Vaporization, retrograde

Unfortunately, the terminology applied to retrograde phenomena has not yet been standardized in the literature. The phenomena described as retrograde vaporization in the preceding pages are sometimes referred to as retrograde condensation and vice versa. Further-... 

The present invention effects a separation of hydrocarbon mixtures into fractions by taking advantage of the effects sometimes referred to as retrograde vaporization and retrograde condensation. These concepts are useful in explaining the theoretical and scientific background upon which the invention is based and will be discussed in detail hereinafter. ... 

Under some conditions, an isobaric increase of T can result in vaporization followed by condensation this is retrograde vaporization. 

New or improved methods are needed to measure local uptake experimentally. Such data can be used to verify the detailed dosage distribution predicted by the models. For example the retrograde catheter and tracheal cannula system used by Com et al. appears promising for transfer-coefficient measurements within segments of the tracheobronchial tree. A similar method was used by Battista and (3oyer to measure the absorption of acetaldehyde vapor in the dog lung. 

The effect of retrograde condensation on a crude oil component such as octane is particularly significant, and small amounts of these heavier components if left in the gas also have a great effect an hydrocarbon dewpoints. Even with extensive gas conditioning cooling it is difficult to remove all crude oil ccanpcnenta from the vapor streams at a pressure of 1500 psl. Note that the K-value for octane at 0°F and 1500 psi is not as low as at 100°F and 1000 psi. 

The pressure at which this dissociation is predicted to occur is called the hydrate pseudo-retrograde pressure at T. Pseudo-retrograde behavior is defined as the disappearance of a dense phase upon pressurization, which is counter-intuitive. This behavior resembles, but is not strictly the same as, vapor-liquid retrograde phenomena (de Loos, 1994). 

Figure 14.12 The top of the (vapor + liquid) isotherm for ( iAr + Kr) at T = 177.38 K. Point (c) is the intersection with the critical locus. The curve marked g gives the composition of the vapor phase in equilibrium with the liquid curve marked 1. The tubes shown schematically to the right demonstrate the changes in phase when the fluid is compressed at a mole fraction given by (a), or at a mole fraction corresponding to (b) where retrograde condensation occurs. Reprinted with permission from M. L. McGlashan, Chemical Thermodynamics, Academic Press, London, 1979, p. 276.

It predicts quite well vapor-liquid-phase equilibria for a multi-component system in the retrograde region but cannot predict the formation of a second liquid phase. 

Consider the enlarged nose section of a single PT loop shown in Fig. 12.5. The critical point is at C. The points of maximum pressure and maximum temperature are identified as MP and MT. The dashed curves of Fig. 12.5 indicate the fraction of the overall system that is liquid in a two-phase mixture of liquid and vapor. To the left of the critical point C a reduction in pressure along a line such as BD is accompanied by vaporization from the bubble point to the dew Point, as would be expected. However, if the original condition corresponds to Point F, a state of saturated vapor, liquefaction occurs upon reduction of the pressure and reaches a maximum at G, after which vaporization takes place until the dew point is reached at H. This phenomenon is called retrograde condensation. It is of considerable importance in the operation of certain deep natural-gas wells where the pressure and temperature in the underground forma-... 

Normal condensation. Retrograde condensation.—The consideration of limiting lines plays an important rdle in all the researches relative to the liquefaction and vaporization of fluid mixtures. The detailed anal3rsis of these researches would exceed the plan of this work so we shall not give it. We shall be content to notice a remarkable consequence of the preceding theories. 

Two further interesting points emerge from a study of fig. 16.5. If the system is maintained at a pressure and the temperature raised, initially only liquid is present. When the liquid curve is crossed at G, A aporization begins. Now, in general, a horizontal line will cut the curve again at a point on the vapour branch of the curve, and this will correspond to complete vaporization. In this particular case, however, the line cuts the liquid curve again at D, between L and K, and at this point the vapour disappears. This phenomenon is known as retrograde... 

Experimental measurements of heat transfer coefficients are reported for three binary mixtures near their lower consolute points. Two of these, respectively n-pentane and n-decane in solution with supercritical CO2, involve vapor--liquid equilibrium whereas the third, triethylamine--water, involves liquid--liquid equilibrium. Anomalously high heat transfer coefficients were found for the supercritical mixtures at compositions which condense on heating (retrograde condensation). 

In our heat transfer experiments, bulk fluid conditions were chosen to be just below the phase coexistence curve on either side of the lower consolute point. Thus, on heating at constant pressure, either evaporation of a liquid or condensation (retrograde) of a vapor took place once a small excess of test section surface temperature over bulk fluid temperature occurred. To be specific, the retrograde condensation region of the vapor--liquid phase coexistence curve of Figure 1 is the region of positive slope to the right of the LCST. 

The hypothesis advanced here is that the observed enhancement is due to thermocapillarity arising from the temperature dependence of the interfacial tension. Although we know of no theory for such a Marangoni effect in binary condensation per se, theory does exist for both mass transfer (M. 11) and heat transfer (16, 12) aeross an interface in the absence of bulk flow. We note that the sign of the derivative of the interfacial tension with respect to temperature is positive near a lower consolute point and that this is in the correct direction to sustain disturbances in condensation rate. Thus, in retrograde condensation, provided a critical temperature gradient normal to the interface is exceeded, a local increase in condensation flux toward the vapor liquid interface will result in its cooling. 

In a dew point flash, the fraction vapor is set at the unity limit, at a specified temperature or pressure. The dependent variables are the pressure or temperature, the heat duty, and the liquid and vapor compositions. The only product is a saturated vapor with composition equal to that of the feed. The equilibrium liquid composition corresponds to the first liquid drop resulting from infinitesimal condensation. As in the bubble point flash, dew points can exist only within certain ranges of temperature and pressure. Referring to Figure 2.1, no dew points can exist at temperatures above the cricondentherm or at pressures above the cricondenbar. At temperatures or pressures where retrograde condensation can occur, there can be two dew points a normal dew point and a retrograde dew point. 

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