Low pressure area

These mechanisms can be observed in many common situations. For example, fog via mixing can be seen in the discharge of breath on a cold day. Fog via adiabatic expansion can be seen in the low-pressure area over the wing of an airplane landing on a humid summer day and fog via condensation can be seen in the exhaust from an automobile air conditioner (if you follow closely enough behind another car to pick up the ions or NO molecules needed for nucleation). All of these occur at a veiy low supersaturation and appear to be keyed to an abundance of foreign nuclei. All of these fogs also quickly dissipate as heat or unsaturated gas is added. 

This is where the outside air intake and recirculated air are brought together before proceeding to the next stage of treatment. As shown in Figure 29.3, it is a low-pressure area, which will induce outside air without the use of another fan if the route has low resistance. 

A pump must have a continuous supply of fluid available to its inlet port before it can supply fluid to the system. As the pump forces fluid through the outlet port, a partial vacuum or low-pressure area is created at the inlet port. When the pressure at the inlet port of the pump is lower than the atmospheric pressure, the atmospheric pressure acting on the fluid in the reservoir must force the fluid into the pump s inlet. This is called a suction lift condition. 

The low density of gases makes it more difficult to keep the bubbles dispersed. The bubbles will move to the low-pressure areas, that is, behind the impellers, in the trailing vortices close to the impeller, behind the baffles, and at the inner side after a bend. The bubbles will coalesce in these areas with high gas holdup. It is very difficult to design reactors without low-pressure regions where the low-density fluid will accumulate. One such reactor is the monolith reactor for multiphase flow [32, 33]. 

Figure 31.12 illustrates that a low-pressure area being developed beneath the slab will draw the radon out of the soil, up the pipe, and exhaust the gas outdoors. If the subslab material consists of tightly packed soil or contains large rocks, the pressure held may not extend to all areas of the soil surrounding the foundation, and allow radon to enter the home where the pressure held does not exist. One way of ensuring the proper extension of the pressure held is to install media beneath the slab prior to the pour that will allow the easy movement of the air, thus helping to extend the pressure held. 

Low-pressure receptors. The low-pressure receptors are located in the walls of the atria and the pulmonary arteries. Similar to baroreceptors, low-pressure receptors are also stretch receptors however, stimulation of these receptors is caused by changes in blood volume in these low-pressure areas. An overall increase in blood volume results in an increase in venous return an increase in the blood volume in the atria and the pulmonary arteries and stimulation of the low-pressure receptors. These receptors then elicit reflexes by way of the vasomotor center that parallel those of baroreceptors. Because an increase in blood volume will initially increase MAP, sympathetic discharge decreases and parasympathetic discharge increases so that MAP decreases toward its normal value. The simultaneous activity of baroreceptors and low-pressure receptors makes the total reflex system more effective in the control of MAP. 

Water is allowed to enter the foam tank from the main stream with as little friction loss as possible, while pressure in the main stream is dropped about 10% through use of an orifice. Liquid in the tank is metered into the low pressure area by a second orifice. The pressure proportioning system offers the advantages of low pressure drop, automatic proportioning over a range of flows and pressures, freedom from external power and the absence of moving parts. Its disadvantages are that the concentrate cannot be resupplied while the system is in operation, the bladders tend to leak and there is an economic maximum limit on size. 

The wind always blows from a high pressure area to a low pressure area. The strength of the wind depends on the pressure differences. When the pressure difference is... 

From such microbubble-dissolution measurements, Bemd (ref. 16,17) outlined a physical model to explain much of the dynamic behavior of film-stabilized microbubbles.- One problematic aspect of this dynamic behavior involved the question of how a gas nucleus can be surrounded by a relatively impermeable film and yet subsequently act to produce cavitation when a gas/water interface is needed to initiate cavitation. Bernd (ref. 16) explains that if the stabilized gas microbubble enters a low-pressure area, the gas within the microbubble will attempt to expand. The surfactant film may also elastically attempt to expand. The surfactant film will then be expanded until essentially the surface tension of the water alone acts to contract the microbubble, since the protective shell no longer acts. The film has either been ruptured upon expansion, or it has expanded until it is ineffectual. Thus the microbubble (i.e., gas nucleus) should be capable of expanding to form a cavitation void or acquire additional gas in the form of water vapor or from surrounding dissolved gas. In addition, Bernd points out that it is reasonable to expect a gas microbubble to acquire such an effective... 

