Residence time distribution of liquids in a continuous tubular thermal processing system part II: Relating hold tube efficiency to processing conditions

Abstract

The concept of efficiency of a holding tube is essential to guarantee the safety of continuously processed fluid foods. A good prediction of efficiency allows a better control of the processing conditions, guaranteeing product safety while decreasing product quality losses due to overprocessing. Different published methods were compared to data obtained in this work and to reported data, to assess their ability to predict tube efficiency in a range of Reynolds number (Re) covering laminar, transient and turbulent flow. Furthermore, a model assuming dispersed plug flow and a power-law relation between Peclet number (Pe) and Re was developed and evaluated. Published models were shown to be, in general, conservative for both laminar and turbulent flow, but often overpredicted the experimental efficiency in the zone of 2100 <Re < 4000. Deviations between predicted and experimental values were very considerable (errors from −25% to 90%). The model proposed has proved to be conservative over the whole range, but more accurate (errors up to 15%).