Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure

Peninnah Ngina Musili; Mark Okongo; Alice Lunani Mulama Murwayi

doi:doi:10.11648/j.ijfmts.20261203.12

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Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure

Peninnah Ngina Musili^*

, Mark Okongo, Alice Lunani Mulama Murwayi

Published in International Journal of Fluid Mechanics & Thermal Sciences (Volume 12, Issue 3)

Received: 4 June 2026 Accepted: 23 June 2026 Published: 9 September 2026

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Abstract

Double diffusive natural convection driven by Simultaneous temperature and concentration gradients are fundamental to many engineering and environmental processes. The buoyancy ratio N, defined as the ratio of solutal to thermal buoyancy forces, critically determines whether thermal or solutal effects dominate the flow structure, heat transfer, and species transport. While most existing studies rely on two-dimensional simplifications and alternative numerical methods, this paper presents a three-dimensional numerical investigation of the effect of the buoyancy ratio on steady, laminar double-diffusive natural convection in a rectangular enclosure with an aspect ratio of 0.5. The continuity, momentum, energy, and concentration equations governing the flow are solved using the finite-volume method with the SIMPLE algorithm on a staggered grid. Parametric simulations are performed for buoyancy ratios N = 1.0, 2.5, 5.0, and 10.0, with fixed Prandtl number Pr = 7.0, Lewis number Le = 2.5, and Rayleigh number Ra = 50000. Results show that increasing the buoyancy ratio from 1.0 to 10.0 significantly enhances the uniformity of the temperature field and enhances vertical heat transfer. Concentration profiles become sharper and more localized as the buoyancy ratio is increased. At a high buoyancy ratio, solutal buoyancy dominates, producing a thin solutal boundary layer and strong stratification, thereby promoting salt fingering. Velocity profiles become stronger, more organized, and more stable as the buoyancy ratio increases. The 3-dimensional nature of the flow reveals that the effect of the buoyancy ratio in the enclosure is isotropic; the primary circulation plane along the z-y plane shows the greatest changes, while the secondary planes (x-y and x-z) show only a significant change. The finite volume method proves to be an effective tool for 3-dimensional parametric studies. The results provide a valuable benchmark for engineering applications where controlling the balance between thermal and solutal buoyancy is crucial, such as chemical reactors, drying systems, and thermal management devices.

Published in	International Journal of Fluid Mechanics & Thermal Sciences (Volume 12, Issue 3)
DOI	10.11648/j.ijfmts.20261203.12
Page(s)	62-75
Creative Commons	This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
Copyright	Copyright © The Author(s), 2026. Published by Science Publishing Group

Keywords

Buoyancy Ratio, Double-Diffusive Convection, Finite Volume Method, 3-D Flow, Heat and Mass Transfer

