A key component in developing atrial digital twins (ADT) - virtual representations of patients’ atria — is the accurate prescription of myocardial fibers which are essential for the tissue characterization. Due to t...
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In this work, we first develop a unified Bhatnagar-Gross-Krook lattice Boltzmann (BGK-LB) model for the d(d ≥ 1)-dimensional linear hyperbolic equation (L-HE), where the natural moments and the DdQ(2d2 + 1) [(2d2 + 1...
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In this work, we develop a phase-field-based lattice Boltzmann (LB) method for a two-scalar model of the two-phase flows with interfacial mass/heat transfer. Through the Chapman–Enskog analysis, we show that the pres...
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The Allen-Cahn equation (ACE) inherently possesses two crucial properties: the maximum principle and the energy dissipation law. Preserving these two properties at the discrete level is also necessary in the numerical...
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The solidification and macro-segregation problem involving unsteady multiphysics and multi-phase fields is typically a complex process with mass, momentum, heat, and species transfers among solid, mushy, and liquid ph...
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The solidification and macro-segregation problem involving unsteady multi-physics and multi-phase fields is typically a complex process with mass, momentum, heat, and constituent transfers among solid, mushy, and liqu...
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The heterogeneous and homogeneous combustion of C3H8/O2/N2 mixtures over Rh was studied at pressures 1-6 bar, catalyst surface temperatures 680-1100 K and C3H8-to-O2 equivalence ratios 0.25-0.52. Non-intrusive laser-b...
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The heterogeneous and homogeneous combustion of C3H8/O2/N2 mixtures over Rh was studied at pressures 1-6 bar, catalyst surface temperatures 680-1100 K and C3H8-to-O2 equivalence ratios 0.25-0.52. Non-intrusive laser-based measurements were applied in a channel-flow catalytic reactor and involved 1-D Raman spectroscopy of major gas-phase species across the channel boundary layer for assessing the catalytic reactivity and planar laser induced fluorescence (PLIF) of the OH radical for monitoring homogeneous combustion. Simulations were performed using a 2-D CFD code with detailed heterogeneous and homogeneous chemical reaction mechanisms. By comparing the Raman-measured and predicted transverse profiles of the limiting C3H8 reactant, the suitability of a detailed surface reaction mechanism was initially evaluated and subsequently a one-step reaction was constructed, which was applicable for the C3H8 total oxidation over Rh at 1-6 bar. The catalytic reactivity of C3H8 over Rh displayed a ∼p0.14 pressure dependence, which was substantially lower than a previously reported ∼p0.70 dependence over Pt. The weak pressure dependence of the C3H8 reactivity on Rh suggested caution when selecting catalysts for high-pressure power systems (recuperative microreactors, small-scale turbines) fueled with C3H8 or LPG. Comparisons of PLIF-measured and predicted distributions of the OH radical indicated that the employed gas-phase reaction mechanism captured the onset of homogeneous ignition at pressures ≥ 3 bar as well as the ensuing flame shapes. Predicted and measured homogeneous ignition distances agreed within 2.5% at 6 bar. With decreasing pressure, the predictions yielded gradually increasing but still modest underpredictions (up to 11.2% at 3 bar) of the homogeneous ignition
The catalytic and gas-phase combustion of fuel-lean H2/CO/O2/N2 mixtures over palladium was studied experimentally and numerically at a global equivalence ratio Φ = 0.285, H2/CO volumetric ratios of 1-4, pressures of...
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The catalytic and gas-phase combustion of fuel-lean H2/CO/O2/N2 mixtures over palladium was studied experimentally and numerically at a global equivalence ratio Φ = 0.285, H2/CO volumetric ratios of 1-4, pressures of 1-8 bar and catalyst surface temperatures of 950-1200 K. In situ planar laser induced fluorescence (PLIF) of the OH radical was used to monitor homogeneous combustion inside a channel-flow catalytic reactor, while 1-D Raman measurements of main gas-phase species concentrations across the channel boundary layer were conducted to evaluate the heterogeneous processes. Simulations were carried out with a 2-D numerical code using detailed heterogeneous and homogeneous chemical reaction mechanisms and realistic transport. The simulated and measured transverse species profiles attested to a transport-limited catalytic conversion of H2 and CO at all operating conditions. The OH-PLIF measurements and the simulations confirmed the establishment of appreciable homogeneous combustion only for p < 4 bar, with progressively diminishing gas-phase contribution as the pressure increased from 4 to 8 bar. This strong pressure dependence reflected the complex pressure/temperature dependence of the homogeneous ignition chemistry as well as the competition between the catalytic and gaseous reaction pathways for H2 and CO consumption. Over the gaseous induction zones, the wall temperatures were below the pressure-dependent upper temperature limit for the decomposition of PdO to metallic Pd. Although palladium catalysts exhibited a “self-regulating” temperature effect due to PdO decomposition, the attained temperatures were still sufficient to ignite homogeneous combustion of the H2/CO/O2/N2 mixtures. This was contrary to hydrocarbon fuels for which gas-phase combustion was largely suppressed over PdO in the pressure range of 1-8 bar. The results suggested that for the elevated p
In this paper, we develop a general rectangular multiple-relaxation-time lattice Boltzmann (RMRT-LB) method for the Navier-Stokes equations (NSEs) and nonlinear convection-diffusion equation (NCDE) by extending our re...
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In this paper, we develop a general rectangular multiple-relaxation-time lattice Boltzmann (RMRT-LB) method for the Navier-Stokes equations (NSEs) and nonlinear convection-diffusion equation (NCDE) by extending our recent unified framework of the multiple-relaxation-time lattice Boltzmann (MRT-LB) method [Chai and Shi, Phys. Rev. E 102, 023306 (2020)], where an equilibrium distribution function (EDF) [Lu et al., Philos. Trans. R. Soc. A 369, 2311 (2011)] on a rectangular lattice is utilized. The anisotropy of the lattice tensor on a rectangular lattice leads to anisotropy of the third-order moment of the EDF, which is inconsistent with the isotropy of the viscous stress tensor of the NSEs. To eliminate this inconsistency, we extend the relaxation matrix related to the dynamic and bulk viscosities. As a result, the macroscopic NSEs can be recovered from the RMRT-LB method through the direct Taylor expansion method. Whereas the rectangular lattice does not lead to the change of the zero-, first- and second-order moments of the EDF, the unified framework of the MRT-LB method can be directly applied to the NCDE. It should be noted that the RMRT-LB model for NSEs can be derived on the rDdQq (q discrete velocities in d-dimensional space, d≥1) lattice, including rD2Q9, rD3Q19, and rD3Q27 lattices, while there are no rectangular D3Q13 and D3Q15 lattices within this framework of the RMRT-LB method. Thanks to the block-lower triangular relaxation matrix introduced in the unified framework, the RMRT-LB versions (if existing) of the previous MRT-LB models can be obtained, including those based on raw (natural) moment, central moment, Hermite moment, and central Hermite moment. It is also found that when the parameter cs is an adjustable parameter in the standard or rectangular lattice, the present RMRT-LB method becomes a kind of MRT-LB method for the NSEs and NCDE, and the commonly used MRT-LB models on the DdQq lattice are only its special cases. We also perform some numeric
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