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. 2024 Apr 26;14(1):9637.
doi: 10.1038/s41598-024-59085-5.

Numerical and experimental investigation of heat transfer enhancement in double tube heat exchanger using nail rod inserts

S A Marzouk  1 , Fahad Awjah Almehmadi  2 , Ahmad Aljabr  3 , Maisa A Sharaf  4
Affiliations

Numerical and experimental investigation of heat transfer enhancement in double tube heat exchanger using nail rod inserts

S A Marzouk et al. Sci Rep. .

Abstract

The Double-tube heat exchanger (DTHX) is widely favored across various industries due to its compact size, low maintenance requirements, and ability to operate effectively in high-pressure applications. This study explores methods to enhance heat transfer within a DTHX using both experimental and numerical approaches, specifically by integrating a nail rod insert (NRI). A steel nails rod insert, 1000 mm in length, is introduced into the DTHX, which is subjected to turbulent flows characterized by Reynolds numbers ranging from 3200 to 5700. Three different pitches of NRI (100 mm, 50 mm, and 25 mm) are investigated. The results indicate a significant increase in the Nusselt (Nu) number upon the insertion of nail rods, with further improvements achievable by reducing the pitch length. Particularly noteworthy is the Nu number enhancement ratio for the 25 mm pitch NRI, which is 1.81-1.9 times higher than that for the plain tube. However, it is observed that pressure drop increases in all configurations with NRI due to heightened turbulence and obstruction by the NRI. Among the various pitch lengths, the 25 mm pitch exhibits the highest pressure drop values. Moreover, exergy efficiency is found to improve across all cases with NRI, corresponding to increased heat transfer, with the 25 mm pitch length showing a remarkable 128% improvement. Numerical analysis reveals that the novel insert enhances flow turbulence through the generation of secondary flows, thereby enhancing heat transfer within the DTHX. This study provides a comprehensive analysis, including temperature, velocity, and pressure drop distributions derived from numerical simulations.

Keywords: CFD; Double tube heat exchanger; Exergy efficiency; Heat transfer enhancement; Nails rod insert.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
A schematic view of the experimental study.
Figure 2
Figure 2
Photograph and schematic view of nails rod inserts (NRI) inside copper tube.
Figure 3
Figure 3
The NRI configurations with different pitches (a) 100 mm, (b) 50 mm, (c) 25 mm.
Figure 4
Figure 4
Numerical model of DTHX with NRI.
Figure 5
Figure 5
Mesh generation for (a) inflation layers at walls, (b) 3D models.
Figure 6
Figure 6
Comparing experimental results with numerical results for Nusselt number.
Figure 7
Figure 7
Variation of pressure drop with Re for experimental and numerical results.
Figure 8
Figure 8
The variation of Nu versus Re for PT and NRI at various pitches.
Figure 9
Figure 9
The ratio of Nu enhancement versus Re for NRI at different pitches (100 mm, 50 mm, and 25 mm).
Figure 10
Figure 10
Pressure drop versus Re for PT and NRI at different pitches, 100 mm, 50 mm, and 25 mm.
Figure 11
Figure 11
Exergy efficacy versus Re for PT and NRI at different pitches (100 mm, 50 mm, and 25 mm).
Figure 12
Figure 12
Contours of temperature distribution of DTHX for (a) PT, (b) NRI at P = 100 mm, (c) NRI at P = 50 mm, and (d) NRI at P = 25 mm.
Figure 13
Figure 13
Streamlines of velocity distribution for (a) PT, (b) NRI at P = 100 mm, (c) NRI at P = 50 mm, and (d) NRI at P = 25 mm.
Figure 14
Figure 14
Contours of the velocity distribution of HX tubes for (a) PT, (b) NRI at P = 100 mm, (c) NRI at P = 50 mm, and (d) NRI at P = 25 mm.
Figure 15
Figure 15
Vectors of the normal velocity for (a) PT, (b) horizontal nails, (c) vertical nails.
Figure 16
Figure 16
Vectors of velocity distribution for different positions of nails.
Figure 17
Figure 17
Cross-section view of velocity distribution for (a) PT, (b) distance = 0.25 m (c) distance = 0.75 m (d) distance = 0.9 m, and (e) distance = 0.5 m.
Figure 18
Figure 18
Pressure distribution in the inner tube for (a) PT, (b) NRI at P = 100 mm, (c) NRI at P = 50 mm, and (d) NRI at P = 25 mm.
See this image and copyright information in PMC

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