Copyright © 2020 by Technical University - Sofia, Plovdiv branch, Bulgaria Online ISSN 2603-459X
© Journal of the Technical University - Sofia
Plovdiv branch, Bulgaria
“Fundamental Sciences and Applications”
Vol. 26, 2020
A critical report of heat transfer and pressure drop in a spirally
grooved tube with twisted tape insert
Daniela Kostadinova
1*
, Plamen Bonev
2
1
Department of Energy Techniques Technical University of Gabrovo, 4 Hadzhi Dimitar
Str. 5300 Gabrovo, Bulgaria Рhone: 0895419429
2
Department of Energy Techniques Technical University of Gabrovo, 4 Hadzhi Dimitar
Str. 5300 Gabrovo, Bulgaria
*
e-mail: didkamail78@abv.bg
Abstract. In this paper are presented performance enhancement parameters of flow of water in a
spirally grooved tube with twisted tape insert. It takes into account Reynolds numbers for fully
turbulent ranges 3000-7000. The twisted tape inserts are divided into two types - clockwise and
anticlockwise having twist ratios 10.16,7.95 3.4 Y and Compared to smooth tube, the heat
transfer enhancement is further augmented by inserting twisted tapes. In spirally grooved tube with
and without twisted tape, heat transfer increases in turbulent range of Reynolds numbers at con-
stant pumping power. Among the three twist ratios (Y = 10.16, 7.95 and 3.4) tested, heat transfer
performance of clockwise twisted tape with Y = 10.16 is found to be the highest at Pr =5.4 in
turbulent ranges of Reynolds numbers.
1. Introduction
To obtain compact heat exchangers and reasonable energy costs, passive heat transfer enhancement
techniques are preferred over active ones. We are going to consider compound heat transfer enhancement
with insertion of a twisted tape in an internally grooved tube [1].
The groove geometry is characterised by groove height e , groove base width
b
t and tip width
t
t ,
helix angle
and the number of starts
s
N .
The axial pitch
a
p of the grooves is given by ( /
s t
D N ) x tan
where
i
D is the nominal internal
diameter of the tube. Webb et al. [1] reported experimental data for 0.024 0.041
i
eD 18 45
s
N
25 45 and 0.015.
t i
t D They developed following correlations for single phase flows
(5.15 Pr 6.29)
0.785
0.283 0.221 0.78
0.108 Re
s
i
e
f N
D
(1)
0.323
0.819 0.33 0.285 0.505
0.00933 Re Pr
s
i
e
Nu N
D
(2)
The correlations are used only for turbulent range of Reynolds numbers. The increase in Nu will
exceed that in f in respect of number of starts
s
N .Compared to a smooth tube Usui et al. [3],
0.291
/
(Re)
( / )
s
E
s
Nu Nu
i f
f f
(3)