The whole two-phase closed thermosyphon collector system
can be treated as a grouping of control volumes evolving in a linear
manner under the sole influence of thermal mechanisms. The
heat transfer process can be seen as an integration of three parts: (i)
the solar heat absorption by the working fluid, (ii) the heat transfer
from the tube evaporator section to the condenser section, and
(iii) the heat exchange between the working fluid and the water in
storage tank.