Numerical Simulation Study On Movement And Distribution Characteristics Of Particulate Matter In Radiant Floor Heating Room

With the rapid development of urbanization in China,people spend more time indoors all year round in recent years.Studies have shown that indoor particulate matter concentration has an important impact on human health.The indoor environment will be relatively closed in winter heating period compared with summer,which is not conducive to the transmission and diffusion of indoor particulate pollutants.Floor radiant heating is widely used in the building environment because of its high comfort and uniform temperature distribution in various heating methods.However,there will also be uneven temperature in the height direction of the room,and the cold penetration of the envelope structure will change the air distribution of the heating room.These factors will have a greater impact on the movement process of indoor particles.Therefore,this paper explored the movement and distribution of particles in a floor radiant heating room under the influence of wall cold penetration based on the Computational Fluid Dynamics(CFD)and Discrete Element Method(DEM)coupling calculation,which is of great significance to the protection of indoor human health.First of all,this paper built a physical model with reference to the size of a living room to analyze the stress of particles in detail.The three-dimensional mathematical model of gas-solid two-phase flow is established by CFD-DEM method.The boundary conditions of the model were set up according to the actual indoor and outdoor environmental parameters.The established mathematical model is used to simulate the experiments in the related literature,and the reliability of the mathematical model was verified by comparing with the experimental data.Then,the mathematical model is used to simulate the change of indoor air field and the movement of 2.5um particles in the radiant floor heating room without the influence of exterior envelope.The concentration,rising height and average velocity of particles in different areas of the heating room under different floor heating temperatures were obtained.The influence of the floor heating temperature on the particle movement was analyzed.The results show that the indoor gas velocity is low when the wall temperature changes around the simulated room are the same.At the same time,the stratification phenomenon of near ground temperature is more obvious with the decreases of floor heating temperature.When a person is in a sitting position,the velocity of particles in the breathing plane(1.4m)is half of that in the ankle plane(0.1m).The distribution of particles in ankle height plane is close to diamond shape with the increase of time.The concentration of particles in the center of the room is the highest,and the velocity of particles along the wall is the fastest.There was no significant correlation between the number of particles and floor temperature in the breathing plane.Subsequently,the changes of indoor air field and temperature field and the movement of particles when the floor radiant heating room has an external wall and window were simulated and analyzed.The variation of particle concentration and particle rising speed with time in different areas of the room was obtained.The influence of outdoor temperature on the distribution of indoor particles with different particle sizes was analyzed.The research found that the airflow in the room circulates around the wall and forms multiple airflow vortices locally,which is affected by outdoor temperature.When the outdoor temperature is-10 ～ 0℃ and below-20℃,the particles in the room will gather in the room area far away from the outer wall.When the outdoor temperature is in the range of-10 ～-20℃,the particles gather in the areas on both sides of the center of the room.The uneven distribution of large-size particles is obvious when the outdoor temperature rises.The unevenness of small particle size particles is more obvious when the outdoor temperature decreases.Finally,the indoor flow field distribution and particle motion of a room with two external walls were simulated.The changes of particle concentration and velocity over time at different locations in the room were obtained.The effects of different floor heating temperatures on the motion and distribution of particles with four sizes of 1,10,20 and100 um were compared and analyzed.The study found that the higher the ground temperature is,the greater the velocity difference of airflow near the ground is.The temperature stratification in horizontal direction is more significant,and the offset angle of updraft increases first and then decreases.And with the increase of floor heating temperature,the number of particles near the inner wall increases,the distribution of indoor particles is more uniform,and the average speed of particles of different sizes is close;the height of the particles rises in the area with higher particle concentration.