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Capillary waves, surface waves whose restoring force is dominated by surface tension, have been an important part of experimental fluid mechanics for many years. Capillary waves are typically generated by a vibrating wave generator which may be the walls of the tank containing the liquid or a separate object. In both cases, a meniscus exists at the interface between the liquid and the wave generator. Though this meniscus is due to the same surface tension that controls capillary waves, its effect on capillary wave formation has not been studied. Herein we present experimental results showing that such a meniscus is needed to form capillary waves, that the lack of a meniscus (a flat interface at the wall) prevents the formation of these waves, and that a meniscus of either positive or negative curvature serves equally well in enabling capillary wave formation. [ABSTRACT FROM AUTHOR]

Knowledge of the evaporative loss from lakes and reservoirs is critical to water resources managers as well as to the overall understanding of the water balance in a given basin, geographical region, or continent. Existing methods for ascertaining evaporation from lakes and reservoirs include point measurements, water balance and mass transfer calculations, and proxy measurements using a pan. Point measurements using the eddy flux covariance method can be accurate, but are resource intensive and unsuited for determining spatial variation over a lake, or for obtaining measurements over many lakes. Mass balance methods cannot provide spatial variability and their accuracy depends on other portions of the water balance that can be challenging to obtain, such as leakage. Similarly, relatively recently deployed scintillation methods provide only an average for a strip across a lake and are also resource intensive and not suited for multi-lake studies. Evaporation pan measurements can also be used, though their accuracy is poor. Herein, we use a combination of Moderate Resolution Imaging Spectroradiometer (MODIS) satellite measurements of water surface temperature, measurements of wind speed, air temperature, and relative humidity from local NWS stations, and a mass transfer method, to demonstrate multi-lake evaporation measurements. Specifically, the seasonal variation in evaporation is obtained for the five major lakes in the Savannah River Basin (in South Carolina, USA): Lakes Jocassee, Keowee, Hartwell, Russell, and Thurmond. Since this approach requires only an existing satellite resource with global coverage and existing NWS stations, this method can potentially be ported to any lake where there is a nearby meteorology station. Hence, this method could be used by both water resource managers and limnologists alike. The possibility is discussed of extending this approach beyond a single basin to encompass an entire geographical region or continent. [ABSTRACT FROM AUTHOR]

Mesler entrainment has been studied extensively in water and, more recently, in silicone oils. Studies of Mesler entrainment in liquids other than these are rare. The extant experimental results in water show significant irreproducibility both in the qualitative characteristics of Mesler entrainment and in the existence or nonexistence of Mesler entrainment when, for example, drops of the same diameter are released from the same height. In contrast, in silicone oils, Mesler entrainment is highly reproducible, essentially occurring either all of the time, or none of the time for a given set of conditions. A goal of the present work was to determine which of these two behaviors is the 'standard' behavior-that is, to determine whether Mesler entrainment is typically repeatable or not. The experimental studies presented herein were conducted in three liquids that have not been the subject of detailed investigation to date: ethyl alcohol, isopropyl alcohol, and methyl alcohol. All of these alcohol results showed behavior very similar to that observed in silicone oils, suggesting that Mesler entrainment is typically repeatable and that water is an atypical fluid, causing irreproducible results. Additionally, we present data obtained in silicone oils and combine that with the alcohol data in an attempt to develop a combination of dimensionless groups that predicts the boundaries within which Mesler entrainment occurs for liquids other than water. [ABSTRACT FROM AUTHOR]

The cross-correlation between surface temperature and subsurface velocity is presented for water undergoing evaporative convection. The surface temperature measurements were obtained via quantitative infrared imaging, and the velocity measurements were obtained using a two-component laser Doppler velocimetry (LDV) system. The water surface was covered with a surfactant monolayer, which did not impede evaporation. The largest measured correlation coefficient was 0.375. Correlation coefficients obtained after shifting the velocity and temperature time traces with respect to each other revealed a peak in the correlation coefficient very close to a zero time shift. The significance of these results and their implications for the remote sensing of underwater objects via infrared imaging are discussed. [ABSTRACT FROM AUTHOR]

Measurements of the decay coefficient are presented for three different surfactants as a function of surface concentration. These measurements were obtained using a circular field of capillary waves. Data was purposely obtained close to the center of the tank, where the wave amplitude is large, and meniscus effects are expected to be small. The theory for linear, standing waves in a circular geometry is developed, without the usual assumption | kr|≫1. The surfactants investigated were: stearic acid, oleyl alcohol and hemicyanine. Measurements of the decay coefficient for hemicyanine have not been obtained heretofore. Several intrinsic benefits of the circular geometry are noted. The potential for improved accuracy in the measurement of surfactant properties using this geometry is suggested. [ABSTRACT FROM AUTHOR]

The effect of surfactants on gas exchange across an air/water interface populated with capillary waves, is considered. Experiments were conducted on capillary waves having a wavelength of 2.87 mm in the presence of oleyl alcohol and stearic acid, as well as on surfaces which were surfactant-free. The presence of these surfactants decreased the gas exchange rate by at most a factor of two when the energy delivered to the tank was held constant. Thus, even in the presence of surfactants, pure capillary waves still caused significant gas exchange, indicating that partially damped capillary waves may play an important role in air/sea gas exchange. When the gas exchange coefficient was plotted as a function of mean square slope, the presence of surfactants was found to negligibly affect the gas exchange rate, with the possible exception of the high wave slope regime for stearic acid. This result suggests that it is principally the kinematics of wave motion which accounts for the enhancement of transport due to the capillary waves investigated here. Moreover, these results agree with those obtained from polychromatic, wind-generated waves, suggesting that, for non-breaking waves, knowledge of the statistics of the wave field may be all that is required to parameterize the gas exchange coefficient. [ABSTRACT FROM AUTHOR]

A noninvasive method for obtaining quantitative images of differential diffusion in liquid-filled lung models is presented. The method utilizes planar fluorescence imaging to obtain differences in concentration fields and was tested on an oscillatory flow of water in a Y-shaped tube. Differences as large as 36% were measured between the concentration fields of two dyes having a factor of 15 difference in their diffusion coefficient. The method is applicable to the study of differential diffusion in any internal flow. The relevance to recent clinical studies of liquid phase respiration (Greenspan et al. 1990) is discussed. [ABSTRACT FROM AUTHOR]

Photobleaching of disodium fluorescein dissolved in water is experimentally investigated using laser induced fluorescence (LIF). It is demonstrated that significant photobleaching occurs on the millisecond time scale, resulting in a large decrease in the fluorescence signal emanating from a constant concentration sample. The importance of avoiding photobleaching when using LIF with disodium fluorescein for concentration measurements in water flow experiments is demonstrated. A half-life for photobleaching is introduced and measured for disodium fluorescein and is shown to be a more appropriate measure than the traditional 'bleaching quantum efficiency'. It is demonstrated that the photobleaching of disodium fluorescein is at least partially reversible. [ABSTRACT FROM AUTHOR]