Water Film Research Articles

Formation of green strength in hydraulically bonded refractory castables at room temperature

A sufficient green strength of refractory castables is necessary to avoid damage during demoulding and heating up of refractory linings and prefabricated parts. However, there is a lack of knowledge on the mechanisms underlying the build-up of green strength in refractory castables. This work focuses on how green strength is formed within the matrix of PCE-dispersed and CA cement bonded refractory castables during their setting.Setting was monitored using several measuring methods, such as sonic velocity, amount of hydrate phases formed from CA cement, ζ-potential (stability resp. coagulation of the matrix suspension), porosity, and specific surface area and was linked to the corresponding increase of green strength of refractory castables during setting.Considered by time after adding water, the first stiffening of the refractory castables is related to the collapse of the rheological system of their matrix suspension (coagulation), resulting in a very low increase in green strength (apparent hardening). This stiffening occurs early if Ca-precipitates are formed together with molecules of the dispersing agent (Ca-PCE, PCE with short side chains) or if the amount of pore water is being reduced below a critical value (rheologically stable matrix due to dispersion of hydrate phases by PCE with long side chains). The major increase in green strength occurs when a significant amount of CA cement reacts to hydrate phases and, correspondingly, water is being bonded. This main increase in green strength may occur directly after stiffening (if CA cement is being hydrated quickly) or several hours after stiffening (if the hydration of CA cement is retarded).Regarding the green strength, the predominant factor influencing the build-up of green strength in refractory castables is the reduction of free water in the pores due to its bond in hydrate phases (reduction of a lubricating, interparticle water film). Minor influences are the reduction in porosity (volume expansion by hydration of CA cement), the increase in the specific surface area (hydrate phases are finer than the initial CA cement particles), and the entanglement of plate-like hydrate phases.

Ultra-efficient and thermally-controlled atmospheric structure deicing strategy based on the Peltier effect

Snow and ice coverage pose significant threats to the safe and stable operation of energy equipment. To address the challenges of high power consumption and thermal damage to materials resulting from prolonged use of thermal ice melting technology, this study developed and tested a low-power, thermally controlled de-icing system. The system employs thermoelectric material as the heating element to minimize power consumption and prevent thermal damage to the substrate material. Compared to traditional thermal elements, it offers advantages such as single-sided heat production, a high thermal performance coefficient, and a rapid temperature rise rate. Investigating the effects of temperature difference and current on the heat production coefficient of the system and conducts comparative experiments on the thermal response of different heating elements in low-temperature environments. Furthermore, to further reduce power consumption and minimize unnecessary sensible heat within the ice layer, the thermal control system is designed to maintain the interface temperature between 3 and 5 ℃. This approach selectively melts the interface ice layer to form a water film, facilitating ice layer removal through gravity and centrifugal force. The de-icing energy density achieved with this method is only 10.31 J/cm2, resulting in a 32.167 % reduction in power consumption compared to continuous heating. For the flat plate heating structure, the study explores the physical mechanism of interface temperature control by establishing the relationship between temperature and current through a thermal circuit model. The calculated results closely align with experimental findings, with the maximum error not exceeding 15 %.

Cadmium pollution exacerbated by drought: Insights from the nanoscale interaction at the clay mineral surface

Drought is a global environmental problem, while the effect of drought-induced unsaturation on the fate of heavy metal ions is still poorly understood, particularly the lack of mechanistic information at the molecular level. This study used molecular dynamics simulations to investigate nanoscale interactions at the montmorillonite surface under different moisture conditions. Compared to the saturated condition, drought increased the amounts and strength of Cd2+ ions adsorbed on the montmorillonite (MMT) surface while decreased the diffusivity, which was especially obvious in extreme drought conditions (θv=21%−7%). This is closely related to the compressed electric double layer, overcompensation of surface charge, and increased ion pair interactions, resulting from the confinement of water films under drought stress. Further analysis showed that the decrease of hydration effect was responsible for the exacerbated cadmium pollution. Therefore, this study may break the stereotypes about the interactions between heavy metal ions and soil minerals. The results suggest that water management (e.g., irrigation) may be prioritized before beginning heavy metal remediation.

Water Condensation in the Nanoscale Pores of Pt/C Catalyst Particles and Its Impact on Catalyst Utilization: A Simulation Based on a Reconstructed Structure from Nanoimaging.

