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Investigation of Micro Heat Pipe Performance Using Nano-Fluid as Working Fluid

Jahani, Kambiz | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41583 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): shafii, Mohammad Behshad; Saboohi, Yadollah
  7. Abstract:
  8. Thermal management of micro-electronic devices is a contemporary issue which is increasingly gaining importance in line with the advances in packaging technology. Immediate and consistent multi-disciplinary research is needed to cater to the prevailing trends of net power and flux levels of upcoming micro-electronics products. Material science, packaging concepts, fabrication technology and novel cooling strategies are some of the key areas requiring synchronal research for successful thermal management. Focusing on the latter area, this thesis presents an experimental study on thermal performance of Micro-Closed Loop Pulsating Heat Pipes (MCLPHPs) which are new entrants in the family of closed passive two-phase heat transfer systems. Pure water, silver nano-fluid water solution and ferro-fluid (magnetic nano-fluid), were employed as working fluids with filling ratios of 20% 40%, 60% and 80% respectively. The test tube was a four-turn micro-pulsating heat pipe, made of a copper capillary tube with an external diameter of 1.5 mm and an internal diameter of 0.508 mm. Two operational orientations were investigated, viz. vertical bottom heated (inclination angle = 90°) and horizontal heated (inclination angle = 0°) orientations. Wall temperature fluctuations were record under various heating power inputs from 4 to 28 W by pitch of 4W. In order to study and measure the efficiency, we compare silver nano-fluid and ferro-fluid at 2 wt% concentration, with pure water. In the case of ferro-fluid, tests are performed with and without applying magnetic field in evaporator section of the MCLMPHP. It was observed that thermal performance of PHP with nano-fluid (silver nano-fluid and magnetic nano-fluid) is better than distilled water under certain conditions. According to the results optimum performance for a system with the water-silver nanofluid was achieved at conditions of 60% filling ratio and 1 K/W of thermal resistance and for the Ferro-Fluid system, these optimal conditions were found to be 60% filling ratio and 0.9 K/W of thermal resistance by applying magnetic field (0.48 T) in the evaporator section employing two NdFeB magnets. In addition, the optimum performance for pure water occurs at a filling ratio of 40% and a thermal resistance of 1.4 K/W. It was concluded that by using nano-fluid as working fluid and by applying magnetic field in the case of ferro-fluid, thermal Resistance of MCLPHP was decreased. In order to investigate the gravity influence on thermal behavior of the system, the system response to five different orientations (hor. 25 º, 45 º, 75 º and ver.) was also compared. According to the results by changing the inclination angle from 90 º to 25 º, the thermal behavior of the system was not changed but in horizontal orientation the evaporator temperature and thermal resistance were increased
  9. Keywords:
  10. Experimental Investigation ; Magnetic Fields ; Ferrofluid ; Nanofluid ; Micro Pulsating Heat Pipe

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