The liquid in a heat pipe can return to the hot end through capillary action, and I believe this is how heat pipes in computer equipment work. They can work in any orientation.

https://en.wikipedia.org/wiki/Heat_pipe

I agree that this is most likely to be a capillary-pumped heat pipe. For more reading about how the wicks work:

http://www.thermalfluidscentral.org/encyclopedia/index.php/C...

The return mechanism is via capillary action; surprisingly, heat pipes work in any orientation, even freefall.

Very high g-forces can prevent them working, though.

I think it's just a metal heat sink, no liquid?

There are a number of different ways to build heat pipes. A few of the common designs typically used in cpu heatsinks and laptops do not rely on gravity or centrifugal force. Based on the skimpy page content, it appears they are using the more common wick/capillary system here. I'm not seeing anything ground breaking in their blurb, but maybe they left out the fancy part.

There's no liquid involved. They use a copper part, similar to the heat sinks on CPUs.

You are wrong. Look at all the other responses. And https://en.wikipedia.org/wiki/Heat_pipe