Variation Of Evaporation Rate Research Articles

Water evaporation from cracked soil under moist conditions as related to crack properties and near‐surface wind speed

AbstractThe impacts of five factors (wind speed, crack width, crack distance, crack depth and crack orientation (compared to wind direction)), on evaporation from cracked soil under moist soil conditions were investigated experimentally. Experiments were carried out under laboratory conditions in a wind tunnel with a 1 m × 1 m × 2.5 m test section using large‐scale (50 cm diameter, 25 cm depth) samples of natural soils wetted to a soil water content of 0.2 g g−1. To reduce the number of necessary experiments, a 2k factorial experimental design was used. Crack widths, crack distances, crack depths and crack orientations of 5–20 mm, 40–100 mm, 50–200 mm and 0–90°, respectively, were used. Effects of each factor on evaporation rate, individually and by interaction between multiple factors, were subsequently calculated. Results showed that individual effects of all five factors on evaporation rate were significant at the 95% level. Wind speed had the largest impact on evaporation rate, followed by crack width, crack distance, crack depth and crack orientation in that order. Overall, the four crack properties together explained 47% of the variations in evaporation rate.Highlights Evaporation from cracked, moist soil under windy conditions was investigated. Crack orientation significantly affects wind conditions close to the surface. Both wind speed and crack properties significantly affected evaporation rate. Crack properties together explained 47% of variations in evaporation rate.

Experimental investigation of evaporation dynamic of sessile droplets in pure vapor environment with low pressures

In order to understand the evaporation dynamic of sessile droplet in pure vapor environment, this paper presented a series of experimental observations on the evolution of thermal patterns and the variation of evaporation rate during water and ethanol droplet evaporation at low pressures. The contact radius of droplet is fixed at 2.5 mm and the height varies from 0.4 to 1.6 mm. Results show that the surface temperature distributions for both water and ethanol are uniform at a high pressure ratio. When the pressure is reduced, a ring-like thermal pattern appears on the water droplet surface, while the gear-like pattern and the cellular flow happen on the ethanol droplet surface. Interestingly, the gear-like pattern is static when the substrate temperature is low, while it will oscillate at a high substrate temperature. Meanwhile, the cellular flow is affected by the droplet height. The evaporation is promoted by reducing the pressure. Moreover, due to the decrease of the evaporation surface area and the increase of surface temperature, the evaporation rate decreases first and then increases with the decrease of the droplet height.

Response surface based experimental analysis and thermal resistance model of a thermoelectric power generation system

In this work, a response surface analysis is carried out on an experimental setup of a combined two-phase flow thermosyphon and thermoelectric generator (TEG) system. Three-level Box-Behnken response surface method is adopted for the design of experiments, and analysis of variance is carried out to gauge the contribution of operating parameters on various performance parameters. Effects of operating parameters such as working pressure, filling ratio, evaporator length, and evaporator temperature are studied. The performance of the system itself is gauged concerning the maximum power obtained, open circuit voltage and short circuit current. With an increase in vacuum pressure and evaporator temperature, performance parameters are found to increase. However, performance parameters under the influence of filling ratio and evaporator length first decrease and then increase due to uneven variation in evaporation rate of working fluid. Experiments also reveal that the performance of the thermosyphon-assisted TEG system is mainly governed by pressure and evaporator temperature, whereas filling ratio and evaporator length have relatively lesser influence.

5. The Effect of Climate Variability on Lake Water Balances and Water Quality in the Apex River Watershed, Baffin Island, Nunavut

