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1
Gelderblom, Hanneke, Oscar Bloemen und Jacco H. Snoeijer. „Stokes flow near the contact line of an evaporating drop“. Journal of Fluid Mechanics 709 (31.08.2012): 69–84. http://dx.doi.org/10.1017/jfm.2012.321.
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AbstractThe evaporation of sessile drops in quiescent air is usually governed by vapour diffusion. For contact angles below $9{0}^{\ensuremath{\circ} } $, the evaporative flux from the droplet tends to diverge in the vicinity of the contact line. Therefore, the description of the flow inside an evaporating drop has remained a challenge. Here, we focus on the asymptotic behaviour near the pinned contact line, by analytically solving the Stokes equations in a wedge geometry of arbitrary contact angle. The flow field is described by similarity solutions, with exponents that match the singular boundary condition due to evaporation. We demonstrate that there are three contributions to the flow in a wedge: the evaporative flux, the downward motion of the liquid–air interface and the eigenmode solution which fulfils the homogeneous boundary conditions. Below a critical contact angle of $133. {4}^{\ensuremath{\circ} } $, the evaporative flux solution will dominate, while above this angle the eigenmode solution dominates. We demonstrate that for small contact angles, the velocity field is very accurately described by the lubrication approximation. For larger contact angles, the flow separates into regions where the flow is reversing towards the drop centre.
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Anderson, Bruce T., Alex C. Ruane, John O. Roads und Masao Kanamitsu. „Estimating the Influence of Evaporation and Moisture-Flux Convergence upon Seasonal Precipitation Rates. Part II: An Analysis for North America Based upon the NCEP–DOE Reanalysis II Model“. Journal of Hydrometeorology 10, Nr. 4 (01.08.2009): 893–911. http://dx.doi.org/10.1175/2009jhm1063.1.
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Abstract In this paper, a diagnostic metric—termed the local-convergence ratio—is used to analyze the contribution of evaporation and atmospheric moisture-flux convergence to model-based estimates of climatological precipitation over the North American continent. Generally, the fractional evaporative contribution is largest during spring and summer when evaporation is largest and decreases as evaporation decreases. However, there appears to be at least three regions with distinct spatiotemporal seasonal evolutions of this ratio. Over both the northern and western portions of the continent, the fractional evaporative contribution peaks in spring and early summer and decreases during fall and into winter. Over the northern portion, this fall decrease is related to an increase in atmospheric moisture-flux convergence associated with enhanced meridional moisture fluxes into the region; over the western coastal regions, the fall decrease in evaporative contribution is associated with a decrease in evaporation and an increase in total moisture-flux convergence, most likely associated with increased storm activity. In contrast, over the central portions of the continent, the fractional evaporative contribution to precipitation remains relatively low in spring—when enhanced low-level jet activity increases the low-level atmospheric moisture flux convergence into the region—and instead peaks in summer and fall—when the moisture-flux convergence associated with the low-level jet decreases and precipitation is balanced predominantly by local evaporation. Finally, over the southwestern United States and northwestern Mexico, the fractional evaporative contribution to precipitation is found to contain a wintertime minimum as well as a secondary minimum during summer. This latter feature is due to a substantial increase in low-level atmospheric moisture-flux convergence associated with the large-scale monsoon circulation that influences this region during this time.
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Rassam, Daud W., und David J. Williams. „A numerical study of steady state evaporative conditions applied to mine tailings“. Canadian Geotechnical Journal 36, Nr. 4 (22.11.1999): 640–50. http://dx.doi.org/10.1139/t99-030.
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The suction profile of a desiccating soil is dependent on the water table depth, the soil-water retention characteristics, and the climatic conditions. In this paper, an unsaturated flow model, which simulates both liquid and vapour flow, was used to investigate the effects of varying the water table depth and the evaporation rate on the evaporative fluxes from a desiccating tailings deposit under steady-state conditions. Results obtained showed that at a critical evaporation rate, beyond which evaporation is no longer dictated by climatic conditions, the matric suction profiles remain basically unchanged. The critical evaporation rate varies inversely with the water table depth. It is associated with the maximum evaporative flux that might be extracted from a soil at steady-state conditions. The time required to establish steady-state conditions is directly proportional to the water table depth, and it acquires a maximum value at the critical evaporation rate. A detailed investigation of the movement of the drying front demonstrated the significance of attaining a matric suction of about 3000 kPa on the contribution to flow in the vapour phase.Key words: matric suction, mine tailings, potential evaporation, steady state evaporative conditions, surface evaporative flux.
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Harris, Daniel J., Jacinta C. Conrad und Jennifer A. Lewis. „Evaporative lithographic patterning of binary colloidal films“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 367, Nr. 1909 (28.12.2009): 5157–65. http://dx.doi.org/10.1098/rsta.2009.0157.
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Evaporative lithography offers a promising new route for patterning a broad array of soft materials. In this approach, a mask is placed above a drying film to create regions of free and hindered evaporation, which drive fluid convection and entrained particles to regions of highest evaporative flux. We show that binary colloidal films exhibit remarkable pattern formation when subjected to a periodic evaporative landscape during drying.
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Anderson, Bruce T., Guido Salvucci, Alex C. Ruane, John O. Roads und Masao Kanamitsu. „A New Metric for Estimating the Influence of Evaporation on Seasonal Precipitation Rates“. Journal of Hydrometeorology 9, Nr. 3 (01.06.2008): 576–88. http://dx.doi.org/10.1175/2007jhm968.1.
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Abstract The objective of this paper is to introduce a diagnostic metric—termed the local-convergence ratio—that can be used to quantify the contribution of evaporation (and transpiration) to the atmospheric hydrologic cycle, and precipitation in particular, over a given region. Previous research into regional moisture (or precipitation) recycling has produced numerous methods for estimating the contributions of “local” (i.e., evaporated) moisture to climatological precipitation and its variations. In general, these metrics quantify the evaporative contribution to the mass of precipitable water within an atmospheric column by comparing the vertically integrated atmospheric fluxes of moisture across a region with the fluxes via evaporation. Here a new metric is proposed, based on the atmospheric moisture tendency equation, which quantifies the evaporative contribution to the rate of precipitation by comparing evaporative convergence into the column with large-scale moisture-flux convergence. Using self-consistent, model-derived estimates of the moisture-flux fields and the atmospheric moisture tendency terms, the authors compare estimates of the flux-based moisture-recycling ratio with the newly introduced local-convergence ratio. Differences between the two ratios indicate that they can be considered complementary, but independent, descriptors of the atmospheric hydroclimatology for a given region.
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Suchan, Jared, und Shahid Azam. „Datasets for the Determination of Evaporative Flux from Distilled Water and Saturated Brine Using Bench-Scale Atmospheric Simulators“. Data 7, Nr. 1 (22.12.2021): 1. http://dx.doi.org/10.3390/data7010001.
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Evaporation from fresh water and saline water is critical for the estimation of water budget in the Canadian Prairies. Predictive models using empirical field-based data are subject to significant errors and uncertainty. Therefore, highly controlled test conditions and accurately measured experimental data are required to understand the relationship between atmospheric variables at water surfaces. This paper provides a comprehensive dataset generated for the determination of evaporative flux from distilled water and saturated brine using the bench-scale atmospheric simulator (BAS) and the subsequently improved design (BAS2). Analyses of the weather scenarios from atmospheric parameters and evaporative flux from the experimental data are provided.
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DasGupta, S., I. Y. Kim und P. C. Wayner. „Use of the Kelvin-Clapeyron Equation to Model an Evaporating Curved Microfilm“. Journal of Heat Transfer 116, Nr. 4 (01.11.1994): 1007–15. http://dx.doi.org/10.1115/1.2911436.
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A Kelvin–Clapeyron change-of-phase heat transfer model is used to evaluate experimental data for an evaporating meniscus. The details of the evaporating process near the contact line are obtained. The heat flux and the heat transfer coefficient are a function of the film thickness profile, which is a measure of both the intermolecular stress field in the contact line region and the resistance to conduction. The results indicate that a stationary meniscus with a high evaporative flux is possible. At equilibrium, the augmented Young–Laplace equation accurately predicts the meniscus slope. The interfacial slope is a function of the heat flux.
