Reynolds Number Calculator — Rectangular Duct
Re for air in rectangular ducting using hydraulic diameter.
HVAC duct flow is turbulent in essentially all real cases — 5 m/s in a 400×250 duct gives Re ≈ 10⁵.
Formula
Reynolds Number Calculator — Rectangular Duct is a free duct reynolds number for process, mechanical and water engineers — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Reynolds Number Calculator — Rectangular Duct
Re for air in rectangular ducting using hydraulic diameter. The calculation implements Re = V·D_h/ν, D_h = 2ab/(a+b) (ASHRAE Handbook — Fundamentals, ch. 21). HVAC duct flow is turbulent in essentially all real cases — 5 m/s in a 400×250 duct gives Re ≈ 10⁵.
How to use Reynolds Number Calculator — Rectangular Duct
- 1Enter Duct width in mm.
- 2Enter Duct height in mm.
- 3Enter Air velocity in m/s.
- 4Enter Kinematic viscosity in ×10⁻⁶ m²/s.
- 5Read Reynolds number, Hydraulic diameter instantly — no submit button needed.
- 6Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Reynolds Number Calculator — Rectangular Duct?
- ✓Implements the standard formula — Re = V·D_h/ν, D_h = 2ab/(a+b)
- ✓Reference cited on-page: ASHRAE Handbook — Fundamentals, ch. 21
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Built-in engineering verdict flags out-of-range results instantly
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Reynolds Number Calculator — Rectangular Duct use?+
It computes Re = V·D_h/ν, D_h = 2ab/(a+b), per ASHRAE Handbook — Fundamentals, ch. 21. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
HVAC duct flow is turbulent in essentially all real cases — 5 m/s in a 400×250 duct gives Re ≈ 10⁵.
Does this work for any fluid?+
Yes — density and viscosity are inputs (with common fluids suggested in the field hints), so the same physics applies to water, oils, gases and process fluids. Compute always runs in SI internally, so unit mix-ups can't corrupt the result.
Is the Reynolds Number Calculator — Rectangular Duct free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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