Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisatio... more Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisation tools is one of the current topics of solar thermal researchers. Of these technologies, Linear Fresnel collectors (LFCs) are the least developed. Therefore, there is plenty of room for the optimisation of this technology. One of the goals of this paper, in addition to the optimisation of an LFC plant, is introducing an applicable optimisation procedure that can be applied for any type of CSP plant. This paper focuses on harvesting maximum solar energy (maximising plant optical efficiency), as well as minimising plant thermal heat loss (maximising plant thermal efficiency), and plant cost (the economic optimisation of the plant), which leads to the generation of cheaper solar electricity from an LFC plant with a fixed power plant cycle (The performance optimisation of this study is based on the plant performance throughout an imaginary summer day). A multi-tube cavity receiver is considered in this study since there is plenty of room for its optimization. For the receiver, optimal cavity shape, tube bundle arrangement, tube numbers, cavity mounting height and insulation thickness are considered, while for the mirror field, the number of mirrors , mirror width, mirror gaps and mirror focal length are considered to achieve the optimisation goals. A multi-stage optimisation process is followed. Firstly, optical (using SolTrace), thermal (using a view area approach) and economic performance are combined in a multi-objective genetic algorithm as incorporated in ANSYS DesignXplorer (DX). This leads to an optimal LFC with a variable focal length for each mirror. After determining a fixed optimal focal length for all the mirrors, a Computational Fluid Dynamics (CFD) approach is used to optimise the thermal insulation of the cavity receiver for minimal heat loss and minimal insulation material. The process is automated through the use of ANSYS Workbench and Excel (coding with Visual Basic for Application (VBA) and LK Scripting in SolTrace). The view area approach provides an inexpensive way of calculating radiation heat loss from the receiver that is shown in the subsequent CFD analysis to be dominating the heat transfer loss mechanisms. The optimised receiver is evaluated at different LFC plant tube temperatures to assess its performance.
CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Mont... more CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Monte Carlo solutions are used as reference. Ray effect and false scattering errors are reduced with refinement. Refinement includes mesh refinement as well as discrete ordinates count. Linear Fresnel and parabolic trough test cases show good comparison. a b s t r a c t The modelling of solar irradiation in concentrated solar power (CSP) applications is traditionally done with ray-tracing methods, e.g. the Monte Carlo method. For the evaluation of CSP receivers, the results from ray-tracing codes are typically used to provide boundary conditions to Computational Fluid Dynamics (CFD) codes for the solution of conjugate heat transfer in the receivers. There are both advantages and disadvantages to using separate software for the irradiation and heat transfer modelling. For traditional ray-tracing methods, advantages are the cost-effectiveness of the Monte Carlo method in modelling reflections from specular surfaces; the ability to statistically assign a sun shape to the rays; the statistical treatment of reflectivity and optical errors (e.g. surface slope errors), to name a few. When considering a complex mirror field and a complex receiver with secondary reflective surfaces, especially with selective coatings to enhance absorption and limit re-radiation losses, standard ray trac-ers may be limited in specifying emissivity and absorptivity, which are both specular and temperature dependent, and are hence not suitable as radiation analysis tool. This type of scenario can be modelled accurately using CFD, through the finite volume (FV) treatment of the radiative transfer equation (RTE) and a banded spectrum approach at an increased computational cost. This paper evaluates the use of CFD in the form of the commercial CFD code ANSYS Fluent v15 and v16 to model the reflection, transmission and absorption of solar irradiation from diffuse and specular surfaces found in linear CSP applications. 2-D CFD solutions were considered, i.e. line concentration. To illustrate and validate the method, two sources were used. The first source was test cases from literature with published solutions and the second a combined modelling approach where solutions were obtained using both FV and ray tracing (with SolTrace). For all the test cases, good agreement was found when suitable modelling settings were used to limit both ray-effect and false scattering errors.
In this article, the magnetohydrodynamic natural convection boundary-layer flow on a sphere in a ... more In this article, the magnetohydrodynamic natural convection boundary-layer flow on a sphere in a porous medium is studied numerically. The porous medium is saturated with an electrically conducting fluid and the fluid is subject to heat generation/absorption. A vis-cous flow model is presented using boundary-layer theory comprising the momentum and energy conservation equations. The governing boundary-layer equations are transformed into non-dimensional form using appropriate reference quantities. The resulting coupled non-linear system of partial differential equations is solved numerically using the differential quadrature method (DQM). The advantage of DQM, which was introduced as a promising method two decades ago, is that the solution is converged with a few grid points and hence the computational costs are reduced. Comparison is made between the results obtained by the DQM method and those obtained using the finite-difference method for the same operating conditions. A validation test is carried out for the case of infinite permeability (i.e. infinite Darcy number). The results of the present study were compared with the results of a similar investigation available in the literature. Close agreement between the two sets of results was noticed. A parametric study was performed in which the effect of various parameters on temperature and velocity fields, local Nusselt numbers, and wall friction coefficient were investigated.
