Enhancement of heat transfer of double tube heat exchanger with inner twisted spiral tube

Abstract EN

Heat transfer and fluid flow characteristics for twisted spiral tubes with different pitch and
depth have been investigated experimentally with respect of smooth tube as a particular
reference.

The effects of the twisted spiral pitch (S) and depth (H) on the thermal performance of
a twisted spiral tubes heat exchanger are investigated.

The effects of inner twisted spiral tube
pitch, depth, Reynolds number and flow arrangement were the main points of interest.

Three
twisted spiral tube with different pitch (S) and three twisted spiral tube at different depth (H) are
examined in this study.

The Reynolds number ranged from 5000 to 50, 000 and from 1400 to
10400 for both inner tube and outer tube sides, respectively, corresponding to water mass flow
rates ranged from 0.03 to 0.3kg/s.

The results showed that, both Nusselt number and friction
factor increased with all values of pitches (S) above that of the smooth tube.

The Nusselt number
of cases of pitches of 3.9, 5.2 and 8.2 mm is 33.6% , 21.4% and 7.6% higher than the smooth tube
on expense of increasing the friction factor by 23.2% , 18.4% and 4.6% , respectively.

Also, the
Nusselt number and friction factor increased with all cases of depth (H) above that of the smooth
tube.

The Nusselt number of cases of depths 1.15, 1.1and 0.6mm is respectively 34.4% , 27.8%
and 10% , respectively, higher than that of the smooth tube.

Also, the friction factor for the
twisted spiral depths (H) of 1.15, 1.1 amd 0.6mm is about 22.8% , 18.4% and 2.3% higher than
that of the smooth tube, respectively.