Modelling of a heated gas-solid fluidised bed using Eulerian based models
- Potgieter, Alicia, Bhamjee, Muaaz, Kruger, Sunita
- Authors: Potgieter, Alicia , Bhamjee, Muaaz , Kruger, Sunita
- Date: 2021
- Subjects: Heated fluidised bed , Computational fluid dynamics , Eulerian
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/488427 , uj:44496 , Citation: Potgieter, A., Bhamjee, M., & Kruger, S.. (2021). Modelling of a Heated Gas-solid Fluidised Bed using Eulerian Based Models. R&D Journal, 37, 45-57. https://dx.doi.org/10.17159/2309-8988/2021/v37a6 , DOI: 10.17159/2309-8988/2021/v37a6
- Description: Abstract: Please refer to full text to view abstract.
- Full Text:
- Authors: Potgieter, Alicia , Bhamjee, Muaaz , Kruger, Sunita
- Date: 2021
- Subjects: Heated fluidised bed , Computational fluid dynamics , Eulerian
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/488427 , uj:44496 , Citation: Potgieter, A., Bhamjee, M., & Kruger, S.. (2021). Modelling of a Heated Gas-solid Fluidised Bed using Eulerian Based Models. R&D Journal, 37, 45-57. https://dx.doi.org/10.17159/2309-8988/2021/v37a6 , DOI: 10.17159/2309-8988/2021/v37a6
- Description: Abstract: Please refer to full text to view abstract.
- Full Text:
Coal combustion models: a review
- Marangwanda, G. T., Madyira, D. M., Babarinde, T. O.
- Authors: Marangwanda, G. T. , Madyira, D. M. , Babarinde, T. O.
- Date: 2019
- Subjects: Coal , Combusion , Computational fluid dynamics
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/406660 , uj:34199 , Citation: Marangwanda, G.T., Madyira, D.M., Babarinde, T.O. 2019 : Coal combustion models: a review. DOI: 10.1088/1742-6596/1378/3/032070.
- Description: Abstract : Computational Fluid Dynamics has been used for optimisation of industrial applications with some level of success. The modest accuracy provided by some of the combustion models in use has left some room for research and improvement. Coal is presented as a fuel with complex chemical properties due to its fossil fuel nature. The devolatilization process of coal is investigated with special attention to the best models that can handle heavy and light volatiles found in coal. The heterogenous char combustion is also presented paying attention to the nature of the char particle during the combustion process. The other processes such as drying, homogenous volatile combustion, radiation models, particle tracking models and turbulent models are investigated in a general manner as they rarely vary with the type of fuel being investigated. A summary of the industrial applications that have successfully utilised the CFD models for optimisation of coal combustion are presented thus helping in drawing the final conclusion.
- Full Text:
- Authors: Marangwanda, G. T. , Madyira, D. M. , Babarinde, T. O.
- Date: 2019
- Subjects: Coal , Combusion , Computational fluid dynamics
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/406660 , uj:34199 , Citation: Marangwanda, G.T., Madyira, D.M., Babarinde, T.O. 2019 : Coal combustion models: a review. DOI: 10.1088/1742-6596/1378/3/032070.
- Description: Abstract : Computational Fluid Dynamics has been used for optimisation of industrial applications with some level of success. The modest accuracy provided by some of the combustion models in use has left some room for research and improvement. Coal is presented as a fuel with complex chemical properties due to its fossil fuel nature. The devolatilization process of coal is investigated with special attention to the best models that can handle heavy and light volatiles found in coal. The heterogenous char combustion is also presented paying attention to the nature of the char particle during the combustion process. The other processes such as drying, homogenous volatile combustion, radiation models, particle tracking models and turbulent models are investigated in a general manner as they rarely vary with the type of fuel being investigated. A summary of the industrial applications that have successfully utilised the CFD models for optimisation of coal combustion are presented thus helping in drawing the final conclusion.
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The fluid flow effect on the inlet injection of the thin film deposition in a square type atomic layer deposition reactor
- Coetzee, Rigardt Alfred Maarten, Lu, Hongliang, Jen, Tien-Chien
- Authors: Coetzee, Rigardt Alfred Maarten , Lu, Hongliang , Jen, Tien-Chien
- Date: 2019
- Subjects: Nanotechnology , Atomic layer deposition , Computational fluid dynamics
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/400082 , uj:33374 , Citation: Coetzee, R.A.M., Lu, H., & Jen, T.C. 2019. The fluid flow effect on the inlet injection of the thin film deposition in a square type atomic layer deposition reactor.
