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<p>In the existing research, the fluid and thermal flow of different configurations of double-twisted, helically coiled tube heat exchangers (<i>DTHCTHEs</i>) was presented numerically. The design addresses the faults of a double-smooth helical tube heat exchanger, which uses a twisted tube as a passive heat transfer technique. The twisted surface changes the flow patterns and turbulence and is expected to augment the characteristics of heat transfer. A <i>3D CFD</i> model was designed and developed via the ANSYS-FLUENT package to predict the thermal performance and fluid flow of different <i>DTHCTHE</i>. The outcomes of key design considerations, such as different twisted cross-sectional profiles (circular, elliptical, triangular, square, pentagonal, and hexagonal) and twisted pitch ratios (6, 9, and ∞), were analyzed. The effects of adding various nanoparticle materials, such as <i>MWCNTs</i>, <i>Al</i><sub><i>2</i></sub><i>O</i><sub><i>3</i></sub>, and <i>Ag,</i> at a concentration of 1% (by volume) to distilled water are also presented. The simulations were carried out in counter-flow at Reynold number,&#xa0;<i>Re,&#xa0;</i>values ranging from 5500 ≤ <i>Re</i><sub><i>i</i></sub> ≤ 17,500 in the inner tube and 3000 ≤ <i>Re</i><sub><i>o</i></sub> ≤ 18,500 in the annulus. The results indicated that <i>U</i><sub><i>o</i></sub><i>A</i><sub><i>o</i></sub> increases by 98.5%, 64.8%, 50.2%, 41%, and 6.2% at the expense of <i>ΔP</i><sub><i>o</i></sub> by 147%, 88.8%, 60.8%, 46.3%, and 16.3%, respectively, for triangular, square, pentagonal, hexagonal, and elliptical twisted cross-section profiles compared with the circular profile. Compared with ∞, the twisted pitch ratio enhances <i>Nu</i> by 37%, 26.1%, 27.6%, 17.3%, and 29.8% at the expense of increasing <i>f</i> by 121.2%, 118.6%, 51.6%, 73.7%, and 41.6%, respectively, for triangular, square, pentagonal, hexagonal, and elliptical profiles at a τ of 6. The addition of <i>MWCNTs</i>, <i>Al</i><sub><i>2</i></sub><i>O</i><sub><i>3</i></sub>, and <i>Ag</i> to water increased <i>Nu</i> by 15.5%, 35%, and 18.3%, respectively, whereas the increase in pressure loss was negligible. The maximum <i>η</i> values reach 1.43, 1.48, 1.52, 1.45, and 1.5 for the triangular, square, pentagonal, hexagonal, and elliptical profiles respectively at <i>τ</i> = 6.</p>

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Fluid and thermal flow in annular side of the double twisted helically coiled tubes heat exchangers under various configurations

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  • 发表日期：

    2025年10月8日

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  • Mahmoud Abdelmagied

摘要

In the existing research, the fluid and thermal flow of different configurations of double-twisted, helically coiled tube heat exchangers (DTHCTHEs) was presented numerically. The design addresses the faults of a double-smooth helical tube heat exchanger, which uses a twisted tube as a passive heat transfer technique. The twisted surface changes the flow patterns and turbulence and is expected to augment the characteristics of heat transfer. A 3D CFD model was designed and developed via the ANSYS-FLUENT package to predict the thermal performance and fluid flow of different DTHCTHE. The outcomes of key design considerations, such as different twisted cross-sectional profiles (circular, elliptical, triangular, square, pentagonal, and hexagonal) and twisted pitch ratios (6, 9, and ∞), were analyzed. The effects of adding various nanoparticle materials, such as MWCNTs, Al2O3, and Ag, at a concentration of 1% (by volume) to distilled water are also presented. The simulations were carried out in counter-flow at Reynold number, Re, values ranging from 5500 ≤ Rei ≤ 17,500 in the inner tube and 3000 ≤ Reo ≤ 18,500 in the annulus. The results indicated that UoAo increases by 98.5%, 64.8%, 50.2%, 41%, and 6.2% at the expense of ΔPo by 147%, 88.8%, 60.8%, 46.3%, and 16.3%, respectively, for triangular, square, pentagonal, hexagonal, and elliptical twisted cross-section profiles compared with the circular profile. Compared with ∞, the twisted pitch ratio enhances Nu by 37%, 26.1%, 27.6%, 17.3%, and 29.8% at the expense of increasing f by 121.2%, 118.6%, 51.6%, 73.7%, and 41.6%, respectively, for triangular, square, pentagonal, hexagonal, and elliptical profiles at a τ of 6. The addition of MWCNTs, Al2O3, and Ag to water increased Nu by 15.5%, 35%, and 18.3%, respectively, whereas the increase in pressure loss was negligible. The maximum η values reach 1.43, 1.48, 1.52, 1.45, and 1.5 for the triangular, square, pentagonal, hexagonal, and elliptical profiles respectively at τ = 6.