Aerosol Diffusion In Isolation Wards And Air Flow Organization Optimization Research

MERS,a new respiratory coronavirus,emerged in Middle East,and spread to some other countries in the world rapidly.Once the MERS virus outbreaks,hospitals will take in a large amount of infected patients.It will make the virus transmitted through patients and hospital staff when a large number of patients crowd into a general ward,which threats to people’s lives and safety and terrifies people mentally.Research on the airflow mechanism of the isolation wards can provide a theoretical basis when it comes to optimizing the air distribution form of general wards.This is of great significance for improving the hospital’s ability to receive patients in the large-scale diffusion of the disease.The paper focuses on purifying droplet aerosol particles released by patients in the ward and figuring out the best airflow organization in the wards.Research has been done as follow.Theoretical research on wall attached jet and numerical simulation is done.Mathematical model of wall attachment jet is established.And both theoretical and simulative results of wall attached length under different air velocity are examined.As is shown in the result,when the velocity of inlet air is 1.9m/s,the length of wall attached length is 3.6m.When the velocity of inlet air increases 1.5 times,wall attached length increases 1.24 times.When the velocity of inlet air increases 1.68 times,wall attached length increases 1.75 times.When the velocity of inlet air increases 1.97 times,wall attached length increases 2.22 times.Mathematical models are established,that patients in general wards release aerosol particles which are driven by gravity,drag force and Brownian force.The change of track and concentration of the aerosol particles released by patients in different ways is analyzed.It is shown in study that in mixed ventilation,the concentration of aerosol particles drops dramatically in the primary releasing stage.However,aerosol particles diffuse into the clean area because of the lack of directional airflow.It takes 50 seconds that the aerosol particles released by patients’ breath for once spread all over the ward.It takes 30 seconds that the aerosol particles released through coughing for once spread all over the ward.And it only takes 15 seconds that the aerosol particles released through sneezing for once spread all over the ward.According to the result,mixed ventilation in the general wards increases the possibility of hospital staff getting infected.The study on velocity field,temperature field and the distribution of aerosol particles released through coughing and sneezing in the isolated wards is also made,which reveals the aerosol particles are influenced by airflow distribution.It is demonstrated that a vertical wall attachment jet stream is formed when vents and outlets are arranged on the ceiling near either wall of the ward.Under the same air change rate,the movement path of aerosol particles released by patients is the shortest.This air flow organization can shorten the length of jet.The location of aerosol particles spread is far from the clean area,which can reduce the risk of hospital staff infected with the disease.Compared with the other three kinds of wall attached jet,the air efficiency of this kind of air flow organization is the highest.Under the condition of vertical wall attachment jet,the paper analyzes and optimizes different air change rates.After comparing the velocity field of airflow in the isolated wards and the distribution and concentration change of aerosol particles,the desirable air change times in the ward is concluded.As is shown in the study,when the air change rate is 20ACH,the number of aerosol particles released through patients’ cough in 100s is decreased by 78.75%,and spread mainly in the contaminated area.The number of aerosol particles released through patients’sneezing in 100s is decreased by 39%.When the air change rate is 24ACH,declining trend of the number of aerosol particles tends to be stable.As a result,in the isolation ward,the optimal air change rate is 20ACH,which can effectively reduce the aerosol particles released from patients’breathing,talking,cough and sneezing.