# What is the physical significance of the Nusselt number for the case of mass transfer in a cylindrical pipe? ### What is the physical significance of the Nusselt number for the case of mass transfer in a cylindrical pipe?

the Nusselt number is a number dimensionless used to characterize the type of transfer thermal between a fluid and a wall. It relates the transfer by convection relative to the transfer by conduction. He is all the higher as convection predominates on conduction.

### How to calculate the Rayleigh number?

This number is actually the product of two numbers, number of Grashof (denoted Gr) and number of Prandtl (denoted Pr), also dimensionless, used to characterize the relative “ease” / “efficiency” of convection and conduction as a mode of heat transfer: Ra=Gr.Pr. .

### How to know in an exercise if the convection is forced or natural?

Whether Ri >> 1, then the natural convection dominates while if laughed

### How to calculate the Biot number?

h – overall heat transfer coefficient (W m-2 K-1) LC – characteristic length (m) λb – thermal conductivity of the body (W m-1 K-1)

### What is forced convection?

The convection oven, also called forced convection is equipped with a central fan or a turbine. Added to this is a resistor allowing the diffusion of pulsed heat. Thus, the fan allows the air heated by the resistance to circulate uniformly throughout the oven.

### How to calculate Newton’s coefficient?

−→ qw = h(Tw − Tf )−→n . time t = 0 (or another relevant temperature of the solid), and let Tf be the temperature of the external fluid: dn = L d¯n and T = Tf + (T0 − Tf ).