WOBBLheatsink.py

Does a 30 W chip stay under 85 C with a 10 CFM, 20 Pa fan blowing along the fins in a 40 C cabinet?

Heat report
2026-10-15 18:29

With 232 L/min of air through its duct, the faces shed heat at 29.8 W/(m2 K) on average, and 30 W brings the hottest point to 77 C against a limit of 85 C.

max temperature

77 C

limit

85 C

mean h

29.8 W/m2K

pressure drop

4.05 Pa

flow

232 L/min

Confidence low

grid convergence failed: pressure drop 3.539 -> 3.868 -> 4.045 Pa over 3 grids, grid convergence index 32% (observed order 2, extrapolated 4.473 Pa), so the grid is too coarse for this answer
residuals: largest final residual 0.0032 (k), every field fell at least 1.4 orders, close to converged, so the key number may still move slightly
wall resolution: y+ on the walls averages 6.53, at most 11.3, for wall functions, so part of the wall sits in the buffer layer, where wall functions are least accurate, though the blended wall function keeps the error to a few percent
operating point: the curve gives 3.58 Pa at 232 L/min, and the fine grid needs 4.05 Pa there (13% apart), so the coarse grid's fit set the flow a little off
hand calculation: heat balance on a uniform skin gives 69.2 C; the FEA skin averages 72.6 C (12% of the rise). Biot 0.00013: the part is nearly isothermal
convective heat transfer from RANS is commonly within 10 to 25% of measurements

Simulation

The part's temperature with the hottest point marked

Checks

status	check	result
pass	mesh quality	102,204 cells, worst non orthogonality 37 degrees and skewness 0.39
fail	grid convergence	pressure drop 3.539 -> 3.868 -> 4.045 Pa over 3 grids, grid convergence index 32% (observed order 2, extrapolated 4.473 Pa), so the grid is too coarse for this answer
pass	iterative convergence	pressure drop swings 0.0061% over the last fifth of 153 iterations
pass	mass conservation	in 0.00387 m3/s, out 0.00387 m3/s (2.1e-05% apart)
warn	residuals	largest final residual 0.0032 (k), every field fell at least 1.4 orders, close to converged, so the key number may still move slightly
warn	wall resolution	y+ on the walls averages 6.53, at most 11.3, for wall functions, so part of the wall sits in the buffer layer, where wall functions are least accurate, though the blended wall function keeps the error to a few percent
pass	flow regime	Re 6361 on the inlet's hydraulic diameter, turbulent
info	hand calculation	a straight smooth duct of the same 60 mm hydraulic diameter and 60 mm length loses 0.0634 Pa by Colebrook, and the part loses 4.05 Pa, 63.86 times that, the rest from turns, junctions and changes of section
warn	operating point	the curve gives 3.58 Pa at 232 L/min, and the fine grid needs 4.05 Pa there (13% apart), so the coarse grid's fit set the flow a little off
pass	mesh convergence	temperature rise at the hottest point settled: 37.1 -> 36.9 -> 37 C over 3 meshes, last change 0.4%
pass	energy balance	heat in 30 W, heat out through the surfaces 30 W (1.1e-07% apart)
warn	hand calculation	heat balance on a uniform skin gives 69.2 C; the FEA skin averages 72.6 C (12% of the rise). Biot 0.00013: the part is nearly isothermal
pass	units and sanity	temperatures between 70.7 and 77 C; radiation is off, it could shed up to about 11.6 W at this temperature (pass --radiation 0.9 for painted or plastic surfaces)
info	lumped estimate	the wetted area of 331 cm2 at the mean 29.8 W/(m2 K) puts a part at one temperature at 73.8 C, and the FEA's hottest point is 77 C
info	heat transfer correlation	Gnielinski's correlation for a straight tube gives 9.35 W/(m2 K) at Re 6361 on the 60 mm hydraulic diameter, and the CFD averages 29.8 W/(m2 K) over the wetted faces, which include entrance regions and turns that raise it

Assumptions

Wobbl guessed: The stream runs along (+0.00, +1.00, +0.00) in the part's coordinates.
Wobbl guessed: The part has no passage of its own, so it sits in a duct of its own cross section, the way a shroud carries a fan's air through a heat sink.
Air at 40 C, density 1.127 kg/m3, viscosity 1.907e-05 Pa s, conductivity 0.0272 W/(m K), Prandtl 0.704.
The stream runs along (+0.00, +1.00, +0.00) in the part's coordinates.
The part has no passage of its own, so it sits in a duct of its own cross section, the way a shroud carries a fan's air through a heat sink.
Steady, incompressible flow with the k omega SST turbulence model and blended wall functions.
Meshed by snappyHexMesh with 102,204 cells on the finest of 3 grids, without boundary layer cells.
The fluid enters at 40 C and warms by 6.83 C, so the films use 43.4 C.
Each face's heat transfer coefficient comes from the CFD with the walls at one uniform temperature, and faces the flow does not reach get still air at 5 W/(m2 K).
One way coupling, so the fluid's properties do not change with the part's temperature.
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.
Surrounding air or coolant at 40 C does not heat up.
Radiation is ignored (conservative).
Contact resistance between parts and internal airflow are not modeled.