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New methods for calculating the inlet hydrodynamic and thermal length in a laminar nanofluid flow by applying entropy generation Theory

  • Date: 2021 Feb 28
  • Authors: مهدی بقراطی
  • Keywords: Nanofluid, inlet length, entropy generation
Several ways have been suggested for obtaining the inlet hydrodynamic and thermal length (lhy and lth). Studying on nanofluid inlet region is more complicated than fully developed region. Blasius, Sparrow, Schlichting, Atkinson and Chen presented different equations due to Reynolds number and diameter of channel to predict lhy. Another method is where maximum velocity reaches to 1.5 times of inlet velocity. In this research the new method due to hydrodynamic entropy generation is presented. The difference between this method and Atkinson equation is 0.8%. Shah and Hanna presented the relations due to Pecklet number and hydraulic diameter of channel to obtain the lth. The other ways to find lth are according to difference of mean temperature and walls temperature, dimensionless temperature and Nusselt number. The new method to predict the lth is due to thermal entropy generation. When the entropy generation approaches to 0.94% of final value, lth value equals to Shah solution