Re: Re: Powerbook Enclosure Change
Originally posted by madamimadam
I am not too sure convection heating is really possible with a laptop.
"Convection" is the process of transfering heat energy via moving matter (ie, air or another fluid normally). Fans cool by convection (moving the heated air away from the heat source). This is in contrast to "conduction", which is the movement of energy through a mass, and "radiation", which is the movement of energy via sub-atomic particles/radiation (depending on your POV on what radiation is, wave or particle, at the particular time).
Traditional cooling mechanisms use conduction to take the heat from an inconvenient source (such as a CPU) to a more convenient/larger surface area object (such as a heat sink), and then convection to disperse the heat into the general atmosphere.
Adding a fan of any sort to the notebook would allow convection to take place. That, of course, is one of the first things notebook manufacturers look at to cool their systems (although noise generated is roughly proportionate to air flow and no one wants a notebook louder than the jet engine outside your airplane window).
While "convection" is also used to describe a process where the heated air moved of its own accord (ie, "up", replaced by downward-flowing cooling air), this is really more properly refered to as "self-convecting". And, no, I don't think a laptop has enough vertical open space to allow for a large degree of air self-convection. And, of course, that would make your keyboard and palm rest the heat sinks, and I don't think Joe Consumer would appreciate hot air convecting up between his fingertips as he types ...
"Heat tubes" rely on self-convection of a fluid (picked for its thermal properties; not often air) within a tube, and are driven by one end of the tube being appreciably higher up than the other end of the tube. Some PC manufacturers (Shuttle comes to mind) have had great success in cooling small-form-factor PCs using heat tubes, along with a more traditional heat-transfer mechanism at the "output" end (heat sink+fan). However, the only possible way I can see this working in a laptop situation is if the heat tube went from the innards of the machine (CPU, GPU, etc) to the "top" of the open laptop screen, allowing the entire back side of the laptop case to essentially act as a heat sink ... but then, of course, the heat tube would have to bend at the screen/body joint, which is a tricky situation (this isn't just wires, but a tubing that
has to remain 100% structurally sound through years of abuse and fairly dramatic heating/cooling cycles,
and provide the cross-sectional area and lack of surface friction required to allow self-convection to take place ... a very tricky materials problem indeed!). Plus, what happens when you "close" the notebook (perhaps to put it in a dock, perhaps to have it continue to play MP3s through your headphones while you catch a quick snooze on the plane), thus removing the vertical differential required for the cooling mechanism? Or, what happens if you don't operate the laptop with the degiend 90 degrees between lid and base? Any catastrophic structural failure of the heating system would destroy your system via overheating within seconds, but also any "slow leak" failure would stand a high chance of causing a short and likewise destroying your system.
So, no, I don't see self-convection, even in the relatively versatile heat tube, as a really near-term possibility on a laptop. But it would be really cool if Apple could do it anyways
...
