INFLUENCE OF INCLINATION ON THE PERFORMANCE OF A WICKLESS HEAT PIPE FOR SOLAR APPLICATIONS

The paper describes an experimental study on the heat transfer inside a wickless heat pipe. In a previous paper [1, 2] an experimental campaign was conducted to ascertain the influence of different filling ratio on the heat transfer. The experiment was made with tubes inclined at 45°. To evaluate the influence of the inclination respect to the horizontal on heat transfer, a new campaign was conducted with the tubes inclined at 30°, to compare the result with those ones obtained with the different inclination. For this purpose the same filling ratio used in the previous campaign was used. The heat pipe is made of copper, the length is 1420 mm, internal diameter is 6 mm, and the vacuum inside is 10-5 bar. The experimental campaign was conducted on the experimental facility named T.O.S.C.A. (Thermal-fluid dynamics Of Solar Cooling Apparatus), which has been designed and constructed to test the influence of various geometrical an thermo-hydraulic parameter on the performance of the wickless heat pipe. The facility was built in the “Thermal-Fluid Dynamics Applied to Energy Systems” laboratory of ENEA-Casaccia Research Centre (Rome), The cooling loop is constituted of a collector coupled with a pump, a dumper and a heat exchanger. Pressurized water flows inside the collector cooling the heat pipe. The condenser section of the heat pipe is immersed in the free stream of the water. The heat pipe is heated by a heater made with an electrical wire wrapped on a length of 85% of the total length. We apply an electrical power, of 70W and 155W, values that simulate the solar power. Flow rate and pressure of the cooling water are constant. We measured the wall temperature of the heat pipe in the three different zone of the heat pipe: evaporator, adiabatic part and condenser; two other thermocouple are inserted in the collector to measure the heat transfer using a power balance.