# Publications

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## 2015 |

Gonzalez-Juez, Esteban D; Jemcov, Aleksandar A Finite Volume Time-Domain Solver to Estimate Combustion Instabilities Journal Article Journal of Propulsion and Power, 31 (2), pp. 632–642, 2015. Abstract | Links | BibTeX | Tags: Combustion, Modelling, OpenFOAM, Thermoacoustic @article{gonzalez2015finite, title = {A Finite Volume Time-Domain Solver to Estimate Combustion Instabilities}, author = { Esteban D Gonzalez-Juez and Aleksandar Jemcov}, doi = {10.2514/1.B35488}, year = {2015}, date = {2015-01-01}, journal = {Journal of Propulsion and Power}, volume = {31}, number = {2}, pages = {632--642}, publisher = {American Institute of Aeronautics and Astronautics}, abstract = {Modeling tools used to estimate thermoacoustic combustion instabilities include classic network models, three-dimensional frequency-domain acoustic solvers, and computational fluid dynamics. Motivated by the large gap in both computational cost and predictive capability between the first two tools and computational fluid dynamics, the present work discusses and tests an approach that bridges this gap: a three-dimensional finite volume, acoustic solver in the time domain. Distinguishing features of the newly developed solver include the ability to capture both linear and nonlinear acoustics, the use of a solution algorithm based on an approximate Riemann solver, and the ability to handle complex geometries with unstructured meshes. This new solver produces results that agree well with analytical solutions for a two-dimensional isothermal cavity and a one-dimensional Rijke tube, as well as with the experimental data of a reheat buzz. For this last problem, a limit cycle is produced with a physical model that bounds heat-release fluctuations. In addition, results from the new acoustic solver for an annular combustor compare well with those of a three-dimensional frequency-domain acoustic solver, demonstrating the capabilities of the new solver to capture multidimensional acoustics.}, keywords = {Combustion, Modelling, OpenFOAM, Thermoacoustic}, pubstate = {published}, tppubtype = {article} } Modeling tools used to estimate thermoacoustic combustion instabilities include classic network models, three-dimensional frequency-domain acoustic solvers, and computational fluid dynamics. Motivated by the large gap in both computational cost and predictive capability between the first two tools and computational fluid dynamics, the present work discusses and tests an approach that bridges this gap: a three-dimensional finite volume, acoustic solver in the time domain. Distinguishing features of the newly developed solver include the ability to capture both linear and nonlinear acoustics, the use of a solution algorithm based on an approximate Riemann solver, and the ability to handle complex geometries with unstructured meshes. This new solver produces results that agree well with analytical solutions for a two-dimensional isothermal cavity and a one-dimensional Rijke tube, as well as with the experimental data of a reheat buzz. For this last problem, a limit cycle is produced with a physical model that bounds heat-release fluctuations. In addition, results from the new acoustic solver for an annular combustor compare well with those of a three-dimensional frequency-domain acoustic solver, demonstrating the capabilities of the new solver to capture multidimensional acoustics. |

Jemcov, Aleksandar; Gonzalez-Juez, Esteban D A Finite Volume Time-Domain Solver to Estimate Combustion Instabilities Conference 53rd AIAA Aerospace Sciences Meeting, 2015, At Kissimmee, FL, 2015. Abstract | Links | BibTeX | Tags: Combustion, Modelling, OpenFOAM, Thermoacoustic @conference{jemcov2015finite, title = {A Finite Volume Time-Domain Solver to Estimate Combustion Instabilities}, author = { Aleksandar Jemcov and Esteban D Gonzalez-Juez}, doi = {10.2514/6.2015-1567}, year = {2015}, date = {2015-01-01}, booktitle = {53rd AIAA Aerospace Sciences Meeting, 2015, At Kissimmee, FL}, abstract = {Even though the damaging effect of thermoacoustic combustion instabilities on combustion systems is well documented, estimating the occurrence of these undesirable phenomena is still very difficult. Modeling tools used for this purpose include classic network models, 3D frequency-domain acoustic solvers, and computational fluid dynamics (CFD). Motivated by the large gap in both computational cost and predictive capability between the first two tools and CFD, the present work discusses an approach that bridges this gap: a 3D acoustic solver in the time domain. Unique aspects of the present solver include the ability to handle both linear and nonlinear acoustics and the use of a solution algorithm based on an approximate Riemann solver. Another notable feature, critical for industrial applications, is the use of a finite volume discretization that can be applied to unstructured meshes of arbitrary shape and complexity. This new acoustic solver is based on the C++ library OpenFOAM. Predictions with this solver are in good agreement with analytical solutions for a 2D isothermal cavity, a 1D Rijke tube, and a 1D model of a reheat buzz.}, keywords = {Combustion, Modelling, OpenFOAM, Thermoacoustic}, pubstate = {published}, tppubtype = {conference} } Even though the damaging effect of thermoacoustic combustion instabilities on combustion systems is well documented, estimating the occurrence of these undesirable phenomena is still very difficult. Modeling tools used for this purpose include classic network models, 3D frequency-domain acoustic solvers, and computational fluid dynamics (CFD). Motivated by the large gap in both computational cost and predictive capability between the first two tools and CFD, the present work discusses an approach that bridges this gap: a 3D acoustic solver in the time domain. Unique aspects of the present solver include the ability to handle both linear and nonlinear acoustics and the use of a solution algorithm based on an approximate Riemann solver. Another notable feature, critical for industrial applications, is the use of a finite volume discretization that can be applied to unstructured meshes of arbitrary shape and complexity. This new acoustic solver is based on the C++ library OpenFOAM. Predictions with this solver are in good agreement with analytical solutions for a 2D isothermal cavity, a 1D Rijke tube, and a 1D model of a reheat buzz. |

