Evaporation Coefficient Of Water Research Articles

Analysis of the evaporation coefficients of water, heavy water, and methanol in a high vacuum environment

The evaporation coefficient of liquids is an important factor for many practical situations but has been poorly understood due to the complexity of the experiments and uncertainty in the measurements. Indeed, the lack of current knowledge about the nature of the evaporation coefficient prevents accurate confirmation of its value. We have determined the evaporation coefficients of three liquids, water, heavy water, and methanol, by fitting Knudsen's evaporation rate equation to past measurements of the temperature of droplet trains and liquid jets evaporating in a high-vacuumed environment. Analysis of available experimental data suggests the value of 1 for the evaporation coefficient (αe) of water, and 0.725 for that of heavy water. A small-jet methanol study predicts αe≈1; however, analysis of experimental data from a large-jet methanol study was an exception—indicating coefficients well over unity (1.5<αe<9). These exceed the suggested maximum theoretical value of unity. We found that considering αe=1 for water, and most of the test fluids, is a fair approximation in a high-vacuumed environment that presents minimal kinetic barriers to evaporation. These results confirm that water should not be considered an anomalous liquid with respect to evaporation. This study provides insight that will help improve the design and development of the many processes in which evaporation plays a key role.

Saliva Droplet Evaporation Experiment and Simple Correlation of Evaporation-falling Curve under Different Temperatures and RH

In the present study, water and saliva droplet evaporation rates are experimentally evaluated in various environmental conditions: temperature and relative humidity. We found that the ratio of saliva residue size to saliva initial droplet size is 0.216. We also found that the saliva correction factor which is defined as a ratio of water evaporation coefficient to saliva evaporation coefficient was not affected by environmental conditions and was determined as 0.857. By considering the evaporation and gravitational settling effects, the saliva airborne lifetime, i.e., the evaporation-falling curve is numerically calculated and characterized. In addition to this numerical calculation results, we present the simple correlation equation for obtaining the evaporation-falling curve under different temperatures and relative humidity.

Cracking prediction of germinated brown rice based on intragranular drying kinetics

During convective drying of wet granular materials like germinated brown rice (GBR), excessively high drying rates can lead to crack formation in the particles. However, cracking characteristics of GBR during exposure to different drying stages, unclear especially the critical conditions for cracking. In this study, experiments and numerical simulations were performed in an attempt to predict the cracking behavior of GBR under different drying stages through intragranular drying kinetics. Our results showed that the variations in cracking probability could be divided into three different stages. This phenomenon was dominated by the close relationship between particle strength and moisture gradient. The cumulative effect of moisture gradient is one of the important leading to crack initiation and evolution. Moreover, a prediction model of cracking probability as a function of drying time was proposed. Finally, the critical water evaporation coefficient was introduced to quantify the cracking safe region of GBR.

A scaling law of particle transport in inkjet-printed particle-laden polymeric drops

Hydrogels with embedded functional particulates are widely used to create soft materials with innovative functionalities. In order to advance these soft materials to functional devices and machines, critical technical challenges are the precise positioning of particulates within the hydrogels and the construction of the hydrogels into a complex geometry. Inkjet printing is a promising method for addressing these challenges and ultimately achieving hydrogels with voxelized functionalities, so-called digital hydrogels. However, the development of the inkjet printing process primarily relies on empirical optimization of its printing and curing protocol. In this study, a general scaling law is proposed to predict the transport of particulates within the hydrogel during inkjet printing. This scaling law is based on a hypothesis that water-matrix interaction during the curing of inkjet-printed particle-laden polymeric drops determines the intra-drop particle distribution. Based on the hypothesis, a dimensionless similarity parameter of the water-matrix interaction is proposed, determined by the hydrogel's water evaporation coefficient, particle size, and mechanical properties. The hypothesis was tested by correlating the intra-drop particle distribution to the similarity parameter. The results confirmed the scaling law capable of guiding ink formulation and printing and curing protocol.

