Q1:  is termed as the __________ number.

ANS:C - Prandtl

The Prandtl number (Pr) is a dimensionless parameter used in fluid mechanics and heat transfer to characterize the relative importance of momentum diffusivity (kinematic viscosity) to thermal diffusivity within a fluid. Mathematically, the Prandtl number is defined as the ratio of momentum diffusivity (kinematic viscosity, ν) to thermal diffusivity (α): Pr=Pr=αν​ Where:

• ν is the kinematic viscosity of the fluid (measured in m2/sm2/s),
• α is the thermal diffusivity of the fluid (measured in m2/sm2/s).

The Prandtl number is important because it provides information about the relative rates of momentum transfer (viscous effects) and heat transfer (conductive and convective effects) within a fluid. A low Prandtl number indicates that momentum diffuses more rapidly than heat, while a high Prandtl number indicates that heat diffuses more rapidly than momentum. Here's what different Prandtl numbers signify:

• Pr < 1: Indicates that momentum diffuses faster than heat. This is typical for fluids with high thermal conductivity compared to their viscosity, such as water and most gases. These fluids tend to have rapid mixing and relatively fast thermal boundary layer development.
• Pr > 1: Indicates that heat diffuses faster than momentum. This is typical for fluids with high viscosity compared to their thermal conductivity, such as oils and some molten metals. These fluids tend to have slower mixing and slower thermal boundary layer development.
• Pr ≈ 1: Indicates that momentum and heat diffuse at similar rates. This occurs for fluids where thermal conductivity and viscosity are of similar magnitude, such as liquid metals. In such cases, the flow and thermal characteristics are influenced by a balance between viscous and thermal effects.

The Prandtl number is commonly used in heat transfer and fluid flow calculations, particularly in forced convection and natural convection problems, where it helps in predicting the behavior of boundary layers, flow regimes, and heat transfer rates. In summary, the Prandtl number provides valuable information about the relative importance of momentum and heat transfer processes within a fluid, helping engineers and researchers understand and analyze fluid flow and heat transfer phenomena more effectively.