Computer-aided design and performance evaluation of an indirect type helical tube ultra-high temperature (UHT) milk sterilizer

Abstract

A laboratory model indirect type helical tube ultra-high temperature (UHT) milk sterilizer was designed and tested. The helical triple tube heat exchanger modeling and simulation was carried out for heating milk from 90°C to 150°C in the annulus of the triple tube using steam in the innermost and outermost tubes. The holding section was designed based on an Arrhenius model to reduce B. stearothermophilus microorganisms in the milk by 8 log cycles at a sterilization temperature of 150°C with a residence time of 2.64 s. The helical double tube cooling section modeling and simulation was carried out to cool milk from 150°C to 90°C by using tap water. The lengths of heating, holding and cooling sections were found to be 2.28, 1.0 and 2.08 m, respectively. The set-up was tested for UHT processing of milk at the flow rate of 135 l/h. The microbial effectiveness of the process was tested separately with inoculated samples of B. subtilis and B. stearothermophilus microorganisms and found to be effective during processing as well as during storage of the UHT processed milk for two months. The quality attributes (i.e. color and viscosity) of the UHT processed milk were also tested during the processing and storage periods. Overall there was no marked change in quality attributes for which the processed milk can be considered unacceptable.