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Martin Sommerfeld - One of the best experts on this subject based on the ideXlab platform.
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euler lagrange computations of pneumatic conveying in a Horizontal Channel with different wall roughness
Powder Technology, 2008Co-Authors: Santiago Lain, Martin SommerfeldAbstract:The present study is related to the particle behaviour and the pressure drop in a particle-laden six meter long Horizontal Channel with rectangular cross-section from both experimental and numerical perspectives. Experiments and calculations are carried out for different spherical glass beads with diameters between 60 and 625 μm and mass loadings up to 1.0 (kg particles/kg gas). Additionally, stainless steel walls with different wall roughness are considered. In all experiments the air volume flow rate is constant in order to maintain a fixed gas average velocity of 20 m/s. As a result, the pressure drop in the Channel is strongly influenced by wall roughness. Higher wall roughness implies higher pressure drop because of the increase in wall collision frequency, whereby momentum is extracted from the fluid due to two-way coupling. The numerical computations were performed by the Euler/Lagrange approach accounting for two-way and four-way coupling. For the calculation of the particle motion all relevant forces (i.e. drag, transverse lift and gravity), inter-particle collisions and wall collisions with wall roughness were considered. The agreement of the computations with the experiments was found to be very good for the gas and particle velocities as well as the pressure drop.
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A study of the pneumatic conveying of non-spherical particles in a turbulent Horizontal Channel flow
Brazilian Journal of Chemical Engineering, 2007Co-Authors: Santiago Lain, Martin SommerfeldAbstract:In this work, the pneumatic conveying of non-spherical isometric particles with different degrees of non-sphericity is studied. The solids mass loading fraction is small enough in order to have a dilute flow, so inter-particle collisions can be neglected. As a first approximation, only the aerodynamic drag force acting on the particles is considered, neglecting the lift forces and the particle rotation. The drag coefficient is calculated using the correlations of Haider and Levenspiel (1989) and Ganser (1993). The numerical simulations are compared with experimental data in a narrow six meters long Horizontal Channel flow laden with quartz and duroplastic particles with mean diameters of 185 and 240 m m, respectively (Kussin, 2004).
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wall roughness effects on pneumatic conveying of spherical particles in a narrow Horizontal Channel
Powder Technology, 2004Co-Authors: Martin Sommerfeld, J KussinAbstract:Abstract The present study is related to an experimental analysis of the particle behaviour in a narrow Horizontal Channel flow (length=6 m, height=35 mm, the length is about 170 Channel heights) for different degrees of wall roughness in the range between 2 and 17 μm. Simultaneous air and particle velocity measurements were realised by using a two-component phase Doppler anemometry (PDA), and the static pressure along the Channel was obtained using thin-film pressure sensors. The particles were spherical glass beads with mean diameters in the range of 60–625 μm. The presented results are restricted to an average conveying velocity of about 20 m/s, and the particle mass loading could reach values of about 2 (the mass loading is defined as the ratio of particle to gas phase mass flow rates), depending on particle size. The results demonstrate the influence of particle size, mass loading and the degree of wall roughness on the particle concentration and velocity profiles in the developed gas-particle flow. Additionally, these data allowed to estimate averaged properties, such as the particle slip velocity, their fluctuation energy, as well as the mean free paths between subsequent wall and interparticle collisions. Wall roughness increases the particle fluctuating energy. Thereby, the wall collision and the interparticle collision mean free paths are reduced. The increasing wall collision frequency with increasing degree of wall roughness results in a higher momentum loss for the particle phase, and hence, the slip velocity as well as the pressure loss also increase remarkably.
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analysis of collision effects for turbulent gas particle flow in a Horizontal Channel part i particle transport
International Journal of Multiphase Flow, 2003Co-Authors: Martin SommerfeldAbstract:Abstract The behaviour of spherical solid particles in a Horizontal Channel flow is analysed using numerical calculations based on the Lagrangian approach. Recent developments in modelling particle motion, wall collisions, wall roughness, and inter-particle collisions are accounted for. The wall roughness model relies on the assumption that the impact angle is composed of the particle trajectory angle and a stochastic component due to wall roughness. A stochastic approach is used to describe inter-particle collisions between the considered particle and a fictitious collision partner which is a representative of the local particle phase. Then the collision probability is calculated on the basis of kinetic theory of gases, but accounting for the velocity correlation of colliding particles in turbulent flows. In order to allow an analysis of wall collisions and inter-particle collisions independent of the effect of particles on the flow, two-way coupling was neglected and flow and turbulence were prescribed. The particle behaviour for different boundary conditions, such as particle size, wall roughness and mass loading is discussed in detail. It is demonstrated that both effects, i.e. wall roughness and inter-particle collisions have a dramatic influence on the particle behaviour in a Horizontal Channel and the particle phase properties of the developed flow. In order to characterise the particle behaviour, the mean free path between wall collisions is introduced. In a second part of this work integral properties are presented in order to reveal the effects of wall roughness and inter-particle collisions. Moreover, the effect of Channel height on the particle phase properties is analysed. Finally, the calculations are compared with detailed measurements by phase-Doppler anemometry in a Horizontal Channel with a height of 35 mm and a length of 6 m for validation.
