Engineering: Heat Transfer in Extruders II—Simultaneous Heating and Cooling
L. Levine. Leon Levine & Associates, Albuquerque, NM, U.S.A. Cereal Foods World 55(1):41-42.
In Levine’s last column (Cereal Foods World, November-December 2009), a discussion about heat transfer in extruders was commenced. The issue of heat losses was discussed and an approximate calculation of the relative heat losses in laboratory and commercial extruders was demonstrated. The calculations illustrated that the heat losses, as a fraction of the total mechanical energy input by the extruder, were negligible in the commercial scale extruder, but were quite significant in the laboratory extruder. The source of this difference was explained as the ever decreasing ratio of extruder surface area to throughput and the size of the extruder is increased. In this column, Levine considers a related problem that has been encountered by numerous people who design/operate extruders—the problem of cooking and cooling in one extruder.