Experimental Study On Convective Heat Transfer Characteristics Of Nanofluids In A Threaded Tube With Twisted Tape Inserts

At present,the enhanced heat transfer of nanofluids and the enhanced heat transfer of the built-in twisted tube have become relatively mature and widely used technical means.Research on nanofluids includes:selection of nanoparticles,preparation of nanofluids,analysis of stability and thermal conductivity,and flow and heat transfer characteristics.However,research on the application of nanofluids in strengthened tubes is not mature.Therefore,this article aims to study the flow of nanofluids in the strengthened tube through a combination of theoretical verification and experiments.First,the effect of dispersant on the stability of nanofluid is compared.Then prepare the nanofluid with the best stability.And measure its thermal conductivity,then theoretical analysis of the strengthening of the built-in twisted threaded tube.Finally,an experimental system for the flow and heat transfer of nanofluids in the tube was designed and established to study its enhanced heat transfer effect.The experiment analyzes the heat transfer characteristics and flow characteristics of nanofluids with different mass fractions of 0.I%-0.5%in a threaded tube with different twisted tape inserts when the Reynolds number is in the range of 6000-17000.The experiments compared the effects of nanofluids mass fraction,twisted tape twist ratio,the number of twisted tapes,double twisted tapes arrangement direction(in the following figure,the double twisted tapes are arranged in the same direction as DT-Co,and the double twisted tapes are arranged in the counter direction as DT-Counter)and the orientation of the twisted tape and the threaded tube thread(in the following picture,the twisted tape and thread pipe thread are arranged in the same direction as Co-T,the twisted tape and thread pipe thread are arranged in the counter direction as Counter-T)and other factors on the flow characteristics and heat transfer characteristics.And compare the typical twisted tape with the improved twisted tape.The improved twisted tapes are perforated twisted tape(PT)and staggered twisted tape(ST).Through experimental analysis,it can be concluded that among the four dispersants,sodium dodecyl benzene sulfonate(SDBS),gum arabic(GA),Cetyl trimethyl sodium bromide(CTAB)and cetyl trimethyl ammonium bromide(1631 chlorine),GA dispersant shows the best effect on the stability of nanofluids.Therefore,follow-up experiments continue to be used.The convective heat transfer characteristics of the nanofluids in the threaded tube with twisted tape inserts is analyzed.The experiment shows that under the same Reynolds number,the convective heat transfer coefficients of the nanofluids prepared by metal nanoparticles and metal oxide nanoparticles are greater than that of deionized water,indicating that their enhanced heat transfer effect is stronger than deionized water.And as the mass fraction of the nanofluids increases,the Nusselt number also increases,and the nanofluids mass fraction reaches the highest value when it reaches 0.5%,which is the best nanofluids mass fraction in the experimental range.For the comparison of the twisted tapes built into the threaded tube,it can be concluded that the addition of twisted tapes in the tube can effectively enhance heat transfer.When the twist ratio is 3,it is the best twist ratio.Increasing the number of twisted tapes can also enhance heat transfer,and the effect of improving twisted tape is better than that of typical twisted tape.Moreover,the perforated twisted tape can not only enhance the heat transfer,but also effectively reduce the flow resistance,which has a very obvious advantage.In this paper,the thermal performance coefficient is used to analyze and evaluate the overall effect of the flow characteristics and heat transfer characteristics of the threaded tube with twisted tape inserts and nanofluids.According to the experimental data,the thermal performance coeffi cient is comprehensively analyzed,and the thermal performance coefficients of the nanofluids are all greater than 1.This also means that the nanofluids has a very significant heat transfer enhancement effect in the threaded tube with twisted tape inserts,which can help in the application of heat exchanger equipment and other systems.At the same time,this experiment compares the correlation between the convective heat transfer and flow resistance coefficient of the threaded tube with twisted tape inserts of nanofluids.