Thermal Modeling And Flow Heat Transfer Characteristics In Flat Tube Of Al₂O₃-H₂O Nanofluid

Heat transfer enhancement technologies is the key of improving the heat transfer efficiency of heat transfer system and deducing the volume and cost of heat transfer device,and one of the keytechnologies of heat transfer enhancement is the heat transfer working medium of high heat transfer perform.With the fast developping of nano technologies,the main method of enhance heat transfer development is nanofuilds replacing traditional heat transfer working medium.But at present the research on the thermophysical property and flow heat transfer characteristics of nanofluids is needed to completed.This paper regarded Al₂O₃-H₂O nanofluid as the research object,to research the thermophysical property and flow heat transfer characteristics in flat tube.It has significance to manufacture heat transform device with high efficiency and compact.The main research contents are as follows:1.The theory model research on the thermal conductivity of nanofluids.Firstly,compiled the experimental data of the Al₂O₃-H₂O nanofluid thermal conductivity,and analyzed the factors influencing the thermal conductivity of nanofluids.Secondly,based on the experimental data,the existing nanofluids thermal conductivity models were compared and analyzed.It was analyzed that the shortcomings of existing nanofluids thermal conductivity models.Nanofluids thermal conductivity prediction model has been established by using multiple linear regression analysis and the Buckinghamπtheory,and compared with the experimental data and the existing thermal conductivity models.the results show that the Al₂O₃-H₂O nanofluid thermal conductivity model established in this paper has wide application range and high accuracy of prediction.2.The theory model research on the thermal viscosity of nanofluids.Firstly,compiled the experimental data of Al₂O₃-H₂O nanofluid viscosity,and analyzed the influence factors of viscosity.And secondly analyzed the existing models of nanofluid viscosity based on the experimental data and analyzed the shortcomings oft the existing nanofluids viscosity models.Finally,established the prediction model of the nanofluids viscosity by using the method of multiple linear regression analysis,and compared with the experimental data and the existing viscosity models.The results show that the nanofluids viscosity model established in this paper has wide application range and high accuracy of prediction.3.The flow heat transfer characteristics research on nanofluids in flat tube.Firstly,the flow heat transfer characteristics of Al₂O₃-H₂O nanofluid which in the flat tube under the laminar flow state has been researched by using single-phase flow and numerical simulation.And the influence of nanoparticle volume fraction,particle diameter,inlet velocity and temperature on the heat flow transfer characteristics of nanofluids which in the flat tube has been analyzed.And the overall performance of Al₂O₃-H₂O nanofluid has been analyzed by using entropy production and PEC.This shows that the convective heat transfer coefficient and pressure drop of Al₂O₃-H₂O nanofluid was higher than base fluid,but the overall performance was less,and was closely related with volume fraction,diameter of particles and fluids temperature.