In this paper, firstly, the applicability of the differential quadrature method (DQM) as an effic... more In this paper, firstly, the applicability of the differential quadrature method (DQM) as an efficient and accurate numerical method for solving the problem of variable viscosity and thermally radiative unsteady magneto-hydrodynamic (MHD) flow over a moving vertical plate with suction and heat flux is investigated. The spatial as well as the temporal domains are discretized using the DQM. The fast rate of convergence of the method is demonstrated and for the cases that a solution is available, comparison is done. Then, effects of the temperature dependence of viscosity and different fluid parameters on the velocity and temperature of transient MHD flow subjected to the above mentioned boundary condition are studied.
Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisatio... more Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisation tools is one of the current topics of solar thermal researchers. Of these technologies, Linear Fresnel collectors (LFCs) are the least developed. Therefore, there is plenty of room for the optimisation of this technology. One of the goals of this paper, in addition to the optimisation of an LFC plant, is introducing an applicable optimisation procedure that can be applied for any type of CSP plant. This paper focuses on harvesting maximum solar energy (maximising plant optical efficiency), as well as minimising plant thermal heat loss (maximising plant thermal efficiency), and plant cost (the economic optimisation of the plant), which leads to the generation of cheaper solar electricity from an LFC plant with a fixed power plant cycle (The performance optimisation of this study is based on the plant performance throughout an imaginary summer day). A multi-tube cavity receiver is considered in this study since there is plenty of room for its optimization. For the receiver, optimal cavity shape, tube bundle arrangement, tube numbers, cavity mounting height and insulation thickness are considered, while for the mirror field, the number of mirrors , mirror width, mirror gaps and mirror focal length are considered to achieve the optimisation goals. A multi-stage optimisation process is followed. Firstly, optical (using SolTrace), thermal (using a view area approach) and economic performance are combined in a multi-objective genetic algorithm as incorporated in ANSYS DesignXplorer (DX). This leads to an optimal LFC with a variable focal length for each mirror. After determining a fixed optimal focal length for all the mirrors, a Computational Fluid Dynamics (CFD) approach is used to optimise the thermal insulation of the cavity receiver for minimal heat loss and minimal insulation material. The process is automated through the use of ANSYS Workbench and Excel (coding with Visual Basic for Application (VBA) and LK Scripting in SolTrace). The view area approach provides an inexpensive way of calculating radiation heat loss from the receiver that is shown in the subsequent CFD analysis to be dominating the heat transfer loss mechanisms. The optimised receiver is evaluated at different LFC plant tube temperatures to assess its performance.
To increase the efficiency of Concentrated Solar Power (CSP) plants, the use of optimization meth... more To increase the efficiency of Concentrated Solar Power (CSP) plants, the use of optimization methods is a current topic of research. This paper focuses on applying an integrated optimization technology to a solar thermal application, more specifically for the optimization of a trapezoidal cavity absorber of an LFR (Linear Fresnel Reflector), also called a Linear Fresnel Collector (LFC), CSP plant. LFR technology has been developed since the 1960s, and while large improvements in efficiencies have been made, there is still room for improvement. Once such area is in the receiver design where the optimal cavity shape, coatings, insulation thickness, absorber pipe selection , layout and spacing always need to be determined for a specific application. This paper uses a commercial tool to find an optimal design for a set of operating conditions. The objective functions that are used to judge the performance of a 2-D cavity are the combined heat loss through convection, conduction and radiation, as well as a wind resistance area. In this paper the effect of absorbed irradiation is introduced in the form of an outer surface of pipe temperature. Seven geometrical parameters are used as design variables. Based on a sample set requiring 79 CFD simulations, a global utopia point is found that minimizes both objectives. The most sensitive parameters were found to be the top insulation thickness and the cavity depth. Based on the results, the Multi-Objective Genetic Algorithm (MOGA) as contained in ANSYS DesignXplorer is shown to be effective in finding candidate optimal designs as well as the utopia point.
In the present study, turbulent flow passing over a four-row finned tube heat exchanger has been ... more In the present study, turbulent flow passing over a four-row finned tube heat exchanger has been simulated by nine different turbulent models. Annular fin has a complex geometry and as a result, very complex phenomena such as flow separation, horseshoe vortices, generated wakes, etc. may be observed. Results have been compared with experimental correlations and in more detail to each other. In addition, capability of numerical models as a flow visualization tool, their strengths and weaknesses have been studied.
