Zhang Xiaotie, Li Hui, Shen Shengnan, Cai Mang
a School of Power and Mechanical Engineering, Wuhan University , Wuhan , China.
J Occup Environ Hyg. 2016;13(5):372-82. doi: 10.1080/15459624.2015.1116697.
This article presents a reverse modeling of the headform when wearing a filtering facepiece respirator (FFR) and a computational fluid dynamics (CFD) simulation based on the modeling. The whole model containing the upper respiratory airway, headform, and FFR was directly recorded by computed tomography (CT) scanning, and a medical contrast medium was used to make the FFR "visible." The FFR was normally worn by the subject during CT scanning so that the actual deformation of both the FFR and the face muscles during contact can be objectively conserved. The reverse modeling approach was introduced to rebuild the geometric model and convert it into a CFD solvable model. In this model, we conducted a transient numerical simulation of air flow containing carbon dioxide, thermal dynamics, and pressure and wall shear stress distribution in the respiratory system taking into consideration an individual wearing a FFR. The breathing cycle was described as a time-dependent profile of the air velocity through the respiratory airway. The result shows that wearing the N95 FFR results in CO2 accumulation, an increase in temperature and pressure elevation inside the FFR cavity. The volume fraction of CO2 reaches 1.2% after 7 breathing cycles and then is maintained at 3.04% on average. The wearers re-inhale excessive CO2 in every breathing cycle from the FFR cavity. The air temperature in the FFR cavity increases rapidly at first and then stays close to the exhaled temperature. Compared to not wearing an FFR, wearers have to increase approximately 90 Pa more pressure to keep the same breathing flow rate of 30.54 L/min after wearing an FFR. The nasal vestibule bears more wall shear stress than any other area in the airway.
本文介绍了佩戴过滤式面罩呼吸器（FFR）时头模的逆向建模以及基于该建模的计算流体动力学（CFD）模拟。通过计算机断层扫描（CT）直接记录包含上呼吸道、头模和FFR的整个模型，并使用医用造影剂使FFR“可见”。在CT扫描过程中，受试者正常佩戴FFR，以便客观保留FFR与面部肌肉接触时的实际变形。引入逆向建模方法来重建几何模型并将其转换为CFD可求解模型。在该模型中，我们对考虑佩戴FFR的个体呼吸系统中包含二氧化碳的气流、热动力学以及压力和壁面剪应力分布进行了瞬态数值模拟。呼吸周期被描述为通过呼吸道的空气速度随时间变化的曲线。结果表明，佩戴N95 FFR会导致二氧化碳积聚、FFR腔内温度升高和压力升高。7个呼吸周期后，二氧化碳的体积分数达到1.2%，然后平均维持在3.04%。佩戴者在每个呼吸周期从FFR腔中重新吸入过量的二氧化碳。FFR腔内的空气温度起初迅速升高，然后接近呼出温度。与不佩戴FFR相比，佩戴FFR后，佩戴者必须增加约90 Pa的压力才能保持30.54 L/min的相同呼吸流量。鼻前庭承受的壁面剪应力比气道中的任何其他区域都要大。
