Water vapor pressure-temperature curves

Curve AB is a portion of the vapor pressure-temperature curve of liquid water. At any temperature and pressure along this line, liquid water is in equilibrium with water vapor. At point A on the curve, these two phases are in equilibrium at 0°C and about 5 mm Hg (more exactly, 0.01°C and 4.56 mm Hg). At B, corresponding to 100°C, the pressure exerted by the vapor in equilibrium with liquid water is 1 atm this is the normal boiling point of water. The extension of line AB beyond point B gives the equilibrium vapor pressure of the liquid above the normal boiling point. The line ends at 374°C, the critical temperature of water, where the pressure is 218 atm. 

Comprehensive tables of vapor-pressure data of common liquids, such as water, common refrigerants, and others, may be found in Refs. [2,3]. For most liquids, the vapor-pressure data are obtained at a few discrete temperatures, and it might frequently be necessary to interpolate between or extrapolate beyond these measurement points. At a constant pressure, the Clausius-Clapeyron equation relates the slope of the vapor pressure-temperature curve to the latent heat of vaporization through the relation... 

Vapor pressure-temperature curves for ethyl ether, ethyl alcohol, and water. 

Interpolation beriveen data For such common liquids as water, many refrigerants, and others, the vapor-pressure-temperature curve has been established at many points. For most liquids, however, only relatively few data are available, so that it is necessary frequently to interpolate between, or extrapolate beyond, the measurements. The curve on arithmetic coordinates (Fig. 7.1) is very inconvenient for this because of the curvature, and some method of linearizing the curve is needed. Most of the common methods stem from the Clausius-Clapeyron equation, which relates the slope of the vapor-pressure curve to the latent heat of vaporization... 

Fig. 2.26. Range of carbon dioxide fugacity (fco ) and temperature for the propylitic alteration (epidote zone) in the Seigoshi area and same active geothermal systems. Seigoshi = propylitic alteration of the Seigoshi district. The curves A-B and A -B are equilibria for epidote (Xpis = 0.30) - K-mica (oK-mica = 0-9) -K-feldspar (aK-feidspar = 0.95) - calcite assemblages at saturated water vapor pressure condition (Shikazono, 1985a).

The work of Sihvonen is complicated not only by its tremendous volume but also by its rather limited accessibility. He has given a review of his work with a fairly complete bibliography (68) another review contains a considerable number of experimental curves (66). At very high temperatures (> 1400° C.) both Meyer and Sihvonen independently observed effects that have not been observed by any other workers. The C + H20 reaction becomes zero-order with respect to water vapor pressure and the activation energy has a value of about 90 keal. per mole (52, 65, 66). Meyer reports identical Arrhenius plots for C + C02 and C -f H20 in this region. The C + 02 reaction... 

Figure A2.1.2 Effect of temperature on vapor pressure measurement. The upper curve is the vapor pressure of pure water, pw°. The lower curve is a system whose partial water vapor pressure, pw, is always a constant fraction of the vapor pressure of pure water. See text for details.

The influence of temperature on the measurement is best illustrated by referring to Figure A2.1.2. Here, the upper curve represents the vapor pressure of pure water, pw°, as a function of temperature, and the lower curve represents a system whose partial water vapor pressure is always a constant fraction, a, of the vapor pressure of pure water. The points E and G representpw° at temperatures T and T2, respectively. The points F and H represent pw at temperatures 7 , and T2, respectively. At both Tx and T2, the ratio of the vapor pressures [pw/pw°]r is a (i.e., the ratios of the lines BF/BE and the lines DH/DG are both equal to a). 

The results of this experiment (Fig. 3) confirmed their suggestion the experimental points practically coincide with the temperature dependence curve of water vapor pressure, especially if one takes into account that the accuracy of the determinatbn of the celt opening temperature was 2"C... 

Fig. 12-1. Surface temperatures expected on the three planets Venus, Earth, and Mars as a function of the water vapor pressure. An increase in the vapor pressure increases the retention of infrared radiation in the atmosphere, raising the temperature via the greenhouse effect. Overlaid is the phase diagram of water. On Earth and Mars the starting (radiation equilibrium) temperatures are low enough for water to condense out when the temperature intersects the condensation curve. On Venus, the temperature rises more rapidly and runs away. [Adapted from Walker (1977), originally modeled by Rasool and DeBergh (1970).]...

The considered radial process in the bentonite annulus is a complicated one with coupled, highly nonlinear flows that involve many things. There are liquid flow and vapor flow as well as conductive and convective heat flow depending on gradients in pressure, water vapor density and temperature. The flow coefficients depend on water properties such as saturation water vapor pressure and dynamic viscosity of water. They also depend on the properties of bentonite water retention curve, hydraulic conductivity and water vapor diffusion coefficient, and thermal conductivity, all of which are functions of degree of water saturation. 

