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 varieties (Tulare, Howard, and Chandler) cultivated in California. Walnuts treated with and without Ethephon were collected from mechanical harvesters. Ethephon treatment was conducted two weeks before harvest to hasten ripening. The walnuts were sorted into two categories, those with hulls and those without hulls (WOH), before measuring their dimensions, density, terminal velocity, and moisture content (MC). For walnuts with hulls at harvest, all measurements were conducted before and after manual removal of the hulls, and these walnuts were categorized as undehulled (UH) and dehulled (DH). The effects of water washing on walnut density and terminal velocity were also determined. The results revealed that the three axial dimensions (L, D₁, and D₂) of walnuts harvested with hulls were significantly greater than those of walnuts harvested without hulls. The average densities for individual WHO, DH, and UH walnuts were 553 ±110 kg m^-3, 716 ±106 kg m^-3, and 878 ±102 kg m^-3, respectively. The corresponding average terminal velocities were 7.9 ±1.2 m s^-1, 10.1 ±1.4 m s^-1, and 14.1 ±1.7 m s^-1. It was found that strong relationships existed between the MC versus the density and terminal velocity of individual walnuts. A terminal velocity of 10 m s^-1 can separate WHO from UH walnuts, and in-shell walnuts can be further sorted into groups with different MCs based on their terminal velocities. This separation can improve processing and energy efficiency in handling and drying operations. There were no significant effects of ethephon treatment and water washing on walnut density and terminal velocity.