Evacuated Heat Pipe Solar Collector.

A tubular evacuated heat pipe solar collector is introduced having rectangular performance characteristics. The heat transfer from the absorber plate (covered with a selective coating) to the water duct is through the heat pipe. In order to avoid cycle delays in the operation of the heat pipe, a trap mechanism has been adopted for the condensed liquid. To avoid any inconveniences which could be caused through no load condition by the vacuum collector, advantage has been taken of the physical features related to the critical point of the fluid operating in the heat pipe: if the critical temperature Tc of the operating fluid is exceeded, the condensation effect will cease. This means that above the critical temperature Tc the heat pipe transfer property will vanish. As a consequence a slight increase in temperature of the condenser will occur, which goes just above the Tc of the liquid which is being used. The choices have fallen on liquids having a Tc between 95 and 115 degree C.