In this study,we perform a numerical investigation of a steady laminar stagnation flow flame stabilized at a wall with the consideration of heat transport,focusing on a lean hydrogen/air mixture with a fuel/air equiva...In this study,we perform a numerical investigation of a steady laminar stagnation flow flame stabilized at a wall with the consideration of heat transport,focusing on a lean hydrogen/air mixture with a fuel/air equivalence ratio 0.6.We discuss the NO emissions and their formation rates under various conditions,such as flow velocity and combustion pressure.It is found that the predominant reaction pathway for NO formation involves NNH radicals,though this changes near the wall surface.Beyond examining the wall's influence on flame structures,the present work focuses on the impact of combustion process on materials.Specifically,the accumulation of atomic hydrogen at the wall surface is explored,which is significant for the consequent modeling of potential hydrogen embrittlement.Additionally,the growth rate of oxide layers on the material surface increases significantly if the combustion pressure and consequently the combustion temperatures are enhanced.These investigations offer valuable insights into how combustion processes affect material,which is useful for designing engineering components under high-temperature environments.展开更多
Though being an important mechanism in systems involving unsteady fluid flows(e.g.,fluids interacting with moving structures,particles in turbulent flows,turbulent flame propagation),the memory effect is usually not c...Though being an important mechanism in systems involving unsteady fluid flows(e.g.,fluids interacting with moving structures,particles in turbulent flows,turbulent flame propagation),the memory effect is usually not considered and has not attracted much attention.The present study tries to highlight the importance of this memory effect based on a variety of examples.In this manner,the three key components characterizing the memory effect can be identified in a general manner.The central mechanism controlling the memory effect is then investigated by studying the flow over a shrinking particle.It is found that the Damköhler number comparing the timescales of the unsteady(trigger)event and of the feedback on the flow directly determines the intensity of the memory effect;a smaller Damköhler number results in a more intense effect.Finally,the flow induced by a flapping wing is considered to demonstrate that the memory effect could be also beneficial for practical applications,for instance for biomimetic locomotion.展开更多
A three-dimensional Direct numerical simulation(DNS)with complex chemistry was employed to examine the statistical behavior of turbulent kinetic energy(TKE)and enstrophy transport equations in hydrogen(Lewis number(Le...A three-dimensional Direct numerical simulation(DNS)with complex chemistry was employed to examine the statistical behavior of turbulent kinetic energy(TKE)and enstrophy transport equations in hydrogen(Lewis number(Le)≈0.4)and dodecane(Le≈4.2)flames.The Karlovitz(Ka)numbers ranged from 4 to 150,involving both the thin and broken reaction zones.Budget analyses of TKE and enstrophy transport equations are performed,and scaling terms in the literature are re-examined.Similar to thin reaction zone flames,viscous dissipation term appears to be the most important term in the TKE balance,while viscous dissipation and vortex-stretching terms are the dominant terms in the enstrophy transport equation at high Ka number.The velocity-pressure gradient and the mean velocity dilatation in the TKE transport equation and the dilatation term in enstrophy budget are found to be affected by the Le.Modified scaling estimations for those terms affected by Le are proposed in this work to account for the Le effects spanning different combustion regimes.This work confirmed that Kolmogorov’s first hypothesis is not valid for low Ka number flames investigated in this study,where the vortex stretching and viscous dissipation terms cannot be scaled with local dissipation and viscosity.At sufficiently high Ka number flames,the vorticity can be scaled with the Kolmogorov time scale,and the mean enstrophy value approaches homogeneous,isotropic,non-reacting turbulence flow,but lower Le fuels require much higher Ka number to achieve that.展开更多
Considering droplet phenomena at low Mach numbers,large differences in the magnitude of the occurring characteristic waves are presented.As acoustic phenomena often play a minor role in such applications,classical exp...Considering droplet phenomena at low Mach numbers,large differences in the magnitude of the occurring characteristic waves are presented.As acoustic phenomena often play a minor role in such applications,classical explicit schemes which resolve these waves suffer from a very restrictive timestep restriction.In this work,a novel scheme based on a specific level set ghost fluid method and an implicit-explicit(IMEX)flux splitting is proposed to overcome this timestep restriction.A fully implicit narrow band around the sharp phase interface is combined with a splitting of the convective and acoustic phenomena away from the interface.In this part of the domain,the IMEX Runge-Kutta time discretization and the high order discontinuous Galerkin spectral element method are applied to achieve high accuracies in the bulk phases.It is shown that for low Mach numbers a significant gain in computational time can be achieved compared to a fully explicit method.Applica-tions to typical droplet dynamic phenomena validate the proposed method and illustrate its capabilities.展开更多