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Panwar, Annu, Maik Renner und Axel Kleidon. „Imprints of evaporative conditions and vegetation type in diurnal temperature variations“. Hydrology and Earth System Sciences 24, Nr. 10 (20.10.2020): 4923–42. http://dx.doi.org/10.5194/hess-24-4923-2020.
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Abstract. Diurnal temperature variations are strongly shaped by the absorption of solar radiation, but evaporation, or the latent heat flux, also plays an important role. Generally, evaporation cools. Its relation to diurnal temperature variations, however, is unclear. This study investigates the diurnal response of surface and air temperatures to evaporative conditions for different vegetation types. We use the warming rate, defined as the increase in temperature in response to absorbed solar radiation in the morning, and evaluate how it changes with evaporative fraction, which is an indicator of the evaporative conditions. Results for 51 FLUXNET sites show that the warming rate of air temperature carries very weak imprints of evaporative fraction across all vegetation types. However, the warming rate of surface temperature is highly sensitive to evaporative fraction with a value of ∼23×10-3 K (W m-2)-1, indicating stronger evaporative cooling for moister conditions. Contrarily, the warming rates of surface and air temperatures are similar at forest sites and carry literally no imprints of evaporative fraction. We explain these contrasting patterns with an analytical surface energy balance model. The derived expressions reproduce the observed warming rates and their sensitivity to evaporative fraction in all vegetation types. Multiplying the warming rate with daily maximum solar radiation gives an approximation for the diurnal surface temperature range (DTsR). We use our model to compare the individual contributions of solar radiation, evaporative conditions, and vegetation (by its aerodynamic conductance) in shaping DTsR and show that the high aerodynamic conductance of forests reduces DTsR substantially more (−56 %) than evaporative cooling (−22 %). We further show that the strong diurnal variation in aerodynamic conductance (∼2.5 times of the mean across vegetation types) reduces DTsR by ∼35 % in short vegetation and savanna but only by ∼22 % in forests. We conclude that diurnal temperature variations may be useful for predicting evaporation for short vegetation. In forests, however, the diurnal variations in temperatures are mainly governed by their high aerodynamic conductance, resulting in negligible imprints of evaporative conditions.
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Suchan, Jared, und Shahid Azam. „Influence of Desaturation and Shrinkage on Evaporative Flux from Soils“. Geotechnics 2, Nr. 2 (22.05.2022): 412–26. http://dx.doi.org/10.3390/geotechnics2020019.
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An assessment of evaporation losses from soils is critical for sustainable agriculture in semi-arid regions. The purpose of this research was to determine the effect of desaturation and shrinkage on evaporative flux from representative soils. Results indicated that the surface area did not change for silty sand (6% volume reduction) and substantially increased for lean clay (17% volume reduction). The evaporative flux for silty sand decreased from 31 to 25 mg/m2∙s in Stage II, remained constant during Stage III, and decreased to 11 mg/m2∙s in Stage IV. In contrast, the lean clay showed a longer Stage II (34 to 14 mg/m2∙s), a near constant Stage III, albeit a similar Stage IV (13 to 3 mg/m2∙s). The air entry and residual suction values were 1 kPa and 100 kPa for silty sand and 5 kPa and 1400 kPa for lean clay. In both soils, the total suction merged with the matric suction at Stage II–Stage III boundary. Furthermore, the shrinkage curve was J-shaped for silty sand with the only void ratio decrease in Stage II, whereas that for the lean clay showed a significant void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV. Under high demand, the silty sand exhibited Stage III and Stage IV evaporation, whereas the lean clay also showed significant flux during Stage II. For the investigated range of water content, the total water loss under high demand was found to be 7 times that under low demand.
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Suchan, Jared, und Shahid Azam. „Influence of Saline Pore Fluid on Soil Behavior during Evaporation“. Geotechnics 2, Nr. 3 (02.09.2022): 754–64. http://dx.doi.org/10.3390/geotechnics2030036.
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Saline conditions govern soil behavior during evaporation, thereby affecting the water budget in semi-arid regions. This research examined the effects of saline pore fluid on soil behavior during evaporation. The results indicated volumetric reductions of about 5% for silty sand and about 15% for lean clay. The evaporative flux for silty sand decreased from 26 mg/m2∙s to 22 mg/m2∙s in StageII, remained at a constant flux in StageIII, and decreased to 13 mg/m2∙s in StageIV. The air entry and residual suction values were found to be 5 kPa and 100 kPa, respectively, and the total suction of about 5000 kPa merged with matric suction near the Stage II/Stage III boundary. The swell–shrink curve (SSC) was J-shaped with the only void ratio decrease in Stage II. In contrast, the evaporative flux for lean clay decreased from 30 mg/m2∙s to 15 mg/m2∙s in StageII, to 10 mg/m2∙s in StageIII, and then to 5 mg/m2∙s in StageIV. The air entry and residual suction values were 5 kPa and 2000 kPa, respectively, and the total suction during Stage II and Stage III ranged from 1000 kPa to 6000 kPa, with an average value of 3500 kPa. The SSC showed a major void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV. Under high demand, the evaporative flux for silty sand was constant at 180 mg/m2∙s in StageIII and decreased to 50 mg/m2∙s in Stage IV, whereas it decreased for the lean clay from 230 mg/m2∙s to 145 mg/m2∙s in StageII, to 95 mg/m2∙s in StageIII, and then to 25 mg/m2∙s in StageIV. For both soils, the total water loss was found to be six times higher than that under low demand.
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Li, Xinhu, und Fengzhi Shi. „Salt precipitation and evaporative flux on sandy soil with saline groundwater under different evaporation demand conditions“. Soil Research 60, Nr. 2 (18.10.2021): 187–96. http://dx.doi.org/10.1071/sr21111.
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Context Salt precipitation and its influence on evaporation have been widely studied in recent years. However, the evolution process of salt precipitation and evaporative flux is poorly understood under various evaporation demand (ED) rate condition, which is defined as the evaporation rate of distilled water from soil under constant radiation conditions. Aims and methods This study investigated the evolution of salt crust and evaporative flux on sand soil columns with fixed saline groundwater at a depth of 20 cm under four ED conditions (29.5, 21.5, 9.0 and 4.0 mm day−1). Key results Evaporation rate significantly decreased in all treatments because the salt crust was elevated and salt domes formed, but the salt patterns of salt precipitation and evaporation exhibited significant differences between different EDs. The homogeneous fine powder crystals precipitated under relatively high ED conditions (29.5 and 21.5 mm day−1), and tended to aggregate and form an elevated salt crust in the initial period of salt precipitation. Consequently, it resulted in a sharp decrease in evaporation during the initial period of salt precipitation. In contrast, discrete and large crystals observed under low ED conditions (9.0 and 4.0 mm day−1), resulted in a stable evaporation stage during the initial period of salt precipitation. The highest relative evaporation rate was observed under the lowest ED condition when the evaporation rate reached stability, which was attributed to the formation of small and discrete salt domes, indicating that both the upward and lateral growth of salt precipitation were influenced by ED. Conclusions and implications The physics of salt crust formation needs to be considered in understanding how salt precipitates on the soil surface.
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Su, Z. „The Surface Energy Balance System (SEBS) for estimation of turbulent heat fluxes“. Hydrology and Earth System Sciences 6, Nr. 1 (28.02.2002): 85–100. http://dx.doi.org/10.5194/hess-6-85-2002.
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Abstract. A Surface Energy Balance System (SEBS) is proposed for the estimation of atmospheric turbulent fluxes and evaporative fraction using satellite earth observation data, in combination with meteorological information at proper scales. SEBS consists of: a set of tools for the determination of the land surface physical parameters, such as albedo, emissivity, temperature, vegetation coverage etc., from spectral reflectance and radiance measurements; a model for the determination of the roughness length for heat transfer; and a new formulation for the determination of the evaporative fraction on the basis of energy balance at limiting cases. Four experimental data sets are used to assess the reliabilities of SEBS. Based on these case studies, SEBS has proven to be capable to estimate turbulent heat fluxes and evaporative fraction at various scales with acceptable accuracy. The uncertainties in the estimated heat fluxes are comparable to in-situ measurement uncertainties. Keywords: Surface energy balance, turbulent heat flux, evaporation, remote sensing
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Katul, Gabriel G., Richard H. Cuenca, Philippe Grebet, James L. Wright und William O. Pruitt. „Analysis of Evaporative Flux Data for Various Climates“. Journal of Irrigation and Drainage Engineering 118, Nr. 4 (Juli 1992): 601–18. http://dx.doi.org/10.1061/(asce)0733-9437(1992)118:4(601).