The applicability of the differential quadrature method (DQM) and incremental differential quadra... more The applicability of the differential quadrature method (DQM) and incremental differential quadrature method
In this paper, the boundary-layer natural convection flow on a permeable vertical plate with ther... more In this paper, the boundary-layer natural convection flow on a permeable vertical plate with thermal radiation and mass transfer is studied when the plate moves in its own plane. A uniform temperature with uniform species concentration at the plate is affected and the fluid is considered to be a gray, absorbing–emitting. A viscous flow model is presented using boundary-layer theory comprising the momentum, energy, and concentration equations, which is solved analytically by means of an excellent method called homotopy analysis method (HAM). First, a comparison between HAM results and those obtained by means of a higher-order numerical method, namely differential quadrature method (DQM), is done. Close agreement of two sets of results indicates the accuracy of the HAM. The velocity, temperature, and concentration distributions are displayed graphically, and a parametric study is performed in which the effect of various parameters on the skin friction, the local Nusselt number (Nn), and the local Sherwood number (Mu) are investigated.
In this article, an analytical solution for a Marangoni mixed convection boundary layer flow is p... more In this article, an analytical solution for a Marangoni mixed convection boundary layer flow is presented. A similarity transform reduces the Navier–Stokes equations to a set of non-linear ordinary differential equations, which are solved analytically by means of the homotopy analysis method (HAM). The results obtained in this study are compared with the numerical results released in the literature. A close agreement of the two sets of results indicates the accuracy of the HAM. The method can obtain an expression that is acceptable for all values of effective parameters and is also able to control the convergence of the solution. The numerical solution of the similarity equations is developed and the results are in good agreement with the analytical results based on the HAM.
This paper presents an analytical solution of the problem of free-convective magnetohydrodynamic ... more This paper presents an analytical solution of the problem of free-convective magnetohydrodynamic flow over a stretched sheet with the Hall effect and mass transfer taken into account. A similarity transform reduces the Navier–Stokes, energy, Ohm law, and mass-transfer equations to a system of nonlinear ordinary differential equations. The governing equations are solved analytically using an analytical method for solving nonlinear problems, namely, the homotopy analysis method. The results are compared with the results of a promising numerical method of differential quadrature developed by the authors. It is shown that there is very good agreement between analytical results and those obtained by the differential quadrature method. The differential quadrature method was validated, and the effects of non-dimensional parameters on the velocity, temperature and concentration profiles were studied.
In this paper, an analytical solution for boundary layer flow over a flat plate with slip flow an... more In this paper, an analytical solution for boundary layer flow over a flat plate with slip flow and constant heat flux surface condition has been presented for the first time. The Navier–Stokes and energy equations are reduced by a similarity transform in order for a set of nonlinear ordinary differential equations to be formed. Then, governing equations will be solved analytically by using a kind of analytic technique for nonlinear problems which has been named the homotopy analysis method (HAM). The obtained results of this study have been compared with the results of differential quadrature method (DQM) as a promising numerical method. Very good agreement has been shown between analytical results and those obtained by DQ. Finally, effects of the Prandtl number and rarefaction parameter K on velocity and temperature profiles are investigated.
CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Mont... more CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Monte Carlo solutions are used as reference. Ray effect and false scattering errors are reduced with refinement. Refinement includes mesh refinement as well as discrete ordinates count. Linear Fresnel and parabolic trough test cases show good comparison. a b s t r a c t The modelling of solar irradiation in concentrated solar power (CSP) applications is traditionally done with ray-tracing methods, e.g. the Monte Carlo method. For the evaluation of CSP receivers, the results from ray-tracing codes are typically used to provide boundary conditions to Computational Fluid Dynamics (CFD) codes for the solution of conjugate heat transfer in the receivers. There are both advantages and disadvantages to using separate software for the irradiation and heat transfer modelling. For traditional ray-tracing methods, advantages are the cost-effectiveness of the Monte Carlo method in modelling reflections from specular surfaces; the ability to statistically assign a sun shape to the rays; the statistical treatment of reflectivity and optical errors (e.g. surface slope errors), to name a few. When considering a complex mirror field and a complex receiver with secondary reflective surfaces, especially with selective coatings to enhance absorption and limit re-radiation losses, standard ray trac-ers may be limited in specifying emissivity and absorptivity, which are both specular and temperature dependent, and are hence not suitable as radiation analysis tool. This type of scenario can be modelled accurately using CFD, through the finite volume (FV) treatment of the radiative transfer equation (RTE) and a banded spectrum approach at an increased computational cost. This paper evaluates the use of CFD in the form of the commercial CFD code ANSYS Fluent v15 and v16 to model the reflection, transmission and absorption of solar irradiation from diffuse and specular surfaces found in linear CSP applications. 2-D CFD solutions were considered, i.e. line concentration. To illustrate and validate the method, two sources were used. The first source was test cases from literature with published solutions and the second a combined modelling approach where solutions were obtained using both FV and ray tracing (with SolTrace). For all the test cases, good agreement was found when suitable modelling settings were used to limit both ray-effect and false scattering errors.
