Numerical Simulation Research On Aerosol Transmission Under Conditions Of Different Air Supply Modes

The outbreak of COVID-19 has brought great disaster to mankind.Epidemic prevention and control has once again become a common concern and urgent problem to be solved.Many respiratory infectious diseases,including novel coronavirus,have been proved to be able to transmitted by aerosol.Airflow on air condition system is an important factor leading to indoor clustering aerosol infection.Based on this,this paper studies the indoor diffusion of bioaerosol under conditions of mixing ventilation,displacement ventilation and under floor air supply.And puts forward relevant suggestions for epidemic prevention and control.Firstly,taking the meeting room as an example,design the mixing ventilation system,displacement ventilation system and under floor air supply system with the same air supply volume,and establish the corresponding physical models respectively.At the same time,the transmission characteristics of respiratory infectious diseases were studied.It was found that the bioaerosol containing pathogens had strong air flow following ability and could be regarded as passive gas.Thus,the standard k-e based on RANS and semi-implicit method for pressure linked equations were used to build the numerical models of indoor air distribution and pollutant diffusion under conditions of mixing ventilation,displacement ventilation and under floor air supply.And verify are provided.Secondly,through numerical simulation,the indoor air distribution,the diffusion trajectory of bioaerosol and the bioaerosol concentration in the breathing zone are obtained and compared when the patients with respiratory infectious diseases are located in two typical positions under the three air supply modes.The SEI（Sustainable exposure index）was used to comprehensively evaluate the infection risk of indoor personnel when patients with respiratory infectious diseases are located in different positions under three air supply modes.Calculate and compare the ventilation efficiency of three air supply modes.The results show that:（1）the meeting room with under floor air supply has the highest ventilation efficiency,the lowest concentration of bioaerosol in the breathing zone,the lowest risk of indoor personnel infection,and satisfactory comfort.In the regular epidemic prevention and control,under floor air supply is recommended for indoor air conditioning.（2）There is an obvious thermodynamic stratification phenomenon in the displacement ventilation meeting room.The bioaerosol is concentrated in the upper turbulent area of the meeting room,and the concentration in the lower unidirectional flow area is close to zero.（3）The closer the patient is to the air inlet,the bioaerosol diffuses more fully,the concentration of bioaerosol in the indoor breathing zone is relatively higher,and the risk of indoor virus transmission is higher;The opposite is true when the patient is close to the air outlet,but it should be noted that the concentration of bioaerosol in the area between the patient and the air outlet is still high.（4）Under the conditions of mixing ventilation,displacement ventilation and under floor air supply,compared with the height of breathing（y=1.2m）in the sitting posture,bioaerosol diffuses more fully in the height of breathing（y=1.5m）in the standing posture,but the overall concentration distribution is similar.It shows that the risk of virus infection is similar in sitting and standing posture when indoor personnel are in the same position.Finally,in order to comprehensively explore the factors of influencing the spread of respiratory infectious disease virus in air conditioning room,the effects of ventilation times and supply air temperature on the spread of indoor biological aerosol were studied.The results show that in most cases,with the increase of air supply speed（ventilation times）,the indoor bioaerosol concentration distribution changes significantly,and the average bioaerosol concentration in the breathing zone decreases significantly.Therefore,when there is an epidemic in the area,increasing the air supply speed of indoor air conditioning within a reasonable range can reduce the risk of indoor infection and prevent the spread of the epidemic.The effect of changing the supply air temperature on the indoor bioaerosol concentration can be ignored.