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Heat Transfer - Engineering

Q1:

Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid

A for fluids in laminar flow.

B for fluids in tubulent flow.

C when Grashhoff number is very important.

D for liquid metals.

ANS:B - for fluids in tubulent flow.

The Dittus-Boelter equation is a correlation commonly used for the determination of the heat transfer coefficient (ℎh) in forced convection heat transfer. It is primarily valid for fluids in turbulent flow. The Dittus-Boelter equation is expressed as: =0.023⋅0.8⋅0.3Nu=0.023⋅Re0.8⋅Pr0.3 Where:

  • Nu is the Nusselt number,
  • Re is the Reynolds number,
  • Pr is the Prandtl number.
This correlation is derived based on experimental data for forced convection heat transfer in pipes and is valid for a wide range of fluids flowing in pipes under turbulent flow conditions. It is not limited to any specific type of fluid or flow regime. However, it is generally not suitable for laminar flow situations. The Grashof number (Gr) is more relevant in natural convection, rather than forced convection, and is not directly associated with the Dittus-Boelter equation. Therefore, the correct statement is: "for fluids in turbulent flow."