Ventilation Patterns

Breathing consists of the cyclic action of the lungs to inspire and expire atmospheric gases. Inspiration occurs when the diaphragm and intercostal muscles contract, generating a negative pressure in the pleura surrounding 

FIGURE 5.19 Relationship of transpleural pressure to volume n normal and asthmatic individuals. 

TABLE 5.6 Effect of Dead Space Volume, Tidal Volume, and Breathing Frequency on Alveolar fentllation at a Fixed Minute Ventilation (V = 58.0 Umin). Modified from Chemiack.  

9 alveolar gas volume Vq, dead space volume V j, tidal volume f, breathing frequency 

Expired minute ventilation, V, defines the gas volume inspired or expired in 1 minute and is given by 

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Ventilation pattern (plumes, etc.) can be considered only in a very limited way. 

All hydrocarbon fire mechanisms and estimates will be affected by to some extent of flame stability features such as varying fuel composition as lighter constituents are consumed, available ambient oxygen supplies, ventilation patterns, and wind effects. Studies into these effects have generally not progressed to the level where precise estimations can be made without scale model tests or on site measurements. 

Where overall large area coverage is necessary or desired, such as the monitoring of facility borders, pump alleys, entire onshore units or offshore modules, "line of sight" IR beam detectors are used, otherwise "point source", catalytic detectors are provided. The point source locations should be at least on either side of the leak point, which at least one of the detectors downstream ventilation pattern. 

Indoor air pollution is a major global public health threat requiring greatly increased efforts in the area of research and policymaking, because people spend more than 80% of their time indoors, mostly in their homes (Li et al., 2005). The relationship between indoor and outdoor PAH concentrations is also an important part of the PAH distribution pattern. The results varied in the cities because of their different emission and ventilation patterns. 

Natural Ventilation - Ventilation that is created by the differences in the distribution of air pressures around a building. Air moves from areas of high pressure to areas of low pressure with gravity and wind pressure affecting the airflow. The placement and control of doors and windows alters natural ventilation patterns. 

Airborne particulates include dust, fume and aerosols. Many such particles are invisible to the naked eye under normal lighting but are rendered visible, by reflection, when illuminated with a strong beam of light. This is the Tyndall effect and use of a dust lamp provides a simple technique for the rapid assessment of whether a dust is present, its flow pattern, leak sources, the effects of ventilation, etc. More sophisticated approaches are needed for quantitative data. Whether personal, spot or static sampling is adopted will depend upon the nature of the information required. 

Detailed measurements of temperature, humidity, airflow, or other parameters are more appropriate to a later stage of profile development. However, chemical smoke can be used to observe airflow patterns and pressure relationships between special use areas or other identified pollutant sources and surrounding rooms. Odors in inappropriate locations may indicate that ventilation system components require adjustment or repair. 

Balanced mechanical supply and exhaust ventilation equipped with an advanced air distribution strategy to accurately control the flow patterns in a work space... 

In some cases, the ventilation process in the room can be simplified and mechanisms of air and contaminant movement under the influence of each of the above factors can be described using simplified theoretical principles of fluid mechanics, empirical data, and observations from numerous research studies. In general, the ventilation process in a room is complex and different factors have a joint effect on airflow patterns and characteristics, in continued spaces and in industrial buildings particularly. 

FIGURE 7.7 Schematics of air supply (o) with inclined jets toward the occupied zone (b) with horizontal jets and occupied zone ventilated by reverse flow (c) with vertical jets. Shaded areas show the effect of buoyant forces on airflow pattern when supply air is excessively heated over the room air" ... 

In rooms where air and contaminant movement is dominated by thernnal energy of heat sources (e.g., in rooms with natural or displacement ventilation), temperature and contaminant stratification along the room height is created. Air supply and exhaust in such rooms are designed not to disturb the natural pattern of air movement created by heat sources cooled air enters the room in... 

FIGURE 7.9 Influence of exhausced airflow on airflow pattern in the naturally ventilated room fo> airflow in the convective plume smaller than exhausted airflow (b) airflow in the convective pluime equal to the exhausted airflow (c) airflow In the thermal plume at the stratification level equal to the exhausted airflow (t, air temperature along the room height, t, - average room temperaoire)... 