## 2013 |

Martin, Scott; Jemcov, Aleksandar; de Ruijter, Bj"orn Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method Inproceedings ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, pp. V01BT04A011–V01BT04A011, American Society of Mechanical Engineers 2013. Abstract | Links | BibTeX | Tags: CMC, Methane, Mixing, Modelling, OpenFOAM, Turbulence @inproceedings{martin2013modeling, title = {Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method}, author = { Scott Martin and Aleksandar Jemcov and Bj"orn de Ruijter}, doi = {10.1115/GT2013-95092}, year = {2013}, date = {2013-01-01}, booktitle = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition}, pages = {V01BT04A011--V01BT04A011}, organization = {American Society of Mechanical Engineers}, abstract = {Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided. The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors.}, keywords = {CMC, Methane, Mixing, Modelling, OpenFOAM, Turbulence}, pubstate = {published}, tppubtype = {inproceedings} } Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided. The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors. |

## 2012 |

Stephens, Darrin W; Tabib, Mandar; Schwarz, Phil; Davis, Mark CFD simulation of bath dynamics in the HIsmelt smelt reduction vessel for iron production Journal Article Progress in Computational Fluid Dynamics, an International Journal, 12 (2-3), pp. 196–206, 2012. Abstract | Links | BibTeX | Tags: Iron-Making, Lagrangian, Modelling, Multiphase, Smelt-Reduction @article{stephens2012cfd, title = {CFD simulation of bath dynamics in the HIsmelt smelt reduction vessel for iron production}, author = {Darrin W Stephens and Mandar Tabib and Phil Schwarz and Mark Davis}, doi = {10.1504/PCFD.2012.047462}, year = {2012}, date = {2012-01-01}, journal = {Progress in Computational Fluid Dynamics, an International Journal}, volume = {12}, number = {2-3}, pages = {196--206}, publisher = {Inderscience Publishers}, abstract = {Computational Fluid Dynamics (CFD) has played a crucial role in enabling the design and scale-up of the HIsmelt ^{ ® direct iron smelting technology. An existing PHOENICS-based CFD model of the molten bath dynamics in the process vessel has been transferred to ANSYS-CFX to improve its accuracy and to enable efficient analysis on an unstructured mesh. The basic model involves Lagrangian particle tracking of iron ore and coal particles through two Eulerian phases representing metal and slag. The model incorporates reactions involving coal devolatilisation, coal dissolution, and ore reduction. The study shows increase in number of particles used improves convergence.},
keywords = {Iron-Making, Lagrangian, Modelling, Multiphase, Smelt-Reduction},
pubstate = {published},
tppubtype = {article}
}
}Computational Fluid Dynamics (CFD) has played a crucial role in enabling the design and scale-up of the HIsmelt <sup align="right"> ® direct iron smelting technology. An existing PHOENICS-based CFD model of the molten bath dynamics in the process vessel has been transferred to ANSYS-CFX to improve its accuracy and to enable efficient analysis on an unstructured mesh. The basic model involves Lagrangian particle tracking of iron ore and coal particles through two Eulerian phases representing metal and slag. The model incorporates reactions involving coal devolatilisation, coal dissolution, and ore reduction. The study shows increase in number of particles used improves convergence. |

## 2011 |

Stephens, Darrin W; Tabib, Mandar; Davis, Mark; Schwarz, Phil CFD simulation of bath dynamics in the HIsmelt smelt reduction vessel for iron production Conference 8th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries, At SINTEF/NTNU, Trondheim Norway, 2011. Abstract | Links | BibTeX | Tags: Iron-Making, Lagrangian, Modelling, Multiphase, Smelt-Reduction @conference{hismeltnorway, title = {CFD simulation of bath dynamics in the HIsmelt smelt reduction vessel for iron production}, author = {Darrin W Stephens and Mandar Tabib and Mark Davis and Phil Schwarz}, doi = {10.13140/RG.2.1.4423.4082}, year = {2011}, date = {2011-06-21}, booktitle = { 8th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries, At SINTEF/NTNU, Trondheim Norway}, abstract = {CFD has played a crucial role in enabling the design and scale-up of the HIsmelt® direct smelting technology. The HIsmelt® Process is a potential replacement for blast-furnace technology owing to its efficiency, cost advantage and lower environmental impact. An existing PHOENICS-based CFD model of the molten bath dynamics in the process vessel has been transferred to ANSYS-CFX to improve its accuracy and to enable efficient analysis on an unstructured mesh. The basic model involves Lagrangian particle tracking of iron ore and coal particles through two Eulerian phases representing metal and slag. The model incorporates reactions involving coal devolatilisation, coal dissolution, and ore reduction. A sensitivity study shows that an increase in the number of particles used improves convergence, and the CFD model has been applied to study a 2.7m diameter pilot smelter.}, keywords = {Iron-Making, Lagrangian, Modelling, Multiphase, Smelt-Reduction}, pubstate = {published}, tppubtype = {conference} } CFD has played a crucial role in enabling the design and scale-up of the HIsmelt® direct smelting technology. The HIsmelt® Process is a potential replacement for blast-furnace technology owing to its efficiency, cost advantage and lower environmental impact. An existing PHOENICS-based CFD model of the molten bath dynamics in the process vessel has been transferred to ANSYS-CFX to improve its accuracy and to enable efficient analysis on an unstructured mesh. The basic model involves Lagrangian particle tracking of iron ore and coal particles through two Eulerian phases representing metal and slag. The model incorporates reactions involving coal devolatilisation, coal dissolution, and ore reduction. A sensitivity study shows that an increase in the number of particles used improves convergence, and the CFD model has been applied to study a 2.7m diameter pilot smelter. |

