follow the current source compilation.

RankCorrelationFormula summaryPublished range

3. History, definitions, and laminar-flow basis

Pipe-flow friction factors developed from pressure-drop experiments into dimensionless engineering correlations.

Darcy friction factorΔp = f_D (L/D) (ρu²/2)

This guide and the Moody diagram use the Darcy friction factor.

Fanning friction factorf_D = 4f_F

Always confirm which convention a paper or software package uses.

Fully developed laminar flow in a circular tube

Re = ρuD/μ　　f_D = 64/Re　　f_F = 16/Re

The current model treats Re < 2000 as laminar.

4. Development of the Moody diagram and Colebrook relation

The Moody diagram is a graphical synthesis of established pipe-flow research.

RegionRange used hereTreatment
LaminarRe < 2000f_D = 64/Re
Critical zone2000 ≤ Re ≤ 4000No universally unique curve.
TurbulentRe > 4000Depends on Re and ε/D.
Moody diagram showing Darcy friction factor versus Reynolds number and relative roughness
Redrawn Moody diagram using the Darcy friction factor.

Colebrook

1/√f_D = −2log₁₀[ε/(3.7D) + 2.51/(Re√f_D)]

Colebrook is implicit and requires iteration; explicit formulas trade some accuracy for direct evaluation.

5. Usage guidance

  1. Confirm the convention.
  2. Check the full calculation range.
  3. Interpret critical-zone results cautiously.
  4. Rerun benchmark cases after changes.

6. Principal references