The heat pipes used in AUCKLAT solar collectors have a boiling point of only 25°C. So when the heat pipe is heated above 25°C, the water vaporizes. This vapor rapidly rises to the top of the heat pipe transferring heat. As the heat is lost at the condenser (top), the vapor condenses to form a liquid (water) and returns to the bottom of the heat pipe to once again repeat the process.
See larger image: Heat Pipe
China