Iqaluit, Nunavut is currently facing a water shortage as its population rises, and its drinking water reservoir, Lake Geraldine, is increasingly insufficient. The City of Iqaluit is currently looking into alternative sources of drinking water to supplement this reservoir. This study investigates the effects of inter-annual climate variability on the water chemistry of twenty Arctic lakes in a continuous permafrost region, and the potential implications of these changes on drinking water availability. The twenty lakes are located in the Niaqunguk (Apex) river watershed, Baffin Island, Nunavut (which is adjacent to the Lake Geraldine watershed at Iqaluit) were sampled annually during late July between 2014-2017. Ion concentrations and stable isotopes were measured for each lake annually throughout the study period to compare variability between lakes and between years. Water chemical and physical properties are used to gain insight into the inputs and outputs of each lake, and the changes in estimated water balance between years. This information will be used to determine the impact of different hydrological conditions on water chemistry. Results of water isotope tracers of the twenty lakes indicate that there are important year-to-year changes in the water stable isotopes, indicating inter-annual variations in evaporation rates, suggesting that these lakes are sensitive to changes in summer climatic conditions. Preliminary analyses of the ionic concentrations of the lakes suggest that ion concentrations generally decrease throughout the study period, and largely vary together, signifying the hydrological processes controlling the lake water balances are related to climate variability. This research will provide insights into the hydrologic response of lakes in a continuous permafrost region to long-term climatic change.

Particle evaporation and hydrodynamics in a shock driven multiphase instability

This paper presents results from 3D numerical simulations of a shock-driven multiphase instability of a gas-particle system with a spherical interface. Two cases, one with an evaporating particle cloud and another with a gas only approximation were run in the hydrodynamics code FLASH. Both cases had an incident Mach number of 1.65 and an effective Atwood number of 0.046. It is shown that the gas only approximation, a classical Richtmyer–Meshkov instability, cannot replicate effects from particles like, lag, clustering, and evaporation. Instead, both gas hydrodynamics and particle properties influence one another and are coupled. Qualitative and quantitative differences in the Richtmyer–Meshkov instability and shock-driven multiphase instability are briefly presented. Coupling between the interface hydrodynamic evolution and particle evaporation is explored further by examination of the multiphase case. Hydrodynamic driven particle clustering is measured through particle spatial distribution statistics and particle-vorticity correlations. It is found that the small particles form vorticity driven small scale clusters quickly while hydrodynamics act to reorganize the particles into larger scale features at later times. Particle evaporation rates are found to vary greatly, even among similar sizes, and show poor agreement with existing 1D evaporation models. The role of hydrodynamic organization in evaporation is shown by examining the spatial distribution of variations in evaporation rate. Small to medium sized particles initially located at the outside of the sphere, in the equatorial region (taking the sphere to have poles aligned with the shock transit direction) are most affected by the hydrodynamic development and show higher evaporation rates, similar to those found with a 1D, one-way coupled, single particle evaporation model.

Triple diagram models for changeability evaluation of precipitation and flow discharge for suspended sediment load in different time scales

Suspended sediment load (SSL) records in streams can be highly variable in time and space, making it difficult to quantify sediment fluxes and to discriminate particular patterns. The deep study on effective factors and their variability in different time scales is, therefore, a vital task. In the present study, the variability of precipitation and streamflow has been analyzed in Gorgan-roud River Basin, Iran in different time scales. Towards this attempt, daily precipitation, streamflow and SSL records spanning during 4 years (i.e. 1982–1985) from the Ghazaghli station situated in the main stem of the Gorgan-roud, were analyzed using Triple Diagram Model. The results indicated that the temporal streamflow and flood frequency variations largely affected the SSL. The results also showed that the pattern of SSL was more apparent by increasing the time span of the recorded data. According to the results, the sediment load in the study station has been affected by different streamflow magnitudes at monthly, seasonal and yearly time scales. According to the results, some 25 % of SSL has been carried out by streamflow probability of 40 % (i.e., 2.5 years of return period), while the transportation of SSL occurred in all ranges of precipitation amount. The amount of SSL moved by less frequent flows and not influenced by precipitation magnitudes, which indicates that the variations of SSL were mainly the result of temporal variations in evaporation rate, soil and vegetation cover conditions, affected precipitation–discharge–SSL relationships.

