A widely used analogy from heat, momentum, and mass transfer analogies. Also known as j-factors, they are used to determine an unknown transfer coefficient when one of the other coefficients is known. It applies to fully developed turbulent flow in pipes, and relates mass and heat transfer coefficients, and friction factors. It was proposed by and named after American chemical engineers Thomas H. Chilton (1899–1973) and Allan P. Colburn (1904–55).