Q1: The ratio of momentum diffusivity to thermal diffusivity is the __________ number.

ANS:A - Prandtl

The Prandtl number, often denoted as Pr, is a dimensionless number used in fluid mechanics and heat transfer to characterize the relative importance of momentum diffusivity to thermal diffusivity in a fluid. It's named after the German physicist Ludwig Prandtl. Mathematically, the Prandtl number is defined as: Pr=Momentum diffusivityThermal diffusivityPr=Thermal diffusivityMomentum diffusivity​ It represents the ratio of the momentum diffusivity (kinematic viscosity) of a fluid to its thermal diffusivity. The kinematic viscosity describes how well momentum diffuses through a fluid, while thermal diffusivity describes how well heat diffuses through the same fluid. A Prandtl number greater than 1 indicates that momentum diffuses more readily than heat, meaning the fluid tends to have more momentum transfer compared to thermal transfer. Conversely, a Prandtl number less than 1 suggests that heat diffuses more readily than momentum. Prandtl numbers are essential in various applications, including the study of boundary layers, convection heat transfer, and fluid flow in engineering systems. They provide insights into the relative dominance of conduction and convection mechanisms in heat transfer processes within a fluid. Different fluids have different Prandtl numbers, and understanding this parameter is crucial in designing and analyzing heat transfer systems.