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analysis of collision effects for turbulent gas particle flow in a Horizontal Channel part ii integral properties and validation
International Journal of Multiphase Flow, 2003Co-Authors: Martin Sommerfeld, J KussinAbstract:Abstract The phenomena of particle–wall collisions including wall roughness and inter-particle collisions in a Horizontal Channel flow are analysed in detail by numerical calculations on the basis of the Lagrangian approach. In order to assess the effects of particle–wall collisions and inter-particle collisions independent on other phenomena, two-way coupling is neglected in this study. Integral values of the particle phase properties, such as mean velocities and fluctuating components averaged over the Channel height are used to demonstrate the consequences of both transport effects. The ratios of the fluctuating components are determined in order to assess the unisotropy of the particles fluctuating behaviour. Additionally, a Channel with a larger height is considered in order to provide information on the scale-up of the effects observed in a narrow Channel. For validating the Lagrangian models describing particle–wall and inter-particle collisions, numerical calculations for different particle size and mass loading are compared with measurements by phase-Doppler anemometry in the developed region of a Channel with 35 mm height and 6 m length. The good agreement between measurements and calculations allow to conclude that the transport phenomena wall collisions and inter-particle collisions are modelled appropriately.
J Kussin - One of the best experts on this subject based on the ideXlab platform.
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wall roughness effects on pneumatic conveying of spherical particles in a narrow Horizontal Channel
Powder Technology, 2004Co-Authors: Martin Sommerfeld, J KussinAbstract:Abstract The present study is related to an experimental analysis of the particle behaviour in a narrow Horizontal Channel flow (length=6 m, height=35 mm, the length is about 170 Channel heights) for different degrees of wall roughness in the range between 2 and 17 μm. Simultaneous air and particle velocity measurements were realised by using a two-component phase Doppler anemometry (PDA), and the static pressure along the Channel was obtained using thin-film pressure sensors. The particles were spherical glass beads with mean diameters in the range of 60–625 μm. The presented results are restricted to an average conveying velocity of about 20 m/s, and the particle mass loading could reach values of about 2 (the mass loading is defined as the ratio of particle to gas phase mass flow rates), depending on particle size. The results demonstrate the influence of particle size, mass loading and the degree of wall roughness on the particle concentration and velocity profiles in the developed gas-particle flow. Additionally, these data allowed to estimate averaged properties, such as the particle slip velocity, their fluctuation energy, as well as the mean free paths between subsequent wall and interparticle collisions. Wall roughness increases the particle fluctuating energy. Thereby, the wall collision and the interparticle collision mean free paths are reduced. The increasing wall collision frequency with increasing degree of wall roughness results in a higher momentum loss for the particle phase, and hence, the slip velocity as well as the pressure loss also increase remarkably.
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analysis of collision effects for turbulent gas particle flow in a Horizontal Channel part ii integral properties and validation
International Journal of Multiphase Flow, 2003Co-Authors: Martin Sommerfeld, J KussinAbstract:Abstract The phenomena of particle–wall collisions including wall roughness and inter-particle collisions in a Horizontal Channel flow are analysed in detail by numerical calculations on the basis of the Lagrangian approach. In order to assess the effects of particle–wall collisions and inter-particle collisions independent on other phenomena, two-way coupling is neglected in this study. Integral values of the particle phase properties, such as mean velocities and fluctuating components averaged over the Channel height are used to demonstrate the consequences of both transport effects. The ratios of the fluctuating components are determined in order to assess the unisotropy of the particles fluctuating behaviour. Additionally, a Channel with a larger height is considered in order to provide information on the scale-up of the effects observed in a narrow Channel. For validating the Lagrangian models describing particle–wall and inter-particle collisions, numerical calculations for different particle size and mass loading are compared with measurements by phase-Doppler anemometry in the developed region of a Channel with 35 mm height and 6 m length. The good agreement between measurements and calculations allow to conclude that the transport phenomena wall collisions and inter-particle collisions are modelled appropriately.
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experimental studies on particle behaviour and turbulence modification in Horizontal Channel flow with different wall roughness
Experiments in Fluids, 2002Co-Authors: J Kussin, Martin SommerfeldAbstract:Detailed measurements in a developed particle-laden Horizontal Channel flow (length 6 m, height 35 mm, the length is about 170 Channel heights) are presented using phase-Doppler anemometry for simultaneous determination of air and particle velocity. The particles were spherical glass beads with mean diameters in the range of 60 µm–1 mm. The conveying velocity could be varied between about 10 m/s and 25 m/s, and the particle mass loading could reach values of about 2 (the mass loading is defined as the ratio of particle to gas phase mass flow rates), depending on particle size. For the first time, the degree of wall roughness could be modified by exchanging the wall plates. The influence of these parameters and the effect of inter-particle collisions on the profiles of particle mean and fluctuating velocities and the normalised concentration in the developed flow were examined. It was shown that wall roughness decreases the particle mean velocity and enhances fluctuating velocities due to irregular wall bouncing and an increase in wall collision frequency, i.e. reduction in mean free path. Thereby, the larger particles are mainly more uniformly distributed across the Channel, and gravitational settling is reduced. Both components of the particle velocity fluctuation were reduced with increasing mass loading due to inter-particle collisions and the momentum loss involved. Moreover, the effect of the particles on the air flow and the turbulent fluctuations was studied on the basis of profiles in the developed flow and turbulence spectra determined for the streamwise velocity component. In addition to the effect of particle size and mass loading on turbulence modulation, the influence of wall roughness was analysed. It was clearly shown that increasing wall roughness also results in a stronger turbulence dissipation due to two-way coupling.
F. C. Lai - One of the best experts on this subject based on the ideXlab platform.
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Electrohydrodynamically Enhanced Forced Convection in a Horizontal Channel by Nonsymmetric Electric Field
Journal of Thermophysics and Heat Transfer, 2020Co-Authors: J. C. Leong, F. C. LaiAbstract:The present study investigates heat transfer enhancement of forced convection in a Horizontal Channel by nonsymmetric electric field. The electrical field is generated from a wire electrode charged...
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Electrohydrodynamically-Enhanced Forced Convection in a Horizontal Channel with Oscillatory Flows
Heat Transfer Engineering, 2010Co-Authors: F. C. Lai, Kongkee TayAbstract:Prior studies on electrohydrodynamically enhanced forced convection in a Horizontal Channel have revealed the existence of oscillatory flows. These oscillatory flows are the product of interactions between the electric body force and flow inertia of the primary flow. It has also been shown that heat transfer can be significantly enhanced when operating in this oscillatory flow mode. It is speculated that heat transfer may be further enhanced by exciting the primary flow in a frequency similar to those observed for the oscillatory flows (i.e., the so-called resonant effect). To verify this speculation, computations have been performed for primary flows excited with a frequency that is either a fraction or multiple of the natural frequency observed in the original oscillatory flows. The results show that an inlet flow excited at the natural frequencies produces the best heat transfer enhancement in the single-cell regime, and the enhancement increases with the Reynolds number. However, the results show an o...
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Correlations for combined heat and mass transfer from an open cavity in a Horizontal Channel
International Communications in Heat and Mass Transfer, 2005Co-Authors: N. M. Brown, F. C. LaiAbstract:Abstract Combined heat and mass transfer from a Horizontal Channel with an open cavity heated from below is numerically examined in this paper. Air is the fluid considered ( Pr = 0.7). The main focus of the study is mass-transfer driven flows (| N | > 1). The governing parameters considered are the buoyancy ratio N , Lewis number Le , Reynolds number Re , and Grashof number Gr . Based on the scale analysis, correlations for the entire convection regime, from natural, mixed, to forced convection, were proposed.
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Effects of buoyancy on electrohydrodynamic-enhanced forced convection in a Horizontal Channel
1998Co-Authors: F. C. LaiAbstract:Buoyancy effects on heat transfer enhancement using an electrohydrodynamic (EHD) technique is numerically examined for laminar forced convection in a Horizontal Channel. Attention is also focused on the effect of added buoyancy on the flow stability. The flow Reynolds numbers and thermal buoyancy strength considered are in the range of 6 x 10 2 ≤ Re ≤ 1.8 x 10 3 and 10 4 ≤ Gr ≤ 10 6 , respectively. The electrical field is generated by positive corona from a wire electrode charged with dc high-voltage (10 ≤ V 0 ≤ 17.5 kV). In terms of an EHD number, this corresponds to 0.36 < N ehd ≤ 23.56. The results show that heat transfer enhancement increases with the applied voltage. For a given electric field, oscillation in the flow and temperature fields is observed for flows at small Reynolds numbers. In addition, the flow and temperature fields become more unstable with an increase in the thermal buoyancy strength. Because of the existence of secondary flows, there is an improvement in heat transfer. However, it is observed that thermal buoyancy has a negligible effect on the heat transfer enhancement for Gr < 10 6
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Enhanced heat transfer in a Horizontal Channel with double electrodes
Industry Applications Conference, 1995. Thirtieth IAS Annual Meeting, IAS '95., Conference Record of the 1995 IEEE, 1995Co-Authors: Jyothis Mathew, F. C. LaiAbstract:Enhancement in heat transfer using electrohydrodynamic (EHD) technique is numerically examined for laminar forced convection in a Horizontal Channel with two electrodes. Attention is also focused on the effect of added electric field on the flow stability. The electrical field is generated by positive corona from wire electrodes charged with a high DC voltage (10⩽V0⩽17.5 kV). The flow Reynolds numbers considered are in the range of 75⩽Re⩽2400. For a given electric field, oscillation in the flow and temperature fields has been observed for flows at small Reynolds numbers. The flow and temperature fields tend to stabilize when the Reynolds number is increased. Due to the existence of secondary flows, there is an improvement in heat transfer and it is most notable far flows at a small Reynolds number. In addition, it is found that heat transfer enhancement increases with the applied voltage
Zhu Huang - One of the best experts on this subject based on the ideXlab platform.
