Comparing the Monte Carlo Method to the Discrete Ordinates Methods in Fluent for Calculating Radiation Heat Transfer in a Small Particle Receiver

2016 ◽  
Author(s):  
Eugene Cho ◽  
Fletcher Miller
Keyword(s):  
Monte Carlo ◽  
Solar Radiation ◽  
Boundary Conditions ◽  
Fortran Program ◽  
Working Fluid ◽  
Discrete Ordinates ◽  
Ansys Fluent ◽  
Discrete Ordinates Method ◽  
Directional Distribution ◽  
Solar Receiver

The Combustion and Solar Energy Laboratory (C&SEL) at San Diego State University is developing a Small Particle Heat Exchange Receiver (SPHER) to absorb and transfer heat from concentrated solar radiation to a working fluid for a gas turbine. The SPHER is to be used with a Concentrated Solar Power (CSP) system where a heliostat field highly concentrates solar radiation on the optical aperture of the SPHER. The solar radiation is volumetrically absorbed by a unique carbon nanoparticle gas mixture within the cavity of the SPHER. This research focuses on comparing a Computational Fluid Dynamics (CFD) model using the ANSYS FLUENT Discrete Ordinates (DO) Model and a program developed by the C&SEL which uses a Monte Carlo Ray Trace (MCRT) method to calculate the spatial and directional distribution of radiation for an idealized solar receiver geometry. Previous research at the C&SEL has shown successful implementation of the MCRT method to calculate the spatial and directional distribution of radiation for an idealized solar receiver geometry. The MCRT method is highly accurate and will serve as the benchmark solution for this research. However the MCRT code takes several days to run, is inflexible to geometry changes, and is cumbersome to implement as the MCRT code needs to be rewritten for each new receiver geometry being considered. These factors necessitate the need to find an alternate method that accurately calculates the spatial and directional distribution of radiation for a solar receiver and can be efficiently implemented for various receiver geometries being studied. The Discrete Ordinates method is a new method for solving the Radiative Transport Equations (RTE) using a FORTRAN program, developed by the C&SEL, and the ANSYS FLUENT Discrete Ordinates model for calculating the RTE. The FORTRAN program calculates the proper inlet radiation boundary conditions that ANSYS FLUENT uses for calculating the RTE. The methodology used for determining the correct CFD mesh, radiative boundary conditions, optimal number of DO theta and phi discretization, as well as the optical properties of the working fluid will be presented in this paper. The main focus of this research is to compare two different methods for solving the Radiative Transport Equations within the idealized SPHER. The solution data for several cases using the previous coupled MCRT method and the ANSYS FLUENT Discrete Ordinates method is presented for both a collimated and diffuse gray radiation approximation. The case studies focus on researching how the MCRT method and Discrete Ordinates method differ when comparing critical receiver parameters such as the mean outlet temperature, wall temperature profile, outlet tube temperature profile, and total receiver efficiency while keeping the total inlet radiation flux of 5 MW and inlet mass flow rate of 5 kg/s constant. This research also presents a study on the optimal Discrete Ordinates angular discretization, as well as a study to determine the solution’s dependence on the number of inlet boundary conditions imposed on the window.

A Comparison Between the Monte Carlo Ray Trace and the FLUENT Discrete Ordinates Methods for Treating Solar Input to a Particle Receiver

2014 ◽  
Author(s):  
Ahmet Murat Mecit ◽  
Fletcher Miller
Keyword(s):  
Monte Carlo ◽  
Solar Energy ◽  
Temperature Fields ◽  
Discrete Ordinates ◽  
Solar Simulator ◽  
Ansys Fluent ◽  
Carrier Fluid ◽  
Concentrated Solar Energy ◽  
Ray Trace ◽  
Solar Receiver

