Research On Convection And Heat Collection Characteristics Of Nanofluid Under Rotors Turbulence Effect

Nanofluid has excellent thermophysical and optical properties,and has excellent performance in the fields of convective heat transfer enhancement and solar photothermal conversion.Based on the team’s research,this article uses Chinese ink nanofluid,a clean and efficient nanofluid,as a convective heat transfer medium in shell and tube heat exchangers and heat collecting medium in direct absorption solar collector,and uses a heat transfer enhancement element – combined rotors – in combination with it.Through experiments and numerical simulation,the process and mechanism of convective and radiant heat transfer of nanofluid under rotors’ turbulence were comprehensively studied,and the effects of nanoparticle mass fraction,rotors’ structure,and layout on heat transfer process were summarized,and an efficient and economical combination method was proposed.According to the differences between convection and radiation heat transfer methods,the research content of this article is mainly divided into the following two parts:In order to study the effect of rotors’ turbulence on the convective heat transfer process of nanofluid,an enhanced heat transfer experimental platform was built.Using different mass fractions of Chinese ink nanofluid prepared by a two-step method as convective heat transfer media,the flow and heat transfer characteristics in tubes under rotors’ turbulence with different structures were studied.Parameters such as the Nussel number Nu,the flow resistance coefficient f and the comprehensive evaluation factor PEC at different Reynolds numbers Re were obtained.The results showed that nanofluid in built-in rotors tube exhibit better enhanced heat transfer performance than in plain tube:When the medium in plain tube is changed from water to nanofluid with a mass fraction of 0.1%,Nu can be increased by 5.72%-12.11%;In the built-in rotors tube,the increase in Nu can reach 11.12%-15.69%.Subsequently,the flow and heat transfer process of nanofluid in a built-in rotor tube was simulated using ANSYS FLUENT,and the synergy angle distributions of velocity,temperature were obtained.The simulation found that the combined rotors has a strong destructive effect on the laminar layer near the wall surface of the heat exchange tube,and can promote the replacement of high-temperature media near the wall surface with low-temperature media in the tube,improving the temperature difference between the media and the tube wall,thereby enabling nanofluid with better thermophysical properties to conduct heat transfer more efficiently.In studying the effect of rotors’ turbulence on the radiation and heat transfer process of nanofluid,a heat collection experimental platform suitable for the dynamic operation of nanofluid was built.Using nanofluid with different mass fractions as heat collection media,the heat collection characteristics of the composite rotors’ turbulence were studied,and parameters such as temperature rise,heat collection efficiency,and power consumption ratio in the circuit within a certain time were obtained.The results showed that the temperature rise and heat collection efficiency in the circuit will be improved by varying degrees after inserting combined rotors into the heat collector tube.When the mass fraction of nanoparticles is high,the enhanced heat collection effect caused by rotors is better.When the nanoparticles mass fraction is 0.2%,the temperature rise in the circuit after inserting the rotors is 56.86%higher than that before inserting the rotors.Subsequently,the turbulent intensity and temperature distribution in the tube under different combinations were obtained via numerical simulation.The results showed that under the turbulence effect of the rotors,the media on the media on the near light side and the backlight side of the tube can be replaced and mixed,enabling the media in the tube to fully absorb solar radiation,thereby improving the heat collection efficiency.