Heat transfer enhancement in a tube with a twisted tape inserted for various length ratios

ABSTRACT

Energy efficiency is a major concern in pipe systems, particularly in applications where heat transfer is significant. Twisted tape insertion is used to enhance heat transfer in pipes. In this numerical study, twisted tapes with various length ratios (LR) (30–100%) were inserted into a tube filled with water. The tube surface was subjected to a uniform heat flux. The Nusselt number (Nu) and friction factor (f) variations were investigated for several Reynolds number values (Re) (2500–10,000) under hydrodynamically developed and thermally developing flow conditions between laminar and turbulent flows in the transition and low-turbulent regime. The results are validated with the available theoretical results and experiments. The maximum Nu enhancement is observed at an LR of 90% based on a factor of 1.55; an LR of 70% demonstrated a similar factor of ~1.5 and a friction factor 3.7 times more than that of plain tubes. This ratio provides the best results for the enhancement factor, which is 1.2 times higher at the maximum level. Consequently, an LR of 70% is considered to be sufficient to obtain an optimum combination of maximum heat transfer and minimum friction combination, and this combination is preferred over completely filling the tube with twisted tape.

KEYWORDS:

• Twisted tape
• length ratio
• pipe
• heat transfer enhancement
• computational fluid dynamics

Nomenclature

A	=	area, [m2]
Cp	=	specific heat, [Jkg-1K–1]
d	=	diameter, [m]
k	=	thermal conductivity, [Wm-1K–1]
l	=	tube length, [m]
LR	=	twisted tape length ratio, [–]
Nu	=	Nusselt number (=hmdi/k), [–]
P	=	pressure, [Pa]
p	=	twisted tape pitch, [m]
Re	=	Reynolds number (=ρUindi/μ), [–]
T	=	temperature, [K]
t	=	twisted tape thickness, [m]
U	=	velocity, [ms−1]
w	=	twisted tape width, [m]
Greek Symbols	=
ρ	=	density
μ	=	dynamic viscosity
η	=	performance enhancement factor
Subscripts	=
i	=	inner surface
in	=	inlet surface
m	=	mean
o	=	outer surface
out	=	outlet surface
Acronyms	=
PT	=	plain tube
TT	=	twisted tape

Acknowledgements

The author graciously acknowledges the support provided by Tubitak Rail Transport Technologies Institute.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This study was supported by Tubitak Rail Transport Technologies Institute.

Notes on contributors

Ayhan Nazmi Ilikan

Ayhan Nazmi İlikan got his B.Sc. degree as a mechanical engineer from Istanbul Technical University in 2006. He got his M.Sc. and Ph.D. degrees in heat transfer and fluid dynamics from the same university in 2008 and 2014, respectively. Furthermore, he graduated from von Karman Institute for Fluid Dynamics, Turbomachinery and Propulsion Department, Master-after-Master Programme with an honour degree in 2009. He worked as an assistant professor at Isik University, between 2014 and 2016. He has been working as a chief researcher at The Scientific and Technological Research Council of Turkey (TUBITAK) Rail Transport Technologies Institute (RUTE) since 2016.