PIV measurements of flow in drying polymer solutions during solvent casting

An experimental method based on confocal microscopy and particle image velocimetry (PIV) is used to characterize the flow in a polymer solution during solvent casting. The flow inside a 200-μm-thick film of a poly(vinyl alcohol) (PVA) solution is visualized near a vertical wall of a mold using confocal microscopy of seed particles during solvent evaporation at 25, 35, and 45°C, and the corresponding velocity vector fields are determined from projections of the confocal images. Flow toward the vertical wall is observed inside the film as well as a slower Marangoni-type counter flow at the film surface during the initial phase of solvent evaporation, resulting from a polymer concentration gradient along the film due to a local variation in evaporation rate. Total volume of the polymer solution in the observation volume as well as solvent evaporation rate are determined as a function of time, both revealing close correlation to average horizontal velocity data from PIV. The PIV measurements show significant differences in the flow velocity fields at different temperatures. The PIV measurements correlate with the solvent evaporation rates as well as the final polymer thicknesses on the vertical wall of the mold. Surface tension and viscosity measurements are taken for different concentrations of PVA solution.

Formation and circulation of dense water in the Persian/Arabian Gulf

The nature and circulation of water masses in the Persian/Arabian Gulf (hereinafter referred to as the Gulf) is investigated by examination of a historic database of hydrographic observations. The densest water forms in winter at the northern end of the Gulf rather than along the warmer southern and western coasts. With the exception of small amounts of water directly above the seafloor, most water flowing out of the Gulf mixes across a density front that separates Gulf Deep Water within the Gulf from the Indian Ocean Surface Water (IOSW). Contrary to previous inferences, the seasonally variable incursion of IOSW into the Gulf peaks in late spring. This timing may be due to seasonal changes in sea surface slope driven by variations in evaporation rate. In order to explain mooring results published elsewhere that show relatively small seasonal changes in the volume flux through the Strait of Hormuz (hereinafter referred to as the Strait), we suggest that this flux is driven by the difference between the density of Gulf Deep Water in the interior of the basin and water at comparable depths outside the Gulf. This density difference varies less than 15% during the year. High rates of vertical mixing in the Strait extend about 200 km westward in response to topographic constriction of tidal flows by islands and shoals.

Intraspecific physiological variability of the gastropod Littorina saxatilis related to the vertical shore gradient in the White and North Seas

Physiological responses to desiccation and temperature stress as well as behavioural responses to fast and abrupt environmental changes were investigated in high- and low-shore Littorina saxatilis (Olivi) from several populations from the White and North Seas. Variations in evaporation rates, resistance to air exposure and to acute and chronic temperature stress between animals from different shore levels were similar in White and North Sea periwinkles, consistent with the adaptive nature of these variations. High-shore snails were found to be able to conserve body water reserves better, to resist higher temperatures and to survive longer under conditions of combined temperature and desiccation stress than their low-shore counterparts. In a temperature range of 25 to 35 °C, the rate of evaporative water loss was positively correlated with temperature in low-shore snails while being largely temperature-independent in high-shore snails. Median lethal time during air exposure in L. saxatilis was negatively but not linearly related to the temperature of exposure. In a temperature range of 30 to 38 °C, the resistance to heat exposure in air was only slightly dependent on the temperature, with Q 10 = 1.4 for the median lethal time; the heat resistance dropped drastically at temperatures above 38 °C, with Q 10 = 593.8. This suggests different mechanisms of temperature resistance in different parts of the studied temperature range. In contrast, behavioural response to extreme salinity fluctuations was not uniform in the high- and low-shore periwinkles from the White and North Seas, which may reflect specific environmental conditions at different shore levels in the two areas studied. Observed physiological and behavioural variations are discussed from the viewpoint of different adaptive strategies employed by eulittoral and eulittoral-fringe animals within populations of a single species.

Textural features of Holocene perennial saline lake deposits of the Taoudenni–Agorgott basin, northern Mali