The present study deals with the theoretical modeling aspects of coupled conductive and radiative... more The present study deals with the theoretical modeling aspects of coupled conductive and radiative heat transfer in the presence of absorbing, emitting and scattering gray medium within twodimensional square furnace including two heat sources. The gray radiative medium is bounded by isothermal walls which are considered to be opaque, diffuse and gray. The well known discrete ordinate method (DOM) is employed to solve the radiative transfer equation (RTE) to obtain the radiative intensity distribution in the participating medium. In order to compute the temperature field inside the medium, the gas energy equation including the conductive and radiative term is solved by finite volume method. By this technique, the effect of radiation conduction parameter, which has a main role on thermal behavior of the conduction-radiation systems, is explored.
A computational approach is presented, which uses the finite volume (FV) method in the Computatio... more A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) sol-ver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the so-called ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric source. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with results of a fully integrated, but expensive 3-D optical and thermal model. It is shown that the less expensive model provides similar results and hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to max-imise the performance of linear CSP reflector layout and receiver configurations.
محققان دانشگاهی و مهندسین شرکتهای بزرگ صنعتی در سراسر دنیا به تحقیق و مطالعه در خصوص مبدلهای حر... more محققان دانشگاهی و مهندسین شرکتهای بزرگ صنعتی در سراسر دنیا به تحقیق و مطالعه در خصوص مبدلهای حرارتی مشغول میباشند کهحاصل آن در قالب کتب و مقالات متنوعی منتشر شده است. با این حال جدا بودن دو دیدگاه صنعتی و دانشگاهی، از نقاط ضعف عمده این تحقیقات است. نویسندگان این کتاب تلاش کردهاند با طرح مباحثی مانند معرفی و بررسی انواع مبدلهای حرارتی، چگونگی انتخاب مبدل، طراحی حرارتی، طراحی مکانیکی، انتخاب مواد، خوردگی در مبدلها، نحوه تمیزکاری، بررسی انواع استانداردهای صنعتی و همچنین آموزش نرم افزارهای مرتبط، مرجعی مناسب جهت مخاطبین هر دو گروه دانشگاهی و صنعتی تهیه کنند. این کتاب در سه قسمت تقریباً مستقل تهیه شده است. قسمت اول آن به معرفی مبدل¬های رایج پرداخته است. در این بخش سعی شده است که با استفاده از تصاویر مختلف، درک بهتری از مطالب انجام گیرد و همچنین کلیه موارد عمومی مربوط به هر مبدل از جمله جنس مواد، روش ساخت، روش-های تمیزکاری، نقاط قوت و ضعف مبدل به تفکیک بیان شود. مخاطبین این بخش جدا از دانشجویان، صنعتگران و مهندسانی هستند که تنها نیاز به کلیاتی در خصوص هر مبدل دارند. قسمت دوم کتاب به طراحی حرارتی اختصاص یافته است و بخش سوم این کتاب نیز به طراحی مکانیکی مبدل پوسته و تیوب بر اساس کد ASME اختصاص دارد. در نهایت در انتهای کتاب، برخی مطالب کمکی نظیر خوردگی، رسوب¬گذاری و نیز بعضی از جداول لازم جهت طراحی و انتخاب مواد به صورت پیوست آورده شده است.
Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisatio... more Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisation tools is one of the current topics of solar thermal researchers. Of these technologies, Linear Fresnel collectors (LFCs) are the least developed. Therefore, there is plenty of room for the optimisation of this technology. One of the goals of this paper, in addition to the optimisation of an LFC plant, is introducing an applicable optimisation procedure that can be applied for any type of CSP plant. This paper focuses on harvesting maximum solar energy (maximising plant optical efficiency), as well as minimising plant thermal heat loss (maximising plant thermal efficiency), and plant cost (the economic optimisation of the plant), which leads to the generation of cheaper solar electricity from an LFC plant with a fixed power plant cycle (The performance optimisation of this study is based on the plant performance throughout an imaginary summer day). A multi-tube cavity receiver is considered in this study since there is plenty of room for its optimization. For the receiver, optimal cavity shape, tube bundle arrangement, tube numbers, cavity mounting height and insulation thickness are considered, while for the mirror field, the number of mirrors , mirror width, mirror gaps and mirror focal length are considered to achieve the optimisation goals. A multi-stage optimisation process is followed. Firstly, optical (using SolTrace), thermal (using a view area approach) and economic performance are combined in a multi-objective genetic algorithm as incorporated in ANSYS DesignXplorer (DX). This leads to an optimal LFC with a variable focal length for each mirror. After determining a fixed optimal focal length for all the mirrors, a Computational Fluid Dynamics (CFD) approach is used to optimise the thermal insulation of the cavity receiver for minimal heat loss and minimal insulation material. The process is automated through the use of ANSYS Workbench and Excel (coding with Visual Basic for Application (VBA) and LK Scripting in SolTrace). The view area approach provides an inexpensive way of calculating radiation heat loss from the receiver that is shown in the subsequent CFD analysis to be dominating the heat transfer loss mechanisms. The optimised receiver is evaluated at different LFC plant tube temperatures to assess its performance.
CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Mont... more CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Monte Carlo solutions are used as reference. Ray effect and false scattering errors are reduced with refinement. Refinement includes mesh refinement as well as discrete ordinates count. Linear Fresnel and parabolic trough test cases show good comparison. a b s t r a c t The modelling of solar irradiation in concentrated solar power (CSP) applications is traditionally done with ray-tracing methods, e.g. the Monte Carlo method. For the evaluation of CSP receivers, the results from ray-tracing codes are typically used to provide boundary conditions to Computational Fluid Dynamics (CFD) codes for the solution of conjugate heat transfer in the receivers. There are both advantages and disadvantages to using separate software for the irradiation and heat transfer modelling. For traditional ray-tracing methods, advantages are the cost-effectiveness of the Monte Carlo method in modelling reflections from specular surfaces; the ability to statistically assign a sun shape to the rays; the statistical treatment of reflectivity and optical errors (e.g. surface slope errors), to name a few. When considering a complex mirror field and a complex receiver with secondary reflective surfaces, especially with selective coatings to enhance absorption and limit re-radiation losses, standard ray trac-ers may be limited in specifying emissivity and absorptivity, which are both specular and temperature dependent, and are hence not suitable as radiation analysis tool. This type of scenario can be modelled accurately using CFD, through the finite volume (FV) treatment of the radiative transfer equation (RTE) and a banded spectrum approach at an increased computational cost. This paper evaluates the use of CFD in the form of the commercial CFD code ANSYS Fluent v15 and v16 to model the reflection, transmission and absorption of solar irradiation from diffuse and specular surfaces found in linear CSP applications. 2-D CFD solutions were considered, i.e. line concentration. To illustrate and validate the method, two sources were used. The first source was test cases from literature with published solutions and the second a combined modelling approach where solutions were obtained using both FV and ray tracing (with SolTrace). For all the test cases, good agreement was found when suitable modelling settings were used to limit both ray-effect and false scattering errors.
In this article, the magnetohydrodynamic natural convection boundary-layer flow on a sphere in a ... more In this article, the magnetohydrodynamic natural convection boundary-layer flow on a sphere in a porous medium is studied numerically. The porous medium is saturated with an electrically conducting fluid and the fluid is subject to heat generation/absorption. A vis-cous flow model is presented using boundary-layer theory comprising the momentum and energy conservation equations. The governing boundary-layer equations are transformed into non-dimensional form using appropriate reference quantities. The resulting coupled non-linear system of partial differential equations is solved numerically using the differential quadrature method (DQM). The advantage of DQM, which was introduced as a promising method two decades ago, is that the solution is converged with a few grid points and hence the computational costs are reduced. Comparison is made between the results obtained by the DQM method and those obtained using the finite-difference method for the same operating conditions. A validation test is carried out for the case of infinite permeability (i.e. infinite Darcy number). The results of the present study were compared with the results of a similar investigation available in the literature. Close agreement between the two sets of results was noticed. A parametric study was performed in which the effect of various parameters on temperature and velocity fields, local Nusselt numbers, and wall friction coefficient were investigated.
In this paper, firstly, the applicability of the differential quadrature method (DQM) as an effic... more In this paper, firstly, the applicability of the differential quadrature method (DQM) as an efficient and accurate numerical method for solving the problem of variable viscosity and thermally radiative unsteady magneto-hydrodynamic (MHD) flow over a moving vertical plate with suction and heat flux is investigated. The spatial as well as the temporal domains are discretized using the DQM. The fast rate of convergence of the method is demonstrated and for the cases that a solution is available, comparison is done. Then, effects of the temperature dependence of viscosity and different fluid parameters on the velocity and temperature of transient MHD flow subjected to the above mentioned boundary condition are studied.
Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisatio... more Increasing the efficiency of concentrating solar power (CSP) technologies by means of optimisation tools is one of the current topics of solar thermal researchers. Of these technologies, Linear Fresnel collectors (LFCs) are the least developed. Therefore, there is plenty of room for the optimisation of this technology. One of the goals of this paper, in addition to the optimisation of an LFC plant, is introducing an applicable optimisation procedure that can be applied for any type of CSP plant. This paper focuses on harvesting maximum solar energy (maximising plant optical efficiency), as well as minimising plant thermal heat loss (maximising plant thermal efficiency), and plant cost (the economic optimisation of the plant), which leads to the generation of cheaper solar electricity from an LFC plant with a fixed power plant cycle (The performance optimisation of this study is based on the plant performance throughout an imaginary summer day). A multi-tube cavity receiver is considered in this study since there is plenty of room for its optimization. For the receiver, optimal cavity shape, tube bundle arrangement, tube numbers, cavity mounting height and insulation thickness are considered, while for the mirror field, the number of mirrors , mirror width, mirror gaps and mirror focal length are considered to achieve the optimisation goals. A multi-stage optimisation process is followed. Firstly, optical (using SolTrace), thermal (using a view area approach) and economic performance are combined in a multi-objective genetic algorithm as incorporated in ANSYS DesignXplorer (DX). This leads to an optimal LFC with a variable focal length for each mirror. After determining a fixed optimal focal length for all the mirrors, a Computational Fluid Dynamics (CFD) approach is used to optimise the thermal insulation of the cavity receiver for minimal heat loss and minimal insulation material. The process is automated through the use of ANSYS Workbench and Excel (coding with Visual Basic for Application (VBA) and LK Scripting in SolTrace). The view area approach provides an inexpensive way of calculating radiation heat loss from the receiver that is shown in the subsequent CFD analysis to be dominating the heat transfer loss mechanisms. The optimised receiver is evaluated at different LFC plant tube temperatures to assess its performance.
To increase the efficiency of Concentrated Solar Power (CSP) plants, the use of optimization meth... more To increase the efficiency of Concentrated Solar Power (CSP) plants, the use of optimization methods is a current topic of research. This paper focuses on applying an integrated optimization technology to a solar thermal application, more specifically for the optimization of a trapezoidal cavity absorber of an LFR (Linear Fresnel Reflector), also called a Linear Fresnel Collector (LFC), CSP plant. LFR technology has been developed since the 1960s, and while large improvements in efficiencies have been made, there is still room for improvement. Once such area is in the receiver design where the optimal cavity shape, coatings, insulation thickness, absorber pipe selection , layout and spacing always need to be determined for a specific application. This paper uses a commercial tool to find an optimal design for a set of operating conditions. The objective functions that are used to judge the performance of a 2-D cavity are the combined heat loss through convection, conduction and radiation, as well as a wind resistance area. In this paper the effect of absorbed irradiation is introduced in the form of an outer surface of pipe temperature. Seven geometrical parameters are used as design variables. Based on a sample set requiring 79 CFD simulations, a global utopia point is found that minimizes both objectives. The most sensitive parameters were found to be the top insulation thickness and the cavity depth. Based on the results, the Multi-Objective Genetic Algorithm (MOGA) as contained in ANSYS DesignXplorer is shown to be effective in finding candidate optimal designs as well as the utopia point.
In the present study, turbulent flow passing over a four-row finned tube heat exchanger has been ... more In the present study, turbulent flow passing over a four-row finned tube heat exchanger has been simulated by nine different turbulent models. Annular fin has a complex geometry and as a result, very complex phenomena such as flow separation, horseshoe vortices, generated wakes, etc. may be observed. Results have been compared with experimental correlations and in more detail to each other. In addition, capability of numerical models as a flow visualization tool, their strengths and weaknesses have been studied.
The applicability of the differential quadrature method (DQM) and incremental differential quadra... more The applicability of the differential quadrature method (DQM) and incremental differential quadrature method
In this paper, the boundary-layer natural convection flow on a permeable vertical plate with ther... more In this paper, the boundary-layer natural convection flow on a permeable vertical plate with thermal radiation and mass transfer is studied when the plate moves in its own plane. A uniform temperature with uniform species concentration at the plate is affected and the fluid is considered to be a gray, absorbing–emitting. A viscous flow model is presented using boundary-layer theory comprising the momentum, energy, and concentration equations, which is solved analytically by means of an excellent method called homotopy analysis method (HAM). First, a comparison between HAM results and those obtained by means of a higher-order numerical method, namely differential quadrature method (DQM), is done. Close agreement of two sets of results indicates the accuracy of the HAM. The velocity, temperature, and concentration distributions are displayed graphically, and a parametric study is performed in which the effect of various parameters on the skin friction, the local Nusselt number (Nn), and the local Sherwood number (Mu) are investigated.