We changed the ammonia concentration and water vapor pressure and measured the ammonia sensor s output under various combinations of the two. The sensor reading response took several seconds because responses took time even if water vapor pressure was varied while keeping ammonia concentration at zero. We attributed this response time to the responsiveness of the system as a whole. The sensor s output was tested in ambient temperature, which varies with time. The response time curve of sensor has been observed at different concentration. Our ammonia sensor is quite capable of detecting even low ammonia concentrations of about 0.01 ppm. 

State of drying of foods [26-29], The peak due to water vaporization in calorimetric curves often masks other phenomena of interest, such as the crystallization or decomposition of carbohydrates. To observe such effects, analyses have to be performed on samples in sealed crucibles (or under pressure). In such cases, however, it is important, for reasons of safety, to remember that the water vapor pressure increases rapidly with temperature, especially above 150°C. At 300 C, the water vapor pressure already amounts to 85 bars ... 

The swelling strain based on ideal mixing and the real swelling strain are plotted together as functions of water activity in Fig. 3. The curves are almost super-posable. Also there is no discemable difference in the water sorption at different temperatures at the same water activity water sorption increases exponentially with the same temperature dependence as the water vapor pressure [e.g., given by the Antoine equation (3)]. 

Isotherms and isobars are drawn from thermal gravimetric measurements using a Me Bain balance well suitable to impose water vapor pressures controlled by means of a "cold point" (ref. 16). The curves are constructed in graduated steps by increasing (or decreasing) pressure or temperature in small successive increments. Before each experiment, the zeolite is activated in situ at 400°C at 10 1 Pa. For adsorption the initial state is the activated state at 350 C, either at a pressure p under isobaric conditions, or at a pressure of 101 Pa under isothermal conditions. The final state is a state close to saturation. For desorption measurements the previous defined initial and final states are reverse. 

Walker [1955] has shown that the thermal dehydration of vermiculite passes through a phase in which there are alternating hydrated and dehydrated layers, and this has been confirmed by Weiss and Roland [1956]. Cillery [1959] has studied the adsorption-desorption characteristics of synthetic smectites in humid atmospheres. He finds that well-defined hydrates exist at definite water vapor pressures, and between the ranges of existence of the hydrates mixed-layer phases are formed. With montmorillonite also, he finds a tendency toward the appearance of a large spacing X-ray diffraction band, indicating hydration in alternate layers. A detailed study of the low-temperature dehydration of montmorillonites and the temperature-pressure curves for montmorillonite, saponite, and vermiculite with various ions has been made by Cowley and Roy [1959]. They find the partly dehydrated phases consist of a mixed-layer structure with fully hydrated and fully dehydrated layers. 

Fig. 1. Pressure required for propagation of decomposition flame through commercially pure acetylene free of solvent and water vapor in long horizontal pipes. Gas initially at room temperature ignition by thermal nonshock sources. Curve shows approximate least pressure for propagation (0), detonation,...

Adsorption Plots. Isotherm plots are the most common method of presenting adsorption data. An isotherm is a curve of constant temperature the adsorbed water content of the adsorbent is plotted against the water partial pressure in equiHbrium with the adsorbent. An isostere plot shows curves of constant adsorbed water content the vapor pressure in equiHbrium with the adsorbent is plotted against temperature. Figure 13 shows isosteres for the three primary adsorbents described previously. In this case, the dew points for the three adsorbents are plotted at 0.5, 5, and 10 kg... 

Figure 28 shows the key features of the humidity chart. The chart consists of the following four parameters plotted as ordinates against temperature on the abscissas (1) Humidity H, as pounds of water per pound of dry air, for air of various relative humidities (2) Specific volume, as cubic feet of dry air per pound of dry air (3) Saturated volume in units of cubic feet of saturated mixture per pound of dry air and (4) latent heat of vaporization (r) in units of Btu per pound of water vaporized. The chart also shows plotted hiunid heat (s) as abscissa versus the humidity (H) as ordinates, and adiabatic humidification curves (i.e., humidity versus temperature). Figure 28 represents mixtures of dry air and water vapor, whereby the total pressure of the mixture is taken as normal barometric. Defining the actual pressure of the water vapor in the mixture as p (in units of mm of mercury), the pressure of the dry air is simply 760 - p. The molal ratio of water vapor to air is p/(760-p), and hence the mass ratio is ... 

If, instead, the air is damped adiabatically with the wet cloth, so that the state of the air varies, the cloth will settle to a slightly different temperature. Each state of air (0, x) is represented by a certain wet bulb temperature 6, which can be calculated from Eq. (4.116) or its approximation (4.123), when the partial pressures of water vapor are low compared with the total pressure. When the state of air reaches the saturation curve, we have an interesting special case. Now the temperatures of the airflow and the cloth are identical. This equilibrium temperature is called the adiabatic cooling border or the thermodynamic wet bulb temperature (6 ). 

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. 

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