- Description: Abstract: In recent years, industry is ever striving to deposit optimal thin films on Nano devices. This strive led to interest in utilising advance Nano-manufacturing techniques that can fabricate ever-decreasing scale products along with films that provide highly uniform, conformal, and pin-hole free quality thin films. Atomic layer deposition provides a technique that fulfil these requirements. However, the understanding of the deposition process within the fabrication of these thin films are still greatly not well-known. The fluid flow patterns and distributions within the atomic layer deposition reactors are rarely investigated and lacks the fluid flow effect incorporated along with the deposition process near the substrate. Per se, these effects due to the geometrical effect of the inlet injection location from the deposited substrate of a square type Gemstar Reactor is investigated. The findings reveal the inlet flow effect, near substrate flow behaviour, and optimal selection for the deposition of aluminium oxide (Al2O3) thin film. The study simulates the fluid flow properties along with the chemical kinetics by utilizing computational fluid dynamics incorporated within ANSYS Fluent Software. The flow and surface reaction of Trimethylaluminium and Ozone as precursors, along with Argon as the purging substance, are incorporated within the atomic layer deposition sequence. The findings reveal close similarities to that of previous literature.
- Full Text:
- Authors: Coetzee, Rigardt Alfred Maarten , Lu, Hongliang , Jen, Tien-Chien
- Date: 2019
- Subjects: Nanotechnology , Atomic layer deposition , Computational fluid dynamics
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/400082 , uj:33374 , Citation: Coetzee, R.A.M., Lu, H., & Jen, T.C. 2019. The fluid flow effect on the inlet injection of the thin film deposition in a square type atomic layer deposition reactor.
- Description: Abstract: In recent years, industry is ever striving to deposit optimal thin films on Nano devices. This strive led to interest in utilising advance Nano-manufacturing techniques that can fabricate ever-decreasing scale products along with films that provide highly uniform, conformal, and pin-hole free quality thin films. Atomic layer deposition provides a technique that fulfil these requirements. However, the understanding of the deposition process within the fabrication of these thin films are still greatly not well-known. The fluid flow patterns and distributions within the atomic layer deposition reactors are rarely investigated and lacks the fluid flow effect incorporated along with the deposition process near the substrate. Per se, these effects due to the geometrical effect of the inlet injection location from the deposited substrate of a square type Gemstar Reactor is investigated. The findings reveal the inlet flow effect, near substrate flow behaviour, and optimal selection for the deposition of aluminium oxide (Al2O3) thin film. The study simulates the fluid flow properties along with the chemical kinetics by utilizing computational fluid dynamics incorporated within ANSYS Fluent Software. The flow and surface reaction of Trimethylaluminium and Ozone as precursors, along with Argon as the purging substance, are incorporated within the atomic layer deposition sequence. The findings reveal close similarities to that of previous literature.
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Experimental investigation and CFD modelling of laser metal deposited hybrid coating on grade five titanium alloy
- Authors: Gharehbaghi, Rezvan
- Date: 2018
- Subjects: Titanium alloys , Metal coating , Pulsed laser deposition , Computational fluid dynamics
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284286 , uj:30697
- Description: M.Ing. (Mechanical Engineering) , Abstract: The aim of this research project is to investigate the effect of laser deposited hybrid coatings (Al-Cu-Fe) on the physical, mechanical and metallurgical properties of titanium alloy (Ti-6Al-4V) by experimental techniques and numerical analysis. Laser Additive Manufacturing is relatively new in the manufacturing industry. Laser metal deposition (LMD) can be used to manufacture freeform shapes, to produce parts from graded porous to fully dense solid structures as well as to directly create various surface coatings on a part. This investigation also enhances the mechanical and corrosion properties of hybrid coatings of Al-Cu-Fe on Ti-6Al-4V alloy applicable in the aerospace industry through LMD technique. Icosahedral Al-Cu-Fe as quasicrystals are a relatively new class of materials which exhibit unusual atomic structure with useful physical and chemical properties. Ti6Al4V/Al-Cu-Fe composites were analysed using optical microscopy, scanning