ANS:A - inversely with thermal conductivity.

The Nusselt number (Nu) and Biot number (Bi) are dimensionless numbers used in heat transfer analysis. The Nusselt number (Nu) is defined as the ratio of convective heat transfer to conductive heat transfer across a fluid boundary layer. It represents the enhancement of heat transfer due to convection compared to conduction alone. The Biot number (Bi) is defined as the ratio of convective heat transfer resistance to conductive heat transfer resistance within a solid medium. It characterizes the relative importance of convection and conduction within the solid. The relationship between the Nusselt number and Biot number varies depending on the specific heat transfer configuration. However, in general:

• The Nusselt number is directly related to the heat transfer coefficient (h), which represents the efficiency of heat transfer across a surface or within a fluid.
• The Biot number is inversely related to the thermal conductivity (k) of the solid material.

• The Nusselt number (Nu) varies directly with the heat transfer coefficient (h).
• The Biot number (Bi) varies inversely with the thermal conductivity (k) of the solid material.