## 2010 |

Stephens, Darrin W; Mohanarangam, Krishna Turbulence Model Analysis of Flow inside a Hydrocyclone Journal Article Progress in Computational Fluid Dynamics, An International Journal, 10 (5/6), 2010. Abstract | Links | BibTeX | Tags: Curvature Correction, Hydrocyclones, Modelling, Stress, Turbulence @article{stephens2009turbulence, title = {Turbulence Model Analysis of Flow inside a Hydrocyclone}, author = {Darrin W Stephens and Krishna Mohanarangam}, doi = {10.1504/PCFD.2010.035370}, year = {2010}, date = {2010-01-01}, booktitle = {7th International Conference on CFD in the Minerals and Process Industries}, journal = {Progress in Computational Fluid Dynamics, An International Journal}, volume = {10}, number = {5/6}, abstract = {Turbulence analysis of flow inside a hydrocyclone is carried out using commercially available CFD software ANSYS CFX (release 11.0) (ANSYS Inc., 2007). CFD software(s) and their turbulence models have come a long way in accurately predicting the flow inside a hydrocyclone. This paper shows, among various turbulence models tested, a two-equation Shear Stress Transport (SST) turbulence model coupled with curvature correction can accurately predict the mean flow behaviour. The same level of accuracy was only found with a SSG Reynolds stress model with a penalty of solving an additional five transport equations. Experimental data of Hsieh (1988) and Monredon et al. (1992) was used to validate our CFD models. }, keywords = {Curvature Correction, Hydrocyclones, Modelling, Stress, Turbulence}, pubstate = {published}, tppubtype = {article} } Turbulence analysis of flow inside a hydrocyclone is carried out using commercially available CFD software ANSYS CFX (release 11.0) (ANSYS Inc., 2007). CFD software(s) and their turbulence models have come a long way in accurately predicting the flow inside a hydrocyclone. This paper shows, among various turbulence models tested, a two-equation Shear Stress Transport (SST) turbulence model coupled with curvature correction can accurately predict the mean flow behaviour. The same level of accuracy was only found with a SSG Reynolds stress model with a penalty of solving an additional five transport equations. Experimental data of Hsieh (1988) and Monredon et al. (1992) was used to validate our CFD models. |

## 2009 |

Mohanarangam, Krishna; Stephens, Darrin W CFD Modeling of floating and settling phases in settling tanks Conference Seventh International Conference on CFD in the Minerals and Process Industries, 2009. Abstract | Links | BibTeX | Tags: ASM, Cenospheres, Floating, Modelling, Multiphase, Oil, Phases, PVC, SST, Tanks @conference{mohanarangam2009cfd, title = {CFD Modeling of floating and settling phases in settling tanks}, author = {Krishna Mohanarangam and Darrin W Stephens}, doi = {10.13140/RG.2.1.5078.7686}, year = {2009}, date = {2009-01-01}, booktitle = {Seventh International Conference on CFD in the Minerals and Process Industries}, journal = {Seventh International Conference on CFD in the Minerals and Process Industries}, pages = {9--11}, abstract = {A Computational Fluid Dynamics (CFD) model for modelling a floating phase has been developed and tested on a settling tank. The current model used for settling tanks is able to predict the settling of solids and the formation of a higher density layer of solids at the bottom of the vessel. Due to the widespread use of settling tanks in water and other chemical industries, floating phases (cenospheres, oil, PVC, etc) form a major part of the separation process. With this in mind, a model has been developed to incorporate both the settling as well as the floating of the secondary phases. The simulations were performed by customizing the commercially available software ANSYS-CFX (release 10.0). Multi-phase simulations were performed with clay, sand and a floating solid (density less than the continuous phase) as the secondary phases. Numerical instability was encountered in the volume fraction of the floating phase at the top boundary, where the floating phase collected, when using the unmodified version of ANSYS-CFX. This was mainly due to the volume fraction tending towards unity without any gradient at the top boundary. To prevent this happening, an extra term that is ignored in the CFX implementation was included in the slip velocity calculation. This essentially sets up a volume fraction gradient of the floating phase. Two variants of particle sizes for the floating phase were used to access this phenomenon. Contour plots of the floating phase volume fraction are presented within the feedwell as well in the cross-section of the tank to depict the preferential concentration of the phase. Further results are also shown for the settling solids. NOMENCLATURE C D drag co-efficient C µ k-ε turbulence model constant C ε1-2 k-ε turbulence model constant d diameter g acceleration due to gravity k Turbulence Kinetic Energy (T.K.E) p pressure r solids fraction Re Reynolds number Sc t Turbulent Schmidt number S1-S2 Diameter of floating species t time U velocity Y mass fraction x,y,z cartesion co-ordinate system ε turbulence dissipation rate μ dynamic viscosity eff}, keywords = {ASM, Cenospheres, Floating, Modelling, Multiphase, Oil, Phases, PVC, SST, Tanks}, pubstate = {published}, tppubtype = {conference} } A Computational Fluid Dynamics (CFD) model for modelling a floating phase has been developed and tested on a settling tank. The current model used for settling tanks is able to predict the settling of solids and the formation of a higher density layer of solids at the bottom of the vessel. Due to the widespread use of settling tanks in water and other chemical industries, floating phases (cenospheres, oil, PVC, etc) form a major part of the separation process. With this in mind, a model has been developed to incorporate both the settling as well as the floating of the secondary phases. The simulations were performed by customizing the commercially available software ANSYS-CFX (release 10.0). Multi-phase simulations were performed with clay, sand and a floating solid (density less than the continuous phase) as the secondary phases. Numerical instability was encountered in the volume fraction of the floating phase at the top boundary, where the floating phase collected, when using the unmodified version of ANSYS-CFX. This was mainly due to the volume fraction tending towards unity without any gradient at the top boundary. To prevent this happening, an extra term that is ignored in the CFX implementation was included in the slip velocity calculation. This essentially sets up a volume fraction gradient of the floating phase. Two variants of particle sizes for the floating phase were used to access this phenomenon. Contour plots of the floating phase volume fraction are presented within the feedwell as well in the cross-section of the tank to depict the preferential concentration of the phase. Further results are also shown for the settling solids. NOMENCLATURE C D drag co-efficient C µ k-ε turbulence model constant C ε1-2 k-ε turbulence model constant d diameter g acceleration due to gravity k Turbulence Kinetic Energy (T.K.E) p pressure r solids fraction Re Reynolds number Sc t Turbulent Schmidt number S1-S2 Diameter of floating species t time U velocity Y mass fraction x,y,z cartesion co-ordinate system ε turbulence dissipation rate μ dynamic viscosity eff |

