Ernst Kraft Wilhelm Nusselt

Ernst Kraft Wilhelm Nusselt (Nuremberg, November 25th 1882 - Munich, September 1st 1957) is a German physicist . It is a pioneer in the study of transfer by convection. Its name remains attached to the adimensional number to which its name was given, the Nombre of Nusselt $Nu$ .

Biography

Ernst Kraft Wilhelm Nusselt is born with Munich the November 25th 1882 from Johannes Nusselt and Pauline Fuchs Nusselt. It makes studies in mechanical engineering with Munich, then with Berlin. It obtains a doctorate in mechanical engineering in Munich.

Scientific work

It is a pioneer in the study of transfer by convection. Its name remains attached to the adimensional number to which its name was given, the Nombre of Nusselt $Nu$ . Nusselt used the dimensional analysis to develop solutions with the problems of transfer of heat in the fluids, where the analytical solutions were too complicated. Its principal work is:

The BASIC Law off Heat Transfer in 1915, on conductivity in isolated materials and on the convection coefficient, where in particular the number of Nusselt appears.
The Film Condensation off Steam in 1916, where it describes film of condensation of any liquid.

In 1930, it makes a description on the similarities between transfer of mass and transfer of energy. This work will be then mainly turned towards industrial applications. They will approach the transfers by radiation and the transfers during a combustion.

Number of Nusselt

See also: Number of Nusselt

The number of Nusselt is a measurement of the intensity of a heat exchange. It represents the report/ratio of conductive resistance on convective resistance.

$Nu_L = \ frac {hL} {k_f}$

H: convection coefficient

L: dimension characteristic of the flow

$k_f$ : thermal conductivity of the fluid

The characteristic Dimension depends on the involved geometry. In the case of a flow in a control, one will take the diameter of the drain, or the hydraulic diameter if control does not have a circular section. In the case of a plane plate, one will take the length of the plate, or the X-coordinate as from the leading edge of the plate. Like all Nombre without dimension, the value of the number of Nusselt strongly depends on the reference variables that one selected, and on the physical significance which one intends to give him (local or total for example). It is in particular important to know, during the use of a correlation, if the convection coefficient H at summer defined compared to a temperature of fixed reference, or at a local temperature of mixture.

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