In polymer electrolyte membrane fuel cells, carbon-supported platinum (Pt/C) catalyst particles require sufficient water condensation within the nanoscale pores to effectively utilize the interior Pt catalysts. Since experimental visualizations with nanoscale precision of this phenomenon are not yet possible, we utilized a Pt/C catalyst particle reconstructed from segmented nanoimaging of a catalyst powder, which served as the computational domain for lattice density functional theory (LDFT) simulation of water condensation. Paired with experimental water uptake data, LDFT successfully simulated high-resolution water condensation, capturing both thin-film and capillary water condensation phenomena. Using a simple proton movement method within the water network, we reproduced the Pt utilization data from a CO stripping experiment. Our findings highlight that at low relative humidity (RH), Pt utilization is influenced by thin water film formations, mainly dictated by the wettability properties of surfaces within primary pores and the Pt/C catalyst particle's exterior. Conversely, at high RH, Pt utilization is attributed to capillary water condensation in medium-to-large sized pores. This approach contributes a qualitative and quantitative discussion on hypotheses regarding the mechanism of Pt utilization, supporting recent studies (e.g., Girod, R.; Nat. Catal. 2023, 6, (5), 383-391).

Water thin films on kaolinite gibbsite and edge surfaces and their effects on surface wettability in relation to geological carbon sequestration

Geological carbon sequestration (GCS) is a promising method to alleviate CO2 emission, while CO2 structural trapping is one of main GCS mechanisms, in which the storage capacity is strongly dependent on CO2-water–rock contact angle. Although CO2-water-kaolite contact angle on basal surfaces has been studied, the knowledge about kaolinite edge surface wettability remains unknown. In this work, we use molecular dynamics (MD) simulations to study CO2-water-kaolinite contact angle on kaolinite gibbsite and edge surfaces under a typical GCS condition (330 K and 200 bar). The common belief is that surface wettability in presence of water is determined by surface hydroxyl (–OH) group density. While the surface –OH group density of kaolinite edge surface is much lower than that of gibbsite surface, both gibbsite and edge surfaces are strongly water-wet. Edge surface is better hydrated than gibbsite surface as both silanol and aluminol groups can form hydrogen bonding with water molecules thanks to large effective water accessible volume around them, while pocket water can further anchor water film. Therefore, the atomic-level surface characteristics dictate interfacial water structures which determine CO2-water-kaolinite contact angle. Our study provides important insights into the effect of surface heterogeneity on interfacial water structures, and kaolinite gibbsite and edge surface wettability which is crucial to the optimization of GCS processes.

Comprehensive laboratory constraints on thermal desorption of interstellar ice analogues

Gas accretion and sublimation in various astrophysical conditions are crucial aspects of our understanding of the chemical evolution of the interstellar medium. To explain grain growth and destruction in warm media, ice mantle formation and sublimation in cold media, and gas line emission spectroscopy, astrochemical models must mimic the gas--solid abundance ratio. Ice-sublimation mechanisms determine the position of snow lines and the nature of gas emitted by and locked inside planetary bodies in star-forming regions. To interpret observations from the interplanetary and extragalactic interstellar mediums, gas phase abundances must be modelled correctly. We provide a collection of thermal desorption data for interstellar ice analogues, aiming to put constraints on the trapping efficiency of water ice, as well as data that can be used to evaluate astrochemical models. We conduct experiments on compact, amorphous H$_2$O films, involving pure ices as well as binary and ternary mixtures. By manipulating parameters in a controlled way, we generate a set of benchmarks to evaluate both the kinetics and thermodynamics in astrochemical models. We conducted temperature-programmed desorption experiments with increasing order of complexity of ice analogues of various chemical compositions and surface coverages using molecular beams in ultrahigh vacuum conditions (1 times 10$^ $ hPa) and low temperatures (10 K). We provide TPD curves of pure ices made of Ar, CO, CO$_2$, NH$_3$, CH$_3$OH, H$_2$O, and NH$_4^+$HCOO$^-$, their binary ice mixtures with compact amorphous H$_2$O, ternary mixtures of H$_2$O : CH$_3$OH : CO, and a water ice made in situ to investigate its trapping mechanisms. Each experiment includes the experimental parameters, ice desorption kinetics for pure species, and the desorption yield (gas--solid ratio) for ice mixtures. From the desorption yields, we find common trends in the trapping of molecules when their abundance is compared to water: compact amorphous water ices are capable of trapping up to 20<!PCT!> of volatiles (Ar, CO, and CO$_2$), sim 3<!PCT!> of CH$_3$OH, and sim 5<!PCT!> NH$_3$ in relation to the water content within the ice matrix; ammonium formate is not trapped in the water ice films, and compact amorphous water ice formed in situ has similar trapping capabilities to a compact amorphous water ice deposited using molecular beams. Deposited or formed in a very compact structure, amorphous water ice of less than 100 layers cannot trap a large fraction of other gases, including CO and CO$_2$. These desorption yields offer insights into the availability of species that can react and form interstellar complex organic molecules during the warm-up phase of ice mantles. Furthermore, in order to be reliable, gas-grain astrochemical models should be able to reproduce the desorption kinetics and desorption yield presented in our benchmark laboratory experiments.

