What is the Nusselt number for laminar flow?
If the Nusselt number is about 1, it represents that the heat transfer is conduction only, but if the value is between 1 and 10, then it shows laminar of slug flow. If the range is more, it is active convection with turbulence in the 100–1000 range.
Why is Nusselt number constant for laminar flow?
In laminar flow in a tube with constant surface temperature, both the friction factor and the heat transfer coefficient remain constant in the fully developed region. Therefore, for fully developed laminar flow in a circular tube subjected to constant surface heat flux, the Nusselt number is a constant.
What is Nusselt number for turbulent flow?
100–1000
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 formula of Nusselt number?
the Nusselt number, which is NuDh = 890. the hydraulic diameter of the fuel channel is Dh = 13,85 mm. the thermal conductivity of reactor coolant (300°C) is: kH2O = 0.545 W/m.K. the bulk temperature of reactor coolant at this axial coordinate is Tbulk = 296°C.
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.
What is the difference between Biot number and Nusselt number?
Biot number indicates how much solid temperature can change quickly based on the convection heat transfer in fluid. Biot number uses thermal conductivity of the body (not fluid), whereas Nusselt number uses thermal conductivity of the fluid.
What is the meaning of 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 less than 1?
Nu can not be less than one since it gives relation between conduction and convection of the liquid.
What is difference between Biot No & Nusselt no?
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.
Why Nusselt number increases with Reynolds number?
It is due to the increase in temperature difference between wall temperature and bulk temperature. Similarly heat transfer rate increases (Fig. 17) with the increase of Reynolds number. For this reason the heat transfer coefficient is also almost constant for different Reynolds number.
What is the difference between Nusselt number 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 does a large Nusselt number mean?
very efficient convection
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 is significance of Biot number?
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 the purpose of Nusselt number?
Nusselt number on the other hand is a non-dimensional heat transfer coefficient. It is used to determine whether the heat transfer is conduction or convection.