References

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[3]	Ho, C. J., & Chang, J. Y. (1994). A study of natural convection heat transfer in a vertical rectangular enclosure with two-dimensional discrete heating: Effect of aspect ratio. International Journal of Heat and Mass Transfer, 37(6), 917-925. https://doi.org/10.1016/0017-9310(94)90217-8
[4]	Mamou, M., Vasseur, P., & Bilgen, E. (1996). Analytical and numerical study of double diffusive convection in a vertical enclosure. Heat and Mass Transfer, 32(1-2), 115-125. https://doi.org/10.1007/s002310050100
[5]	Nishimura, T., Wakamatsu, M., & Morega, A. M. (1998). Oscillatory double-diffusive convection in a rectangular enclosure with combined horizontal temperature and concentration gradients. International Journal of Heat and Mass Transfer, 41(11), 1601-1611. https://doi.org/10.1016/S0017-9310(97)00201-6
[6]	Mohamad, A. A., & Bennacer, R. (2002). Double-diffusion natural convection in an enclosure filled with a saturated porous medium. Numerical Heat Transfer, Part A: Applications, 41(5), 453-470. https://doi.org/10.1080/10407780290059564
[7]	Costa, V. A. F. (2004). Double-diffusive natural convection in parallelogrammic enclosures. International Journal of Heat and Mass Transfer, 47(14-16), 2913-2926. https://doi.org/10.1016/j.ijheatmasstransfer.2004.02.013
[8]	Abu-Nada, E., Masoud, Z., Oztop, H. F., & Campo, A. (2010). Effect of nanofluid variable properties on natural convection in enclosures. International Journal of Thermal Sciences, 49(3), 479-491. https://doi.org/10.1016/j.ijthermalsci.2010.07.006
[9]	Kuznetsov, G. V., & Sheremet, M. A. (2011). Natural convection in an enclosure with double diffusive conjugate natural convection. International Journal of Heat and Mass Transfer, 54(1-3), 456-465. https://doi.org/10.1016/j.ijheatmasstransfer.2010.09.009
[10]	,Anderson, D., Tannehill, J. C., Pletcher, R. H., Munipalli, R., & Shankar, V. (2020). Computational Fluid Mechanics and Heat Transfer. CRC Press.
[11]	Belazizia, A., Benissaad, S., & Abboudi, S. (2012). Double-diffusion natural convection of binary fluid in a square enclosure with top active vertical wall. Advances in Theoretical and Applied Mechanics, 5(3), 119-131.
[12]	Elsherbiny, S. M., & Ragab, E. H. (2013). Laminar natural convection in inclined rectangular cavities with a localized heat source. Alexandria Engineering Jour- nal, 52(3), 249-257. https://doi.org/10.1016/j.aej.2012.12.004
[13]	Ridha, B., & Mounir, B. (2014). Effect of buoyancy ratio on double-diffusive mixed convection in a double-lid driven rectangular cavity. Heat Transfer Engineering, 35(5), 456-467. https://doi.org/10.1080/01457632.2013.819539
[14]	Falahat, A. (2014). Effect of aspect ratio on laminar natural convection in a partially heated enclosure. Universal J. Mech. Eng, 2(1), 28-33.
[15]	Aly, A. M., & Raizah, Z. A. (2016). Double-diffusive natural convection in an enclosure filled with nanofluid using ISPH method. Alexandria Engineering Journal, 55(4), 3037-3052. https://doi.org/10.1016/j.aej.2016.07.004
[16]	Koufi, L., Cherif, Y., Younsi, Z., & Naji, H. (2019). Double-diffusive natural convection in a mixture-filled cavity with walls' opposite temperatures and concentrations. Heat Transfer Engineering, 40(15), 1268-1285. https://doi.org/10.1080/01457632.2018.1457770
[17]	Xu, H., Luo, Z., Lou, Q., Zhang, S., & Wang, J. (2019). Lattice Boltzmann simulations of the double-diffusive natural convection and oscillation characteristics in an enclosure with Soret and Dufour effects. International Journal of Thermal Sciences, 136, 159-171. https://doi.org/10.1016/j.ijthermalsci.2018.12.012
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APA Style

Musili, P. N., Okongo, M., Murwayi, A. L. M. (2026). Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure. International Journal of Fluid Mechanics & Thermal Sciences, 12(3), 62-75. https://doi.org/10.11648/j.ijfmts.20261203.12

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ACS Style

Musili, P. N.; Okongo, M.; Murwayi, A. L. M. Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure. Int. J. Fluid Mech. Therm. Sci. 2026, 12(3), 62-75. doi: 10.11648/j.ijfmts.20261203.12

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AMA Style

Musili PN, Okongo M, Murwayi ALM. Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure. Int J Fluid Mech Therm Sci. 2026;12(3):62-75. doi: 10.11648/j.ijfmts.20261203.12

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@article{10.11648/j.ijfmts.20261203.12,
  author = {Peninnah Ngina Musili and Mark Okongo and Alice Lunani Mulama Murwayi},
  title = {Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure},
  journal = {International Journal of Fluid Mechanics & Thermal Sciences},
  volume = {12},
  number = {3},
  pages = {62-75},
  doi = {10.11648/j.ijfmts.20261203.12},
  url = {https://doi.org/10.11648/j.ijfmts.20261203.12},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ijfmts.20261203.12},
  abstract = {Double diffusive natural convection driven by Simultaneous temperature and concentration gradients are fundamental to many engineering and environmental processes. The buoyancy ratio N, defined as the ratio of solutal to thermal buoyancy forces, critically determines whether thermal or solutal effects dominate the flow structure, heat transfer, and species transport. While most existing studies rely on two-dimensional simplifications and alternative numerical methods, this paper presents a three-dimensional numerical investigation of the effect of the buoyancy ratio on steady, laminar double-diffusive natural convection in a rectangular enclosure with an aspect ratio of 0.5. The continuity, momentum, energy, and concentration equations governing the flow are solved using the finite-volume method with the SIMPLE algorithm on a staggered grid. Parametric simulations are performed for buoyancy ratios N = 1.0, 2.5, 5.0, and 10.0, with fixed Prandtl number Pr = 7.0, Lewis number Le = 2.5, and Rayleigh number Ra = 50000. Results show that increasing the buoyancy ratio from 1.0 to 10.0 significantly enhances the uniformity of the temperature field and enhances vertical heat transfer. Concentration profiles become sharper and more localized as the buoyancy ratio is increased. At a high buoyancy ratio, solutal buoyancy dominates, producing a thin solutal boundary layer and strong stratification, thereby promoting salt fingering. Velocity profiles become stronger, more organized, and more stable as the buoyancy ratio increases. The 3-dimensional nature of the flow reveals that the effect of the buoyancy ratio in the enclosure is isotropic; the primary circulation plane along the z-y plane shows the greatest changes, while the secondary planes (x-y and x-z) show only a significant change. The finite volume method proves to be an effective tool for 3-dimensional parametric studies. The results provide a valuable benchmark for engineering applications where controlling the balance between thermal and solutal buoyancy is crucial, such as chemical reactors, drying systems, and thermal management devices.},
 year = {2026}
}

