Evaporation Front Research Articles

Disc and atmosphere composition of multi-planet systems

In protoplanetary discs, small millimetre-centimetre-sized pebbles drift inwards which can aid in planetary growth and influence the chemical composition of their natal discs. Gaps in protoplanetary discs can hinder the effective inward transport of pebbles by trapping the material in pressure bumps. In this work, we explore how multiple planets change the vapour enrichment by gap opening. For this, we extended the chemcomp code to include multiple growing planets and investigated the effect of 1, 2, and 3 planets on the water content and C/O ratio in the gas disc as well as the final composition of the planetary atmosphere. We followed planet migration over evaporation fronts and found that previously trapped pebbles evaporate relatively quickly and enrich the gas. We also found that in a multi-planet system, the atmosphere composition can be reduced in carbon and oxygen compared to the case without other planets, due to the blocking of volatile-rich pebbles by an outer planet. This effect is stronger for lower viscosities because planets migrate further at higher viscosities and eventually cross inner evaporation fronts, releasing previously trapped pebbles. Interestingly, we found that nitrogen remains super-stellar regardless of the number of planets in the system such that super-stellar values in N/H of giant planet atmospheres may be a tracer for the importance of pebble drift and evaporation.

Evaporation from Porous Rock: Deciphering the Importance of Measuring the Evaporation Front Depth

Evaporation from Porous Rock: Deciphering the Importance of Measuring the Evaporation Front Depth

Analysis of experimental and simulation data of evaporation‐driven isotopic fractionation in unsaturated porous media

AbstractStable water isotopologs can add valuable information to the understanding of evaporation processes. The identification of the evaporation front from isotopolog concentration depth profiles under very dry soil conditions is of particular interest. We compared two different models that describe isotopolog transport in a drying unsaturated porous medium: SiSPAT‐Isotope and DuMux. In DuMux, the medium can dry out completely whereas in SiSPAT‐Isotope, drying is limited to the residual water saturation. We evaluated the impact of residual water saturation on simulated isotopic concentration. For a low residual water saturation, both models simulated similar isotopolog concentrations. For high residual water saturation, SiSPAT‐Isotope simulated considerably lower concentrations than DuMux. This is attributed to the buffering of changes in isotopolog concentrations by the residual water in SiSPAT‐Isotope and an additional enrichment due to evaporation of residual water in DuMux. Additionally, we present a comparison between high‐frequency experimental data and model simulations. We found that diffusive transport processes in the laminar boundary layer and in the dried‐out surface soil layer need to be represented correctly to reproduce the observed downward movement of the evaporation front and the associated peak of isotopolog enrichment. Artificially increasing the boundary layer thickness to reproduce a decrease in evaporation rate leads to incorrect simulation of the location of the evaporation front and isotopolog concentration profile.

Moisture patterns and fluxes in evolving tafoni developed in arkosic sandstone in temperate climate

AbstractCavernous weathering forms have long been studied and discussed as enigmas in geomorphology. Recently, their evolution has been shown to be controlled by moisture patterns, which are still poorly understood. For the first time, capillary water and vapor fluxes were characterized in detail at tafone in a temperate climate of central Europe using a wide range of methods adapted from soil hydrology. Time domain reflectometry showed that moisture flows from the rock interior to the evaporation front in the shallow subsurface of both — the backwalls and the outer surface. When overland flow occurs on the outer surfaces (after heavy rains), 10 mm/day can infiltrate and flow toward the backwalls. The main sources of water for tafone are the influx of water from the rock interior and the infiltration of overland flow after heavy rains, while condensation of air humidity is a minor source. Influx from the rock interior is coupled to the evaporation rate, which varies between 100 and 300 kg/m2/year in summer and less than 15 kg/m2/year in winter. More water evaporates from the backwall of the tafone than from the outer surface, and more salt is deposited in the backwalls, resulting in predominant salt weathering in the backwalls. The tafoni studied thus evolve, and the cavities deepen. Tafoni in arid and semi‐arid environments generally show a much higher contrast between evaporation rates from backwalls and outer surfaces than tafoni and honeycombs in temperate and coastal environments. Tafoni in temperate settings are therefore more susceptible to degradation when evaporation decreases or inflow to the tafone increases. This study also shows that microtensiometers can be used to determine moisture content with high spatial resolution, while time domain reflectometry allows accurate characterization of moisture patterns with depth.

