## 7 Conclusions  
An investigation of the flow field and thermohydraulic behaviors of a tube mounted with continuous V-rib twisted tapes (CVRTs) was carried out. The influences of attack angles (\(\beta\)) of \(15^{\circ}\), \(30^{\circ}\), and \(45^{\circ}\), and the tape arrangement were examined in turbulent flow. This was conducted to determine the optimal thermal performance parameters under similar pumping power conditions. The principal findings are as follows:  
Figure 17: Comparisons between the current and previous studies [9; 10; 32; 33; 34]. The continuous V-rib twisted tapes (CVRTs) generated swirl and longitudinal vortex flows, enhancing heat transfer rate by promoting fluid mixing between the inner flow and wall areas, while concurrently diminishing the thermal boundary thickness. For a particular Reynolds number (\(Re\)), both the Nusselt number (\(Nu\)) and the friction factor (\(f\)) increased with attack angle (\(\beta\)). The variation in the friction factor with respect to the angle of attack closely aligns with the turbulent flow characteristics observed in the numerical analysis. Utilization of continuous V-rib twisted tape (CVRT) installed over the investigated range resulted in increased \(Nu\) and \(f\) that surpassed those of a plain tube by approximately 1.38-1.76 and 2.5-3.83 times, respectively. The dependence of the Nusselt number on the angle of attack exhibits a trend that is in good agreement with the turbulence behavior predicted by computational fluid dynamics. The Nusselt numbers generated by utilization of continuous V-rib twisted tapes (CVRTs) with \(\beta\) values of \(15^{\circ}\), \(30^{\circ}\), and \(45^{\circ}\) were 76, 71, and 66% greater than those of the plain tube, and 13, 9.2, and 5.7%, superior to those of a TT, respectively. The backward-arranged continuous V-rib twisted tape (CVRT) revealed better heat transfer, lower pressure losses, and higher thermal performance index values. The presented results suggest that attack angles (\(\beta\)) and the tape arrangement significantly influenced the _TPI_, which reached its highest value, 1.13, at \(\beta=15^{\circ}\) in a backward arrangement. This study overlooked the effect of rib depth on heat transfer rate, pressure drop, and TPI. In the future, it will be beneficial to determine the rib depth to achieve a better tradeoff between enhanced heat transfer and reduced pressure loss, thereby improving TPI. Additionally, increasing rib depth could strengthen the flow along the length of the surface, while increasing the spacing between ribs may reduce pressure drop without significantly compromising the heat transfer rate. The present results suggest that the V-rib attack angles (\(\beta\)) play a crucial role in enhancing heat transfer characteristics in tubes fitted with continuous V-rib twisted tapes (CVRT). Reducing the attack angle (\(\beta\)) improves heat transfer rates and thermal performance. The thermal performance index exceeds unity at low Reynolds numbers, suggesting that CVRTs can reduce the size and cost of thermal systems. This design is not only thermally efficient but also practical in terms of fabrication, requiring only a pair of meshing gears and a twisting device. This simplicity enhances its feasibility for industrial-scale applications, where both performance and ease of manufacture are critical. Therefore, the CVRT configuration offers a promising solution for future thermal system designs. Conceptualization, P.N. ; Software, Y.D. ; Validation, Y.D. ; Formal analysis, K.W., V.C., P.N., N.M. and M.H. ; Investigation, Y.D. and V.C. ; Data curation, Y.D., N.M. and M.H. ; Writing--original draft, Y.D. and K.W. ; Writing--review & editing, V.C. and S.E.-a. ; Supervision, S.E.-a. ; Project administration, V.C. ; Funding acquisition, V.C. All authors have read and agreed to the published version of the manuscript. This research was funded by King Mongkut's Institute of Technology, Ladkrabang (Grant No. RE-KRIS/FF68/31), has received funding support from the NSRF.