Estimation of Heat and Mass Transfer Coefficients During Air-Freezing of Cucumber

Abstract

Freezing of foods involves coupled heat and mass transfer. It is essential to optimally design the freezing equipment and maximise the efficiency of the freezing process. Therefore, it is necessary to estimate the heat and mass transfer coefficients. In this study, the surface heat and mass transfer coefficients were estimated employing the Hilbert equation as well as the corresponding thermal and diffusive boundary layers during freezing of unpeeled cucumber at low air temperatures (−10 to −18 and −25°C). The estimated mean heat transfer coefficients ranged from 10.99 W m−2 K−1 for 0.5 m s−1 up to 40.07 W m−2 K−1 for 5.0 m s−1. The respective mass transfer coefficients ranged from 8.98 up to 32.40 m s−1. The estimated heat transfer coefficients were compared with the respective ones calculated from Dincer and Dincer and Cengeli during air-cooling (22 to 2°C) of unpeeled cucumbers of similar size as well as other agricultural cylindrical products.