Evapotranspiration and its components over a rainfed spring maize cropland under plastic film on the Loess Plateau, China

Aim of study: To determine seasonal variations in evapotranspiration (ET) and its components; and ascertain the key factors controlling ET and its components in a rainfed spring maize field under plastic film.Area of study: Shouyang County in Shanxi Province on the eastern Loess Plateau, ChinaMaterial and methods: Eddy covariance system combined with micro-lysimeters and meteorological observing instruments were used in the field. The manual method was used to measure the green leaf area index (GLAI) during the growing season.Main results: In 2015 and 2016, the growing season ET accounted for 80% and 79% of annual ET, respectively. Soil evaporation (E) accounted for 36% and 33% of the growing season ET in 2015 and 2016, respectively. The daily crop coefficient increased with increasing GLAI until a threshold of ~3 m2 m−2 in the canopy-increasing stage, and decreased linearly with decreasing GLAI in the canopy-decreasing stage. At equivalent GLAI, daily basal crop coefficient and soil water evaporation coefficient were generally higher in the canopy-increasing and -decreasing stages, respectively. During the growing season, the most important factor controlling daily ET, T, and E was net radiation (Rn), followed by GLAI for daily ET and T, and soil water content at 10-cm depth for daily E; during the non-growing season, daily ET was mainly controlled by Rn.Research highlights: The daily crop coefficient and its components reacted differently to GLAI in the canopy-increasing and -decreasing stages.

Influence of Soil Coverage on Evapotranspiration and Dual Crop Coefficients on Soybean

Crop coefficient (Kc) study is the main tool used to determine the plant water consumption enabling irrigation management. The dual Kc is related to the evaporation coefficient of water from the soil (Ke), therefore, the objective of the work was to evaluate the influence of the soil coverage, in the variability of the crop evapotranspiration (ETc) of soybean and the dual Kc. The Kc values were determined by the ratio between ETc and ETo (reference evapotranspiration). ETo was estimated using the methodology proposed by Penman-Monteith FAO-56. The ETc values were obtained by the water input and output ratio of the weighing lysimeters system for the culture development phases established as initial; development; intermediate and final. The culture presented a cycle of 118 days for both treatments; the volume of the water precipitated and supplied by irrigation was 786.4 and 89 mm, respectively. The water consumption determined by ETc during the crop cycle was 699.10; 672.57; 649.06; 724.02; 643.46 and 638.12 mm, respectively for levels 0; 2; 4; 6; 8 and 10 t ha-1 of the dry mass of Brachiaria. The average dual Kc obtained was 1.60; 1.48; 1.40; 1.53; 1.42 and 1.47, respectively for coverings and a reduction in Kc was observed for treatments with soil coverage. Yield and development of the root system, were increase on soil coverage of 2 and 4 t ha-1.

Evapotranspiration and crop coefficients in two irrigated wheat cultivars

ABSTRACT In the state of Mato Grosso, Brazil, wheat is an alternative to the current production system, mainly in irrigated crops, with new cultivars improved for this environment and system. The objective was to determine the evapotranspiration of the irrigated wheat crop and the dual coefficients of cultivars for the Brazilian Midwest. The experiment was conducted in the field using 12 weighing lysimeters and mini-lysimeters, filled by soil monoliths. The wheat cultivars BRS-254 and BRS-394 were used in the first and second years, respectively. Reference evapotranspiration was obtained by the Penman-Monteith equation and crop evapotranspiration by the mass difference in the lysimeters. Basal crop coefficient and soil water evaporation coefficient were determined according to the crop development stages in both years of cultivation. The mean ETc and ETo values were 3.87, 3.49 mm d-1 and 4.10 and 3.23 mm d-1, respectively, in the first and second cultivation cycles, with higher values of ETc recorded in the reproductive stages of the crop, flowering and grain filling. The basal crop coefficients and soil water evaporation coefficients estimated by weighing lysimeters composed of soil monoliths are: Kcb - 0.42, 0.78, 0.94, 0.74 and 0.47 and Ke - 0.72, 0.52, 0.39, 0.58 and 0.13 for the cultivar BRS-254, and Kcb - 0.28, 0.27, 0.65, 0.98 and 0.66 and Ke - 1.04, 0.96, 0.65, 0.34 and 0.51 for the cultivar BRS-394, at the stages of emergence, tillering, flowering, maturation and harvest, respectively.

