Liquid drops in gases

In general, oscillations may be oblate-prolate (H8, S5), oblate-spherical, or oblate-less oblate (E2, FI, H8, R3, R4, S5). Correlations of the amplitude of fluctuation have been given (R3, S5), but these are at best approximate since the amplitude varies erratically as noted above. For low M systems, secondary motion may become marked, leading to what has been described as random wobbling (E2, S4, Wl). There appears to have been little systematic work on oscillations of liquid drops in gases. Such oscillations have been observed (FI, M4) and undoubtedly influence drag as noted earlier in this chapter. Measurements (Y3) for 3-6 mm water drops in air show that the amplitude of oscillation increases with while the frequency is initially close to the Lamb value (Eq. 7-30) but decays with distance of fall. 

For liquid drops in gases the terminal velocity is so large that the inequality is obeyed and oscillation has essentially no effect on transfer. For drops and bubbles in liquids, the effect of oscillation on transfer is significant. 

Liquid Drops in Gases Liquid drops falling in stagnant gases appear to remain spherical and follow the rigid sphere drag relationships up to a Reynolds number of about 100. Large drops will deform,... 

An objection to this theory is that it has been based on data from the saturated vapors of the fuels and not from dilute air-vapor mixtures. The existence of liquid drops in the dilute fuel mixture drawn through the carburetor, hot intake manifold, and mixed with the hot residual gases in the hot cylinder is doubtful. Also, the fact that such extremely volatile fuels as ethyl ether knock strongly cannot be explained. The fact that some of the most volatile gasolines knock more readily than heavier grades has been attributed to the presence of impurities in the latter which act in an antiknock capacity. 

The amount of processing required in the field depends upon the composition of the gas and the temperature and pressure to which the gas will be exposed during transportation. The process engineer is trying to avoid liquid drop-out during transportation, since this may cause slugging, corrosion and possibly hydrate formation (refer to Section 10.1.3). For dry gases (refer to Section 5.2.2) the produced fluids are... 

Heat exchangers for liquids normally have a pressure drop in the range 0.35 to 0.7 bar (see Chapter 15). For gases, heat exchangers have a pressure drop typically between 1 bar for high-pressure gases (10 bar and above), down to 0.01 bar for gases under vacuum conditions (see Chapter 15). 

The increase in velocity seen as part of the Venturi effect simply demonstrates that a given number of fluid particles have to move faster through a narrower section of tube in order to keep the total flow the same. This means an increase in velocity and, as predicted, a reduction in pressure. The resultant drop in pressure can be used to entrain gases or liquids, which allows for applications such as nebulizers and Venturi masks. 

Different gases (such as nitrogen) are normally used as the adsorbate if the surface area of a solid needs to be examined. The gas is cooled by liquid nitrogen. The tap to the sample bulb is opened, and the drop in pressure is determined. In the surface area calculations, a value of 0.162 nm2 is used for the area of an adsorbed nitrogen molecule. 

Give 0.2 ml of cone, sulfuric acid to 1 - 2 ml of aqueous sample. Concentrate the liquid carefully in a hood at about 130 °C and then heat to 280 °C until white fog appears. After cooling, add one to two drops of cone, nitric add and heat again until nitrous gases are visible. After cooling, add 2 ml of Soln. D, boil the solution for a short period, and fill up to 5.0 ml with ddH20. 

As indicated in Chapter 2, liquid drops falling through gases have such extreme values of y and k that they must be treated separately from bubbles and drops in liquids. Few systems have been investigated aside from water drops in air, discussed above, and what data are available for other systems (FI, G5, L5, V2) show wide scatter. Rarely have gases other than air been used, and some data for these cases [e.g. (L5, N2)] cannot be interpreted easily because of evaporation and combustion effects. Results for drops in air at other than room temperature (S8) differ so radically from results of other workers that they cannot be used with confidence. 

This form of correlation was used by Beard (B3) to suggest a correlation for water drops in air under different atmospheric conditions. It should be used with caution for gases with properties widely different from air under atmospheric conditions, but the range of liquid properties covered is broad. 

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