I see lots of fancy names for what this little device is - Stirling, Rankine, fluidyne - but, seriously, it really is just a simple pump that uses thermal syphoning. Heating the water makes it expand, drawing up cold water as the hot water pushes out. It isn't rocket surgery 8-), and overly complicating the explanation certainly wont help those not even smart enough to get one of these little devices to float...