Experimental and simulation studies of heat transfer in high-humidity hot air impingement blanching (HHAIB) of carrot

Abstract

A mathematical model was presented to characterise heat transfer in high-humidity hot air impingement blanching (HHAIB) of cuboid carrots. The model accounts for condensation heat transfer and predicts the sample’s core temperature evolution with time. The simulation was performed at different relative humidity of 20%, 40%, 60%, 80% with constant temperature of 383K. Results showed that the heat transfer process of HHAIB is divided into two stages based on vapor–liquid phase transition, namely a condensing heat transfer segment and a non-condensing heat transfer segment. In the initial stage of HHAIB, a comprehensive and intense condensation occurred on the sample surface leading to high heat transfer coefficient and greatly enhancing heat transfer, but at the same time creating a huge temperature gradient in the sample. The relative humidity of 40%–60% at 383K could not only enhance the heat transfer rate but also improve the homogeneity of temperature distribution in the sample. Simulated core temperatures were compared with experimental measurements, showing good agreement with a coefficient of determination R2 of 0.991. The findings of current work provide theoretical basis to better design and control of the process conditions of HHAIB as it elucidates the heat transfer characteristic taking account condensation phenomenon and illustrates the temperature distribution and evolution profiles.