electron microscopy (SEM) with energy dispersive microscopy (EDS), indentation testing, x-ray diffraction (XRD) analysis. The hardness and wear resistance performances of the laser coatings were examined by high diamond dura scan microhardness tester and CERT UMT-2 reciprocating sliding machine. The anti-corrosion performances were evaluated by linear polarization technique in 3.5 M NaCl. It was found that the geometrical properties (deposit width and height, heat affected zone (HAZ) height), dilution rate, aspect ratio and powder efficiency of each sample remarkably increased with increasing laser power due to the laser-material interaction. However, the geometrical properties decrease with increasing scanning speed. Solidification began with formation of some large particles such as Al and Fe. The atomic migration of Cu into Ti lattice resulted in the formation of β-Ti phase during cooling and travels a longer distance in the Ti lattice than other elements which opens more crystallographic structure of the β matrix. It was observed that there was higher number of titanium and aluminium presented in the composite as per the theoretical expectation. The indentation testing reveals that Ti6Al4V/Al-Cu-5Fe composite has the highest mean hardness value and it decreases with increasing laser power at scanning speed of 0.8 m/min and 1 m/min. The corrosion and wear resistance of titanium alloy was improved by depositing Al-Cu-Fe quasicrystalline coating. The results obtained from numerical simulation using CFD analysis demonstrated that Ti6Al4V/Al-Cu-10Fe has the highest dilution rate, aspect ratio and HAZ height, and this corresponded with the experimental results. Finally, it was found that Ti6Al4V/Al-Cu-Fe composite have useful mechanical, physical and...
- Full Text:
- Authors: Gharehbaghi, Rezvan
- Date: 2018
- Subjects: Titanium alloys , Metal coating , Pulsed laser deposition , Computational fluid dynamics
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284286 , uj:30697
- Description: M.Ing. (Mechanical Engineering) , Abstract: The aim of this research project is to investigate the effect of laser deposited hybrid coatings (Al-Cu-Fe) on the physical, mechanical and metallurgical properties of titanium alloy (Ti-6Al-4V) by experimental techniques and numerical analysis. Laser Additive Manufacturing is relatively new in the manufacturing industry. Laser metal deposition (LMD) can be used to manufacture freeform shapes, to produce parts from graded porous to fully dense solid structures as well as to directly create various surface coatings on a part. This investigation also enhances the mechanical and corrosion properties of hybrid coatings of Al-Cu-Fe on Ti-6Al-4V alloy applicable in the aerospace industry through LMD technique. Icosahedral Al-Cu-Fe as quasicrystals are a relatively new class of materials which exhibit unusual atomic structure with useful physical and chemical properties. Ti6Al4V/Al-Cu-Fe composites were analysed using optical microscopy, scanning electron microscopy (SEM) with energy dispersive microscopy (EDS), indentation testing, x-ray diffraction (XRD) analysis. The hardness and wear resistance performances of the laser coatings were examined by high diamond dura scan microhardness tester and CERT UMT-2 reciprocating sliding machine. The anti-corrosion performances were evaluated by linear polarization technique in 3.5 M NaCl. It was found that the geometrical properties (deposit width and height, heat affected zone (HAZ) height), dilution rate, aspect ratio and powder efficiency of each sample remarkably increased with increasing laser power due to the laser-material interaction. However, the geometrical properties decrease with increasing scanning speed. Solidification began with formation of some large particles such as Al and Fe. The atomic migration of Cu into Ti lattice resulted in the formation of β-Ti phase during cooling and travels a longer distance in the Ti lattice than other elements which opens more crystallographic structure of the β matrix. It was observed that there was higher number of titanium and aluminium presented in the composite as per the theoretical expectation. The indentation testing reveals that Ti6Al4V/Al-Cu-5Fe composite has the highest mean hardness value and it decreases with increasing laser power at scanning speed of 0.8 m/min and 1 m/min. The corrosion and wear resistance of titanium alloy was improved by depositing Al-Cu-Fe quasicrystalline coating. The results obtained from numerical simulation using CFD analysis demonstrated that Ti6Al4V/Al-Cu-10Fe has the highest dilution rate, aspect ratio and HAZ height, and this corresponded with the experimental results. Finally, it was found that Ti6Al4V/Al-Cu-Fe composite have useful mechanical, physical and...