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steady mixed convective flow and heat transfer from tandem square cylinders in a Horizontal Channel
Numerical Heat Transfer Part A-applications, 2017Co-Authors: Renan Yuan, Zhu HuangAbstract:ABSTRACTThe two-dimensional laminar steady mixed convective flow and heat transfer around two identical tandem square cylinders confined in a Horizontal Channel are simulated by the high-accuracy multidomain pseudo-spectral method. The blockage ratio of the Channel is chosen as 0.1, whereas the spacing between the cylinders is fixed with four widths of the cylinder. The Prandtl number is fixed at 0.7, the Reynolds number (Re) is studied in the range 5 ≤ Re ≤ 60, and the Richardson number (Ri) demonstrating the influence of thermal buoyancy ranges from 0 to 1. Numerical results reveal that, with the thermal buoyancy effect, the mixed convective flow remains steady. The variations of the overall drag and lift coefficients and the Nusselt numbers, are presented and discussed. Furthermore, the influence of thermal buoyancy on fluid flow and heat transfer is discussed and analyzed.
B. Ghasemi - One of the best experts on this subject based on the ideXlab platform.
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Cooling enhancement of two fins in a Horizontal Channel by nanofluid mixed convection
International Journal of Thermal Sciences, 2012Co-Authors: I. Pishkar, B. GhasemiAbstract:Abstract This paper presents a numerical study of the thermal performance of two fins mounted on the bottom wall of a Horizontal Channel and cooled with either pure water or a Cu–water nanofluid. The bottom wall of the Channel is heated at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The top wall is adiabatic. The effects of pertinent parameters such as the Reynolds and Richardson numbers, the solid volume fraction, and the distance and the thermal conductivity of the fins on their thermal performance are studied. The results of the numerical simulation indicate that the heat transfer rate of fins is significantly affected by the distance and the thermal conductivity of the fins. The influence of the solid volume fraction on the increase of heat transfer is more noticeable at higher values of the Reynolds number. The fins behave differently in terms of their thermal performances at higher values of the Reynolds number.
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EFFECT OF NANOPARTICLES ON MIXED CONVECTION HEAT TRANSFER IN A Horizontal Channel WITH HEAT SOURCE
2012Co-Authors: I. Pishkar, B. GhasemiAbstract:A numerical investigation of mixed convection heat transfer with nanofluid and pure water from a heat source in a Horizontal Channel is performed. The walls of the Channel are adiabatic and the heat source is placed at the bottom wall of the Channel. Free flow at cold temperature enters Channel and takes heat from heat source. Discretization of the continuity, momentums and energy equations are achieved through a finite volume method and solved with SIMPLE method. The Brownian motion of nanoparticles is simulated to determine the thermal conductivity of the nanofluid. The results show that using the nanofluid caused to heat diffusion and average temperature of source to increase. Also, increase in solid volume fraction causes increase in heat transfer especially at high Reynolds number. It is understand that with increase in ratio of length to height of source in its constant area, heat transfer decreases first and then increases.
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a numerical study of mixed convection in a Horizontal Channel with a discrete heat source in an open cavity
European Journal of Mechanics B-fluids, 2009Co-Authors: S M Aminossadati, B. GhasemiAbstract:This article aims to numerically investigate mixed convection heat transfer in a two-dimensional Horizontal Channel with an open cavity. A discrete heat source is considered to be located on one of the walls of the cavity. Three different heating modes are considered which relate to the location of the heat source on three different walls (left, right and bottom) of the cavity. The analysis is carried out for a range of Richardson numbers and cavity aspect ratios. The results show that there are noticeable differences among the three heating modes. When the heat source is located on the right wall, the cavity with an aspect ratio of two has the highest heat transfer rate compared to other cavity heating modes. Moreover, when the heat source is located on the bottom wall, the flow field in the cavity with an aspect ratio of two experiences a fluctuating behaviour for Richardson number of 10. The results also show that at a fixed value of Richardson number, all three different heating modes show noticeable improvements in the heat transfer mechanism as the cavity aspect ratio increases.