Q1: h.D/K is called the __________ number.

ANS:A - Nusselt

The Nusselt number (Nu) is a dimensionless parameter used in heat transfer correlations to characterize the heat transfer coefficient (ℎh) of a fluid flow relative to the thermal conductivity (K) of the fluid or the material through which heat is being transferred. It represents the ratio of convective heat transfer to conductive heat transfer for a given flow regime. The Nusselt number is defined differently depending on the specific heat transfer situation, such as forced convection, natural convection, or boiling. However, in general, it is expressed as: =ℎ⋅Nu=Kh⋅L​ where:

• ℎh is the convective heat transfer coefficient, which represents the rate of heat transfer between the fluid and the solid surface.
• L is a characteristic length scale of the system, such as the diameter of a pipe in forced convection or the height of a vertical plate in natural convection.
• K is the thermal conductivity of the fluid or the material through which heat is being transferred.

The Nusselt number provides valuable information about the efficiency of heat transfer in a system. A higher Nusselt number indicates enhanced convective heat transfer relative to conductive heat transfer, while a lower Nusselt number suggests that conductive heat transfer dominates. Different correlations and empirical relationships exist to predict the Nusselt number for specific flow configurations and boundary conditions. These correlations are often based on experimental data and may vary depending on factors such as flow velocity, fluid properties, and geometric characteristics of the system. In summary, the Nusselt number is a dimensionless parameter used to quantify the relative importance of convective heat transfer compared to conductive heat transfer in a given heat transfer situation.