Pressure, types barometric

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 noncondensable gases eventually reach the condenser (unless vented from an effect above atmospheric pressure to the atmosphere or to auxiliary vent condensers). These gases will be supplemented by air dissolved in the condenser water and by carbon dioxide given off on decomposition of bicarbonates in the water if a barometric condenser is used. These gases may be removed by the use of a water-jet-type condenser but are usually removed by a separate vacuum pump. 

The absolute, barometric pressure is not normally required in ventilation measurements. The air density determination is based on barometric pressure, but other applications are sufficiently rare. On the other hand, the measurement of pressure difference is a frequent requirement, as so many other quantities are based on pressure difference. In mass flow or volume flow measurement using orifice, nozzle, and venturi, the measured quantity is the pressure difference. Also, velocity measurement with the Pitot-static tube is basically a pressure difference measurement. Other applications for pressure difference measurement are the determination of the performance of fans and air and gas supply and e. -haust devices, the measurement of ductwork tightness or building envelope leakage rate, as well as different types of ventilation control applications. 

Aftercondensers operate at atmospheric pressure. They do not affect the steam economy or ejector performance, but they do avoid the nuisance of exhausting steam to the atmosphere, thus, they allow steam to be recovered. They also serve as silencers on the ejectors, and with barometric types they can absorb odors and corrosive apors. 

Fignre 7.7b shows the fate of the filtrate as it is sucked from the filter cloth. Two tanks called vacuum receivers are provided for the two types of filtrates the filtrate removed while the segments are still submerged in the tank and the residual filtrate removed when the segments are already out of the tank. Vacuum receivers are provided to trap the filtrate so that the filtrate will not flood the vacuum pump. Also note the barometric seal. As shown, this is in parallel connection with the suction vacuum of the filter. The vacuum pressure is normally set up to a value of 66 cm Hg below atmospheric. Any vacuum set for the filter will correspondingly exert an equal vacuum to the barometric seal, on account of the parallel connection. Hence, the length of this seal should be set equivalent to the maximum vacuum expected to be utilized in the operation of the filter. If, for example, the filter is to be operated at 51 cm. 

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.

Your textbook lists five types of pressures atmospheric pressure, barometric pressure, gauge pressure, absolute pressure, and vacuum pressure. 

The major exposure of the population to natural radiation arises from inhalation of the short-lived radioactive progeny of the radioactive noble gas radon-222, which in turn is a sixth-generation radioactive decay product of natural uranium. The amount of radon-222 present in the air depends on many factors (e.g., gas permeability in soil and rock, relative humidity, and barometric pressure) but is necessarily linked to the geological concentration of the uranium parent radionuclide. There is about an eightfold range of concentrations of uranium in different types of rocks and soils. 

Condensers.—From a thermal standpoint, condensers may be classified as mixing (horizontal independent jet, injector or barometric) and non-mixing (surface) types.. The equations above given for feed-water heaters will apply as an error on the safe side, x may be taken as 1.0. The value of ti is determined by the available supply of cooling water in this latitude under summer conditions, it is rarely below 70°. That of to will be in surface condensers 6 to 10° below tj and that of t2 the same amount below U- The value of to determines the best possible vacuum. Orrok gives k = SfiOr VF, for clean copper tubes, where V = water velocity in tubes, feet per second, r = ratio of partial pressure of steam to total pressure in the condenser. If condensers and vacuum pumps are tight, r == 0.95. 

Drying Under Vacuum,—The most common type is the standard shelf dryer arranged very similarly to the apparatus shown in Fig. 31. However, the housings have to be built substantially in order to withstand the outside pressure. The vapors are condensed in either surface or barometric condensers. This type... 

M. Nonchemical physical exposures in the workplace are important because they can cause systemic effects that mimic chemical toxidromes. The most important example is heat stress, which is a major occupational health issue. Other relevant nonchemioal, work-related physical exposure types include ionizing radiation, nonionizing radiation (such as ultraviolet, infrared, and microwave exposure), and increased barometric pressure (eg, among caisson workers). Except for extremes of exposure, the adverse effects of these physical factors are generally associated with chronic conditions. 

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