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Hasan, Mohammad Nasim, Sheikh Mohammad Shavik, Kazi Fazle Rabbi, Khaled Mosharraf Mukut und Md Muntasir Alam. „Thermal transport during thin-film argon evaporation over nanostructured platinum surface: A molecular dynamics study“. Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanomaterials, Nanoengineering and Nanosystems 232, Nr. 2-3 (Juni 2018): 83–91. http://dx.doi.org/10.1177/2397791418802498.
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Investigation of thermal transport characteristics of thin-film liquid evaporation over nanostructured surface has been conducted using molecular dynamics simulation with particular importance on the effects of the nanostructure configuration for different wall–fluid interaction strengths. The nanostructured surface considered herein comprises wall-through rectangular nanoposts placed over a flat wall. Both the substrate and the nanostructure are of platinum while argon is used as the evaporating liquid. Two different wall–fluid interaction strengths have been considered that essentially emulate both hydrophilic and hydrophobic wetting conditions for three different nanostructure configurations. The argon–platinum molecular system is first equilibrated at 90 K and then followed by a sudden increase in the wall temperature at 130 K that induces evaporation of argon laid over it. Comparative effectiveness of heat and mass transfer for different surface wetting conditions has been studied by calculating the wall heat flux and evaporative mass flux. The results obtained in this study show that heat transfer occurs more easily in cases of nanostructured surfaces than in case of flat surface. Difference in behavior of argon molecules during and after the evaporation process, that is, wall adsorption characteristics, has been found to depend on the surface wetting condition as well as on presence and configuration of nanostructure. A thermodynamic approach of energy balance shows reasonable agreement with the present molecular dynamics study.
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Ceperley, Natalie C., Theophile Mande, Nick van de Giesen, Scott Tyler, Hamma Yacouba und Marc B. Parlange. „Evaporation from cultivated and semi-wild Sudanian Savanna in west Africa“. Hydrology and Earth System Sciences 21, Nr. 8 (22.08.2017): 4149–67. http://dx.doi.org/10.5194/hess-21-4149-2017.
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Abstract. Rain-fed farming is the primary livelihood of semi-arid west Africa. Changes in land cover have the potential to affect precipitation, the critical resource for production. Turbulent flux measurements from two eddy-covariance towers and additional observations from a dense network of small, wireless meteorological stations combine to relate land cover (savanna forest and agriculture) to evaporation in a small (3.5 km2) catchment in Burkina Faso, west Africa. We observe larger sensible and latent heat fluxes over the savanna forest in the headwater area relative to the agricultural section of the watershed all year. Higher fluxes above the savanna forest are attributed to the greater number of exposed rocks and trees and the higher productivity of the forest compared to rain-fed, hand-farmed agricultural fields. Vegetation cover and soil moisture are found to be primary controls of the evaporative fraction. Satellite-derived vegetation index (NDVI) and soil moisture are determined to be good predictors of evaporative fraction, as indicators of the physical basis of evaporation. Our measurements provide an estimator that can be used to derive evaporative fraction when only NDVI is available. Such large-scale estimates of evaporative fraction from remotely sensed data are valuable where ground-based measurements are lacking, which is the case across the African continent and many other semi-arid areas. Evaporative fraction estimates can be combined, for example, with sensible heat from measurements of temperature variance, to provide an estimate of evaporation when only minimal meteorological measurements are available in remote regions of the world. These findings reinforce local cultural beliefs of the importance of forest fragments for climate regulation and may provide support to local decision makers and rural farmers in the maintenance of the forest areas.
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Mukunthan, Shriram, Jochen Vleugels, Toon Huysmans, Kalev Kuklane, Tiago Sotto Mayor und Guido De Bruyne. „Thermal-Performance Evaluation of Bicycle Helmets for Convective and Evaporative Heat Loss at Low and Moderate Cycling Speeds“. Applied Sciences 9, Nr. 18 (05.09.2019): 3672. http://dx.doi.org/10.3390/app9183672.
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The main objective of the study was to investigate the thermal performance of five (open and closed) bicycle helmets for convective and evaporative heat transfer using a nine-zone thermal manikin. The shape of the thermal manikin was obtained by averaging the 3D-point coordinates of the head over a sample of 85 head scans of human subjects, obtained through magnetic resonance imaging (MRI) and 3D-printed. Experiments were carried out in two stages, (i) a convective test and (ii) an evaporative test, with ambient temperature maintained at 20.5 ± 0.5 °C and manikin skin temperature at 30.5 ± 0.5 °C for both the tests. Results showed that the evaporative heat transfer contributed up to 51%–53% of the total heat loss from the nude head. For the convective tests, the open helmet A1 having the highest number of vents among tested helmets showed the highest cooling efficiency at 3 m/s (100.9%) and at 6 m/s (101.6%) and the closed helmet (A2) with fewer inlets and outlets and limited internal channels showed the lowest cooling efficiency at 3 m/s (75.6%) and at 6 m/s (84.4%). For the evaporative tests, the open helmet A1 showed the highest cooling efficiency at 3 m/s (97.8%), the open helmet A4 showed the highest cooling efficiency at 6 m/s (96.7%) and the closed helmet A2 showed the lowest cooling efficiency at 3 m/s (79.8%) and at 6 m/s (89.9%). Two-way analysis of variance (ANOVA) showed that the zonal heat-flux values for the two tested velocities were significantly different (p < 0.05) for both the modes of heat transfer. For the convective tests, at 3 m/s, the frontal zone (256–283 W/m2) recorded the highest heat flux for open helmets, the facial zone (210–212 W/m2) recorded the highest heat flux for closed helmets and the parietal zone (54–123 W/m2) recorded the lowest heat flux values for all helmets. At 6 m/s, the frontal zone (233–310 W/m2) recorded the highest heat flux for open helmets and the closed helmet H1, the facial zone (266 W/m2) recorded the highest heat flux for the closed helmet A2 and the parietal zone (65–123 W/m2) recorded the lowest heat flux for all the helmets. For evaporative tests, at 3 m/s, the frontal zone (547–615 W/m2) recorded the highest heat flux for all open helmets and the closed helmet H1, the facial zone (469 W/m2) recorded the highest heat flux for the closed helmet A2 and the parietal zone (61–204 W/m2) recorded the lowest heat flux for all helmets. At 6 m/s, the frontal zone (564–621 W/m2) recorded highest heat flux for all the helmets and the parietal zone (97–260 W/m2) recorded the lowest heat flux for all helmets.
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MURISIC, N., und L. KONDIC. „On evaporation of sessile drops with moving contact lines“. Journal of Fluid Mechanics 679 (18.04.2011): 219–46. http://dx.doi.org/10.1017/jfm.2011.133.
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We consider theoretically, computationally and experimentally spontaneous evaporation of water and isopropanol drops on smooth silicon wafers. In contrast to a number of previous works, the solid surface we consider is smooth and therefore the droplets' evolution proceeds without contact line pinning. We develop a theoretical model for evaporation of pure liquid drops that includes Marangoni forces due to the thermal gradients produced by non-uniform evaporation, and heat conduction effects in both liquid and solid phases. The key ingredient in this model is the evaporative flux. We consider two commonly used models: one based on the assumption that the evaporation is limited by the processes originating in the gas (vapour diffusion-limited evaporation), and the other one which assumes that the processes in the liquid are limiting. Our theoretical model allows for implementing evaporative fluxes resulting from both approaches. The required parameters are obtained from physical experiments. We then carry out fully nonlinear time-dependent simulations and compare the results with the experimental ones. Finally, we discuss how the simulation results can be used to predict which of the two theoretical models is appropriate for a particular physical experiment.
