Numerical investigation of flow structure and convective heat transfer enhancement inside the tube using different geometries of twisted tapes insert

In the present work, a numerical study on the heat transfer and fluid flow features in straight tubes isdone. The thesis simulation includes both tubes with and without twisted tapes. The flow regime isconsidered turbulent with Re numbers of ۳۳۳۳, ۴۳۳۳, ۵۳۳۳, ۶۳۳۳, and ۰۳۳۳. The study is not timedependent.Simulation is ۳ -D and includes ۳ main steps: ۱ - investigation of pitches of twisted tapes. ۲-investigation of the twisted tapes with several blades. ۳ - investigation of twisted tapes with cut edges. Theresults of the Nu number represent that the addition of a twisted tape insert is beneficial in increasing heattransfer. As can be seen, the optimum twisting pitch is found to be ۳۱۱۵ cm. Looking into the pressure droppenalty, it can be observed that straight tubes with twisted tape have a higher pressure drop. Twisted tapewith a pitch of ۳۱۱۵ cm has more friction factor. Twisted tape with a pitch of ۳۱۱۵ cm has the highestproductivity index. Therefore, this pitch will be used in the next step. According to Nu number, both doubleand triple-twisted tapes are better than single-twisted tapes however, it is obvious that the impact isconsiderable only in high Re numbers. It can be observed that the triple case has more friction factor thandouble and single. The biggest gap is related to Re=۳۳۳۳. In this Re number triple case’s friction factor isabout ۳۰۳ more than the single case and almost %۱۰۳ more than the double case. Based on the productivityindex, for a low Re number meaning that lower than ۴۳۳۳, single twisted tape can be better, and for a higherRe number than ۴۳۳۳, triple twisted tape can be better. Ultimately, based on P.I., among ۳ cases of tripletwisted tapes with ۳۱۱۵ pitches with ۱, ۲ cut edges and without cut edge, case ۲ ( triple twisted tapes with۳۱۱۵ pitches with ۱ cut edge) has better results.

Keywords:

Numerical analysis , Convective heat transfer , turbulent flow , Twisted tape , pressure drop