191,925 research outputs found
3-D simulation of gases transport under condition of inert gas injection into goaf
No full textTo prevent coal spontaneous combustion in mines, it is paramount to understand O2 gas distribution under condition of inert gas injection into goaf. In this study, the goaf was modeled as a 3-D porous medium based on stress distribution. The variation of O2 distribution influenced by CO2 or N2 injection was simulated based on the multi-component gases transport and the Navier-Stokes equations using Fluent. The numerical results without inert gas injection were compared with field measurements to validate the simulation model. Simulations with inert gas injection show that CO2 gas mainly accumulates at the goaf floor level; however, a notable portion of N2 gas moves upward. The evolution of the spontaneous combustion risky zone with continuous inert gas injection can be classified into three phases: slow inerting phase, rapid accelerating inerting phase, and stable inerting phase. The asphyxia zone with CO2 injection is about 1.25~2.4 times larger than that with N2 injection. The efficacy of preventing and putting out mine fires is strongly related with the inert gas injecting position. Ideal injections are located in the oxidation zone or the transitional zone between oxidation zone and heat dissipation zone.Peer reviewed
Phase-Function Normalization in the 3-D Discrete-Ordinates Solution of Radiative Transfer – PART I: Conservation of Scattered Energy and Asymmetry Factor
No full textThe conditions for which conversation of scattered energy and phase-function asymmetry factor after discrete-ordinates methods (DOM) directional discretization for 3-D radiative transfer in anisotropic scattering media breaks down are examined. Directional discretization in anisotropic scattering media is found to alter the scattering asymmetry factor—a second-type of ‘‘false scattering.’’ Phase-function normalization which conserves scattered energy alone cannot correct this problem, and conservation of the asymmetry factor is simultaneously required. A normalization technique developed by the authors, which was successfully tested in 2-D asymmetric cylindrical-coordinate radiative transfer analysis, is intensively examined and validated with benchmark problems in 3-D Cartesian coordinates. In Part I of this study, the degree of anisotropy for which normalization is necessary to conserve these inherent quantities is presented for various phase-function approximations and discrete quadrature sets.Peer reviewed
Data supporting: "Symmetry Breaking in Particle-Forming Diblock/Homopolymer Blends"
No full textInput and output files for self-consistent field theory calculations compatible with Polymer Self-Consistent Field (PSCF)Cheong, Guo Kang; Bates, Frank S; Dorfman, Kevin D. (2020). Data supporting: "Symmetry Breaking in Particle-Forming Diblock/Homopolymer Blends". Retrieved from the University Digital Conservancy, https://doi.org/10.13020/xfwb-9k72
Flow and heat transfer inside a new diversion-type gas heating device
No full textThe present paper characterizes ethylene glycol flow and heat transfer inside a new diversion-type gas heating device. A 2-D natural convection heat transfer model was built and solved by the finite volume method with unstructured body-fitted grids. The numerical model was first validated through temperature comparison with experimental measurements in a conventional device structure. Then analyses and comparisons of the flow fields and temperature distributions with use of different guide plate structures were carried out. The numerical results show that using the guide plate structures can form better organized flow patterns that augment heat transfer. The heat required for heating up the gas passing through the heating device can be reduced by 3% via installing two guide plates.Peer reviewed
First-principles investigation on thermal properties and infrared spectra of imperfect graphene
No full textIn this study we used first-principles density functional theory to investigate the thermal and optical properties of graphene. Graphene phonon properties were first calculated by the density-functional perturbation theory and then used to acquire thermal properties such as the specific heat, free and total energy, and entropy, as well as the infrared and Raman spectra. Results show that the peaks of phonon density of states at about 40 and 45.5 THz in the perfect graphene (G) were shifted to 40.5 and 46 THz in the imperfect graphene (G-D), respectively. There are peaks at 16.5, 19, 25, and 43.5 THz in the G-D curve, while there is no obvious peak at same frequencies in that of the G. The specific heat and entropy are lower for the G-D than for the G at temperature > 280 K, but the tendency is slightly reversed at temperature 1300 K, but lower at temperature below 1250 K than for the G. In the infrared (IR) spectrum, no absorption peak exists for perfect graphene, but strong absorption is found at about 233, 830 and 1392 cm-1 for the G-D. The character peak of sp2 carbon atom in-plane vibration in the Raman spectrum is shifted from 1589 cm-1 for the G to 1530 cm-1 for the G-D. The defects in the G-D caused the peaks and splits in the IR and Raman spectra.Peer reviewe
Unsteady simulation for optimal arrangement of dedusting airduct in coal mine heading face
