Heat transfer enhancement of solar collector tube enhanced by swirling flow

Heat transfer capability was one of the key factors that restricted the collecting efficiency of the parabolic trough collector tube. In this paper, a swirl-enhanced solar collector tube with a cyclone inserted at the inlet of the metal tube was purposed to improve the heat transfer capability of the collector tube. The cyclone induced a swirling flow and improved the convection inside the tube, thereby enhancing the heat transfer capacity of the tube. The advantage of the cyclone tube was not changing the structure and processing technology of the original heat collector tube. A numerical model was established to study the flow and heat transfer characteristics of the cyclone tube using Ansys CFX software. The results demonstrated that the swirling flow was over a distance exceeding 1 m and the fluctuations in turbulent kinetic energy was within a distance of approximately 0.2 m. The heat transfer capacity was significantly enhanced within this 0.2 m region and the maximum normalized Nusselt number reached 2.81. Finally, the influences of the blade length and the blade numbers on the heat transfer capability were researched. Results showed that cyclone with short blades and more blades resulted in better enhancing effects.