基于改进的双作物系数法估算辽河三角洲芦苇湿地蒸散量

PDF HTML阅读 XML下载 导出引用 引用提醒 基于改进的双作物系数法估算辽河三角洲芦苇湿地蒸散量 DOI: 10.5846/stxb201810272317 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学青年基金项目（41405109）；辽宁省科技厅重点研发计划指导计划项目（2018108004）；中国气象局气候变化专项（CCSF201819） Evapotranspiration estimation of Phragmites australis wetland in the Liaohe River Delta based on the improved dual crop coefficient method Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以辽河三角洲湿地芦苇群落为研究对象，利用涡动相关通量、小气候梯度要素、群落内水面蒸发量以及芦苇群落生长参数等数据，基于FAO-56模型的双作物系数法，分别计算作物系数Kc、基础作物系数Kcb和水面蒸发系数Kw，分析其日变化动态及主导影响因子，建立基于生物因子和环境因子的小时尺度双作物系数模型。结果如下：（1）芦苇生长初期，Kc和Kcb的日变化呈现早晚高、中午略低的多峰波动曲线；在快速生长期和稳定生长期，Kc和Kcb白天波动幅度较小，早晚波动幅度较大；生长末期，Kc和Kcb夜晚波动幅度较大，白天呈现多峰波动曲线；Kw白天较小、夜晚较高，生长初期白天的数值显著高于其他时期。（2）相关分析表明，气温、相对湿度、风速、株高和叶面积指数是Kc、Kcb和Kw的影响因子；基于生物因子和环境因子重新构建双作物系数模型，基于改进的双作物系数法模拟芦苇群落蒸散，决定系数R2达0.894。（3）利用改进的双作物系数模型和FAO-56模型，对辽河三角洲芦苇群落的蒸发与蒸腾过程进行模拟，实现芦苇群落蒸发过程与蒸腾过程的分离，解决了实际观测无法直接获取芦苇群落蒸腾量的问题，同时提高了芦苇群落蒸散的模拟精度。（4）调整了FAO推荐的芦苇单作物系数常数值，调整后的作物系数更适用于辽河三角洲芦苇湿地。 Abstract:Phragmites australis wetland in the Liaohe River Delta of Northeastern China was selected as a research object. Based on the dual crop coefficient of FAO-56 model and the observed data (including flux data, microclimate gradient data, water evaporation, growth parameters of P. australis, etc.) in Panjin Wetland Ecosystem Research Station, the crop coefficient (Kc), the basal crop coefficient (Kcb), and the water evaporation coefficient (Kw) were calculated. The diurnal dynamics of three coefficients and their influencing factors were analyzed. Dual crop coefficient model at hour scale was established using the biological factors and environmental factors. The results are as follows:(1) In the initial growth stage, the diurnal variation of Kc and Kcb showed multi-peak fluctuation with higher values in the morning and evening and lower values at noon; during the rapid development and stable stage, the fluctuation ranges of Kc and Kcb were smaller in the daytime and larger at night; at the end of growth season, Kc and Kcb fluctuated greatly at night and presented multi-peak curves in the daytime. Kw was smaller in the daytime and higher at night, with the daytime values in the initial stage higher than those of the other stages. (2) The correlation analysis showed that the influencing factors of Kc, Kcb, and Kw were air temperature, relative humidity, wind speed, plant height, and leaf area index. The dual coefficient model was reconstructed with the biological and environmental factors. Thus, the simulation of the evapotranspiration in P. australis wetland was improved with the determination coefficient R2 reaching 0.894. (3) Using the improved dual crop coefficient model and FAO-56 model, the evaporation and transpiration of P. australis wetland in the Liaohe River Delta were simulated. This could solve the problem that transpiration is unobtainable from direct observation and improve the accuracy of evapotranspiration simulation. (4) We adjusted the constant value of P. australis crop coefficient recommended by FAO which was more suitable for the Liaohe River Delta wetland. 参考文献 相似文献 引证文献

Monitoring Crop Evapotranspiration and Crop Coefficients over an Almond and Pistachio Orchard Throughout Remote Sensing