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TY  - JOUR
T1  - Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure
AU  - Peninnah Ngina Musili
AU  - Mark Okongo
AU  - Alice Lunani Mulama Murwayi
Y1  - 2026/09/09
PY  - 2026
N1  - https://doi.org/10.11648/j.ijfmts.20261203.12
DO  - 10.11648/j.ijfmts.20261203.12
T2  - International Journal of Fluid Mechanics & Thermal Sciences
JF  - International Journal of Fluid Mechanics & Thermal Sciences
JO  - International Journal of Fluid Mechanics & Thermal Sciences
SP  - 62
EP  - 75
PB  - Science Publishing Group
SN  - 2469-8113
UR  - https://doi.org/10.11648/j.ijfmts.20261203.12
AB  - Double diffusive natural convection driven by Simultaneous temperature and concentration gradients are fundamental to many engineering and environmental processes. The buoyancy ratio N, defined as the ratio of solutal to thermal buoyancy forces, critically determines whether thermal or solutal effects dominate the flow structure, heat transfer, and species transport. While most existing studies rely on two-dimensional simplifications and alternative numerical methods, this paper presents a three-dimensional numerical investigation of the effect of the buoyancy ratio on steady, laminar double-diffusive natural convection in a rectangular enclosure with an aspect ratio of 0.5. The continuity, momentum, energy, and concentration equations governing the flow are solved using the finite-volume method with the SIMPLE algorithm on a staggered grid. Parametric simulations are performed for buoyancy ratios N = 1.0, 2.5, 5.0, and 10.0, with fixed Prandtl number Pr = 7.0, Lewis number Le = 2.5, and Rayleigh number Ra = 50000. Results show that increasing the buoyancy ratio from 1.0 to 10.0 significantly enhances the uniformity of the temperature field and enhances vertical heat transfer. Concentration profiles become sharper and more localized as the buoyancy ratio is increased. At a high buoyancy ratio, solutal buoyancy dominates, producing a thin solutal boundary layer and strong stratification, thereby promoting salt fingering. Velocity profiles become stronger, more organized, and more stable as the buoyancy ratio increases. The 3-dimensional nature of the flow reveals that the effect of the buoyancy ratio in the enclosure is isotropic; the primary circulation plane along the z-y plane shows the greatest changes, while the secondary planes (x-y and x-z) show only a significant change. The finite volume method proves to be an effective tool for 3-dimensional parametric studies. The results provide a valuable benchmark for engineering applications where controlling the balance between thermal and solutal buoyancy is crucial, such as chemical reactors, drying systems, and thermal management devices.
VL  - 12
IS  - 3
ER  -

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Author Information

Peninnah Ngina Musili

Faculty of Science and Technology, Chuka University, Meru, Kenya

Contact Email

http://orcid.org/0009-0001-0901-7381
Mark Okongo

Department of Physical Sciences, Chuka University, Chuka, Kenya

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Alice Lunani Mulama Murwayi

Department of Physical Sciences, Chuka University, Chuka, Kenya

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Plain Text BibTeX RIS

APA Style

Musili, P. N., Okongo, M., Murwayi, A. L. M. (2026). Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure. International Journal of Fluid Mechanics & Thermal Sciences, 12(3), 62-75. https://doi.org/10.11648/j.ijfmts.20261203.12

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ACS Style

Musili, P. N.; Okongo, M.; Murwayi, A. L. M. Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure. Int. J. Fluid Mech. Therm. Sci. 2026, 12(3), 62-75. doi: 10.11648/j.ijfmts.20261203.12

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AMA Style

Musili PN, Okongo M, Murwayi ALM. Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure. Int J Fluid Mech Therm Sci. 2026;12(3):62-75. doi: 10.11648/j.ijfmts.20261203.12