The airflow pattern in rooms ventilated by linear attached jets with L/H ratio greater than that for effectively ventilated rooms was studied by Schwenke and Muller. The results of their air velocity measurements ami visualization studies indicate that there are secondary vortexes formed downstream in the room and in the room corners. The number of downstream vortexes and their size depend upon the room length (Fig. 736b). Mas,s transfer between the primary vortex and the secondary vortex depends upon the difference in characteristic air velocities in the corresponding flows (/, and Ui and can be described using the Stanton number, St . ... 

The influence of room transverse cross-section configuration on airflow patterns created by air jets supplied through round nozzles in proximity to the ceiling was studied by Baharev and Troyanovsky and Nielsen (see Fig. 7.37). Based on experimental data, they concluded that when the room width B is less than 3.5H, the jet attaches to the ceiling and spreads, filling the whole width of the room in the manner of a linear jet. The reverse flow develops under the jet. When B > 4H, the reverse flow also develops along the jet sides. Baharev and Troyanovsky indicated that air temperature and velocity distribution in the occupied zone is more uniform when the jet develops in the upper zone and the occupied zone is ventilated by the reverse flow. Thus, they proposed limiting room width to 3-3.5H,. 

Air supplied in confined space by downward vertical jets creates a similar flow pattern as in the case of air supply by horizontal nonattached jets. With vertical air supply, the occupied zone is ventilated directly by air jets. Grimitlyn suggests that the area of occupied zone ventilated by one jet be sized based on the jet s cross-sectional area at the point it enters the occupied zone. The jet cross-sectional area and configuration depend upon the height of the air supply, the type of air jet, and diffuser characteristics ( K, and K, ). 

Heselberg, P., S. Murakami, and C.-A. Roulet. 1996. Annex 26 Air flow patterns m large enclosures. In Ventilation of Large Spaces in Buildings. Part 3 Analysis and Prediction Techniques. LEA,... 

This section will describe general features of airflow patterns and then present information on the dimensions and locations of recirculating (stagnant) zones around the building envelope, which determine wind pressures and contaminant dilution. This knowledge allows one to select the locations of stacks and air intakes and to calculate infiltration and natural ventilation rates. 

W. Dittes, New concepts for air flow patterns in industrial halls—-Calculation of the ventilation efficiency, in Ventilation 94 Proceedings of the 4th International Symposium on Ventilation for Contaminant Control, vol. 1. Stockholm, Sweden, 1994. 

German guidelines base the division on the resulting airflow pattern within the room rather than distribution methods. They suggest that airflow patterns be divided into four categories hall-filling mixed flow zonewise mixed flow low-momentum, low-turbulence flow for the air supply in the work region and zonewise displacement ventilation. 

In the stratification strategy the supply air is used to substitute the outgoing air from the ventilated (in most cases occupied) zone, thus preventing circulation patterns between the zones. The supply air has to be distributed in such a way that the buoyancy flows are not disturbed. Exhaust air openings are to be located downstream in order to avoid reverse currents within the room. The location of the contaminant sources and the heat sources causing density differences must be the same in order to carry out the contaminants with equal or higher density than air. 

The zoning method offers better contaminant removal and thermal effectiveness than with mixing, limited control of the flow patterns in the ventilated zone, and the ability to avoid stagnant areas with high local concentrations in the ventilated zone. However, partial mixing of contaminants in the ventilated zone decreases its effectiveness. 

Figure 9.23 shows a typical arrangement of this method of ventilation. The resulting airflow patterns in this arrangement will not ensure satisfactory air distribution in many industrial environments. 

The initial performance test for all local ventilation systems is a smoke test, which provides easy airflow visualization between the source and the hood, it helps to identify, with little effort, the main features of airflow patterns. Such a test, recorded by a video camera, allows performance comparisons to be made before and after improvements. Real contaminant or tracer gas measurements are necessary in the case of more detailed testing. 

In industrial ventilation the majority of air velocity measurements are related to different means of controlling indoor conditions, like prediction of thermal comfort contaminant dispersion analysis adjustment of supply airflow patterns, and testing of local exhausts, air curtains, and other devices. In all these applications the nature of the flow is highly turbulent and the velocity has a wide range, from O.l m in the occupied zone to 5-15 m s" in supply jets and up to 30-40 m s in air curtain devices. Furthermore, the flow velocity and direction as well as air temperature often have significant variations in time, which make measurement difficult. 

Acetanilide, p-chloro-acetanilide, 2,5-dichloro-acetanilide Apply sample solution and treat with chlorine vapor in the trough chamber for 20 s, then heat to 60°Cfor 5 min in a ventilated drying cupboard. Various chlorination patterns are produced. [44]... 

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