Bulk Thermal Conductivity of Unhulled Pistachio Nuts

One of the most important thermal properties of unhulled pistachio nuts, namely bulk thermal coductivity, was evaluated as the function of moisture content and temperature. The moisture content of nuts ranged from 20.9% on the wet basis to 51.8% (moisture content at harvest time) and the temperature ranged from +20°C to +40°C. In order to measure the thermal conductivity of agricultural materials, a specific probe was developed. Thermal conductivity was measured in transient state by calculating the maximum instant slope, using the line heat source which was assembled in the probe. Bulk thermal conductivity varied significantly with moisture content and temperature. It ranged from 0.1145 to 0.1904 W/mK and increased with moisture content in the range of 20.9-51.8% on the wet basis. Furthermore, increasing the temperature from 20 to 40°C raised the average thermal conductivity from 0.1448 to 0.1585 W/mK. The conducted tests on two varieties of nuts (Akbari and Kallehghoochi) demonstrated that the thermal conductivity of Kallehghoochi cultivar is lower than that of the Akbari cultivar at α=0.05. Quadratic regression equations were developed depicting the effect of moisture content and temperature on thermal conductivity.