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@article{10.11648/j.ijfmts.20261203.12,
  author = {Peninnah Ngina Musili and Mark Okongo and Alice Lunani Mulama Murwayi},
  title = {Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure},
  journal = {International Journal of Fluid Mechanics & Thermal Sciences},
  volume = {12},
  number = {3},
  pages = {62-75},
  doi = {10.11648/j.ijfmts.20261203.12},
  url = {https://doi.org/10.11648/j.ijfmts.20261203.12},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ijfmts.20261203.12},
  abstract = {Double diffusive natural convection driven by Simultaneous temperature and concentration gradients are fundamental to many engineering and environmental processes. The buoyancy ratio N, defined as the ratio of solutal to thermal buoyancy forces, critically determines whether thermal or solutal effects dominate the flow structure, heat transfer, and species transport. While most existing studies rely on two-dimensional simplifications and alternative numerical methods, this paper presents a three-dimensional numerical investigation of the effect of the buoyancy ratio on steady, laminar double-diffusive natural convection in a rectangular enclosure with an aspect ratio of 0.5. The continuity, momentum, energy, and concentration equations governing the flow are solved using the finite-volume method with the SIMPLE algorithm on a staggered grid. Parametric simulations are performed for buoyancy ratios N = 1.0, 2.5, 5.0, and 10.0, with fixed Prandtl number Pr = 7.0, Lewis number Le = 2.5, and Rayleigh number Ra = 50000. Results show that increasing the buoyancy ratio from 1.0 to 10.0 significantly enhances the uniformity of the temperature field and enhances vertical heat transfer. Concentration profiles become sharper and more localized as the buoyancy ratio is increased. At a high buoyancy ratio, solutal buoyancy dominates, producing a thin solutal boundary layer and strong stratification, thereby promoting salt fingering. Velocity profiles become stronger, more organized, and more stable as the buoyancy ratio increases. The 3-dimensional nature of the flow reveals that the effect of the buoyancy ratio in the enclosure is isotropic; the primary circulation plane along the z-y plane shows the greatest changes, while the secondary planes (x-y and x-z) show only a significant change. The finite volume method proves to be an effective tool for 3-dimensional parametric studies. The results provide a valuable benchmark for engineering applications where controlling the balance between thermal and solutal buoyancy is crucial, such as chemical reactors, drying systems, and thermal management devices.},
 year = {2026}
}

Copy | Download

TY  - JOUR
T1  - Effect of Buoyancy Ratio on Double-Diffusive Natural Convection Flow in a Rectangular Enclosure
AU  - Peninnah Ngina Musili
AU  - Mark Okongo
AU  - Alice Lunani Mulama Murwayi
Y1  - 2026/09/09
PY  - 2026
N1  - https://doi.org/10.11648/j.ijfmts.20261203.12
DO  - 10.11648/j.ijfmts.20261203.12
T2  - International Journal of Fluid Mechanics & Thermal Sciences
JF  - International Journal of Fluid Mechanics & Thermal Sciences
JO  - International Journal of Fluid Mechanics & Thermal Sciences
SP  - 62
EP  - 75
PB  - Science Publishing Group
SN  - 2469-8113
UR  - https://doi.org/10.11648/j.ijfmts.20261203.12
AB  - Double diffusive natural convection driven by Simultaneous temperature and concentration gradients are fundamental to many engineering and environmental processes. The buoyancy ratio N, defined as the ratio of solutal to thermal buoyancy forces, critically determines whether thermal or solutal effects dominate the flow structure, heat transfer, and species transport. While most existing studies rely on two-dimensional simplifications and alternative numerical methods, this paper presents a three-dimensional numerical investigation of the effect of the buoyancy ratio on steady, laminar double-diffusive natural convection in a rectangular enclosure with an aspect ratio of 0.5. The continuity, momentum, energy, and concentration equations governing the flow are solved using the finite-volume method with the SIMPLE algorithm on a staggered grid. Parametric simulations are performed for buoyancy ratios N = 1.0, 2.5, 5.0, and 10.0, with fixed Prandtl number Pr = 7.0, Lewis number Le = 2.5, and Rayleigh number Ra = 50000. Results show that increasing the buoyancy ratio from 1.0 to 10.0 significantly enhances the uniformity of the temperature field and enhances vertical heat transfer. Concentration profiles become sharper and more localized as the buoyancy ratio is increased. At a high buoyancy ratio, solutal buoyancy dominates, producing a thin solutal boundary layer and strong stratification, thereby promoting salt fingering. Velocity profiles become stronger, more organized, and more stable as the buoyancy ratio increases. The 3-dimensional nature of the flow reveals that the effect of the buoyancy ratio in the enclosure is isotropic; the primary circulation plane along the z-y plane shows the greatest changes, while the secondary planes (x-y and x-z) show only a significant change. The finite volume method proves to be an effective tool for 3-dimensional parametric studies. The results provide a valuable benchmark for engineering applications where controlling the balance between thermal and solutal buoyancy is crucial, such as chemical reactors, drying systems, and thermal management devices.
VL  - 12
IS  - 3
ER  -

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