You're lecturing us in thermodynamics and you say that?
What the hell.
Side note:
bosozoku was talking about putting a thermal pad between the CPU's heatsink and the bottom case thereby using the bottom case as a huge heatsink. I think it would work.
I will quote this post simply to show the futility of it.
Please read further on convective currents so that you understand why convective heat rises.
In fact, please read the difference between conductive heat, convective heat and radiated heat (infrared) before you read any further so that you understand it.
But let's see what happens when you duct CPU heat directly to the bottom of the case.
Firstly, we will ignore the fact that the bottom of the case sits on your lap, and as it heats up, it will become increasingly less comfortable.
So the case starts to heat up – it's hottest point being the point at which the CPU directly sinks to it – and starts to exchange heat with any air that surrounds it (or any other thermally conductive surface it comes into contact with – such as your skin). Whilst the case itself is a conductor, the parts of the case that are farthest from the heat source will be the coolest, as the case radiates heat at the same time as it conducts it.
As there is very little air exchange underneath the laptop, convective heat will build up in this area until both the air and case reach similar temperatures (thermal equilibrium). A small amount of air will exchange due to convection, but it will not be very efficient – unless the bottom of the laptop is raised off any surface.
If anyone doesn't believe me, feel the bottom of your laptop case right now and compare it to the top.
So where does that heat eventually go? If the heat exchange materials are the same (air), the highest rate of heat transfer goes towards the steepest thermal gradient – the inside of the case until it, too, reaches thermal equilibrium or is exhanged via airflow inside the case.
Of course, you don't even need to understand all this.
Because if passive convective case cooling was more efficient – and indeed more comfortable to sit on your lap – than active heatsink cooling, then every laptop manufacturer would be doing it.
But they don't. So there's your answer.
