Built Environment & Energy Laboratory
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Liu, W., van Hooff, T., An, Y., Hu, S., Chen, C.* (2020). Modeling transient particle transport in transient indoor airflow by fast fluid dynamics with the Markov chain method. Building and Environment, 186, 107323. (Particle dispersion, Infectious particle, Building)

It is crucial to accurately and efficiently predict transient particle transport in indoor environments to improve air distribution design and reduce health risks. For steady-state indoor airflow, fast fluid dynamics (FFD) + Markov chain model increased the calculation speed by around seven times compared to computational fluid dynamics (CFD) + Eulerian model and CFD + Lagrangian model, while achieving the same level of accuracy. However, the indoor airflow could be transient, if there were human behaviors involved like coughing or sneezing and air was supplied periodically. Therefore, this study developed an FFD + Markov chain model solver for predicting transient particle transport in transient indoor airflow. This investigation used two cases, transient particle transport in a ventilated two-zone chamber and a chamber with periodic air supplies, for validation. Case 1 had experimental data for validation and the results showed that the predicted particle concentration by FFD + Markov chain model matched well with the experimental data. Besides, it had similar accuracy as the CFD + Eulerian model. In the second case, the prediction by large eddy simulation (LES) was used for validating the FFD. The simulated particle concentrations by the Markov chain model and the Eulerian model were similar. The simulated particle concentrations by the Markov chain model and the Eulerian model were similar. The computational time of the FFD + Markov chain model was 7.8 times less than that of the CFD + Eulerian model.

Pan, Y., Lin, C.-H., Wei, D., Dong, Z., Chen, C.* (2020). Computer-aided design of a new cabin supply air nozzle in commercial airplanes for reducing particle deposition. Building and Environment, 186, 107324. (Particle deposition, PM2.5, Aircraft cabin)

Enhanced soiling is frequently observed near the multi-slot cabin supply air nozzles in twin-aisle commercial airplanes, which would increase the cleaning and maintenance costs. This study proposed a computer-aided design approach to develop a new cabin supply air nozzle for reducing particle deposition in commercial airplanes. In the new nozzle, the slot dividers were removed to reduce particle deposition, while the shape of the plenum was re-designed using computational fluid dynamics (CFD) to ensure supply air uniformity. The new nozzles were fabricated using a 3D printing technique. The performance of the new cabin supply air nozzles was compared with that of the original multi-slot nozzles by both experimental measurements and numerical simulations, in terms of supply air velocity distribution, particle deposition, pressure drop, noise level, and weight. The results show that the new cabin supply air nozzles can significantly reduce particle deposition on the target surface in comparison to the original multi-slot nozzles, while providing similar airflow and temperature distributions in the aircraft cabin. Furthermore, the new nozzles exhibited better supply air uniformity, lower pressure drop, lower noise level, and were lighter in weight than the original multi-slot nozzles

Xia, T., Bian, Y., Shi, S., Zhang, L., Chen, C.* (2020). Influence of nanofiber window screens on indoor PM2.5 of outdoor origin and ventilation rate: an experimental and modeling study. Building Simulation, 13, 873–886. (Particle penetration/filtration, PM2.5, Building)

When the outdoor PM2.5 pollution is severe, if the windows are open, the occupants tend to be exposed to higher indoor PM2.5 of outdoor origin. However, if the windows are closed, the ventilation rate tends to be insufficient for removing air pollutants generated indoors. Opening windows with the use of nanofiber window screens can be an alternative strategy that can balance between indoor PM2.5 of outdoor origin and ventilation rate. This study fabricated a number of nanofiber window screens and conducted a series of experiments in a laboratory setup to measure the PM2.5 removal efficiency and pressure drop with different window opening angles. A simple model was then developed for predicting the pressure drop, and the measured data was used to validate the model. Finally, the measured data and the validated model were used for two application cases. In the natural ventilation case, the use of nanofiber window screens can effectively reduce indoor PM2.5 of outdoor origin, and the ventilation rate can be improved when compared with infiltration in the house. However, the nanofiber window screens could not reduce the PM2.5 level in the kitchen with a range hood when the cooking PM2.5 emission rate was high. 

