What is the difference between U tube and heat pipe collectors?
U tube collectors have a copper pipe, attached to a heat absorbing fin, running from the top of the solar vacuum tube and making a U turn at the bottom. Heat pipe collectors have copper heat pipes inside the evacuated tubes, with water only flowing past the header of the collector. Both collectors stand high pressure and look the same externally but the U tube can be used in any orientation. Heat pipes can not work lying flat; the bottom of the pipe must be lower than the head.
