A Nusselt number of value one (zero) represents heat transfer by pure conduction. A value between one (zero) and 10 is characteristic of slug flow or laminar flow. A larger Nusselt number corresponds to more active convection, with turbulent flow typically in the 100–1000 range.

What does the Nusselt number tell you?

A Nusselt number of value one (zero) represents heat transfer by pure conduction. A value between one (zero) and 10 is characteristic of slug flow or laminar flow. A larger Nusselt number corresponds to more active convection, with turbulent flow typically in the 100–1000 range.

What is the Nusselt number and why is it useful what fluid properties are needed to calculate the Nusselt number at what temperature should these properties be calculated?

A Nusselt number of Nu=1 for a fluid layer represents heat transfer across the layer by pure conduction. The larger the Nusselt number, the more effective the convection. A larger Nusselt number corresponds to more effective convection, with turbulent flow typically in the 100–1000 range.

What is the difference between Nusselt and Biot number?

Biot number uses thermal conductivity of the body (not fluid), whereas Nusselt number uses thermal conductivity of the fluid. The differences between Biot and Nusselt number is in definition of heat transfer coefficient, which is defined as: h=-k (dT/dn)w/(Tw-T0).

What is the physical significance of Nusselt number and Prandtl number?

Nusselt calculates the transference of heat relative to pure conduction. Prandtl represents how big is the viscous boundary layer relative to thermal boundary layer.

What does the Nusselt modulus or Nusselt number physically mean?

the ratio of the temperature gradient at the surface [(∂T / ∂y)y=0] to the reference temperature gradient [(Tw – T∞) / l] 6. The Nusselt modulus or Nusselt number is a convenient measure of. a. rate of heat transfer.

What is the significance of Reynolds number and Nusselt number?

– The Nusselt number (Nu=h*L / kf) is the ratio of convection to pure conduction heat transfer, where kf is the conductivity of the fluid. – The Reynolds number (Re=v*L / {kinematic viscosity}) is the ratio of the inertia and viscous forces.

What is the famous dittus Boelter correlation for?

The Dittus-Boelter correlation may be used for small to moderate temperature differences, Twall – Tavg, with all properties evaluated at an, averaged temperature Tavg.

What is Biot number used for?

The numerical value of Biot Number (Bi) is a criterion which gives a direct indication of the relative importance of conduction and convection in determining the temperature history of a body being heated or cooled by convection at its surface.

Why do we use Biot number?

The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. It is named after the eighteenth century French physicist Jean-Baptiste Biot (1774–1862), and gives a simple index of the ratio of the thermal resistances inside of a body and at the surface of a body.

What is Nusselt number and Prandtl number?

Nusselt number is an important parameter that can contribute to a better rate of heat exchange. It is basically a function of Reynolds and Prandtl number. The correlation is provided in Eq. (6).

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.

Why is Nusselt number constant?

First, there is a laminar boundary layer, next a transition and then the turbulent boundary layer. This is an external flow and the temperature of the flow outside the boundary layer is always constant. Both the local and averaged Nusselt numbers are larger for q=const.

Where did the dittus and Boelter equation come from?

Winterton showed the likely creator of the modern version of the Dittus and Boelter equation was actually McAdams. The following note further investigates Winterton’s claim and finds conclusive evidence that the Dittus and Boelter equation did indeed originate with McAdams.

How do you define Stanton number for mass transfer?

Stanton number is a dimensionless number that represents the ratio of heat transfer coefficient to heat capacity of a fluid. Stanton number indicates the degree of amount of heat delivered by fluid when there is heat transfer between solid surface and fluid.

What is the significance of Biot and Fourier number?

Fourier number is also known as dimensionless time and have effect on temperature before the steady state achieved. Biot number arises when we use third kind of boundary condition (i.e convective heat transfer in presence of external fluid surface). Both have significant effect on temperature distribution.

What does a low Biot number mean?

Because the Biot number is the ratio between the external resistance of a body to convection energy exchange and internal resistance to transmitting energy by conduction, a small Biot number implies low resistance to transmission by conduction, and therefore very low temperature gradients within the body; thus leading …

What is Fourier and Biot number?