Characterizing the Thermal Conductivity of Fruits & Honey
Researchers face significant challenges in accurately characterizing the thermal conductivity of agricultural products. The data is necessary in properly designing and optimizing commercial food storage and production processes, ensuring a safe and efficient food supply. Reliable thermal conductivity data is essential to understanding freezing, thawing and cooking processes.
Testing the thermal conductivity of such organic materials in the past has been a cumbersome and messy job with inadequate characterization options. Guarded hot plate and other traditional techniques require large sample volumes, unpractical or unrepresentative sample formats, and take hours to administer.
Recent work conducted in collaboration with Dr. Andre Levechenko of Advance Al-Thermo LLC (Princeton, NJ) highlights application of C-Therm’s TCi Thermal Conductivity Analyzer in the rapid, non-destructive characterization of various agricultural commodities. The TCi Thermal Conductivity Analyzer employs the modified transient plane source (MTPS) technique. The one-sided interfacial technique provides the necessary flexibility to measure solids, liquids, powders and pastes, making it an optimal tool for the variety of formats of foods and agricultural products.
Fruits are complex solids whose major component is water, and the thermal conductivity of fruit is thus very close to that of water. (The water content for the majority of fruits studied is between 85-92 wt %.) The thermal conductivities for the fruits tested is between 0.42 and 0.56 W/(m·K). See Figure 1.
Levchenko’s work additionally extended to the characterization of honey. Among other nutrients, honey contains large amounts of carbohydrates. The thermal conductivity of honey is 0.377 measured with the TCi. While some older published reports place the value for honey to be as high as 0.493 W/(m·K), honey contains only 15 - 18 wt% of water, so its thermal conductivity is dominated by the carbohydrates. The thermal conductivity of various sugars are in the range of 0.2-0.3 W/(m·K). Therefore the thermal conductivity of honey is significantly lower than water as reported by Levchenko.
To learn more about the TCi analyzer click here.
For more details on the thermal conductivity characterization of fruits and agricultural commodities, refer to the Canadian Thermal Analysis Society's (CTAS) 2012 annual conference proceedings.