Effects of ageing and moisture content on thermal properties of cassava roots using response surface methodology

Abstract

Cassava farmers often leave the roots in the ground for months after maturity due to its poor storability after harvest coupled with non-­‐availability of acceptable storage alternatives. This practice leads to physiological changes in the roots which may affect their thermal properties. This study therefore investigated the influence of tuber age and moisture content on the thermal properties of cassava roots. Freshly harvested cassava roots were peeled, cut into cylindrical shape of length 5cm and diameter 3.5 cm and then conditioned to moisture contents of 50, 55, 60, 65 and 70% (wet basis). The thermal properties were determined at 12, 15 and 18 Months After Planting (MAP) using the KD 2 Pro that measures the properties simultaneously based on the transient line heat source method. The mean thermal conductivity ranged from 0.4770 to 0.5654, 0.4804 to 0.5530 and 0.4302 to 0.6102 W/mK at these ages respectively. The thermal diffusivity also ranged from 1.588 to 2.426, 1.614 to 0.1972 and 1.610 to 2.020m²/s while the specific heat capacity ranged from 2.3626 to 3.1495, 2.4900 to 3.7538 and 3.4222 to 3.8830 kJ/kg.K ages 12, 15 and 18 MAP respectively. Second order polynomial models described the relationship between the parameters studied. Analysis of variance showed that age, moisture content and their interactions significantly influenced the thermal diffusivity. Age alone had no influence on the thermal conductivity, but moisture content and its interactions with age. Specific heat was influenced by neither age nor moisture content