Mixed Convection of Magnetic Nanofluids in Channels Filled with a Porous Medium in the Presence of External Magnetic Field

Fadaei, Farzad | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50025 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Molaei, Asghar; Shahrokhi, Mohammad
  7. Abstract:
  8. In this research work, mixed convection heat transfer of ferrofluids (i.e., magnetite nanoparticle) in a circular pipe fully filled with a porous medium in the presence of constant and alternating magnetic fields has been investigated both numerically and experimentally. The duct was heated by a heating coil and the magnetic field was applied via four electromagnets with U shaped ferrite cores and a frequency inverter. The nanoparticles were synthesized using co-precipitation method and coated with a surfactant (i.e., Tween 80) and doubled distilled water was used as the base fluid. To characterize the synthesized nanoparticles, various analyzing techniques such as VSM, SEM, and XRD were conducted and the average particle size of nanoparticles were evaluated to be around 30 nm. ِDifferent concentration of nanoparticles (i.e., 0.5, 0.75, and 1 Vol%) were used to prepare nanofluid to launch out into the experimental set up to evaluate the heat-transfer coefficient in the presence /absence of magnetic field with a variable frequencies from 0 to 50 Hz, magnetic field intensity from 0 to 600 G, and Reynolds number values of 500 and 1400. The obtained experimental results indicate that for a given Reynolds number, the heat-transfer coefficient increases with an increase in the volumetric concentration of nanoparticles and magnetic field intensity and its frequency. The experimental runs were carried out with/-(out) the porous medium in the circular pipe. The presence of porous medium can increase the heat transfer rate due to the enhancement of effective thermal conductivity, fluid mixing and transfer surface area. It was found that this enhancement in the heat transfer coefficient was 18.38% for the volumetric nanoparticle concentration of 1%, and Reynolds number value of 1400, in the absence of the applied magnetic field, whereas this enhancement was 11.73% in the presence of applied magnetic field with an intensity of 600 G. Moreover, it was found that applying an alternating magnetic field with the same intensity and frequency of 50 Hz can increase the heat-transfer coefficient up to 9.58%. The behavioure of the experimental system was simulated numerically and the results were compared with the experimental ones. A good agreement was observed between experimental data and simulation results. To investigate the effectof system geometry and Magnetic field source on the heat transfer rate three different simulation studies were carried out; i) rotating magnetic fields on the heat-transfer coefficient ferrofluids passing through a rectangular duct, ii) static fields induced by a current carrying wire or permanent magnet on the heat-transfer coefficient of ferrofluid passing through a circular pipe, and iii) magnetic field induced by a solenoid on the heat-transfer coefficient of ferrofluid passing through a circular pipe, partially field by a porous medium
  9. Keywords:
  10. Magnetic Fields ; Convection Heat Transfer ; Nanofluid ; Porous Media ; Magnetic Nanofluids ; External Magnethic Field

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