CFD investigation of room ventilation for improved operation of a downdraft table: novel concepts.

We report a computational fluid dynamics (CFD) study of containment of airborne hazardous materials in a ventilated room containing a downdraft table. Specifically, we investigated the containment of hazardous airborne material obtainable under a range of ventilation configurations. The desirable ventilation configuration should ensure excellent containment of the hazardous material released from the workspace above the downdraft table. However, increased airflow raises operation costs, so the airflow should be as low as feasible without compromising containment. The airflow is modeled using Reynolds Averaged Navier Stokes equations with a high Reynolds number k-epsilon turbulence model. CFD predictions are examined for several ventilation configurations. Based on this study, we find that substantial improvements in containment are possible concurrent with reduction in airflow, compared with the existing design of ventilation configuration

CFD investigation of room ventilation for improved operation of a downdraft table: novel concepts.

We report a computational fluid dynamics (CFD) study of containment of airborne hazardous materials in a ventilated room containing a downdraft table. Specifically, we investigated the containment of hazardous airborne material obtainable under a range of ventilation configurations. The desirable ventilation configuration should ensure excellent containment of the hazardous material released from the workspace above the downdraft table. However, increased airflow raises operation costs, so the airflow should be as low as feasible without compromising containment. The airflow is modeled using Reynolds Averaged Navier Stokes equations with a high Reynolds number k-epsilon turbulence model. CFD predictions are examined for several ventilation configurations. Based on this study, we find that substantial improvements in containment are possible concurrent with reduction in airflow, compared with the existing design of ventilation configuration

Minimizing decomposition of vaporized hydrogen peroxide for biological decontamination of galvanized steel ducting.

The behavior of vaporous hydrogen peroxide (VHP) was examined in clean, room-scale galvanized steel (GS) and polyvinylchloride-coated steel air ducts, to understand how it might be used to decontaminate larger ventilation systems. VHP injected into the GS duct decreased in concentration along the length of the duct, whereas VHP concentrations in the polyvinylchloride coated duct remained essentially constant, suggesting that VHP decomposed at the GS surface. However, decomposition was reduced at lower temperatures (approximately 22 degrees C) and higher flow rates (approximately 80 actual cubic meter per hour). A computational fluid dynamics model incorporating reactive transport was used to estimate surface VHP concentrations where bioaerosol contamination is likelyto reside, and also showed that VHP decomposition was enhanced at bends within the duct, compared to straight sections. Use of G. stearothermophilus indicators, in conjunction with model estimates, indicated that a concentration-contact time of approximately 100 mg/L H2O2(g) x min was required to achieve a 6 log reduction of indicator spores in clean GS duct, at 30 degrees C. When VHP is selected for building decontamination, this work suggests the most efficacious strategy may be to decontaminate GS ducting separately from the rest of the building, as opposed to a single decontamination event in which the ventilation system is used to distribute VHP throughout the entire building

Tracer Gas Transport under Mixed Convection Conditions in an Experimental Atrium: Comparison Between Experiments and CFD Predictions

We compare computational fluid dynamics (CFD) predictions using a steady-state Reynolds Averaged Navier-Stokes (RANS) model with experimental data on airflow and pollutant dispersion under mixed-convection conditions in a 7 x 9 x 11m high experimental facility. The Rayleigh number, based on height, was O(10{sup 11}) and the atrium was mechanically ventilated. We released tracer gas in the atrium and measured the spatial distribution of concentrations; we then modeled the experiment using four different levels of modeling detail. The four computational models differ in the choice of temperature boundary conditions and the choice of turbulence model. Predictions from a low-Reynolds-number k-{var_epsilon} model with detailed boundary conditions agreed well with the data using three different model-measurement comparison metrics. Results from the same model with a single temperature prescribed for each wall also agreed well with the data. Predictions of a standard k-{var_epsilon} model were about the same as those of an isothermal model; neither performed well. Implications of the results for practical applications are discussed