For micro/nano particles in the process of the thermal spraying processcontrol measures, according to the principle of similarity, in thermal spraying workshop for prototype, combining the theory of gas-solid two-phase flow, thermal spraying workshop similar experimental model is established, under the condition of different ventilation and dust removal of micro/nano powder in thermal spraying workshop movement and the diffusion regularity of experiment research. The results show that mechanical ventilation can significantly reduce the concentration of micro-nano dust particles in thermal spraying workshop. The higher the ventilation flow per unit time, the lower the concentration of micro-nano dust particles in the respiratory layer of the workshop, and the shorter the removal time. Under the condition of the same ventilation rate, the combination of the bottom and the side of the workshop is more beneficial to the removal and settlement of the respirable layer micro-nano dust particles than the side strong ventilation alone.

The diffusion process of micro-nano dust inthermal sprayingpowderworkshop is essentially gas-solid two-phase flow. According to the motion law of gas-solid two-phase flow and the analysis of basic motion equation, the physical quantities involved mainly include air density, gas pressure, airflow velocity, aerodynamic viscosity coefficient, particle size, particle density, particle velocity, particle movement time, gravity acceleration, geometric size, etc.

Based on the principle of dimensional analysis, seven similarity criterion Numbers are derived: stokes criterion number, homogeneity criterion number, euler criterion number, froude criterion number, Reynolds number number, gas-solid phase density criterion number, and motion criterion number.Generally limited by actual experimental conditions, it is often difficult or difficult to realize that similar model and prototype meet all similar criteria at the same time. Therefore, under the condition of ensuring sufficient accuracy, the number of similar criteria is simplified according to the actual situation, that is, the approximate similar model is established.

Considering the actual movement of micro/nano dust particles in thermal spraying workshop, the similarity criterion number can be simplified as the geometric similarity criterion number and the ventilation rate ratio of the exhaust outlet.

The layout of similar experimental model (referred to as "experiment box") in the thermal spraying workshop is consistent with the actual workshop structure. There are 8 air inlets on the upper end and 3 air outlets on the side, and the remaining surfaces are sealed. All sides of the experiment box are made of colorless transparent acrylic sheets (commonly known as "plexiglass"), and all sizes are designed according to similar models. Micro-nano particle dispersion device is installed on the left side of the experiment box to simulate the dust source in the process of thermal spraying. Honeycomb floor is adopted at the bottom of the workshop, and the whole system is relatively complex, so it is simplified. 9 air outlets are set at the bottom of the experimental box, and centrifugal fan is adopted at one end as the negative pressure source.

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