Over-pressure ratio

Fig. 7.28. Calculated maximum over-pressure ratio (referred to the initial pressure) in the exothermic centre for stoichiometric methane, acetylene, ethylene and ethane with air at (a) 1 atm, (b) 1500 K. Initial radius of the centre is 1 mm. Geometry is cylindrical. From...

Rotary compressors are also PDC types, but where refrigerant flow rotates during compression. Unhke the reciprocating type, rotaiy compressors have a built-in volume ratio which is defined as volume in cavity when the suc tion port is closed (V = m vj over the volume in the cavity when the discharge port is uncovered (V = m vj). Built-in volume ratio determines for a given refrigerant and conditions the pressure ratio which is ... 

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. 

Figure 1-3. Development of engine pressure ratio over the years.

Figure 2-21 show the effect of 5% by weight of steam injection at a turbine inlet temperature of 2400 °F (1316 °C) on the system. With about 5% injection at 2400°F (1316 °C) and a pressure ratio of 17 1, an 8.3% increase in work output is noted with an increase of about 19% in cycle efficiency over that experienced in the simple cycle. The assumption here is that steam is injected at a pressure of about 60 psi (4 Bar) above the air from the compressor discharge and that all the steam is created by heat from the turbine exhaust. Calculations indicate that there is more than enough waste heat to achieve these goals. 

Large power turbines over 50 80 MW, these are frame-type turbines, the new large turbines are operating at very high firing temperatures about 2400°F (1315°C) with cooling provided by steam, at pressure ratios approaching 35 1. 

Application of this procedure to inadvertently ignited safety valve discharges can involve a special problem. Certain combinations of pressure ratio and length of safety valve riser can result in choked flow, with a pressure discontinuity at the exit. The pressure of the jet then adjusts to atmospheric pressure in a system of shock waves or expansion waves over a distance of a few pipe diameters. These waves can affect the local mixing of the jet with the crosswind. Since the calculation procedure incorporates correlations for subsonic jets, it cannot be expected to be entirely accurate in this case. Nevertheless, since the wave system... 

Plots of efficiency against pressure ratio for the full injection EGT plant, for a maximum to minimum temperature 5, are shown in Fig. 6.9, compared with lower values of efficiency in the dry CBTX plant. There are. several points to be noted first that an increase in efficiency is worthwhile, up to 10% secondly that the total water injection is up to over 10% of the air mass flow and thirdly that the optimum pressure ratio increases to about 8, from about 5 for that of the dry cycle. 

Overdriven Detonation The unstahle condition that exists during a defla-gration-to-detonation transition (DDT) before a state of stable detonation is reached. Transition occurs over the length of a few pipe diameters and propagation velocities of up to 2000 m/s have been measured for hydrocarbons in air. This is greater than the speed of sound as measured at the flame front. Overdriven detonations are typically accompanied by side-on pressure ratios (at the pipe wall) in the range 50-100. A severe test for detonation flame arresters is to adjust the run-up distance so the DDT occurs at the flame arrester, subjecting the device to the overdriven detonation impulse. 

The gas continues to expand isentropically and the pressure ratio w is related to the flow area by equation 4,47. If the cross-sectional area of the exit to the divergent section is such that >r 1 = (10,000/101.3) = 98.7, the pressure here will be atmospheric and the expansion will be entirely isentropic. The duct area, however, has nearly twice this value, and the flow is over-expanded, atmospheric pressure being reached within the divergent section. In order to satisfy the boundary conditions, a shock wave occurs further along the divergent section across which the pressure increases. The gas then expands isentropically to atmospheric pressure. 

Most fluidized-bed processes operate within the temperature and pressure ranges of ambient to 1100°C and ambient to 70 bar, respectively. Over this temperature range, gas viscosity increases by a factor of about 3 to 4, depending upon the type of gas. If the pressure of the system remains constant while temperature is changed, the gas density decreases over this temperature range by a factor of 1373/293 = 4.7. If system pressure is increased without changing temperature, the gas density is increased by the same factor as the pressure ratio—which would be approximately 70 1 for a change in pressure from ambient to 70 bar. 

The calculation to determine the expansion factor can be completed once y and the frictional loss terms 2 Kf are specified. This computation can be done once and for all with the results shown in Figures 4-13 and 4-14. As shown in Figure 4-13, the pressure ratio ( f - P2)/Pi is a weak function of the heat capacity ratio y. The expansion factor Yg has little dependence on y, with the value of Yg varying by less than 1 % from the value at y = 1.4 over the range from y = 1.2 to y = 1.67. Figure 4-14 shows the expansion factor for y = 1.4. 

S02 vapor pressure (pgn2) was measured by dynamic saturation and by a gas-sensing S02 electrode over solutions containing 0.5 to 2.0 M sodium citrate at pH 3.5 to 5 with up to 1 M NaHSOj, Na2S04, and NaCl. Pgo2 was measured at 25° to 168°C pH at 25° to 95°C. Both pH and the vapor pressure ratio Ps02/pH20 were independent of temperature. The composition and temperature dependence of the data are correlated by the semiempirical expressions ... 

There are few studies in literature reporting pure gas permeabilities as well as separation factors of mixtures. Vuren et al. (1987) reported Knudsen diffusion behavior of pure gases for y-alumina membranes with a mean pore radius of 1.2 nm. Separation experiments with a 1 1 H2/N2 mixture showed, that the theoretical Knudsen separation factor [of 3.7, Equation 6.4)j for this mixture could be obtained (Keizer et al. 1988 see also Figure 6.2). In Figure 6.2, the effect of process parameters is also demonstrated. The separation factor is a function of the pressure ratio over the membrane, which is the ratio of the pressure on the permeate-side to that on the feed-side. For pressure ratios approaching unity, which means the pressure on both sides of the... 

The recuperated Brayton cycle approaches Carnot efficiency in the ideal limit. As compressor and turbine work are reduced, the average temperatures for heat addition and rejection approach the cycle limit temperature. The limit is reached as compressor and turbine work (and cycle pressure ratio) approach zero and fluid mass flow per unit power output approaches infinity. It can be expected from this that practical recuperated Brayton cycles would operate at relatively low pressure ratios, but be very sensitive to pressure drop. With tire assumption of constant gas specific heat over the cycle temperature range, a good assumption for helium, the cycle efficiency of a recuperated Brayton cycle may be expressed ... 

Substituting t = t T, V = V g,. .. with t = avll3g 213,. .. from the top right-hand columns, we find that ph vh and g disappear (a valuable check on the algebra) and leave only the ratios of a, jS,. .. These equations are given in lines % for Stokes law , for the mass transfer nr, for the over-pressure due to surface tension and for the gas law in the first equality of the line (the second equality is obtained by substituting for nr). There are two coefficients composed of physical quantities K for mass transfer and 2 for surface tension. If the numerical constants are chosen to be... 

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