Performance studies of novel all-glass heat pipe evacuated collector tube integrating numerical simulation and experiment method

• Published in: Solar energy 2023-03, Vol.253, p.491-500
• Main Authors: Gong, Jing-hu, Sun, Zhi-hao, Wang, Jun, Lund, Peter D.
• Format: Article
• Language: English
• Subjects: All-glass ECT; Flow field; Heat pipe; Thermal expansion; Thermal stress
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2023.02.028

Metal heat pipe evacuated collector tube (ECT) suffer from cracks in the joint between the glass outer layer and the metal heat pipe due to the large difference in thermal expansion coefficients of glass and metal, resulting in non-industrialization. In this paper, the metal heat pipe is replaced with a glass heat pipe to form an all-glass heat pipe ECT to address the air-tight sealing problem. The results show that the thermal stress at the seal joint is approximately zero, below 0.279 MPa, far below than the bearing range of 40-120 MPa. At the same time, it was also shows that by adding a reflective film to the lower half of the outer layer glass, the optical efficiency was increased by 0.17 %. The energy output in the quasi-equilibrium state is 87 W, which is 8 W higher in the simulation. Water-vapor directly reaches the condensation section to reduce the formation of vortices under conditions where it absorbs sufficient energy to overcome its own gravity and ambient pressure, thus reducing heat loss and increasing thermal efficiency. Fig. 1. All-glass heat pipe vacuumed collector. [Display omitted] •A metal heat pipe is replaced with glass to form an all-glass heat pipe evacuated collector tube.•Maximum thermal stress of 0.279 MPa is well below than the bearing range of 40–120 MPa.•All-glass structure fully copes with the transient local heating changes.•Optical efficiency is increased by 0.17% by the addition of the reflective film.•Yielding an energy output of 87 W in the quasi-thermal equilibrium state. Metal heat pipe evacuated collector tube (ECT) suffer from cracks in the joint between the glass outer layer and the metal heat pipe due to the large difference in thermal expansion coefficients of glass and metal, resulting in non-industrialization. In this paper, the metal heat pipe is replaced with a glass heat pipe to form an all-glass heat pipe ECT to address the air-tight sealing problem, and a reflective film was added to the lower part of the outer tube to improve energy. According to these results, the thermal stress of 0.279 MPa is well below the bearing range of 40–120 MPa, and the maximum thermal strain of 0.175 mm/mm is also far less than the affordable value of 120 mm/mm, inducting the all-glass structure fully copes with the transient local heating changes. The optical efficiency is increased by 0.17 % by the addition of the reflective film, and yielding an energy output of 87 W and a maximum volume fraction of 4.8 % for liquid–water i