No description available.

In the arid southwestern United States, where water is a limiting factor in agricultural and industrial development, a sizeable portion of the annual precipitation may be lost through evapotranspiration. In Arizona such losses account for approximately 95 per cent of the annual precipitation. Tamarisk (Tamarix pentandra Pall.) is estimated to occupy over one million acres of the flood plains and streambanks in the southwest. Although reported to use a large quantity of water, accurate estimates of evapotranspiration are unknown. Evapotranspiration processes are complex and depend on many interrelationships of the soil-plantatmosphere system. Although, water use by tamarisk has been intensively studied, evapotranspiration measurements under different climatic and hydrologic conditions are not available. The evapotranspiration tent was selected to measure evapotranspiration rates of tamarisk under varying climatic and hydrologic conditions. Intensive investigations of the enclosure effect of the tent were performed. Modifications of the tent reduced serious enclosure effects of the original tent. Evapotranspiration rates measured by the tent agreed favorably with rates computed by Penman's equation. Evapotranspiration rates for an area where the water table depth was approximately 20-feet was greater than an area where the Water table depth was 14-feet. This deviation, which may be attributed to salinity, led to a laboratory investigation of the effects of salinity on transpiration rates of tainarisk. An intensive laboratory study was conducted to determine the effect of salinity on transpiration rates of tamarisk at different vapor pressure deficits. Results indicated that the effect of salinity is dependent on vapor pressure deficit. Transpiration rates were linearily related to vapor pressure deficits at low salinity levels, but a curvilinear relationship was obtained at high salinity levels. An estimate of saturation deficit of the mesophyll cells was determined by extrapolation of transpiration and vapor pressure deficit relationships. These data indicate minimial increases in salt concentrations in the stomatal cavities as indicated by small increases in the mesophyll saturation deficits as the salinity of the root substrate was increased. Root permeability tests were conducted on plants subjects to varying salinity and vapor pressure deficit levels. Results indicated a significant reduction only at the highest salinity and vapor pressure deficit levels.

No description available.

In this experimental investigation the evaporative behaviour of liquid droplets of both pure fluids and fluids containing nanoparticles was studied. Initial tests were conducted on drops of pure volatile liquids using IR thermography, and the effect of substrate material, drop composition, and substrate temperature was investigated. The effect of the addition of nanoparticles to the liquid drops was then investigated using a contact angle analyser which could record the drop profile in time. The effects of liquid composition, nano-particle composition, nanoparticles concentration, substrate hydrophobicity, and substrate temperature were all studied. Results obtained from IR thermography showed that there exists interfacial temperature instabilities in evaporating volatile drops, the appearance of these fluctuations was found to be dependent on the liquid and substrate in question and are self generated temperature gradients resulting from non-uniform evaporation. A stability analysis was conducted and the results give a good agreement with experimental results. The addition of nanoparticles to a liquid drop was found to alter the evaporative behaviour by enhancing pinning of the drop contact line and preventing the drop radius from shrinking. By manipulating the concentration of the particles suspended in a drop, a stick-slip evaporative process was achieved, leading to rings of particulate material formed upon total evaporation. By varying parameters such as substrate hydrophobicity, nanoparticle concentration, liquid composition, and substrate temperature, many distinct nanoparticle deposit patterns were observed upon total evaporation. It was shown that by varying these parameters, many different patterns could be achieved, and that inside these deposit patterns regular formations such as particulate rings, radial lines, and cellular structures were present.

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Recent studies showed that evaporation of water can induce surface tension gradients along the water surface and ultimately lead to convection, known as Marangoni convection. This study was devoted to visualization and characterization of the evaporation-induced, surface-tension-driven convection in water using laser-based measurement techniques. The evaporation of water at various low vapor-phase pressures in the absence of buoyancy driven flow was investigated. Strong symmetric convection was observed and its velocity field was measured using stereo particle image velocimetry. The temperature field obtained from using both a thermocouple and planar laser induced fluorescence indicated that no buoyancy driven flow was generated. The strength of the convection was found to be correlated with the evaporation rate of water. In addition, the estimated Marangoni number exceeded the critical value for onset of Marangoni convection. It can be concluded that the observed evaporative convection of water can only be Marangoni convection.

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The research described in this dissertation is predicated on the hypothesis that remotely sensed information from climatological satellites can be used to estimate the actual evapotranspiration from agricultural crops to improve irrigation scheduling and water use efficiency. The goal of the enabling research program described here was to facilitate and demonstrate the potential use of satellite data for the rapid and routine estimation of water use by irrigated crops in the Yaqui Valley irrigation scheme, an extensive irrigated area in Sonora, Mexico. The approach taken was first, to measure and model the evapotranspiration and crop factors for wheat and cotton, the most common irrigated crops in the Yaqui Valley scheme. Second, to develop and test a high-resolution (4 km x 4 km) method for determining cloud cover and solar radiation from GOES satellite data. Then third, to demonstrate the application of satellite data to calculate the actual evaporation for sample crops in the Yaqui Valley scheme by combining estimates of potential rate with relevant crop factors and information on crop management. Results show that it is feasible to provide routine estimates of evaporation for the most common crops in the Yaqui Valley irrigation scheme from satellite data. Accordingly, a system to provide such estimates has been established and the Water Users Association, the entity responsible for water distribution in Yaqui Valley, can now use them to decide whether specific fields need irrigation. A Web site (tekapucemitson. mx) is also being created which will allow individual farmers to have direct access to the evaporation estimates via the Internet.

No description available.

The ζ-adsorption isotherm was used along with Gibbsian thermodynamics to determine an expression for the surface tension of solid-vapour interface. This expression was examined at low pressures to predict the surface tension of solids in the absence of adsorption, γS0. The method indicated the same value of γS0 for a solid using different vapour adsorption isotherms. A method based on the system stability was developed to predict the contact angle. The findings indicated that the contact angle is a thermodynamic property which depends on the state of the system. Furthermore, the dependence of contact angle on the curvature of three-phase contact line was described by the adsorption at the solid-liquid interface without the introduction of line tension. The energy transport mechanisms during steady-state evaporation of water-sessile droplets were studied. By suppressing the buoyancy-driven convection, the active modes of energy transport were thermal conduction and thermocapillary convection. The experiments on Cu, Au (111) and PDMS showed that the dominant mode of energy transport varies along the liquid-vapor interface. Near the droplet apex, thermal conduction provides enough energy for the evaporation. However, close to three-phase contact line where most of the evaporation occurs, thermocapillary convection is by far the dominant mode of energy transport. In the evaporation experiments on PDMS, the measured directions of thermocapillary convection were opposite of the predicted ones by other studies, since the energy carried by thermocapillary convection was neglected in the previous studies. The study was followed by examination of temperature boundary condition and energy transport at the solid-liquid interface. It was concluded that there is an adsorbed layer at the solid-liquid interface with different thermal properties compared to those of bulk liquid phase. This layer causes a resistance (Kapitsa resistance) and consequently a temperature discontinuity at the adsorbed layer-bulk liquid interface. Due to the high resistance at this interface, only a small portion of energy conducted by solid substrate enters directly to the bulk liquid phase. The remainder was transported through the adsorbed layer to the three-phase contact line. This energy was then distributed along the liquid-vapour interface by thermocapillary convection to be consumed by the evaporation process.