Vapor pressure curve, water

Fig. 5. Vapor pressure of water over sulfuric acid solutions. Percentage of H2SO4 noted on each curve.

Assume that a boiler feed water is being pumped at 180 °F. Read the chart in Figure 3-46 and the water vapor pressure curve, and follow over to read NPSH reduction = 0.45 feet. A pump selected for the sertice requires 6 feet cold water service NPSHr ... 

A glance at the vapor pressure curve for butane will, however, reveal that in winter there is a possibility of butane vapor liquefying after the vaporizer if the temperature is allowed to fall in the pipeline, even at moderate pressure. For this reason, such pipework is usually heated, either by electrical tapes or, if available, by steam or hot-water lines. 

Fig. 4. The vapor pressure curves of pure water and of saturated aqueous...

The only parts of Fig. 5 which can meaningfully be described as solubility in a compressed gas are WX and XV. However, a very different situation arises if the saturated vapor pressure curve cuts the critical curve (M—N of Fig. 3). Figure 4 shows that this does not happen for the three sodium halides. The complete course of the critical curve is not known, but enough is known in the case of the sodium chloride system51 75 for it to be clear that it rises well above the maximum of the saturated vapor pressure curve. However, it is cut by the vapor pressure curves of less soluble salts such as sodium carbonate and sodium sulphate.40 87 The (p, T) projection of a system of the type water + sodium chloride is... 

Using the example of Reference [6], assume a pump with characteristic curve and added temperature rise data as shown on Figure 3-59 is to handle boiler feed water at 220°F, with a system available NPSHA = 18.8 feet. The vapor pressure of water at 220°F is 17.19 psia from steam tables and the SpGr = 0.957. Correcting the 18.8 feet NPSHa psia = 18.8 (l/[2.31/0.957)] = 7.79 psia at 220°F. 

A feature of the phase diagram in Fig. 8.12 is that the liquid-vapor boundary comes to an end at point C. To see what happens at that point, suppose that a vessel like the one shown in Fig. 8.13 contains liquid water and water vapor at 25°C and 24 Torr (the vapor pressure of water at 25°C). The two phases are in equilibrium, and the system lies at point A on the liquid-vapor curve in Fig. 8.12. Now let s raise the temperature, which moves the system from left to right along the phase boundary. At 100.°C, the vapor pressure is 760. Torr and, at 200.°C, it has reached 11.7 kTorr (15.4 atm, point B). The liquid and vapor are still in dynamic equilibrium, but now the vapor is very dense because it is at such a high pressure. 

Use the vapor-pressure curve in Fig. 8.3 to estimate the boiling point of water when the atmospheric pressure is... 

If the lid is removed, and the external surroundings have partial pressure Ph2o less than 23.8 Torr ( relative humidity < 100% ), then water will evaporate from the beaker into the surroundings until the beaker is empty, because only vapor is stable under these conditions. However, if the external surroundings have partial pressure Ph2o >23.8 Torr, water will condense from the surroundings to fill the beaker, because only liquid is stable under these conditions. Thus, the saturation vapor pressure ( 100% relative humidity ) corresponds to the unique concentration (partial pressure) of water vapor that can coexist at equilibrium in the atmosphere above liquid water at 25°C. Other (T, P) points on the vapor-pressure curve can be interpreted analogously. 

Figure 7.1-5. Pressure-temperature diagram of the system propane/water [13]. a, Propane gas/water b, propane gas/propane hydrate c, propane liquid/water d, propane liquid/propane hydrate e, propane gas/ice f, hydrate curve g, vapor pressure curve of propane.

The process of vaporization/condensation at constant temperature can be explained by the points D, E and F on Figure 2.1. Water either would condense or vaporize at constant temperature as the pressure approaches point E on the vapor-pressure curve. 

Liquid and vapor are at equilibrium along the vapor pressure curves shown for pure water (solid line) and an aqueous solution (dashed line). The vapor pressure is lower for the solution, in accord with Raoult s law, and thus the boiling point is increased (liquids boil at 1 atm)... 

Just as a solid has a characteristic melting point, a liquid has a characteristic boiling point. At one atmosphere, pure water boils at 100°C, pure ethanol (ethyl alcohol) boils at 78.5°C, and pure diethyl ether boils at 34.6°C. The vapor pressure curves shown in Fig. 

Figure 15.1 Diethyl ether, ethyl alcohol (ethanol), and water vapor pressure curves.

This paper deals with the degradation of substances like PVC, Tetrabromobisphenol A, y-HCH and HCB in supercritical water. This process is called "Supercritical Water Oxidation", a process which gained a lot of interest in the past. The difference between subcritical and supercritical processes is easy to recognize in the phase diagram of water. The vapor pressure curve of water terminating at the critical point, i.e. at 374 °C and 221 bar. The relevant critical density is 0.32 g/cm3. This corresponds to approx. 1/3 of the density of normal liquid water. Above the critical point, a compression of water without condensation, i.e. without phase transition is possible. It is within this range that supercritical hydrolysis and oxidation are carried out. The vapor pressure curve is of special importance in subcritical hydrolysis as well as in wet oxidation. 

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