Bian, Y., Chen, C., Wang, R., Wang, S., Pan, Y., Zhao, B., Chen, C.*, Zhang, L.* (2020). Effective removal of particles down to 15 nm using scalable metal-organic framework-based nanofiber filters. Applied Materials Today, 20, 100653. (Particle filtration, Ultrafine particle, Building)

Air pollution is currently a huge threat to human health, which leads to heavy demand for efficient air filters for filtration. Among which, ultrafine particles (UFPs, diameter less than 100 nm) can especially result in more severe health diseases. Here, a scalable metal-organic framework (MOF)-based nanofiber filter for high-efficiency particles ranged from 15 nm to 10 μm removal with facile and rapid one-step fabrication is originally presented. Note that the proposed strategy is only applicable for MOFs that do not require heating during synthesis. The MOF-filter has a high filtration efficiency of 99.1% for UFPs. For particle with size down to 15 nm, the filter also exhibits remarkable removal efficiency of 98.8%. The related particle removal mechanisms for the MOF composite filter were studied systematically. Furthermore, the durability and cleanability of MOF-filter were also validated. This work may shed light on the development of nanofibrous heterostructures for high-efficient nanoparticles removal, which hold great promise for reducing health risks. 

Pan, Y., Lin, C.-H., Wei, D., Chen, C.* (2020). Influence of surface roughness on particle deposition distribution around multi-slot cabin supply air nozzles of commercial airplanes. Building and Environment, 176, 106870. (Particle deposition, Particulate matter, Aircraft cabin)

Enhanced soiling due to particle deposition is often observed around multi-slot cabin supply air nozzles in commercial airplanes. This study aimed to investigate the influence of surface roughness on the particle deposition distribution around multi-slot cabin supply air nozzles of commercial airplanes. This investigation constructed a half-row cabin mockup installed with three 3D-printed supply air nozzles of a twin-aisle commercial airplane. A cutting method was proposed to measure the detailed particle deposition velocity distribution on the target surface of the nozzles covered by different grades of sandpaper with different roughness heights. This study also conducted numerical calculations for the particle deposition velocity distribution using an Eulerian particle deposition model. Both the experimental and modeling results show that strong particle deposition occurred on the cut samples near the slot dividers. When the surface roughness height was greater than or equal to 6 µm, the particle deposition velocity increased significantly with the surface roughness height. However, when the surface roughness height was less than or equal to 3 µm, the particle deposition velocity was relatively insensitive to the surface roughness. The analysis indicated that polishing the surfaces of cabin supply air nozzles may not effectively solve the problem of enhanced soiling in the aircraft cabin. 

Xia, T., Chen, C.* (2020). Toward understanding the evolution of incense particles on nanofiber filter media: its influence on PM2.5 removal efficiency and pressure drop. Building and Environment, 172, 106725. (Particle filtration, Particulate matter, Building)

Nanofiber filter media can potentially reduce exposure to PM2.5 in indoor environments because of the filters’ high particle-removal efficiency. To facilitate such filter use, this study conducted a series of experiments to understand the evolution of wetting liquid aerosols, taking incense particles as an example, on nanofiber filter media and the influence of this evolution on PM2.5 removal efficiency and pressure drop. Scanning electron microscope images were also taken to observe the nanoscale interactions between incense particles and the nanofiber network. The results show that the PM2.5 removal efficiency at first decreased as the loading mass increased, because interactions between the particles and the nanofiber network enlarged the pores. The evolution of pressure drop may consist of two stages, i.e., a first stage with a linear relationship, and a second stage with a steep increase in pressure drop with the loading mass. When the pore size became small enough, in addition to inertial impaction and Brownian diffusion, the capture mechanism of interception also became significant. Consequently, the second stage, with a steep increase, tended to occur. Finally, methods for establishing empirical equations for PM2.5 removal efficiency and pressure drop as a function of loading mass were proposed. 

Bian, Y., Wang, S., Zhang, L.*, Chen, C.* (2020). Influence of fiber diameter, filter thickness, and packing density on PM2.5 removal efficiency of electrospun nanofiber air filters for indoor applications. Building and Environment, 170,106628. (Particle filtration, Particulate matter, Building)

Electrospinning is a versatile technique to fabricate nanofiber filters with high PM2.5 removal efficiency and relatively low pressure drop. The eletrospun nanofiber filters may therefore be applied in buildings to reduce indoor exposure to PM2.5 and the associated adverse health effects. This study investigated the influence of various filter parameters, including fiber diameter, filter thickness, and packing density, on the PM2.5 removal efficiency. In this work, 25 nylon electrospun nanofiber filters with different filter parameters were prepared, and the PM2.5 removal efficiency of each sample was measured at five different face velocities. In total, 125 sets of measured data were obtained. The results show that the PM2.5 removal efficiency of nylon electrospun nanofiber filters was negatively associated with the fiber diameter, and positively associated with the thickness of the filter. However, there was no clear correlation between PM2.5 removal efficiency and packing density. This investigation further developed a semi-empirical model for predicting the PM2.5 removal efficiency of nylon nanofiber filters. The accuracy of the model was satisfactory with a median relative error of 7.9%.

2019 Particle