The experimental characterization of particle dynamics in fluidized beds is of great importance in fostering an understanding of solid phase motion and its effect on particle properties in granulation processes, Commo...The experimental characterization of particle dynamics in fluidized beds is of great importance in fostering an understanding of solid phase motion and its effect on particle properties in granulation processes, Commonly used techniques such as particle image velocimetry rely on the cross-correlation of illumination intensity and averaging procedures. It is not possible to obtain single particle velocities with such techniques. Moreover, the estimated velocities may not accurately represent the local particle velocities in regions with high velocity gradients. Consequently, there is a need for devices and methods that are capable of acquiring individual particle velocities. This paper describes how particle tracking velocimetry can be adapted to dense particulate flows. The approach presented in this paper couples high-speed imaging with an innovative segmentation algorithm for particle detection, and employs the Voronoi method to solve the assignment problem usually encountered in densely seeded fows. Lagrangian particle tracks are obtained as primary information, and these serve as the basis for calculating sophisticated quantities such as the solid-phase flow field, granular temperature, and solid volume fraction. We show that the consistency of individual trajectories is sufficient to recognize collision events.展开更多
Rovers on Mars and the Moon analyze the local geology by collecting samples of the upper layer in containers and ovens.After the analysis,the complete discharge of samples from the reservoir must be ensured.Because of...Rovers on Mars and the Moon analyze the local geology by collecting samples of the upper layer in containers and ovens.After the analysis,the complete discharge of samples from the reservoir must be ensured.Because of the low atmospheric pressure,reduced gravity,and different grain shapes of the bulk material,the discharge process is very different compared to that on Earth.In this study,the behavior of lunar regolith JSC-1A in closed containers during discharge was investigated by analyzing the flow in an hourglass under the Earth's atmosphere.Reproducible fluidization of the top particle layer was observed during the outflow of the upper half of the hourglass.These particles were fluidized by the displacement flow initiated by failing particles in the completely closed container.This complex problem was simulated by coupling computational fluid dynamics (CFD)with the discrete element method (DEM). A CFD-DEM simulation with 1million particles was performed.Because billions of particles are present in the actual system,the use of a coarse graining approach was required.In addition,high-speed camera measurements were used to determine the velocities of individual particles to validate the simulation. The fluidization effect was successfully simulated using the coupled method.展开更多
The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method t...The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method to simulate fluid-particle interactions in two-phase particulate flows. Two grids are used in the simulation： a fixed uniform Eulerian grid for the fluid phase and a Lagrangian grid that is attached to and moves with the immersed particles. Forces are calculated at each Lagrangian point. To exchange numerical information between the two grids, discrete delta functions are used. The resulting DF IB-LBM approach is then successfully applied to a variety of reference flows, namely the sedimentation of one and two circular particles in a vertical channel, the sedimentation of one or two spheres in an enclosure, and a neutrally buoyant prolate spheroid in a Couette flow. This last application proves that the developed approach can be used also for non-spherical particles. The three forcing schemes and the different factors affecting the simulation （added mass effect, corrected radius） are also discussed.展开更多
The influence of minute amounts of additives on pressure drop is an interesting fundamental phenomenon, potentially with important practical applications. Change of the pressure drop in a quasi-two-dimensional channel...The influence of minute amounts of additives on pressure drop is an interesting fundamental phenomenon, potentially with important practical applications. Change of the pressure drop in a quasi-two-dimensional channel flow using various additives is experimentally investigated. Tests were conducted for a wide range of concentrations（100 ppm-500 ppm） and Reynolds numbers（16 000-36 000） with two polymers and four rigid fibers used as additive. Maximum drag reduction of 22% was observed for xanthan gum. However, xanthan gum loses its drag-reducing property rapidly. It was also seen that drag reduction percentage of xanthan gum remains almost constant for different Reynolds numbers. Guar flour demonstrated good drag reduction property at high Reynolds numbers. Drag reduction of 17.5% at Re= 33 200 using 300 ppm solution was observed. However, at low Reynolds numbers guar flour will cause an increase in pressure drop. Fiber fillers（aspect ratio=21） have been tested as well. In contrast to polymers, they increased the drag for the range of examined concentrations and Reynolds numbers. Polyacrylonitrile fiber with three different aspect ratios（106, 200, 400） was also used, which showed an increase in pressure drop at low aspect ratios. Polyacrylonitrile fibers of larger lengths（6 mm） demonstrated minor drag-reducing effects（up to 3%）.展开更多