No full textTo optimize dedusting efficiency in coal mines, a model of dust movement in heading roadway with far-pressing-near-absorption ventilation system was built. The empirical drag force model was applied into the unsteady inter phase coupling modeling of air and dust flow. The Discrete Phase Modeling in Fluent was employed to solve the problem and unstructured grids were utilized to mesh the complex 3-D roadway with different airduct allocations. Results show that the dedusting efficiency with the dedusting fan in the air return side is obviously better than that with the fan in the middle of the heading machine. The dedusting efficiency decreases within creasing distance between air inlet and heading section. When this distance is 2.0mwith airduct in the air return side, it has the best dedusting efficiency; in which the dust concentration in the front of roadway after 60 seconds of digging and cutting decreases from 1150mg/m3 to 365mg/m3; the average dust concentration in roadway decreases from 597mg/m3 to 144mg/m3; and the total dedusting efficiency reaches up to 75.88%.Peer reviewe
Phase-Function Normalization in the 3-D Discrete-Ordinates Solution of Radiative Transfer – PART II: Benchmark Comparisons
No full textRadiative transfer in a cubic enclosure, subject to varying conditions, is determined using the discrete-ordinates method (DOM) with the two normalization techniques introduced in Part I of this study. Their predictions are compared with Monte Carlo simulations. For all cases, false scattering due to directional discretization cannot be corrected when the old technique, which solely conserves scattered energy, is implemented; and thus, signifi- cant discrepancies exist when compared to Monte Carlo results. The new technique, which conserves both scattered energy and the asymmetry factor, is able to retain original scatter- ing properties after directional discretization, leading to improved accuracy when compared to Monte Carlo. In addition, a parametric study is presented to gauge the impact of asym- metry-factor conservation on media with various optical properties. Finally, the impact of normalization is investigated for both ultrafast radiative transfer and ballistic incidence with varying incident angle.Peer reviewed
Improved treatment of anisotropic scattering in radiation transfer analysis using the finite volume method
No full textDiscretization of the integral anisotropic-scattering term in the equation of radiative transfer will result in two kinds of numerical errors: alterations in scattered energy and asymmetry factor. Though quadrature flexibility with large angular directions and further solid-angle splitting in the finite volume method (FVM) allow for reduction/minimization of these errors, computational efficiency is adversely impacted. A phase-function normalization technique to get rid of these errors is simpler and is applied to the three-dimensional (3-D) FVM for the first time to improve anisotropic radiation transfer computation accuracy and efficiency. FVM results are compared to Monte Carlo and discrete-ordinates method predictions of radiative heat transfer in a cubic enclosure housing a highly anisotropic participating medium. It is found that the FVM results generated using the normalization technique conform accurately to the results of the other two methods with little impact on computational efficiency.Peer reviewed
Guo, R., Wang, J.M., Zhang, W., He, D., Yu, J. & Yang, D.M. (2022) Pteris pseudoamoena (Pteridaceae), a new species from Guangxi, China and Vietnam. Phytotaxa 550 (3): 215-223.
No full textGuo, R., Wang, J.M., Zhang, W., He, D., Yu, J., Yang, D.M. (2022): Guo, R., Wang, J.M., Zhang, W., He, D., Yu, J. & Yang, D.M. (2022) Pteris pseudoamoena (Pteridaceae), a new species from Guangxi, China and Vietnam. Phytotaxa 550 (3): 215-223. Phytotaxa 552 (4): 277-277, DOI: https://doi.org/10.11646/phytotaxa.552.4.6, URL: http://dx.doi.org/10.11646/phytotaxa.552.4.
Comparison of Quadrature Schemes in DOM for Anisotropic Scattering Radiative Transfer Analysis
No full textThe commonly implemented level-symmetric SN quadrature set for the discrete-ordinates method suffers from a limitation in discrete direction number to avoid physically unrealistic weighting factors. This limitation can have an adverse impact for determining radiative transfer, as directional discretization results in angular false scattering errors due to distortion of the scattering phase function in addition to the ray effect. To combat this limitation, several higher-order quadrature schemes with no directional limitation have been developed. Here, four higher-order quadrature sets (Legendre-equal weight, Legendre-Chebyshev, triangle tessellation, and spherical ring approximation) are implemented for determination of radiative transfer in a 3-D cubic enclosure containing participating media. Heat fluxes obtained at low direction number are compared to the SN quadrature and Monte Carlo predictions to gauge and compare quadrature accuracy. Investigation into the reduction/elimination of angular false scattering with increase in direction number, including heat flux accuracy with respect to Monte Carlo and computational efficiency, is presented. It is found that while the higher-order quadrature sets are able to effectively minimize angular false scattering, the number of directions required is extremely large, and thus it is more computationally efficient to implement proper phase-function normalization to obtain accurate results.Peer reviewed
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