فهرست مطالب

Applied Fluid Mechanics - Volume:9 Issue: 3, May-Jun 2016

Journal Of Applied Fluid Mechanics
Volume:9 Issue: 3, May-Jun 2016

  • Special Issue 2
  • تاریخ انتشار: 1395/01/26
  • تعداد عناوین: 9
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  • Boulahlib Mohamed Salah, Boukhalfa Abdelkrim Pages 177-188
    An experimental procedure with post processing to measure the temperature fields in premixed turbulent flame is presented. Temperature measurements were performed on turbulent premixed flame CH4-air with an equivalence ratio It utilizes the Fine Wire Compensated Thermometry (FWCT) technique. Using fine wire thermocouples for a temporal resolution of the measurement in high temperature requires specific treatment of these values. When the temperature of the environment is high, the radiant loss becomes important. The temperature measured by the hot junction is less than the environment temperature. These losses are estimated by one model, which make it possible to correct the difference between thermocouple temperature and gas temperature. Temperature measure by Fine Wire Compensated Thermocouple requires knowledge of flow velocity, the experimental conditions, the acquisition parameters (sampling frequency) for post-processing. In addition to this, the catalytic effect was incorporated to the final balance equation. The flame temperature and its fluctuations are analyzed by digital processing algorithms. Measurements validation made by the FWCT technique with optical measurement methods (Rayleigh scattering) shows a good agreement.
    Keywords: Experimental, Premixed combustion, Fine wire, Compensation, Thermometry
  • C. Hemmer, F. Convert, Catalin Popa, Guillaume Polidori Pages 189-195
    Thermal comfort in buildings is an important property for the quality of indoor environments, but also for the quantity of energy to be supplied by heating equipment. It is therefore important to understand and control the heat exchanges that come into play in the electric heaters. The electric heaters transfer their energy to the environment by convection and radiation. This paper presents a 3D numerical study of turbulent and steadyairflow, in a living space (width 3.4m, 4.5m length and 2.6m height). The influence of the electric heater position in the room will be reviewed to improve the thermal comfort and energy performance of the system. Transport equations of mass, momentum and energy are solved numerically using the finite volume method. Also, the radiative heat exchanges between surfaces are considered.
    Keywords: Thermal comfort, Electric heater, Natural convection, Radiation, CFD
  • S. Martel, M. Dostie, Y. Mercadier Pages 197-205
    The use of two-phase ejectors to improve refrigeration systems encounters today a great interest. However, modeling of such devices with low void fraction at the entrance of the motive nozzle, presents significant challenges. The choking conditions and the discontinuities appearing in a two-phase flow in a nozzle are not well documented and some works are needed to better anticipated flow behavior under these conditions. This paper presents a steady state two-phase flow model including new choking criterions for one-dimensional conservative systems. The present model is a two-fluid, one pressure model with thermal equilibrium and mechanical disequilibrium. As a first step, this model is used to study the flow in the motive nozzle of an ejector.
    Keywords: Two phase flow, Critical flow, Critical location, Nozzle flow
  • Sawsen Rezig, Rosario Toscano, Gilles Rusaouen, Vincent Lozano Pages 207-212
    3-D Lagrangian Particle Tracking (3DLPT) is becoming widely used to characterize the convective indoor air movements in large scale spaces. The need to implement a robust algorithm led us to develop a multi-scale based approach to detect features (Helium filled soap bubbles). On the other hand, theparticle tracking is another challenging problem. To this end, a new tracking algorithm based on fuzzy Kalman filtering is proposed in this paper. The Kalman filter is used to optimally estimate the new position of the particles based on their actual position. In our approach, the initial particle positions are represented with multivariate fuzzy sets.
    Keywords: Indoor airflow, 3D PTV, Particle detection, Temporal tracking, Kalman filtering, Fuzzy logic
  • K. Ameur, Z. Aidoun, M. Ouzzane Pages 213-222
    In this study, it is proposed to lift the no-slip constraint imposed in the Homogenous equilibrium Model (HEM) for two-phase ejector design and analyse its effects on performance. Two models accounting for slip are used: the first, currently available in the literature is due to Moody and the second, developed by the authors is proposed as an alternative. Firstly, in order to avoid the direct computation of the velocity of sound in two-phase flow close to critical conditions, it is proposed to maximise the mass flow rate in the nozzle without recourse to the Mach number, since the computation of this latter in two-phase conditions has not yet gained consensus. Secondly, the introduction of a slip factor accounting for the velocity difference between vapour and liquid phases has allowed achieving remarkable improvements of critical flow computations, especially when using the newly developed approach by the authors. Thirdly a test facility for two-phase ejectors using R134a as refrigerant has been built for further studies. First results have allowed to validate the models predictions of the critical flow over a large interval of operating conditions. Lastly, analysis indicates that neglecting interphase slip may have a significant impact on two-phase ejector design. In this way and under some ejector inlet conditions, the prediction gap between HEM and the new model falls in the range of 13 to 23% in terms of compression ratio and in the range of 33 to 39% for the nozzle throat diameter.
