Evacuated heat pipe solar collector

A tubular evacuated solar collector with rectangular performance characteristics is introduced. The heat transfer from the absorber plate with selective coating to the water tubing occurs via a heat pipe system. In order to avoid any delay in the operation of the heat pipe due to superheating of the vapour, we have introduced a trap mechanism for the condensed liquid. To avoid the disadvantage of the high no-load condition of the vacuum collectors we have used the physical features of the critical point of the heat pipe working fluid.

Above the critical temperature, T_c of the working fluid the condensation effect will disappear. This means that above T_c the heat transfer property of a heat pipe will vanish. This will cause only a slight increase of the condenser temperature above T_c of the liquid used. For our heat pipe system we have chosen working liquids with critical temperature between 95–115°C.