In this paper, an experimental study has been carried to enhance the effectiveness of a two-phase closed thermosyphon (TPCT) type heat pipe. For this purpose, three different designs have been developed by modifying the internal structure so as not to interfere with the physical operation of TPCT. Three heat pipes with different internal structures were manufactured with additional pipes placed longitudinally inside the evaporator and condenser sections of the normal (conventional) TPCT. Ionized pure water is used as a working fluid at the same rate in Normal, Type-1, Type-2, and Type-3 heat pipes. TPCTs are positioned at three different inclination angles, 26°, 41°, and 56°, to see the performance effect not only among themselves but also on the changes made by the gravitational effect. For each tilt angle, four TPCTs were simultaneously powered by solar energy on three different days. As a result of the experiments carried out in July, it has been observed that the optimum inclination angle for solar water heated TPCT is 26°. In addition, it was found that with the increase of the angle of tilt, the thermal resistance (R) of the heat pipes also increased and the heat transferability of the TPCT decreased. Comparing the new designs and normal TPCT, Type-2 acted better at tilt angles of both 26° and 41^oAs a result, the heat transfer and efficiency of normal TPCT have been improved by almost 14% with Type-2 at the tilt angle of 26°.