In California, water is a perennial concern. As competition for water resources increases due to growth in population, California’s tree nut farmers are committed to improving the efficiency of water used for food production. There is an imminent need to have reliable methods that provide information about the temporal and spatial variability of crop water requirements, which allow farmers to make irrigation decisions at field scale. This study focuses on estimating the actual evapotranspiration and crop coefficients of an almond and pistachio orchard located in Central Valley (California) during an entire growing season by combining a simple crop evapotranspiration model with remote sensing data. A dataset of the vegetation index NDVI derived from Landsat-8 was used to facilitate the estimation of the basal crop coefficient (Kcb), or potential crop water use. The soil water evaporation coefficient (Ke) was measured from microlysimeters. The water stress coefficient (Ks) was derived from airborne remotely sensed canopy thermal-based methods, using seasonal regressions between the crop water stress index (CWSI) and stem water potential (Ψstem). These regressions were statistically-significant for both crops, indicating clear seasonal differences in pistachios, but not in almonds. In almonds, the estimated maximum Kcb values ranged between 1.05 to 0.90, while for pistachios, it ranged between 0.89 to 0.80. The model indicated a difference of 97 mm in transpiration over the season between both crops. Soil evaporation accounted for an average of 16% and 13% of the total actual evapotranspiration for almonds and pistachios, respectively. Verification of the model-based daily crop evapotranspiration estimates was done using eddy-covariance and surface renewal data collected in the same orchards, yielding an R2 ≥ 0.7 and average root mean square errors (RMSE) of 0.74 and 0.91 mm·day−1 for almond and pistachio, respectively. It is concluded that the combination of crop evapotranspiration models with remotely-sensed data is helpful for upscaling irrigation information from plant to field scale and thus may be used by farmers for making day-to-day irrigation management decisions.

Determination of crop and soil evaporation coefficients for estimating evapotranspiration in a paddy field

Accurate estimation of evapotranspiration is important in efficient water management for improving water use efficiency. In order to obtain evapotranspiration and evaporation beneath the canopy using the Food and Agriculture Organization (FAO) method, pan evaporation was used instead of reference evapotranspiration calculated by the Penman-Monteith equation with detailed meteorological data. The total crop coefficient and soil evaporation coefficient were determined using actual measured daytime evapotranspiration and evaporation by the Bowen ratio energy balance and lysimeter, respectively, in a rice paddy field in Japan. The average evapotranspiration was 5.3 mm/d, 4.4 mm/d, 7.4 mm/d and 6.3 mm/d and crop coefficient was 0.79, 1.18, 1.01 and 0.86 for the initial stage, development stage, middle-season stage and late-season stage, respectively. The evaporation was low and almost constant with an average value around 0.77 mm/d when the leaf area index (LAI) reached 3. The proposed average crop coefficients for different growing stages were applied to estimate daytime evapotranspiration and found suitable. A simple soil water evaporation coefficient model was developed using leaf area index for practical use and it was found that it could accurately estimate evaporation. Keywords: evapotranspiration, evaporation, paddy field, lysimeter, leaf area index (LAI), Bowen ratio energy balance DOI: 10.25165/j.ijabe.20171004.2290 Citation: Yan H F, Zhang C, Oue H, Peng G J, Darko R O. Determination of crop and soil evaporation coefficients for estimating evapotranspiration in a paddy field. Int J Agric & Biol Eng, 2017; 10(4): 130–139.

Surprising Effects of Hydrochloric Acid on the Water Evaporation Coefficient Observed by Raman Thermometry

The kinetics and energetics of cloud droplet and aerosol formation in the atmosphere are strongly influenced by the evaporation and condensation rates of water, yet the magnitude and mechanism of evaporation remains incompletely characterized. Of particular import (and controversy) is the nature of interfacial water pH and its potential effects on evaporation rate and environmental reactivity. We have used Raman thermometry measurements of freely evaporating microdroplets to determine evaporation coefficients (γ) for two different hydrochloric acid solutions, both of which result in a significant deviation from γwater. At 95% confidence, we find the evaporation coefficient for 1.0 M HCl to be 0.24 ± 0.04, a ∼60% decrease relative to pure water, and for 0.1 M HCl to be 0.91 ± 0.08, a ∼45% increase relative to pure water. These results suggest a large perturbation in the surface structure induced by either hydronium ions adsorbing to the water surface or by the presence of a Cl–···H3O+ ion-pair moiety in th...