- Full Text:
An experimental and computational fluid dynamics investigation of a counter/parallel flow solar air heater
- Potgieter, Martin Schalk Willem
- Authors: Potgieter, Martin Schalk Willem
- Date: 2016
- Subjects: Computational fluid dynamics , Air flow , Solar air conditioning
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/233557 , uj:23847
- Description: M.Ing. (Mechanical Engineering) , Abstract: The use of renewable energy sources has attracted a great deal of attention over the past two decades due to the increase in fossil fuel prices. The focus has been on the use of these energy sources to produce electricity and hence replace the current energy sources used for energy sources, such as coal and radioactive materials, used for electricity generation. These renewable energy sources may however be implemented on a smaller scale to reduce the electricity demand of private residences and industry. The solar air heater (SAH) is one such application. An SAH is a simple and inexpensive device used for heating air by means of solar energy. These devices may be used in a variety of applications such as space heating, pre heating for industrial applications, drying of various materials and pre heating for solar water desalinators. The present research is aimed at evaluating the unique SAH design in terms of its thermal efficiency and temperature distributions within the SAH. The specific SAH design presented in this investigation has received little attention in literature. Numerical SAH models available in literature rely on assumptions which make the models possibly unsuitable for use on the proposed SAH. The SAH will be evaluated using a commercial CFD package based on the finite volume method. The solar load model (SLM) was implemented to calculate the heat input to the SAH. The surface to surface (S2S) radiation model was implemented to account for radiative heat transfer within the SAH. Initially the Reynolds stress model (RSM) turbulence model was employed to model the turbulence within the domain. The shear stress transport (SST) k-ω turbulence model and Re-Normalisation Group (RNG) k-ε turbulence models were also investigated as part of a turbulence sensitivity study. The solution provided by the CFD investigation is shown to be mesh independent by means of a full mesh sensitivity study. The results obtained from the CFD models were validated experimentally. An SAH was constructed and tested under actual operating conditions. Air temperature measurements were made at the inlet and the outlet of both ducts of the SAH. Eight further temperature measurements were made at various points throughout the SAH. The direct solar radiation was measured by means of a pyrheliometer and the total(global) solar radiation was recorded by means of a pyranometer. The average conversion efficiency observed for the SAH ranged between 23% and 83% and the average collector efficiency between 11% and 44%. The values vary from test to test and are also dependant on the solar radiative input power used for the calculation. The thermal efficiency values predicted by the CFD models showed good agreement with the experimentally derived values. The CFD model over predicted the thermal efficiency by between 9.01% and 6.75% of the measured quantity, depending on the solar radiative power input used. The comparison of modelled temperatures in the SAH with the measured temperatures showed good qualitative agreement but do not compare well quantitatively for all points of comparison. The average error between predicted temperature and experimental results for the various points of comparison is 9.165 K. The maximum and minimum...
- Full Text:
- Authors: Potgieter, Martin Schalk Willem
- Date: 2016
- Subjects: Computational fluid dynamics , Air flow , Solar air conditioning
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/233557 , uj:23847
- Description: M.Ing. (Mechanical Engineering) , Abstract: The use of renewable energy sources has attracted a great deal of attention over the past two decades due to the increase in fossil fuel prices. The focus has been on the use of these energy sources to produce electricity and hence replace the current energy sources used for energy sources, such as coal and radioactive materials, used for electricity generation. These renewable energy sources may however be implemented on a smaller scale to reduce the electricity demand of private residences and industry. The solar air heater (SAH) is one such application. An SAH is a simple and inexpensive device used for heating air by means of solar energy. These devices may be used in a variety of applications such as space heating, pre heating for industrial applications, drying of various materials and pre heating for solar water desalinators. The present research is aimed at evaluating the unique SAH design in terms of its thermal efficiency and temperature distributions within the SAH. The specific SAH design presented in this investigation has received little attention in literature. Numerical SAH models available in literature rely on assumptions which make the models possibly unsuitable for use on the proposed SAH. The SAH will be evaluated using a commercial CFD package based on the finite volume method. The solar load model (SLM) was implemented to calculate the heat input to the SAH. The surface to surface (S2S) radiation model was implemented to account for radiative heat transfer within the SAH. Initially the Reynolds stress model (RSM) turbulence model was employed to model the turbulence within the domain. The shear stress transport (SST) k-ω turbulence model and Re-Normalisation Group (RNG) k-ε turbulence models were also investigated as part of a turbulence sensitivity study. The solution provided by the CFD investigation is shown to be mesh independent by means of a full mesh sensitivity study. The results obtained from the CFD models were validated experimentally. An SAH was constructed and tested under actual operating conditions. Air temperature measurements were made at the inlet and the outlet of both ducts of the SAH. Eight further temperature measurements were made at various points throughout the SAH. The direct solar radiation was measured by means of a pyrheliometer and the total(global) solar radiation was recorded by means of a pyranometer. The average conversion efficiency observed for the SAH ranged between 23% and 83% and the average collector efficiency between 11% and 44%. The values vary from test to test and are also dependant on the solar radiative input power used for the calculation. The thermal efficiency values predicted by the CFD models showed good agreement with the experimentally derived values. The CFD model over predicted the thermal efficiency by between 9.01% and 6.75% of the measured quantity, depending on the solar radiative power input used. The comparison of modelled temperatures in the SAH with the measured temperatures showed good qualitative agreement but do not compare well quantitatively for all points of comparison. The average error between predicted temperature and experimental results for the various points of comparison is 9.165 K. The maximum and minimum...
