On 02/02/17 09:09, A. Dumas wrote:
> On 01/02/2017 22:11, rickman wrote:
>> On 2/1/2017 3:36 PM, druck wrote:
>>> On 31/01/2017 23:03, rickman wrote:
>>>> There would appear to be something wrong with your numbers.  If you
>>>> raise the ambient temperature 1 degree, the core of the CPU should rise
>>>> 1 degree.  If you lower the ambient temperature 1 degree, the core of
>>>> the CPU should lower 1 degree.
>>>
>>> Only if there is a perfect heat transfer between the chip's core and the
>>> surrounding environment.
>>
>> I'm not sure what *you* mean by "perfect heat transfer", but I can
>> assure you, all heat created in the CPU is transferred to the
>> environment.
>
> In perfect convective heat transfer, the heat transfer coefficient will
> be constant and "Newton's law of cooling" applies, so then yes, with
> changing ambient temperature a new equilibrium will be reached where the
> temperature difference is the same as before; i.e. 1 degree hotter room
> = 1 degree hotter cpu.
>
> BUT... to quote Wikipedia: "The heat transfer coefficient is often
> relatively independent of temperature in purely conduction-type cooling,
> but becomes a function of the temperature in classical natural
> convective heat transfer. In this case, Newton's law only approximates
> the result when the temperature changes are relatively small."
>
> In open cases, Newton's law will almost certainly be a good
> approximation. Maybe the lack of circulation in druck's fridge explains
> the slight divergence there, and I don't know WHAT happened in the car.
>
Its horrendously complex. Radiation is to the 4th power of temperature,
and empirical data shows that convection is massively dominated by the
ability of air to get way from the heatsink either cost its blown, or
because there is a good path for convection.

Strapping a huge heatsink on a chip in a closed box merely delays the
onset of thermal issues, it doesn't solve them


--
“Some people like to travel by train because it combines the slowness of
a car with the cramped public exposure of 
an airplane.”

Dennis Miller

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