Natural Convective Nanofluid Flows Immersed in Oscillating Magnetic Fields Simulated by a Sub-Continuous Lattice Boltzmann Model

Pengxiang Sui, Yan Su, Liyong Sun

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Natural convective nanofluid flows immersed in oscillating magnetic fields are simulated with a sub-continuous nondimensional lattice Boltzmann model. The effective electrical conductivity model is built including coupled effects of nanoparticle concentrations and two Knudsen numbers. Effects of directions, frequencies, and strength amplitudes of the magnetic fields are studied in wide ranges of Hartmann numbers (0:1 ≤ Haf,L ≤ 600) and Rayleigh numbers (103 ≤ Raf,L ≤ 107). To achieve higher values of cycle averaged Nusselt numbers Nu cf ,L, optimal magnetic directions are along or opposite from the gravity directions. Effects of the magnetic frequency f̃B are negligible, in the conduction dominating lower Rayleigh number regime of Raf,L < 104. In the convection dominating regime, Nu cf ,L increase with Raf,L in orders of Ra0f,L:48 and Ra0f,L:45 for vertical and horizontal magnetic directions, respectively, and maximum values of Nu cf,L appear at the optimal magnetic frequency of f̃B ¼ 1=5cs MaLðL=ULÞ for all magnetic directions. With Raf,L as high as 106, the oscillating amplitudes of the transient wall mean Nusselt numbers Nuf,L increase with increasing Haf ,L, but the cycle averaged Nusselt numbers Nu cf,L decrease from 9.35 to 1.42 with increasing Haf,L in the transient regime of 5 ≤ Haf,L ≤ 500. Meanwhile, heat transfer patterns transit back from convection to conduction dominating patterns with increasing Haf ,L, as illustrated by transient streamlines and isotherms.

Original languageEnglish (US)
Article number011401
JournalASME Journal of Heat and Mass Transfer
Issue number1
StatePublished - Jan 1 2024

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering
  • Mechanics of Materials
  • General Materials Science

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