## 2006 |

Rackemann, Darryn W; Broadfoot, Ross; Stephens, Darrin W Improved CFD modelling of natural circulation vacuum pans Inproceedings Australian Society of Sugar Cane Technologists, pp. 462, 2006. Abstract | Links | BibTeX | Tags: Circulation, Heat Transfer, Modelling, Performance, Simulation, Vacuum Pan, Validation @inproceedings{rackemann2006improved, title = {Improved CFD modelling of natural circulation vacuum pans}, author = {Darryn W Rackemann and Ross Broadfoot and Darrin W Stephens}, doi = {10.13140/RG.2.1.1867.5046}, year = {2006}, date = {2006-01-01}, booktitle = {Australian Society of Sugar Cane Technologists}, journal = {PROCEEDINGS-AUSTRALIAN SOCIETY OF SUGAR CANE TECHNOLOGISTS}, volume = {28}, pages = {462}, abstract = {Numerical and especially CFD modelling are becoming cost-effective and reliable ways to develop improvements in vessel designs. Simulating boiling in crystallisation vacuum pans is a very complex process that needs to consider non-isothermal conditions, multi-component, multiphase boiling and condensation. This level of complexity which has been captured in the SRI CFD model was previously too complicated for most CFD software. With improvements to the software, these complex physical processes can now be modelled, albeit a little cumbersomely. This paper details the development of CFD models to predict the circulation patterns and heat transfer occurring in natural circulation crystallisation vacuum pans. Model validation involved checking the circulation velocities predicted by the CFD model with circulation velocity data measured on factory pans. The predictions were in reasonable agreement with factory measurements. The validated CFD model was used to investigate the effect of altering key dimensions on batch pans and on two different continuous pan designs. The batch pan investigations included: • Increasing the volumetric region above the calandria by flaring the pan body; • Reducing the clearance underneath the calandria; and • Changing the dimensions of the tubes (tube diameter and length) while maintaining the same heat transfer area and keeping the evaporation rate constant. The effect of variations in pan geometry, massecuite viscosity and operating level above the calandria were considered for the batch pan simulations. These results provide interesting insight into the complicated processes involved in the operation of natural circulation vacuum pans.}, keywords = {Circulation, Heat Transfer, Modelling, Performance, Simulation, Vacuum Pan, Validation}, pubstate = {published}, tppubtype = {inproceedings} } Numerical and especially CFD modelling are becoming cost-effective and reliable ways to develop improvements in vessel designs. Simulating boiling in crystallisation vacuum pans is a very complex process that needs to consider non-isothermal conditions, multi-component, multiphase boiling and condensation. This level of complexity which has been captured in the SRI CFD model was previously too complicated for most CFD software. With improvements to the software, these complex physical processes can now be modelled, albeit a little cumbersomely. This paper details the development of CFD models to predict the circulation patterns and heat transfer occurring in natural circulation crystallisation vacuum pans. Model validation involved checking the circulation velocities predicted by the CFD model with circulation velocity data measured on factory pans. The predictions were in reasonable agreement with factory measurements. The validated CFD model was used to investigate the effect of altering key dimensions on batch pans and on two different continuous pan designs. The batch pan investigations included: • Increasing the volumetric region above the calandria by flaring the pan body; • Reducing the clearance underneath the calandria; and • Changing the dimensions of the tubes (tube diameter and length) while maintaining the same heat transfer area and keeping the evaporation rate constant. The effect of variations in pan geometry, massecuite viscosity and operating level above the calandria were considered for the batch pan simulations. These results provide interesting insight into the complicated processes involved in the operation of natural circulation vacuum pans. |