Accelerated carbonation of recycled concrete aggregate in semi-wet environments: A promising technique for CO2 utilization

The practical implementation of accelerated carbonation for recycled waste concrete is impeded by sluggish carbonation efficiency. In contrast to previous carbonation enhancement schemes using high-pressure gas and/or complex pre-/post-processing, this study introduces a novel semi-wet carbonation method that achieves high-efficiency carbonation of recycled concrete aggregates (RCA) in a practically simple way. A noteworthy carbonation degree of 10.6 % was achieved within 30 min at room temperature and ambient pressure, which enhanced the RCA by reducing the water absorption rate and porosity by 3.6 % and 20 % respectively. The formed CaCO3 is primarily in calcite form with poorer crystallinity and smaller grain size and the formed silica gel features a lower polymerization degree compared with those formed in wet carbonation. It is due to that the carbonation reactions for the semi-wet scenario happen at the spatially confined water film of the solid-liquid interface. Moreover, the addition of sodium bicarbonate significantly accelerated the semi-wet carbonation, which is due to the weak alkaline environment lowering the CO2 speciation free energy as revealed by reactive molecular dynamics simulations. The proposed semi-wet carbonation method provides a promising way of pushing industrial CO2 capture and utilization.

Modes of Nanodroplet Formation and Growth on an Ultrathin Water Film.

Using nanobubbles as geometrical confinements, we create a thin water film (∼10 nm) in a graphene liquid cell and investigate the evolution of its instability at the nanoscale under transmission electron microscopy. The breakdown of the water films, resulting in the subsequent formation and growth of nanodroplets, is visualized and generalized into different modes. We identified distinct droplet formation and growth modes by analyzing the dynamic processes involving 61 droplets and 110 liquid bridges within 31 Graphene Liquid Cells (GLCs). Droplet formation is influenced by their positions in GLCs, taking on a semicircular shape at the edge and a circular shape in the middle. Growth modes include liquid mass transfer driven by Plateau-Rayleigh instability and merging processes in and out-of-plane of the graphene interface. Droplet growth can lead to the formation of liquid bridges for which we obtain multiview projections. Data analysis reveals the general dynamics of liquid bridges, including drawing liquids from neighboring residual water films, merging with surrounding droplets, and merging with other liquid bridges. Our experimental observations provide insights into fluid transport at the nanoscale.

Electrochemical redox of arsenic (III) and Cu (II) mixtures with ultraflat Au(111) thin films in water

The ability to detect trace concentrations of arsenite, As (III), in real water solutions is impacted by co-contamination of other metals and co-occurring ions. The presence of copper (II) ions are the most likely co-contaminant in natural waters to interfere with electrochemical As (III) detection, due to the close oxidation potentials of Cu (II) and As (III). The use of well-oriented ultraflat Au(111) thin film electrodes provided increased peak separation and sensitivity for electrochemical deposition and oxidation of Cu (II) and As (III) in 0.5 M sulfuric acid compared to an Au wire electrode. However, mixtures of Cu (II) and As (III) altered the oxidation peak positions during both cyclic voltammetry (CV) and linear stripping voltammetry (LSV) analysis. Calibration curves using the standard additions method in trace concentrations were conducted for Cu, As, and Cu & As solutions. Sweeping the potential at 10 mV s−1 during CV in Cu & As mixtures resulted in a sequential deposition condition where a layer of Cu inhibited co-deposition of As to the electrode. In contrast, the rapid potential stepping of LSV to a potential where Cu and As reduction simultaneously occurs produced a peak profile different from Cu or As alone. A larger oxidation peak during LSV was also observed when both Cu and As were present. X-ray photoelectron spectroscopy indicates a Cu-As alloy is formed on the surface after LSV deposition.SYNOPSIS: Analysis of Cu (II), As (III) and Cu (II) & As (III) mixtures suggests that a Cu3As intermetallic phase is formed during LSV which impacts trace As detection even in trace Cu conditions. This has important implications for the ability to determine As concentrations near the MCL of 10 µg L−1 in natural water systems which may contain Cu (II) and other co-contaminants.

Effect of water film evaporation on the shale gas transmission in inorganic nanopores under viscosity.