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Heat transfer in two and three-dimensional single span greenhouses
- Authors: Kruger, S. , Pretorius, L.
- Date: 2016
- Subjects: Greenhouse , Natural ventilation , Computational fluid dynamics
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/214272 , uj:21260 , Citation: Kruger, S & Pretorius, L. 2016. Heat transfer in two and three-dimensional single span greenhouses.
- Description: Abstract: The purpose of this paper is to investigate the heat transfer in two-dimensional and three-dimensional cavities representing a single span greenhouse. This investigation is conducted numerically using Computational Fluid Dynamics (CFD). The heat transfer and temperature fields driven by buoyancy forces are investigated. The research commences with the validation of a few fundamental geometries used as the building blocks for a large commercial greenhouse. The first fundamental geometry is a square filled with air. The CFD results for a square cavity are first evaluated against experimental results found in the literature for both two and three dimensional cavities. The heat transfer inside the cavities is then investigated and compared to those found in the literature. A reasonably good comparison between the numerical CFD results and the experimental results was found for both the two- and three-dimensional cavities. Based on the validated CFD models, two three-dimensional single span greenhouses containing a pitched roof were investigated to determine the effect of design alterations on the heat transfer within the cavity. The results were also compared to two-dimensional greenhouses with a 30 and 45 degree roof angle respectively. Results found that there are significant differences between the two and three-dimensional cases when the average Nusselt number is considered, especially for a greenhouse containing a roof angle of 45 degrees. Temperature distributions were also found to vary significantly throughout the three-dimensional greenhouses.
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- Authors: Kruger, S. , Pretorius, L.
- Date: 2016
- Subjects: Greenhouse , Natural ventilation , Computational fluid dynamics
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/214272 , uj:21260 , Citation: Kruger, S & Pretorius, L. 2016. Heat transfer in two and three-dimensional single span greenhouses.
- Description: Abstract: The purpose of this paper is to investigate the heat transfer in two-dimensional and three-dimensional cavities representing a single span greenhouse. This investigation is conducted numerically using Computational Fluid Dynamics (CFD). The heat transfer and temperature fields driven by buoyancy forces are investigated. The research commences with the validation of a few fundamental geometries used as the building blocks for a large commercial greenhouse. The first fundamental geometry is a square filled with air. The CFD results for a square cavity are first evaluated against experimental results found in the literature for both two and three dimensional cavities. The heat transfer inside the cavities is then investigated and compared to those found in the literature. A reasonably good comparison between the numerical CFD results and the experimental results was found for both the two- and three-dimensional cavities. Based on the validated CFD models, two three-dimensional single span greenhouses containing a pitched roof were investigated to determine the effect of design alterations on the heat transfer within the cavity. The results were also compared to two-dimensional greenhouses with a 30 and 45 degree roof angle respectively. Results found that there are significant differences between the two and three-dimensional cases when the average Nusselt number is considered, especially for a greenhouse containing a roof angle of 45 degrees. Temperature distributions were also found to vary significantly throughout the three-dimensional greenhouses.
