화학공학
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.