English

The objective of the present study was to determine the crop coefficient (Kc) of wheat and soil water evaporation (Ke) in Maring&aacute;, PR, Brazil. Wheat crop evapotranspiration (ETc) was determined through the water balance method, using drainage lysimeters integrated with soil moisture measurements. The ETo was calculated using the Penman-Monteith equation with climate data from an automatic weather station, then Kc was calculated. Microlysimeters were built, using PVC pipes with 100 mm diameter and 150 mm length, which were weighted every day to obtain the quantity of water evaporated and then the soil water evaporation coefficient (Ke) was calculated. The calculated values of Kc were compared with values presented by FAO 56. The calculated Kc were 0.67, 0.67, 1.01, 1.03 and 0.42 for tillering, stem extension, heading, flowering and ripening, respectively. The values of Kc presented high correlation and precision as compared to FAO model. The values of evaporation determined through microlysimeters were greater as compared to the ETo during the beginning of the experiment, when soil was uncovered and decreased during the crop development. &nbsp; Key words: FAO 56, wheat, drainage lysimeters, microlysimeters, evapotranspiration.

The influence of the surface composition of mixed monolayer films on the evaporation coefficient of water.

We explore the dependence of the evaporation coefficient of water from aqueous droplets on the composition of a surface film, considering in particular the influence of monolayer mixed component films on the evaporative mass flux. Measurements with binary component films formed from long chain alcohols, specifically tridecanol (C13H27OH) and pentadecanol (C15H31OH), and tetradecanol (C14H29OH) and hexadecanol (C16H33OH), show that the evaporation coefficient is dependent on the mole fractions of the two components forming the monolayer film. Immediately at the point of film formation and commensurate reduction in droplet evaporation rate, the evaporation coefficient is equal to a mole fraction weighted average of the evaporation coefficients through the equivalent single component films. As a droplet continues to diminish in surface area with continued loss of water, the more-soluble, shorter alkyl chain component preferentially partitions into the droplet bulk with the evaporation coefficient tending towards that through a single component film formed simply from the less-soluble, longer chain alcohol. We also show that the addition of a long chain alcohol to an aqueous-sucrose droplet can facilitate control over the degree of dehydration achieved during evaporation. After undergoing rapid gas-phase diffusion limited water evaporation, binary aqueous-sucrose droplets show a continued slow evaporative flux that is limited by slow diffusional mass transport within the particle bulk due to the rapidly increasing particle viscosity and strong concentration gradients that are established. The addition of a long chain alcohol to the droplet is shown to slow the initial rate of water loss, leading to a droplet composition that remains more homogeneous for a longer period of time. When the sucrose concentration has achieved a sufficiently high value, and the diffusion constant of water has decreased accordingly so that bulk phase diffusion arrest occurs in the monolayer coated particle, the droplet is found to have lost a greater proportion of its initial water content. A greater degree of slowing in the evaporative flux can be achieved by increasing the chain length of the surface active alcohol, leading to a greater degree of dehydration.

Temperature dependence of the vapor pressure and evaporation coefficient of supercooled water

We report measurements of the vapor pressure of water over the supercooled temperature range 248 to 273 K derived from evaporation kinetics measurements of single water droplets. Accurate measurements of the relative humidity of the surrounding gas phase are derived from comparative and sequential measurements of the evaporation kinetics of droplets containing sodium chloride. The temperature dependence of the vapor pressure of supercooled water is shown to conform closely to the parameterization provided by Murphy and Koop (2005) once the uncertainties in experimental and thermophysical parameters are accounted for by ensuring an accurate representation of evaporation rates at temperatures above 273 K. Further, from a sensitivity analysis of all of the data over the full temperature range from 248 to 293 K, we can conclude that the evaporation coefficient of water, and thus the mass accommodation coefficient, is greater than, or equal to, 0.5.

Note: On the evaporation coefficient of water

Note: On the evaporation coefficient of water

J054031 音波共鳴法による水の蒸発係数測定([J05403]マイクロ・ナノスケールの熱流体現象(3))

We propose a new method for measurement of the evaporation coefficient using sound resonance experiment based on a theory of molecular gas dynamics. The evaporation coefficient is one of the parameters contained in the kinetic boundary condition. The evaporation coefficient of water is determined from the pressure amplitude of resonant sound wave in a cylindrical space bounded by a sound source and a vapor-liquid interface. By comparing the pressure amplitude with a linear theory based on molecular gas dynamics, we prove that the evaporation coefficient of water is about 1.0 around 300K.