In this article, an analytical solution for a Marangoni mixed convection boundary layer flow is p... more In this article, an analytical solution for a Marangoni mixed convection boundary layer flow is presented. A similarity transform reduces the Navier–Stokes equations to a set of non-linear ordinary differential equations, which are solved analytically by means of the homotopy analysis method (HAM). The results obtained in this study are compared with the numerical results released in the literature. A close agreement of the two sets of results indicates the accuracy of the HAM. The method can obtain an expression that is acceptable for all values of effective parameters and is also able to control the convergence of the solution. The numerical solution of the similarity equations is developed and the results are in good agreement with the analytical results based on the HAM.
This paper presents an analytical solution of the problem of free-convective magnetohydrodynamic ... more This paper presents an analytical solution of the problem of free-convective magnetohydrodynamic flow over a stretched sheet with the Hall effect and mass transfer taken into account. A similarity transform reduces the Navier–Stokes, energy, Ohm law, and mass-transfer equations to a system of nonlinear ordinary differential equations. The governing equations are solved analytically using an analytical method for solving nonlinear problems, namely, the homotopy analysis method. The results are compared with the results of a promising numerical method of differential quadrature developed by the authors. It is shown that there is very good agreement between analytical results and those obtained by the differential quadrature method. The differential quadrature method was validated, and the effects of non-dimensional parameters on the velocity, temperature and concentration profiles were studied.
In this paper, an analytical solution for boundary layer flow over a flat plate with slip flow an... more In this paper, an analytical solution for boundary layer flow over a flat plate with slip flow and constant heat flux surface condition has been presented for the first time. The Navier–Stokes and energy equations are reduced by a similarity transform in order for a set of nonlinear ordinary differential equations to be formed. Then, governing equations will be solved analytically by using a kind of analytic technique for nonlinear problems which has been named the homotopy analysis method (HAM). The obtained results of this study have been compared with the results of differential quadrature method (DQM) as a promising numerical method. Very good agreement has been shown between analytical results and those obtained by DQ. Finally, effects of the Prandtl number and rarefaction parameter K on velocity and temperature profiles are investigated.
CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Mont... more CFD is presented as a ray-tracing tool for linear focus CSP. Test cases from literature with Monte Carlo solutions are used as reference. Ray effect and false scattering errors are reduced with refinement. Refinement includes mesh refinement as well as discrete ordinates count. Linear Fresnel and parabolic trough test cases show good comparison. a b s t r a c t The modelling of solar irradiation in concentrated solar power (CSP) applications is traditionally done with ray-tracing methods, e.g. the Monte Carlo method. For the evaluation of CSP receivers, the results from ray-tracing codes are typically used to provide boundary conditions to Computational Fluid Dynamics (CFD) codes for the solution of conjugate heat transfer in the receivers. There are both advantages and disadvantages to using separate software for the irradiation and heat transfer modelling. For traditional ray-tracing methods, advantages are the cost-effectiveness of the Monte Carlo method in modelling reflections from specular surfaces; the ability to statistically assign a sun shape to the rays; the statistical treatment of reflectivity and optical errors (e.g. surface slope errors), to name a few. When considering a complex mirror field and a complex receiver with secondary reflective surfaces, especially with selective coatings to enhance absorption and limit re-radiation losses, standard ray trac-ers may be limited in specifying emissivity and absorptivity, which are both specular and temperature dependent, and are hence not suitable as radiation analysis tool. This type of scenario can be modelled accurately using CFD, through the finite volume (FV) treatment of the radiative transfer equation (RTE) and a banded spectrum approach at an increased computational cost. This paper evaluates the use of CFD in the form of the commercial CFD code ANSYS Fluent v15 and v16 to model the reflection, transmission and absorption of solar irradiation from diffuse and specular surfaces found in linear CSP applications. 2-D CFD solutions were considered, i.e. line concentration. To illustrate and validate the method, two sources were used. The first source was test cases from literature with published solutions and the second a combined modelling approach where solutions were obtained using both FV and ray tracing (with SolTrace). For all the test cases, good agreement was found when suitable modelling settings were used to limit both ray-effect and false scattering errors.
The present study deals with the theoretical modeling aspects of coupled conductive and radiative... more The present study deals with the theoretical modeling aspects of coupled conductive and radiative heat transfer in the presence of absorbing, emitting and scattering gray medium within twodimensional square furnace including two heat sources. The gray radiative medium is bounded by isothermal walls which are considered to be opaque, diffuse and gray. The well known discrete ordinate method (DOM) is employed to solve the radiative transfer equation (RTE) to obtain the radiative intensity distribution in the participating medium. In order to compute the temperature field inside the medium, the gas energy equation including the conductive and radiative term is solved by finite volume method. By this technique, the effect of radiation conduction parameter, which has a main role on thermal behavior of the conduction-radiation systems, is explored.