An innovative drying method for on-site and precast walls – Efficiency in accelerating the drying of reduced-scale earth-lime-hemp composites

The drying of construction materials is a challenge regarding structure’s durability and costly construction delays. Long drying periods induce high-moisture content that leads to fungal growth risks. This study presents the development of an innovative forced convection drying method, inspired by unglazed transpired solar wall system and repurposed here for its drying potential at the wall scale. This method employs a metal perforated panel placed at a short distance from the material to dry. This creates an air cavity between them where forced convection is applied with ambient air penetrating through the perforated panel. The moistened air is evacuated thanks to an air circuit composed of a fan and an extraction duct. Two panel configurations with round and cross-shaped perforations are investigated and compared to a natural convection reference. The efficiency of the method is evaluated on Earth-Lime-Hemp composites. With forced convection method, the evaporation front moves moisture towards the near wall forced convection surface and leads to more efficient moisture removal. The results demonstrate a 50 % reduction in drying time using forced convection drying compared to natural convection drying in an open area. Both panel configurations show similar efficiency. The proposed drying method meets the challenges above-mentioned and is applicable for both prefabricated elements and on-site construction. Additionally, it can be effective for the restoration after water damage, enhancing overall construction resilience.

Mathematical modelling of impurity deposition during evaporation of dirty liquid in a porous material

When a contaminated liquid evaporates from within a porous material, the impurities or dirt accumulate and deposit within the pore space. This occurs during the cleaning of filters and fouling of textiles, and is related to the ‘coffee-ring’ problem. To investigate how and where dirt is deposited in the pore space, we present a model for the motion of an evaporation front through a porous material, and the related accumulation, transport, and deposition of dirt, assuming that the liquid remains stationary. For physically relevant parameters, vapour transport out of the porous material is quasi-steady and we derive a single ordinary differential equation describing the motion of the evaporation front in time. Model solutions exhibit spatially non-uniform profiles of the deposited dirt-layer thickness through the porous material. The dirt accumulation and evaporation problems are coupled: deposited dirt hinders vapour transport through the porous material, slowing the evaporation. We identify two scenarios in which the porous material becomes clogged with dirt. Accumulation of suspended dirt at the evaporating interface along with slow dirt diffusion results in the deposited dirt layers clogging the pores at the evaporating interface, halting the drying and trapping liquid in the porous material. Alternatively, slow dirt deposition results in the suspended dirt being pushed far into the porous material by the evaporation, eventually leaving only dirt (with no liquid) in the pore space. We investigate the dynamics of both clogging scenarios, characterising the parameter regimes for which each occurs. Both clogging scenarios must be avoided in practice since they may be detrimental to future filter efficacy or textile breathability.

Sodium chloride crystallization in a model porous medium during drying with a receding sharp front

Visualization experiments in a model porous medium are presented in this work to study the interplay between salt precipitation and gas–liquid displacement during evaporation for the drying situation characterized by a receding sharp drying front. Various types of salt subflorescence are distinguished depending on the location of the subflorescence growth, namely, away from the drying front in the region predominantly occupied by gas or in the liquid-saturated region. A distinction is also made regarding the subflorescence that develops in the predominantly gaseous region depending on the degree of occupation of the pores by the subflorescence structure. The experiment confirms that the capillary liquid films can be a pathway for the dissolved salt transport. As a result of the capillary film effect, the evaporation front must be distinguished from the drying front and subflorescence structures can develop in the vicinity of the evaporation front away from the drying front. It is also shown that the pinning of the evaporation front leads to an anomalous drying front kinetics with a drying front position varying linearly with time and not according to the classical scaling with the square root of time.

