Experimental investigation of heat transfer performance of corrugated tube with spring tape inserts

ABSTRACT

Turbulent forced convection in a corrugated tube with spring tape is investigated experimentally, for Reynolds numbers from 10,000 to 50,000. The working fluid is air. Experiments are performed for different pitch and spring ratios. Results show that Nusselt numbers can be increased considerably, depending on pitch and spring ratios. An overall assessment, considering the friction losses, is achieved using the thermo-hydraulic performance parameter. The latter is observed to take values larger than unity for all cases, where quite high values around 2.8 occur for cases with smallest pitch and spring ratios. Predictive Nusselt number and friction factor correlations are proposed.

KEYWORDS:

• Heat transfer enhancement
• corrugated tube
• spring tape

Nomenclature

A	=	tube inner wall surface area, m2
b	=	breadth of spring tape, m
cp	=	mean isobaric heat capacity, J/kgK
d	=	corrugation height, m
D	=	inner diameter of test tube, m
f	=	Darcy friction factor
h	=	convective heat transfer coefficient, W/m2K
H	=	winding pitch of spring, m
I	=	current, A
k	=	fluid thermal conductivity, W/mK
L	=	tube length, m
m	=	mass flow rate, kg/s
Nu	=	Nusselt number
Δp	=	pressure drop, N/m2
P	=	corrugation pitch of tube wall, m
Pr	=	Prandtl number
Rw	=	Wall thermal resistance, K/W
qW	=	Wall heat flux
Re	=	Reynolds number based on D and V
s	=	spring ratio
T	=	temperature, K
V	=	bulk velocity for plain tube (corrugation and spring tape free), m/s; voltage V
W	=	width of spring tape, m
y	=	pitch ratioGreek Symbols
ρ	=	fluid density, kg/m3Subscripts
b	=	bulk
e	=	electric
i	=	inlet
o	=	outlet
ow	=	outer wall
w	=	inner wall
0	=	plain tube (corrugation and spring tape free)

Acknowledgments

The authors would like to gratefully acknowledge Sam Casting, MCKV Institute of Engineering (MCKVIE) and Jadavpur University, India for their support in this research.