Under the condition of fluid temperature below 100 C, the
thermal efficiency of the proposed PTC increased with the
increase of fluid temperature, due to the increase of Reynolds
number caused by the increasing fluid temperature, and finally
reached a relatively stable level of 67%. Frosting, especially in
the morning, on the surface of the reflector seriously weakened
the thermal efficiency, which just maintained less than 26%.
The thermal efficiency was improved with a larger fluid flow
rate, whereas weakened by a large wind velocity. In this study,
the thermal efficiencies for the fluid flow rate of 0.13 m3/h, 0.36
m3/h and 0.55 m3/h were 30%, 58% and 67%, respectively. The
final thermal efficiencies in the conditions of wind velocity of
1.7 m/s and 5.0 m/s were 67% and 56%, respectively, which indicated
that the heat loss of the proposed PTC was sensitive to the
heat convection.