CO2 flow modeling in a coupled wellbore and aquifer system: Details of pressure, temperature, and dry-out

In order to understand the details of thermal and hydrologic processes attending CO2 injection into a deep aquifer in the context of Carbon Capture and Storage (CCS), we have carried out coupled well-reservoir simulations of CO2 injection using the simulator T2WELL-ECO2M. We focus on the injection of cold, dry CO2 into a warm aquifer and analyze in detail the thermal and hydraulic processes of the coupled well-reservoir system. The results demonstrate the effectiveness of T2WELL in accurately modeling non-isothermal, multiphase flow, phase changes, and identifying dry-out regions in porous media.We simulated heat exchange with the ambient environment, friction effects, convection, exothermic dissolution in brine, and cooling due to both Joule-Thomson effect and water vaporization. The temperature profile within the wellbore deviated from the geothermal profile, impacting CO2 properties at the bottomhole. The simulation revealed the presence of three fronts in the formation: the CO2 saturation, thermal, and evaporation fronts. The thermal and evaporation fronts were located farther behind the saturation front, indicating limited dry-out and thermal effects near the wellbore.This simulation capability and insights gained in this study form a foundation for ongoing work such as sensitivity analyses, injection optimization, performance assessment, and operational decision support.

Understanding the Effect of Seasonal Climate Variability on the Salinity in Unsaturated Agricultural Soil

Salinization/desalinization processes in the soil vadose zone are important to define agricultural irrigation and drainage schedules, especially in reclaimed crop areas. Numerical modeling of soil–climate interaction is a very helpful tool to understand soil salinity distribution and solute transport and therefore define efficient desalination solutions. A finite element analysis program Code_Bright was used to perform a coupled thermo-chemo-hydraulic analysis aiming at investigating the effect of climate actions on the distribution of soil salinity in depth, by modeling solute transport in the vadose zone under fresh/saline groundwater supply. The analysis separated first the effect of rain infiltration and evaporation, and then a real climate was considered as the boundary condition. A downward flow pattern induced by rainfall in the unsaturated zone resulted in a nonlinear salt leaching process. Significant differences in salt concentration between the surface and lower layer caused by rainfall resulted in a decrement in the leaching efficiency. Evaporation causes water to move upward and salt transport to the surface, thus enhancing the soil salinity above the evaporation front. The salinity above the groundwater table and below the evaporation front were less affected regardless of the salinity of the supplied groundwater. The model simulated the salt leaching process during the wet seasons and salt accumulation processes during the dry ones. The soil salinity and saturation at the soil surface have significantly responded to seasonal climate variability. A typical seasonal climate variability would result in a low salt leaching efficiency through years in the coastal reclamation area. These results would be helpful for the design of soil salinization management strategies, such as reducing salt accumulation by reducing evaporation or leaching the surface salt in the dry season, and increasing the drainage to promote leaching in the wet season.

Investigation of the kinetics of spontaneous boiling-up of superheated n-pentane in a glass tube with defects of the inner surface. II. Evaporation front

An experimental study of the kinetics and dynamics of spontaneous boiling-up of superheated n-pentane in a thermostated glass tube was carried out using high-speed video recording. The boiling-up occurred both at steady atmospheric pressure (in the temperature range from 100.3 to 125.3 °C) and during pressure reduction (from 105.3 to 135.3 °C). The top of the tube is sealed. The linear propagation velocity of an evaporation front of a superheated liquid has been calculated from the video frames. It has been shown that this value lies in the range from 0.30 to 2.23 m/s, increases with the depth of entry into the metastable region, and depends on the configuration of the liquid-vapor interface.

Drying Behaviour of Western Hemlock with Schedules Developed for Norway Spruce and Scots Pine