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Benilov, E. S. „Dynamics of a drop floating in vapor of the same fluid“. Physics of Fluids 34, Nr. 4 (April 2022): 042104. http://dx.doi.org/10.1063/5.0088421.
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Evaporation of a liquid drop surrounded by either vapor of the same fluid, or vapor and air, is usually attributed to vapor diffusion, which, however, does not apply to the former setting, as pure fluids do not diffuse. The present paper puts forward an additional mechanism, one that applies to both settings. It is shown that disparities between the drop and vapor in terms of their pressure and chemical potential give rise to a flow. Its direction depends on the vapor density and the drop's size. In undersaturated or saturated vapor, all drops evaporate, but in oversaturated (yet thermodynamically stable) vapor, there exists a critical radius: smaller drops evaporate, whereas larger drops act as centers of condensation and grow. The developed model is used to estimate the evaporation time of a drop floating in saturated vapor. It is shown that, if the vapor-to-liquid density ratio is small, so is the evaporative flux; as a result, millimeter-sized water drops at temperatures lower than [Formula: see text] survive for days. If, however, the temperature is comparable (but not necessarily close) to its critical value, such drops evaporate within minutes. Micron-sized drops, in turn, evaporate within seconds for all temperatures between the triple and critical points.
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Eloyan, Karapet, Alexey Kreta und Egor Tkachenko. „Two-phase cooling system with controlled pulsations“. EPJ Web of Conferences 196 (2019): 00021. http://dx.doi.org/10.1051/epjconf/201919600021.
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One of the promising ways of removing large heat fluxes from the surface of heat-stressed elements of electronic devices is the use of evaporating thin layer of liquid film, moving under the action of the gas flow in a flat channel. In this work, a prototype of evaporative cooling system for high heat flux removal with forced circulation of liquid and gas coolants with controlled pulsation, capable to remove heat flux of up to 1,5 kW/cm2 and higher was presented. For the first time the regime with controlled pulsation is used. Due to pulsations, it is possible to achieve high values of critical heat flux due to a brief increase in the flow rate of the liquid, which allows to "wash off" large dry spots and prevent the occurrence of zones of flow and drying.
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Shkarah, Ahmed Jassim, Mohd Yusoff Bin Sulaiman und Md Razali bin Hj Ayob. „Analytical Solutions of Heat Transfer and Film Thickness with Slip Condition Effect in Thin-Film Evaporation for Two-Phase Flow in Microchannel“. Mathematical Problems in Engineering 2015 (2015): 1–15. http://dx.doi.org/10.1155/2015/369581.
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Physical and mathematical model has been developed to predict the two-phase flow and heat transfer in a microchannel with evaporative heat transfer. Sample solutions to the model were obtained for both analytical analysis and numerical analysis. It is assumed that the capillary pressure is neglected (Morris, 2003). Results are provided for liquid film thickness, total heat flux, and evaporating heat flux distribution. In addition to the sample calculations that were used to illustrate the transport characteristics, computations based on the current model were performed to generate results for comparisons with the analytical results of Wang et al. (2008) and Wayner Jr. et al. (1976). The calculated results from the current model match closely with those of analytical results of Wang et al. (2008) and Wayner Jr. et al. (1976). This work will lead to a better understanding of heat transfer and fluid flow occurring in the evaporating film region and develop an analytical equation for evaporating liquid film thickness.
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Duan, Fei, und C. A. Ward. „Investigation of Local Evaporation Flux and Vapor-Phase Pressure at an Evaporative Droplet Interface“. Langmuir 25, Nr. 13 (07.07.2009): 7424–31. http://dx.doi.org/10.1021/la900337j.
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Aminzadeh, Milad, Peter Lehmann und Dani Or. „Evaporation suppression and energy balance of water reservoirs covered with self-assembling floating elements“. Hydrology and Earth System Sciences 22, Nr. 7 (26.07.2018): 4015–32. http://dx.doi.org/10.5194/hess-22-4015-2018.
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Abstract. The growing pressure on natural freshwater resources and the projected climate variability are expected to increase the need for water storage during rainy periods. Evaporative losses present a challenge for the efficiency of water storage in reservoirs, especially in arid regions with chronic water shortages. Among the available methods for suppressing evaporative losses, self-assembling floating elements offer a simple and scalable solution, especially for small reservoirs. The use of floating elements has often been empirically based; we thus seek a framework for systematic consideration of floating element properties, local climate and reservoir conditions to better predict evaporative loss, energy balance and heat fluxes from covered water reservoirs. We linked the energy balance of the water column with energy considerations of the floating elements. Results suggest significant suppression of evaporative losses from covered reservoirs in which incoming radiative energy is partitioned to sensible and long wave fluxes that reduce latent heat flux and thus increase the Bowen ratio over covered water reservoirs. Model findings were consistent with laboratory-scale observations using an uncovered and covered small basin. The study offers a physically based framework for testing design scenarios in terms of evaporation suppression efficiency for various climatic conditions; it hence strengthens the science in the basis of this important water resource conservation strategy.
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de Lozar, Alberto, und Juan Pedro Mellado. „Mixing Driven by Radiative and Evaporative Cooling at the Stratocumulus Top“. Journal of the Atmospheric Sciences 72, Nr. 12 (24.11.2015): 4681–700. http://dx.doi.org/10.1175/jas-d-15-0087.1.
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Abstract The stratocumulus-top mixing process is investigated using direct numerical simulations of a shear-free cloud-top mixing layer driven by evaporative and radiative cooling. An extension of previous linear formulations allows for quantifying radiative cooling, evaporative cooling, and the diffusive effects that artificially enhance mixing and evaporative cooling in high-viscosity direct numerical simulations (DNS) and many atmospheric simulations. The diffusive cooling accounts for 20% of the total evaporative cooling for the highest resolution (grid spacing ~14 cm), but this can be much larger (~100%) for lower resolutions that are commonly used in large-eddy simulations (grid spacing ~5 m). This result implies that the κ scaling for cloud cover might be strongly influenced by diffusive effects. Furthermore, the definition of the inversion point as the point of neutral buoyancy allows the derivation of two scaling laws. The in-cloud scaling law relates the velocity and buoyancy integral scales to a buoyancy flux defined by the inversion point. The entrainment-zone scaling law provides a relationship between the entrainment velocity and the liquid evaporation rate. By using this inversion point, it is shown that the radiative-cooling contribution to the entrainment velocity decouples from the evaporative-cooling contribution and behaves very similarly as in the smoke cloud. Finally, evaporative and radiative cooling have similar strengths, when this strength is measured by the integrated buoyancy source. This result partially explains why current entrainment parameterizations are not accurate enough, given that most of them implicitly assume that only one of the two mechanisms rules the entrainment.
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Blyth, Eleanor, John Gash, Amanda Lloyd, Matthew Pryor, Graham P. Weedon und Jim Shuttleworth. „Evaluating the JULES Land Surface Model Energy Fluxes Using FLUXNET Data“. Journal of Hydrometeorology 11, Nr. 2 (01.04.2010): 509–19. http://dx.doi.org/10.1175/2009jhm1183.1.
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Abstract Surface energy flux measurements from a sample of 10 flux network (FLUXNET) sites selected to represent a range of climate conditions and biome types were used to assess the performance of the Hadley Centre land surface model (Joint U.K. Land Environment Simulator; JULES). Because FLUXNET data are prone systematically to undermeasure surface fluxes, the model was evaluated by its ability to partition incoming radiant energy into evaporation and how such partition varies with atmospheric evaporative demand at annual, seasonal, weekly, and diurnal time scales. The model parameters from the GCM configuration were used. The overall performance was good, although weaknesses in model performance were identified that are associated with the specification of the leaf area index and plant rooting depth, and the representation of soil freezing.
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Rubert, Gisele Cristina Dotto, Débora Regina Roberti, Marcelo Bortoluzzi Diaz und Osvaldo Luiz Leal de Moraes. „ESTIMATIVA DA EVAPOTRANSPIRAÇÃO EM ÁREA DE PASTAGEM EM SANTA MARIA – RS“. Ciência e Natura 38 (20.07.2016): 300. http://dx.doi.org/10.5902/2179460x20237.
