Formula used
How to use
Select a calculation mode first. Choose units matching every entered value. Then provide all visible required inputs.
Press Calculate to process the selected method. Review warnings before accepting engineering conclusions. Export results after checking assumptions carefully.
Use film-temperature fluid properties when possible. Confirm each correlation fits its range. Consult design standards for final equipment selection.
Example data
| Mode | Example inputs | Expected output |
|---|---|---|
| Basic coefficient | Q = 12,000 W, A = 8 m², ΔT = 30 K | h = 50 W/m²·K |
| Plane wall | hi = 500, ho = 25, L = 6 mm, k = 16 | U near 23.7 W/m²·K |
| LMTD | 150/100°C hot, 20/70°C cold, counter flow | LMTD near 80 K |
| Dittus–Boelter | Re = 50,000, Pr = 7, k = 0.6, D = 0.025 m | h from Nu·k/D |
Typical heat-transfer coefficient ranges
| Service | Approximate range |
|---|---|
| Natural convection, gases | 2–25 W/m²·K |
| Forced convection, gases | 25–250 W/m²·K |
| Natural convection, liquids | 50–1,000 W/m²·K |
| Forced convection, liquids | 100–20,000 W/m²·K |
| Boiling or condensation | 2,500–100,000 W/m²·K |
These ranges remain approximate. Surface geometry and fluid state matter greatly. Verify values against trusted design references.
Important assumptions
Most modes assume steady one-dimensional heat transfer. Constant properties are applied during calculations. Radiation requires absolute Kelvin temperatures internally.
Fouling factors use area-based resistance units. Pipe U values depend on area basis. Always state that basis in reports.
Boiling and condensation need specialised correlations. Phase changes can alter local coefficients strongly. Use certified methods for safety-critical designs.
Frequently asked questions
What is a heat-transfer coefficient?
It measures heat transferred per area. It also depends on temperature difference. Higher values indicate stronger thermal exchange.
What is the difference between h and U?
The value h describes one convection boundary. The value U combines all resistances. U includes walls, fouling, and both fluids.
Why does area basis matter?
Inside and outside pipe areas differ. Their reported U values therefore differ. Heat duty remains identical using consistent areas.
When should LMTD be used?
Use LMTD for changing stream temperatures. It represents the exchanger temperature driving force. Apply correction factors when geometry requires them.
What causes an invalid LMTD?
Terminal differences must remain positive. Temperature crossing can invalidate simple assumptions. Recheck stream directions and entered temperatures.
Which Nusselt correlation should I choose?
Choose one matching geometry and regime. Check Reynolds and Prandtl validity ranges. Avoid extrapolation beyond published correlation limits.
Where should fluid properties be evaluated?
Film temperature often provides useful properties. Some correlations specify bulk or wall values. Follow each correlation's original definition.
How does fouling affect U?
Fouling adds thermal resistance. Added resistance lowers the overall coefficient. Cleaning can therefore recover exchanger performance.
Can radiation be combined with convection?
Yes, coefficients may be added locally. Both mechanisms need the same temperature difference. Large differences require careful nonlinear treatment.
Are preset properties exact?
No, preset properties are approximate. Temperature and pressure change fluid behaviour. Replace them with verified project data.
Can this replace professional design software?
No, it supports preliminary engineering checks. Complex exchangers require detailed local analysis. Validate final designs using recognised standards.