Abstract The Holocene salt lake deposits of the Taoudenni–Agorgott basin, northern Mali, mainly consist of sediments with a high glauberite (Na2Ca(SO4)2) content. The remainder of the deposits largely consists of salt beds with a bloedite (Na2Mg(SO4)2·4H2O), thenardite (Na2SO4) or halite (NaCl) composition. A petrographical study of the deposits demonstrates that they formed in a perennial lake that experienced a gradual decrease in water depth. Textural features of the glauberite-dominated deposits are found to be related to water depth, through the control that this factor exerts on the sensitivity of the lake to changes in water supply and to short-term variations in evaporation rates. In this way, layering — due to variations in glauberite content and crystal size — is inferred to be typical of deposits that formed in shallow water, whereas unstratified deposits are the product of high lake level stages. Halite textures are found to be indicative of the place within the water column where crystal growth occurred (along the lake bottom or higher), which is mainly determined by water depth and partly by evaporation rates. The oldest halite beds are largely unaltered cumulate deposits, whereas the youngest layers developed exclusively through bottom growth. The basal part of one thick halite bed at a level between these two groups of halite layers developed by an alternation of both types of growth, in response to variations in evaporation rates. Variations in mineralogical composition between and within the salt beds that formed during the earliest periods with a higher salinity, up to the first stage with halite formation, record a change in lake water chemistry with time but they are in one instance also determined by an early diagenetic mineral transformation.

Environmental conditions for treatment of burned patients by the exposure method

The influence of the thermal environment on evaporation and heat loss from patients with severe burns treated by exposure has been studied. Simple heat transfer equations can be used to predict changes resulting from alterations in environmental conditions and these have been tested using phantoms. The method relies upon the derivation of surface diffusion resistances to describe the moisture properties of burn wounds. Clinical measurements revealed wide variations in evaporation rates and diffusion resistances for different wounds. Evaporation rates changed by less than 30 per cent during the first 5–6 days following injury, after which evaporation from partial skin thickness wounds gradually fell whereas that from full skin thickness wounds tended to remain higher. Raising ambient temperature can compensate for increased evaporative heat losses. Patients can be treated at ambient temperatures of 32–35°C in the intensive care room with a specially designed airflow system. However, raising the temperatures of standard wards with no special airflow or temperature control facilities often caused patients to sweat, further increasing heat loss.

On periodic sweating from the human skin during rest and exercise.

The rhythmic variations in the water evaporation rate (gm-2h-1,) from the dorsal side of the forearm have been studied. The evaporation rate is estimated by calculating the difference between the vapour pressures at two distinct points on a line perpendicular to the evaporative surface. Using autocorrelation technique it is found that the evaporation rate is periodic with a period of around 0.7 s. This value is consistent, at rest as well as prior to profuse sweating in exercise, for all the subjects included in the investigation. During profuse sweating the period becomes slightly longer. It is suggested that the variations in the evaporation rate reflect the periodic activity in the sudomotor nerves.

The hydrodynamic stability of rapidly evaporating liquids at reduced pressure

The hydrodynamic stability of a pure liquid undergoing steady rapid evaporation at reduced pressure is examined using linear stability analysis. Results show that the rapidly evaporating liquid is unstable to local variations in evaporation rate, local surface depressions being produced by the force exerted on the surface by the rapidly departing vapour and sustained liquid flows being driven by the resultant shear exerted on the liquid surface by the vapour. The coupling of this ‘differential vapour recoil’ mechanism to the Marangoni effect is investigated and the importance of inertial heat transfer, fluid inertia and viscous dissipation at the interface to system stability is resolved.

Field Measurement of Evaporation from Soil Shrinkage Cracks

AbstractWeighing lysimetry was used to determine evaporative fluxes from a natural shrinkage crack and from an artificially induced soil shrinkage crack. Evaporation from the soil surface, except at the crack opening, was prevented by covering the lysimeter with plastic film. Evaporation rates from the natural and induced crack averaged about 0.6 mm/day computed on the basis of the surface area of the lysimeter. The horizontal soil water flux in the liquid phase to the crack wall was quite low, indicating that most of the measured evaporation resulted from vapor transport from some distance in the soil pores to the crack walls. Diurnal variations in evaporation rates were closely related to diurnal changes in vapor pressure deficit of the atmosphere above the soil surface. Evaporation rates from the natural/crack experiment were practically the same when the crack and soil surface were exposed to the atmosphere as when only the crack opening was exposed. Therefore, most evaporation from cracked, dry clay soil occurs because of the presence of shrinkage cracks. The results suggest a possibility for conserving water by partially filling the shrinkage cracks with dry soil or mulch to reduce evaporation. The low evaporation rates measured, however, make the feasibility of such a practice doubtful.