Mandelic acid is an enantiomer of interest in many areas,in particular for the pharmaceutical industry.One of the approaches to produce enantiopure mandelic acid is through crystallization from an aqueous solution.We ...Mandelic acid is an enantiomer of interest in many areas,in particular for the pharmaceutical industry.One of the approaches to produce enantiopure mandelic acid is through crystallization from an aqueous solution.We propose in this study a numerical tool based on lattice Boltzmann simulations to model crystallization dynamics of(S)-mandelic acid.The solver is first validated against experimental data.It is then used to perform parametric studies concerning the effects of important parameters such as supersaturation and seed size on the growth rate.It is finally extended to investigate the impact of forced convection on the crystal habits.Based on there parametric studies,a modification of the reactor geometry is proposed that should reduce the observed deviations from symmetrical growth with a five-fold habit.展开更多
Nowadays,the design of fixed packed bed reactors still relies on empirical correlations,which,especially for small tube to particle diameter ratios,are mostly too inaccurate because of the presence of wall effects.The...Nowadays,the design of fixed packed bed reactors still relies on empirical correlations,which,especially for small tube to particle diameter ratios,are mostly too inaccurate because of the presence of wall effects.Therefore,the simulation of fixed packed bed reactors plays an important role to predict and control the flow and process parameters in such,nowadays and in the future.Because of its straightforward applicability to non-uniform packings with particles of arbitrary shapes,the immersed boundary method(IBM)has advantages over other numerical methods and is used more and more frequently.This paper compares two approaches of IBMs for the simulation of fixed bed reactors with spherical shaped particles.The classic,smooth approach is compared to the straightforward to implement blocked-off method for velocity fields above the fixed bed for particle Reynolds numbers of 300 and 500.Results from experimental inline PIV-measurements of the reactor to be simulated serve as a basis for comparison.Very good agreement with the experiment is found for both simulation methodologies with higher resolutions,considering the more stable flow at a particle Reynolds number of 300.Differences in the different IBM approaches occurred for the more unsteady flow at a particle Reynolds number of 500.Compared to the blocked-off method,the smooth IBM reflects the formation of additional jets and recirculation zones better right above the bed,though increasing the fluid mesh resolution improves the accuracy of the blocked-off method.Overall,a more diffusive behaviour is found for the blocked-off simulations due to the stairstep representation,which is avoided by using interpolation stencils as in the smooth IBM.With higher mesh refinement in the blocked-off IBM this effect can be reduced,but this also increases the computational effort.展开更多
A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular...A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.展开更多
基金financial support by the DFG (project H2MAT3D,project number 523879740 within the DFG-SPP 2419 HyCAM)the Deutsche Forschungsgemeinschaft (DFG),Germany for its support within Project TH881/38-1 (DADOREN)。
文摘In this study,we perform a numerical investigation of a steady laminar stagnation flow flame stabilized at a wall with the consideration of heat transport,focusing on a lean hydrogen/air mixture with a fuel/air equivalence ratio 0.6.We discuss the NO emissions and their formation rates under various conditions,such as flow velocity and combustion pressure.It is found that the predominant reaction pathway for NO formation involves NNH radicals,though this changes near the wall surface.Beyond examining the wall's influence on flame structures,the present work focuses on the impact of combustion process on materials.Specifically,the accumulation of atomic hydrogen at the wall surface is explored,which is significant for the consequent modeling of potential hydrogen embrittlement.Additionally,the growth rate of oxide layers on the material surface increases significantly if the combustion pressure and consequently the combustion temperatures are enhanced.These investigations offer valuable insights into how combustion processes affect material,which is useful for designing engineering components under high-temperature environments.
