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Heat and Mass Transfer Research - Volume:5 Issue: 1, Winter and Spring 2018

Journal of Heat and Mass Transfer Research
Volume:5 Issue: 1, Winter and Spring 2018

  • تاریخ انتشار: 1397/02/14
  • تعداد عناوین: 7
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  • AhmadReza Rahmati *, A. Gheibi Pages 1-9
    The lattice Boltzmann method (LBM) was used to analyze two-dimensional (2D) non-Fourier heat conduction with temperature-dependent thermal conductivity. To this end, the evolution of wave-like temperature distributions in a 2D plate was obtained. The temperature distributions along certain parts of the plate, which was subjected to heat generation and constant thermal conductivity conditions, were also derived and compared. The LBM results are in good agreement with those reported in other works. Additionally, the temperature contours at four different times in which steady state conditions can be achieved were analyzed. The results showed that thermal conductivity increased with rising temperature. Given the material’s considerable effectiveness in transferring heat energy under heat generation conditions, the temperature gradient of the plate decreased to a level lower than that observed under constant thermal conductivity.
    Keywords: Non-Fourier conduction, lattice Boltzmann method, variable thermal conductivity, constant thermal conductivity, heat generation
  • Alireza Falahat, Reza Bahoosh *, Aminreza Noghrehabadi Pages 11-26
    This study numerically investigated heat transfer and fluid flow characteristics in a novel cylindrical heat sink with helical minichannels for the laminar flow of fluid with temperature-dependent properties. A finite volume method was employed to obtain the solution of governing equations. The effects of helical angle, channel aspect ratio, and Reynolds number, which were regarded as main parameters, were determined. The overall performance of the heat sink was also analyzed on the basis of the thermal performance factor and the augmentation entropy generation number. Results showed that a decrease in the channel helix angle and an increase in the channel aspect ratio and Reynolds number enhance the average heat transfer coefficient and pressure drop in the heat sink. The thermal performance factor and entropy generation minimization method revealed that an aspect ratio of 1.2 enables the best heat sink performance at all helix angles. When the helix angle decreases, performance increases, especially at low aspect ratios.
    Keywords: Cylindrical helical minichannels heat sink, Thermal performance factor, Thermal resistance, Entropy generation, Channel aspect ratio
  • Seyed Masoud Vahedi, Farzad Parvaz *, Roohollah Rafee, Mohsen Khandan Bakavoli Pages 27-38
    One of the main concerns of researchers is the separation of suspended particles in a fluid. Accordingly, the current study numerically investigated the effects of a conical section on the flow pattern of a Stairmand cyclone by simulating single-cone and dual-cone cyclones. A turbulence model was used to analyze incompressible gas-particle flow in the cyclone models, and the Eulerian–Lagrangian approach was employed to examine particle movement. Despite the simplicity of cyclone geometry, internal two-phase flow in such devices is very complicated and anisotropic. This flow was therefore analyzed using a Reynolds stress model. The numerical results were then compared with those of experimental studies. To track calcium carbonate particles, drag and gravity forces were considered in the Lagrangian model. The findings indicated that adding a second conical section at the bottom of the cyclones increases tangential velocity and expands the Rankine vortex region. Moreover, an increasing trend of descending flow occurs. Increasing the number of conical sections elevates pressure drop at all velocities. Finally, the dual-cone cyclone has higher efficiency than the typical cyclone because the smaller end of the former limits particle motion and increases collection performance.
