室内空气稳定性对人体呼吸微环境的影响

发布时间：2018-05-09 11:42

本文选题：呼吸 + 微环境　；参考：《湖南大学》2014年博士论文

【摘要】：越来越多的研究开始关注人的呼吸活动以及人体周围微环境，因为这个靠近身体的吸气及呼气区域直接关系到人体健康和疾病的传播。但是，人的呼吸活动非常复杂，受到很多因素的影响，例如，人体代谢水平及活动状态、通风策略、室内空气稳定性、人体周围空气温度、湿度及速度等。本文主要针对室内空气稳定性与人体呼吸微环境的关系进行详细的研究。一些研究指出当室内采用置换通风方式时，由于温度分层的存在，可能造成呼气中的污染物如CO2、飞沫等在一定的高度分层凝滞，因而对室内其他人员造成潜在的疾病传播风险。本文利用室内空气稳定性的概念对这一现象进行解释。室内空气稳定性指室内空气抵抗竖直方向运动的能力，可以通过室内温度梯度的方向进行判定。通过利用假人实验、真人实验以及仿真人体模型计算三种手段，针对混合通风形成的中性状态以及置换通风形成的稳定状态对人体呼吸周围微环境的影响进行研究。三种方法相互验证。按可靠性高低排序，依次为真人实验、假人实验以及CFD模拟，，但操作难度及实验成本的依次降低。真人实验可以为其他两种方法提供了可靠的验证，但是操作难度较大。假人模型及计算机人体模型在一定程度上能够模拟人体的呼吸特点，由于模型的简化可能导致模拟结果与实际人体呼吸之间的偏差，更准确可靠的模型及模拟方法需要进一步的研究。本文的另一条主线是围绕室内空气稳定对人体呼吸微环境的作用展开。利用上述三种方法对人体呼气气流扩散规律以及身体周围热羽流发展进行了详细的研究，主要得到如下几个结论：（1）通过烟气可视化实验，发现通过假人嘴巴的间歇呼气与持续射流有很多相似之处，比如卷吸作用、射流形状等。利用峰值速度描述脉动的呼气气流速度剖面时，发现了与自由射流类似的速度分布特点。据此，呼气速度、浓度与温度衰减规律利用与自由射流相似的表达式进行描述。无论是持续呼气还是间歇呼气，气流轨迹及弯曲程度都会受到呼气初始角度、阿基米德数（Ar）、室内空气稳定性以及身体散热量的影响。可以观察到，稳定状态的空气会抑制呼气气流向上弯曲的程度，并会削弱呼气气流发展过程中的卷吸作用，降低了呼气与周围空气的掺混的能力。（2）不同的气流组织形式及不同的身体代谢水平导致人体周围气流分布特点不同，并且造成呼气气流穿透距离以及速度与浓度衰减率不同。稳定状态导致呼出的污染物浓度分层，而中性状态下污染物可以迅速地被通风稀释。随着温度梯度的增大，污染物在室内分层的高度会下降。室内空气稳定性影响呼气的速度及浓度在水平方向的衰减速率。置换通风由于带来稳定的室内温度层结，在一定程度上会抑制污染物在竖直方向的扩散，因此不适合如病房、诊所等有污染源的场合。（3）通过对比实验结果发现，人体模型的尺寸对于身体周围气流分布影响明显，利用与人体尺寸接近的数值模型对于研究人体微环境问题更具有优势。而且，模拟结果发现，研究此类问题时选择适当的呼吸模式也非常重要。数值模拟方法一方面弥补了实验方法的不足，提供了更详尽的人体呼吸微环境的信息，另一方面数值模拟的可靠性需要通过实验数据进行验证。模拟结果显示，室内空气稳定性作用随着温度梯度的增大而增强，进而对身体热羽流的抑制作用以及对呼气弯曲趋势的抑制作用增强。稳定的空气除了抑制气流竖直方向运动以外，还可能造成水平方向的呼气气流扩散作用增强。室内空气稳定性对呼吸的作用主要体现在影响呼气气流的扩散、抑制身体周围热羽流的发展以及改变人体周围污染物分布等方面。不同的通风策略可能形成不同的稳定性条件，进而影响呼气中污染物在室内的扩散规律，为了降低疾病传播风险，充分考虑特定气流组织形式下的室内空气稳定性特点是非常必要的。
[Abstract]:More and more research has begun to pay attention to the breathing activity of people and the microenvironment around the human body , because the inspiratory and expiratory regions close to the body are directly related to the health of the human body and the spread of the disease . However , the human respiratory activity is very complex and is influenced by many factors , for example , the human body metabolism level and the active state , the ventilation strategy , the indoor air stability , the air temperature , humidity and speed around the human body , and the present paper mainly studies the relationship between the indoor air stability and the human breath microenvironment .

According to the concept of indoor air stability , this paper explains the effect of indoor air stability on the micro - environment around human breath by using the concept of indoor air stability . The indoor air stability refers to the ability of indoor air to resist vertical movement and can be determined by the direction of indoor temperature gradient .

The real - person experiment can provide reliable verification for the other two methods , but the operation difficulty and the experimental cost are reduced in sequence . The real - person experiment can provide reliable verification for the other two methods , but the operation difficulty is large . The dummy model and the computer human body model can simulate the breathing characteristics of the human body to a certain extent .

Another main line of this paper is to study the effect of indoor air stabilization on human breathing microenvironment . The diffusion law of expiratory flow and the development of hot plume around body are studied in detail using the above three methods .

( 1 ) Through the visualization experiment of flue gas , it is found that the intermittent exhalation through the artificial mouth has many similarities with the continuous jet , such as the suction effect , the shape of the jet , etc . The velocity profile of the expiratory flow similar to that of the free jet is described by means of the velocity profile of the expiratory flow .

( 2 ) Different forms of air flow and different levels of body metabolism result in different characteristics of airflow distribution around the body , and the penetration distance and velocity of the expiratory flow are different . The steady state results in the concentration stratification of exhaled pollutant . As the temperature gradient increases , the pollutant can be rapidly diluted by ventilation . As the temperature gradient increases , the pollutant can be rapidly diluted in the horizontal direction . The displacement ventilation can inhibit the diffusion of pollutants in the vertical direction due to the stability of the indoor temperature stratification . Therefore , it is not suitable for occasions such as wards , clinics and the like .

( 3 ) By comparing the experimental results , it is found that the size of the human body model has obvious influence on the distribution of the air flow around the body , and the numerical model which is close to the size of the human body is very important for the study of the human micro - environment problem .

The effect of indoor air stability on respiration is mainly reflected in the influence of the diffusion of expiratory flow , the inhibition of the development of hot plume around the body , and the change of the distribution of pollutants around the body . Different ventilation strategies may form different stability conditions , thus affecting the diffusion law of pollutants in the chamber . In order to reduce the risk of disease transmission , it is necessary to take fully into account the characteristics of indoor air stability in the form of specific air flow tissue .

【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU834

【参考文献】