Application of the acid hydrolysis of sucrose as a temperature indicator in continuous thermal processes

The hydrolysis of sucrose in an acid medium was used as a temperature indic ator to measure holding temperatures in a continuous thermal-processing uni t. From a theoretical analysis, target conversion (chi) and errors in both acid concentration and conversion measurements were found to affect signifi cantly the accuracy of predicted temperatures, whereas errors in the determ ination of the fluid mean residence time did not show a significant effect. For different pasteurisation temperatures (70 degrees C < T < 86 degrees C ) and flow rates (4800 < Re < 11,300), the acid concentration in the medium was adjusted so that different extents of reaction could be tested, as the reaction rate was found to increase exponentially with [H+]. Nitric acid s olutions were circulated through the unit, a sucrose solution was continuou sly fed to the entrance of the holding tube and sucrose concentration was a nalysed at the half way part and at the exit of the holding tube. The tempe rature of the holding section was then estimated from the measured conversi on. These results compared well with thermocouple measurements, with deviat ions of less than 4 degrees C for conversions between 0.4 and 0.7, whereas greater errors were obtained for both low and high conversions. (C) 1999 El sevier Science Ltd. All rights reserved.