    Keywords: Eulerian-Lagrangian, Reynolds Stress Model, Turbulent flow, Gas-Particle flow
  • Mohammad Hemmat Esfe *, Seyfolah Saedodin Pages 39-49
    The present paper focuses on problem of mixed convection fluid flow and heat transfer of Al2O3-water nanofluid with temperature and nanoparticles concentration dependent thermal conductivity and effective viscosity inside Lid-driven cavity having a hot rectangular obstacle. The governing equations are discretized using the finite volume method while the SIMPLER algorithm is employed to couple velocity and pressure fields. Using the developed code, the effects of cavity inclination angle, diameter and solid volume fraction of the Al2O3 nanoparticles on the flow and thermal fields and heat transfer inside the cavity are studied. The results show that at all solid volume fraction the average Nusselt number has inverse relationship with nanoparticles diameter. Also the results have clearly indicated that with increasing slope of the cavity to 90 degree, heat transfer continuously decreases at all studied Richardson numbers© 2017 Published by Semnan University Press. All rights reserved.
    Keywords: Nanofluid, Variable properties, Solid volume fraction, lid-driven cavity, Diameter of nanoparticles
  • Omid Ghaffarpasand* Pages 51-68
    The present study considers the numerical examination of an unsteady thermo-solutal mixed convection when the extra mass and heat diffusions, called as Soret and Dufour effects, were not neglected. The numerical simulations were performed in a lid-driven cavity, where the horizontal walls were kept in constant temperatures and concentrations. The vertical walls were well insulated. A finite volume method based on SIMPLE algorithm was utilized to solve the coupled governing equations. Numerical simulations are performed for wide combinations of Soret and Duofour coefficients and are given by streamlines, isotherms, isoconcentrations, fluid velocities, average Nusselt and Sherwood numbers. The influences of pertinent parameters on the various heat transfer modes, i.e. convective and conductive modes, as well as the total kinematic energy of the studied thermo-solutal system are also analyzed.
    Results demonstrate that Soret and Dufour effects insignificantly influence the fluid flow and transport phenomena when flow is affected to some extent by the forced convection. It is also achieved that the extra heat diffusion, Dufour effect, affects heat transfer by creating thermal eddies especially when flow is dominated by the natural convection. Besides, the conductive mode of heat transfer is attenuated by Dufour coefficient.
    Keywords: Double-diffusive convection, Soret, Dufour effects, Heat, mass transfer, Conduction
  • M.H. Tavakoli *, Zahra Taheri Ghahfarokhi Pages 69-77
    For a Czochralski growth of Ge crystal, thermal fields have been analysed numerically using the three-dimensional finite volume method (FLUENT package). The arrangement used in a real Czochralski crystal growth lab included a graphite crucible, heat shield, heating device, thermal insulation and chamber including two gas outlets. We have considered two cases for calculations, which are configuration containing (a) only gas and (b) melt and gas, related to initial stages of the growth process (seeding process). It has been assumed that the growth system is in steady state, fluids are incompressible Newtonian fluids and the flow is laminar. It was shown that the thermal field in the growth setup is completely three-dimensional. Especially, the temperature field at the melt free surface has not a uniform radial distribution due to the three-dimensional orientation of Argon flow above it.
    Keywords: Computer simulation, Fluid flow, Heat transfer, Czochralski method
  • masoud khajenoori, Ali Haghighi Asl * Pages 79-85
    The chance of developing lung cancer is increased through being exposed to cigarette smoke illustrated by studies. It is vital to understand the development of particular histologic-type cancers regarding the deposition of carcinogenic particles, which are present in human airway. In this paper, the mass transfer and deposition of cigarette smoke, inside the human airway, are investigated applying the finite element method. The mass transfer and depositions of four types of critical cigarette smoke, namely 1, 3-butadiene, acrolein, acetaldehyde and carbon monoxide (CO), in a complete human-airway model (from mouth to B3 generation), under inhalation conditions, have been simulated. In this study, concentration distribution in inhalation is evaluated. The vapour deposition was modelled with 30 and 80 L.min-1 volumetric flow rates. Therefore, a two-dimensional model of human airway from the mouth to generation B3 was reconstructed. Then, for simulating the mass transfers and deposition fraction, the low-Reynolds-number (LRN) k–ω turbulence equation was used.
    Keywords: Lung airway, Cigarette smoke, Nano-particle, Mass transfers, Deposition