Cross ventilation

Cross-drafts The unwanted or wanted movement of air within a space, which may be natural or mechanical. See Cross ventilation. 

Cross ventilation Ventilation that takes place by the circulation of air introduced at one side of the room and extracted at the other side. 

A cross-ventilation by inlets and outlets at opposite sides of an enclosure supports efficient purging. Enclosures showing a simple geometry without... 

Overall, JP-8 air concentrations according to surrogate markers, such as total hydrocarbons, naphthalene, and benzene, appeared to be highest in aircraft fuel tanks, especially those containing explosion-suppression foam (Carlton and Smith 2000 Egeghy and Rappaport 2001). The increased air concentrations appear to result from the tendency of foam to absorb fuel. At elevated temperatures inside the tank, the fuel volatilizes to yield higher air concentrations of JP-8. Fuel tanks with appropriate cross ventilation have much lower interior air concentrations of JP-8. 

Hypochlorite (bleach) can be used at full strength for clothing or environmental decontamination. Consider cross-ventilation to blow contaminated vapors away from personnel and equipment being decontaminated. 

Hot work is performed in confined spaces where the hot work space contains partitions, balconies, or other structural barriers to the extent that they significantly obstruct cross ventilation. 

Until recently most industrial scale, and even bench scale, bioreactors of this type were agitated by a set of Rushton turbines having about one-thind the diameter of the bioreactor (43) (Fig. 3). In this system, the air enters into the lower agitator and is dispersed from the back of the impeller blades by gas-fiUed or ventilated cavities (44). The presence of these cavities causes the power drawn by the agitator, ie, the power requited to drive it through the broth, to fall and this has important consequences for the performance of the bioreactor with respect to aeration (35). k a has been related to the power per unit volume, P/ U, in W/m and to the superficial air velocity, in m/s (20), where is the air flow rate per cross-sectional area of bioreactor. This relationship in water is... 

Figure 31-1 shows a cross sechon of a gasoline engine with the positive crankcase ventilation (PCV) system. 

When you have pursued source control options and have increased ventilation rates and efficiency to the limits of your expertise, you must decide how important it is to pursue the problem further. If you have made several unsuccessful efforts to control a problem, then it may be advisable to seek outside assistance. The problem is probably fairly complex, and it may occur only intermittendy or cross the borders that divide traditional fields of knowledge. It is even possible that poor indoor air quality is not the actual cause of the complaints. Bringing in a new perspective at this point can be very effective. 

The value of the coefficient of turbulent diffusion, D, depends upon the air change rate in the ventilated space and the method of air supply. Studies by Posokhin show that approximate D values for locations outside supply air jets is equal to 0.025 m-/s. Air disturbance caused by operator or robot movement results in an increase in the D value of at least two times. Studies by Zhivov et al. showed that the D value is affected by the velocity and direction of cross-drafts against the hood face, and the presence of an operator e.g., for a cross-draft directed along the hood face with velocity u = 0.5 m/s with D = 0.15 m-/s (with the presence of an operator), an increase to = 1.0 m/s results in D = 0.3 m-/s. 

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,. 

Detailed experimental data were obtained by Sadovskaya on a physical model in isothermal conditions. She has found that the confined air jet has two critical cross-sections (Fig. 7.38). In the first cross-section, where the ratio of jet cross-sectional area to the area of ventilated space equals 0.24, the jet... 

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, ). 

The ventilation model is a simple flow network with one zone and the different openings modeled as airflow links from the hall to outside Fig. 11.52). For the flow through the roof hood, two additional nodes were considered between the different cross-sections through which the air flows (Fig, 11.53). 

The most frequently applied mechanical manometers in ventilation applications are fluid manometers, bur the following types are also used. The Bourdon tube is a small-voiume tube with an elliptic cross-section bent to the shape of a circular arc, the C-type. One end is open to the applied pressure while the other end is closed. The pressure inside the tube causes an elastic defonnation ot the tube and displaces the closed end, which is then converted, by means of a linkage mechanism, into the movement of a pointer. The Bourdon tube may be of a spiral or helical design as well. 

Because all measurement methods and instruments are sensitive to the velocity profile, the choice of the measurement cross-section is of vital importance. In most ventilation systems there is seldom enough straight duct to allow a fully developed velocity profile to develop, which is the most favorable for flow measurement. Thus, the principle in selecting the measurement cross-section is to find the place where the velocity profile is as near to the fully developed profile as possible. In practice the distance from the nearest source of disturbance upstream is maximized, ensuring that the distance to the nearest downstream disturbance is at least 3 to 5 duct diameters. 

Adequate ventilation is provided by means of openings at the top of high points and the bottom of low points. These openings shall have a free open area of 1/150 of the cross-section area of the duct or 0.05 m, whichever is the greater. 

In hospitals today a wide variety of complex equipment is used in the course of patient treatment. Humidifiers, incubators, ventilators, resuscitators and other apparatus require proper maintenance and decontamination after use. Chemical disinfectants used for this purpose have in the past through misuse become contaminated with opportunist pathogens, such as Ps. aeruginosa, and ironically have contributed to, rather than reduced, the spread of cross-infection in hospital patients. Disinfectants should only be used for their intended purpose and directions for use must be followed at all times. 

Chemoreceptor response to increased arterial hydrogen ion concentration. An increase in arterial hydrogen ion concentration, or a decrease in arterial pH, stimulates the peripheral chemoreceptors and enhances ventilation. This response is important in maintaining acid-base balance. For example, under conditions of metabolic acidosis, caused by the accumulation of acids in the blood, the enhanced ventilation eliminates carbon dioxide and thus reduces the concentration of H+ ions in the blood. Metabolic acidosis may occur in patients with uncontrolled diabetes mellitus or when tissues become hypoxic and produce lactic acid. An increase in arterial hydrogen ion concentration has no effect on the central chemoreceptors. Hydrogen ions are unable to cross the blood-brain barrier. 

The ventilation capacity required for drying amounts to 0.4-0.5 m3/hen/h at a backpressure of 500-1000 Pa in the heat exchanger tubes. The pressure is determined from the volume of air, the length and cross-section of the perforated ducts. For good drying, the pressure at the end of the perforated duct must be at least 300-350 Pa. This is the lowest pressure at which the air can be blown out of the holes at a speed of ca 20/m/sec., so that it can be distributed over the manure on the belt at a speed of 0.5-2.0 m/sec. 

Mass production parts bumpers, soundproofing shields, cross-pieces, inserts for dashboards, seat frames, containers, welding helmets, ventilator housings, base of lawn-mowers, taping of pipes, pipelines, tanks, long fibre reinforced injected parts. 

The facility should be constructed of materials that facilitate cleaning. Heating, ventilation, and air conditioning (HVAC) systems should be of adequate capacity to produce environmental conditions that comply with employee and animal health and safety standards and should be designed to prevent cross-contamination. 

To determine the fate of formaldehyde and formic acid in a coal mine, an unused shaft about 120 m long and 6 m2 in cross sectional area was selected for study. With a ventilation air flow of 190 m3/min and an engine exhaust flow of 1.5 m3/min, complete exhaust dispersion and dilution was observed in about 10 m. Samples collected in the mine air downstream of the diesel engine indicate no significant change in formic acid concentration at increasing distances from the engine (Table VIII). This is certainly not consistent with the loss of formaldehyde in the same interval. The mechanism for loss of formaldehyde is apparently not a gas phase oxidation to formic acid. Interaction with surfaces may be a more suitable explanation of the observed reduction in formaldehyde concentrations. 

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