Local Nusselt Number

October 07, 2024 Post a Comment

Local nusselt number

To calculate the cladding surface temperature, we have to know: the outer diameter of the cladding is: d = 2 x rZr,1 = 9,3 mm. the Nusselt number, which is NuDh = 890. the hydraulic diameter of the fuel channel is Dh = 13,85 mm.

Is Nusselt number a local heat flux?

Local and average Nusselt number The local Nusselt number thus describes the local heat transfer coefficient and thus the local heat flux. However, the heat transfer can also be related to the entire system as such or to a longer section.

What is difference between Biot No & Nusselt no?

Biot numbers much larger than 1 indicate more difficult problems due to non-uniformity of temperature fields within the object. It should not be confused with Nusselt number, which employs the thermal conductivity of the fluid and hence is a comparative measure of conduction and convection, both in the fluid.

What does Nusselt number depends on?

For a rectangular channel, the Nusselt number depends on the channel aspect ratio αc=a/b and the wall boundary conditions.

What is meant by Nusselt number?

The Nusselt number is defined as the ratio of convection heat transfer to fluid conduction heat transfer under the same conditions.

Can Nusselt number be zero?

Moreover, convective heat transfer (V>=0) must be equal to or greater than the conductive heat transfer (V=0). That's why Nu must be equal to or greater than 1. Correction: Nu should be greater than 1. As convection is defined as the heat transferred between a surface and a moving fluid, velocity must not be 0.

What is the minimum value of Nusselt number?

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 Prandtl number and Nusselt number?

Nusselt number is the ratio of convection heat transfer to pure conduction heat transfer, (K- Thermal conductivity of fluid) Reynolds number is the ratio of the inertia to the viscous forces avting on a fluid. Prandtl number is the ratio of the momentum and thermal diffusivities. Cite.

What is the significance of Nusselt number in convection?

268): “Then the Nusselt number may be interpreted as the ratio of heat transfer by convection to conduction across the fluid layer of thickness L. A larger value of the Nusselt number implies enhanced heat transfer by convection.”

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.

What is meant by Biot number?

Bi is the Biot number, which is a dimensionless number that represents the ratio of the resistance to heat transfer from the inside of the body to the surface of the body (52).

What is 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 high Nusselt number mean?

A large Nusselt number means very efficient convection: For example, turbulent pipe flow yields Nu of order 100 to 1000. (From Frank M. White, Heat Transfer)

Can the Nusselt number be less than 1?

However, you have also been told that the Nusselt Number is the “ratio of convective to conductive heat transfer”, and are wondering if there was only a tiny amount of motion, then the additional heat transfer would be less than that by conduction, so the Nusselt Number would be less than 1. You are absolutely right!

What Reynolds number is laminar flow?

As indicated previously, if the Reynolds number is less than 2000, the flow is considered to be laminar. This is also known as viscous flow.

How do you find the Nusselt number of water?

Formula

Nusselt Number : Nu = hL/k.
Convection Heat Transfer Coefficient : k = Nuk/L.
Characteristic Length : L = Nuk/h.
Thermal Conductivity of the Fluid : k = hL/Nu.
Where, Nu = Nusselt Number, h = Convection Heat Transfer Coefficient, L = Characteristic Length, k = Thermal Conductivity of the Fluid.

How is Prandtl number calculated?

To calculate the Prandtl number: Multiply dynamic viscosity with the specific heat of the fluid. Divide the product by the thermal conductivity of the fluid.

What is K in heat transfer?

k: The factor k is called the thermal conductivity constant. The thermal conductivity constant k is larger for materials that transfer heat well (like metal and stone), and k is small for materials that transfer heat poorly (like air and wood).

Where is Prandtl number used?

A dimensionless number approximating the ratio of momentum diffusivity to thermal diffusivity. The Prandtl Number is often used in heat transfer and free and forced convection calculations.

What is the range of Prandtl number?

Prandtl Number are unit-less. The Prandtl numbers of fluids range from less than 0.01 for liquid metals to more than 100,000 for heavy oils (Table below). Note that the Prandtl number is in the order of 10 for water.