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Biomedical subjects

M R Flynn

Publications and source records attributed to M R Flynn.

11 recordsLinked to original sources
PubMed1996

Experimental and numerical studies on the impact of work practices used to control exposures occurring in booth-type hoods.

The observation that the between-worker variance component of exposure is significant for those performing the same tasks suggests that work practices are an important determinant of exposure. Decisions to implement engineering controls may be less than optimal if these work practices are not carefully identified. This study examines the position of the worker with respect to an object and the airflow direction in a large booth-type hood, and its implications for control of exposure. Experiments are conducted in a wind-tunnel using a mannequin and tracer gas techniques to measure exposures in the various positions at different air velocities. Smoke-wire, flow-visualization techniques are employed to correlate the exposures with the airflow patterns. Numerical predictions of these flow patterns and exposures compare favorably with experimental data, despite limitations. Further work is underway to examine more realistic situations such as spray-painting applications.

Air Pollutants, Occupational↗
PubMed1995

Computational simulation of worker exposure using a particle trajectory method.

The velocity field downstream of a worker is approximated with a discrete vortex algorithm. This information is used to calculate trajectories of massless tracer 'particles' released from a point-source of contaminant. Concentrations in the plane of this source are estimated by averaging over a number of such trajectories. Approximations include: (1) representing the worker by a two-dimensional elliptical cylinder; and (2) representing tracer gas contaminant by massless particles generated without momentum. These particles are transported by both vortex shedding and turbulent diffusion. Computer-predicted mean concentrations in the near-wake region downstream of the worker compare well with results from wind-tunnel tracer gas experiments employing a mannequin. Subsequently, the concept of a computational breathing zone is introduced, and predictions of worker exposure are made. These simulations of time-integrated breathing zone concentration also compare well with measured values.

Air Movements↗
PubMed1995

Three-dimensional finite-element simulation of a turbulent push-pull ventilation system.

A finite-element formulation with penalty approach to enforce continuity is employed here to simulate the three-dimensional velocity field resulting from a simple push-pull ventilation configuration. An analytic expression for the length scale and a transport equation for turbulent kinetic energy are coupled with the momentum equations. A coaxial square hood and jet are arranged with cross-draught perpendicular to the common centreline. Numerical predictions of the velocity and turbulence kinetic energy fields are evaluated in the plane of symmetry with hot film anemometry, and smoke-wire flow visualizations. The agreement of the simulated jet trajectories with flow visualizations is reasonable, as are velocities. Predictions of turbulence kinetic energy are not as good, particularly near the hood face. Despite the limitations the numerical approach is useful in assessing the impact of cross-draughts on the push-pull arrangement.

Air↗
PubMed1992

The effect of contaminant source momentum on a worker's breathing zone concentration in a uniform freestream.

Several factors affecting breathing zone concentration were examined in a paint spray booth by using a tracer gas method. The variables in the study include contaminant momentum, the presence of a flat plate downstream of the worker, the distance between the contaminant source and the body, and the worker's motion. A dramatic reduction in breathing zone concentration was observed when the spray gun emitted contaminants with high momentum. Reductions of 30-50% were observed because of the other variables. The source momentum effect was studied, subsequently, in a wind tunnel by measuring the breathing zone concentration of a mannequin with various flows through jets of different diameter, at varying freestream velocities. A functional relationship was determined between nondimensional breathing zone concentration and contaminant source momentum. This relationship is supported by numerical simulations. The effect of contaminant momentum on the near-wake flow field is discussed in conjunction with results from the numerical simulations.

Air Movements↗
PubMed1991

Airflow pattern around a worker in a uniform freestream.

The effect of boundary layer separation on worker exposure is an important factor in the design of local exhaust ventilation. Three-dimensional airflow around a mannequin is examined by using flow visualization techniques and hot-film anemometry. Above the chest, a downwash effect is noted; from the chest to the elbows, a combination of downwash and vortex shedding is observed; and from the waist to the hip, vortex shedding appears to be dominant. A coherent vertical flow structure is observed close to the body. Vortex shedding frequency is determined by using hot-film anemometry. The dimensions of the reverse flow region and the area of the vortices are estimated from flow visualization videos.

Humans↗
PubMed1991

Modeling a worker's exposure from a hand-held source in a uniform freestream.

The phenomenon of boundary layer separation can be an important factor in determining a worker's exposure to toxic airborne pollutants. A conceptual model was developed to understand this phenomenon and to predict the average concentration in the reverse flow region downstream of a worker in a uniform freestream. Subsequently, the assumptions of this model were tested experimentally in wind tunnel studies. On the basis of these results, a revised model is presented and validated by using a tracer gas method. The revised model provides a reasonable estimate of the average concentration in the reverse flow region of the mannequin. Empirical models are presented that relate both the average concentration in the reverse flow region and the breathing zone concentration to the body dimensions and the freestream air velocity. Applications and limitations of the results are discussed.

Air Movements↗
PubMed1991

Discrete vortex methods for the simulation of boundary layer separation effects on worker exposure.

The discrete vortex method is a numerical technique for the solution of the two-dimensional Navier-Stokes equations in vorticity-transport form. The technique is employed here, with appropriate modifications, to simulate boundary layer separation around a worker and to assess the implications for exposure. Approximations include: (1) representation of the worker as a two-dimensional elliptical cylinder; and (2) contaminant transport by vortex shedding exclusively. The model results in estimates of breathing zone concentration that are in reasonable agreement with laboratory wind tunnel experiments.

Air Movements↗
PubMed1990

Computer simulation in the design of local exhaust hoods for shielded metal arc welding.

Computer simulations were used to examine competing exhaust hood configurations for shielded metal arc welding. The welder's breathing zone concentration appears to be an inverse linear function of the computer-predicted hood capture efficiency. Hood aspect ratio, hood flow, and the welder's position relative to the hood all have a significant effect on the breathing zone concentration. The height of the hood above the welding surface showed no significant effect in reducing breathing zone concentration. Further examination of breathing zone concentration as a function of capture efficiency is needed before reliable design methods can be developed using this parameter.

Air Movements↗
PubMed1988

Prediction and measurement of velocity into flanged slot hoods.

A model describing the three-dimensional velocity field into a flanged slot hood has been developed using potential flow theory. Modeling the slot as an elliptical aperture allows use of the potential function to develop expressions for the velocity components (vx,vy,vz) at any point (x,y,z). Experiments were performed to measure velocities in front of six slot hoods. Experimental results were compared with velocities predicted by two models: an equal area ellipse with the same length to width ratio as the slot and an ellipse inscribed within the slot.

Air Pollution↗
PubMed1987

Empirical validation of theoretical velocity fields into flanged circular hoods.

Previously presented theoretical models of the three-dimensional velocity field into a flanged circular hood, both with and without crossdraft, are examined by hot film anemometry. A final model with empirical modifications is selected and validated. Computer generated streamline maps, which enable visualization of the effects of crossdrafts on hood performance, are presented. The theoretical basis for capture efficiency using the model is discussed.

Mathematics↗