Trang, Simon CT; Stephens, Darrin W; Schwarz, Phil Modelling heat transfer in the dripper zone of a heap leaching operation Conference Fifth International Conference on CFD in the Process Industries, 2006. Abstract | Links | BibTeX | Tags: Heat Transfer, Leaching, Modelling, Solver @conference{trang2006modelling, title = {Modelling heat transfer in the dripper zone of a heap leaching operation}, author = {Simon CT Trang and Darrin W Stephens and Phil Schwarz}, doi = {10.13140/RG.2.1.1343.2167}, year = {2006}, date = {2006-01-01}, booktitle = {Fifth International Conference on CFD in the Process Industries}, journal = {a a}, abstract = {A computational fluid dynamics (CFD) solver ANSYS- CFX is used to model the heat transfer in the region near the surface of a leach heap when drippers are buried. The potential for natural convection to occur above the dripper level, thus substantially increasing heat loss from the heap, is investigated. A parameter analysis is performed which shows that the factors that may be important to the initiation of natural convection are permeability, the depth at which the drippers are buried and the space between each dripper. The current study shows that permeability is the only parameter which has a profound effect on heat loss by natural convection. }, keywords = {Heat Transfer, Leaching, Modelling, Solver}, pubstate = {published}, tppubtype = {conference} } A computational fluid dynamics (CFD) solver ANSYS- CFX is used to model the heat transfer in the region near the surface of a leach heap when drippers are buried. The potential for natural convection to occur above the dripper level, thus substantially increasing heat loss from the heap, is investigated. A parameter analysis is performed which shows that the factors that may be important to the initiation of natural convection are permeability, the depth at which the drippers are buried and the space between each dripper. The current study shows that permeability is the only parameter which has a profound effect on heat loss by natural convection. |

Jemcov, Aleksandar; Jojic, Branimir Numerical Modeling of Combustion Instability in Rijke Tube Inproceedings CFD2006 CFD Society of Canada, CFD Society of Canada 2006. Abstract | Links | BibTeX | Tags: Combustion, Modelling, Rijke Tube @inproceedings{jemcov2006numerical, title = {Numerical Modeling of Combustion Instability in Rijke Tube}, author = { Aleksandar Jemcov and Branimir Jojic}, url = {https://www.researchgate.net/profile/Aleksandar_Jemcov/publication/265160842_Numerical_Modeling_of_Combustion_Instability_in_Rijke_Tubes/links/54009ec70cf2bba34c1a4f59.pdf?origin=publication_detail_rebranded&ev=pub_int_prw_xdl&msrp=qXvYaIM1NoaBwk22r3y7phomPdDKE1ybkMDPT6xQ6n7Gc6pSIC4e1VsVMR1ejNnMKtqgjwyg0q1a1AjIKzLbLg%3D%3D_5yTaQFK%2B%2FOwiX4OawttpSFVDsxGtrkqmBqvsoX6MESNK8PqdP70ULOlxLqfRHb4GZ0okByXELkL%2FpSt%2FcikNWw%3D%3D}, year = {2006}, date = {2006-01-01}, booktitle = {CFD2006 CFD Society of Canada}, organization = {CFD Society of Canada}, abstract = {Numerical modeling of combustion instability in Rijke tubes and the development of a new physical model for the fluctuating chemical reaction source term in the energy equation is the main focus of this paper. Although physical and numerical combustion instability model was developed and tested on Rijke tube, the final goal of this work is to develop the model that can be used for combustion instability simulation in rocket and air breathing jet engines. The approach taken here consists of the decomposition of the governing equations into a mean flow field equation that contains turbulence and chemical reaction terms, and a perturbation equation that contains nonlinear acoustic and interaction terms responsible for coupling between mean and perturbed flow. The resulting set of equations consists of the Navier-Stokes equations that describe mean flow, and nonlinear acoustic equations that describe perturbed flow. The nonlinear acoustic equations contain spatially varying coefficients whose values are determined by the mean flow. In addition, the nonlinear acoustic equations contain a forcing term that is a perturbation of the chemical reactions source term from the energy equation. This term together with spatially varying coefficients represents coupling between the mean and nonlinear acoustic fields. A new form of the forcing term that models coupling of fluctuations in the pressure field with fluctuations in energy release due to chemical reactions is proposed here. The basis of this model is in the evaporation rate controlled combustion mechanism that was singled out by time scale analysis and validated by numerical experiments of combustion instability in a Rijke tube with n-decane fuel. Results of the numerical simulations show the crucial role of the nonlinear nature of the fluctuating forcing term in the appearance of instabilities.}, keywords = {Combustion, Modelling, Rijke Tube}, pubstate = {published}, tppubtype = {inproceedings} } Numerical modeling of combustion instability in Rijke tubes and the development of a new physical model for the fluctuating chemical reaction source term in the energy equation is the main focus of this paper. Although physical and numerical combustion instability model was developed and tested on Rijke tube, the final goal of this work is to develop the model that can be used for combustion instability simulation in rocket and air breathing jet engines. The approach taken here consists of the decomposition of the governing equations into a mean flow field equation that contains turbulence and chemical reaction terms, and a perturbation equation that contains nonlinear acoustic and interaction terms responsible for coupling between mean and perturbed flow. The resulting set of equations consists of the Navier-Stokes equations that describe mean flow, and nonlinear acoustic equations that describe perturbed flow. The nonlinear acoustic equations contain spatially varying coefficients whose values are determined by the mean flow. In addition, the nonlinear acoustic equations contain a forcing term that is a perturbation of the chemical reactions source term from the energy equation. This term together with spatially varying coefficients represents coupling between the mean and nonlinear acoustic fields. A new form of the forcing term that models coupling of fluctuations in the pressure field with fluctuations in energy release due to chemical reactions is proposed here. The basis of this model is in the evaporation rate controlled combustion mechanism that was singled out by time scale analysis and validated by numerical experiments of combustion instability in a Rijke tube with n-decane fuel. Results of the numerical simulations show the crucial role of the nonlinear nature of the fluctuating forcing term in the appearance of instabilities. |

