Abstract:

Global warming is at the forefront of today's environmental problems. It is a general belief that the solution to this problem is through clean energy sources. Solar energy is one of these clean energy sources, and it is used in electrical energy production, hot water preparation, drying and many industrial applications today. However, the efficiency of photovoltaic systems commonly used in electricity generation are relatively low. Also, there is a limit in the fluid temperature to be obtained with flat plate collectors. Drying applications with planar collectors also increase the required collector area. Therefore, research and development studies are ongoing in which solar energy can be evaluated with higher efficiency. In this study, a solar collector with evacuated tube and series connected U-pipe was tested indoors and efficiency curves were formed. In the study, 10 vacuum tubes with an outer diameter of 70 mm and series connected steel tubes with a diameter of 8 mm placed inside them were used. A closed cycle was created with circulation pumps and a plate heat exchanger integrated into the system, and measurements were performed under indoor conditions using a solar simulator. An average of 902 W/m2 radiation intensity from the simulator to the solar collector is provided by halogen lamps. The experiments were carried out at 3 different values for the fluid flow rate in the U-pipes and with 4 different inlet temperatures. In the experimental study, it was observed that the collector efficiency ranged between 60% and 78%. The pressure drop between the inlet and outlet of the U-tube solar collector varies between 59-65 kPa. Looking at the analysis results, the use of a series-connected steel tube collector with a large diameter evacuated tube provides an increase in the collector outlet temperature, but since the pressure drop is high, the pumping power should also be taken into account in the system selection.

Keywords: