Vol. 4, No. 2, Issue special, Year 2011
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Hot Air Engines|
Invented in 1816, the hot-air engines have known significant commercial success in the nineteenth century, before falling into disuse. Nowadays they enjoy a renewed interest for some specific applications. The "hot-air engines" family is made up of two groups: Stirling engines and Ericsson engines. The operating principle of Stirling and Ericsson engines, their troubled history, their advantages and their niche applications are briefly presented, especially in the field of micro-combined heat and power, solar energy conversion and biomass energy conversion. The design of an open cycle Ericsson engine for solar application is proposed. A first prototype of the hot part of the engine has been built and tested. Experimental results are presented.
2011, Vol. 4, No. 2, special, pp 1-8
Laminar Sinusoidal and Pulsatile Flows in a Curved Pipe|
M. Jarrahi†, C. Castelain and H. Peerhossaini
Two components of pulsatile flow (i.e. steady flow and sinusoidal flow) are studied separately by particle image velocimetry (PIV).The topology of the secondary flow structures, axial vorticities and transverse strain rates in a pure sinusoidal flow and also in a steady flow are compared to those in a pulsatile flow through a curved pipe. The experimental setup provides different conditions for the flow entering a 90° circular curved pipe of diameter 0.04 m and curvature radius 0.22m. Pulsatile flows were studied for two stationary Reynolds numbers, Rest=420 and Rest=600. The frequency parameters α=10.26 and α=14.51 were chosen to study pure sinusoidal flow (α=r0(ω/ν)0.5). Pulsating conditions were obtained by combining steady and sinusoidal flow for (Rest=600, α=10.26), (Rest=600, α=14.51) and (Rest=420, α=14.51). The results of this study contribute to a better understanding of mixing in a developing laminar flow through curved pipes (helical and twisted/chaotic mixers) in steady state flow, pure sinusoidal flow and pulsatile flow.
2011, Vol. 4, No. 2, special, pp 21-26
Immersed Boundary Method for the Solution of 2D Inviscid Compressible Flow Using Finite Volume Approach on Moving Cartesian Grid|
S.M.H. Karimian and M. Ardakani
In this study, two-dimensional inviscid compressible flow is solved around a moving solid body using Immersed Boundary Method (IBM) on a Cartesian grid. Translational motion is handled with a Cartesian grid generated around the body which moves with body on a background grid. In IBM, boundaries are immersed within the grid points. In this paper solution domain is discretized using finite volume approach. To implement boundary conditions on immersed boundaries, a set of Ghost finite volumes are defined along the wall boundaries. Boundary conditions are used to assign flow variables on these Ghost finite volumes. Governing equations are solved using dual time step method of Jameson. Finally, numerical results obtained from the present study are compared with the other numerical results to evaluate the correct performance of the present algorithm and its accuracy.
2011, Vol. 4, No. 2, special, pp 27-36
Heat Transfer of Non-Newtonian Dilatant Power Law Fluids in Square and Rectangular Cavities|
I. Vinogradov, L. Khezzar and D. Siginer
Steady two-dimensional natural convection in fluid filled cavities is numerically investigated for the case of non-Newtonian shear thickening power law liquids. The conservation equations of mass, momentum and energy under the assumption of a Newtonian Boussinesq fluid have been solved using the finite volume method for Newtonian and non-Newtonian fluids. The computations were performed for a Rayleigh number, based on cavity height, of 105 and a Prandtl number of 100. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. The simulations have been carried out for aspect ratios of 1 and 4. Comparison between the Newtonian and the non-Newtonian cases is conducted based on the dependence of the average Nusselt number on angle of inclination. It is shown that despite significant variation in heat transfer rate both Newtonian and non-Newtonian fluids exhibit similar behavior with the transition from multi-cell flow structure to a single-cell regime.
2011, Vol. 4, No. 2, special, pp 37-42
Modeling and Simulation of Interfacial Turbulent Flows|
E. Shirani, F. Ghadiri and A. Ahmadi
Majority of the fluid flows in nature and industries are turbulent flows. Due to their complexity, modeling and simulation of turbulent flows are still among the top research topics in the field of fluid mechanics. The objective of this work is to consider the turbulence effects at the interface. The presence of interface affects the turbulence structures and they become anisotropic near the interface. In this work, the main objective is to consider the fluctuations of the interface topology and their effects on the volume fraction and the surface tension force at the interface. These effects are important under some circumstances especially when the shape of the interface changes rapidly and abruptly. The surface tension forces and the volume fraction-velocity fluctuation correlation have also important impact on the interface topology and its complicated features such as coalescence and breakup. Different new models are presented and the impacts of those parameters on the flow at the interface are presented in this work. In developing the models for mean velocity-volume fraction fluctuations the inhomogeneity of the flow at the interface is taken into account. Both Reynolds Averaged Navier-Stokes Equations and the Large Eddy Simulation Techniques were used to simulate turbulent interfacial flows and implement the novel models introduced in this work. The Kelvin-Helmholtz instability, two-dimensional and three dimensional jets, and water/oil phase separation were simulated numerically and the results were compared with corresponding valid data and the accuracy of the models was examined.
2011, Vol. 4, No. 2, special, pp 43-49
Numerical Simulation of Buoyancy-Induced Micropolar Fluid Flow between Two Concentric Isothermal Spheres|
M. Khoshab and A.A. Dehghan
Natural convection heat transfer between two differentially heated concentric isothermal spheres utilizing micropolar fluid is investigated numerically. The two-dimensional governing equations are discretized using control volume method and solved by employing the alternating direction implicit scheme. Results are presented in the form of streamline and temperature patterns, local and average Nusselt numbers, over the heated and cooled boundaries for a wide range of Rayleigh numbers, Prandtl numbers and dimensionless vortex viscosity dimensionless micro-inertia density and microrotation boundary condition (n) for radius ratio of 2. The goal of this work is to investigate heat transfer characteristics of natural convection in the annulus between concentric spheres using micropolar theory. It is shown that micropolar fluids give lower heat transfer values than those of the Newtonian fluids. It is also found that the average Nusselt number increases with increasing Rayleigh and Prandtl numbers. On the other hand, it is disclosed that increasing the vortex viscosity reduces the heat transfer rate. The results are compared with the data available in the open literatures, and an excellent agreement was obtained. Finally, a correlation between the average Nusselt number, Rayleigh number and material parameter is presented.
2011, Vol. 4, No. 2, special, pp 51-59
Vortex Structure in the Wall Region of an Impinging Plane Jet|
A. Koched, M. Pavageau and F. Aloui
The work presented here comes within a research program dealing with vortex detection in the impingement region of a planar jet. In this study, experiments have been performed for a submerged turbulent water slot jet impinging normally on a flat plate, and an emphasis was put on the flow field characteristics. For this purpose, particle image velocimetry (PIV) have been employed. A comprehensive fluid mechanical data includes instantaneous and mean flow field, variance of normal and cross velocity fluctuations have been presented. The present work is also concerned with the flow structure in the impingement region where the transfers (heat/mass) occur. An attempt has been made to understand the flow structure by employing the vortex detection criteria on the instantaneous velocity vector field. Accordingly, the PIV measurements were carried out for four different Reynolds numbers: 3000, 6000, 11000 and 16000, and at three different planes: a plane parallel to the impingement plate, transverse plane of the jet and a plane perpendicular to the jet. A method of filtration, based on proper orthogonal decomposition (POD) technique was applied first to the instantaneous velocity and filtered velocity database is then used for vortex detection. Further, the results about the size, shape, spatial distribution and energy content of the detected vortices have been provided.
2011, Vol. 4, No. 2, special, pp 61-69
Drying and Heating Modelling of Granular Flow: Application to the Mix-Asphalt Processes|
L. LeGuen, F. Huchet and P. Tamagny
Concrete asphalt is a hydrocarbon material that includes a mix of mineral components along with a bituminous binder. Prior to mixing, its production protocol requires drying and heating the aggregates. Generally performed in a rotary drum, these drying and heating steps within mix asphalt processes have never been studied from a physical perspective. We are thus proposing in the present paper to analyze the drying and heating mechanisms when granular materials and hot gases are involved in a co-current flow. This process step accounts for a large proportion of the overall energy consumed during hot-mix asphalt manufacturing. In the present context, the high energy cost associated with this step has encouraged developing new strategies specifically for the drying process. Applying new asphalt techniques so that an amount of moisture can be preserved in the asphalt concrete appears fundamental to such new strategies. This low-energy asphalt, also referred to as the "warm technique", depends heavily on a relevant prediction of the actual moisture content inside asphalt concrete during the mixing step. The purpose of this paper is to present a physical model dedicated to the evolution in temperature and moisture of granular solids throughout the drying and heating steps carried out inside a rotary drum. An initial experimental campaign to visualize inside a drum at the pilot scale (i.e. 1/3 scale) has been carried out in order to describe the granular flow and establish the necessary physical assumptions for the drying and heating model. Energy and mass balance equations are solved by implementing an adequate heat and mass transfer coupling, yielding a 1D model from several parameters that in turn drives the physical modeling steps. Moreover, model results will be analyzed and compared to several measurements performed in an actual asphalt mix plant at the industrial scale (i.e. full scale).
2011, Vol. 4, No. 2, special, pp 71-80
Experimental and Numerical Investigations of Two-Phase Electrolysis Processes - Electrical Energy Conversion in Hydrogen Production|
Z. Derhoumi, P. Mandin, R. Wuthrich and H. Roustan
During two-phase electrolysis processes, for example for hydrogen production, there are bubbles which are created at electrodes. This implies a great vertical motion source in the normal earth gravity field and then a quite important natural two-phase convection. All other fields are then affected. Heat, mass and electricity transfers are modified due to both bubbles screening (at surface and in volume) and to bubbles transport promotion. Many numerical modeling for two-phase processes such as kerosene pulverization in engines or coal combustion sciences have shown the difficulties of these multi-physics processes. Both particles and reactor scales must be considered according with a strong coupling modeling. In these processes the particles injection is “in the flow”. In boiling or electrolysis processes, a new difficulty is added: particles birth or injection is strongly coupled to the local flow properties and leads to a complex boundary condition at surfaces. Electrical and electrochemical properties and processes are disturbed. This disturbance can lead to the modification of the local current density and to anode effects for example. There is few works concerning the local modelling of electrochemical processes during a two-phase electrolysis process. There are also few local experimental measurements in term of chemical composition, temperature or current density which will allow the numerical calculations validation. The present work shows the started numerical modeling strategy and the first results, both experimental and numerical obtained.
2011, Vol. 4, No. 2, special, pp 81-87
Mixed Boundary Conditions for Two-Dimensional Transient Heat Transfer Conduction under Lattice Boltzmann Simulations|
R. Chaabane, F. Askri and S.B. Nasralla
In this paper, lattice Boltzmann implementations of several types of boundary conditions are introduced and numerically demonstrated. A thermal lattice BGK model is used to simulate thermal fields for flows. The unknown thermal distribution functions at the boundary are subjected to the bounce back concept which is determined consistently with Dirichlet and/or Neumann and/or convective boundary conditions. A consistency analysis using heat transfer conduction is given and the algorithms are numerically tested in two space dimensions with respect to accuracy, numbers of iterations and CPU time. The method is used to simulate conduction transfer problems; numerical results and reference’s solutions are found in satisfactory agreement for thermal fields.
2011, Vol. 4, No. 2, special, pp 89-98
A Novel Approach to Study the Performance of Finned-Tube Heat Exchangers under Frosting Conditions|
A.L. Bendaoud, M. Ouzzane, Z. Aidoun and N. Galanis
Frost accumulation due to moist air flowing on a refrigeration coil cold surface impacts negatively on performance. The frost layer growth has an insulating effect in terms of heat transfer and causes the increase of the air pressure drop by blocking the free flow area across the coil. In this paper a new modeling approach, accounting for heat and mass transfer as well as the hydrodynamics of the problem, is proposed. A related FORTRAN program was developed, allowing the study of a large range of complex refrigerant circuit configurations. This model predicts the dynamic behavior of a refrigeration coil under dry and frosting conditions. Comparaisons were made based on the frost mass accumulation and pressure drop across the coil and the results were found to agree reasonably well with experimental results reported in the literature. The model was then applied to study an evaporator typically employed in supermarkets. In terms of refrigerant temperature glide, it was shown that the glide decrease with time because of the decrease of the refrigeration capacity of the coil during the frosting. Further, the air pressure drop is strongly affected by the variation of the free flow area.
2011, Vol. 4, No. 2, special, pp 9-20
A Reynolds Stress Closure for Compressible Turbulent Flow|
H. Khlifi and T. Lili
Several studies of compressible flows show that the pressure-strain is the main indicator of the structural compressibility effects. Undoubtedly, this term controls the change in the Reynolds stress anisotropy. Regarding the model of Adumitroiae et al., the slow part of the pressure strain correlation like the Rotta model uses the standard coefficient C1. The model predictions do not show large differences when compressibility increases. Correction of this coefficient using the turbulent Mach number is proposed. The two forms model of Adumitroiae et al. (with and without correction of ) are considered to study compressible mixing layers . The obtained results show that the predictions of the proposed compressibility correction model agree with the experiment results of Goebel and Dutton.
2011, Vol. 4, No. 2, special, pp 99-104
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