Rackemann, Darryn W; Plaza, Floren; Stephens, Darrin W Steam side calandria modelling of vacuum pans and evaporators Conference Australian Society of Sugar Cane Technologists, 28 , 2006. Abstract | Links | BibTeX | Tags: Calandria, Heat Transfer, Modelling, Steam Flow, Vacuum Pan @conference{rackemann2006steam, title = {Steam side calandria modelling of vacuum pans and evaporators}, author = {Darryn W Rackemann and Floren Plaza and Darrin W Stephens}, doi = {10.13140/RG.2.1.2916.0801}, year = {2006}, date = {2006-01-01}, booktitle = {Australian Society of Sugar Cane Technologists}, journal = {PROCEEDINGS-AUSTRALIAN SOCIETY OF SUGAR CANE TECHNOLOGISTS}, volume = {28}, abstract = {The heat transfer and condensation of steam within the steam belt and the steam chest surrounding the calandria tubes of vacuum pans and evaporators were investigated using computational fluid dynamics (CFD) modelling techniques. The flow of steam in evaporators and vacuum pans is an aspect that is not usually given much attention but it can influence the productivity of these vessels. The latent heat of the steam provides the heat to the juice or massecuite which induces the formation of vapour bubbles and drives the circulation of the fluid within the vessel. Strong and uniform circulation of the massecuite in vacuum pans increases the production capacity and improves the quality of the sugar produced. Non-uniform heating by the steam on the outside of the calandria tubes can contribute to uneven and inconsistent heat transfer to the juice or massecuite within the vessel. As a consequence under these circumstances the installed heating surface is not effectively utilised. Inconsistent heating can affect the performance of vacuum pans since it influences the circulation of massecuite and the crystallisation rate of sugar. The CFD modelling investigation into the steam side operation of the calandria of vacuum pans and evaporators was preliminary in nature but has shown promising results. The results of the CFD simulations were compared against measured data to determine the applicability of the CFD model. The condensation physics of the CFD model currently has limitations, yet despite these, the CFD model has identified some deficiencies in the flow of steam within the calandria. The investigations into different geometries for steam flow into evaporators and vacuum pans and the results of CFD simulations are detailed and discussed. Some of the proposed modifications resulted in predicted improvements to the distribution of steam within the calandria. }, keywords = {Calandria, Heat Transfer, Modelling, Steam Flow, Vacuum Pan}, pubstate = {published}, tppubtype = {conference} } The heat transfer and condensation of steam within the steam belt and the steam chest surrounding the calandria tubes of vacuum pans and evaporators were investigated using computational fluid dynamics (CFD) modelling techniques. The flow of steam in evaporators and vacuum pans is an aspect that is not usually given much attention but it can influence the productivity of these vessels. The latent heat of the steam provides the heat to the juice or massecuite which induces the formation of vapour bubbles and drives the circulation of the fluid within the vessel. Strong and uniform circulation of the massecuite in vacuum pans increases the production capacity and improves the quality of the sugar produced. Non-uniform heating by the steam on the outside of the calandria tubes can contribute to uneven and inconsistent heat transfer to the juice or massecuite within the vessel. As a consequence under these circumstances the installed heating surface is not effectively utilised. Inconsistent heating can affect the performance of vacuum pans since it influences the circulation of massecuite and the crystallisation rate of sugar. The CFD modelling investigation into the steam side operation of the calandria of vacuum pans and evaporators was preliminary in nature but has shown promising results. The results of the CFD simulations were compared against measured data to determine the applicability of the CFD model. The condensation physics of the CFD model currently has limitations, yet despite these, the CFD model has identified some deficiencies in the flow of steam within the calandria. The investigations into different geometries for steam flow into evaporators and vacuum pans and the results of CFD simulations are detailed and discussed. Some of the proposed modifications resulted in predicted improvements to the distribution of steam within the calandria. |

