From the first group of
experiments, it was possible to note that, for a constant filling ratio
of 20%, better rates of thermal energy gain have been obtained
with elliptical cross section wickless heat pipe. This is due to its
higher surface area to volume ratio compared to the circular and
semi-circular wickless heat pipe. Besides, the optimum filling ratio
of elliptical cross section heat pipe is 10%. This behavior can be
attributed to the increase of heat capacity of the collector with the
increase of filling ratio. Finally, second group of experiments
confirmed that higher efficiencies could be reached with elliptical
cross section wickless heat pipe and a filling ratio of 10% in a wide
range of inlet temperature and mass flow rate of cooling water.