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Experimental Study of Forced Convective Heat Transfer Inside a Tube under the Effect of a Rotary Magnetic Ball by Applying an External Magnetic Field Application in Oil and Petrochemical Industry Heat Exchangers

Mansouri, Morteza | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57054 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Kazemzadeh Hannani, Siamak; Bijarchi, Mohammad Ali
  7. Abstract:
  8. As cost associated with obtaining energy has escalated on a global level, proper utilization and energy loss prevention has become more important and worthy of consideration. Methods of enhancing forced convection heat transfer through pipes prominently consist of geometry modifications, implementation of more efficient mechanisms and substituting 5 outdated hardware with more effective equipment. In the following paper, a novel technique employing rotation of bipolar magnetic spheres on inner surface of the tube using a rotating magnetic field has been explored for the first time and the outcomes have been promising. The rotating magnetic field is generated by a function generator and a Rodin Star Coil. The external magnetic field spins the spheres in the tube which consequently rotates the fluid flowing through the tube. As spheres revolve around the axis of the tube and rotate around their own axis, the hydraulic boundary layers are stirred which prevents their growth as they become turbulent. This will accelerate the transition from laminar flow to turbulant flow, thus increasing the forced convection heat transfer rates. An undesirable consequence of this technique is increased pressure drop across the pipe. In this article, effects of the rotational velocity of the spheres, their placement and their sequence of rotation as well as turbulator geometry on pressure drop, heat transdfer and thermal performance factor is studied in Reynolds numbers ranging from 180 to 2133, under constant heat flux. results from experiment show that on average, Nusselt number and coefficient of friction obtained through experimentation exhibited an increase of 98 % and 106 % relative to the plain tube when the turbulators were operating in active mode. When the turbulatoers operated in passive mode, these coefficients increased by 24% and 96% respectively. Under both modes of operation a decline is perceived in thermal performance factor, indicating that turbulators are more effective in low 20 Reynolds numbers and laminar flows. As the rotational speed of turbulators is decreased, Nusselt number also diminishes by 11.1 %. Using magnetic cylinders instead of magnetic spheres causes an increase of coefficient of friction by 10.5 % and a reduction of Nusselt number by 8 %. In all geometric configurations, Nusselt number increased with Reynolds number, while coefficient of friction lessened. In configurations that the turbulators were placed near the end of the tube, lower average Nusselt numbers were documented
  9. Keywords:
  10. Convective Forced Heat Transfer ; Rodin Star Coil ; Magnetic Rotating Sphere ; Rotating Magnetic Field ; Internal Forced Convection Heat Transfer Coefficient ; Heat Exchangers

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