## 2001 |

Stephens, Darrin W Studies on modelling circulation in sugar vacuum pans PhD Thesis James Cook University, 2001. Abstract | Links | BibTeX | Tags: Axi-Symmetric, Calandria, Circulation, Flow, Heat Transfer, Mass Flow Rate, Model, Modelling, Quasi-Static, Saturation, Vacuum Pan @phdthesis{stephens2001studies, title = {Studies on modelling circulation in sugar vacuum pans}, author = {Darrin W Stephens}, doi = {10.13140/RG.2.1.4325.1048}, year = {2001}, date = {2001-01-01}, school = {James Cook University}, abstract = {This thesis presents an investigation into mathematical modelling of natural circulation in high grade batch vacuum pans. Batch vacuum pans are an important part of a sugar factory, with the circulation in such vessels being a key factor in successful sucrose extraction. The flow within a batch vacuum pan is laminar with three phases (molasses, crystal and vapour) present, and is driven by buoyancy, which results from vapour formation due to boiling. Numerical modelling of natural circulation in batch vacuum pans has been limited in the past by computational power and available computer software, and has suffered from the necessity for very restrictive assumptions to make modelling possible. The thesis uses computational fluid dynamics (CFD) as a tool to develop an improved batch vacuum pan model to investigate the detailed distribution of velocity and temperature within a batch vacuum pan at various stages throughout the strike. A segmented modelling approach has been developed where the vacuum pan is divided into two segments: the space inside the calandria tubes (the calandria tube segment), and the remaining part consisting of a downtake and the space above and below the calandria (the external flow segment). The external flow segment is modelled using the standard CFD approach, whereas the calandria tube segment is represented by a one-dimensional finite volume model. The two segments are coupled together to obtain the overall model of the entire vacuum pan. The calandria tube segment is the key to the vacuum pan model as the majority of the driving force for natural circulation is developed from the vapour formed due to boiling within the calandria tubes. The one-dimensional constant wall temperature tube model developed within this thesis demonstrates, for most parameters, reasonable agreement with previous experimental data. The tube model results have been presented in the form of characteristic curves showing pressure difference, heat transfer and evaporation rate as functions of mass flow rate. These curves provide a new insight into the boiling process within calandria tubes. Improvement of the one-dimensional model predictions would require more experimental data pertaining to the volume fraction distribution in the axial and radial directions, as well as an improved correlation for the boiling heat transfer coefficient. Quasi-static, two-dimensional, axi-symmetric CFD simulations of the vacuum pan were performed for three discrete levels of filling, representing the start, middle and end of the batch process. It was found that the magnitude of the flow speed through the tubes decreases drastically with increasing level within the vacuum pan. This reduction has two causes: first, the effect of increased viscosity with increasing head; and second the effect of the increased boiling point with increasing head. Both of these effects combine to give a much lower heat transfer rate within the tubes, thus producing less vapour to drive the flow. As the head above the calandria increases, the size, strength and existence of recirculation zones also increases. These recirculation zones do not provide any assistance in circulating the flow through the tubes. The simulations provide an improved understanding of the mechanisms producing natural circulation and allow suggestions of possible improvements to vacuum pan designs. With the large change in fluid viscosity from start to finish of the boiling process, combined with the change in saturation profile due to the increasing head, it is difficult to conceive a batch vacuum pan design that will operate at the maximum heat transfer and evaporation point for all times during the strike. The model developed produces a preliminary tool for analysis of vacuum pan operation, and may be applied to both batch and continuous pans. The segmented modelling approach, which is a novel contribution of this work, also provides a framework for future model improvements as new experimental data becomes available.}, keywords = {Axi-Symmetric, Calandria, Circulation, Flow, Heat Transfer, Mass Flow Rate, Model, Modelling, Quasi-Static, Saturation, Vacuum Pan}, pubstate = {published}, tppubtype = {phdthesis} } This thesis presents an investigation into mathematical modelling of natural circulation in high grade batch vacuum pans. Batch vacuum pans are an important part of a sugar factory, with the circulation in such vessels being a key factor in successful sucrose extraction. The flow within a batch vacuum pan is laminar with three phases (molasses, crystal and vapour) present, and is driven by buoyancy, which results from vapour formation due to boiling. Numerical modelling of natural circulation in batch vacuum pans has been limited in the past by computational power and available computer software, and has suffered from the necessity for very restrictive assumptions to make modelling possible. The thesis uses computational fluid dynamics (CFD) as a tool to develop an improved batch vacuum pan model to investigate the detailed distribution of velocity and temperature within a batch vacuum pan at various stages throughout the strike. A segmented modelling approach has been developed where the vacuum pan is divided into two segments: the space inside the calandria tubes (the calandria tube segment), and the remaining part consisting of a downtake and the space above and below the calandria (the external flow segment). The external flow segment is modelled using the standard CFD approach, whereas the calandria tube segment is represented by a one-dimensional finite volume model. The two segments are coupled together to obtain the overall model of the entire vacuum pan. The calandria tube segment is the key to the vacuum pan model as the majority of the driving force for natural circulation is developed from the vapour formed due to boiling within the calandria tubes. The one-dimensional constant wall temperature tube model developed within this thesis demonstrates, for most parameters, reasonable agreement with previous experimental data. The tube model results have been presented in the form of characteristic curves showing pressure difference, heat transfer and evaporation rate as functions of mass flow rate. These curves provide a new insight into the boiling process within calandria tubes. Improvement of the one-dimensional model predictions would require more experimental data pertaining to the volume fraction distribution in the axial and radial directions, as well as an improved correlation for the boiling heat transfer coefficient. Quasi-static, two-dimensional, axi-symmetric CFD simulations of the vacuum pan were performed for three discrete levels of filling, representing the start, middle and end of the batch process. It was found that the magnitude of the flow speed through the tubes decreases drastically with increasing level within the vacuum pan. This reduction has two causes: first, the effect of increased viscosity with increasing head; and second the effect of the increased boiling point with increasing head. Both of these effects combine to give a much lower heat transfer rate within the tubes, thus producing less vapour to drive the flow. As the head above the calandria increases, the size, strength and existence of recirculation zones also increases. These recirculation zones do not provide any assistance in circulating the flow through the tubes. The simulations provide an improved understanding of the mechanisms producing natural circulation and allow suggestions of possible improvements to vacuum pan designs. With the large change in fluid viscosity from start to finish of the boiling process, combined with the change in saturation profile due to the increasing head, it is difficult to conceive a batch vacuum pan design that will operate at the maximum heat transfer and evaporation point for all times during the strike. The model developed produces a preliminary tool for analysis of vacuum pan operation, and may be applied to both batch and continuous pans. The segmented modelling approach, which is a novel contribution of this work, also provides a framework for future model improvements as new experimental data becomes available. |

