Heat transfer modeling during high-humidity hot air impingement blanching of grapes

During high-humidity hot air impingement blanching (HHAIB) of fruits and vegetables, the process effect on the product and subsequent process depends on the operating fluid parameters. In this regard, heat transfer phenomenon during applying the pretreatment is not well known. In this study, the mechanisms of heat transfer during the HHAIB of grape berries were investigated via developing an appropriate mathematical model. Numerical simulation of the model was performed using COMSOL software at temperature of 110?, fluid velocities of 2, 6, and 10 m s(-1), and relative humidities of 20%, 40%, 60%, and 80%. The heat transfer caused by the impinging jet and condensation on the grape surface were considered. The center and surface temperature of the grape berries were predicted. Taking the appropriate heat transfer rate and uniformity of temperature distribution in grape berries into account, the relative humidity range of 40%-60% and the velocity of 10 m s(-1) were selected for the process. Comparison of the predicted and measured values for the center temperature of the grape berry statistically validated the simulation task with a determination coefficient (R-2) of 0.993 and root mean square error of 1.347.Practical ApplicationsNowadays, the demand for organic foods has increased. The high-humidity hot air impingement blanching (HHAIB) is a safe, effective, and controllable nonchemical method that can be used instead of chemical pretreatment in raisin production. In terms of applying the HHAIB pretreatment for grape drying, little research has been done. Thus, there is still no complete understanding of the heat transfer during its application. Numerical simulations are beneficial tools for accurate designing and optimization of thermal processes. Thus, it is necessary to use mathematical modeling to understand HHAIB mechanisms for industrialization.