Determining moisture content (MC) distribution during the drying of porous materials such as wood is crucial for developing drying schedules and assessing their suitability to achieve optimised processes. This study aimed to determine the causes of the unique drying behaviour and the well-known unusual longer drying time of western hemlock compared to other similar softwoods. In situ X-ray computed tomography (CT) was used to study the evolution of MC in timber during the drying process. The drying behaviour of western hemlock (Tsuga heterophylla (Raf.) Sarg.) was compared with Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) from green to oven-dried condition with industry-proposed drying schedules used for steering a custom-made experimental kiln combined with a CT scanner. CT scanning was performed at 30 min intervals during the complete drying period of 30 h, and the CT images were processed to calculate the MC evolution within the specimen. Western hemlock showed a considerably slower capillary-phase drying and did not go into the transition and diffusion phases when a schedule adapted to pine and spruce drying was applied for its drying. CT images and MC gradient calculations showed a lower drying rate and severe non-uniformity in MC distribution, which could be due to the effect of higher green MC and the presence of wet pockets. Furthermore, the evaporation front at the first 5 h of drying receded faster into the hemlock specimen, and as drying proceeded, it slowed down compared to other specimens.

Nucleation of a Vapor Phase and Vapor Front Dynamics Due to Boiling-Up on a Solid Surface

The effect of temperature and pressure on the nucleation of the vapor phase and the velocity of the vapor front in the initial stage of activated boiling-up of n-pentane on the surface of a quartz fiber was studied. Using a developed approach combining the “pump-probe” and laser Doppler velocimetry methods, this velocity was tracked in the course of sequential change in the degree of superheating with respect to the liquid–vapor equilibrium line. The studied interval according to the degree of superheating was 40–100 °C (at atmospheric pressure). In order to spatiotemporally localize the process, the activation of boiling-up at the end of the light guide was applied using a short nanosecond laser pulse. A spatial locality of measurements was achieved in units of micrometers, along with a time localization at the level of nanoseconds. An increase in temperature at a given pressure was found to lead to an increase in the speed of the transition process with a coefficient of about 0.2 m/s per degree, while an increase in pressure at a given temperature leads to a decrease in the transition process speed with a coefficient of 25.8 m/s per megapascal. The advancement of the vapor front velocity measurements to sub-microsecond intervals from the first signs of boiling-up did not confirm the existence of a Rayleigh expansion stage with a constant velocity.

Experimental study on the detection of frozen diffused ammonia blockage in the inactive section of a variable conductance heat pipe

Variable Conductance Heat Pipes (VCHP) are mainly employed to cool down electronic systems in spacecraft applications, as they can handle high temperature fluctuations in their cold source, preventing thus the systems from damaging. These fluctuations, as well as ultra-low temperatures, are always present in outer space, and one of the key steps in a VCHP design is therefore to make sure that they endure these conditions. However, not much has been written about their resilience during and after a long exposition to subfreezing conditions, i.e. temperatures lower than the freezing point of the working fluid. In this paper we implement and validate a computational routine based on a modified Flat-Front Approach to predict the VCHP temperature profile and to determine the location of the gas–vapor front. Then we continuously expose an ammonia/stainless-steel VCHP to temperatures below the ammonia freezing point for 211 h, to later examine the formation and subsequent dynamics of a thin block of frozen ammonia which is diffused into the inactive part of the heat pipe condenser. We describe as well how a strong correlation between the adiabatic section and the reservoir temperatures is maintained (or broken) upon the occurrence (or absence) of the blockage of frozen ammonia.

How accretion of planet-forming disks influences stellar abundances

Millimeter-sized dust grains experience radial velocities exceeding the gas velocities by orders of magnitude. The viscous evolution of the accretion disk adds disk material onto the central star’s convective envelope, influencing its elemental abundances, [X/H]. At the same time, the envelope mass shrinks as the stellar age increases, amplifying the rate of abundance change. Therefore, the elemental abundances of the star are sensitive to disk processes that alter the composition and timing of disk accretion. We performed numerical 1D log-radial simulations integrating the disk advection-diffusion equation, while accounting for evaporation and condensation of chemical species at the evaporation fronts. They reveal a peak of refractory abundance within the first 2 Myr of Δ[X/H] ~ 5 × 10−2 if grain growth is significant, but subsequent accretion diminishes previous refractory abundance increases for long-lived disks. Planet formation can reduce the abundance of dust species whose evaporation fronts lie within the planet’s orbit by preventing solids from reaching the inner edge once the planet starts opening a gap exerting a pressure bump exterior to its orbit and consequently blocking inward drifting pebbles. We expect the accretion of the solar protoplanetary disk with Jupiter present to have changed the Sun’s elemental abundances by ~1 × 10−2 throughout its lifetime. These considerations were also applied to the HD106515 wide binary system. We find that measurements of Δ[X/H] are in reasonable agreement with results from simulations where the observed giant planet around HD106515 A is included and if HD106515B’s disk formed planetesimals more efficiently. Simulations where the planet formed inside the water ice line are more favorable to agree with observations. Even though the general changes in the stellar abundances due to disk accretion are small, they are detectable at current sensitivities, indicating that the methods presented here can be used to constrain the planet formation pathway.

