Ansys 12.0 CFX 官方教程 18.pptVIP

Radiation Modeling C-* ANSYS, Inc. Proprietary ? 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory #002598 Training Manual C-* ANSYS, Inc. Proprietary ? 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory #002598 Appendix CRadiation Modeling Introduction to CFX  Radiation Thermal radiation is electromagnetic radiation which arises as a result of a temperature difference between the surface of an object and its surrounding Atrium Example The Radiative Transport Equation (RTE) Describes the propagation of radiative energy through a media which is itself emitting radiation, absorbing radiation and scattering radiation. integro-differential equation (very computationally expensive to solve) Radiative Transport Equation Several radiation models are available which provide approximate solutions to the RTE Each radiation model has its assumptions, limitations, and benefits 1) Rosseland Model (Diffusion Approximation Model) 2) P-1 Model (Gibb’s Model/Spherical Harmonics Model) 3) Discrete Transfer Model (Shah Model) 4) Monte Carlo Model (not available with the ANSYS CFD-Flo product) Radiation Models The Rosseland Model Method: A new diffusion term is added to the energy equation Limitations: Only valid for optically thick and linearly anisotropic material (thickness/depth greater than 10) Not valid near walls Benefits: Does not require any boundary conditions since surfaces are treated as black (Emissivity = 1.0) Examples: Heat transfer through hot glass Heat transfer through semitransparent material Rosseland Model The P-1 Model Assumptions: Radiation intensity is isotropic or direction independent at a given location in space Method: An additional transport equation is solved Limitations: Only valid for optical thickness/depth greater than 1. Not valid for transparent walls Needs boundary conditions on all external surfaces Benefits: Valid for non-black surfaces, non-constant properties, anisotropic scattering, and near walls Ex