# Can smartphones be cooled with natural convection? [closed]

Like this:

I believe it's called "Buoyancy-driven ventilation". Natural airflow will occur when there is a large difference between interior and exterior air. All you would need is to poke some holes in the outer case for cold air to get in and other holes for hot air to get out. So for example if the exterior air is 17C, and the interior air of the phone (which is in thermal contact with the chipset though some aluminum or graphite sheet) is 45C, you'd no longer have to see the phone throttle its performance to lower its temps. It would cool itself through natural ventilation like a woman in a burqa. You can run a game at constant 60 fps indefinitely on this phone while all other phones start at 60 fps and end up at 25 fps after just 5 to 20 minutes of gameplay. Why can't this be done? What are the physical limitations of a smartphone preventing it?

## closed as off-topic by John Rennie, Jon Custer, ACuriousMind♦Dec 16 '16 at 0:38

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• Hi, I think this an design/engineering question rather than a physics question. You could try askign on the Engineering Stack Exchange. – John Rennie Dec 15 '16 at 18:20
• But it's to do with how heat tranfers – Pong Lenis Dec 15 '16 at 18:21
• The physics answer is yes. The real question is if that is enough cooling for a given phone in a given configuration under a given use. – Jon Custer Dec 15 '16 at 18:43
• Right, this is an engineering question. The reason that this does not happen is that people like small phones, so we have engineered away all of the free airspace within the body of the phone itself. – CR Drost Dec 15 '16 at 18:44
• @Jon Custer well actually it's still a physics question since you'd need to apply some physics formula about natural convection to know if the space of air inside the phone is enough and how large the cross sectional area of the ventilation holes would be and how many degrees Celsius you're likely to decrease with such a setup, etc – Pong Lenis Dec 15 '16 at 18:48

For a chimney to work effectively, it needs to be tall: then, a small difference in density can provide a reasonable change in pressure. Secondly, the chimney needs to have an appropriate aspect ratio. For small channels, slow flow follows Poiseuille's equation, in which the flow rate goes as $\Delta p a^2$ - make the channel half as big, and you need 4x more pressure to get the same air flow. And you need air flow in order to carry the heat away.

The bottom line is - the size of a phone is too small for this to work effectively at the temperature difference you can tolerate on the processor.

• So how much difference is it likely to make in a phone with convection vs one completely sealed off? Like 1 or 2 degrees Celsius at the most? – Pong Lenis Dec 15 '16 at 19:17
• The effect will be small - and once you add ventilation, you add places for water and dust to get in. Dust at low flow velocities will quickly settle and clog up your heat sink - if you have ever looked inside an old laptop you will know what I am talking about. Also - the space inside the phone is very tight: to create sufficiently large air channels it would have to be much larger. You're better off coupling the processor to the metal case of the phone, and using the entire external surface as a heat sink. – Floris Dec 15 '16 at 19:22
• In short, it's a pretty hare-brained idea. As one might expect from someone who chooses a user ID of this kind. – Pirx Dec 15 '16 at 20:22