Tracking X-Ray Source Movement in a Retracting Flux Tube

Solar flares produce sources of localized, enhanced X-ray emission, thought to be due to the acceleration of nonthermal electrons and the transport of energy away from the reconnection site. The 2002 November 28 C1.6 limb flare showed clear X-ray source motion in the Reuven Ramaty High Energy Solar Spectroscopic Imager observations at 3–10 keV propagating from the apex of the flaring arcade, down toward the footpoints, and then rising back into the corona. Previous work attempted to model this motion using simulations driven by heating with an electron beam or thermal conduction front, finding reasonable agreement only if there were large initial densities. This work extends the previous model by considering a flux tube that retracts through a current sheet away from a magnetic reconnection site. The retraction model includes drag to slow motion in the current sheet, which allows us to vary the energy released by the retraction. This retraction causes a dense and superhot plug of material to form at the loop apex, naturally causing a thermal X-ray source to form in the corona. We find that the observed X-ray source motion, however, is most likely thermal and a signature of the evaporation fronts after initially filling the flux tube.

Pore-scale modeling of gravity-driven superheated vapor flooding process in porous media using the lattice Boltzmann method

In this work, a hybrid method combining interparticle-potential multiphase LBM, finite difference method and characteristic-line wetting scheme, is developed for pore-scale simulation of superheated vapor displacing liquid, driven by gravity, in a porous geometry. The influence of injected vapor superheat, surface wettability and gravity on two-phase displacement and heat transfer processes is investigated. Results show that in thermal displacement, the vapor-liquid interface is unstable and trapped liquid blobs gradually evaporate into vapor. At low vapor superheat degrees, the displacement efficiency, as compared to isothermal displacement, is significantly improved, but it reduces as the vapor superheat degree rises due to the shift of displacement patterns. At all contact angles considered, the displacement always exhibits viscous fingering, although vapor flowpaths become wider with increasing surface wettability. The final vapor saturation is insensitive to surface wettability, but reducing contact angle leads to a less even temperature distribution inside vapor and a decrease in final average vapor temperature. In addition, increasing gravity is found to reduce vapor front temperature, but it almost has no effect on final average vapor temperature because the final average vapor temperature does not only depend on specific interfacial length but also on fingering number and inlet flow rate.

Experimental and numerical studies of dynamic variation of liquid water and water vapor flow in the vadose zone

In arid and semi-arid regions, the depth of water table has a significant effect on evaporation. The soil in these regions is unsaturated, and the transport of liquid water and water vapor is accompanied by variation of the water table depth. In this study, we designed a laboratory experimental apparatus to conduct evaporation experiments of soil under shallow and deep water table conditions through continuous monitoring of water content and temperature variation in the vadose zone. A numerical model was used to simulate the coupled transport of liquid water, water vapor and heat in the vadose zone under two different water table elevations. The experimental and numerical results were in good agreement. Liquid water and water vapor fluxes driven by pressure head and temperature gradient were calculated and analyzed to illustrate the distribution of the water content. Both isothermal liquid flux and thermal vapor flux dominates the variation of water content. By determining the location of the evaporation front and analyzing its dynamic variation, we found that the evaporation front ranged from the surface to a depth of 2.5 cm under a shallow water table. For a deep water table, the evaporation front was nearly at a constant depth of 15 cm.