A computational approach is presented, which uses the finite volume (FV) method in the Computatio... more A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) sol-ver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the so-called ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric source. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with results of a fully integrated, but expensive 3-D optical and thermal model. It is shown that the less expensive model provides similar results and hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to max-imise the performance of linear CSP reflector layout and receiver configurations.
محققان دانشگاهی و مهندسین شرکتهای بزرگ صنعتی در سراسر دنیا به تحقیق و مطالعه در خصوص مبدلهای حر... more محققان دانشگاهی و مهندسین شرکتهای بزرگ صنعتی در سراسر دنیا به تحقیق و مطالعه در خصوص مبدلهای حرارتی مشغول میباشند کهحاصل آن در قالب کتب و مقالات متنوعی منتشر شده است. با این حال جدا بودن دو دیدگاه صنعتی و دانشگاهی، از نقاط ضعف عمده این تحقیقات است. نویسندگان این کتاب تلاش کردهاند با طرح مباحثی مانند معرفی و بررسی انواع مبدلهای حرارتی، چگونگی انتخاب مبدل، طراحی حرارتی، طراحی مکانیکی، انتخاب مواد، خوردگی در مبدلها، نحوه تمیزکاری، بررسی انواع استانداردهای صنعتی و همچنین آموزش نرم افزارهای مرتبط، مرجعی مناسب جهت مخاطبین هر دو گروه دانشگاهی و صنعتی تهیه کنند. این کتاب در سه قسمت تقریباً مستقل تهیه شده است. قسمت اول آن به معرفی مبدل¬های رایج پرداخته است. در این بخش سعی شده است که با استفاده از تصاویر مختلف، درک بهتری از مطالب انجام گیرد و همچنین کلیه موارد عمومی مربوط به هر مبدل از جمله جنس مواد، روش ساخت، روش-های تمیزکاری، نقاط قوت و ضعف مبدل به تفکیک بیان شود. مخاطبین این بخش جدا از دانشجویان، صنعتگران و مهندسانی هستند که تنها نیاز به کلیاتی در خصوص هر مبدل دارند. قسمت دوم کتاب به طراحی حرارتی اختصاص یافته است و بخش سوم این کتاب نیز به طراحی مکانیکی مبدل پوسته و تیوب بر اساس کد ASME اختصاص دارد. در نهایت در انتهای کتاب، برخی مطالب کمکی نظیر خوردگی، رسوب¬گذاری و نیز بعضی از جداول لازم جهت طراحی و انتخاب مواد به صورت پیوست آورده شده است.
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این کتاب در سه قسمت تقریباً مستقل تهیه شده است. قسمت اول آن به معرفی مبدل¬های رایج پرداخته است. در این بخش سعی شده است که با استفاده از تصاویر مختلف، درک بهتری از مطالب انجام گیرد و همچنین کلیه موارد عمومی مربوط به هر مبدل از جمله جنس مواد، روش ساخت، روش-های تمیزکاری، نقاط قوت و ضعف مبدل به تفکیک بیان شود. مخاطبین این بخش جدا از دانشجویان، صنعتگران و مهندسانی هستند که تنها نیاز به کلیاتی در خصوص هر مبدل دارند. قسمت دوم کتاب به طراحی حرارتی اختصاص یافته است و بخش سوم این کتاب نیز به طراحی مکانیکی مبدل پوسته و تیوب بر اساس کد ASME اختصاص دارد. در نهایت در انتهای کتاب، برخی مطالب کمکی نظیر خوردگی، رسوب¬گذاری و نیز بعضی از جداول لازم جهت طراحی و انتخاب مواد به صورت پیوست آورده شده است.
این کتاب در سه قسمت تقریباً مستقل تهیه شده است. قسمت اول آن به معرفی مبدل¬های رایج پرداخته است. در این بخش سعی شده است که با استفاده از تصاویر مختلف، درک بهتری از مطالب انجام گیرد و همچنین کلیه موارد عمومی مربوط به هر مبدل از جمله جنس مواد، روش ساخت، روش-های تمیزکاری، نقاط قوت و ضعف مبدل به تفکیک بیان شود. مخاطبین این بخش جدا از دانشجویان، صنعتگران و مهندسانی هستند که تنها نیاز به کلیاتی در خصوص هر مبدل دارند. قسمت دوم کتاب به طراحی حرارتی اختصاص یافته است و بخش سوم این کتاب نیز به طراحی مکانیکی مبدل پوسته و تیوب بر اساس کد ASME اختصاص دارد. در نهایت در انتهای کتاب، برخی مطالب کمکی نظیر خوردگی، رسوب¬گذاری و نیز بعضی از جداول لازم جهت طراحی و انتخاب مواد به صورت پیوست آورده شده است.