| In industrial production,enhanced heat transfer technology has been popular,but improving heat transfer efficiency has been a hot research topic.In this paper,the combination of nanofluids and left-right twisted tape is proposed to enhance the heat transfer efficiency.The flow and heat transfer of nanofluids in a tube with left-right twisted tapes are numerically simulated by using the FLUENT software of ANSYS software package.The calculation range is laminar flow(Reynolds number Re = 400 ～ 1800),The effects of left-right twisted tape structure and nanofluids properties on heat transfer enhancement were investigated.First of all,this paper analyzes the problems of tube + water,tube + nanofluids,tube +water with traditional twisted tape,tube + nanofluids with traditional twisted tape and 180 °Round tube without notch twisted tape + water and built-in 180 ° The six combinations of tube and nanofluids without left-right twisted tape were studied numerically.The results show that the heat transfer effect of the round tube without left-right twisted tape is better than that of the traditional twisted tape with single twisted direction.Among the six combinations,The results show that nanofluids is used as working fluid.the round tube with left-right twisted tape has the highest Nu number and PEC value,and has the best heat transfer effect and comprehensive performance.Secondly,this paper analyzes the heat transfer characteristics,resistance characteristics and comprehensive performance of a circular tube heat exchanger with 1.2% Cu O water-based nanofluids as working fluid and different notches,twist ratios and twist angles.It is found that the twist ratio,notch shape and twist angle of the twisted tape all affect the heat transfer enhancement effect.Under the same working condition,the torsion ratio of the twisted tape decreases,the Nusselt number increases,but the friction resistance increases,the comprehensive performance index increases,and the comprehensive performance is improved.When the twisted tape with torsion ratio of 3 is inserted,the comprehensive heat transfer performance is the best;The results show that with the increase of notch area,the friction resistance friction value decreases,but the Nusselt number Nu value decreases,the comprehensive performance index PEC value decreases and the comprehensive performance becomes worse.The heat transfer effect of the notchless twisted tape is the best;When the torsion angle decreases,the Nusselt number of the heat exchanger increases,and the heat transfer effect is enhanced,but the friction resistance increases.The fluid needs to consume more energy to overcome the friction resistance.The PEC value of the comprehensive performance index decreases,and the comprehensive performance is improved.The reinforcing effect of friction twisted tape is the best.Finally,this paper analyzes the water-based nanofluids with different volume concentrations and particle types as working fluid,and the built-in torsion ratio of 90°.The heat transfer characteristics,pressure drop characteristics and comprehensive performance index of the round tube heat exchanger without notched twisted tape are studied.It is found that the Nusselt number,friction coefficient,resistance and PEC increase with the increase of the volume concentration of nanoparticles;The Nusselt number,friction coefficient and comprehensive performance index of the heat exchanger change with the change of the type of nanoparticles.Cu O water-based nanofluids have the best heat transfer effect and comprehensive performance.In the various combinations studied in this paper,the Cu O water-based nanofluids with a volume concentration of 1.2% is used as working fluid,the Nusselt number,friction coefficient and comprehensive performance index of the heat exchanger model with torsion ratio of 3 and 90° twisted tape without notch can reach 4.51 ～ 7.22,7.59 ～ 14.49 and 2.29 ～2.58 respectively,which shows the best comprehensive heat transfer performance. |
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