Research On Convection And Boiling Heat Transfer Characteristics Of Nanofluid

In recent years,the new type of heat transfer working fluid—nanofluid has attracted the attention of scholars because of its advantages such as high thermal conductivity,and it has great research significance in the field of strengthening heat transfer.The current research on nanofluids is mainly aimed at the preparation of nanofluids,the stability research and the experimental research on convection and boiling heat transfer.There are few researches on numerical simulation methods,especially the numerical research on boiling heat transfer of nanofluids.The study is based on ANSYS Fluent software,and conducts a comprehensive study on the fluid flow and mass and heat transfer of the nanofluid in the pipe,as well as the boiling and evaporation phase transition process.The main research contents of this study include the following:(1)It systematically summarized the existing mathematical simulation and research methods of nanofluid flow and heat transfer,and summarize the main processing methods and the most suitable simulation methods for nanofluid simulation research At the same time,the concrete realization mechanism of three main wall boiling models including RPI wall evaporation boiling simulation,non-equilibrium subcooled boiling model,and critical heat flow condition model were discussed,and the most suitable interphase interaction force model and the modified model of wall evaporation boiling considering the effect of nanoparticles was also discussed;(2)A comprehensive numerical simulation study on the forced convection heat transfer process of nanofluids in a section of loop.It is concluded that when the number of radial nodes of the ring tube is 10,the number of axial nodes is 2101,and the thickness of the first layer grid is between 0.06?0.09 mm,it has the best test comparison accuracy.In addition,the simulation results obtained by the RNG model are the closest to the test results,while the Nusselt number calculated by the SST model is significantly different from the test results.The multi-component single-phase flow model is more suitable for the simulation of small volume fraction nanofluids and the accuracy of the Eulerian model is more suitable for the simulation of large volume fraction nanofluids.Moreover,the optimal concentration of A1203 nanoparticles should be controlled between 0.5%and 1%,so that both convection heat exchange efficiency and economy can be considered.(3)A detailed numerical simulation study on the supercooled boiling heat transfer of pure water in a straight pipe.It is concluded that when the Y+ value of the first layer grid is between 20?60 and the aspect ratio of the overall grid is between 2?5,the overall simulation calculation has the best experimental contrast verification.At the same time,the research results show that the Coulomb number has no obvious effect on the overall heat transfer coefficient,but the increase in the Coulomb number can increase the overall evaporation,and the surface tension has little effect on the boiling evaporation process.Moreover,the simulation results of RPI and Non-equilibrium wall evaporation models are closest to the experimental values,while the total heat transfer coefficient simulated by the full CHF model is higher than the experimental values.(4)The numerical simulation of the nanofluid supercooled boiling evaporative heat transfer is the most suitable simulation method that it treated the nanoparticles and the base liquid as an independent one phase,and the steam constitutes the second phase of the Eulerian+Species model The Eulerian three phase flow model is not suitable for simulating the boiling heat transfer process of high concentration nanoparticles.At the same time,the increase in the fraction of nanoparticles is beneficial to raising the overall temperature of the nanofluid in the pipe,but it can play a certain role in inhibiting the evaporation and boiling phenomenon near the wall surface.