Setting up continuous induction heating system, and investigation of its applicability for heating of cherry juice experimentally and mathematically

Induction heating is a heating method applied by generating heat under magnetic field in materials having ferromagnetic properties. In this thesis, a ferromagnetic tubular continuous induction heating system was set up, and the applicability of this system in heating of sour cherry juice was investigated by experimentally and mathematically. It was aimed to heat the sour cherry juice from 27±2°C to the target temperature of 75°C. The effects of the different flow rates (200-250-300 ml/min) and different pipe wall temperatures (80-90-100 °C) on heating characteristics, some quality attributes (Total monomeric anthocyanin, ascorbic acid, total phenolic content, color, pH and titratable acidity, turbidity) of sour cherry juice and performance characteristics (energy and exergy efficiencies, improvement potential) of the process was investigated. The optimum condition for induction heating process was determined by considering changes in quality attributes exergy efficiency. As a conventional heating method, the process was applied in a double pipe heat exchanger for the process condition similar to the optimum induction heating condition, by using hot water as a heating medium. The effects of heating methods on some quality attributes of sour cherry juice and exergy efficiency of heating process were compared. Additionally, theoretical investigation of continuous induction heating process was performed by using finite element method. The process time to reach target temperature decreased as the flow rate decreased and set pipe wall temperature increased. It was found that ascorbic acid content and phenolic compound content decreased by %15.3-28.2 and %5.27-10.7, respectively, as the flow rate increased. It was found that the effects of different induction heating conditions on total monomeric anthocyanin, color, turbidity, pH and titratable acidity values were similar. Energy and exergy efficiencies of induction heating process was in the range of % 44.45-81.27 and 38.82-74.76, respectively. The efficiency values increased as the flow rate increased and set pipe wall temperature decreased. The optimum condition of induction heating process was predicted (desirability 0.90) as the flow rate of 209 ml/min and set pipe wall temperature of 86°C. In validation tests, the differences between experimental and predicted values for responses were lower than 5%. The quality properties and exergy efficiency for optimum induction heating process were higher than those of conventional heating process, statistically (p<0.05). Induction heating process was also investigated by finite element method numerically. For the experimental process conditions applied, the changes of exit temperature of sour cherry juice, temperature distribution and velocity profile inside the pipe depending on time were predicted. It was determined that the statistical errors between numeric model predictions and experimental values were low enough, hence the compatibility of the model was good. It is expected that the present thesis having the detailed data on the utilization of induction heating for heating of fruit juice will provide valuable information to literature. Keywords: Fruit juice, heat exchanger, electrical, quality, energy, modelling