Q1: The ratio of hydrodynamic boundary layer to thermal boundary layer thickness in case of liquid metals is

ANS:A - < 1

In the context of liquid metals, the ratio of hydrodynamic boundary layer thickness (δh\delta_{\text{h}}δh​) to thermal boundary layer thickness (δt\delta_{\text{t}}δt​) is generally greater than 1.

Explanation:

1. Boundary Layer Thickness:
   • Hydrodynamic Boundary Layer Thickness (δh\delta_{\text{h}}δh​): This refers to the distance from the solid surface where the velocity of the fluid reaches approximately 99% of the free-stream velocity. It characterizes the thickness of the layer where viscous effects dominate.
   • Thermal Boundary Layer Thickness (δt\delta_{\text{t}}δt​): This refers to the distance from the solid surface where the temperature of the fluid reaches approximately 99% of the bulk temperature. It characterizes the thickness of the layer where thermal diffusion dominates.
2. Liquid Metals:
   • Liquid metals typically have high thermal conductivity and low viscosity compared to other liquids.
   • Due to their high thermal conductivity, the thermal boundary layer (δt\delta_{\text{t}}δt​) tends to be thinner compared to the hydrodynamic boundary layer (δh\delta_{\text{h}}δh​).
3. Ratio of Boundary Layer Thickness:
   • The ratio δhδt\frac{\delta_{\text{h}}}{\delta_{\text{t}}}δt​δh​​ for liquid metals is generally greater than 1. This indicates that the hydrodynamic boundary layer thickness is larger than the thermal boundary layer thickness.

Conclusion:

Therefore, in the case of liquid metals, the ratio of hydrodynamic boundary layer thickness to thermal boundary layer thickness (δhδt\frac{\delta_{\text{h}}}{\delta_{\text{t}}}δt​δh​​) is greater than 1. This is due to the dominance of viscous effects in forming a thicker hydrodynamic boundary layer compared to the thinner thermal boundary layer influenced by high thermal conductivity.