Nusselt, Ernst Kraft Wilhelm

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(b. Nuremberg, Germany, 25 November 1882; d. Munich, Germany, 1 September 1957), heat transfer, thermodynamics.

Nusselt was the first significant contributor to the subject of analytical convective heat transfer. He completed his schooling at a time when the problems of heating and cooling in the increasingly high performance power equipment of the early twentieth century finally demanded accurate analysis. For a century Fourier’s mathematical theory of heat conduction in rigid media had provided the only analytical attack on the problem, but it was inadequate to predict the heat flux in a flowing fluid. In 1915 Nusselt cut the Gordian knot. Although analytical solutions to the appropriate fluid-flow equations were so intrinsically complicated that they had to await the more fundamental work of others, Nusselt used dimensional analysis to show, in a single stroke, the functional form that such solutions would have to take. He thus made it possible to generalize limited experimental data.

Nusselt was the son of Johannes Nusselt, a factory owner, and Pauline Fuchs Nusselt. He completed his early education in Nuremberg in 1900 and then enrolled at the Technische Hochschule in Munich to study mechanical engineering. After six semesters he transferred to the Technische Hochschule of Charlottenburg, in Berlin, where he completed his studies. He then returned to Munich and passed his mechanical engineering diploma examination there.

Nusselt began his studies toward a doctorate in mechanical engineering in Munich, and from 1906 through 1907 he served as an assistant to Oskar Knoblauch, who was also the teacher of another early heat transfer luminary, Ernst Schmidt. He completed the degree in August 1907, and from then until 1925 he moved about Germany from post to post. From September 1907 to June 1909 he was assistant to the well-known thermodynamicist Richard Mollier at the Technische Hochschule in Dresden. He then worked in the heat technology division of the Sulzer brothers’ firm in Switzerland (1909–1911). He returned to the mechanical laboratory in Dresden in 1913 and held indefinite teaching appointments until 1917. From January 1918 through March 1919 he returned to industry and worked at the Badische Anilin- and Soda-Fabrik in Ludwigshafen. In April 1920 he was appointed professor at the Technische Hochschule in Karlsruhe. In 1925, Nusselt was named to the chair in theoretical mechanics at the Technische Hochschule in Munich. He retired from this post in 1952 and was succeeded by Schmidt.

Two of Nusselt’s most important works were completed during his years in Dresden. His paper on the similitude of convective heat transfer, “The Basic Law of Heat Transfer” (1915), followed his earlier work on the thermal conductivity of insulating materials and some work with heat convection coefficients. The scope of his 1915 paper, however, was far broader; in this work he set up the dimensionless functional equations for both natural and forced convection. He thus reduced the large number of physical variables that appear in the boundary layer equations to the familiar dimensionless groups that today bear the names “Nusselt number,” “Reynolds number,” “Prandtl number,” and “Grash of number.” He also noted additional groups that are needed when physical properties vary or when the full equations of motion are used to define natural convection. It was thus possible for experimentalists to reduce limited data into these few parameters and to form simple empirical equations among them. Such correlations have, in most cases, preceded heat transfer theory down to the present day.

His other major contribution during this period was a paper entitled “The Film Condensation of Steam” (1916), in which he provided a clear-headed and simple description of the film condensation of any liquid by linearizing the temperature profile and ignoring inertia in the liquid. Subsequent efforts to refine this heat transfer prediction have failed to alter his numerical results, except for liquid metals and the most extreme heat fluxes.

Nusselt’s later works branched into radiant heat transfer, combustion, and a variety of applications of heat transfer and thermodynamics to power equipment. In 1930 he provided an important description of the similarity between heat and mass transfer, and in 1934 and 1944 he published the first and second volumes, respectively, of a book on technical thermodynamics.

Nusselt was married on December 12, 1917, while teaching at Dresden, to Susanne Thurmer. The couple had two daughters and one son. Nusselt was an energetic man, strongly inner-directed, soft-spoken, and self-contained. He was an avid mountain climber throughout his life, and he appears to have equated the methodical assault of a mountain to the kind of assault a man should make on the problems that beset him. He brought this same kind of energy and concentration to his technical work. He was, however, circumspect and, perhaps, even cautious.

During the 1930’s and 1940’s German scientists made great advances in heat transfer. But Nusselt did not wield great influence within the peer group that controlled this field. It was probably not in his makeup to do so, and he is known to have suffered from a chronic internal ailment during these years. Although he was an exacting taskmaster with his students, he apparently lacked charisma and he was not a good lecturer.

In 1947 Nusselt’s son, Dietrich, also a mountaineer, fell to his death on the east wall of the Riffelkopf in the Wetterstein Gebirge. Nusselt did little more in his remaining years, and upon his retirement he left the university completely and lived out his life in relative seclusion.


I. Original Works. G. Lück and G. Kling (see below) both provide a bibliography of over 50 major works. Nusselt’s most important writings include “Das Grundgesetz des Wärmeüberganges,” in Gesundheits Ingenieur, 38 (1915), 872; “Die Oberflachenkondensation des Wasserdampfes,” in Zeitschrift des Vereines deutscher Ingenieure, 60 (1916), 541, 569; “Warmeubergang, Diffusion and Verdunstung,” in Zeitschrift für angewandte Mathematik and Physik, 10 (1930), 105; and Technische Thermodynamik, 2 vols. (Berlin, 1934, 1944). Nusselt’s autobiographical deposition for the American occupation force after World War II provides a wealth of personal detail.

II. Secondary Literature. Poggendorff, VIIa, 455, lists several biographical articles; the most extensive is G. Kling in Chemie-Ingenieur-Technik, 24 (1952), 597–608, which includes a bibliography of works by both Nusselt and his co-workers. G. Lück’s article on Nusselt’s retirement in Gesundheits Ingenieur, 74 (1953), 7–8, also provides a similar bibliography. Allgemeine Warmetechnik, 3 (1952), 161–163, includes a bibliography and a list of Nusselt’s doctoral students and their theses.

John H. Lienhard