Characterization of Physical and Aerodynamic Properties of Walnuts

The objective of this research was to study the physical and aerodynamic properties of freshly harvested walnuts. Measurements were carried out for three walnut varieties, Tulare, Howard and Chandler cultivated in California, USA. The nuts treated with and without Ethephon were collected from mechanical harvesters. The nuts were sorted into two categories, those with hull and those without hull before measuring nut dimension, density, terminal velocity and moisture content (MC). For nuts with a hull at harvest, all measurements were conducted before and after manual removal of the hulls and were characterized as undehulled and dehulled nuts. The effect of water washing on the nut density and terminal velocity was also determined. The results revealed that three axial dimensions (L, D1 and D2) were in the range of 42.2 - 59.4, 36.4 - 54.4 and 35.86 - 51.4 mm, respectively for walnuts with hull and 30.7 - 44.4, 27.7 - 42.2 and 25.1 - 40.5 mm, respectively for walnuts without hull. The average densities for dehulled and undehulled walnuts were 553±110, 716±106 and 878±102 kg/m3, respectively. The corresponding average terminal velocities were 7.9±1.2, 10.1±1.4 and 14.1±1.7 m/s. It was found that strong relationships existed between the MC versus the density and terminal velocity of individual nuts. A terminal velocity of 10 m/s can separate the dehulled from undehulled walnuts, and then the in-shell walnuts can be further sorted into groups with different MCs based on desired terminal velocities. This separation can improve processing and energy efficiency in handling and drying operations. There was no significant effect of ethephon treatment and water washing on the nut density and terminal velocity.