The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward Flows
Buoyancy effects in vertical, upward laminar flows can result in an augmentation in heat transfer rates to supercritical CO<sub>2</sub> (sCO<sub>2</sub>) near its pseudocritical temperature (T<sub>PC</sub>). This is in contrast to corresponding flows in the turbul...
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MDPI AG
2023-01-01
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| Series: | Fluids |
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| Online Access: | https://www.mdpi.com/2311-5521/8/1/30 |
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| author | Krishnamoorthy Viswanathan Gautham Krishnamoorthy |
| author_facet | Krishnamoorthy Viswanathan Gautham Krishnamoorthy |
| author_sort | Krishnamoorthy Viswanathan |
| collection | DOAJ |
| description | Buoyancy effects in vertical, upward laminar flows can result in an augmentation in heat transfer rates to supercritical CO<sub>2</sub> (sCO<sub>2</sub>) near its pseudocritical temperature (T<sub>PC</sub>). This is in contrast to corresponding flows in the turbulent regime, or laminar sCO<sub>2</sub> flows (with minimum buoyancy effects), where a deterioration in heat transfer near T<sub>PC</sub>, followed by a recovery phase, have been observed. To exploit these sCO<sub>2</sub> heat transfer enhancement characteristics and improve heat exchange efficiencies, the location of the T<sub>PC</sub> pinch point and the variables controlling these buoyancy effects need to be identified. To fill this void, numerical simulations of sCO<sub>2</sub> (at inlet: 8.2 MPa, 265 K) in vertical circular tubes of diameters (D) 0.2–2 mm, heated with constant wall heat fluxes (Q) of 1–4 kW/m<sup>2</sup>) and inlet Reynolds numbers (Re) of 100, 400, were carried out. The tube lengths were varied to maintain an exit temperature of 320 K (T<sub>PC</sub>~309 K). The results indicated that buoyancy-augmented laminar heat transfer rates may be expected when Gr/Re<sup>2.7</sup> > 10<sup>−4</sup> (Gr = Grashof number). A modified Nusselt number correlation in terms of (Gr/Re) is proposed and is observed to fit the observed variations within a mean absolute percentage error < 15%, in most regions. |
| first_indexed | 2024-03-09T12:45:07Z |
| format | Article |
| id | doaj.art-a92524954dbc401b97007591c41c1884 |
| institution | Directory Open Access Journal |
| issn | 2311-5521 |
| language | English |
| last_indexed | 2024-03-09T12:45:07Z |
| publishDate | 2023-01-01 |
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| series | Fluids |
| spelling | doaj.art-a92524954dbc401b97007591c41c18842023-11-30T22:13:13ZengMDPI AGFluids2311-55212023-01-01813010.3390/fluids8010030The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward FlowsKrishnamoorthy Viswanathan0Gautham Krishnamoorthy1Department of Chemical Engineering, University of North Dakota, Grand Forks, ND 58202-7101, USADepartment of Chemical Engineering, University of North Dakota, Grand Forks, ND 58202-7101, USABuoyancy effects in vertical, upward laminar flows can result in an augmentation in heat transfer rates to supercritical CO<sub>2</sub> (sCO<sub>2</sub>) near its pseudocritical temperature (T<sub>PC</sub>). This is in contrast to corresponding flows in the turbulent regime, or laminar sCO<sub>2</sub> flows (with minimum buoyancy effects), where a deterioration in heat transfer near T<sub>PC</sub>, followed by a recovery phase, have been observed. To exploit these sCO<sub>2</sub> heat transfer enhancement characteristics and improve heat exchange efficiencies, the location of the T<sub>PC</sub> pinch point and the variables controlling these buoyancy effects need to be identified. To fill this void, numerical simulations of sCO<sub>2</sub> (at inlet: 8.2 MPa, 265 K) in vertical circular tubes of diameters (D) 0.2–2 mm, heated with constant wall heat fluxes (Q) of 1–4 kW/m<sup>2</sup>) and inlet Reynolds numbers (Re) of 100, 400, were carried out. The tube lengths were varied to maintain an exit temperature of 320 K (T<sub>PC</sub>~309 K). The results indicated that buoyancy-augmented laminar heat transfer rates may be expected when Gr/Re<sup>2.7</sup> > 10<sup>−4</sup> (Gr = Grashof number). A modified Nusselt number correlation in terms of (Gr/Re) is proposed and is observed to fit the observed variations within a mean absolute percentage error < 15%, in most regions.https://www.mdpi.com/2311-5521/8/1/30buoyancylaminar heat transfersupercritical CO<sub>2</sub>Grashof number |
| spellingShingle | Krishnamoorthy Viswanathan Gautham Krishnamoorthy The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward Flows Fluids buoyancy laminar heat transfer supercritical CO<sub>2</sub> Grashof number |
| title | The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward Flows |
| title_full | The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward Flows |
| title_fullStr | The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward Flows |
| title_full_unstemmed | The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward Flows |
| title_short | The Effects of Buoyancy on Laminar Heat Transfer Rates to Supercritical CO<sub>2</sub> in Vertical Upward Flows |
| title_sort | effects of buoyancy on laminar heat transfer rates to supercritical co sub 2 sub in vertical upward flows |
| topic | buoyancy laminar heat transfer supercritical CO<sub>2</sub> Grashof number |
| url | https://www.mdpi.com/2311-5521/8/1/30 |
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