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HỘI THẢO QUỐC TẾ ATiGB LẦN THỨ CHÍN - The 9 ATiGB 2024 7

3D NUMERICAL INVESTIGATION OF
HEAT TRANSFER PROCESS IN A DOUBLE PIPE

LONGITUDINAL FINED HEAT EXCHANGER

Son Thanh Nguyen
Faculty of Mechanical Engineering
The University of Danang - University of Technology and Education
ntson@ute.udn.vn
Abstract: In this research, a numerical investigation is the mean Nusselt numbers of the hot and cold fluid flow of
done on the influence of geometrical and operating case 1 (x = 75%) have smallest value in three cases.
parameters on heat transfer process in a double pipe Additionally, the thermal effectiveness of the double pipe
longitudinal fined heat exchanger. With Reynolds numbers longitudinal fined heat exchanger increases with increasing
of the hot fluid flow Reh from 5000 to 17000 for case 1, 2 the Reynolds numbers of the hot fluid flow and decreasing
and 3 (x = 75%, 50% and 37.5% respectively) of double the ratio x. The thermal effectiveness of the double pipe
pipe longitudinal fined heat exchanger were investigated. longitudinal fined heat exchanger obtained maximum of ε =
The results of the study show that mean Nusselt numbers of 16.35% corresponding to Reh = 17000 and x = 37.5%.
the hot fluid flow increase with Reynolds numbers of the Keywords: Double pipe heat exchanger; CFD simulation;
hot fluid flow increases in all cases, but mean Nusselt Heat transfer; Longitudinal fins.
numbers of the cold fluid flow has decreased trend; in there,
1. INTRODUCTION rate and pressure drop. Pethkool et al. [10] used a
corrugated pipe as the central pipe of a double-pipe
Nowadays, double pipe heat exchangers are heat exchanger to investigate its impacts on heat
widely used in industry and our daily life, such as in transfer rate and pressure drop. They found that
power generation, chemical industries, as well as considerable rises in heat transfer and pressure drop
refrigerators and ventilators [1, 2]. This is because are obtained with the increases in depth and torsional
they have a wide working temperature range, can step of the corrugated pipe. Agarwal and Rao [11]
work at high pressure, and have low design and experimentally investigated thermal and frictional
maintenance costs. However, to design an efficient characteristics of oil flow in a double-pipe heat
double pipe heat exchanger, many considerations are exchanger containing twisted tape inserts with
needed factors, such as investment cost, equipment constant wall temperature. Their results show that the
lifespan, shape, size, especially heat transfer and friction factor can be increased by 3.13 - 9.71 times
pressure loss. And this is still a research hotspot in compared to straight pipes, while Nusselt number are
recent years. raised by 2.28–5.35 and 1.21 - 3.70 times with respect
So far, a plethora of researches have been to straight pipes at constant flow rate and power,
proposed to improve efficiency of double pipe heat respectively.
exchanger, such as installing turbulators [3], using In recent years, computational fluid dynamics
porous materials [4], introducing nanofluids [5], (CFD) simulations are based on the Navier-Stokes
modifying passages [6], etc… However, to the best of equation, used to describe the motion of fluids, which
our knowledge, changing geometrical configuration is can clarify the complex flow and heat transfer
a straightforward but very effective approach. Indeed, patterns inside double pipe heat exchangers with
a simple modification of geometry that not only much more details but rather reduced cost. So CFD
increases heat transfer remarkably, but also does not has been largely employed in scientific investigations
affect pressure drop too much is favorable: Zhang et and engineering applications of double-pipe heat
al. [7], Barga and Saboya [8] researched on helical exchangers. Sun and Zhang [12] conducted a
fins arrangement and continuous longitudinal numerical study on the impact of large vortices on
rectangular fins to increase heat transfer. Designing thermal and flow characteristics of turbulent airflows
double pipe heat exchangers with fins proves to be a in a fin-and-tube heat exchanger. Their outcomes
cost-effective approach, given their affordability reveal that heat transfer coefficient in larger pipes is
when compared to pristine tube surfaces. Sadighi et higher than that in smaller pipes by 20 - 30%. Sharifi
al. [9] used corrugated pipes as both inner and outer et al. [13] used CFD to study the effects of helical
pipes and investigated their effects on heat transfer wire inserts on heat transfer and pressure drop in a
rate and pressure drop. Their results indicate that the double pipe heat exchanger. Their results show that
induced turbulence obviously increases heat transfer regarding the heat-exchanger containing coiled wire

ISBN: 978-604-80-9779-0