Chapter 6 examines what, in the authors opinion, are three important applications of vacuum technology in the chemical sciences. First, its use in chemical technology is clearly defined and, in many applications, the requirement for systems operating below 10 6 Pa is obvious. In both cases, typical systems are considered and quantified. The third topic concentrates on a technique (differential pumping) which is widely used in systems where high- and low-pressure areas must be interfaced. Specific systems are discussed to illustrate the usefulness of the technique. 

The southeasterly processes are also observed mostly during the cold time of the year they are related to the situation when the high-pressure area is located over the east of the European part of Russia and Kazakhstan, while its spur extends into the western regions of the European part of Russia. In so doing, the Balkan Peninsula and the Mediterranean Sea experience the influence of a low-pressure area while the Mediterranean cyclones displace to the southwest of the Black Sea and favor the strengthening of the southeasterly wind in its eastern part. While this process develops, the airflows mostly feature an easterly direction over the northwest of the sea and a southerly direction over its southwestern part. 

The sound waves produced by the speakers cause pressure variations in the tube. In low-pressure areas the gas cools in high-pressure areas the gas becomes hot. The hot areas are cooled by a heat exchanger and over time the gas in the tube becomes very cold. Garrett s acoustic refrigerator uses 205 watts of power to cool its main compartment to 4°C and the freezing compartment to -22°C. 

A feature of shock waves not yet considered is that there is inevitably a low pressure or rarefaction wave produced at the diaphragm at the same time as the shock wave. This moves initially in the opposite direction from the shock wave but is reflected by the back wall of the tube, and so eventually follows the main shock wave down the tube. Relative to laboratory coordinates this rarefaction wave travels with the local velocity of sound in the gas. This is considerably less than that of the shock wave because of the substantially lower temperature, but superimposed on it is the flow motion of the driver gas towards the low-pressure region. This has the result that the rarefaction wave tends to catch up with the shock wave. Because of the simplifications it allows, it is convenient to make the measurements on the shocked gas before the rarefaction arrives. This consideration is an important one in deciding on the relative positions of the diaphragm and observation points, and on the relative lengths of the high- and low-pressure areas . For a reason considered below, measurements are also sometimes made after the shock wave has been reflected from the front wall, but before the rarefaction wave has arrived. Such a situation is only used where absolutely necessary because it is now felt that the shock front is significantly distorted on reflection. 

Frequently, weather systems involve a close interaction among fronts, cyclones, and anticyclones. The weather system shown in Fig. 4-16 has a large cyclone (low-pressure area) located at 180° west. A warm front, indicated by a line with semicircles pointing in the direction of movement, extends eastward from the cyclone, while a cold front, indicated by a line with triangles pointing in the direction of movement, extends southward. An occluded front extends a short distance northward. Note that clouds and precipitation are associated with this system, especially to the north of the low-pressure area and along the fronts. 

FIGURE 4-18 Tracing of a satellite photo showing cloud formation along fronts, as well as the relationship between low-pressure areas (cyclones) and fronts. Note the correspondence between the cyclones and fronts in this figure and the idealized patterns shown later in Fig. 4-20 for the genesis of a cyclone. Pressures are in millibars dotted lines show the west coast of North America and Hudson Bay (adapted from FAA, 1965). 

FIGURE 4-21 A surface weather chart for 1200 GMT (700 EST), March 5, 1964, showing information available at each observation station. The chart also shows high- and low-pressure areas, fronts, and isobars constructed by interpolation between stations. (900 or 1000 millibars need to be added as appropriate to values see text. Adapted from FAA, 1965). 

Cloud cover, surface wind direction and speed, temperature, dew point, and precipitation are indicated by symbols at each weather reporting station. Interpretation of the weather in a region is facilitated by the identification of high-pressure and low-pressure areas, the delineation of frontal systems, and the construction of isobars. Isobars are lines of constant atmospheric pressure that are interpolated between observation points, and are so named because pressure often is presented using the unit of the bar, which is equivalent to 106 dyn/cm2 or 0.9869 atm. On some maps, such as shown in Fig. 4-21, pressure is given in millibars as a shorthand notation, only the last two digits are presented. The user must add either 900 or 1000 millibars to the value shown, whichever brings the value closest to 1 bar. 

Both the low Ao terms in the h segments and low pressure, area products in the 1 segments suggest the formation of aggregates in these spread monolayers. 

Another weather-related variable that can impact heater excess O2 is the atmospheric (barometric) pressure. Atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. Low pressure areas have less air mass above their location, whereas high pressure areas have more air mass above their location. As the atmospheric pressure changes, the air density also changes due to the compression effect of the air mass. 

Macroscale. Phenomena occurring on scales of thousands of kilometers, such as semipermanent high- and low-pressure areas that reside over the oceans and continents. (The term synoptic is commonly used to denote macroscale.)... 

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