A new type of high temperature solar receiver for Brayton Cycle power towers is being designed and built in the Combustion and Solar Energy Laboratory at San Diego State University under a DOE Sunshot Award. The Small Particle Solar Receiver is a pressurized vessel with a window to admit concentrated solar radiation that utilizes a gas-particle suspension for absorption and heat transfer. As the particles absorb the radiation that enters the receiver through the window, the carrier fluid (air in this case) heats which oxidizes the particles and the flow leaves the receiver as a clear gas stream. After passing through an in-line combustor if needed, this hot gas is used to power a turbine to generate electricity. The numerical modelling of the receiver is broken into three main pieces: Monte Carlo Ray Trace (MCRT) method (written in FORTRAN), ANSYS Fluent (CFD), and the User Defined function (written in C code) for oxidation. Each piece has its advantages, disadvantages, and limitations and the three pieces are coupled to finalize the calculation. While we have successfully demonstrated this approach to obtaining the velocity and temperature fields, one big challenge to this method is that the definition of the geometry is a time consuming programming task when using MCRT. On the other hand, arbitrary geometries can be easily modelled by Computational Fluid Dynamics (CFD) codes such as FLUENT. The goal of this study is to limit the use of MCRT method to determining the appropriate input boundary condition on the outside of the window of the receiver and to use the built-in Discrete Ordinates (DO) method for all the radiation internal to the receiver and leaving the receiver due to emission. To reach the goal, this paper focuses on the DO method implemented within FLUENT. An earlier study on this subject is based and advanced. Appropriate radiation input for the DO method is extensively discussed. MIRVAL is used to simulate the heliostat field and VEGAS is used to simulate a lab-scale solar simulator; both of these codes utilize the MCRT method and provide intensity information on a surface. Output from these codes is discretized into DO parameters allowing the solution to proceed in FLUENT. Suitable benchmarks in FLUENT are used in a cylindrical geometry representing the receiver for the comparison and validation. This method will allow FLUENT to be used for a variety of problems involving concentrated solar energy.

Experimental and Numerical Studies of Short Pulse Propagation in Model Systems

2002 ◽  
Author(s):  
Sunil Kumar ◽  
Zhixiong Guo ◽  
Janice Aber ◽  
Bruce Garetz
Keyword(s):  
Monte Carlo ◽  
Pulse Propagation ◽  
Short Pulse ◽  
Model Systems ◽  
Discrete Ordinates ◽  
Pulsed Lasers ◽  
Discrete Ordinates Method ◽  
Numerical Studies ◽  
Tissue Phantoms ◽  
Good Agreement

In this paper experimental and numerical studies of the propagation of short-pulsed lasers through scattering and absorbing media are presented. Experimental results of a 60 ps pulse laser transmission in tissue phantoms are obtained and compared with Monte Carlo simulations. Good agreement between the Monte Carlo simulation and experimental measurement is found. Three models are developed for the simulation of short pulse transport. Benchmark comparisons among the Monte Carlo (MC), transient discrete ordinates method (TDOM) and transient radiation element method (TREM) are conducted.

Angular False Scattering in Radiative Heat Transfer Analysis Using the Discrete-Ordinates Method With Higher-Order Quadrature Sets

2013 ◽  
Author(s):  
Brian Hunter ◽  
Zhixiong Guo
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Phase Function ◽  
Radiative Heat ◽  
Higher Order ◽  
Heat Transfer Analysis ◽  
Discrete Ordinates ◽  
Equal Weight ◽  
Participating Media ◽  
Discrete Ordinates Method

The SN quadrature set for the discrete-ordinates method is limited in overall discrete direction number in order to avoid physically unrealistic negative directional weight factors. Such a limitation can adversely impact radiative transfer predictions. Directional discretization results in errors due to ray effect, as well as angular false scattering error due to distortion of the scattering phase function. The use higher-order quadrature schemes in the discrete-ordinates method allows for improvement in discretization errors without an overall directional limitation. In this analysis, 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. Radiative heat fluxes, calculated at low direction number, are compared to the SN quadrature and Monte Carlo predictions to gauge quadrature accuracy. Additionally, investigation into the reduction of angular false scattering with sufficient increase in direction number using higher-order quadrature, including heat flux accuracy with respect to Monte Carlo and computational efficiency, is presented. While higher-order quadrature sets are found to effectively minimize angular false scattering error, it is found to be much more computationally efficient to implement proper phase function normalization for accurate radiative transfer predictions.

Sign in / Sign up

Export Citation Format

Share Document