Automatic flow interruption bronchoscope: a laboratory study.

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

A simple steady state model of the distribution of vertical temperature in broiler houses without internal air circulation.

1. The vertical temperature profile in a broiler house depends on several factors: ground temperature, heat production by the birds, heating of litter by resting birds, stratification and radiation, microbial heat production in the litter, moisture loss from litter and natural convection around the birds. The effect on the vertical temperature profile is calculated for each factor and the effects are finally combined to estimate vertical temperature distribution. 2. The vertical temperature profile in a commercial broiler house depends on the age of the birds. Influential factors for young broilers are ground temperature and stratification. For older broilers, influential factors are floor construction and ground-water table, heat production of broilers and litter, the behaviour of the broilers and air circulation in the house. 3. Temperatures in the living zone can differ appreciably, by a maximum of about 4 degrees C, from mean house temperature. 4. The velocity of air induced by the heat production of the broilers is about 5 cm/s. This provides good air mixing in the living zone.

Air Movements↗

PubMed1995

Experimental considerations for the study of contaminant dispersion near the body.

Experimental considerations are discussed for conducting controlled studies of the dispersion of contaminants released near a mannequin. A 183 cm x 183 cm cross section wind tunnel was modified to study the low velocity range of 10 to 100 cm/sec (20 to 200 ft/min). Installation of a removable biplanar slat grid produced turbulent intensities up to 15%. The results of validation testing for selected experimental components are reported, including (1) a minimum, unambiguous velocity measurement capability of 2.0 cm/sec (4.0 ft/min); (2) a minimum required integration interval for velocity and contaminant measurements of at least 3 min; (3) a determination that smoke streamline plume settling may be a problem at velocities < or = approximately 15 cm/sec (approximately 30 ft/min); (4) a determination that a 14% tunnel blockage by the mannequin was not of consequence for frontal measurements; and (5) a finding that the biplanar grid produced turbulence spectra representative of low velocity indoor settings. A deceleration zone was noted that extended 50 cm upstream from the mannequin, with freestream velocities reduced 50 to 60%, 2.5 cm from the chest. A contaminant tracer released as a point source 60 cm upstream typically dispersed laterally only 10 to 15 cm and diluted by a factor of 10(4) before reaching the chest.

Air Movements↗