Study On Characteristics Of Respiratory Microenvironment In Air-Supplied Safety Helmet

An air-supplied safety helmet is a widely used respiratory protective equipment that provides the necessary protection for the head and respiratory system by isolating the head and respiratory system from the external environment.The uneven distribution of airflow in the respiratory microenvironment inside the protective helmet,fluctuating pressure,heat accumulation,rising temperature and carbon dioxide accumulation can affect the safety and comfort of the wearer.This paper combines the methods of theoretical modeling,experimental research and numerical simulation together,of which the theoretical modeling results and experimental test results are used as the basis for the numerical simulation,and finally,the characteristics of the breathing microenvironment of air-supplied safety helmets are investigated by numerical simulation.By the analysis of the protective helmet and the human-computer system of the human head,the main factors influencing the internal parameters of the respiratory microenvironment were the metabolic heat dissipation of the human head,the respiratory effect of the human body,and the internal air supply parameters of the helmet.Based on the analysis of heat transfer,heat dissipation and heat regulation mechanisms in the human body,and according to the fuzzy charactersitic of human body temperature regulation,combine with the structure and tissue distribution of the head,a fuzzy control model of heat transfer and heat dissipation in the human head was constructed,and the results of this model are closer to the measured values than other models under the same calculation conditions.A breathing parameter acquisition system was designed,and breathing experiments were conducted to obtain parameters such as respiratory pressure and respiratory rate at different labor intensities,and mathematical expressions of respiratory pressure curves were also obtained.Gas chromatographic analysis of the exhaled gas samples that collected during the experiment are perfomed,and the exhaled gas composition at the corresponding labor intensity was obtained.The experimental results provided a basis for setting the breathing boundary conditions in the numerical simulation.A head cooling experiment under convective conditions was conducted,and the temperature data of the head-facial skin under convective conditions and the subject's local subjective heat sensation data of the head were obtained and the head-facial skin cooling laws were analyzed.The results show a significant difference in the rate of cooling,the amplitude of cooling and the final stable temperature in different facial regions.Regression analyses were performed on facial mean temperature and thermal sensation.and obtained the equation for the relationship between average temperature and thermal sensation.The results can be used to quantitatively evaluate the local thermal sensation in the head.A virtual 3D simulation environment for breathing microenvironmental properties of air-supplied safety helmets is constructed and numerical simulation studies of microenvironmental properties are performed.The characteristics of the internal pressure fluctuation,temperature distribution,airflow distribution,gas composition distribution and re-inhalation of different gases in the microenvironment under different labor intensity and various air supply parameters are obtained.An optimization scheme was proposed and validated by numerical simulations for the problems of respiration in the microenvironment,such as instantaneous negative pressure due to respiration,heat accumulation,temperature increase and CO2 and H2O gas accumulation due to uneven airflow distribution.The results show that the addition of air supply outlets at suitable locations leads to a more even distribution of airflow in the respiratory microenvironment.It eliminates heat buildup at the top and oblique rear,lowering the temperature inside the respiratory microenvironment,resulting in a more even head temperature distribution.While eliminating heat buildup and improving CO2 and H2O re-inhalation problems,the reduction in thermal sensation in the head caused by increased airflow is avoided.