What does a high value of Prandtl number indicate?

A high Pr number (> 5) means that heat transfer is more favorable to occur by fluid momentum than by thermal diffusion. In other words, high Pr number means that heat transfer is favored to occur by fluid momentum rather than by fluid conduction.

What material do you expect to have a high Prandtl number and why?

Thermal diffusivity dominates in the case of mercury. Engine oils have a high Prandtl number and so the convective component of heat transfer is higher.

In which mode of heat transfer is the convection?

The three types of heat transfer Heat is transfered via solid material (conduction), liquids and gases (convection), and electromagnetical waves (radiation). Heat is usually transfered in a combination of these three types and seldomly occurs on its own.

What is effective Prandtl number?

The following equation shows us the effective Prandtl number: Preff = ν/α + νt/αt. where νt is kinematic turbulent viscosity and αt is turbulent thermal diffusivity.

What is the value of Prandtl number for liquid metals?

0.01 to 0.001
For liquid metals the Prandtl number is very small, generally in the range from 0.01 to 0.001. This means that the thermal diffusivity, which is related to the rate of heat transfer by conduction, unambiguously dominates.

What does a low Prandtl number mean?

If Prandtl number is small, it tells us that thermal diffusion is dominant in comparison to momentum diffusion. That is for a given fluid flow problem, the flow conditions remaining the same, if we want higher heat transfer rate we have to use a fluid that has lower Prandtl number. Cp/k) is a fluid property.

How do I use Prandtl number?

The Prandtl number is a dimensionless number defined as the ratio of momentum diffusivity to thermal diffusivity. The Prandtl number equals the specific heat capacity times the dynamic viscosity divided by the thermal conductivity.

What is the physical significance of the Prandtl number does the value of the Prandtl number depend on the type of flow or the flow geometry?

The Prandtl number is a fluid property that does not depend on the type of flow or flow geometry. The values of , cp and k are known to change with temperature so the Prandtl number will change with temperature.

Which is the fastest mode of heat transfer?

Radiation
Heat energy can propagate through any media or vacuum at the speed of light. Radiation can take place in any state of matter. Hence, radiation is the fastest mode among these modes of heat transmission.

What is the significance of Prandtl number in heat transfer?

In heat transfer problems, the Prandtl number controls the relative thickness of the momentum and thermal boundary layers. When Pr is small, it means that the heat diffuses quickly compared to the velocity (momentum). This means that for liquid metals the thickness of the thermal boundary layer is much bigger than the velocity boundary layer.

What is the significance of the Prandtl number for liquid metals?

When Pr is small, it means that the heat diffuses quickly compared to the velocity (momentum). This means that for liquid metals the thickness of the thermal boundary layer is much thinker than the velocity boundary layer. The mass transfer analog of the Prandtl number is the Schmidt number.

What is Prandtl number and Schmidt number?

Prandtl number. When Pr is small, it means that the heat diffuses quickly compared to the velocity (momentum). This means that for liquid metals the thickness of the thermal boundary layer is much bigger than the velocity boundary layer. The mass transfer analog of the Prandtl number is the Schmidt number .

Why do gases have Prandtl numbers of 1?

The Prandtl numbers of gases are about 1, which indicates that both momentum and heat dissipate through the fluid at about the same rate. Heat diffuses very quickly in liquid metals (Pr<<1) and very slowly in oils (Pr>>1) relative to momentum.