Why is Nusselt number less than 1?

It is clear from earlier statement that the Nusselt number can never be less than 1 because the convective flux can be zero but the molecular flux term will be similar in the numerator and the denominator. Therefore, the minimum value of Nusselt number is 1 when the convective flux is zero.

What does a high Nusselt number?

A Nusselt number of order unity would indicate a sluggish motion little more effective than pure fluid conduction: for example, laminar flow in a long pipe. A large Nusselt number means very efficient convection: For example, turbulent pipe flow yields Nu of order 100 to 1000.

What does Nusselt number depend on?

The Nusselt number in the fully developed laminar flow is constant and depends on the channel geometry and the wall heat transfer boundary condition.

What is the Nusselt number for water?

Calculation of the Prandtl number the thermal conductivity of saturated water at 300°C is: kH2O = 0.545 W/m.K. the dynamic viscosity of saturated water at 300°C is: μ = 0.0000859 N.s/m.

What are the physical significance of Nusselt no and prandtl no?

Reynolds determines if the flow is laminar or turbulent. Nusselt calculates the transference of heat relative to pure conduction. Prandtl represents how big is the viscous boundary layer relative to thermal boundary layer.

How do I increase my Nusselt number?

When k is increased by nano material effect, thermal conductivity of fluid increases which results in higher heat transfer from the surface and consequent higher convection coefficient and Nu number. when thermal conductivity increase, the heat transfer coefficient and following that Nu number increase.

What is local Nusselt number?

The local Nusselt number is defined as Nux=(x−x0) q/(k(Ts−Tref)), where q is the measured convective heat flux, Ts and Tref surface and reference (the location of the reference point is located just upstream of the heater) temperatures and k the thermal conductivity of air.

What is the relationship between Nusselt number and Reynolds number?

In turbulent flow, the boundary layer gets thinner as Reynolds number increases in the same pipe, thus, the Nusselt number depends on Reynolds number.

How is the Nusselt number of a fully developed flow changing along the position?

In developing flow inside pipes the Nu number changes along the axial position. After the flow is fully developed the Nu number remains constant along the axial position (Nu=4.36 for laminar flow, constant heat flux at wall, circular pipe). It is a coefficient indicating the rate at which a geometry transfer heat.

What is the average Nusselt number a function of?

Nusselt number is a measure of the ratio between heat transfer by convection (α) and heat transfer by conduction alone (λ/L). Convective heat transfer relationships are usually expressed in terms of Nusselt number as a function of Reynolds Number and Prandtl Number.