Aerosol generated from a human cough can be a potential major indoor health risk due to the possible transmission of infectious respiratory diseases to surrounding individuals within the same room and even could spread out via air-ventilation/conditioning systems. This study aims to investigate the transport characteristics and trajectory of coughed aerosols under the influence of conditioned air ventilation as well as near-by human breathing zone using computational fluid dynamics (CFD). An experimental system consisting of air-conditioned space with multiple inlets and outlets, a cough simulator and a receiver was built to validate the CFD predictions. The comparison is in good agreement. The CFD model was established as a transient three-dimensional multiphase multicomponent Eulerian–Lagrangian model and numerically solved using commercial software ANSYS Fluent. Both gas and liquid phases were modelled as multicomponent mixtures. With this CFD model, the indoor transport and trajectory of coughed aerosols can be accounted for the distributions of portions inhaled by each manikin, deposited on surfaces of manikins and chamber walls, as well as recirculated back into the ventilation system. Results reveal that the aerosol source location and the ambient air movement can be crucial factors of aerosol trajectory in terms of direct and indirect influence.

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Spray flash evaporation is an ultrafast evaporation phenomenon that happens when the superheated liquid is sprayed into a low-pressure environment, which has gained more attention due to the great potential in the enhancement of evaporation capacity. In the isolated evaporation of spray flash, the latent heat is selfsupplied by droplets, leading to a temperature reduction in droplet residue. In an evaporator with active vapor extraction (vacuuming), there can be a significant temperature difference between the extracted vapor and discharged liquid of droplet residue. The overall evaporation capacity and the non-equilibrium in temperature between the extracted vapor and liquid residue, however, depend strongly upon the geometric design of evaporation chamber, the spray characteristics, and associated operation conditions including feeding flow rate and temperature and vacuuming pressure. Quantification of such a complicated system requires the establishment of a physical modeling and corresponding numerical simulation. This paper presents a three-dimensional CFD modeling and simulation, using ANSYS software, to investigate an isolated evaporation of spray flash in a cylindrical chamber with active vapor extraction. Due to the polydispersed atomization in spray, a two-way-coupled Lagrangian-Eulerian modeling is adopted. Discrete phase model with user-defined functions (UDF) is applied to simulate the coupled heat, mass and momentum transfer between droplets and vapor. The simulated results are compared with the experimental measurements, which shows a good agreement.

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