Analytical and numerical characterisation of terminal velocities of Tenebrio molitor larvae in a new, asymmetrical zigzag based separation system

Abstract

Separation of Tenebrio molitor larvae from unwanted residues, like frass, feed or exuviae is a key process step for an industrial scale plant. One method to separate larvae from residues is using a zigzag air classifier. For designing and for an efficient operation of a zigzag air classifier, the terminal velocity is a key parameter to separate larvae from different residues with a high separation sensitivity. In this work, the terminal velocities of different larvae sizes are evaluated analytically, numerically and experimentally. For this, the sizes of 3 week to 12 week old larvae were used to calculate and simulate the terminal velocity. To validate the results, an experiment was carried out and compared with the analytical and numerical data. For this, a model for T. molitor larvae was designed to calculate the surface and volume of a larva to produce equivalent spheres with the same physical properties as a real larva. The results are showing similar curves with terminal velocities from 5 m/s for young larvae (3 weeks old) to 12 m/s for older larvae (12 weeks old). The deviations between each method are 1 m/s for smaller larvae and 1.5 m/s for bigger larvae. In further experiments and simulations, approaches with calculation methods for non-spherical particles are necessary to achieve results closer to reality due to the cylindrical shape of T. molitor larvae.