Numerical research of an internal and external-corrugated tube-in-tube helical coil heat exchanger

ABSTRACT

To effectively enhance the heat transfer of a tube-in-tube helical coil heat exchanger, a novel internal and external-corrugated tube-in-tube helical coil was proposed by improving both the inner and outer tubes. The impact of the corrugation layout on the annular region’s heat transfer property was simulated. The effect of periodically distributed corrugations on flow patterns and the local Nusselt on the inner tube wall was explored. Furthermore, by comparing the fluid’s velocity and temperature field contour in traditional helical coil and novel helical coil, the enhanced heat transfer mechanism was discovered. Finally, the effects of Re, dimensionless depth H, and dimensionless pitch S of corrugations on the annular region’s heat transfer, flow resistance and entropy generation were analyzed. The results showed that annular region’s heat transfer could be improved due to the periodically distributed corrugations. The local Nu distribution on the corrugated inner tube wall was similar to that of ordinary inner tube, while changed periodically due to the continuous influence of corrugations. The number of Nu and f increased by 53% ~72% and 40% ~120% with the dimensionless corrugation depth and dimensionless pitch being 0.15 and 1.5, respectively. The comprehensive heat transfer performance PEC reached 1.2 ~ 1.6, and cross-arranged inner and outer tube corrugations were more favorable for heat transfer than the corresponding arrangement, when Re = 6000, H3 structure has the highest $S_t$, $S_f$ and $S_{\mathit{gen}}$, which are 0.934W/K, 0.379 W/K and 1.312W/K, respectively. Increasing H and decreasing S could enhance the Nu, f and entropy generation. The values of PEC decreased with increasing S, while with the increment of H, PEC increased and decreased, respectively when Re was in the range of (2000, 4000) and (4000, 6000). In the study range, changing H and S could increase Nu by 40.3%–97.3%, 31.7%–96.8%, and f by 11.7%–176.5%, 16.4%–180.9%, respectively. The final comprehensive heat transfer performance increased by 12.8%-65.9%. Finally, the prediction correlation formulas of Nu and f in NTTHC annular region with high correlation is proposed.

KEYWORDS:

• Tube-in-tube helical coil
• heat exchanger
• corrugation
• enhanced heat transfer
• numerical simulation

Nomenclature

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Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Notes on contributors

Jinxing Wu

Jinxing Wu holds a Ph.D from the East China University of Science and Technology, China. Currently, he is director of the Centre for Energy Saving Technology Research and of Thermal Energy and Power Engineering Department, Zhengzhou University. He is interested in the heat exchanger and burner to conserve energy, resource usage, and pollution reduction. He specializes in the optimization of structure.

Yadong Zhu

Yadong Zhu is a master’s student from Zhengzhou University, mainly engaged in the research of heat transfer enhancement of heat exchanger.

Can Gao

Can Gao is a master’s student from Zhengzhou University, mainly engaged in the research of heat transfer enhancement of heat exchanger

Dongyang Ding

Dongyang Ding is a master’s student from Zhengzhou University, mainly engaged in the research of heat transfer enhancement of heat exchanger.