Mathematical Simulation of Honeycomb Weathering via Moisture Transport and Salt Deposition

Honeycomb weathering is a common phenomenon found on various rock surfaces all around the world. However, honeycomb formation mechanisms are still poorly understood. In this study, we propose a model describing moisture transport within the sandstone and erosion resulting from salt deposition during evaporation of moisture off the rock surface. The moisture transport model is based on the non-linear diffusion equation, where the volumetric moisture content is a combined parameter accounting for the moisture and gas (vapor) content. The moisture transport model accounts for the several-orders-of-magnitude decrease in moisture diffusivity, observed during drying. It was assumed that erosion occurs when the evaporation front is located close to the rock surface. The depth of erosion is proportional to the moisture flow rate through the drying surface. The ABAQUS finite-element software suite was used for numerical solution of the non-linear diffusion equation. The iterative scheme of erosion simulation for different drying cycles was implemented using the Python programming language. Computations were conducted in the 2D setting for the square model with dimensions of 50 mm × 50 mm. Simulation results demonstrate the possibility of obtaining various landform shapes (honeycombs, tafoni) by varying only the value of the distribution of moisture content at the bottom side, simulating the rate of internal wetting of rock.

Understanding the dynamics of evaporation from stony soils via laboratory experiments and numerical modeling

Stones and rock fragments are typically found within soil profiles across various landscapes. However, knowledge on, and understanding of, their impact on hydraulic functions and processes are still lacking. Specifically, the presence of stones within the soil profile may increase water storage and availability to vegetation and reduce plant mortality in drylands. However, physically-based testing of stones effect on soil water budget components is overlooked. Experiments under laboratory conditions from soil columns, with two volume content t levels and two sizes of stones, were carried out in this research. Our results reveal that stoniness reduces the duration of stage-1 evaporation (S1) and consequently the overall cumulative evaporation, proportionally to their volumetric content and to the initial soil water content. The effect of stone size on evaporation was minor during S1 but was more pronounced during stage-2 (S2) — when the evaporation front migrates downward — with smaller stones reducing evaporation more than the larger ones. A recent evaporation model, assuming that transient evaporation is a succession of steady state solutions, was applied to explain the 2-phases evaporation process in a stony profile. The model results indicate that apart from changing the effective porosity of the soil profile by replacing a soil volume by stones, stoniness affects mainly the hydraulic conductivity function but practically not the water retention curve. Stoniness induced an increase in the tortuosity-related parameters compared with those of the stone-free soil. This observation was strengthened by the fact that both measured and modelled data reveal that stoniness has not affected the downward movement of the water table level during drying. Although we tested two stone sizes only and further experiments are required for a broader understanding, we suggest that the outcoming insights may improve estimates of water budget components in stony soil profiles and their response to global climatic changes.

Consistent description of phase-change processes in substances with density contrast: A finite volume based approach

Phase-change is an important phenomenon and usually it causes a concomitant change in the density of the underlying materials. As applications of phase-change grow, it is important to develop numerical tools that can model this phase-change behaviour accurately; many efforts have improved the ability of numerical algorithms to do so; however, with materials in which phase-change causes significant change in density, these approaches are inadequate in predicting the phase-change interface or the temperature profiles during this process. To address these limitations, we present a “moving mesh” method that explicitly accounts for volumetric expansion during the melting (or, evaporation) process by introducing liquidus or vapour cells at appropriate locations adjacent to the interface. This moving mesh approach is used in conjunction with the apparent heat capacity method implemented through a finite volume scheme to represent the one-dimensional propagation of the melting (or, vapour) front during heating. This new algorithm has been validated for the Stefan's analytical solution, in addition to verifying the conservation of energy principle. We subsequently use our approach to investigate phase-change phenomena for a host of materials with a large gamut of density contrasts between the various phases, and compare the results to those obtained using a fixed-grid approach. The moving mesh method forecasts an early commencement of melting (or, evaporation) at a given position, a comparatively rapid movement of the front, and a larger volume fraction of the molten (or, vapour) phase, for substances that expand upon phase change, while the opposite is observed for the melting of ice, considered as a special case in this study. We hope that the proposed scheme will be adopted in addressing phase-change problems involving significant density contrasts.