Evaporative rate analysis

Methods for determining surface cleanliness are too involved for online evaluation, so that simple tests such as water break are employed. Recently, Buser reported a rapid method based on surface tension (15). Evaporative rate analysis (16) has also been used to determine surface cleanliness as well as more sophisticated methods employing scanning auger spectroscopy (17. 18). 

Determining when the coating film is completely cured is very important. The standard methods are generally well accepted, but the data obtained are not always reproducible. A new method called evaporation rate analysis (ERA) is the most objective and reproducible [107]. 

Evaporative rate analysis (ERA) measures the evaporation rate of a radioactive-tagged material from a surface. Organic contaminants dissolved in the solution reduce the evaporation rate and, by cahbration, the amount of organic present can be determined. The MESERAN (measurement and evaluation of surfaces by ERA), is a commercially available ERA instrument, Ruorescent molecules can be observed at high resolution using a laser confocal microscope (LCM). 

Evaporative rate analysis (ERA) (cleaning) Evaporative rate analysis measures the evaporation rate of a radioactive-tagged material that is absorbed by the contaminants on the surface. 

MERESAN Measurement and evaluation of surfaces by evaporative rate analysis... 

By assuming the Langmuir expression for the evaporation of a droplet with the Rosin-Rammler size distribution law, Sacks (74) found that the theoretical evaporation rate of a kerosine spray was about 100 times the experimentally observed values. He concluded that the Langmuir expression is based on the single drop and neglects the vapor pressure of the surrounding air, which would tend to inhibit vaporization in a spray. Consideration of the effects of dissociation of combustion products plus the effects of thermal conductivity for the vapors enabled Graves (33) to derive a theoretical curve for combustion rate which compared favorably with experimental data. However, the use of Probert s analysis to determine combustion efficiency, yielded efficiencies which were much lower than experimentally observed results. 

Evaporation rates for pheromone components under field conditions were measured by residual analysis. 

The final results depend upon the water analysis, which is no better than 3 significant figures because of the evaporation rate of the water. 

These two models illustrate how the properties of the compound influence the rate of evaporation from water under static conditions. Environmental conditions such as wind speed and turbulence in the water phase will have a marked influence on rates of evaporation that would reduce gradients and also reduce the width of the interfacial diffusion layers and systematic analysis of these effects have been discussed. Other variables will affect evaporation rates by controlling the actual concentration of the compound in solution. Suspended sediments and/or DOM would act in this manner. Weak acids and bases would only evaporate as the neutral species since the complementary anions or cations would be more water soluble and essentially have no vapor pressure. Consequently, environmental pH relative to pA values will be a consideration. It should be mentioned that compounds may distribute into the vapor phase by other processes than evaporation. Formation of aerosols, for example, can be a factor. 

The present model assumes that ingredients diffuse and evaporate independently, whereas thermodynamic and mass transport considerations dictate that interactions must occur in concentrated mixtures (Cussler, 1997). Careful analysis of the evaporation rates in Vuilleumier etal. (1995) shows this to be the case The musk ingredient, compound XII in Table 10.2, depressed the initial evaporation rates of... 

Vuilleumier, C., Flament, I., and Sauvegrain, R (1995). Headspace analysis study of evaporation rate of perfume ingredients applied onto skin. Ini J. Cosmet. Sci, 17, 61-76. 

---