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Wilhelm Nusselt (November 25, 1882 - September 1, 1957) was a German engineer and scientist.

He was born November 25, 1882, at Nürnberg, Germany. He studied mechanical engineering at the Technische Hochschulen of Berlin-Charlottenburg and Munchen and graduated (as a Diplom-Ingenieur)in 1904. He conducted advanced studies in mathematics and physics and became an assistant to O. Knoblauch at the Laboratory for Technical Physics in Munchen. He completed his doctoral thesis on the "Conductivity of Insulating Materials" in 1907, using the "Nusselt Sphere" for his experiments. From 1907 to 1909 he worked as an assistant to Mollier in Dresden, and qualified for a Professorship with his work on "Heat and Momentum Transfer in Tubes".

In 1915, Nusselt published his pioneering paper: The Basic Laws of Heat Transfer, in which he for the first time derived the dimensionless numbers now known as the principal parameters in the similarity theory of heat transfer directly from the basic differential equations of fluid flow and heat transfer. In the same paper he states:

"It is often claimed in the literature, that heat transmission from a body be due to three reasons:the radiation,the conduction, and the convection. This subdivision of heat transmission in conduction and convection gives the impression as if we had to do with two independent phenomena.From this one had to conclude, that heat might also be transferred by convection without any contribution of conduction. This, however is not true."

Despite this, the phrase of the "three mechanisms" of heat transfer is still found in many textbooks. Other famous works were concerned with the film condensation of steam on vertical surfaces, the combustion of pulverized coal and the analogy between heat and mass transfer in evaporation. Found among the primarily mathematical works of Nusselt are the well known solutions for laminar heat transfer in the entrance region of tubes, for heat exchange in cross-flow and the basic theory of regenerators.

Nusselt was a professor at the University of Karlsruhe then Technische Hochschule of Karlsruhe from 1920-1925 and at Munchen from 1925 until his retirement in 1952. He was awarded the Gauss-Medal and the Grashof Commemorative Medal. Nusselt died in Munchen on September 1, 1957.