Gas pressure, units

Alternatively, but not commonly, propulsion of the solutions can be achieved by gravity-based units, which rely on the difference in height between the solution(s) reservoir(s) and the flow lines of the manifold. Also, gas-pressure units, which rely on the action of pressure by an inert gas inside the vessels, which contain the solutions, can be used. Both these uncommon propulsion units yield pulse-free flow but require periodic refilling of solution reservoirs and adjustment of the desired flow rate is very difficult. 

Gases exert pressure because their molecules move freely and collide with any surface in their paths. Gas pressure units include millimeters of mercury (mmHg), torr, pascals, and atmospheres. One atmosphere equals 760 mmHg, or 760 torr. 

The values of the thermodynamic properties of the pure substances given in these tables are, for the substances in their standard states, defined as follows For a pure solid or liquid, the standard state is the substance in the condensed phase under a pressure of 1 atm (101 325 Pa). For a gas, the standard state is the hypothetical ideal gas at unit fugacity, in which state the enthalpy is that of the real gas at the same temperature and at zero pressure. 

Most gas-fired, heavy-duty gas turbines installed as of 1996 operate at gas pressures between 1.2 and 1.7 MPa (180—250 psig). However, aero derivative gas turbines and newer heavy-duty units can have such high air-inlet compression ratios as to require booster compressors to raise gas inlet pressures, in some cases as high as 5.2 MPa (750 psig). 

Units and Concentration. In the gaseous as well as the condensed phases, molecular concentration by molecular species is of prime importance. By convention, total pressure in a MaxweUian gas is used as though it indicates the quaUty of the vacuum and as though MaxweUian gases were the rule rather than the exception (12). In general, in dynamic systems, gas pressure (or its partial pressure components) is neither isotropic nor an adequate indicator of molecular significance. 

The problem presented to the designer of a gas-absorption unit usually specifies the following quantities (1) gas flow rate (2) gas composition, at least with respect to the component or components to be sorbed (3) operating pressure and allowable pressure drop across the absorber (4) minimum degree of recoverv of one or more solutes and, possibly, (5) the solvent to be employed. Items 3, 4, and 5 may be subject to economic considerations and therefore are sometimes left up to the designer. For determining the number of variables that must be specified in order to fix a unique solution for the design of an absorber one can use the same phase-rule approach described in Sec. 13 for distillation systems. 

To make the flaw grow, say by 1 mm, we have to tear the rubber to create 1 mm of new crack surface, and this consumes energy the tear energy of the rubber per unit area X the area of surface torn. If the work done by the gas pressure inside the balloon, plus the release of elastic energy from the membrane itself, is less than this energy the tearing simply cannot take place - it would infringe the laws of thermodynamics. 

Pressures Turboexpanders ean be designed to operate at up to 3,000 psi and higher inlet pressures as required by eonditions. Expansion pressure ratios ean also be adjusted for eaeh proeess over a wide range. A majority of effieient expansion ratios are below 5 1, although pressure ratios up to 10 1 ean be aeeommodated with reasonable effieieney. Smaller, lower pressure units are popular for air separation and helium liquefaetion. Intermediate pressure (100-1,000 psi) and high pressure expanders (1,000-3,000 psi) are widely used in natural gas proeessing and industrial gas liquefaetion. 

In most units, the flue gas pressure is reduced to atmospheric pressure across an orifice chamber. The orifice chamber is a vessel containing a series of perforated plates designed to maintain a given back-pressure upstream of the regenerator pressure control valve. 

A Hare stack was used to dispose of surplus fuel gas, from the gas holder by a booster through valves B and C. Valve C was normally left open because valve B was more accessible. One day the worker responsible for the gas holder saw that the gas pressure had started to fall. He got gas from another unit, but a half hour later the gas holder was sucked in. Another flare stack at a different plant had to be taken out of service for repair. A worker at this plant therefore locked open valves A and B so that he could use the "gas holder flare stack." He had done this before, though not recently, and some changes had been made since he last used the flare stack. He did not realize that this action would result in the gas holder emptying itself through valves C and B. He told three other men what he was going to do but he did not tell the gas holder worker because he did not know that this man needed to know. 

Equations (12.40) to (12.45) describe the velocities u, v, w, the temperature distribution T, the concentration distribution c (mass of gas per unit ma.ss of mixture, particles per volume, droplet number density, etc.) and pressure distribution p. These variables can also be used for the calculation of air volume flow, convective air movement, and contaminant transport. 

The flare stack shown in Figure 1.9 was used to dispose of surplus fuel gas, which was delivered from the gas holder by a booster through valves B and C. Valve C was normally left open because valve B was more accessible. One day the worker responsible for the gas holder saw that the gas pressure had started to fall. He therefore imported some gas from another unit. Nevertheless, a half hour later the gas holder was sucked in. 

The dimensionless ratio R is the ratio of the maximum deflagration pressure, in absolute pressure units, to the maximum initial pressure, in consistent absolute pressure units. For gas/air mixtures, R shall be taken as 9.0 for dust/air mixtures, R shall be taken as 10.0. 

The pressure drop due to condensing is usually negligible in a unit of this type. As a maximum, it may be taken as one half of the gas flow drop calculated for one baffle. This would be 1.16/8 = 0.145 psi for the condensing portion. Note that this does not recognize tube supports at 50% cut area, but for pressure units, this pressure drop will be nil. 

The effect of density of the air or gas entering the suction of the second (and/or third, etc.) fan is significant for high-pressure units operating individually above about 15 in. of water static. The static pressure rise in the second fan corrected for suction pressure is as follows, neglecting losses. ... 

Figure 23.8 is a schematic illustration of such a unit. It is desirable for each boiler to have its own economizer. Where one economizer is installed to take the exhaust gases from more than one boiler special considerations must be taken into account. These will include gas-tight isolation dampers. Consideration must be made of flue-gas pressures at varying loads and maximum and minimum combined heat load to match economizer and a pumped feedwater ringmain. Economizers may be used for both forced-draft and induced-draft boilers, and in both cases, the pressure drop through the economizer must be taken into account when sizing the fans. 

---