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The eddy covariance technique was used to estimate the sensible and latent heat flux between the atmosphere and the Pampa Biome in the period from 20 November 2013 to 20 November 2014. Annual Evapotranspiration (ET) was 1021 mm, corresponding to 55% of the annual precipitation. The ET is highly correlated with the net radiation (97%). The Bowen ratio was indicated that most of the available energy was used for the evaporation. The evaporative fraction remained about average, with greater variability in the colder months.
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GUO, W., und R. NARAYANAN. „Interfacial instability due to evaporation and convection: linear and nonlinear analyses“. Journal of Fluid Mechanics 650 (15.03.2010): 363–89. http://dx.doi.org/10.1017/s002211200999348x.
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Interfacial instability arising from evaporation of a single component liquid is investigated using linear and weakly nonlinear analysis. Evaporative convection is studied taking into account the fluid dynamics of both liquid and vapour phases as well as lateral rigid sidewalls. Both open and closed systems are addressed. The nature of the bifurcation and the change in heat flux in the nonlinear regime are determined. It is shown that depending upon the aspect ratio of the geometry, either supercritical or subcritical branching behaviour is possible.
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Arieli, Yehuda, Neomi Feinstein, Pnina Raber, Michal Horowitz und Jacob Marder. „Heat stress induces ultrastructural changes in cutaneous capillary wall of heat-acclimated rock pigeon“. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 277, Nr. 4 (01.10.1999): R967—R974. http://dx.doi.org/10.1152/ajpregu.1999.277.4.r967.
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In heat-acclimated rock pigeons, cutaneous water evaporation is the major cooling mechanism when exposed at rest to an extremely hot environment of 50–60°C. This evaporative pathway is also activated in room temperature by a β-adrenergic antagonist (propranolol) or an α-adrenergic agonist (clonidine) and inhibited by a β-adrenergic agonist (isoproterenol). In contrast, neither heat exposure nor drug administration activates cutaneous evaporation in cold-acclimated pigeons. To elucidate the mechanisms underlying this phenomenon, we studied the role of the ultrastructure and permeability of the cutaneous vasculature. During both heat stress and the administration of propranolol and clonidine, we observed increased capillary fenestration and endothelial gaps. Similarly, propranolol increased the extravasation of Evans blue-labeled albumin in the skin tissue. We concluded that heat acclimation reinforces a mechanism by which the activation of adrenergic signal transduction pathways alters microvessel permeability during heat stress. Consequently the flux of plasma proteins and water into the interstitial space is accelerated, providing an interstitial source of water for sustained cutaneous evaporative cooling.
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Lay, J. H., und V. K. Dhir. „Shape of a Vapor Stem During Nucleate Boiling of Saturated Liquids“. Journal of Heat Transfer 117, Nr. 2 (01.05.1995): 394–401. http://dx.doi.org/10.1115/1.2822535.
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The transport processes occurring in an evaporating two-dimensional vapor stem formed during saturated nucleate boiling on a heated surface are modeled and analyzed numerically. From the heater surface heat is conducted into the liquid macro/microthermal layer surrounding the vapor stems and is utilized in evaporation at the stationary liquid–vapor interface. A balance between forces due to curvature of the interface, disjoining pressure, hydrostatic head, and liquid drag determines the shape of the interface. The kinetic theory and the extended Clausius–Clapeyron equation are used to calculate the evaporative heat flux across the liquid–vapor interface. The vapor stem shape calculated by solving a fourth-order nonlinear ordinary differential equation resembles a cup with a flat bottom. For a given wall superheat, several metastable states of the vapor stem between a minimum and maximum diameter are found to be possible. The effect of wall superheat on the shape of the vapor stem is parametrically analyzed and compared with limited data reported in the literature.
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HADLEY, NEIL F., MICHAEL C. QUINLAN und MICHAEL L. KENNEDY. „Evaporative Cooling in the Desert Cicada: Thermal Efficiency and Water*sol;Metabolic Costs“. Journal of Experimental Biology 159, Nr. 1 (01.09.1991): 269–83. http://dx.doi.org/10.1242/jeb.159.1.269.
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Using plant xylem water for evaporative cooling, the desert cicada Diceroprocta apache can maintain a body temperature as much as 5°C below ambient (Ta=42°C). Simultaneous measurements of water loss and gas exchange for cicadas feeding on perfused twigs show substantial increases in transpiration at temperatures at which evaporative cooling begins (between 37 and 38°C), but only modest increases in Vo2 and Vco2. The extent and duration of evaporative cooling depend on the cicada's hydration state and the rate of water flux from cuticular pores located on the surface of the thorax and abdomen.
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Sharma, P. K., A. K. Sinha und T. N. Chaudhaby. „Upward flux of water and deep-placed P in relation to soil texture, water table depth and evaporation rate“. Journal of Agricultural Science 104, Nr. 2 (April 1985): 303–7. http://dx.doi.org/10.1017/s0021859600043963.
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SummaryUpward flux of water and deep-placed (8–10 cm) P was studied in columns of sandyloam and silty clay loam, with water tables of 60 and 90 cm, each subjected to potential evaporation rates of 2–2 and 7–5 mm/day, for 15 days. An amount of 300 mg P/kg soil, labelled with 20 /tCi 32P/g P, was applied as diammonium hydrogen orthophosphate.Evaporation losses increased with increase in potential evaporation (PE) and decrease in depth to water table in both soils, but the ratio of actual to potential evaporation (AE/PE) decreased with increasing PE, indicating that the evaporative losses in both the soils were mainly controlled by their hydraulic conductive properties. Under no circumstances did AE equal PE. Evaporation, in general, was higher from sandy loam than from silty clay loam.Corresponding to water flux, total upward P flux increased with increasing PE and decreasing depth to water. In the sandy loam, with 2–2 mm PE/day, 21 % of the deepplaced P moved to the soil surface with the 60 cm water table, against 5 % with the 90 cm water table. Under 7–5 mm PE/day, 39% P migrated to the surface with the 60 cm water table, but no 3aP was detected at the surface with the 90 cm water table. In the silty clay loam, however, P movement was much restricted.
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Suchan, Jared, und Shahid Azam. „Determination of Evaporative Fluxes Using a Bench-Scale Atmosphere Simulator“. Water 13, Nr. 1 (01.01.2021): 84. http://dx.doi.org/10.3390/w13010084.
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An accurate determination of evaporative fluxes is critical for efficient water management in semi-arid climates such as in the Canadian Prairies. The main achievements of this research are the design and operation of a bench-scale atmosphere simulator, performance evaluation using selected weather scenarios pertaining to regional atmospheric conditions, validation using established empirical correlations, and estimation of evaporation rates and the amount for a typical local water body. Results indicate that the measured data achieved the target values for the various parameters and the data were found to be stable during the 3-h test duration. The vapour flux was found to have large variation during summer (0.120 g∙s−1∙m−2 during the day and 0.047 g∙s−1∙m−2 at night), low variation during spring (0.116 g∙s−1∙m−2 during the day and 0.062 g∙s−1∙m−2 at night), and negligible change during fall (0.100 g∙s−1∙m−2 during the day and 0.076 g∙s−1∙m−2 at night). The measured vapour flux was generally within one standard deviation of the equality line when compared with that predicted by both the mass-transfer equations and the combination equations. The average evaporation ranged from 4 mm∙d−1 to 8 mm∙d−1 during the day and decreased to 1 mm∙d−1 to 3 mm∙d−1 at night. The 24-h evaporation was found to be 8 ± 1 mm∙d−1 from late April through late October. Likewise, the cumulative annual evaporation was found to be 1781 mm, of which 82% occurs during the day and 18% at night.
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Shukla, Digvijay, und Pradipta Kumar Panigrahi. „Digital holographic study of vapor transport of heavy hydrocarbon from heated well cavity“. Journal of Physics: Conference Series 2116, Nr. 1 (01.11.2021): 012079. http://dx.doi.org/10.1088/1742-6596/2116/1/012079.
