692 research outputs found

    Challenges and progress on the modelling of entropy generation in porous media: a review

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    Depending upon the ultimate design, the use of porous media in thermal and chemical systems can provide significant operational advantages, including helping to maintain a uniform temperature distribution, increasing the heat transfer rate, controlling reaction rates, and improving heat flux absorption. For this reason, numerous experimental and numerical investigations have been performed on thermal and chemical systems that utilize various types of porous materials. Recently, previous thermal analyses of porous materials embedded in channels or cavities have been re-evaluated using a local thermal non-equilibrium (LTNE) modelling technique. Consequently, the second law analyses of these systems using the LTNE method have been a point of focus in a number of more recent investigations. This has resulted in a series of investigations in various porous systems, and comparisons of the results obtained from traditional local thermal equilibrium (LTE) and the more recent LTNE modelling approach. Moreover, the rapid development and deployment of micro-manufacturing techniques have resulted in an increase in manufacturing flexibility that has made the use of these materials much easier for many micro-thermal and chemical system applications, including emerging energy-related fields such as micro-reactors, micro-combustors, solar thermal collectors and many others. The result is a renewed interest in the thermal performance and the exergetic analysis of these porous thermochemical systems. This current investigation reviews the recent developments of the second law investigations and analyses in thermal and chemical problems in porous media. The effects of various parameters on the entropy generation in these systems are discussed, with particular attention given to the influence of local thermodynamic equilibrium and non-equilibrium upon the second law performance of these systems. This discussion is then followed by a review of the mathematical methods that have been used for simulations. Finally, conclusions and recommendations regarding the unexplored systems and the areas in the greatest need of further investigations are summarized

    GPU Accelerated Multiple-Relaxation-Time Lattice Boltzmann Simulation of Convective Flows in a Porous Media

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    A two-dimensional (2D) multiple-relaxation-time (MRT)-lattice Boltzmann method (LBM) is used for porous media with the Brinkman–Forchheimer extended Darcy model to investigate the natural and mixed convection flows in a square cavity. This Brinkman–Forchheimer model is directly applied by using the forcing moments as a source term. A Tesla K40 NVIDIA graphics card has been used for the present graphics processing unit (GPU) parallel computing via compute unified device architecture (CUDA) C platform. The numerical results are presented in terms of velocity, temperature, streamlines, isotherms, and local and average Nusselt numbers. For the wide range of Rayleigh numbers, (Ra = 103 to 1010), Reynolds numbers, Darcy numbers, and porosities, the average Nusselt number is compared with the available results computed by finite element method (FEM) and single-relaxation-time (SRT) lattice Boltzmann method-LBM and, showing great compliance. The results are also validated with the previous experimental results. The simulations speed up to a maximum of 144x using CUDA C in GPU compared with the time of FORTRAN 90 code using a single core CPU simulation

    Mathematical Modeling for Nanofluids Simulation: A Review of the Latest Works

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    Exploiting nanofluids in thermal systems is growing day by day. Nanofluids having ultrafine solid particles promise new working fluids for application in energy devices. Many studies have been conducted on thermophysical properties as well as heat and fluid flow characteristics of nanofluids in various systems to discover their advantages compared to conventional working fluids. The main aim of this study is to present the latest developments and progress in the mathematical modeling of nanofluids flow. For this purpose, a comprehensive review of different nanofluid computational fluid dynamics (CFD) approaches is carried out. This study provides detailed information about the commonly used formulations as well as techniques for mathematical modeling of nanofluids. In addition, advantages and disadvantages of each method are rendered to find the most appropriate approach, which can give valid results

    Lattice Boltzmann simulation of a storage tank with an immersed tube bundle heat exchanger

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    Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.A rectangular storage tank with an immersed cylindrical tube bundle heat exchanger has been simulated by Lattice Boltzmann Method (LBM). The details of transient temperature distributions and flow streamlines in the nearby field of each tube are clearly demonstrated as well as the complexity of the overall flow field and the extent of the mixing during discharge. The LBM makes the directly simulation possible and the computational speed is increased comparing to a conventional porous medium model simulation. The transient averaged Nusselt numbers of the tube bundle have been obtained, which can also be applied in other applications such as numerical simulations of porous medium models.dc201

    Mixed Convection in a Square Cavity Filled with Porous Medium with Bottom Wall Periodic Boundary Condition

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    Transient mixed convection heat transfer in a confined porous medium heated at periodic sinusoidal heat flux is investigated numerically in the present paper. The Poisson-type pressure equation, resulted from the substituting of the momentum Darcy equation in the continuity equation, was discretized by using finite volume technique. The energy equation was solved by a fully implicit control volume-based finite difference formulation for the diffusion terms with the use of the quadratic upstream interpolation for convective kinetics scheme to discretize the convective terms and the temperature values at the control volume faces. The numerical study covers a range of the hydrostatic  pressure sinusoidal  amplitude  range and  time  period  values  of . Numerical results show that the pressure contours lines are influenced by hydrostatic head variation and not affected with the sinusoidal amplitude and time period variation. It is found that the average Nusselt number decreases with time and pressure head increasing and decreases periodically with time and amplitude increasing. The time averaged Nusselt number decreases with imposed sinusoidal amplitude and cycle time period increasing

    Simulation of steady mixed convection in a lid-driven cavity filled with newtonian fluid by finite volume method

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    The steady mixed convection flow in a lid-driven cavity was simulated. The cavity was filled with a Newtonian fluid, both vertical walls are adiabatic, while the horizontal walls were either fixed cold and uniformly/oscillatory heated. Firstly, the effect of internal heat generation or absorption on the fluid flow and heat transfer behaviours was studied. The moving upper wall was uniformly heated while the bottom wall was kept cold. The effect of magnetic field on fluid flow and heat transfer was analysed in the second problem. An inclined magnetic field was considered in the third problem. In the fourth problem, the flow inside an inclined cavity was simulated, where the top wall was subjected to an heated oscillating temperature. Finally, the mixed convection within an inclined cavity with the presence of an inclined magnetic field was studied. The dimensionless governing equations were formulated by using appropriate reference variables. These equations were solved using the finite volume method. The convection-diffusion terms were discretized using the power law scheme while the pressure and velocity components were coupled using the SIMPLE algorithms. The resultant matrices were then solved iteratively using the Tri- Diagonal Matrix Algorithm coded in FORTRAN90. The present solutions obtained were then compared with those of previous studies and a good agreement was found. The numerical results were presented in the forms of isotherm and streamline. It was found that the heat transfer rate in an inclined cavity increased mildly for both forced convection dominated and mixed convection dominated regimes. However, for natural convection dominated regime, the heat transfer rate decreased when the inclination angle was 30◦ and increased when the inclination angles reached 60◦. The presence of external forces would affect the local heat transfer and fluid flow behaviours significantly
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