基金support of the National Natural Science Foundation of China(No.52300183).
文摘Though being an important mechanism in systems involving unsteady fluid flows(e.g.,fluids interacting with moving structures,particles in turbulent flows,turbulent flame propagation),the memory effect is usually not considered and has not attracted much attention.The present study tries to highlight the importance of this memory effect based on a variety of examples.In this manner,the three key components characterizing the memory effect can be identified in a general manner.The central mechanism controlling the memory effect is then investigated by studying the flow over a shrinking particle.It is found that the Damköhler number comparing the timescales of the unsteady(trigger)event and of the feedback on the flow directly determines the intensity of the memory effect;a smaller Damköhler number results in a more intense effect.Finally,the flow induced by a flapping wing is considered to demonstrate that the memory effect could be also beneficial for practical applications,for instance for biomimetic locomotion.
基金supported by the National Natural Science Foundation of China(Grant Nos.91752201 and 11672123)Shenzhen Science and Technology Program(Grant Nos.JCYJ20170412151759222,JCYJ20180302173952945,and KQTD20180411143441009)+1 种基金Department of Science and Technology of Guangdong Province(Grant No.2019B21203001)Project No.LCH-2019011 under the Joint Program of Shenzhen Clean Energy Research Institute and SUSTech through contract CERI-KY-2019-003.
文摘A three-dimensional Direct numerical simulation(DNS)with complex chemistry was employed to examine the statistical behavior of turbulent kinetic energy(TKE)and enstrophy transport equations in hydrogen(Lewis number(Le)≈0.4)and dodecane(Le≈4.2)flames.The Karlovitz(Ka)numbers ranged from 4 to 150,involving both the thin and broken reaction zones.Budget analyses of TKE and enstrophy transport equations are performed,and scaling terms in the literature are re-examined.Similar to thin reaction zone flames,viscous dissipation term appears to be the most important term in the TKE balance,while viscous dissipation and vortex-stretching terms are the dominant terms in the enstrophy transport equation at high Ka number.The velocity-pressure gradient and the mean velocity dilatation in the TKE transport equation and the dilatation term in enstrophy budget are found to be affected by the Le.Modified scaling estimations for those terms affected by Le are proposed in this work to account for the Le effects spanning different combustion regimes.This work confirmed that Kolmogorov’s first hypothesis is not valid for low Ka number flames investigated in this study,where the vortex stretching and viscous dissipation terms cannot be scaled with local dissipation and viscosity.At sufficiently high Ka number flames,the vorticity can be scaled with the Kolmogorov time scale,and the mean enstrophy value approaches homogeneous,isotropic,non-reacting turbulence flow,but lower Le fuels require much higher Ka number to achieve that.