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Abstract Thin film evaporative cooling is one of the liquid cooling technologies, capable of removing high heat flux with lower junction temperature due to the utilization of latent heat of vaporization. To understand the various transport processes involved in vapour phase during thin film evaporation, evaporation from a heated well cavity of diameter 3 mm and height 2 mm is studied using Digital holographic interferometry technique. A flat disk-shaped vapour cloud is appeared for heated as well as not- heated well surface case. This signifies radial outward natural convection instead of pure diffusion. A higher vapour concentration is obtained at each time instants for heated surface case due to the higher evaporation rate as compared to non-heated, ambient case.
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Folkins, Ian, und Randall V. Martin. „The Vertical Structure of Tropical Convection and Its Impact on the Budgets of Water Vapor and Ozone“. Journal of the Atmospheric Sciences 62, Nr. 5 (01.05.2005): 1560–73. http://dx.doi.org/10.1175/jas3407.1.
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Abstract Convective clouds in the Tropics that penetrate the boundary layer inversion preferentially detrain into a shallow outflow layer (2–5 km) or a deep outflow layer (10–17 km). The properties of these layers are diagnosed from a one-dimensional model of the Tropics constrained by observed mean temperature and water vapor profiles. The mass flux divergence of the shallow cumuli (2–5 km) is balanced by a mass flux convergence of evaporatively forced descent (downdrafts), while the mass flux divergence of deep cumulonimbus clouds (10–17 km) is balanced by a mass flux convergence of clear-sky radiative descent. The pseudoadiabatic temperature stratification of the midtroposphere (5–10 km) suppresses cloud outflow in this interval. The detrainment profile in the deep outflow layer is shifted downward by about 1.5 km from the profile one would anticipate based on undilute pseudoadiabatic ascent of air from the boundary layer. The main source of water vapor to most of the tropical troposphere is evaporative moistening. Below 12 km, evaporatively forced descent plays an important role in the vertical mass flux budget of the Tropics. This gives rise to a coupling between the water vapor and mass flux budgets, which, between 5 and 10 km, provides a constraint on the variation of relative humidity with height. Between 12 and 15 km, the observed relative humidity profile can be reproduced by assuming a simple first-order balance between detrainment moistening and subsidence drying. The mean ozone profile of the Tropics can be reproduced using a simple one-dimensional model constrained by the cloud mass flux divergence profile of the diagnostic model.
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Pittaway, P., V. Martínez-Alvarez und N. Hancock. „Contrasting suspended covers reveal the impact of an artificial monolayer on heat transfer processes at the interfacial boundary layer“. Water Science and Technology 72, Nr. 9 (17.07.2015): 1621–27. http://dx.doi.org/10.2166/wst.2015.379.
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The highly variable performance of artificial monolayers in reducing evaporation from water storages has been attributed to wind speed and wave turbulence. Other factors operating at the interfacial boundary layer have seldom been considered. In this paper, two physical shade covers differing in porosity and reflectivity were suspended over 10 m diameter water tanks to attenuate wind and wave turbulence. The monolayer octadecanol was applied to one of the covered tanks, and micrometeorological conditions above and below the covers were monitored to characterise diurnal variation in the energy balance. A high downward (air-to-water) convective heat flux developed under the black cover during the day, whereas diurnal variation in the heat flux under the more reflective, wind-permeable white cover was much less. Hourly air and water temperature profiles under the covers over 3 days when forced convection was minimal (low wind speed) were selected for analysis. Monolayer application reduced temperature gain in surface water under a downward convective heat flux, and conversely reduced temperature loss under an upward convective heat flux. This ‘dual property’ may explain why repeat application of an artificial monolayer to retard evaporative loss (reducing latent heat loss) does not inevitably increase water temperature.
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Mohammed, Maged, Nashi K. Alqahtani, Hafiz M. Asfahan und Muhammad Sultan. „Evaporation-Assisted Humidification–Dehumidification Cycles for Desalination Application in Tropical and Subtropical Regions“. Water 15, Nr. 6 (15.03.2023): 1125. http://dx.doi.org/10.3390/w15061125.
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The present study aims to evaluate the performance of evaporation-assisted humidification–dehumidification (E-HDH) desalination, specifically direct evaporative (DE-HDH), indirect evaporative (IE-HDH), and Maisotsenko evaporative (ME-HDH) systems. To achieve this, a thermodynamic modeling approach is utilized, which incorporates the wet bulb effectiveness method, psychrometric relationships of humid air, and equations that govern heat and mass balance. The key performance indicators of the studied E-HDH desalination systems are estimated concerning operating parameters. The results show that the ME-HDH system is capable of producing a comparatively higher water production rate (WPR) ranging between 0.01 and 7.92 g/s as compared to the DE-HDH and IE-HDH systems. The sensible cooling flux was observed to be high at a dry-bulb temperature (Tdb) of 50 °C and relative humidity (RH) < 0.2, having a value of 5.26 kW for the DE-HDH system, followed by the ME-HDH system (3.23 kW) and the IE-HDH system (3.11 kW) due to relatively high mass flow rates. The latent heat flux was observed to be relatively high in the case of the ME-HDH system. Minimum specific energy consumption was observed from the ME-HDH system, and consequently, a maximum gain output ratio (3.32) was realized. In addition, the study realized that an increment in air velocity and wet bulb effectiveness significantly improves the WPR. In accordance with the climatic conditions of the studied Saudi Arabia cities, it has been realized that Al-Hofuf and Riyadh produce relatively high WPRs with minimum energy consumption. In the case of Al-Hofuf, the average WPR was recorded as 185.51 kg/day, followed by Riyadh (180.33 kg/day). The energy required was estimated to be 0.042 kWh/kg and 0.034 kWh/kg for both cities, accordingly.
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Eloyan, K. S., und D. V. Zaitsev. „Thin film evaporative cooling system for high heat flux applications“. Journal of Physics: Conference Series 1105 (November 2018): 012084. http://dx.doi.org/10.1088/1742-6596/1105/1/012084.
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Tan, Xiao Qian, und Li Jiu Wang. „Slag-Clay Foam Cement as Roof Material for Passive Evaporative Cooling“. Advanced Materials Research 194-196 (Februar 2011): 890–94. http://dx.doi.org/10.4028/www.scientific.net/amr.194-196.890.
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The objective of this study is to propose a light weight and suitable strength material as roof surface which can detain rainwater during rainy day and lower room temperature in sunny day by passive evaporative cooling. So blast furnace slag was used as the main raw material and clay as the subordinate ingredient to synthesize an alkali-activated cement matrix at room temperature. Furthermore the cement matrix were made into porosity by injecting prepared foam and attempted to improve strength by incorporation of short polypropylene fiber. Finally, the dry density of 453 kg/m3 and compressive strength of 4.5MPa porous roof material (slag-clay porous material) was gained. Variations of room temperature and heat flux transfer across porous material roof slab have been measured. The results showed that roof covered with slag-clay porous material can satisfactorily lower room temperature and reduce heat flux, as compared with OPC (ordinary Portland cement) roof layer simply. Covering slag-clay porous material layer as roof surface can create a more effective cooling system by utilizing its water absorption and evaporation capability during canicule, which provides a new approach to low carbon and energy saving technological development.
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Kurta, Allen, Gary P. Bell, Kenneth A. Nagy und Thomas H. Kunz. „Water balance of free-ranging little brown bats (Myotis lucifugus) during pregnancy and lactation“. Canadian Journal of Zoology 67, Nr. 10 (01.10.1989): 2468–72. http://dx.doi.org/10.1139/z89-348.
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This study provides the first measurements of daily water flux in free-ranging bats during pregnancy and lactation. We used the wash-out rate of tritiated water from the body water pool to calculate daily water flux in 10 pregnant and 14 lactating little brown bats (Myotis lucifugus). Average water influx was 6.16 ± 0.47 (SE) mL/day during pregnancy and 6.91 ± 0.37 mL/day during lactation; average efflux was 6.27 ± 0.44 and 7.07 ± 0.36 mL/day during pregnancy and lactation, respectively. Using data from the literature, we partitioned daily flux into major components. Our calculations indicated that most (> 62%) water influx was preformed water in the insect diet. Drinking water represented 23–26% of daily influx. Although previous studies indicated that evaporative losses greatly exceeded urinary losses in laboratory-maintained M. lucifugus, urinary and evaporative losses were comparable in our free-ranging bats. Urinary losses represented 46% of water efflux during pregnancy and 35% during lactation. Over 80% of all water efflux occurs during the 8-h night.
