Q1: Grashoff number, which is defined as g . β(T_s - T_∞) ρ². L³/μ², is proportional to the ratio of buoyancy force to __________ force.

ANS:A - viscous

Viscous forces arise due to the internal friction within a fluid as it flows. When a fluid flows past a solid surface or through a confined space, adjacent fluid layers experience shear stresses due to differences in velocity. These shear stresses result in frictional forces between the fluid layers, which are referred to as viscous forces. In the context of the Grashof number, which characterizes natural convection flows, the viscous force represents the resistance of the fluid to flow, primarily due to its viscosity. When the Grashof number is high, indicating significant buoyancy forces relative to viscous forces, the fluid motion is dominated by buoyancy-driven natural convection. Conversely, when the Grashof number is low, viscous forces dominate, and the flow behavior resembles forced convection, where the fluid motion is primarily driven by external forces such as pumps or fans. Therefore, in the Grashof number, the viscous force represents the resistance of the fluid to flow, which influences the relative importance of buoyancy-driven natural convection in heat transfer processes.