TRANSPORT PROCESSES DURING STERILIZATION OF VERTICAL AND 5-DEGREE HORIZONTAL DEAD-LEGS

Experimental temperature profiles and biological kill data from dead-e nded tubes of various diameters and lengths commonly used in biotechno logy applications were compared to those predicted by a finite element model for steam-in-place (SIP) sterilization at 122 degrees C. Diamet er was shown experimentally and numerically to have a significant effe ct with larger diameter tubes exhibiting greater buoyant driven convec tive flow and more rapid sterilization. The overall Grashof number was shown to be the significant parameter relating magnitude of convectiv e flow to tube diameter and varied as the diameter cubed. Analysis of air/steam mixture flow patterns showed air displacement from 0.4 cm di ameter tubes to be due primarily to molecular diffusion, whereas 1.0 a nd 1.7 cm tubes showed a two-stage convective flow pattern. There exis ts a critical diameter of 0.4 cm below which SIP sterilization due to buoyancy driven flow does not occur and steam bleeders should be used.