What is a normal Nusselt number?
A Nusselt number of value one represents heat transfer by pure conduction. A value between one 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.
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 does a Nusselt number of 1 mean?
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.
What are Nusselt number correlations used for?
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.
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.
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 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. Nusselt number can be used for heat exchangers, because fluid convection dominates, calculation of the heat transfer coefficient of various flows such as in pipes.
How do you find the average Nusselt number in fluent?
In Fluent the surface nusselt number is calculated based upon the formula ((h_eff*L_ref) / k) where h_eff is heat transfer coefficient and L_ref is reference length which you define in refernce values panel and k is thermal conductivity.
What is the significance of Nusselt number?
Significance of Nusselt number. Thisrelates in-between convective and conductive heat transfer for the similartypes of fluids. It also helps in enhancing the convective heat transfer through a fluid layer relative to conductive heat transfer for the same fluid. It is useful in determining the heat transfer coefficient of the fluid.
How do you calculate the average Nusselt number?
Nusselt number equation | Nusselt number formula Average Nusselt Number can be formulated as: Nu = Convective heat transfer / conductive heat transfer Nu = h/ (k/L c)
What is the Nusselt number in fluid mechanics?
It is a dimensionless number, closely related to the fluid’s Rayleigh number. A Nusselt number of value one represents heat transfer by pure conduction. A value between one and 10 is characteristic of slug flow or laminar flow.
How do you find the Nusselt number from Reynolds number?
The Nusselt number can be obtained using the following equation where h is convection heat transfer coefficient, λ is air thermal conductivity, Ts is average surface temperature and T∞ is the free stream air temperature and D is the thickness of the heat sink. Figure 5.6. Nusselt number variation at different Reynolds numbers.