Study On The Characteristics Of Nanofluid Flow And Heat Transfer Enhancement In A Built-in Twisted Tape Tube

In the context of energy issues,research in the field of enhanced heat transfer has begun to shift from macro-optimization of heat exchange equipment to enhancing the heat transfer effect of heat exchange working fluids.Nanofluid is a new type of heat transfer fluid made by mixing nanometer-level solid particles with high thermal conductivity into the traditional heat transfer fluid.It can enhance the efficiency of the heat exchange system and has attracted great attention from scholars.This paper takes water as the base liquid and adds nanofluids made of Al₂O₃ and CuO nanoparticles as the research object.The experimental research on the forced convection heat transfer of nanofluids in circular tubes and built-in self-rotating twisted tapes tubes is carried out,and the nanofluids are analyzed.The heat transfer characteristics,resistance characteristics and comprehensive evaluation coefficients of fluids.The main work content and conclusions are summarized as follows:Firstly,the stability and heat transfer mechanism of nanofluids were studied and analyzed.The single-particle Al₂O₃-water nanofluid,CuO-water nanofluid and the mixed-particle Al₂O₃+CuO-water nanofluid were prepared by the "two-part method",and there was no obvious precipitation after standing for 12 hours,which met the experimental requirements.An experimental system for nanofluid flow and heat transfer in a built-in self-rotating twisted tapes tube was established.Experiments were carried out on the forced convection heat transfer of nanofluids of different types and volume fractions.The experimental results show that the volume fraction will affect the flow and heat transfer of the nanofluid.The convective heat transfer intensity of the nanofluid will increase with the increase of its volume fraction,and the drag coefficient will also increase at the same time.Under the same working conditions of a single nanofluid,the Nusselt number of the nanofluid is greater than that of the traditional heat transfer fluid,and the Nusselt number of the Al₂O₃-water nanofluid is greater than that of the Cu O-water nanofluid.As the Reynolds number and volume fraction increase,the heat transfer enhancement ratio of nanofluids gradually decreases.Compared with water as the heat transfer fluid,the heat transfer has been enhanced,and the comprehensive evaluation coefficients of Al₂O₃-water nanofluids compared to CuO-water nanofluids are the largest respectively 1.73 and 1.70.The relationship between the convection heat transfer and the resistance coefficient of the two nanofluids is fitted,and the errors of the relationship are less than 10%.The heat transfer characteristics and resistance coefficient trends of the mixed nanofluid are similar to those of the single nanofluid.At the same volume fraction,the Nusselt number of the mixed nanofluid is larger than that of the single nanofluid,the heat transfer performance is enhanced,and the resistance coefficient increases accordingly.Comparing the comprehensive evaluation coefficients between the two,it is found that the overall strengthening performance of the mixed nanofluid is not significantly changed compared with that of the single nanofluid.Considering that the preparation process of the mixed nanofluid is cumbersome,the advantages in practical applications are not strong.A comparative analysis of the three heat transfer enhancement technologies of nanofluid and self-rotating twisted tapes alone and the combination of the two,the Nusselt number of the self-rotating twisted tapes alone is greater than that of the nanofluid alone,and the two are combined The Nusselt number is the largest when in use.The increase in flow resistance of nanofluid is not obvious,and the flow resistance will be significantly increased when the self-rotating twisted tapes is added.The composite use of nanofluid and self-rotating twisted tapes has the largest comprehensive evaluation coefficient,which improves the heat transfer performance the most.