    Keywords: Two, phase ejector, Critical flow, Modeling, Slip flow, Experiments
  • A. Omara, A. Bourouis, Said Abboudi Pages 223-233
    A numerical study was conducted to investigate thermal non equilibrium natural convection heat transfer in a square porous cavity with partial active vertical walls. The left vertical side wall is partially heated while the right side wall is partially cooled. The remaining portions of the vertical side walls as well as the top and bottom of the cavity are adiabatic. Depending on the location of hot part and cold part, respectively on the left and right side walls, different cases may be obtained. In this study we are limited to two cases: Upper-Lower and Lower-Upper active walls. The Brinkman Forchheimer extended Darcy model is used in the present study. Moreover, the two equations model is used to take into account separately local temperatures of the fluid and the solid. The resulting governing equations are solved by finite volume method and the standard SIMPLER algorithm. Numerical experiments have been carried out for a wide range of parameters, namely: Rayleigh number, Darcy number, inter-phase heat transfer coefficient and modified conductivity ratio. The obtained results reveal that the location of the hot and cold parts on the vertical side walls has a significant influence on the flow structure and the rate of heat transfer within the enclosure.
    Keywords: Partially active walls, Non, Darcy Brinkman, Forchheimer model, Numerical approach, Local thermal non, equilibrium model
  • Koutoua Simon Kassi, Marie, Isabelle Farinas, Issouf Fofana, Christophe Volat Pages 235-243
    In this paper, experimental and numerical investigations were conducted to study the aging impact on the cooling capacity of mineral oils in power transformers. The experimental investigations had three objectives. Firstly the study of the impact of oil aging on its physicochemical properties using two diagnostic techniques which are: DDP (Dissolved Decay Products) according to ASTM (American Society for Testing and Materials)-D6802 standard and Interfacial Tension (IFT) according to ASTM-D971 standard. Secondly,the study of the impact of oil aging on its viscosity according to ASTM D445. Finally the development of empirical equations depicting oil viscosity changes, to be implemented in the numerical model. To achieve this, accelerated thermal aging tests of mineral oil samples were conducted in laboratory conditions according to ASTM D-1934standard. Data from experimental investigations were used to conduct the numerical investigations. A 2D axisymmetric numerical model was developed with COMSOL Multiphysics 4.3a to study the cooling capability of oil aged at different levels. The results indicate that the oil physicochemical properties are affected by aging. Furthermore the results show that the oil viscosity increase with aging and give a good correlation between viscosity and aging indicators. Finally it was found that sludge from oil oxidation byproduct contributes to the formation of hotspots and this leads to a significant increase of hotspot temperature in the power transformers.
    Keywords: Power transformer, Viscosity, Aging indicators, CFD, Axisymmetric model, Hotspot, Sludge, Temperature, Velocity, Horizontal duct, Vertical duct, zigzag cooling, Disc, type winding
  • Anh Dung Tran Le, D. Samri, M. Rahim, O. Douzane, G. Promis, C. Maalouf, M. Lachi, T. Langlet Pages 245-252
    Hemp concrete has been used more and more in building construction because hemp is a renewable plant, recyclable and does not degrade within time. Up to now, many simulation tools use the sorption isotherms that describe the relationship between relative humidity of air and the moisture content to predict the humidity in porous materials. However, the sorption capacity of material depends on temperature. The objective of this paper is to study the impact of the temperature dependency of the sorption curves on the hygrothermal behavior of a hemp concrete building envelope. Numerical models to describe the coupled heat and mass transfer in porous materials are presented and validated against experimental data. In addition, the effect of temperature-dependent sorption on the hygrothermal profiles of a hemp concrete wall submitted to outdoor real conditions has been conducted. The results show that taking the influence of temperature on the sorption characteristics into account is necessary for better prediction of the hygrothermal behavior of a hemp concrete building envelope.
    Keywords: Hygrothermal behavior, Temperature, dependent sorption, Hemp concrete
  • H. E. Mghari, H. Louahlia, Gualous Pages 253-258
    This paper presents an experimental study of capillary steam condensation in two circular glass microtubes (480μm and 280μm diameters). It described the experimental set up and micro instrumentation used to analyze condensation inside a microtube. Experimental results concerns effect of the pressure and cooling heat flux on the condensation flow regimes in microtube. Along the flow direction, annular, slug, plug, mist and bubbly flow patterns are observed in the microtube. Our attention is focused on the analysis of pressure drop, and hydrodynamic characteristics of slug flow because it is one of the basis two-phase flow pattern in condensation inside microchannels.
    Keywords: Condensation, Microtube, Flow structures, Two, phase flow, Capillary regime