基金support provided by the Deutsche Forschun-gsgemeinschaft(DFG,German Research Foundation)through the project GRK 2160/1“Droplet Interaction Technologies”and through the project no.457811052
文摘Considering droplet phenomena at low Mach numbers,large differences in the magnitude of the occurring characteristic waves are presented.As acoustic phenomena often play a minor role in such applications,classical explicit schemes which resolve these waves suffer from a very restrictive timestep restriction.In this work,a novel scheme based on a specific level set ghost fluid method and an implicit-explicit(IMEX)flux splitting is proposed to overcome this timestep restriction.A fully implicit narrow band around the sharp phase interface is combined with a splitting of the convective and acoustic phenomena away from the interface.In this part of the domain,the IMEX Runge-Kutta time discretization and the high order discontinuous Galerkin spectral element method are applied to achieve high accuracies in the bulk phases.It is shown that for low Mach numbers a significant gain in computational time can be achieved compared to a fully explicit method.Applica-tions to typical droplet dynamic phenomena validate the proposed method and illustrate its capabilities.
基金funding of this work by the German Federal Ministry of Science and Education(BMBF) as part of the InnoProfile-Transfer project NaWiTec(03IPT701X)
文摘The experimental characterization of particle dynamics in fluidized beds is of great importance in fostering an understanding of solid phase motion and its effect on particle properties in granulation processes, Commonly used techniques such as particle image velocimetry rely on the cross-correlation of illumination intensity and averaging procedures. It is not possible to obtain single particle velocities with such techniques. Moreover, the estimated velocities may not accurately represent the local particle velocities in regions with high velocity gradients. Consequently, there is a need for devices and methods that are capable of acquiring individual particle velocities. This paper describes how particle tracking velocimetry can be adapted to dense particulate flows. The approach presented in this paper couples high-speed imaging with an innovative segmentation algorithm for particle detection, and employs the Voronoi method to solve the assignment problem usually encountered in densely seeded fows. Lagrangian particle tracks are obtained as primary information, and these serve as the basis for calculating sophisticated quantities such as the solid-phase flow field, granular temperature, and solid volume fraction. We show that the consistency of individual trajectories is sufficient to recognize collision events.
文摘Rovers on Mars and the Moon analyze the local geology by collecting samples of the upper layer in containers and ovens.After the analysis,the complete discharge of samples from the reservoir must be ensured.Because of the low atmospheric pressure,reduced gravity,and different grain shapes of the bulk material,the discharge process is very different compared to that on Earth.In this study,the behavior of lunar regolith JSC-1A in closed containers during discharge was investigated by analyzing the flow in an hourglass under the Earth's atmosphere.Reproducible fluidization of the top particle layer was observed during the outflow of the upper half of the hourglass.These particles were fluidized by the displacement flow initiated by failing particles in the completely closed container.This complex problem was simulated by coupling computational fluid dynamics (CFD)with the discrete element method (DEM). A CFD-DEM simulation with 1million particles was performed.Because billions of particles are present in the actual system,the use of a coarse graining approach was required.In addition,high-speed camera measurements were used to determine the velocities of individual particles to validate the simulation. The fluidization effect was successfully simulated using the coupled method.
文摘The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method to simulate fluid-particle interactions in two-phase particulate flows. Two grids are used in the simulation： a fixed uniform Eulerian grid for the fluid phase and a Lagrangian grid that is attached to and moves with the immersed particles. Forces are calculated at each Lagrangian point. To exchange numerical information between the two grids, discrete delta functions are used. The resulting DF IB-LBM approach is then successfully applied to a variety of reference flows, namely the sedimentation of one and two circular particles in a vertical channel, the sedimentation of one or two spheres in an enclosure, and a neutrally buoyant prolate spheroid in a Couette flow. This last application proves that the developed approach can be used also for non-spherical particles. The three forcing schemes and the different factors affecting the simulation （added mass effect, corrected radius） are also discussed.
