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A simulation model for the gas flow and the powder particle flow between the powder nozzle and the melt pool surface has been developed , which reveals the volume percentage of different gas types and so the quality of the shield gas atmosphere .
 simulation, model, gas, powder particle, powder, nozzle, melt pool, volume, gas, quality, gas
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 simulation, model, gas, powder particle, powder, nozzle, melt pool, volume, gas, quality, gas