Free convection

Free convection losses are usually negligible, so only forced convection can be taken into account, if:

Red > 2G where fr= ~Ta)


where Red is the Reynolds number referred to the diameter, d, of the wire, Gr is the Grashof number, which measures the relative importance of the buoyancy force with respect to the viscous force, b is the coefficient of thermal expansion (= 1/T for perfect gases), g is the acceleration of gravity, n is the kinematic viscosity.

For the reference probe Gr = 5.3 x 10-6, so the minimum speed for which the free convection can be ignored is 5 cm/s.

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