(380g) A Hybrid Lattice Boltzmann-Random Walk Method for Multiphase Heat Transfer

The transport phenomena within multiphase flows plays a key role in the operation of catalytic reactors, calciners, fluidized beds, and porous media. However, a fundamental understanding of the physics within these complicated systems still remains elusive. Direct numerical simulation has been shown to be an effective method for obtaining high fidelity predictions of the heat transfer within multiphase flows. Most commonly, particle-resolved immersed boundary [4, 5] or thermal lattice Boltzmann [3] methods are employed. Here we utilize a hybrid framework where the velocity field is resolved by the lattice Boltzmann method and temperature field by random walk particle tracking (Brownian tracers). Due to the simplicity of the algorithm and boundary conditions, random walk particle tracking offers an efficient means of simulating scalar transport within complex geometries. However, interfaces pose a significant challenge to the random walk framework [1, 2], due to the discontinuous change in material properties – e.g., a particle and fluid with different diffusivities. We derive a technique for handling discontinuities in the diffusivity, arising at a particle-fluid interface, and implement said method within the tracer algorithm. Verification of the code is completed against a host of systems: dispersion within a stagnant particle-fluid assembly, a hot sphere in contact with an unbounded fluid, a cooling sphere in contact with an unbounded fluid, and unbounded flow past a hot sphere. Predictions made by the new code are found to be in agreement with analytical solutions and previous works.

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[2] Hoteit, H., Mose, R., Younes, A., Lehmann, F., Ackerer, P., 2002. Three-Dimensional Modeling of Mass Transfer in Porous Media Using the Mixed Hybrid Finite Elements and the Random-Walk Methods. Mathematical Geology 34, 435–456. doi:10.1023/A:1015083111971

[3] Kruggel-Emden, H., Kravets, B., Suryanarayana, M.K., Jasevicius, R., 2016. Direct numerical simulation of coupled fluid flow and heat transfer for single particles and particle packings by a LBM-approach. Powder Technology 294, 236–251. doi:10.1016/j.powtec.2016.02.038

[4] Sun, B., Tenneti, S., Subramaniam, S., 2015. Modeling average gas–solid heat transfer using particle-resolved direct numerical simulation. International Journal of Heat and Mass Transfer 86, 898–913. doi:10.1016/j.ijheatmasstransfer.2015.03.046

[5] Tavassoli, H., Kriebitzsch, S.H.L., van der Hoef, M.A., Peters, E.A.J.F., Kuipers, J.A.M., 2013. Direct numerical simulation of particulate flow with heat transfer. International Journal of Multiphase Flow 57, 29–37. doi:10.1016/j.ijmultiphaseflow.2013.06.009