Q1: Natural convection is characterised by

ANS:A - Grashhoff number

The correct term is the Grashof number, not "Grashhoff." The Grashof number (Gr) is a dimensionless parameter used in fluid mechanics to characterize natural convection flows. It represents the ratio of buoyancy forces to viscous forces within a fluid flow system. The formula for the Grashof number is typically expressed as: 32Gr=ν2g⋅β⋅ΔT⋅L3​ Where:

• g is the acceleration due to gravity,
• β is the coefficient of thermal expansion,
• ΔT is the temperature difference between the fluid and its surroundings,
• L is a characteristic length (such as the height of the fluid layer),
• ν is the kinematic viscosity of the fluid.

The Grashof number is used to determine the significance of buoyancy forces relative to viscous forces in a fluid flow. When the Grashof number is small, viscous forces dominate, and the flow behavior is similar to forced convection. When the Grashof number is large, buoyancy forces dominate, and the flow behavior is characteristic of natural convection. In natural convection, where fluid motion is driven by density variations caused by temperature differences, the Grashof number plays a crucial role in determining the intensity and pattern of the convective heat transfer. Higher Grashof numbers indicate stronger buoyancy-driven flows and more vigorous heat transfer. Therefore, the Grashof number is an essential parameter in the analysis and design of natural convection systems, such as heat exchangers, cooling towers, and solar collectors.