Heat exchanger

A heat exchanger comprising an elongated housing having an inlet and an outlet, a conveying screw rotatably mounted in said housing for conveying material therealong between said inlet and outlet, said conveying screw including a cylindrical body having opposite ends, a hollow interior and an outer surface, a tubular helical flight extending along said outer surface of said body and having opposite flight end portions, said helical flight defining a material engaging surface, said material engaging surface having an inner surface portion positioned closely adjacent said outer surface of said cylindrical body, and said material engaging surface extending outwardly from said inner surface portion whereby material can be conveyed upon screw rotation, attachment means for attaching said flight end portions to said body in communication with said hollow interior, said tubular helical flight being substantially unattached to said body intermediate said flight end portions, and means for introducing heat exchange medium to said hollow interior for transfer through said tubular helical flight.