Moisture dependent thermal properties of peanut pods, kernels, and shells

Abstract

The specific heat, thermal conductivity, and thermal diffusivity, of peanut pods, kernels, and shells were evaluated as a function of moisture content. The specific heat and thermal conductivity were measured using purpose-built vacuum flask calorimeter and transient-state heat transfer apparatus, respectively. The specific heat was determined by mixing hot water with sample maintained at ambient temperature in the calorimeter and incorporating temperature-correction into calculations. Thermal conductivity was determined in 60-min experiments after checking for time-correction in the calculations. Thermal diffusivity was calculated using formula method. Thermal properties, as a function of moisture content, were fitted using linear equations. The specific heats of peanut pods, kernels, and shells increased linearly from 2.1 to 3.3, 1.9 to 2.8, and 2.7 to 4.1 kJ kg −1 °C −1 , respectively, with the corresponding increase in moisture content from 5.2 to 23.7, 5.0 to 30.6, and 3.5 to 28.7% (d.b.). The specific heat of shells was the highest, followed by pods and kernels. The thermal conductivity of peanut pods, kernels, and shells increased linearly from 0.12 to 0.16, 0.15 to 0.19, and 0.11 to 0.18 W m −1 °C −1 , respectively, with increasing moisture content (m.c.). The thermal conductivity of shells was the lowest, followed by pods and kernels. The thermal diffusivity of peanut pods and kernels decreased from 2.8 × 10 −7 to 2.3 × 10 −7 and 1.1 × 10 −7 to 1.0 × 10 −7 m 2 s −1 , respectively, with an increase in m.c. But, the diffusivity of shells increased from 5.9 × 10 −7 to 6.7 × 10 −7 m 2 s −1 . The thermal diffusivity of shells was the highest, followed by pods and kernels. These data will be useful for thermal processing, storage, and processing applications involving peanuts.