Numerical investigation of forced convection heat transfer from a sphere at low Prandtl numbers
Direct numerical simulations of the flow and forced convective heat transfer around a sphere at Reynolds numbers between = 500 and = 1000 are performed. We investigate the effects of the Prandtl number ( ) on the forced convective heat transfer from a sphere for various fluids having = 0.01, 0.1, 0....
| Autores: | , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/375226 |
| Acceso en línea: | https://hdl.handle.net/2117/375226 https://dx.doi.org/10.1016/j.ijthermalsci.2022.107970 |
| Access Level: | acceso abierto |
| Palabra clave: | Heat -- Transmission Heat -- Convection Convective heat transfer Sphere Nusselt number Low Prandtl number Thermal wake Calor -- Transmissió Calor -- Convecció Àrees temàtiques de la UPC::Física::Termodinàmica |
| Sumario: | Direct numerical simulations of the flow and forced convective heat transfer around a sphere at Reynolds numbers between = 500 and = 1000 are performed. We investigate the effects of the Prandtl number ( ) on the forced convective heat transfer from a sphere for various fluids having = 0.01, 0.1, 0.7. At the larger Prandtl number, the convective transport due to the vortex shedding process dominates over the diffusive transport. As the Prandtl number decreases, diffusive effects become important. Moreover, the thermal boundary layer increases with decrements of the Prandtl number, which results in a reduction in the local and mean non-dimensional heat transfer coefficient. It is seen that at = 500 and = 750, the vortex shedding process is asymmetric, which results not only in a non-zero lift coefficient, but in an asymmetric temperature field in the wake of the sphere at ≥ 0.1. The dual asymmetry in the flow and the convective heat transfer is smooth out when the Prandtl number reaches = 0.01 as the heat diffusion dominates and asymmetries in the vortex formation zone are no longer relevant in the heat transport. The descend in Prandtl number also produces an attenuation of the temperature fluctuations and thereby, in the turbulent heat transfer. As a direct consequence, two factors emerge at = 0.01: (1) a lower decay ratio of the temperature in the wake centreline, and (2) a larger wake spread compared to higher Prandtl numbers. |
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