The objective of this study is to develop a model for continuous sterilizer and to optimize its size and operation conditions which have great importance in biochemical engineering.
At first, a model for continuous heat exchanger type sterilizers which are most popular in industry, was developed. The shape of the sterilizer was cylindrical and heat was transferred through its wall. Heat source was saturated steam. It was assumed that the properties of the stream, such as density, viscosity, heat capacity and heat conductivity, were functions of temperature. And it was also assumed that the inlet stream was Poiseulle flow or plug flow. The continuity equation, the equation of motion and the thermal energy equation was solved simultaneously by finite difference method(FEM) to calculate profiles of temperature and velocity of the stream. A model for microwave sterilization which has many advantages over conventional sterilization systems, was also developed. Microwave sterilization is one of the heat sterilization system in which the medium is heated by microwave.
In this study, the simulations of two sterilization systems were carried out and then the results of those simulations were compared. It was found that there were gradients of temperature and velocity in the radial direction at the inside of continuous heat exchanger type sterilizer. In case of Poiseulle flow as the inlet stream, these gradients were so stiff that the ratio of ln ($N_0$/N) between the center and the region around the wall varied from 10 to 1000. However when the inlet stream was plug flow, the distribution of the residence time was so uniform that the ratio was relatively small compared to that of Poiseulle flow. But due to the gradients of temperature in the radial direction, much differences in ln ($N_0$/N) values was occurred, which result in an ineffective sterilization process. It was difficult to overcome these differences in the conventional model. But microwave sterilization could heat materials uniformly and quickly. So microwave sterilization could be the more effective system than the conventional one.