基金financial support of the German research foundation (DFG) within the graduate college for micro-macro-interactions in structured media and particle systems (GRK 1554)
文摘The influence of minute amounts of additives on pressure drop is an interesting fundamental phenomenon, potentially with important practical applications. Change of the pressure drop in a quasi-two-dimensional channel flow using various additives is experimentally investigated. Tests were conducted for a wide range of concentrations（100 ppm-500 ppm） and Reynolds numbers（16 000-36 000） with two polymers and four rigid fibers used as additive. Maximum drag reduction of 22% was observed for xanthan gum. However, xanthan gum loses its drag-reducing property rapidly. It was also seen that drag reduction percentage of xanthan gum remains almost constant for different Reynolds numbers. Guar flour demonstrated good drag reduction property at high Reynolds numbers. Drag reduction of 17.5% at Re= 33 200 using 300 ppm solution was observed. However, at low Reynolds numbers guar flour will cause an increase in pressure drop. Fiber fillers（aspect ratio=21） have been tested as well. In contrast to polymers, they increased the drag for the range of examined concentrations and Reynolds numbers. Polyacrylonitrile fiber with three different aspect ratios（106, 200, 400） was also used, which showed an increase in pressure drop at low aspect ratios. Polyacrylonitrile fibers of larger lengths（6 mm） demonstrated minor drag-reducing effects（up to 3%）.
基金support by the EU-program ERDF(European Regional Development Fund)within the Research Center for Dynamic Systems(CDS).S.A.H.acknowledges the financial support of the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)in TRR 287(Project-ID 422037413).
文摘Mandelic acid is an enantiomer of interest in many areas,in particular for the pharmaceutical industry.One of the approaches to produce enantiopure mandelic acid is through crystallization from an aqueous solution.We propose in this study a numerical tool based on lattice Boltzmann simulations to model crystallization dynamics of(S)-mandelic acid.The solver is first validated against experimental data.It is then used to perform parametric studies concerning the effects of important parameters such as supersaturation and seed size on the growth rate.It is finally extended to investigate the impact of forced convection on the crystal habits.Based on there parametric studies,a modification of the reactor geometry is proposed that should reduce the observed deviations from symmetrical growth with a five-fold habit.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-Project-ID 422037413-TRR 287Gefordert durch die Deutsche Forschungsgemeinschaft(DFG)-Projektnummer 422037413-TRR 287.
文摘Nowadays,the design of fixed packed bed reactors still relies on empirical correlations,which,especially for small tube to particle diameter ratios,are mostly too inaccurate because of the presence of wall effects.Therefore,the simulation of fixed packed bed reactors plays an important role to predict and control the flow and process parameters in such,nowadays and in the future.Because of its straightforward applicability to non-uniform packings with particles of arbitrary shapes,the immersed boundary method(IBM)has advantages over other numerical methods and is used more and more frequently.This paper compares two approaches of IBMs for the simulation of fixed bed reactors with spherical shaped particles.The classic,smooth approach is compared to the straightforward to implement blocked-off method for velocity fields above the fixed bed for particle Reynolds numbers of 300 and 500.Results from experimental inline PIV-measurements of the reactor to be simulated serve as a basis for comparison.Very good agreement with the experiment is found for both simulation methodologies with higher resolutions,considering the more stable flow at a particle Reynolds number of 300.Differences in the different IBM approaches occurred for the more unsteady flow at a particle Reynolds number of 500.Compared to the blocked-off method,the smooth IBM reflects the formation of additional jets and recirculation zones better right above the bed,though increasing the fluid mesh resolution improves the accuracy of the blocked-off method.Overall,a more diffusive behaviour is found for the blocked-off simulations due to the stairstep representation,which is avoided by using interpolation stencils as in the smooth IBM.With higher mesh refinement in the blocked-off IBM this effect can be reduced,but this also increases the computational effort.
基金funded by the Deutsche For-schungsgemeinschaft(DFG,German Research Foundation)-422037413-CRC/TRR 287"BULK-REACTION".
文摘A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.
