Study On The Diffusion Of High-temperature Particulate Pollutants Near The Wall Of Industrial Buildings

In the industrial production,many high temperature processes such as welding release high concentration mixture of particles and airflow in a short time,these particles have the characteristics of high temperature and small particle size,which will spread rapidly indoors and directly threaten the safety of working environment and the health of workers.There are few studies on the two-phase flow near the wall of the pollution source.Therefore,the study on the migration and diffusion of high-temperature particle pollutants near the wall will provide a theoretical basis for more reasonable and effective control of such pollutants in the future.In this paper,the welding experiment is used to study diffusion law of high temperature particulate pollutantsthe.Through the welding experiment,we have a preliminary understanding of the variation of temperature and velocity of welding fumes,and provide effective boundary conditions for subsequent simulation studies.Afterwards,based on previous research methods,the true motion state of the pollutants in the flow field was combined.The simulation method was used to study the diffusion of the instantaneously emitted high-temperature particles in the steady-state flow field and the unsteady flow field.Comparing the temperature,velocity changes,following and the distribution of particles,we found that,(1)In the steady flow field,particles of different particle sizes can quickly rise to the top of the plant.In the unsteady flow field,for the temperature T=673K,the particle size d=1,5 and 10μm particles quickly rise to central location of the factory,then slowly rise to the top of the factory,particle size d=20μm and 30μm particles rising a certain height after it will fall back;(2)The rising velocity of particles in the steady flow field is much greater than that in the unsteady flow field.In the steady flow field,the number of particles from the airflow is much smaller than that in unsteady flow.(3)In the steady flow field,the diffusion radius of particles in horizontal direction is much smaller than that in unsteady flow field.In the steady state flow field,the particles in different diffusion radius keep moving upward.In the unsteady flow field,the particles in the larger diffusion area have started to move downwards at bottom of the factory.In the steady flow field,particulate transfer to the near-wall region,in unsteady flow field,particles migrate away from the wall.From this,it can be seen that the object of this study,that is,the welding process of high-temperature particulate and air currents instantaneously emitted,if the research method that the former particles diffuse in the steady-state flow field is used,there will be large deviations in the prediction of the diffusion and migration of the particles.Based on the above analysis,in this paper,the method of calculating the motion of particles in the unsteady flow field is used to study the diffusion of high temperature particles distributed instantaneously at the near wall under different influence factors.Starting from the change of temperature and velocity of particulate,the following characteristics and particle horizontal directional diffusion of particles are explored at different particles sizes and initial temperatures.The main conclusions obtained are as follows,(1)After the high-temperature particulate matter with an initial temperature of T=673K is emitted,the temperature decays to 300 K in a short time,and then it slowly decreases,the smaller the particle size and the higher the initial temperature,the faster the decay;with the temperature decay,the speed of the particulate matter first increases and then decreases,and the larger the particle size,the greater the maximum speed,but the faster the decay.With the temperature decay,the velocity of the particulates first increases and then decreases,and the larger the particle size,the greater the maximum velocity,but the faster the attenuation.(2)For the following of particles,the smaller the particle size of and temperature the particles,the less the number of out of the air in the process of movement.The initial temperature T=673K,particle size d=1,5 and 10μm particles more than 95% can reach the upper center of the factory,more than 80% of the particles can reach the area close to the roof.However less than 70% of particle size d = 30 μm particles can reach the upper center of the factory,and only 42% of the particles can reach the area close to the roof.For the particle size d=10 μm,the initial temperature T=373,473,573 and 673 K particles of the number are basically the same at different heights,only with a difference in the exercise time,and the time of the particles with lower initial temperature is longer.(3)For the diffusion in the horizontal direction,the smaller the particle size and the higher the initial temperature,the horizontal diffusion is more pronounced at the same time.Compared with the particle size,the initial temperature has a significant effect on the horizontal diffusion.In areas with large diffusion radii,particulate matter has fallen back at t=1s.The distribution of particles in the horizontal direction shows a Gaussian distribution initially.as the particles move asymmetrically,they gradually deviate from the Gaussian distribution,and the smaller the particle size,the higher the initial temperature is,the more obvious the offset is,they slowly deviate from the Gaussian distribution,and the smaller the particle size and the higher the initial temperature,the more obvious the migration of particles.