Vapor measurement

The proper installation of both orifice plates and Venturi-type flow tubes requires a length of straight pipe upstream and downstream of the sensor, ie, a meter mn. The pressure taps and connections for the differential pressure transmitter should be located so as to prevent the accumulation of vapor when measuring a Hquid and the accumulation of Hquid when measuring a vapor. For example, for a Hquid flow measurement in a horizontal pipe, the taps are located in the horizontal plane so that the differential pressure transmitter is either close-coupled or connected through downward sloping connections to allow any trapped vapor to escape. For a vapor measurement in a horizontal pipe, the taps should be located on the top of the pipe and have upward sloping connections to allow trapped Hquid to drain. 

FIGURE 6.25 Because enthalpy is a state property, the enthalpy of sublimation can be expressed as the sum of the enthalpies of fusion and vaporization measured at the same temperature. 

Generation of Material Vapors. The magnitude of heat required to generate vapors from a material depends on the thermal stability of the material. As the temperature or heat flux is increased, generation rate of vapors, measured in terms of mass loss of the material, increases and the following relationship is satisfied (2,3) ... 

Wiederhold, P.R. 1997. Water Vapor Measurement Methods and Instrumentation . Dekker, New York. 

The result of the uncertainty analysis was promising. The expected relative uncertainty with respect to the sought quantities is in the range of 7%, with a 95% confidence interval. The most uncertain measurand is the water vapor, that is, the water vapor measurements are believed to contribute the biggest error. 

Sorokin and Lankard illuminated cesium and rubidium vapors with light pulses from a dye laser pumped by a ruby giant-pulse laser, and obtained two-step excitation of Csj and Rbj molecules (which are always present in about 1 % concentration at atomic vapor pressures of 10" - 1 torr) jhe upper excited state is a repulsive one and dissociates into one excited atom and one ground-state atom. The resulting population inversion in the Ip level of Cs and the 6p level of Rb enables laser imission at 3.095 jum in helium-buffered cesium vapor and at 2.254 pm and 2.293 /zm in rubidium vapor. Measurements of line shape and frequency shift of the atomic... 

Scottish chemist, physicist, and physician. Professor of chemistry at Glasgow. He clearly characterized carbon dioxide ( fixed air ) as the gas which makes caustic alkalies mild, and distinguished between magnesia and lime. He discovered the latent heats of fusion and vaporization, measured the specific heats of many substances, and invented an ice calorimeter. 

Because enthalpy is a state function, the enthalpy of sublimation of a substance is the same whether the transition takes place in one step, directly from solid to gas, or in two steps, first from solid to liquid, then from liquid to gas. The enthalpy of sublimation of a substance must therefore be equal to the sum of the enthalpies of fusion and vaporization measured at the same temperature (Fig. 6.23) ... 

TDLAS System Hardware for Water Vapor Measurement... 

The regression equation constants found from enthalpy-of-formation data for the 1-chloro31a and l-iodoalkanes31b, and the 2-methyl-2-chloroalkanes are close enough to those generated from direct enthalpy-of-vaporization measurements to conclude that the selected values are reasonably accurate, at least with respect to their differences. 

We start with their simplest systems and we first consider the parent hydrocarbons benzene and cyclopropane themselves. This enthalpy of formation difference (5i9(Ph, cypr H) is (29.3 0.9) kJ mol Turning now to the simple alkyl derivatives, and 1 and 11, X = Me in particular, we recall that there are no direct experimental data for the enthalpy of formation of gaseous methylcyclopropane but only for the corresponding liquid. Accepting the archival enthalpy of vaporization value from Kolesov and Kozina " is equivalent to accepting their value for the enthalpy of formation of methylcyclopropane,.namely 24.3 kJ mo We so deduce a value for (5i9(Ph, Cypr Me) of [26.1 ( >0.9)] kJ mol some 3 kJ moT different fom that for the parent hydrocarbons. We are not particularly bothered by this 3 kJ moT discrepancy—we recall in footnote 23 a 6 kJmoT spread of values suggested for the enthalpy of vaporization of methylcyclopropane. It is conceptually simplest, and procedurally most precise, to use the identical approach to compare ethylbenzene and ethylcyclopropane, for there are no enthalpy of vaporization measurements for the latter 3MR species. Encouragingly, consistency of results is obtained —the value of i9(Ph, Cypr Et) equal to 26.5 kJmoT is nearly identical to that of i9(Ph, Cypr Me). 

Baseline drift compensation using this synchronous modulation/detection strategy requires a significant amount of additional hardware to be built around the sensor. Consider, for example, a vapor-measurement instrument. In this case, the modulator could consist of a valve that can alternately expose the sensor to... 

A number of alternative vaporization processes have previously been suggested for K2SO4. However, one or more of the postulated reaction products [K20( ,g), S03(g)] have a sufficiently positive free energy of formation so that the proposed alternate reaction paths lead to an insignificant partial pressure of evaporation products compared to reactions [1] and [2]. Most of the previous K2SO4 vaporization measurements are thought to be in error because of container material reactions or, possibly, creep of liquid K2SO4 from the metal container (usually a platinum metal). 

We do not measure water vapor directly in the stratosphere. Again we can possibly infer it from the hydrate ion distribution, but this is more difficult because here you have to rely on a thermodynamic equilibrium distribution, which can be altered due to the electric field. Therefore we feel that this method is not very useful because there exist better methods for measuring water vapor. Therefore I simply cannot argue the question. There are no parallel water vapor measurements. As far as the troposphere is concerned, the dew point is measured on the earth in parallel to the nitric acid measurements. But here, as you have seen, we have only so far obtained four data points and that would be premature to discuss anything. 

Can this formula (6) represent with sufficient exactness the tensions of saturated vapors measured by observers This is a question treated by many authors and which has been recently examined in a very thorough manner by J. Bertrand. ... 

None of these vapor measurements distinguish the H bonding interaction specifically but combine it with the intermolecular attraction. In generd, this means they have an additional deficiency relative to the spectral methods. 

B. Equilibrium Water Vapor Measurement in a Sealed Vial... 

Figure 21 Temperature and water vapor concentration during freeze-drying [22], Temperature measured with ( ) BTM, ( ) Pt 100 water vapor measured with mass spectrometer.

Venus atmosphere is so dry that Earth-based and spacecraft measurements of the water-vapor abundance are extremely difficult. Historically, many of the in situ water-vapor measurements gave values much higher than the actual water-vapor content. However, reliable values are now available from several sources including the Pioneer Venus mass spectrometer, spectrophotometer experiments on Venera 11-14, Earth-based FTIR spectroscopy of Venus lower atmosphere on the nightside, and IR observations during the Galileo and Cassini flybys of Venus. 

These values were based on the heat capacity and enthalpy of vaporization measurements of Hlldenbrand et... 

Somorjai and Lester [40] detail some of the problems likely to be encountered in vaporization measurements. These include (i) the effects of variations of with crystal surface, which are particularly important in the use of polycrystalline samples (ii) the self-cooling resulting from the endothermic vaporization, which may cause temperature gradients in the sample, especially at high fluxes and (iii) the complications caused by vapour-vapour collisions when measurements are made in a significant partial pressure of vapour. 

The relevant point here is that a gas collected over water is moist that is, it is saturated with water vapor. Measuring the atmospheric pressure at which the gas is collected, we can write... 

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