Barometric pressure changes

Eqs (14-21) and (14-23) are important inasmuch as they show how changes in barometric pressure affect the volume of air added or subtracted within a soil. The harmonic variation imposed for the sake of illustration can be approximated for any locality where data or barometric changes are available. Buckingham computed the mean pressure... 

Figure 1.12 Pressure terminology. The standard atmosphere is shown by the heavy horizontal line. The dashed line illustrates the atmospheric (barometric) pressure, which changes from time to time. Point Q in the figure is a pressure of 19.3 psi referred to a complete vacuum or 5 psi referred to the barometric pressure (2) is the complete vacuum, O represents the standard atmosphere, and 0 illustrates a negative relative pressure or a pressure less than atmospheric. This type of measurement is described in the text as a vacuum type of measurement. Point (D also indicates a vacuum measurement, but one that is equivalent to an absolute pressure above the standard atmosphere.

Errors of omission result from an insutHcient rigor in following strict laboratory protocols. For example, to determine the rate kinetics of a gas-phase reaction, the necessary measurements include composition at the entrance and exit, reactor volume, flow rate, pressure, and temperature. When the reactor is operated at atmospheric pressure—that is, the effluent exits to the atmosphere—the actual operating pressure is invariably different from 1.01325 bar. Not only does it depend on the elevation above sea level but also the meteorological conditions. Within hours, the barometric pressure may change by as much as 5%. 

There are problems to be considered and avoided when using Hquid-in-glass thermometers. One type of these is pressure errors. The change in height of the mercury column is a function of the volume of the bulb compared to the volume of the capillary. An external pressure (positive or negative) which tends to alter the bulb volume causes an error of indication, which may be small for normal barometric pressure variations but large when, for example, using the thermometer in an autoclave or pressure vessel. 

The ideal air/gas ratio is that which is marginally higher than stoichiometric. It is not possible to run a burner with no excess air for various reasons (e.g. changing ambient temperature, a slight change in calorific value, variation in barometric pressure, wear of control equipment, etc.). All of these and other factors dictate that the burner is operated with sufficient excess air to avoid the production of carbon monoxide in any quantity. 

TTie HP 6890 series features electronic pneumatics control which provides complete electronic control of all gas pressures and flows. On-board sensors automatically compensate for ambient temperature changes and barometric pressure differences to provide more accurate and reproducible results routinely. This reduces recahbration frequency and improves laboratory productivity. It also decreases system operating costs, allows a faster set-up time, and reduces equihbradon time after set-points are changed from one method to the other. 

The Barometrically Enhanced Remediation Technology (BERT ) removes and recovers volatile organic contaminants from soil by enhancing the natural air exchange that occurs in soil as a response to changes in atmospheric pressure. This process is sometimes referred to as barometric pumping or passive soil vapor extraction. The process is a low-cost complement to conventional active-extraction methods because investment and maintenance costs are low and no power is needed. The passive process is better suited than conventional methods for certain problems. 

Fuze, Barometric or Air-Pressure. A fuze that functions as a result of change in pressure exerted by the surrounding air. Usually the change in pressure occurs by reason of travel from a region of one ambient pressure to a region of different ambient pressure... 

Wrong The chief engineer failed to realize that the vacuum pressure indicator was not equipped with a barometric pressure compensator. An ordinary vacuum pressure indicator or pressure gauge reads the pressure difference between the vacuum system and atmospheric pressure. When ambient temperatures drop, the barometer rises or ambient pressure goes up. An ordinary vacuum pressure gauge or indicator would then read an improved vacuum. But in reality, the vacuum has not changed. 

Figure 8. Measured and modeled results for 02 volume % within the unsaturated zone, showing oxygen transport in response to barometric pressure changes. The simulated 4% vol 02 is shown as a solid band. Reprinted with permission from Elberling et al. (1998). Copyright 1998, American Geophysical Union.

When groundwater is brought to the surface and stored in sample containers, the exposure to oxygen in air, the effects of daylight, and the differences in temperature and barometric pressure will cause irreversible chemical changes in a water sample, which in turn will change some of the water quality parameters. That is why water quality parameters should be measured in situ and with as little disturbance to the groundwater as possible. 

While in general the ratio of S0/6o is not great, it is obvious that changes in barometric pressure do exert an effect on soil behavior. The addition or depletion of air and other gases from the soil, coupled with gas diffusion as well as seasonal temperature changes, makes the soil a living entity with a respiratory system. 

Contaminants in the soil compartment are associated with the soil, water, air, and biota phases present. Transport of the contaminant, therefore, can occur within the water and air phases by advection, diffusion, or dispersion, as previously described. In addition to these processes, chemicals dissolved in soil water are transported by wicking and percolation in the unsaturated zone.26 Chemicals can be transported in soil air by a process known as barometric pumping that is caused by sporadic changes in atmospheric pressure and soil-water displacement. Relevant physical properties of the soil matrix that are useful in modeling transport of a chemical include its hydraulic conductivity and tortuosity. The dif-fusivities of the chemicals in air and water are also used for this purpose. 

What if a rapid change in barometric pressure occurs, such as hurricanes or severe storms ... 

Because of the interaction of many factors, especially the numerous temperature effects on both transpiration and photosynthesis, the effects of elevation on WUE are complex. Diffusion coefficients depend inversely on ambient (barometric) pressure [Z) = D 0(F0/F)(T/273)1 8 Eq. 8.9]. Barometric pressure averages 0.101 MPa at sea level, 0.079 MPa at 2000 m, and about 0.054 MPa at 5000 m. Thus diffusion coefficients are nearly twice as large at 5000 m as at sea level owing to the pressure change, which correspondingly increases the gas-phase conductances based on Ac (e.g., Eq. 8.2), whereas those based on AN (Eq. 8.8) are unchanged. The rate of decrease of ambient air temperature with increasing elevation, termed the lapse rate, can be — 5°C per kilometer of... 

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