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Modelling of the multiphase interactions in a hydrocyclone using Navier-Stokes and Lattice Boltzmann based computational approaches
- Authors: Bhamjee, Muaaz
- Date: 2016
- Subjects: Multiphase flow , Computational fluid dynamics , Navier-Stokes equations , Lattice Boltzmann methods
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/225122 , uj:22730
- Description: D.Ing. (Mechanical Engineering) , Abstract: Please refer to full text to view abstract
- Full Text:
- Authors: Bhamjee, Muaaz
- Date: 2016
- Subjects: Multiphase flow , Computational fluid dynamics , Navier-Stokes equations , Lattice Boltzmann methods
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/225122 , uj:22730
- Description: D.Ing. (Mechanical Engineering) , Abstract: Please refer to full text to view abstract
- Full Text:
Computational fluid dynamics modelling of electrostatic precipitators
- Authors: Schmitz, Walter
- Date: 2014-07-15
- Subjects: Electrostatic precipitation , Computational fluid dynamics , Computational fluid dynamics modelling
- Type: Thesis
- Identifier: uj:11679 , http://hdl.handle.net/10210/11401
- Description: D.Ing. (Mechanical Engineering) , Most coal fired power stations in South Africa are equipped with Electrostatic Precipitators (ESP's). With the ongoing reduction of allowable emissions, as negotiated with the Chief Air . Pollution Control Officer (CAPCO) of the Department of Environmental Affairs and Tourism (DEAT), ways to reduce emissions are sought. In the case of emission levels exceeding the values set by the controlling authority load losses are required for compliance. This however has the effect of plant operating inefficiently and a loss of revenue will result. Specifically in times of growing demand, when more and more of the currently installed generation capacity is required to satisfy the demand, forced load reductions are not desirable. Performance enhancement of ESP's can be achieved by means of system optimisation. Research was initiated to achieve the capability of modelling important dynamic aspects of ESP performance using Computational Fluid Dynamics (CFD). This modelling capability would create the opportunity to investigate the different influencing factors which govern the dust collection efficiency. In the past ESP flow has been modelled by means of mathematical modelling with various degrees of success world-wide. It was found that the accuracy of flow modelling as presently carried outby researchers world wide, is not sufficient to represent the complex inlet flow. Commercially available performance simulation software is based on empirical modelling principles and do not include the complexity of flow fields and re-entrainment and thus results have been limited in accuracy. Computational fluid dynamics software is commercially available and widely used to simulate industrial flow for plant design and optimisation. This technology has been applied with increasing confidence and success in the past. However, often the physical phenomena relevant for the performance simulation of the plant is not integrated into the code and specialised user routines are created to achieve a valid performance model. This research study introduces a unique integrated simulation methodology based on a commercial CFD code. The work focuses on the accurate modelling of fluid flow and collection dynamics in an ESP. User subroutines have been created to simulate particle charging, collection and re-entrainment. The results of the simulations are compared to measurement at actual plant.
- Full Text:
- Authors: Schmitz, Walter
- Date: 2014-07-15
- Subjects: Electrostatic precipitation , Computational fluid dynamics , Computational fluid dynamics modelling
- Type: Thesis
- Identifier: uj:11679 , http://hdl.handle.net/10210/11401
- Description: D.Ing. (Mechanical Engineering) , Most coal fired power stations in South Africa are equipped with Electrostatic Precipitators (ESP's). With the ongoing reduction of allowable emissions, as negotiated with the Chief Air . Pollution Control Officer (CAPCO) of the Department of Environmental Affairs and Tourism (DEAT), ways to reduce emissions are sought. In the case of emission levels exceeding the values set by the controlling authority load losses are required for compliance. This however has the effect of plant operating inefficiently and a loss of revenue will result. Specifically in times of growing demand, when more and more of the currently installed generation capacity is required to satisfy the demand, forced load reductions are not desirable. Performance enhancement of ESP's can be achieved by means of system optimisation. Research was initiated to achieve the capability of modelling important dynamic aspects of ESP performance using Computational Fluid Dynamics (CFD). This modelling capability would create the opportunity to investigate the different influencing factors which govern the dust collection efficiency. In the past ESP flow has been modelled by means of mathematical modelling with various degrees of success world-wide. It was found that the accuracy of flow modelling as presently carried outby researchers world wide, is not sufficient to represent the complex inlet flow. Commercially available performance simulation software is based on empirical modelling principles and do not include the complexity of flow fields and re-entrainment and thus results have been limited in accuracy. Computational fluid dynamics software is commercially available and widely used to simulate industrial flow for plant design and optimisation. This technology has been applied with increasing confidence and success in the past. However, often the physical phenomena relevant for the performance simulation of the plant is not integrated into the code and specialised user routines are created to achieve a valid performance model. This research study introduces a unique integrated simulation methodology based on a commercial CFD code. The work focuses on the accurate modelling of fluid flow and collection dynamics in an ESP. User subroutines have been created to simulate particle charging, collection and re-entrainment. The results of the simulations are compared to measurement at actual plant.
