He father was Stian Lydersen who was captain in the Norwegian merchant fleet, and Lene Marie Lydersen. Lydersen married Ragnhild Haugen in 1946. Their children are Lars Lydersen and :no:Stian_Lydersen|Stian Lydersen.
Background and education
Lydersen grew up in the coastal village Narestø at Flosta in the Aust-Agder county. He completed examen artium in 1938. In 1943 he graduated with a master's degree in engineering from the Machine Department at NTH. He then worked as an assistant for professor Adolf Watzinger at NTH for three years. Next, he was employed at Kværner Brug in Oslo for two years. He returned to NTH in 1948, where he taught refrigeration engineering, and completed the degree of Doctor Technicae in 1950.
Scientific work
Chemical engineering had developed as a discipline of its own in the United States since around 1900, based on needs in industry. For many years, NTH followed the German tradition, where machine engineers carried out such tasks. But after World War II, NTH oriented itself more towards USA. In 1949, NTH established its own Department of Chemical Engineering. Sven G. Terjesen, who was second cousin of Lydersen, was the first professor at the department. He encouraged Lydersen to qualify for a scientific position in the new discipline. In 1952 to 1955, Lydersen worked with professor Olaf H. Hougen at University of Wisconsin in Madison. Hougen had established one of the world's leading centers for chemical engineering. Lydersen and Hougen became good friends, and started a long lasting cooperation between the chemical engineering departments in Trondheim and Madison. During his stay in the US, Lydersen was also employed at Miller Brewing Company in Milwaukee for a shorter period. While in the United States, Lydersen developed a method for the estimation of critical properties for temperature, pressure and volume, based on already published data. This method is a group contribution method, and is also referred to as the Lydersen method. Determination of physical data became a central research activity when he returned to NTH, now also based on his own measurements. The results are published in chemical engineering handbooks. He received a position at NTH as docent in 1955, and full professor from 1958. He authored or co-authored several publications on determination of enthalphy and vapour pressure for organic substances. Lydersen had several patents. He authored one textbook in chemical engineering in Norwegian, and two textbooks in English: Fluid flow and heat transfer from 1979, Mass transfer in engineering practice from 1983, and an English/French/German/Spanish Dictionary of chemical engineering from 1992. He received the Distinguished Service Citation Award at University of Wisconsin in 1980.
The Norwegian language conflict
The Norwegian language conflict is a controversy within Norwegian culture and politics related to the two written versions of the Norwegian language: Bokmål and Nynorsk. Local communities organized referendums to decide the language version in the localelementary schools. Lydersen strongly felt that it would be more just to let the parents decide this. He became an active member of the Riksmål Society, as a board member and leader. He was a member of the Vogt-committee 1964–1966, and the Language council of Norway 1972–1994.
Publications
Untersuchungen über Wärmeübergang und Druckfall in Kugelstapeln beim Durchblasen von Luft. Mit Anwendung auf das Gefrieren von Nahrungsmitteln in Luftstrom, dr.avh., Trondheim 1950
Fra sprogstridens historie, 1965
Kjemiteknikk, Trondheim 1972
Fluid flow and heat transfer, Wiley, Chichester 1979
Mass transfer in engineering practice, Wiley, Chichester 1983
Ordbok for kjemiteknikk, Trondheim 1988
Dictionary of chemical engineering, Chichester 1992
