Effect of Dissolved Air

Effect of Dissolved Air. The presence of dissolved air in a sample can give rise to two effects (a) a reaction between the sample and the dissolved air, (b) a multicomponent mixture effect. Kay and co-workers have shown that, for substances for which it is expected that the second effect is the most important, usually the critical pressure is most affected and often the difference between degassed and air-saturated samples is 0.02 to 0.03 MPa. The critical temperatures of air-saturated substances were found to differ by up to 0.9 K from those of degassed substances. However, many substances and mixtures react with dissolved air and in such cases often the observed critical properties vary with time. 

Decomposition of the Sample. Many substances decompose near their critical points and a large number of mixtures which do not react at room temperature, react at the critical point. It is obviously important that decomposition or reaction of the components in a mixture is kept to a minimum and the extent of reaction is known. A simple check is to measure the critical properties of both of the pure components and one mixture as a function of the time the sample has been kept near the critical point.  

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Most measurements of densities of liquids below their normal boiling points are made in the presence of air. Densities reported here refer to liquids in equilibrium with a gas phase consisting of a mixture or air and vapor at a total pressure of one atmosphere below the normal boiling point and of vapor at the equilibrium vapor pressure above the boiling point. Thus air is not regarded as an impurity. The effect of dissolved air and other gases on the densities of liquid hydrocarbons has been reported by Ashcroft and Ben Isa [97-ash/ben], The differences they observed between the density of a liquid saturated with air at 1 atm and 298.15 K and the air free liquid are shown in Table 1. 

Figure 4 — Time effects of dissolved air on pump s NPSH...

The difference between a freezing point determined in the presence of air at a pressure of one atmosphere and the triple-point temperature will depend on the effect of dissolved air and on the pressure difference. The presence of dissolved gas in the liquid phase always lowers the transition temperature. The amount by which it does so can be calculated from the freezing point depression equations if the solubility is known and ideal behaviour is assumed. The effect of pressure can be calculated from the Clapeyron equation... 

Steinke ME, Kandlikar SG (2004) Control tind effect of dissolved air in water during flow boiling in microchannels, Int. J. Heat tind Mass Trtinsfer 47 1925-1935... 

Very recently, Zhang et al. investigated the effect of dissolved air on the behaviour of water in a very thin gap between a hydrophobic and a hydrophilic surface [16]. They found that very thorough degassing had no influence on film behaviour, which suggests that if a thin gap is present between liquid and solid this is more likely to be vapour or vacuum than air. 

For oxidative detection removal of dissolved air from the mobile phase is necessary to prevent air bubble formation at the column outlet, which disturbs the electrolysis process. Vacuum filtration usually is sufficient to remove enough air for bubble-free operation. However, air readily redissolves in the mobile phase. Continuous helium sparging is therefore the only effective degassing method for longer periods. 

The corrosion rate of steel increases proportionally with temperature up to about 180°F (80°C) in open air systems. At higher temperatures, oxygen is driven from the system and corrosion rates decline significantly. The effect of dissolved oxygen on the rate of mild steel corrosion is shown in FIGURE 6-13. 

What is the effect of dissolved salt on air-water partitioning How is this effect related to the total salt concentration ... 

Cathodic protection is sometimes beneficial to avoid cavitation, not because of the reduced rate of corrosion but because of the cushioning effect of hydrogen evolved on the surface. Removal of dissolved air is often beneficial because dissolved gases more easily nucleate cavitating bubbles at low pressures. 

Gas impurities. Limited gas solubility can provoke formation gas phase (nucleation), contenting not a vapour but this gas mainly. This effect will decrease Th-Tn as well. In our runs this effect is not important as concentrations of dissolved air and hydrogen jr oxygen are negligible. 

Carbon dioxide from air dissolves in water to make carbonic acid, which has two acidic protons. Later in this chapter, we explore potential effects of dissolving massive amounts of this acid in the ocean. Carbonic acid from CO2 and amino acids from proteins are examples of polyprotic acids—those having more than one acidic proton. 

Henry found that lead dissolves in water impregnated with nitrous air (nitric oxide), investigated the effect of fixed air (carbon dioxide) on plants, and the preservation of sea water from putrefaction by quicklime. He published on the advantages of literature and philosophy, on magnesia, and on fermentation (including a substitute for yeast), He published Memoirs of Albert de Haller Warrington, 1783 (price 2S. 6d.). Some of Henry s writings were collected and published (price 2S. 6d.) as ... 

Recycling the eluent is often effective in removing reactive components Once stable iso-cratic chromatography has been achieved, the eluent can be recycled from a vessel covered for minimizing solvent evaporation and dust collection. It is usual to recycle the eluent for some hours up to a few weeks and, provided that the solvent reservoir is sealed, the eluent composition only changes slowly with time. This enables the detector to remain switched on continuously in order to achieve maximal stability since the electrolyzed mobile phase contains lower amounts of dissolved air and electroactive substances. The column performance will also be more stable. Recycling is best for... 

The vapor pressure may be dependent on the amount of the dissolved, not the entrained, air in the Hquid. This issue is important to appHcations of cooling-water double-suction pumps (58,59). Because of the unknowns, a safety margin is always recommended for use to minimise the effects of cavitation. 

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