Li, W. and Yu, Z. (2024) Heat transfer enhancement of supercritical carbon dioxide in eccentrical helical tubes. International Journal of Heat and Mass Transfer, 221, 125041. (doi: 10.1016/j.ijheatmasstransfer.2023.125041)
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Abstract
A type of eccentrical helical tube (EHT) was proposed for more efficient and compact supercritical carbon dioxide (SCO2) heat exchangers in refrigeration systems. The forced convective heat transfer of SCO2 flowing in three designed eccentrical helical tubes with pitches of 25, 50 mm and eccentricities of 0.9, 1.5 mm was simulated by using the three-dimensional steady Reynolds-averaged Navier-Stokes equations, shear stress transport turbulence model and energy equation in ANSYS CFX 2019 R2 at mass fluxes of 200, 400 kg/m2s, inlet pressures of 8, 9 MPa, outwards wall heat fluxes of 12, 24 kW/m2. The flow and heat transfer models were validated in the plain tube with experimental mean heat transfer coefficient and empirical Darcy friction factor. Influences of pitch, eccentricity and operational conditions on heat transfer enhancement were identified. Flow pattern, heat transfer mechanism and vortex kinematics were clarified. Heat transfer enhancement of SCO2 in the EHT was compared with water and air in the EHT, twisted elliptical tube and conical tube, respectively. A pitch of 25 mm and eccentricity of 1.5 mm at 6 mm tube diameter can achieve a better thermal-hydraulic performance. A higher SCO2 mass flux raises Nusselt number and reduces friction factor, a higher inlet pressure and a larger wall heat flux reduces Nusselt number but increases friction factor. The ratio is ranged in 2.52–1.68 and drops off with increasing inlet pressure and nominal Reynolds number, the ratios , and curves show a concave shape near the pseudocritical point ranged in 1.68–1.06 and 1.06–1.55, 1.23–0.83 and 0.83–1.30, 0.67–0.50 and 0.50–0.92 at the pitch of 25 mm and eccentricity of 1.5 mm, inlet pressure of 8 MPa, mass flux of 400 kg/m2s, and wall heat flux of 12 kW/m2. A helical flow pattern with a core flow occurs in the EHT, the local heat transfer coefficient can be correlated to absolute helicity. The high-wall shear stress on the ridge of the EHT is responsible for the heat transfer enhancement. The value of the EHT is in between the twisted elliptical tube and the conical tube, but the and values are comparable.
| Item Type: | Articles |
|---|---|
| Additional Information: | The paper has financially benefited from EPSRC investment (EP/T022701/1, EP/V042033/1, EP/P028829/1, EP/N020472/1, EP/N005228/1, EP/V030515/1, EP/W027593/1) in the UK. |
| Keywords: | Supercritical carbon dioxide, eccentrical helical tube, heat transfer enhancement, eccentrical helical tube, heat exchanger, computational fluid dynamics. |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Li, Dr Wenguang and Yu, Professor Zhibin |
| Creator Roles: | |
| Authors: | Li, W., and Yu, Z. |
| College/School: | College of Science and Engineering > School of Engineering > Systems Power and Energy |
| Journal Name: | International Journal of Heat and Mass Transfer |
| Publisher: | Elsevier |
| ISSN: | 0017-9310 |
| ISSN (Online): | 1879-2189 |
| Published Online: | 15 December 2023 |
| Copyright Holders: | Copyright © 2023 The Author(s) |
| First Published: | First published in International Journal of Heat and Mass Transfer 221:125041 |
| Publisher Policy: | Reproduced under a creative commons licence |
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