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A computational fluid dynamics and experimental investigation of an airflow window
- Authors: Bhamjee, Muaaz
- Date: 2012-07-19
- Subjects: Computational fluid dynamics , Airflow , Windows , Ventilation
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/376598 , uj:8846 , http://hdl.handle.net/10210/5259
- Description: M.Ing. , The characterisation of the flow field and thermal performance of supply air windows (airflow windows operating in supply mode) have been a topic of interest for at least two decades. Computational Fluid Dynamics (CFD) as well as other simulation methods have been used to model and characterise the flow field, temperature distributions and thermal performance of the supply air window in recent years. Where experimental validation of the velocity (only outlet velocity) and temperature predictions has been provided the error between experiment and CFD (and other forms of simulation) is in the order of 50 % and 3 ◦C (10-13 %), respectively. Furthermore, a large part of the literature does not have experimental validation of the simulation results. The significant error in many of the studies, that provide experimental val- idation of the velocity field, is attributed to inappropriate turbulence mod- els, unrealistic boundary conditions, neglecting significant three-dimensional effects, solar radiation effects not entirely accounted for, mesh sensitivity studies neglected and material properties of glass and air assumed constant. The aim of this research was to characterise a supply air window in terms of its velocity field, temperature distributions and thermal performance. This was done by mathematically modelling the fluid dynamics and heat trans- fer processes in a supply air window and solving the model in a commer- cial CFD code, namely ANSYS Fluent 12.1. Furthermore, an experimental rig was designed, constructed and used to measure the flow field and tem- peratures with the aim of validating the CFD models. The CFD models incorporated appropriate turbulence models, realistic boundary conditions, three-dimensional effects, solar radiation, temperature dependent material properties and a mesh sensitivity study. The CFD models and experiments were setup for forced and natural flow conditions. Laser Doppler Velocimetry has not been used for velocity field measure- ments in an airflow window to date. The experimental setup made use of Laser Doppler Velocimetry to measure the velocity field and turbulence in- tensities. The Laser Doppler Velocimeter (LDV) probe was positioned using a three axis computer controlled traversing mechanism. Furthermore, flow visualisation experiments were done to qualitatively capture the flow field. The results from the CFD are partially in good agreement with the exper- imental work. Qualitatively the flow field as predicted by CFD is in good agreement with the results from the flow visualisation experiments. Quan- titatively the results from the CFD are in good agreement with the tem- perature measurements, however, there is noticeable error between the LDV readings and the velocities as well as turbulence intensity values predicted by CFD. The error, with regards to velocity and turbulence intensity, may be attributed to the experimental error caused by problems with flow seeding as well as the isotropic turbulence assumption inherent in the turbulence model (SST k − ω) used.
- Full Text:
- Authors: Bhamjee, Muaaz
- Date: 2012-07-19
- Subjects: Computational fluid dynamics , Airflow , Windows , Ventilation
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/376598 , uj:8846 , http://hdl.handle.net/10210/5259
- Description: M.Ing. , The characterisation of the flow field and thermal performance of supply air windows (airflow windows operating in supply mode) have been a topic of interest for at least two decades. Computational Fluid Dynamics (CFD) as well as other simulation methods have been used to model and characterise the flow field, temperature distributions and thermal performance of the supply air window in recent years. Where experimental validation of the velocity (only outlet velocity) and temperature predictions has been provided the error between experiment and CFD (and other forms of simulation) is in the order of 50 % and 3 ◦C (10-13 %), respectively. Furthermore, a large part of the literature does not have experimental validation of the simulation results. The significant error in many of the studies, that provide experimental val- idation of the velocity field, is attributed to inappropriate turbulence mod- els, unrealistic boundary conditions, neglecting significant three-dimensional effects, solar radiation effects not entirely accounted for, mesh sensitivity studies neglected and material properties of glass and air assumed constant. The aim of this research was to characterise a supply air window in terms of its velocity field, temperature distributions and thermal performance. This was done by mathematically modelling the fluid dynamics and heat trans- fer processes in a supply air window and solving the model in a commer- cial CFD code, namely ANSYS Fluent 12.1. Furthermore, an experimental rig was designed, constructed and used to measure the flow field and tem- peratures with the aim of validating the CFD models. The CFD models incorporated appropriate turbulence models, realistic boundary conditions, three-dimensional effects, solar radiation, temperature dependent material properties and a mesh sensitivity study. The CFD models and experiments were setup for forced and natural flow conditions. Laser Doppler Velocimetry has not been used for velocity field measure- ments in an airflow window to date. The experimental setup made use of Laser Doppler Velocimetry to measure the velocity field and turbulence in- tensities. The Laser Doppler Velocimeter (LDV) probe was positioned using a three axis computer controlled traversing mechanism. Furthermore, flow visualisation experiments were done to qualitatively capture the flow field. The results from the CFD are partially in good agreement with the exper- imental work. Qualitatively the flow field as predicted by CFD is in good agreement with the results from the flow visualisation experiments. Quan- titatively the results from the CFD are in good agreement with the tem- perature measurements, however, there is noticeable error between the LDV readings and the velocities as well as turbulence intensity values predicted by CFD. The error, with regards to velocity and turbulence intensity, may be attributed to the experimental error caused by problems with flow seeding as well as the isotropic turbulence assumption inherent in the turbulence model (SST k − ω) used.
