How the MacBook Pro 13″ Cools Itself

Posted on December 19, 2011

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Looking at the MBP 13, you can see that a lot of careful thought has gone into designing the chassis, and it has been so successful that the main unibody design hasn’t changed since 2008 when it was first released.

Cooling is possibly the most important factor in x86 mobile devices. Cramming ~35 watt components into a chassis less than an inch thick is likely to result in some serious heat issues if not done properly, and we’ve some examples of that from other notebook manufacturers, and the infamous first generation MacBook Air which was plagued by overheating problems.

Dust Trails

Looking at the design of a laptop, it is often quite difficult to determine how air flows inside the laptop to cool the components down, but luckily I got my hands on a MacBook Pro 13 which has been in a dusty environment and it shows air flow inside the chassis beautifully.

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We can see that most of the cooling air enters through the left side of the large vent under the notebooks hinge. What’s interesting is that the air doesn’t take a direct path to the fan, but instead travels around the motherboard before entering fan cage. On the lower side, this would be where the RAM is located, and this is possibly how the RAM modules (often overlooked in notebook cooling) are cooled.

MacBook Pro Cooling

One place which I did not expect air flow to occur are the ports on the left side. From the dust trails left behind, there appears to be almost the same amount of air flowing through the ports as the main vent. The path which this air takes is very important, as it would travel over the top side of the motherboard and many of the components such as the sound card and various other controllers. Air would also travel over the copper plates which draw heat from the Core 2 Duo CPU and Nvidia 320M chipset. It would be interesting to see the effect of blocking these ports on the temperature of the system.

Moving cooling air over the chassis and heat plates themselves as well as the heatsink fins is an effective method for maintaining cool chassis temperatures, as seen in the Acer Timeline 3810T where cooling air is redirected over the chassis and the CPU heat plate before cooling the heatsink fins. Many notebooks before the Acer 3810T tend only to cool the heatsink fins and leave the heat plate air stagnant, resulting in hotspots.

Laminar Wall Jet

How the air rows around the chassis is important. The dust trails left behind indicate a smooth air flow with little turbulence which is extremely important in cooling. Jet engines use a similar technique (known as the Laminar Wall Jet) to blast non turbulent air over the combustion chamber walls, keeping the outer skin cool and preventing heat transmission to the wing fuel tanks. A smooth air flow is important, as turbulent flow would result in a build up of hotspots where hot air is not expelled effectively. The old practice of adding lots of air vents onto the laptop chassis was never an effective method of cooling, as air intake would be turbulent and not expelled properly.

Laminar to Turbulent

A laminar flow quickly tuns into a turbulent mess

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The MacBook Pro and Acer Timeline 3810T manage to cool themselves so effectively without a myriad of extraneous air vents because air has a relatively direct and clean route from intake to exhaust. Adding air vents to the bottom of the chassis would probably cause the components to run hotter as turbulent air flow prevents hot air from escaping.

Cooling the Hard Drive

Interestingly, the hard drive doesn’t appear to be air cooled. There is no opening at the front of the notebook to allow air to circulate, and there doesn’t appear to be many dust trails around the hard disk area. I assume that the hard drive is cooled almost entirely by conduction through the side mounted support screws or simple convection to the metal chassis.

This appears to be very effective; the hard disk drive on the MacBook Pro 13 never reaches over 40 degrees, even on continuous load (the same hard drive will reach 60 degrees on my old HP DV2000). High performance 7200RPM drives should be fine in the MBP.

No Air-Flow through the Keyboard

Rummaging through the innards of the MacBook Pro, I also came across something else. Some reviews on other sites suggest that the MBP draws air in through the keyboard much like the Lenovo IdeaPad U300 or Sony Vaio Z (2011). I can confirm that this is indeed utter rubbish; there is no gap through the keyboard in which air can enter. It is also characterised by the fact that it is possible to run the notebook under full load with the lid closed and the components to run no hotter than if the lid was open. Having the keyboard as an air intake would probably require more air movement as seen in the 2011 Vaio Z with its dual fans.

Cooling in the 2010 vs 2011 models

The 2010 and 2011 MacBook Pro’s essentially have the same cooling design, however due to some architectural differences in the chipset, CPU and GPU, the heatsink in both models differ.

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The 2010 13″ MacBook Pro Heatsink. Image from iFixit.

The 2010 MacBook Pro has a 2 chip solution with a 25W Core 2 Duo CPU and a Nvidia 320M chipset which communes another ~12W under load. The heatsink must therefore be in contact with both chips to cool them down sufficiently, especially under load.

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The 2011 13″ MacBook Pro’s main heatsink and Platform Controller Heatsink towards the left. Image from iFixit.

The 2011 MacBook Pro’s cooling is slightly more interesting. The Core i5/7 CPU integrates many chipset functions and also the GPU into a 35W component. The main heatsink is in contact with this die and not the second platform controller chip (which presumably uses little power). The Platform controller however has its own simple heatsink/heat spreader which also draws heat from the Thunderbolt controller. Heat is then lost through conduction and air flow inside the chassis. Joining the Platform Controller heatsink to the main CPU heatsink (as it is on the 2010 model) will cause the CPU’s heat output to be conducted to the Platform controller, resulting in higher operating temperatures.