Heat Transfer - Engineering

Q1:

At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe ?

A 0.5

B < 0.5

C > 0.6

D < 0.1

ANS:C - > 0.6

In the turbulent core of a fluid flowing through a heated pipe, conduction becomes negligible when the Prandtl number (Pr) is less than 0.1. Explanation:

  • The Prandtl number (Pr) is a dimensionless number that represents the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity. It quantifies the relative importance of momentum and thermal diffusivities in a fluid.
  • For most common fluids, such as water and air, with Prandtl numbers greater than 0.1, conduction is typically significant and contributes to heat transfer.
  • However, in the turbulent core of a fluid flow, where convective heat transfer dominates, the fluid mixes rapidly, reducing the significance of thermal boundary layers and enhancing heat transfer rates.