Shugang Wang

An under-aisle air distribution system facilitating humidification of commercial aircraft cabins

n Abstractn n Air environment in aircraft cabins has long been criticized especially for the dryness of the air within. Low moisture content in cabins is known to be responsible for headache, tiredness and many other non-specific symptoms. In addition, current widely used air distribution systems on airplanes dilute internally generated pollutants by promoting air mixing and thus impose risks of infectious airborne disease transmission. To boost air humidity level while simultaneously restricting air mixing, this investigation uses a validated computational fluid dynamics (CFD) program to design a new under-aisle air distribution system for wide-body aircraft cabins. The new system supplies fully outside, dry air at low momentum through a narrow channel passage along both side cabin walls to middle height of the cabin just beneath the stowage bins, while simultaneously humidified air is supplied through both perforated under aisles. By comparing with the current mixing air distribution system in terms of distribution of relative humidity, CO2 concentration, velocity, temperature and draught risk, the new system is found being able to improve the relative humidity from the existent 10% to the new level of 20% and lessen the inhaled CO2 concentration by 30%, without causing moisture condensation on cabin interior and inducing draught risks for passengers. The water consumption rate in air humidification is only around 0.05kg/h per person, which should be affordable by airliners.n n

Inverse identification of the release location, temporal rates, and sensor alarming time of an airborne pollutant source

UNLABELLEDnWith an accidental release of an airborne pollutant, it is always critical to know where, when, and how the pollutant has been released. Then, emergency measures can be scientifically advised to prevent any possible harm. This investigation proposes an inverse model to identify the release location, the temporal rate profile, and the sensor alarming time from the start of a pollutant release. The first step is to implement the inverse operation to the cause-effect matrix to obtain the release rate profiles for discrete candidate scenarios with concentration information provided by one sensor. The second step is to interpret the occurrence probability of each solution in the first step with the Bayesian model by matching the concentration at the other sensor. The proposed model was applied to identify a single pollutant source in a two-dimensional enclosure using measurement data and in a three-dimensional aircraft cabin with simulated data. The results show that the model is able to correctly determine the pollutant source location, the temporal rate profile, and the sensor alarming time. The known conditions for input into the inverse model include a steady flow field and the valid temporal concentrations at two different locations.nnnPRACTICAL IMPLICATIONSnThe proposed inverse model can tell where, when, and how a gaseous pollutant has been accidently released based on the monitoring concentrations measured by two sensors. This methodology can be useful for providing emergency protection to indoor occupants.

Quantify impacted scope of human expired air under different head postures and varying exhalation rates

n Abstractn n Many researches indicate human respiration flow and background ventilation are two important aspects leading to possible respiratory disease spread. However, current studies on respiration flow and the resulted exhaled pollutant dispersion are limited, because different head postures, respiration mode, breath rate, room ventilation and so on, can exert profound impacts that are not understood very clearly. To evaluate the role of head postures on transmission of human exhaled pollutants, this study uses a computational fluid dynamics (CFD) program to study the exhalation flow of a sitting adult in a calm indoor office. Four different head postures are considered: sitting upright viewing front, sitting upright but head tilted viewing upward, sitting upright but head turned viewing the lateral, and sitting but pillowing head on a table. Based on the decay percentage of a gas concentration, the impacted scope of expired air is identified. The common posture by sitting upright viewing front is selected to investigate the change of impacted scope with increasing exhalation rates. The experimental test is also carried out using a breathing thermal manikin. This study finds out that the impacted scope of expired air under different head postures is different. The horizontal impacted distance is highly dependent on the specified threshold concentration. If a person sits around at a table and makes a deep exhalation, other people shall be apart from him/her with a larger distance to be free from the exhaled pollutant exposure, once his/her thermal plume is blocked by the table.n n

Various air distribution modes on commercial airplanes. Part 1: Experimental measurement

Airplanes currently distribute conditioned air by overhead diffusers or personal gaspers to the passenger cabin. Such an air distribution mode promotes air mixing; therefore, it has low ventilation efficiency and may impose considerable risks of draft to the passengers. To remedy the above problems, an under-aisle displacement air distribution mode and a personal air distribution mode are proposed. The under-aisle air mode supplies conditioned air from perforated panels in the aisles, whereas the personalized air mode applies the under-aisle air mode as background ventilation and simultaneously supplies outdoor conditioned air from the chair–armrest-embedded terminals to the passengers inhalation region. To evaluate the three air distribution modes, a twin-aisle aircraft cabin mockup with a Boeing 767 as the prototype is constructed. The airflow pattern and temperature profiles are measured by a three-dimensional ultrasonic anemometer, and the ventilation efficiency is evaluated by the CO2 tracer gas concentration. This study finds that the personalized air distribution mode coupled with the under-aisle air supply as the background ventilation is promising to improve the current cabin environment. Unstable airflows are ubiquitous on airplanes and require advanced test instruments for better characterization.

Various air distribution modes on commercial airplanes—Part 2: Computational fluid dynamics modeling and validation

Both experimental test and numerical modeling can be used to investigate air distribution on commercial airplanes. Numerical modeling by computational fluid dynamics has gained popularity; however, current computational fluid dynamics modeling efforts are concentrated primarily on the mixing-air distribution mode. To fully evaluate computational fluid dynamics modeling for different air distribution modes, the flow, heat transfer, and pollutant species transport in a twin-aisle aircraft cabin mockup is modeled. Three air distribution modes, namely the mixing, under-aisle displacement, and personal air distribution modes, are studied. The steady renormalization group k-ϵ model together with the standard wall function has been employed for turbulence modeling and the near-wall treatment. The experimental data in terms of the velocity field, temperature, and CO2 concentration profiles are applied to validate the numerical models. This study finds that the renormalization group k-ϵ model is able to solve major air distribution parameters in reasonable agreement with the measured values. When carrying out the steady computational modeling by resolving the Reynolds-averaged Navier-Stokes equations, it should be noted that the models may underestimate the turbulent mixing effect.

Measuring detachment of Aspergillus niger spores from colonies with an atomic force microscope

Detachment of fungal spores from moldy surfaces and the subsequent aerosolization can lead to adverse health effects. Spore aerosolization occurs when the forces for aerosolization exceed the binding forces of spores with their colonies. The threshold force to detach a spore from a growing colony remains unknown. This investigation measured the detachment of spores of Aspergillus niger from a colony using an atomic force microscope (AFM). The spores were first affixed to the cantilever of the AFM with ultraviolet curing glue, and then, the colony was moved downward until the spores detached. The threshold detachment forces were inferred from the deflection of the cantilever. In addition, the spores were aerosolized in a wind tunnel by a gradual increase of the blowing air speed. The forces measured by the AFM were compared with the hydrodynamic forces for aerosolization. The AFM measurements revealed that a force of 3.27xa0±xa00.25 nN was required to detach a single spore from the 4-day-old colony, while 1.98xa0±xa00.13 nN was sufficient for the 10-day-old colony. Slightly smaller detachment forces were observed by the AFM than were determined by the aerosolization tests.