Calculator Inputs
Example Data Table
| Case | Heat load | Material | Air coefficient | Fins | Fin size | Expected use |
|---|---|---|---|---|---|---|
| Small driver board | 18 W | Aluminum 6061 | 12 W/m²K | 12 | 25 × 50 × 1.5 mm | Natural airflow |
| Power module | 45 W | Aluminum 6061 | 35 W/m²K | 18 | 35 × 80 × 2 mm | Low fan airflow |
| Compact inverter | 90 W | Copper | 75 W/m²K | 24 | 45 × 100 × 2.5 mm | Moderate fan airflow |
Formula Used
The calculator models a straight fin with a corrected length. It then combines fin area, exposed base area, convection, radiation, and thermal resistance.
Fin parameter: m = √(hP / kAc)
Corrected fin length: Lc = L + Ac / P
Fin efficiency: ηf = tanh(mLc) / mLc
Total area: At = Af + Ab
Overall surface efficiency: ηo = 1 - (Af / At)(1 - ηf)
Radiation coefficient: hr = 4εσTf³
Convection resistance: Rconv = 1 / (ηo htotal At)
Total junction resistance: Rtotal = Rsa + Rinterface + Rjc
Junction temperature: Tj = Ta + Qdesign × Rtotal
How To Use This Calculator
- Enter the heat load produced by the device.
- Add ambient and maximum junction temperatures.
- Enter junction, interface, and base resistance values.
- Select a material preset, or enter custom conductivity.
- Select airflow, then adjust the convection coefficient if needed.
- Enter fin count and fin dimensions in millimeters.
- Use emissivity when radiation is included.
- Press the calculate button and review the result above the form.
- Use the CSV or PDF button after calculation.
Heat Sink Efficiency Guide
Basic Idea
A heat sink removes heat from a device. It spreads heat into fins. The fins add surface area. Air then carries heat away. Efficiency tells how much of that fin area works well. A perfect fin would stay at base temperature. Real fins cool along their length. The tip is usually cooler than the root.
Why Efficiency Matters
A larger heat sink is not always better. Thin long fins may look powerful. Yet they can lose temperature quickly. Low conductivity also reduces useful area. Airflow changes the answer too. Strong airflow improves convection. It can also make weak fin sections more useful. This calculator links those effects in one estimate.
Important Inputs
Heat load is the power that must leave the component. Ambient temperature is the air temperature near the sink. The convection coefficient describes air cooling strength. Natural air uses lower values. Forced air uses higher values. Material conductivity shows how easily heat travels through fins. Aluminum is common. Copper conducts better but weighs more. Fin count, length, width, and thickness define the working surface.
Reading The Result
Fin efficiency shows the average fin temperature effect. Overall surface efficiency includes fins and exposed base area. Thermal resistance predicts temperature rise per watt. A lower value is better. Junction temperature combines the sink, interface, and device resistance. The safety factor raises the design heat load. This helps when airflow, dust, or power changes later.
Design Tips
Start with honest power data. Use the hottest nearby air temperature, not room temperature. Add interface resistance for pads, grease, or clips. Check that fins are not too close for the fan or natural airflow path. Increase base area before adding very thin tall fins. Improve airflow when thermal resistance remains high. Always compare predicted junction temperature with the device rating.
Practical Limits
This tool gives an engineering estimate. It assumes steady heat flow. It treats fins as uniform shapes. It does not replace prototype testing. Real layouts include spreading resistance, blocked airflow, mounting pressure, and radiation changes. Still, the method is useful for early choices. It helps compare heat sink designs before buying hardware. Record test temperatures and refine assumptions after each build. Repeat checks when fans age often.
FAQs
What is heat sink efficiency?
Heat sink efficiency shows how effectively the fin and base surfaces remove heat. It compares ideal surface area with the useful area after temperature drop along each fin.
What is fin efficiency?
Fin efficiency is the ratio of real fin heat transfer to ideal fin heat transfer. Long, thin, or low conductivity fins usually have lower efficiency.
What does overall surface efficiency mean?
Overall surface efficiency combines fin efficiency with exposed base area. It gives one useful factor for calculating the heat sink convection resistance.
How should I choose the convection coefficient?
Use low values for still air. Use higher values for fan cooling. If unsure, start conservative and compare the result with real temperature testing.
Should radiation be included?
Radiation can matter for warm, dark, exposed surfaces. It is usually smaller than forced convection, but it may help in natural airflow designs.
Why is interface resistance important?
Thermal pads, grease, clips, and mounting pressure affect heat flow. Interface resistance can raise junction temperature even when the heat sink looks large.
What is a good safety factor?
A common early estimate uses 10% to 30%. Use more when airflow is uncertain, dust may build up, or power can rise during operation.
Can this replace physical testing?
No. It is best for early design and comparison. Final products need real testing because airflow, mounting, and enclosure effects can change results.