Carine Habchi

Improved thermal performance of face mask using phase change material

The purpose of this work is to develop a mathematical model to study the thermal performance of a cloth face mask in which phase change material (PCM) is encapsulated as compared to a cloth mask alone. The thermal performance is assessed by the ability to reduce heat loss and water vapor transfer from the exhaled air to inhaled air as well as to reduce the potential for condensation in the mask fabric layers. The mathematical model incorporated all the complex transport mechanisms of heat and moisture, including the realistic breathing pattern for the air passing through the fabric. The core assumption of the model of non-local-thermo-equilibrium was validated by performing experiments on a common cotton cloth mask. The model predicted well the experimentally measured air temperature through a cotton cloth mask during sudden changes in thermal inflow conditions. The validated model was used to perform a parametric study to determine environmental conditions and PCM material characteristics for the enhanced performance of the cloth mask. It was found that a considerable increase in the reclaiming of sensible and latent energy was reached for the same ambient conditions by the introduction of PCM with melting temperature of 22℃ and PCM mass fraction of 20%. Furthermore, the incorporation of PCM allows inhalation of colder outdoor conditions with a high range of relative humidity without condensation at ambient temperatures lower than 12℃, which is not possible without PCM. For higher temperatures than 12℃, the introduction of PCM enlarged the possible range of relative humidity reached without condensation.

Chair Fans as Energy Efficient Strategy to Aid Localized Ventilation

Abstract . Nowadays, the air conditioning industry is deviating from the conventional mixing ventilation technique towards localized ventilation. Displacement ventilation and ceiling personalized ventilation are localized systems presenting a high potential in insuring good indoor air quality while reducing the energy consumption compared to mixing ventilation. In this work it is proposed to enhance their performance by assisting them with chair fans controlling the behavior of occupants’ convective plumes.

Transient Model for Particle Dispersion Generated by High Momentum Respiratory Activities in Spaces Ventilated by Displacement Ventilation System

A transient zonal model wit is developed to study particle distribution resulting from transient respiratory activities in spaces ventilated by displacement ventilation system (DV). Two transient sub-models are coupled: a transport model of exhaled particles computing the percentage of generated particles penetrating the infected thermal plume and tracking the exhaled jet propagation, and a transport model predicting particle exchange between the different affected layers and regions. A parametric study was performed to determine the effect of different factors on the risk of cross-infection between the occupants: exhalation velocity, DV flow rate, distance separating the occupants and particle diameter. It was observed that with the increase of the DV flow rate, the ventilation effectiveness increases reducing particle accumulation in the breathing zone. The risk of cross-contamination becomes higher for reduced separating distance between the occupants, and for increased cough velocity, as the momentum of released droplets and their quantity increase. Therefore, it was found that to reduce cross-infection, measures can be considered as avoiding getting close to an infected occupant and covering the mouth during a cough. In addition, assisting DV system by chair fans is expected to reduce cross-contamination by increasing the strength of the rising thermal plumes.Copyright