- Full Text:
Comparative study of the performance of displacement vs conventional ventilation using CFD
- Authors: Madyira, D.M. , Bhamjee, M.
- Date: 2010
- Subjects: Computational fluid dynamics , Ventilation , Airflow , Windows
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15550 , uj:15673 , Madyira, D.M. & Bhamjee, M. 2010. Comparative study of the performance of displacement vs conventional ventilation using CFD. In: Proceedings of the Third LASTED African Conference Modelling and Simulation (AfricaMS 2010), 6-8 September 2010, Gaborone, Botswana:149-156.
- Description: Abstract The purpose of this paper is to compare the performance of displacement and mixing ventilation techniques focusing mainly on temperature and velocity distributions for a site in South Africa. These metrics are central to the performance of ventilation systems. The comparison is based on experimentally obtained data validating a computational fluid dynamics (CFD) model. CFD simulations are becoming a key tool in investigating performance of heating, ventilation and air conditioning (HVAC) systems. Experimental measurements are conducted in a specially designed test chamber incorporating under floor air distribution supplied from a split HVAC system. Focusing on energy efficiency and thermal comfort, the results of the investigation reveal that displacement ventilation has superior performance over conventional ventilation for the cooling period. Despite these benefits, adoption of this technology has been slow, especially in the South African market. This prompted one of the local engineering consulting companies to initiate this research work with a view to develop local knowledge on the benefits of adopting this technology given the power deficit that the country is currently facing. Displacement ventilation therefore continues to prove that it has demonstrable potential in reducing power consumption while achieving the same, and in some cases better, indoor air quality and thermal comfort.
- Full Text: false
- Authors: Madyira, D.M. , Bhamjee, M.
- Date: 2010
- Subjects: Computational fluid dynamics , Ventilation , Airflow , Windows
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15550 , uj:15673 , Madyira, D.M. & Bhamjee, M. 2010. Comparative study of the performance of displacement vs conventional ventilation using CFD. In: Proceedings of the Third LASTED African Conference Modelling and Simulation (AfricaMS 2010), 6-8 September 2010, Gaborone, Botswana:149-156.
- Description: Abstract The purpose of this paper is to compare the performance of displacement and mixing ventilation techniques focusing mainly on temperature and velocity distributions for a site in South Africa. These metrics are central to the performance of ventilation systems. The comparison is based on experimentally obtained data validating a computational fluid dynamics (CFD) model. CFD simulations are becoming a key tool in investigating performance of heating, ventilation and air conditioning (HVAC) systems. Experimental measurements are conducted in a specially designed test chamber incorporating under floor air distribution supplied from a split HVAC system. Focusing on energy efficiency and thermal comfort, the results of the investigation reveal that displacement ventilation has superior performance over conventional ventilation for the cooling period. Despite these benefits, adoption of this technology has been slow, especially in the South African market. This prompted one of the local engineering consulting companies to initiate this research work with a view to develop local knowledge on the benefits of adopting this technology given the power deficit that the country is currently facing. Displacement ventilation therefore continues to prove that it has demonstrable potential in reducing power consumption while achieving the same, and in some cases better, indoor air quality and thermal comfort.
- Full Text: false
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