A model for the transient flow of thermoplastics in annular hot runners

Annular hot runner systems, in which the inner surface is heated and the outer surface cooled, are being used increasingly in the injection molding of thermoplastics. In this paper a computer model which has been developed to calculate transient pressure, temperature, and velocity fields is described. Using the properties of acrylonitrile‐butadiene‐styrene for illustration, some detailed temperature and velocity profiles computed with the model are presented for atypical hot runner section. The effects of a number of design and operating variables on the pressure drop are also presented.