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Lee, Hyung Ju, Chan Ho Jeong, Dae Yun Kim, Chang Kyoung Choi und Seong Hyuk Lee. „Solid–Liquid Interface Temperature Measurement of Evaporating Droplet Using Thermoresponsive Polymer Aqueous Solution“. Applied Sciences 11, Nr. 8 (09.04.2021): 3379. http://dx.doi.org/10.3390/app11083379.
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The present study aims to measure the solid–liquid interface temperature of an evaporating droplet on a heated surface using a thermoresponsive polymer. Poly(N-isopropylacrylamide) (pNIPAM) was used owing to its sensitive optical and mechanical properties to the temperature. We also measured the refractive index variation of the pNIPAM solution by using the surface plasmon resonance imaging (SPRi). In particular, the present study proposed a new method to measure the solid–liquid interface temperature using the correlation among reflectance, refractive index, and temperature. It was found that the reflectance of a pNIPAM solution decreased after the droplet deposition. The solid–liquid interface temperature, estimated from the reflectance, showed a lower value at the center of the droplet, and it gradually increased along the radial direction. The lowest temperature at the contact line region is present because of the maximum evaporative cooling. Moreover, the solid–liquid interface temperature deviation increased with the surface temperature, which means solid–liquid interface temperature should be considered at high temperature to predict the evaporation flux of the droplet accurately.
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Liu, Rong, Jun Wen, Xin Wang, Zuoliang Wang, Yu Liu und Ming Zhang. „Estimates of Daily Evapotranspiration in the Source Region of the Yellow River Combining Visible/Near-Infrared and Microwave Remote Sensing“. Remote Sensing 13, Nr. 1 (25.12.2020): 53. http://dx.doi.org/10.3390/rs13010053.
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The spatial variation of surface net radiation, soil heat flux, sensible heat flux, and latent heat flux at different times of the day over the northern Tibetan Plateau were estimated using the Surface Energy Balance System algorithm, data from the FY-2G geostationary meteorological satellite, and microwave data from the FY-3C polar-orbiting meteorological satellite. In addition, the evaporative fraction was analyzed, and the total evapotranspiration (ET) was obtained by the effective evaporative fraction to avoid the error from accumulation. The hourly change of latent heat flux presented a sound unimodal diurnal variation. The results showed the regional ET ranged between 2.0 and 4.0 mm over the Source Region of the Yellow River. The conditional expectations of surface energy components during the experimental period of the study area were statistically analyzed, and the correspondence between different surface temperatures and the effective energy distribution was examined. The effective energy distribution of the surface changed significantly with the increase in temperature; in particular, when the surface temperature exceeded 290 K, the effective energy was mainly used for surface ET. The aim of this study was to avoid the use of surface meteorological observations that are not readily available over large areas, and the findings lay a foundation for the commercialization of land surface evapotranspiration.
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Alkhaier, F., Z. Su und G. N. Flerchinger. „Reconnoitering the effect of shallow groundwater on land surface temperature and surface energy balance using MODIS and SEBS“. Hydrology and Earth System Sciences Discussions 8, Nr. 5 (23.09.2011): 8671–700. http://dx.doi.org/10.5194/hessd-8-8671-2011.
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Abstract. The possibility of observing shallow groundwater depth and areal extent using satellite measurements can support groundwater models and vast irrigation systems management. Besides, these measurements help bringing groundwater effect on surface energy balance within land surface models and climate studies. To inspect the MODIS capacity of detecting shallow groundwater effect on land surface temperature and surface energy balance in an area within Al-Balikh River basin in northern Syria, we investigated the interrelationship between in-situ measured water table depths and land surface temperatures of MODIS. Further, we used the Surface Energy Balance System (SEBS) to calculate surface energy fluxes, evaporative fraction and daily evaporation, and inspected their relationships with water table depths. In agreement with the findings of a companion paper (Alkhaier et al., 2011), we found that daytime temperature increased and nighttime temperature decreased with increasing water table depth. Where water table depth increased, net radiation, latent and ground heat fluxes, evaporative fraction and daily evaporation decreased, while sensible heat flux increased. The clear observed relationships resulted from meeting both conditions concluded in the companion paper, i.e. high potential evaporation and big contrast in air temperature. Moreover, the prevailing conditions in this study area helped SEBS producing accurate estimates. We conclude that MODIS is suitable for shallow groundwater effect detection since it has proper imaging times and appropriate sensor accuracy; nevertheless, its coarse spatial resolution is disadvantageous.
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Carrier, Odile, Noushine Shahidzadeh-Bonn, Rojman Zargar, Mounir Aytouna, Mehdi Habibi, Jens Eggers und Daniel Bonn. „Evaporation of water: evaporation rate and collective effects“. Journal of Fluid Mechanics 798 (09.06.2016): 774–86. http://dx.doi.org/10.1017/jfm.2016.356.
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We study the evaporation rate from single drops as well as collections of drops on a solid substrate, both experimentally and theoretically. For a single isolated drop of water, in general the evaporative flux is limited by diffusion of water through the air, leading to an evaporation rate that is proportional to the linear dimension of the drop. Here, we test the limitations of this scaling law for several small drops and for very large drops. We find that both for simple arrangements of drops, as well as for complex drop size distributions found in sprays, cooperative effects between drops are significant. For large drops, we find that the onset of convection introduces a length scale of approximately 20 mm in radius, below which linear scaling is found. Above this length scale, the evaporation rate is proportional to the surface area.
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Zhang, Zhao, Xuesheng Wang, Qinzhu Chen und Ting Zhang. „Experimental study on enhanced heat transfer tubes in falling film evaporation“. Journal of Physics: Conference Series 2029, Nr. 1 (01.09.2021): 012042. http://dx.doi.org/10.1088/1742-6596/2029/1/012042.
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Abstract The vertical tube falling film evaporation experimental platform was built, and the falling film evaporation heat transfer experiment was carried out. Comparative study was carried out between two types of enhanced heat transfer tubes, which are converging-diverging tube and the transversally corrugated tube, to explore their heat transfer characteristics of falling film evaporation. The results show that the falling film evaporative heat transfer coefficient of the two tubes increases with the increase of the unit peripheral flow rate, the heat transfer temperature difference, heat flux and the Reynolds number of the flash steam. The falling film evaporation heat transfer coefficient of the converging-diverging tube is about 1.09 times that of the transversally corrugated tube. According to the experimental data, the falling film evaporation heat transfer correlations of these two types of tubes were obtained. These results provide a useful reference for the using of transversally corrugated tube and converging-diverging tube in vertical falling film evaporator.
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ZHANG, JIN, STEPHEN J. WATSON und HARRIS WONG. „Fluid flow and heat transfer in a dual-wet micro heat pipe“. Journal of Fluid Mechanics 589 (08.10.2007): 1–31. http://dx.doi.org/10.1017/s0022112007007823.
