دانلود رایگان مقاله انگلیسی ارزیابی عملکرد لوله های مبدل حرارتی turbular با نوارهای مستطیلی محور های متناوب - اشپرینگر 2018

Abstract

This paper describes the numerical results of the heat transfer enhancement mechanism of tubes containing rectangular-cut twisted tapes with alternate axes (ARC-TTs). Influence of the length of cut ratio (LR = L/w = 2.0, 2.4 and 2.8) and width of cut ratio (WR = W/w = 0.7, 0.8 and 0.9) on the heat transfer rate, friction factor and thermal performance characteristics are presented. The contour plots of predicted streamlines, velocity field, temperature field, and local Nusselt number distribution are also given for a better understanding of heat transfer mechanism. The results of the tube containing a classical twisted tape are also reported, for comparison. It can be observed that the use of ARC-TTs results in more disordered streamlines and higher turbulent intensity than that of the classical twisted tape. The numerical results also show that heat transfer and friction loss decrease as Length of cut ratio (LR) and Width of cut ratio (WR) increase while thermal performance factor shows reverse trend. In the studied range, utilizing ARC-TTs offers thermal performance factor up to 1.5.

5. Conclusions

The heat transfer, friction factor and Thermal enhancement factor (TEF) characteristics of turbulent flow in the tubes containing rectangular-cut twisted tapes with alternate axes (ARC-TTs) with different Width of cut ratios (WR) and Length of cut ratios (LR) have been numerically investigated for Reynolds number ranging from 5000 to 15000. The simulations for the alternate axis twisted tape and classical twisted tape have also been performed, for comparison. The major findings are concluded below.

• ARC-TTs as the modified twisted tapes give 14.68- 38.85 % higher Nusselt numbers than the typical twisted tape but 2.16-10.88 % lower than the alternate axis twisted tape.

• ARC-TTs cause 8.71-44.44 % and 16.04-46.89 % lower friction factors than the typical twisted tape and the alter- nate axis twisted tape, respectively.

• Nusselt number and friction factor decrease with increasing Width of cut ratio (WR) and Length of cut ratio (LR).

• Thermal enhancement factor (TEF) increases with in- creasing Width of cut ratio (WR) and Length of cut ratio (LR). The maximum Thermal enhancement factor (TEF) of 1.5 is obtained by using the tube with WR = 0.9 and LR = 2.8 at the lowest Reynolds number of 5000.