Q1: Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is

ANS:A - 0.1

Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, mainly when the Prandtl number (PrPr) is less than 1, not when it is 0.1. The Prandtl number is the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity: Pr=momentum diffusivitythermal diffusivity=Pr=thermal diffusivitymomentum diffusivity​=αν​ A fluid with a Prandtl number less than 1 indicates that its momentum diffusivity is lower than its thermal diffusivity. In such fluids, the momentum boundary layer thickness is smaller than the thermal boundary layer thickness. Consequently, in the buffer zone (the region near the entrance of the pipe where the flow transitions from a fully developed laminar profile to a turbulent profile), convection (fluid flow) dominates over thermal conduction. This means that convection is the primary mechanism of heat transfer in this region. Therefore, conduction is less significant in the buffer zone for a fluid flowing through a heated pipe when the Prandtl number is less than 1.