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Micro heat pipes have been used to cool micro electronic devices, but their heat transfer coefficients are low compared with those of conventional heat pipes. In this work, a dual-wet pipe is proposed as a model to study heat transfer in micro heat pipes. The dual-wet pipe has a long and narrow cavity of rectangular cross-section. The bottom-half of the horizontal pipe is made of a wetting material, and the top-half of a non-wetting material. A wetting liquid fills the bottom half of the cavity, while its vapour fills the rest. This configuration ensures that the liquid–vapour interface is pinned at the contact line. As one end of the pipe is heated, the liquid evaporates and increases the vapour pressure. The higher pressure drives the vapour to the cold end where the vapour condenses and releases the latent heat. The condensate moves along the bottom half of the pipe back to the hot end to complete the cycle. We solve the steady-flow problem assuming a small imposed temperature difference between the two ends of the pipe. This leads to skew-symmetric fluid flow and temperature distribution along the pipe so that we only need to focus on the evaporative half of the pipe. Since the pipe is slender, the axial flow gradients are much smaller than the cross-stream gradients. Thus, we can treat the evaporative flow in a cross-sectional plane as two-dimensional. This evaporative motion is governed by two dimensionless parameters: an evaporation number E defined as the ratio of the evaporative heat flux at the interface to the conductive heat flux in the liquid, and a Marangoni number M. The motion is solved in the limit E→∞ and M→∞. It is found that evaporation occurs mainly near the contact line in a small region of size E−1W, where W is the half-width of the pipe. The non-dimensional evaporation rate Q* ~ E−1 ln E as determined by matched asymptotic expansions. We use this result to derive analytical solutions for the temperature distribution Tp and vapour and liquid flows along the pipe. The solutions depend on three dimensionless parameters: the heat-pipe number H, which is the ratio of heat transfer by vapour flow to that by conduction in the pipe wall and liquid, the ratio R of viscous resistance of vapour flow to interfacial evaporation resistance, and the aspect ratio S. If HR≫1, a thermal boundary layer appears near the pipe end, the width of which scales as (HR)−1/2L, where L is the half-length of the pipe. A similar boundary layer exists at the cold end. Outside the boundary layers, Tp varies linearly with a gradual slope. Thus, these regions correspond to the evaporative, adiabatic and condensing regions commonly observed in conventional heat pipes. This is the first time that the distinct regions have been captured by a single solution, without prior assumptions of their existence. If HR ~ 1 or less, then Tp is linear almost everywhere. This is the case found in most micro-heat-pipe experiments. Our analysis of the dual-wet pipe provides an explanation for the comparatively low effective thermal conductivity in micro heat pipes, and points to ways of improving their heat transfer capabilities.
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Faghri, Amir, und Dmitry Khrustalev. „High Flux Evaporative Mini-Channel Heat Sink with Axial Capillary Grooves“. Journal of Enhanced Heat Transfer 3, Nr. 3 (1996): 221–32. http://dx.doi.org/10.1615/jenhheattransf.v3.i3.60.
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Amon, Cristina H., S. C. Yao, C. F. Wu und C. C. Hsieh. „Microelectromechanical System-Based Evaporative Thermal Management of High Heat Flux Electronics“. Journal of Heat Transfer 127, Nr. 1 (01.01.2005): 66–75. http://dx.doi.org/10.1115/1.1839586.
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This paper describes the development of embedded droplet impingement for integrated cooling of electronics (EDIFICE), which seeks to develop an integrated droplet impingement cooling device for removing chip heat fluxes over 100W/cm2, employing latent heat of vaporization of dielectric fluids. Micromanufacturing and microelectromechanical systems are used as enabling technologies for developing innovative cooling schemes. Microspray nozzles are fabricated to produce 50–100 μm droplets coupled with surface texturing on the backside of the chip to promote droplet spreading and effective evaporation. This paper examines jet impingement cooling of EDIFICE with a dielectric coolant and the influence of fluid properties, microspray characteristics, and surface evaporation. The development of micronozzles and microstructured surface texturing is discussed. Results of a prototype testing of swiss-roll swirl nozzles with dielectric fluid HFE-7200 on a notebook PC are presented. This paper also outlines the challenges to practical implementation and future research needs.
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Grossiord, Charlotte, Bradley Christoffersen, Aura M. Alonso-Rodríguez, Kristina Anderson-Teixeira, Heidi Asbjornsen, Luiza Maria T. Aparecido, Z. Carter Berry et al. „Precipitation mediates sap flux sensitivity to evaporative demand in the neotropics“. Oecologia 191, Nr. 3 (20.09.2019): 519–30. http://dx.doi.org/10.1007/s00442-019-04513-x.
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Chattree, M., und S. Sengupta. „Heat Transfer and Evaporation From Heated Water Bodies“. Journal of Heat Transfer 107, Nr. 4 (01.11.1985): 779–87. http://dx.doi.org/10.1115/1.3247504.
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It is known that there is a sharp temperature gradient in a thin water layer at the air-water interface. Systematic measurements of this temperature difference and meteorological parameters were made at a cooling pond in East Mesa, CA. The water loss was measured directly, and the water temperatures were in the range of 30–46°C. Existing formulae which use the surface temperature difference and wind speeds to predict the net heat flux have been examined. Examination of the well-known Saunders’ equation shows that a parameter λ does not have a constant value. Nondimensional correlations have been developed to predict the net heat flux and the evaporative heat flux at the interface. A dimensional correlation which includes the effect of the surface temperature variation is found to give the most accurate prediction of the net heat flux.
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Cleverly, James, James R. Thibault, Stephen B. Teet, Paul Tashjian, Lawrence E. Hipps, Clifford N. Dahm und Derek Eamus. „Flooding Regime Impacts on Radiation, Evapotranspiration, and Latent Energy Fluxes over Groundwater-Dependent Riparian Cottonwood and Saltcedar Forests“. Advances in Meteorology 2015 (2015): 1–14. http://dx.doi.org/10.1155/2015/935060.
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Radiation and energy balances are key drivers of ecosystem water and carbon cycling. This study reports on ten years of eddy covariance measurements over groundwater-dependent ecosystems (GDEs) in New Mexico, USA, to compare the role of drought and flooding on radiation, water, and energy budgets of forests differing in species composition (native cottonwoodversusnonnative saltcedar) and flooding regime. After net radiation (700–800 W m−2), latent heat flux was the largest energy flux, with annual values of evapotranspiration exceeding annual precipitation by 250–600%. Evaporative cooling dominated the energy fluxes of both forest types, although cottonwood generated much lower daily values of sensible heat flux (<−5 MJ m−2 d−1). Drought caused a reduction in evaporative cooling, especially in the saltcedar sites where evapotranspiration was also reduced, but without a substantial decline in depth-to-groundwater. Our findings have broad implications on water security and the management of native and nonnative vegetation within semiarid southwestern North America. Specifically, consideration of the energy budgets of GDEs as they respond to fluctuations in climatic conditions can inform the management options for reducing evapotranspiration and maintaining in-stream flow, which is legally mandated as part of interstate and international water resources agreements.
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Abu-Zaid, M., und A. Atreya. „Transient Cooling of Hot Porous and Nonporous Ceramic Solids by Droplet Evaporation“. Journal of Heat Transfer 116, Nr. 3 (01.08.1994): 694–701. http://dx.doi.org/10.1115/1.2910924.
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This paper presents the results of an experimental investigation into transient cooling of low-thermal-conductivity porous and nonporous ceramic solids by individual water droplets. The initial surface temperature (Ts) of both solids ranged from 75 to 200°C. Both solids were instrumented with several surface and in-depth thermocouples and had the same thermal properties. This enabled investigation into the similarities and differences in the thermal behavior of porous and nonporous solids during droplet evaporation. The measured and theoretical contact temperatures, for both solids, were found to be in good agreement until they became equal to the boiling point of water (which occurs at an initial solid surface temperature of 164°C). Further increase in the initial solid surface temperature did not change the measured contact temperature. Instead, it became roughly constant at a value slightly greater than the boiling point of water. During the droplet evaporation process, surface and in-depth temperatures for the nonporous solid remain nearly constant, whereas for the porous solid there was a continuous decrease in these temperatures. A thermocouple in the porous matrix at the same location as that of the nonporous matrix cools faster under identical conditions, indicating an energy sink in the vicinity of the thermocouple. Also, evaporation time for the nonporous solid was found to be larger than that of the porous solid for the same droplet size and under the same conditions. These observations confirm that there is both in-depth and lateral penetration of water in the porous solid. The transient temperature measurements were used to determine the following quantities: (i) the recovery time (time required by the surface to recover to its initial temperature), and (ii) the size of surface and in-depth zones affected by the droplet. The instantaneous evaporation rate, and the instantaneous average evaporative heat flux for the nonporous solid, were also determined from video measurements of the droplet diameter on the solid surface and the transient temperature measurements. It was found that the average evaporative heat flux is higher for smaller droplets because of their smaller thickness on the hot surface.