## 2000 |

McBain, Geordie D; Stephens, Darrin W Low Grash of number convective heat transfer across a spherical cavity Inproceedings Proc. of the 7th Australasian Heat and Mass Transfer Conference, 2000. Abstract | Links | BibTeX | Tags: Cavity, Flow, Grashof, Heat Transfer, Model, Modelling, Temperature @inproceedings{mcbain2000low, title = {Low Grash of number convective heat transfer across a spherical cavity}, author = {Geordie D McBain and Darrin W Stephens}, doi = {10.13140/RG.2.1.4194.0324}, year = {2000}, date = {2000-01-01}, booktitle = {Proc. of the 7th Australasian Heat and Mass Transfer Conference}, abstract = {The increase in heat transfer rate across a spherical fluid-filled cavity embedded in a highly conducting solid with a horizontal temperature gradient is investigated analytically and numerically. Analytically, the low Grashof number asymptotic expansion is extended to second-order for the temperature field. This provides the lowest order correction to the overall Nusselt number. This prediction and the associated flow and temperature fields are compared with specially obtained numerical solutions of the full nonlinear equations. Agreement is excellent for Rayleigh numbers less than a few thousand.}, keywords = {Cavity, Flow, Grashof, Heat Transfer, Model, Modelling, Temperature}, pubstate = {published}, tppubtype = {inproceedings} } The increase in heat transfer rate across a spherical fluid-filled cavity embedded in a highly conducting solid with a horizontal temperature gradient is investigated analytically and numerically. Analytically, the low Grashof number asymptotic expansion is extended to second-order for the temperature field. This provides the lowest order correction to the overall Nusselt number. This prediction and the associated flow and temperature fields are compared with specially obtained numerical solutions of the full nonlinear equations. Agreement is excellent for Rayleigh numbers less than a few thousand. |

## 1999 |

Stephens, Darrin W; Harris, Jonathan A Modelling convective boiling of molasses Conference 2nd International Conference on CFD in the Minerals and Processing Industries, CSIRO, Melbourne, Australia, 1999. Abstract | Links | BibTeX | Tags: Boiling, Flow, Heat Transfer, Model, Modelling, ODE, Pressure, Two-Phase @conference{stephens1999modelling, title = {Modelling convective boiling of molasses}, author = {Darrin W Stephens and Jonathan A Harris}, doi = {10.13140/RG.2.1.2359.0242}, year = {1999}, date = {1999-01-01}, booktitle = {2nd International Conference on CFD in the Minerals and Processing Industries, CSIRO, Melbourne, Australia}, abstract = {One-and two-dimensional numerical models of forced convective boiling of molasses in a calandria tube are described. The flow in the tube is considered to be composed of two phases (molasses and steam). The one-dimensional model solves a simplified set of ODEs describing the non-equilibrium boiling process. The two-dimensional model is based on the Eulerian/Eulerian multi-phase approach as implemented in the CFX-4.2 CFD code, and solves for the distribution of volume fraction and the temperature and velocity of each phase, along with global parameters such as pressure drop and evaporation rate. Solutions are presented for a case with similar conditions to those expected in a batch vacuum pan. The results show that the flow in the tube is complex and multi-dimensional. Vapour forms both at the wall (due to direct heating) as well as in the centre (due to bulk boiling). The observed features of the flow from the numerical simulation are qualitatively similar to available experimental observations made by previous investigators, although quantitative agreement has yet to be achieved.}, keywords = {Boiling, Flow, Heat Transfer, Model, Modelling, ODE, Pressure, Two-Phase}, pubstate = {published}, tppubtype = {conference} } One-and two-dimensional numerical models of forced convective boiling of molasses in a calandria tube are described. The flow in the tube is considered to be composed of two phases (molasses and steam). The one-dimensional model solves a simplified set of ODEs describing the non-equilibrium boiling process. The two-dimensional model is based on the Eulerian/Eulerian multi-phase approach as implemented in the CFX-4.2 CFD code, and solves for the distribution of volume fraction and the temperature and velocity of each phase, along with global parameters such as pressure drop and evaporation rate. Solutions are presented for a case with similar conditions to those expected in a batch vacuum pan. The results show that the flow in the tube is complex and multi-dimensional. Vapour forms both at the wall (due to direct heating) as well as in the centre (due to bulk boiling). The observed features of the flow from the numerical simulation are qualitatively similar to available experimental observations made by previous investigators, although quantitative agreement has yet to be achieved. |

## 1998 |

Stephens, Darrin W; Harris, Jonathan A Numerical modelling of two-phase flow a benchmark solution Conference Australasian Fluid Mechanics Conference, 13 , 1998. Abstract | Links | BibTeX | Tags: Eulerian, Flow, Heat Transfer, MATLAB, Model, Modelling, Multiphase, ODE, Two-Phase @conference{stephens1998numerical, title = {Numerical modelling of two-phase flow a benchmark solution}, author = {Darrin W Stephens and Jonathan A Harris}, doi = {10.13140/RG.2.1.2621.1681}, year = {1998}, date = {1998-01-01}, booktitle = {Australasian Fluid Mechanics Conference}, journal = {continuity}, volume = {13}, abstract = {This paper explores a simple test problem that can be used for the validation of Eulerian two-phase flow CFD models. Validation results are presented for a commercial CFD code with multi-phase flow capability, namely CFX-4.2, produced by AEA Technology. The results show that CFX-4.2 exhibits virtually perfect agreement with all 12 test cases over a full range of input parameters using a very moderate mesh.}, keywords = {Eulerian, Flow, Heat Transfer, MATLAB, Model, Modelling, Multiphase, ODE, Two-Phase}, pubstate = {published}, tppubtype = {conference} } This paper explores a simple test problem that can be used for the validation of Eulerian two-phase flow CFD models. Validation results are presented for a commercial CFD code with multi-phase flow capability, namely CFX-4.2, produced by AEA Technology. The results show that CFX-4.2 exhibits virtually perfect agreement with all 12 test cases over a full range of input parameters using a very moderate mesh. |