Articles
THERMAL PROPERTIES AND THERMAL IMAGE BRUISE DETECTION IN APPLES
Article number
599_26
Pages
231 – 235
Language
English
Abstract
Grading is an essential process during packing to remove defected apples (Malus Domestica Borkh.), returning benefits to apple industry and consumers. As an alternative to other grading techniques (e.g., grading by hand, CCD camera, near-infrared (NIR) reflection or transmission), thermal imaging also detects bruises in apples.
The evidence of bruise in thermal images during transient heating indicated that thermal properties were different between bruised and sound tissues, mainly due to thermal diffusivity (
) differences.
This article discusses the measurement of the components and the validation of thermal imaging bruise detection using finite element (FE) modelling and the measured components.
Thermal conductivity (k), specific heat (Cp) and density (
) which are components of in the relationship =k/(•Cp), were measured individually for bruised and sound tissues using the modified Fitchs method, differential scanning calorimetry, and density=mass/volume, respectively.
Results revealed that k was approximately 20% higher and was approximately 5% higher in bruised than in sound tissues, while Cp was unchanged.
The k-value dominates changes in, resulting in of 14.3% higher in bruised than in sound tissues.
Applying to the simulation accordingly, the FE model showed that surface temperature of bruises (with greater ) warmed up more slowly than that of sound tissues (with smaller ) during heating scenarios, comparable to the findings of bruise detection by thermal imaging. Hence, a bruise may serve as a thermal window to transfer heat to or from the interior of apples.
The FE model not only illustrated a linkage between thermal properties and heat transfer of bruised apples but also provided flexibility for the design of thermal image bruise detection system.
The evidence of bruise in thermal images during transient heating indicated that thermal properties were different between bruised and sound tissues, mainly due to thermal diffusivity (
) differences.This article discusses the measurement of the
components and the validation of thermal imaging bruise detection using finite element (FE) modelling and the measured components.Thermal conductivity (k), specific heat (Cp) and density (
) which are components of in the relationship =k/(•Cp), were measured individually for bruised and sound tissues using the modified Fitchs method, differential scanning calorimetry, and density=mass/volume, respectively.Results revealed that k was approximately 20% higher and
was approximately 5% higher in bruised than in sound tissues, while Cp was unchanged.The k-value dominates changes in
, resulting in of 14.3% higher in bruised than in sound tissues.Applying
to the simulation accordingly, the FE model showed that surface temperature of bruises (with greater ) warmed up more slowly than that of sound tissues (with smaller ) during heating scenarios, comparable to the findings of bruise detection by thermal imaging. Hence, a bruise may serve as a thermal window to transfer heat to or from the interior of apples.The FE model not only illustrated a linkage between thermal properties and heat transfer of bruised apples but also provided flexibility for the design of thermal image bruise detection system.
Publication
Authors
J. Varith, G.M. Hyde, J.K. Fellman
Keywords
Apple, bruise, thermal properties, thermal imaging, finite element
Online Articles (98)