Thermal Mechanical Characteristics Analysis Of Trough Solar Collector With Microencapsulated Phase Change Slurries

With the rise of renewable energy,the use of solar heat has gradually become a hot topic.Sunlight is a renewable energy source,which can provide a steady stream of energy for human production and life,and has the advantages of no pollution,low cost,and renewable.Among the various heat utilization methods,the most widely used is a parabolic trough solar collector,which has the advantages of low cost,low energy consumption,and mature technology.However,the bottom of the heat collecting tube is reflected by a non-uniformly concentrated light reflected by a parabolic mirror,the temperature distribution on the wall surface of the tube is uneven,and there are factors such as temperature gradients and excessive thermal stress,which can easily cause the heat collecting tube to deform and rupture the glass sleeve.Phase change microcapsules are tiny particles with heat storage and exothermic properties,which can effectively reduce the temperature along the fluid and improve the heat transfer efficiency of the fluid.In order to strengthen the fluid heat transfer,reduce the thermal stress of the tube wall and improve the safety coefficient of the absorber,this paper uses phase change suspension as the working fluid to study the thermal performance of the suspension in the heat collecting tube.In view of the low heat transfer effect and high thermal stress of tube wall of traditional water-based and oil-based solar collectors,three-dimensional modeling of parabolic trough solar collectors was carried out with suspension as the working fluid.The optic-thermal-mechanical coupling problem of solar thermal tude is solved by combining the Monte Carlo ray-trace method,the finite volume method and the finite element method,The Monte Carlo ray tracing method is used to simulate the solar energy system and analyze its optical performance,The heat transfer and thermal stress of microcapsuled phase change material slurries in a collector tube were numerically studied by using Eulerian-Eulerian multiphase flow model.Then,the obtained temperature field distribution of the heat sink is introduced into the structural analysis model to study the thermal stress distribution of the heat sink with different concentrations of suspension.The results show that the temperature of the wall of the absorber tube is unevenly distributed because the outer wall surface of the conventional heat-collecting tube is subjected to non-uniform solar heat flux.The phase-change microcapsule suspension enhanced the convective heat transfer in the conventional collector tube,which not only reduced the wall temperature along the collector tube,but also reduced the circumferential temperature difference of the absorber tube,and homogenized the temperature distribution of the collector tube.The equivalent thermal stress in the circumferential direction of the collector tube is a petal-shaped distribution,which appears near the five positions corresponding(θ =5°,θ =90°,θ =175°,θ =225°,and θ = 315 °).Local equivalent stress peak.The axial thermal stress at the inner wall surface of the heat sink tube at θ = 90 ° is compressive stress,which acts on the entire tube side,while the radial thermal stress and tangential thermal stress are tensile stresses,which are mainly applied at the inlet and outlet ends.The higher the concentration of the phase change microcapsule suspension,the better enhancement effect,the smaller the thermal stress of the heat collecting tube,and the higher the minimum value of the safety coefficient of the heat collecting tube,but the resulting pressure drop will also increase.Compared with conventional solar collectors,the new solar collector effectively homogenizes the solar flux distribution on the outer wall of the heat pipe and reduces the nonuniformity of the temperature distribution on the wall of the heat pipe by adding a secondary mirror and the center of the heat pipe deviates from the focus of the parabolic mirror.compared with traditional water-based solar collectors,the suspension also effectively reduces the temperature difference of the tube wall of the heat sink,and the temperature distribution becomes more uniform as the concentration of the suspension increases.However,compared with conventional collectors,the convective heat transfer coefficient and pressure drop of the collector tubes have not changed much.the circumferential equivalent thermal stress on the inner wall surface of the collector tube outlet reached a local maximum at θ = 270 °,θ =187°,θ =353°.Compared with before improvement,the equivalent stress,axial,radial and tangential thermal stresses are all reduced.The axial thermal stress at θ = 90 ° of the inner wall of the heat pipe is tensile stress,which acts on the whole tube side,while the radial and tangential thermal stresses are tensile stress,which acts on the whole tube side.as the thermal stress is reduced,the minimum value of the safety factor of the improved collector tube wall is effectively increased,and the minimum value of the safety factor is also increased with the increase of the suspension concentration.