Radiative heat transfer in FLiBe molten salt participating medium in a vertical heated tube under forced and mixed convection laminar flows
Abstract
The contribution of radiative heat transfer (RHT) to convective heat transfer in a heated vertical pipe with laminar flow and constant wall temperature, for FLiBe molten salt, is investigated computationally. The combined effects of conduction in the fluid, forced convection, buoyancy, temperature-dependent physical properties, and thermal radiation are investigated. The P1 approximation is employed in the discretization of the Radiative Transfer Equation (RTE). The COMSOL Multiphysics software is used to generate the numerical solutions. The theoretical analysis developed here demonstrates that only for intermediate values of the optical thickness, i.e. the participating media effects are expected to be important. This analysis is confirmed computationally and a value of is shown to lead to the highest increase in overall heat transfer behavior. Under forced convection, the Nusselt ratio reaches a peak value of at and , and is less than for . Under aiding-flow mixed convection, reaches a peak of at and is less than for . Under opposing-flow mixed convection, reaches a peak of at and is less than 1.1 for . RHT effects on the overall heat transfer are most pronounced in opposing mixed convection, where is observed at The sensitivity to wall emissivity is evaluated; in forced convection, the peak is at ε = 0 (reflective wall) and at ε (absorptive wall). Finally, the sensitivity to pipe diameter is also discussed. Overall, for a vertical heated tube, radiative heat transfer effects lead to enhancement of heat transfer by as high as a factor of two, and they depend on the optical thickness of the flow, mixed convection environment ( and direction of flow relative to the gravitational force), surface emissivity, and entrance effects.
- Authors:
-
- Univ. of Wisconsin, Madison, WI (United States). Dept. of Mechanical Engineering
- Univ. of California (United States). Dept. of Nuclear Engineering
- Publication Date:
- Research Org.:
- Univ. of Wisconsin, Madison, WI (United States)
- Sponsoring Org.:
- USDOE Office of Nuclear Energy (NE), Nuclear Energy University Program (NEUP); USDOE
- OSTI Identifier:
- 1850528
- Alternate Identifier(s):
- OSTI ID: 1810958
- Grant/Contract Number:
- NE0008680
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Nuclear Engineering and Design
- Additional Journal Information:
- Journal Volume: 368; Journal Issue: C; Journal ID: ISSN 0029-5493
- Publisher:
- Elsevier
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; Nuclear Science & Technology; Radiative heat transfer; FLiBe; Molten salt; Mixed convection; Participating media; Optical thickness
Citation Formats
Abou Dbai, Mohamed, Scarlat, Raluca O., and Trujillo, Mario F. Radiative heat transfer in FLiBe molten salt participating medium in a vertical heated tube under forced and mixed convection laminar flows. United States: N. p., 2020.
Web. doi:10.1016/j.nucengdes.2020.110775.
Abou Dbai, Mohamed, Scarlat, Raluca O., & Trujillo, Mario F. Radiative heat transfer in FLiBe molten salt participating medium in a vertical heated tube under forced and mixed convection laminar flows. United States. https://doi.org/10.1016/j.nucengdes.2020.110775
Abou Dbai, Mohamed, Scarlat, Raluca O., and Trujillo, Mario F. Thu .
"Radiative heat transfer in FLiBe molten salt participating medium in a vertical heated tube under forced and mixed convection laminar flows". United States. https://doi.org/10.1016/j.nucengdes.2020.110775. https://www.osti.gov/servlets/purl/1850528.
@article{osti_1850528,
title = {Radiative heat transfer in FLiBe molten salt participating medium in a vertical heated tube under forced and mixed convection laminar flows},
author = {Abou Dbai, Mohamed and Scarlat, Raluca O. and Trujillo, Mario F.},
abstractNote = {The contribution of radiative heat transfer (RHT) to convective heat transfer in a heated vertical pipe with laminar flow and constant wall temperature, for FLiBe molten salt, is investigated computationally. The combined effects of conduction in the fluid, forced convection, buoyancy, temperature-dependent physical properties, and thermal radiation are investigated. The P1 approximation is employed in the discretization of the Radiative Transfer Equation (RTE). The COMSOL Multiphysics software is used to generate the numerical solutions. The theoretical analysis developed here demonstrates that only for intermediate values of the optical thickness, i.e. τD~O1, the participating media effects are expected to be important. This analysis is confirmed computationally and a value of τD≈4 is shown to lead to the highest increase in overall heat transfer behavior. Under forced convection, the Nusselt ratio Nutotal/Nuno-rad reaches a peak value of 1.76 at τD=4 and z/D=200, and is less than 1.1 for τD<0.1andτD>60. Under aiding-flow mixed convection, Nutotal/Nuno-rad reaches a peak of 1.34 at τD=4.2 and is less than 1.1 for τD<0.4andτD>36. Under opposing-flow mixed convection, Nutotal/Nuno-rad reaches a peak of 1.81 at τD=4.2 and is less than 1.1 for τD<0.2andτD>50. RHT effects on the overall heat transfer are most pronounced in opposing mixed convection, where Nutotal/Nuno-rad is 2.26 observed at z/D=50. The sensitivity to wall emissivity is evaluated; in forced convection, the peak Nutotal/Nuno-rad is 1.66 at ε = 0 (reflective wall) and 2.04 at ε =1 (absorptive wall). Finally, the sensitivity to pipe diameter is also discussed. Overall, for a vertical heated tube, radiative heat transfer effects lead to enhancement of heat transfer by as high as a factor of two, and they depend on the optical thickness of the flow, mixed convection environment (Gr/Re2 and direction of flow relative to the gravitational force), surface emissivity, and entrance effects.},
doi = {10.1016/j.nucengdes.2020.110775},
journal = {Nuclear Engineering and Design},
number = C,
volume = 368,
place = {United States},
year = {Thu Sep 17 00:00:00 EDT 2020},
month = {Thu Sep 17 00:00:00 EDT 2020}
}
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