Temperature Dependence of the Evaporation Coefficient of Water in Air and Nitrogen under Atmospheric Pressure: Study in Water Droplets

The evaporation coefficients of water in air and nitrogen were found as a function of temperature by studying the evaporation of a pure water droplet. The droplet was levitated in an electrodynamic trap placed in a climatic chamber maintaining atmospheric pressure. Droplet radius evolution and evaporation dynamics were studied with high precision by analyzing the angle-resolved light scattering Mie interference patterns. A model of quasi-stationary droplet evolution accounting for the kinetic effects near the droplet surface was applied. In particular, the effect of thermal effusion (a short-range analogue of thermal diffusion) was discussed and accounted for. The evaporation coefficient alpha in air and in nitrogen were found to be equal. The alpha was found to decrease from approximately 0.18 to approximately 0.13 for the temperature range from 273.1 to 293.1 K and follow the trend given by the Arrhenius formula. The agreement with condensation coefficient values obtained with an essentially different method by Li et al. [Li, Y.; Davidovits, P.; Shi, Q.; Jayne, J.; Kolb, C.; Worsnop, D. J. Phys. Chem. A. 2001, 105, 10627] was found to be excellent. The comparison of experimental conditions used in both methods revealed no dependence of the evaporation/condensation coefficient on the droplet charge nor the ambient gas pressure within the experimental parameters range. The average value of the thermal accommodation coefficient over the same temperature range was found to be 1 +/- 0.05.

Isotope Fractionation of Water during Evaporation without Condensation

The microscopic events engendering liquid water evaporation have received much attention over the last century, but remain incompletely understood. We present measurements of isotope fractionation occurring during free molecular evaporation from liquid microjets and show that the isotope ratios of evaporating molecules exhibit dramatic differences from equilibrium vapor values, strong variations with the solution deuterium mole fraction, and a clear temperature dependence. These results indicate the existence of an energetic barrier to evaporation and that the evaporation coefficient of water is less than unity. These new insights into water evaporation promise to advance our understanding of the processes that control the formation and lifetime of clouds in the atmosphere.

Molecular dynamics simulation of a thin water layer evaporation and evaporation coefficient

This work investigates the evaporation of a thin water layer into vacuum using molecular dynamics simulations based on TIP4P model for intermolecular potential. The results of simulation reveal micro-scale physical phenomena near the liquid–vapor interface such as evaporation, condensation, recoil after evaporation or condensation, and molecular exchanges. The simulations show that the hydrogen bond has a significant effect on the molecular behavior near the interface and may reduce the evaporation coefficient. This study also demonstrates that the combination of molecular dynamics simulations and the classical Schrage model may provide an elegant methodology to determine the evaporation coefficient of water at different temperatures or corresponding saturation pressures.

BASAL CROP COEFFICIENTS AND WATER USE FOR EARLY MATURITY COTTON

Field studies were conducted in central Arizona to develop basal crop coefficients (Kcb) for an earlymaturing,upland cotton. Cotton evapotranspiration (ETc) rates were determined from soil water depletion measurementsmade during the season in both small and large level basins in 1993 and 1994. Values for Kcb were developed from theETc data and an estimated grass-reference evapotranspiration (ETo), based on weather data. The basal cropcoefficient procedure presented in the recently published Food and Agriculture Organization (FAO), Irrigation andDrainage Paper No. 56 was used to estimate the soil water evaporation coefficient (Ke) following periods of irrigationand rain and, thus, quantify the amount of soil evaporation. A separate analysis was conducted to evaluate the waterstress coefficient (Ks) for conditions of low soil water. The developed Kcb data were used to derive two Kcb polynomialcurves as functions of days past planting (DPP) and cumulative growing degree days (CGDD). A third curve was derivedfrom the data using the FAO straight-line method. When used in irrigation management procedures, any of the threeKcb curves presented should result in good estimates of daily ETc for an early-maturity cotton, grown under climaticconditions similar to those for these studies.