Question

What is the physical significance of the Nusselt number? How is it defined?

Short answer

Answer: The Nusselt number represents the enhancement in heat transfer due to convection as compared to pure conduction, with a higher number indicating a more efficient heat transfer. It is defined as the ratio of the convective heat transfer coefficient (h) to the conductive heat transfer coefficient (k) and characteristic length (L), expressed as Nu = (hL)/k.

Step-by-step solution

Physical Significance of the Nusselt number

The Nusselt number represents the enhancement in heat transfer due to convection as compared to pure conduction. A higher Nusselt number indicates that there is a larger effect of convection, leading to more efficient heat transfer. Conversely, a lower Nusselt number suggests that conduction plays a more significant role in heat transfer.

Definition of the Nusselt number

The Nusselt number (Nu) is defined as the ratio of convective heat transfer coefficient (h) to the conductive heat transfer coefficient (k) and characteristic length (L): Nu = \frac{hL}{k} where, - h: convective heat transfer coefficient (W/m²K) - L: characteristic length (m) - k: thermal conductivity of the fluid (W/mK) The Nusselt number is a dimensionless number, and it is used to compare the heat transfer efficiency of fluids in various heat transfer situations, such as forced convection, natural convection, or boiling and condensation.