| In recent years,with the outbreak of infectious diseases such as SARS and H1N1,interpersonal pollutant transmission have been widely concerned by the public health and academic.The droplets produced by respiratory activities such as breathing,talking,coughing,sneezing,etc.,carry pathogenic bacteria such as viruses,bacteria,and fungi,which can be widely spread among people in various ways.Displacement ventilation which is widely used in industrial buildings,civil buildings and public buildings has the advantages of good thermal comfort and energy saving.When the pollutants are captured by the plume of the heat source in displacement ventilation,the cleaning area and the pollutant area are formed,which can ensure the air quality in the breathing area of the human.For expiratory droplets and droplet nuclei,the distribution of pollutants is affected by factors such as distance between two manikin,temperature gradient,etc.,which may deviate from the traditional two-zone model,resulting in increased risk of interpersonal pollutant transmission.Therefore,it is of great significance to study the influencing factors of interpersonal droplet transmission under displacement ventilation,and propose effective measures to minimize the risk of interpersonal disease transmission.This paper takes the clean room of the State Key Laboratory of Green Building in Western China as the object to simulate.With the design requirements of displacement ventilation,the diffusion,distribution and interpersonal transmission of expiratory droplets are discussed using three-dimensional numerical model with precise description of geometric features on human.At the same time,the risk of interpersonal disease transmission is assessed by quantifying inhaled droplets of susceptible.In addition,the experiment was carried out to verify the reliability of numerical simulation method.Then,three major influencing factors of interpersonal disease transmission that are droplet size,distance between two manikin and temperature gradient of displacement ventilation are studied.In this part,respiratory process was simplified and unsteady discrete phase was tracked in steady flow field.With the design requirements of displacement ventilation,the results show that: 1.The size of droplets nuclei with 10?m is quite different in motion,distribution and interpersonal transport as 5?m.2.It makes litter sense to increase the distance between two manikins for reducing the risk of interpersonal disease transmission when the distance is larger than 1.5 meter.However,there is significance when the distance is less than 1 meter.3.The risk of interpersonal disease transmission become higher with the increase of temperature gradient when the distance between two manikins is less than 1 meter.However,the temperature gradient of displacement ventilation has little effect on the interpersonal droplet transport when the distance between two manikins is more than 1.5 meter.Therefore,minimizing the temperature gradient by increasing the amount of ventilation volume is important for controlling the spread of disease in high-density environments.Finally,the paper uses real respiratory boundary conditions to study the interpersonal droplet transport under different temperature gradients of displacement ventilation.The results show that the real respiratory boundary has a great influence on the diffusion and movement of droplets,but the transient flow field of interpersonal droplets transmission is consistent with steady flow field.Therefore,it is reasonable and reliable to study the influencing factors of the interpersonal droplet transport in displacement ventilation with steady flow field.If more precise description of the diffusion and motion behavior of droplets is required,transient flow field in response to real human respiratory state should be used in numerical calculation. |
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