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The heat convection coefficient α can be calculated with dimensionless numbers,

from similarity theory

Nu 
  , W (1.12)
L

2
where α c – heat convection coefficient, W/m ·K;
L – characteristic dimension, m;

λ – thermal conductivity of the fluid, W/m·K.

Nu - Nusselt number

Nu = F (Pr; Gr; Re)

It means, that the Nusselt number is a function of the product of Prandtl number,

Grashof number and Reynolds number.

Dimensionless Numbers

In the equation of Nusselt number

 C p
Pr  , (1.13)


2
where μ – absolute viscosity, kg/(m·s) or Ns/m ;
C p – specific heat, J/(kg·K);

λ – thermal conductivity of the fluid, W/m·K.

, (1.14)

where L – characteristic dimension, m;

3
ρ – density, kg/m ;
β – coefficient of thermal expansion, 1/K;

2
g – gravitational acceleration, m/s ;

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