Calculator Inputs
Select the variable you want to solve. Leave that target field blank. All temperatures are entered in °C.
Example Data Table
| Case | h (W/m²·K) | A (m²) | Ts (°C) | T∞ (°C) | ΔT (°C) | Q (W) | q" (W/m²) |
|---|---|---|---|---|---|---|---|
| Hot pipe in still air | 12 | 1.8 | 95 | 30 | 65 | 1,404 | 780 |
| Heated plate with fan cooling | 45 | 2.4 | 120 | 35 | 85 | 9,180 | 3,825 |
| Cold coil in warm room | 28 | 3.1 | 8 | 24 | -16 | -1,388.8 | -448 |
Formula Used
Newton’s Law of Cooling
Q = h × A × (Ts − T∞)
Heat Flux
q" = Q / A = h × (Ts − T∞)
Convection Thermal Resistance
Rconv = 1 / (h × A)
Nusselt Number
Nu = (h × L) / k
Here, Q is heat transfer rate, h is the convection coefficient, A is exposed area, Ts is surface temperature, T∞ is bulk fluid temperature, L is characteristic length, and k is fluid thermal conductivity.
How to Use This Calculator
- Choose the variable you want to calculate from the Solve For menu.
- Enter the known values for convection coefficient, area, and temperatures.
- Leave the target variable blank if you are solving for it.
- Add characteristic length and conductivity if you also want the Nusselt number.
- Provide an operating time to estimate total transferred energy.
- Click Calculate. The result section appears below the header and above the form, where you can also export CSV or PDF.
Frequently Asked Questions
1. What does this calculator solve?
It solves convection heat transfer rate, convection coefficient, area, surface temperature, or fluid temperature. It also reports heat flux, thermal resistance, Nusselt number, and optional energy over time.
2. What does a negative heat transfer rate mean?
A negative value means heat flows from the surrounding fluid toward the surface. This commonly appears when the fluid is warmer than the surface being cooled.
3. Which temperature unit should I enter?
Enter both temperatures in °C. Because the calculation uses a temperature difference, Celsius works correctly as long as both values use the same scale.
4. When is the Nusselt number shown?
The Nusselt number is calculated only when convection coefficient, characteristic length, and fluid thermal conductivity are all provided and greater than zero.
5. Can I use it for heating and cooling cases?
Yes. The sign of the heat transfer result indicates direction. Positive values usually mean the surface loses heat, while negative values indicate the surface gains heat.
6. Is area the total exposed area?
Yes. Use the full surface area directly exposed to the moving or still fluid. Excluding covered or insulated sections improves accuracy.
7. Can this replace detailed CFD or correlation methods?
No. This tool is ideal for engineering estimates and checks. Detailed geometry, turbulence, and varying properties still require correlations, experiments, or simulation.
8. Why add operating time?
Operating time converts heat transfer rate into total transferred energy. That helps for energy balances, heater sizing checks, and process batch estimates.