Impact of room airflow interaction on metabolic CO2 exposure

CFD simulations were performed to investigate occupants’ exposure to metabolic CO2 in a room with mechanical ventilation. A meeting room occupied by six adult people performing sedentary activity was simulated. Five of the six occupants were simulated to exhale air with realistic CO2 content, while one occupant was inhaling, i.e. the exposed occupant. Both exhalation and inhalation were simulated with constant flow rates. Two air distribution patterns were considered, mixing and displacement air distribution, each was combined with chilled ceiling, as summer conditions were simulated. For both air distribution patterns, the influence of solar gain of 200 W, which was simulated as heated vertical surface (window), and the distance between the occupants facing each other were studied. The simulation results revealed the importance of buoyancy flows generated by heated vertical surfaces for the pollution distribution. It was found out that compared to the case without solar heat gain, the presence of solar gain increased the inhaled CO2 level by 26.9 % in the case of displacement ventilation, while it reduced the exposure by 4.5 % when the outdoor air was distributed by mixing ventilation. The distance between the occupants facing each other did not affect considerably the exposure.

Non-Linear Behavior of Electrothermal Flows

Recently, electrokinetic flows have raised the interest of scientific community. Driving flow with an electric field leads to promising applications for mixing, concentration and pumping application in lab on chip. However, current models are still inaccurate and in many cases dont fit the measured data. The work presented here is mainly focused on AC electrothermal flows (ACET) carried out in microwells. An AC electric field is applied between 3 interdigitated gold electrodes. Using μPIV (μ Particle Image Velocity) vortex flows are characterized. The competition between light induced (LEF), AC induced electrothermal (ACET) and buoyancy flows (BF) is discussed. Based on those experimental observations, a new theory is tackled. It takes into account the observed instability like behaviour and the discrepancy of the voltage influence on velocities at high conductivity.

Engineered and Natural Marine Seep, Bubble-Driven Buoyancy Flows

Bubble-plume upwelling flows were studied in the marine environment through dye releases into engineered plumes and a natural hydrocarbon seep plume. For engineered plumes, these experiments measured the water column–averaged upwelling flow Vup(zo) from release depth zo to the sea surface, for a wide range of flows Q, and zo. From Vup(zo), the local upwelling flow Vup(z), where z is depth, was calculated and found to vary with Q as Vup(z) ∼ Q0.23 for plumes strong enough to penetrate a shallow, thermally stratified layer, which was in good agreement with published relationships between Vup(z) and Q. These data were used to interpret data collected at a natural marine seep. For the seep, the upwelling flow decelerated toward the sea surface in contrast to the engineered plumes, which accelerated toward the sea surface. Data showed the seep bubble-plume upwelling flow lifted significantly colder and more saline water. The increased density difference between this upwelling fluid and the surrounding fluid most likely caused the deceleration. Midwater-column bubble measurements showed downcurrent detrainment of smaller bubbles from the bubble plume.

Nanoparticle Concentration in Buoyancy Flows

The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement in buoyancy-driven nanofluids. In this study, a two-dimensional rectangular enclosure with isothermal vertical walls and adiabatic horizontal surface is filled with 27nm Al2O3 - H2O nanofluid. The volume fraction is varied between 0 to 12%. Results shows that for small volume fraction, 0.2≤Φ≤2%, the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction, Φ>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number but the rate of thermal diffusion is enhanced.