Improving the Heat Storage of Evacuated Tube Solar Collectors by Inserting Metallic Strips and Using a Secondary Evacuated Tube

Abstract

      Nowadays, there is a fierce race to exploit and maximize the usage of solar energyall around the world because not only is it environmentally friendly, but also, it is a sustainable source of energy. Solar collectors convert the solar radiation coming from the Sun into heat energy, which can be used in many application, e.g. domestic heating. The objective of this research is to improve the thermal performance of evacuated tube-heat pipe solar collectorsin an affordable way by inserting metallic strips and oil inside the evacuated tube in order to enhance the heat transfer from the evacuated tube into the heat pipe. Three various metallic strips have been examined, i.e. iron, aluminum and copper strips.Moreover, the effect of using two evacuated tubes instead of one, has been examined, where one tube is placed at the focal line of the parabolic trough, i.e. the primary tube, while the secondary tube is placed beside or above the primary tube.Two identical solar collectors, i.e. evacuated tube parabolic trough solar collectors, have been built and examined, one is a standard collector and it is used as a reference for comparison, whilethe other is a collector with modifications. It has been found that using copper strips in the evacuated tube instead of the aluminum fin that comes with the evacuated tube and attached to the heat pipe, enhances the heating of the heat pipe, when compared to the aluminum fin, iron strips and aluminum strips. Furthermore, it has been found that filling the evacuated tube with oil and copper strips increases the heat storage capability of the tube, such that the solar collector can still supply heat energy even after sunset. Adding a secondary evacuated tube beside or above the primary tube makes use of the unfocused sunlight, which enhances the overall heating capability of the collector.