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Heat Transfer - Engineering

Q1:

Which of the following is concerned with both heat and mass transfer ?

A Lewis relationship

B Nusselt number

C Kutateladze number

D Froude number

ANS:A - Lewis relationship

The Lewis relationship is concerned with both heat and mass transfer. The Lewis number (Le) is defined as the ratio of thermal diffusivity to mass diffusivity. It quantifies the relative importance of heat transfer to mass transfer in a fluid. Specifically, it compares the rate at which temperature diffuses through a fluid to the rate at which concentration (or species) diffuses through the same fluid. Lewis number (Le)=Lewis number (Le)=Dα​ Where:

  • α is the thermal diffusivity of the fluid,
  • D is the mass diffusivity of the fluid.
A Lewis number greater than 1 indicates that thermal diffusion is more significant than mass diffusion, while a Lewis number less than 1 indicates the opposite. Therefore, the Lewis relationship is concerned with both heat and mass transfer.