Heat sink
Does a 15 W chip stay under 85 C without a fan?
You ask
Will a 15 W chip stay under 85 C on this heat sink without a fan?
Wobbl runs
$ wobbl thermal heatsink.py -m 6063-t5 --power "15 W" \ --heat-faces "bottom and box 17.5,17.5,-1,42.5,42.5,0.5" \ --film "6 W/m2K @ all" --ambient "40 C" --radiation 0.85 \ --limit "85 C"Checks
- passmesh convergence
- passenergy balance
- passhand calculation
- passunits and sanity
OKHottest point reaches 70.3 C (limit 85 C) at (30, 29.9, 0) mm at steady state.
- Max temperature
- 70.3 C
- Limit
- 85 C
- Power
- 15 W
- Confidence
- high
summary.txt
OK. Hottest point reaches 70.3 C (limit 85 C) at (30, 29.9, 0) mm at steady state. Confidence: high. passed mesh convergence, energy balance, hand calculation, units and sanitymax temperature: 70.3 Climit: 85 Cpower: 15 Wmesh nodes: 137,258 Checks: [pass] mesh convergence: temperature rise at the hottest point settled: 30.3 -> 30.2 -> 30.3 C over 3 meshes, last change 0.2% [pass] energy balance: heat in 15 W, heat out through the surfaces 15 W (3.1e-07% apart) [pass] hand calculation: heat balance on a uniform skin gives 68.1 C; the FEA skin averages 68.1 C (0.0029% of the rise). Biot 3.1e-05: the part is nearly isothermal [pass] units and sanity: temperatures between 67.1 and 70.3 C Assumptions: - Aluminum 6063-T5: conductivity 209 W/(m K), specific heat 900 J/(kg K), density 2700 kg/m3. - Heat enters through bottom and box 17.5,17.5,-1,42.5,42.5,0.5. - Convection uses a fixed film coefficient; real coefficients vary with temperature and airflow. - Surrounding air or coolant at 40 C does not heat up. - Radiation with emissivity 0.85. - Contact resistance between parts and internal airflow are not modeled. Images: temperature: images/temperature.pngReport: report.htmlAbout this example
This extruded 6063 aluminum heat sink has a 60 x 60 mm base with nine 30 mm fins and sits in a 40 C cabinet with no fan. A 15 W chip touches the middle 25 x 25 mm of the base, still air takes heat away at about 6 W/(m2 K), and the anodized surface radiates with an emissivity of 0.85.
| Result | Value |
|---|---|
| Hottest point (under the chip) | 70.3 C, below the 85 C limit |
| Coolest point (fin tips) | 67.1 C |
| Mesh convergence | rise of 30.3, 30.2, 30.3 C over three meshes |
| Energy balance | 15 W in, 15 W out through convection and radiation |
| Hand calculation | a uniform skin shedding 15 W by convection and radiation sits at 68.1 C, and the FEA skin averages 68.1 C |
The aluminum spreads heat so well (Biot number 3e-5) that the whole sink is within 3 C, which means the margin comes from how much surface the fins give the air. Doubling the cooling with a small fan would roughly halve the 30 C rise.
Run it yourself
$ git clone https://github.com/sohan-bhat/wobbl$ cd wobbl/examples/heat-sink && ./run.shThe part, the script and every output are in examples/heat-sink on GitHub.