Final answer:
The formula for the average Nusselt number for laminar flow in a pipe is Nu = 1.86 * (Re*Pr*d/L)^0.333 * (mu/mu_s)^0.14. The type of flow, laminar or turbulent, is determined by the Reynolds number, which is defined as NR = 2pvr, with laminar flow being characterized by NR below 2000.
Step-by-step explanation:
The question is asking for the formula for the average Nusselt number for laminar flow conditions. In heat transfer, the Nusselt number (Nu) is a dimensionless number which is the ratio of convective to conductive heat transfer across a boundary. For laminar flow in a pipe, the most commonly used correlation for the average Nusselt number is derived from the work of Sieder and Tate, which is given by Nu = 1.86 * (Re*Pr*d/L)^0.333 * (mu/mu_s)^0.14, where Re is the Reynolds number, Pr is the Prandtl number, d is the diameter of the pipe, L is the length of the pipe, mu is the dynamic viscosity of the fluid, and mu_s is the dynamic viscosity of the fluid at the surface temperature.
The Reynolds number (NR) is crucial in determining the type of flow. The Reynolds number for flow in a tube of uniform diameter is defined as NR = 2pvr, where 'p' is the fluid density, 'v' is the mean velocity of the fluid, and 'r' is the radius of the tube. For NR below about 2000, the flow is considered laminar and the aforementioned Nusselt number formula can be utilized.