Microsoft Surface Pro 3 had a liquid cooling system to keep the device cool even when running CPU intensive tasks for a longer period of time. SP3 had a horseshoe-shaped copper heat pipe filled with water. The apex of the horseshoe covers the CPU and during heating, the water inside the pipe is transformed into vapor, which then travels down the heatpipe to the fan portion where it condenses, and travels back to the CPU. Even though it works fine, heat was still concentrated to a particular area of the device.
In Surface Pro 4, Microsoft has improved the liquid cooling system.
The SP4 actually boils/evaporates liquid inside a metal tube that touches the processor, and that vapor travels to two places inside the SP4 to condense back into a liquid: one to the fan, and the other under where the kickstand normally rests. The one under the kickstand allows the fan to rarely run, unless under extremely demanding tasks. So for web browsing, and normal day-to-day activities, you’ll no longer have the fan run as you did in the Surface Pro 3. And when the surface is under pressure with the fan running, the heat will be more evenly distributed – not all concentrated in a big hot spot – making the SP4 feel a bit cooler.
Yesterday, Microsoft also announced that they have implemented similar liquid cooling system in the Lumia 950 and Lumia 950 XL Windows 10 Mobile devices.