EVAPORATION IN EAST AFRICA

Abstract Following a decision to estimate potential evaporation from meteorological observations rather than from evaporation pans, 53 agricultural meteorological stations were established over East Africa with the co-operation of several departments of three governments. Supplementary information from an additional 123 less well equipped stations was incorporated into the preparation of maps of monthly potential open water evaporation, using the Penman estimate. Annual values of potential evaporation range from more than 2,600 mm to less than 1,400 mm with 70% of the area of East Africa having potential evaporation rates, of between 1,800 and 2,200 mm per annum. There are marked seasonal variations in evaporation rates, mainly dependent on patterns of cloud cover, but average monthly rates rarely fall below 90 mm even in highland areas. These high rates of water demand have serious implications for the management of water catchments, land planning, crop breeding, tillage techniques, ground water recharge...

Local advection over crops and fallow 1 Changes in evaporation rates along a 17-km transect in the Sudan Gezira

Changes in evaporation from small dishes, and in temperature and vapour pressure of the air, were observed in the Sudan Gezira, where large cotton fields are interspersed amongst uncropped dry fallows. Lateral movement of energy resulted in high evaporation rates near the leading edges of irrigated fields and in a progressive decrease, of about 30%, in evaporative demand within the leading 60 m of a cotton field. Evaporation rates increased as the wind blew across dry, uncropped fields lying downwind of the cotton. Water losses from evaporimeters, with similar exposures, decreased at the rate of nearly 2% per km over a transect of 17 km (about 10 miles). The lateral variations in evaporation rates were due to changes in temperature, vapour pressure deficit, and wind speed along the transect. Advection was found to be less apparent in temperate conditions in England than in the hot arid climate of the Sudan.

EVAPORATION OF WATER PROM APPLES IN RELATION TO TEMPERATURE AND ATMOSPHERIC HUMIDITY

SUMMARY.A technique has been described for determining by a weighing method the rate of evaporation of water from certain isolated plant organs (apples and pears) under conditions of constant temperature and constant atmospheric humidity.The rate of evaporation from Bramley's Seedling apples at constant temperature and humidity changes steadily throughout the storage phase; decreasing at first rapidly and then more slowly towards a more or less steady state. It is evident that the rate of evaporation is conditioned by certain internal factors, the nature of which is at present unknown; the magnitude of the control exerted by these factors is observed to change with time. No sharp changes in rate occur during this period, and so far it has not been possible to correlate the smooth transition with phenomena of metabolic activity, such as change in osmotic pressure of the cell solutions.The relation between evaporation rate and R.H. at constant temperature shows a marked deviation from the linear, as exhibited by a free‐water surface. There is an increase in the rate of evaporation with decreasing R.H. down to about 65 per cent. R.H.; a gradual decline in the rate of increase being shown for each decrement of R.H. The resistance to outward movement of water vapour would therefore appear to change with change of external vapour pressure. Below about 65 per cent. R.H. it would seem that a steady rate might be expected, when internal resistances would become Hmiting.At constant R.H. and temperatures between the limits of 3 and 15° C. the rate of evaporation is more nearly approximate to the vapour‐pressure deficit of the external atmosphere.The variation in evaporation rate between individual apples of the same variety under the same conditions of temperature and humidity is considerable. These variations cannot be attributed to differences in the thickness of the cuticles, since a marked negative correlation between evaporation rate and thickness of cuticle was found in Cox's Orange Pippin apples. Other factors such as frequency of distribution and size of lenticels and the structure of the stem and calyx ends of the fruit probably exert a controlling influence over the magnitude of evaporation rate.The increase in rate of evaporation which occurs with fungal invasion of the tissues would seem to indicate that, although in the healthy fruit some control over the supply of water to the evaporating surface is exerted by the cortical tissues, the extent of this control is small in comparison with that exerted by the epidermis.Grateful acknowledgment is made to Drs Franklin Kidd and Cyril West for their very helpful criticism and advice, and to Miss Ursula Tetley for her co‐operation.