Airflow flow indicators

Fig. 7.6.4 Back-flow detection with the microsilicon sensor element. Comparison of the in dicated air mass of a microsilicon and of a hot-wire air-flow meter. The microsilicon airflow meter indicates the back flow that appears periodically...

Figure 8 Continuous recordings of airflow (Flow) and esophageal pressure (Pes) in a long-term ventilator-dependent patient with COPD during a brief period of unassisted breathing. Arrows indicate ineffective inspiratory efforts—inspiratory efforts not associated with inspiratory flow. In one study (41), ineffective inspiratory efforts were recorded in 40% of long-term ventilator-dependent patients with COPD but not in patients with COPD who were successfully weaned after a period of prolonged ventilatory support. Abbreviations Pes, esophageal pressure COPD, chronic obstructive pulmonary disease. Source From Ref. 41.

If a wet vacuum is to be used for pickup of detergent-germicide solution from the floor, the manufacturer s recommendations on filter life should be followed. In addition, the operation of the vacuum should be closely observed for evidence of operating changes such as restricted airflow or, conversely, increased flow indicating filter failure. Liquids collected in the vacuum cleaner after floor mopping will contain disinfectant material. These liquids may be poured down a convenient floor drain as local regulations permit, except for cleanup of wastes from an overt spill. These collected liquids should be autoclaved or treated with disinfectant solution before disposal. 

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,. 

The operation of flow dampers can cause pressure fluctuations in the ductwork system. Measurements by Melin indicate that pressure oscillations in an exhaust system can cause instabilities in the airflow through a fume cupboard sufficient to give rise to outward leakage of contamination, especially when a person stands in front of the cupboard. 

Supply Air When designing workbenches, it is essential that the supply air face area be large enough to cover the contained area. Therefore it is important to have some indication of the operator s range of movements for all intended operations. Moreover, for efficient protection the supply airflow must be adequate to get a stable flow field that will not be affected by ambient disturbances. In industrial applications the suitable mean supply air velocities are typically between 0.2 and 0.45 m s h Low velocities should be used when the distance between the supply air unit and the operator is small or for cool supply air. High velocities are applicable at greater distances and in hot environments, with thermal comfort being considered. 

Figure 2.34 Experimentally measured temperature at sensing points indicated in Figure 2.35 and oxygen concentration as a function of time. Hydrogen flow 1 Ndm3 min-1 cooling airflows each 20 Ndm3 min-1 cooling inlet temperature 30 °C [67] (by courtesy of Springer-Verlag).

Figure 7-6. Schematic illustration of originally nonturbulent air (straight anrows in upwind side on left) flowing over the top of a flat leaf, indicating the laminar sublayer (shorter straight anrows), the turbulent region (curved arrows), and the effective boundary layer thickness, 5bl. The length of an arrow indicates the relative speed, and the curvature indicates the local direction of air movement. A similar airflow pattern occurs on the lower leaf surface.

The airflow schematics of the two systems (Figs 24 and 25) indicate airhandling units with return air or recirculated air, having a percentage of fresh air added. Fig. 25 is a schematic diagram of an air-handling system serving rooms with horizontal unidirectional flow, vertical unidirectional flow and turbulent flow, for rooms A, B and C, respectively. 

The effect of swirl distribution in the burner on droplet size and velocity distribution, flow, and flame characteristics is reported. Three examined swirl distributions are 50°/30 , 50 /—30°, and 65°/30 , where the first number indicates the swirl vane angle of the inner annulus and the second number refers to that at the outer annulus. Three airflow distributions of 25%/75%, 50%/50%, and 75%/25% were examined for each swirl distribution. The first percentage number indicates the fraction of the total combustion airflow through the inner annulus, while the second number refers to that at the outer annulus. The results presented here are for swirl distributions of 65 /30° and 50 /30° only, where the total airflow was held constant to maintain a fixed equivalence ratio of 0.4. 

In the flow case, the air register dampers should be automatically actuated for open/shut positions, because on losing one flame out of several, local air deficiency can occur. This cannot happen with the p/Ap control system. In the latter case an extra amount of air excess will result, which is not unsafe. In the p/Ap system, it is necessary to keep air registers in one position while firing, because Ap is used as an airflow indication. 

Figure 14.2 has the shape described above, with a distinct kink in it near a flow rate ratio of 10. This is typical of such systems and indicates that the change described above does not take place smoothly If the system is made of glass, so that the flow pattern can be observed, it will be seen that several distinctly different flow patterns are formed as the airflow rate is increased. 

A randomized, placebo-controlled trial examined the effects of menthol (10 mg nebulized twice daily for 4 weeks) on airway hyperresponsiveness in 23 patients with mild to moderate asthma. The diurnal variation in the peak expiratory flow rate (a value reflecting airway hyperexcitability) was decreased but the forced expiratory volume was not significantly altered. This indicated an improvement of airway hyperresponsiveness without affecting airflow limitation (Tamaoki et al., 1995). Later in vivo research examined the effect of menthol on airway resistance cansed by capsaicin- and neurokinin-induced bronchoconstriction there was a significant decrease in both cases by inhalation of menthol at 7.5 pg/L air concentration. The in vitro effect of menthol on bronchial rings was also studied. It was concluded that menthol attenuated bronchoconstriction by a direct action on bronchial smooth muscle (Wright et al., 1997). 

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