Preface
With the growth of industrialization,air pollution has become an increasingly serious concern in China.Air pollution has deleterious effects on public health.In China,particulate matter with an aerodynamic diameter of less than 2.5μm (PM2.5),which is small enough to gain entry into the thoracic region of the respiratory system resulting in respiratory and cardiovascular diseases,has become the fourth most common health concern.It is reported that 350,000 to 500,000 people die prematurely each year as a result of outdoor air pollution in China.A common solution to prevent inhalation of air pollutants,especially PM2.5,is to wear a respirator in daily life.This book first studies the mechanism of particles adsorption and rebound by respirator fibers,then it studies the flow-field of N95 filtering facepiece respirator (FFR),and proposes a method to improve the flow-field distribution and improve respiratory comfort.Finally,it investigates the contact characteristics between a respirator and a headform,and proposes a novel technology to improve the wearing comfort and fit of FFR wearers.
Chapter 1 of this book is the Introduction.Chapter 2 and Chapter 3 study the filtration performance of multi-fiber filters,the mechanism of particles adsorption by respirator fibers,and particle rebound by the cross-scale analysis.Chapter 2 investigates the pressure drops and filtration efficiency with different fiber arrangements,fiber diameters,face velocities and particle sizes.The layered structures with the same fiber diameters and total solid volume fraction (SVF) are compared.Then,methods to optimize the dense-sparse structure so as to achieve a better filtration performance by using less tiny fibers in the front-row and removing some fibers in the back-row are discussed.In Chapter 3,the interaction between the particle and fiber surface is studied using a self-developed Fortran code and an adherence criterion to determine whether a particle will rebound from or adhere to a solid surface is proposed.The effects of particle rebound characteristics on the morphology of particle depositions are also analyzed.
Chapters 4 to 7 study the flow-field in the upper respiratory system when the N95 FFR is worn.In Chapter 4,a transient numerical simulation of air flow containing carbon dioxide,thermal dynamics,pressure and wall shear stress distribution in the respiratory system is conducted for an individual wearing an FFR.In Chapter 5,the distribution characteristics of water vapor condensation on the inner surface of a FFR are studied under different breathing conditions,including different environmental temperatures and breathing patterns.In Chapter 6,micro-climate features in the deadspace of an N95 FFR considering water vapor condensation are studied.It simulates the temperature and water vapor distribution in the deadspace of N95 FFR using the computational fluid dynamics method.Then,it experimentally measures the temperature,relative humidity and bacteria distribution inside N95 FFR.Chapter 7 quantitatively investigates the flow characteristics and respiratory deposition of particles.A computational fluid dynamic method is used to assess the velocity,concentration and inhalation levels of indoor particles using a mankind realistic upper respiratory tract.An experiment is also performed to measure the PM2.5 concentrations.
Chapter 8 and Chapter 9 examine optimization of the respiratory design to improve the flow-field and increase the comfort of wearers.In Chapter 8,an improved FFR designed to increase the comfort of wearers during low-moderate work is presented.The newly developed respirator helps lower the deadspace temperature and CO2 level by an active ventilation fan.Chapter 9 focuses on the development of an FFR with an intelligent control fan which has better comfort and permeability.A fan with intelligent control can reduce the temperature and humidity and CO2 concentration.
Chapter 10 and Chapter 11 investigate the contact characteristics between a respirator and a headform.Chapter 10 presents a computational study on contact pressure and the resultant deformation between an N95 FFR and a newly developed digital headform.In Chapter 11,the effects of four typical facial expressions (calmness,happiness,sadness,and surprise) on the contact characteristics between an N95 FFR and a headform are investigated.
Chapter 12 proposes a novel technology to produce customized face seal design for improving the wearing comfort and fit of FFR wearers.Experimental results showed that the newly designed FFR face seal provided the subjects with an improved contact pressure.
Mr.Wei Li for Chapters 2 to 3,Mr.Xiaotie Zhang for Chapter 4 and Chapter 8,Miss Yu Rao for Chapter 5,Mr.Quan Yang for Chapters 6 to 7,Mr.Song Zhou for Chapter 9,Mr.Mang Cai for Chapters 10 to 12,Mr.Fuhao Cui and Mr.Dongqi Zhang are responsible for the organization and verification of the book.Professor Hui Li contributes to the finite element simulation and CFD simulation.
This book is supported by Hubei Provincial Natural Science Foundation of China (Grant No.2015CFB307),the Science and Technology Planning Program of Shenzhen (Grant No.JCYJ20170816171733384),the Fundamental Research Funds for the Central Universities of China (Grant No.2042014kf0034),and the scholarship from China Scholarship Council (CSC) under the Grant CSC No.201606275005.Authors gratefully acknowledge all the support.