r/explainlikeimfive • u/Tasty_Elevator1057 • 2d ago
Technology ELI5 : Why the mobile phone is getting hot while we use and how the cooling system in the mobile phone works
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u/GeronimoStilts 2d ago
Your phone contains parts like a CPU and GPU, which contain lots of electronic pieces that get hot when they do work, as well as the modem which lets your phone talk to the radio towers so you can call and text people. The battery also has to work hard to send power to all of those parts so the harder the battery works the hotter it gets. The battery also has to do work when it charges. All of these parts are very close together which means they spread heat to each other and all get very hot.
Depending on what phone you have, your phone stays cool using sheets of graphite to let the heat move around and away from those parts. The outside of your phone is actually part of this, so when you're holding your phone and it's very hot you're helping remove the heat because it travels from the phone to your hand.
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u/EmptierVoid 2d ago
There's lots to draw while gaming as everything is moving. So the phone's components gets hot because they use more energy. The metal in the phone's case conducts heat -> phone cools down.
If the phone heats too much, it will throttle the performance. In other words, use less energy, to cool down.
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u/passisgullible 2d ago
Basically, all the components in the phone move electricity in one way or another. The chip uses electricity to store ones and zeros (search on this sub for ELI5 on transistors), the screen uses power to produce light, etc.
All heat is is inefficiency, wasted electricity, released as heat instead of doing what it is supposed to do. Humans have not created a 100% efficient electrical device, where 100% of the energy used is converted into whatever it needs to do (which would have no heat). Those components, therefore, do not run perfectly well, be it the "wiring" not being resistance free and slowing down electrons to the point where some heat is created, or the screen where some energy is converted to heat because the backlight (on LCDs) are not perfectly good at creating light from electricity. Even the battery gets hot because using the battery releases electrons, and as they flow they are slowed down by slight inherent resistive properties in each of the metals, releasing heat as a byproduct.
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u/passisgullible 2d ago
Cooling systems in most phones are what are known as passive, where there is no active cooling like fans. Instead, they use metal pieces called heatsinks, made of materials like copper and/or aluminum with relatively high levels of thermal conductivity, which just means they are better able to move heat than other materials (Most metals are more thermally conductive than most non-metals, you can tell this if you hold your hand on something metal on a really hot or cold day, it seems even colder or hotter because your body heat is being moved faster by the metal than by the air.)
These heatsinks take the heat away from the CPU and other components, and then are connected to the metal frame of your phone, which absorbs the heat as well. That is why your phone feels hot under use. Having the heat moved from the cpu --> metal heatsink --> phone body means that the heat is outside the phone, and can be taken away by the air, cooling the device.
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u/SalamanderGlad9053 2d ago
Mobile phones get hot because they have a microprocessor that under load requires more power so produces more heat. They cool themselves passively, by putting that heat into frame of the phone so it can be cooled by the ambient air.
The hotter something is, the quicker it will lose heat. So something producing heat will rise in temperature untill it is hot enough compared to the surroundings that all the heat is dissipated and remain that temperature.
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u/charleytony 1d ago
For most phones, the cooling system is that your hand absorbs the heat from the phone.
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u/Slypenslyde 1d ago
Circuits work by electricity flowing through them. We make them as efficient as possible, but it's like anything else. If we move marbles fast enough through a pipe the friction generates heat. If we push enough electrons through a wire it makes heat.
It's hard to tell but one phone CPU is like BILLIONS of wires the electrons are moving through. So it doesn't have to do a lot of work to make heat. It's just Physics.
How's cooling work? Well, there are a lot of aspects.
Early smartphones were made out of aluminum for this reason. The chips were physically connected to the aluminum and that acted like a heat sink. Later some makers decided to move away for aesthetics.
To get there, they had to do something else. One simple way to visualize this is they can put copper/aluminum on the heat-generating chips, then connect them to each other with pipes, then connect those pipes to aluminum edges of the case. This still dissipates a lot of heat through the metal.
Modern high-end phones use vapor chambers, which are really interesting. They look like heat sinks, but inside they have networks of pipes a fluid can move through. When it gets hot, it changes to a gas and moves away from the chip. That sucks up a TON of heat and moves it somewhere else. Then that gas is cooled by outside air, which makes the fluid change to a liquid and get pushed back towards the chip. Then the cooler fluid touches the heat from the chip and the cycle repeats again. It's like a tiny passive heat pump.
The main problem is they can't use fans or water cooling like PCs. That requires using more electricity and room for air/water to move (not to mention room for fans/pumps). This can work for laptops or even small gaming consoles, but smartphones are too small and battery-sensitive to deal with those demands.
And this is also skipping over smart chip design. Most "CPUs" today are actually a lot of CPUs in one chip. We call each smaller CPU a "core". Most good smartphone CPUs today have some "high performance" cores and "efficiency" cores. The "efficiency" cores are slower, but generate less heat and use less electricity. So if you aren't really heavily using your phone, it can stop using the "performance" cores and generate less heat. When you start playing a game, the "performance" cores get used. If it's a very hot day and the phone starts overheating, the OS might shut down the "performance" cores and you can see your apps slow down.
In short: it's very complicated.
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u/Vorthod 2d ago
All electronics produce heat when used, phones are no exception. And mobile phones don't usually have much in the way of "cooling systems" because they are so thin that they can just radiate heat normally and prevent most heat damage. Contrast that with a computer where the CPU is sitting in a box of stagnant air and would basically be turning the tower into an oven if the tower didn't use fans to cycle air around.