Abstract:

Objective The unreasonable nozzle structure of a foreign fiber sorting machine leads to the inconsistency of the airflow velocity of the inner and outer nozzles and the rapid attenuation of the nozzle airflow velocity, which affects the exclusion rate of the foreign fiber in the cotton flow. The purpose of this paper is to optimize the cavity structure and nozzle structure, aiming to achieve consistent airflow velocities of the inner and outer nozzles with a higher initial velocity, so as to improve the exclusion rate of foreign fibers.

Method The Fluent module of ANSYS software was adopted to model the nozzle structure of CS808 foreign fiber sorting machine. The simulation parameters were set according to the actual working conditions of the foreign fiber sorting machine. The flow field characteristics of the original nozzle structure were analyzed by fluid dynamics simulation. Two improvement schemes of optimizing the cavity structure and nozzle structure were then proposed and simulated. The velocity contour was drawn and the effects before and after improvement were compared.

Results The simulation results showed useful insight of the nozzle structure. The unequal distances between the inner/outer nozzles and the nozzle inlet caused inconsistent airflow velocities between the inner and outer nozzles, which was proven detrimental to the removal of foreign fibers in the cotton flow. In order to address this issue, an optimization scheme was proposed by adding a flow-splitting baffle inside the nozzle to transform the original ″one-to-four″ airflow distribution structure into a hierarchical ″one-to-two-to-four″ distribution structure. Before optimization, the airflow velocity difference between the inner and outer nozzles was approximately 40 m/s, and this difference was kept within 5 m/s after optimization. In order to improve the airflow stability in the outer flow field, three nozzle-shape improvement schemes, i.e., straight-hole, conical, and double-arc types, were proposed and numerically simulated. The results indicated that the straight-hole nozzle offered optimal effect in enhancing airflow stability, with a significantly lower airflow velocity attenuation rate within the 0-30 mm range of the outer flow field compared to the other two nozzles. The two optimization schemes were combined and simulated under the same operating conditions as the original exclusion nozzle. The simulation results demonstrated that the velocity difference between the inner and outer sides of the optimized nozzle was smaller than that of the original one, both inside the nozzle and in the outer flow field. The airflow velocity of the optimized nozzle reached a minimum value of 60 m/s at 55 mm in the outer flow field, with the original nozzle's velocity dropping to a minimum of 20 m/s at 35 mm in the external flow field.

Conclusion The unreasonable structure of the original nozzle is the main reason for the uneven velocity of the inner and outer airflow and the rapid attenuation of the airflow velocity. By adding a baffle in the nozzle cavity, the airflow velocity of the inner and outer nozzles can be effectively balanced. The improvement of the nozzle shape also has a certain delay effect on the attenuation of the nozzle velocity. These improvements ensure the efficiency of subsequent cotton foreign fiber removal to a certain extent. The improvement of the exclusion efficiency in the practical application of the improved scheme proposed needs to be further verified in theory and practical applications.

Key words: foreign fiber sorting machine, exclusion rate, nozzle structure, optimization design, airflow stability, numerical simulation