5. Comparison of different heat transfer modes

The thermal powers exchanged by an assumed very large surface at temperature T are shown in figure 14 . These comparative powers are generated at a temperature difference of 1 K :

• by radiation between two walls ;

• by conduction in helium between two walls separated by 1 cm ;

• by natural or forced convection in helium around a horizontal rod 1 cm in diameter; in the case of forced convection, helium is assumed to move around the rod at a speed of 1 m/s.