text: As the chemical engineering profession developed in the first half of the 20th century, the concept of "unit operations" arose as being needed in the education of undergraduate chemical engineers. The theories of mass, momentum and energy transfer were being taught at that time only to the extent necessary for a narrow range of applications. As chemical engineers began moving into a number of new areas, problem definitions and solutions required a deeper knowledge of the fundamentals of transport phenomena than those provided in the textbooks then available on unit operations.
  In the 1950s, R. Byron Bird, Warren E. Stewart and Edwin N. Lightfoot stepped forward to develop an undergraduate course at the University of Wisconsin–Madison to integrate the teaching of fluid flow, heat transfer, and diffusion. From this beginning, they prepared their landmark textbook Transport Phenomena.