Shale gas reservoirs generally have ultra-low water saturation, and the water in reservoirs is closely bound to the walls of inorganic nanopores, forming a water film structure on the hydrophilic surface. When shale gas enters the inorganic nanopores, the water films in the inorganic pores will be removed by evaporation instead of being driven away by the gas, which increases the difficulty of predicting production during shale gas extraction. Based on molecular dynamics simulations, a water film evaporation model is proposed, considering the evaporation of water films during shale gas transport and the influence of water film evaporation on the shale gas transport mechanism. The Green-Kubo method is employed to calculate the viscosity of the water film. The evaporation flux of the water film under the influence of viscosity is discussed in the evaporation model. The transport mechanisms of shale gas in nanopores and the effect of water film evaporation on shale gas transport mechanisms are analyzed in detail. The result indicates that the water films in the inorganic nanopores are constrained on the hydrophilic surface, and the viscosity normal to the surface of the water film of 4Å is 0.005 26 Pa⋅S, which is 6.12 times the reference value of viscosity at 298K. In the process of water film evaporation, the evaporation flux of the water film is influenced by viscosity. In the study of the shale gas transport mechanism, water films in inorganic nanopores can hinder the surface diffusion of the methane molecules adsorbed on boundary and significantly reduce the mass flux of shale gas.

Magnetic Nanoparticles Produced by Pulsed Laser Ablation of Thin Cobalt Films in Water

Magnetic Nanoparticles Produced by Pulsed Laser Ablation of Thin Cobalt Films in Water

P‐9.4: Aerial Reflection Screen Using Soapy Water or Thin Films for Aero Signage Which is Floating in the Air and Enables to Make Images Invisible from Back

P‐9.4: Aerial Reflection Screen Using Soapy Water or Thin Films for Aero Signage Which is Floating in the Air and Enables to Make Images Invisible from Back

From sedimentation to consolidation of kaolinite: A molecular dynamic study

The consolidation of clay is the main measure for reclamation project, which is related to the compressibility, permeability, and coupling effect of clay-water. However, the mechanism of consolidation of clay remains unclear. This study focuses on the microscopic consolidation property of kaolinite using Molecular Dynamics (MD) simulation method. The nano-scale consolidation model was established to reproduce the sedimentation to consolidation. According to the different distribution of water film in pores, the consolidation process could be divided into different stages: (1) in the process of sedimentation and primary consolidation, the drainage occurred continuously except the strongly bound water; (2) just a part of the strongly bound water could be drained during the secondary consolidation. The minimum consolidation stress which can cause significant consolidation was found to be 0.1 GPa in a narrow throat of about 1 nm at nano-scale. The evolution of interparticle spacing between kaolinite particles during the consolidation process was analyzed to reflect the role of interparticle water on the pore water pressure and effective stress. Besides, models with different wettability show that the drainage of water on hydrophilic basal surface was difficult, while water molecules on hydrophobic basal surface are more easily expelled and have directional flow paths.

On icicle ripples

Natural icicles have an overall conical shape modulated by surface ripples. It has been noted from many observations of icicles formed in nature and in the laboratory that the wavelength of the ripples has a very narrow spectrum between about 8 and 12 mm and that, as time evolves, the phase of the ripples migrates upwards. In this pedagogical review, I explore some of the physical mechanisms that can cause and mediate the formation and migration of ripples on icicles using simple mathematical models. To keep the mathematics more straightforward and transparent, I confine attention to two dimensions. A key physical parameter is the surface tension between the film of water that coats an icicle and the air that surrounds it, which causes a phase shift between the film–air interface and the ice–film interface. I show that the wavelength of ripples is dominantly proportional to the cube root of the square of the gravity-capillary length times the thickness of the water film. At high film-flow rates, advection-dominated heat transfer coupled with the interfacial phase shift becomes the dominant driver of instability. Gibbs–Thomson undercooling provides an unexpectedly large stabilisation of small wavelengths at these large flow rates, sufficient to maintain wavelength selection at millimetre scales.

Calculation of hydrogen adsorption isotherms and Henry coefficients with mixed CO2 and CH4 gases on hydroxylated quartz surface: Implications to hydrogen geo-storage

Hydrogen is a clean fuel that is becoming increasingly popular in addressing future energy challenges, however, its viable storage requires an understanding of its interaction with underground rock minerals. For this purpose, this study focuses on developing adsorption isotherms and Henry coefficients for hydrogen in hydroxylated quartz surfaces, which are predominant in sandstone and shale rocks. In this study, a molecular-scale hydroxylated quartz structure with a pore space is generated and the Monte Carlo (MC) simulation is utilized to assess the adsorption isotherms and Henry coefficients. Initially, the CO2 adsorption with the hydroxylated quartz is matched with the published data to determine the accuracy of MC simulation and the mineral-fluid interaction. After that, the concentration of H2 within the pore is progressively increased and the competitive adsorption is calculated under various subsurface temperature and pressure conditions. Additionally, CH4 is introduced to understand the competitive adsorption dynamics between H2 and CH4. The findings indicate that increasing pressure results in increasing molecules of hydrogen that monotonically increase H2 adsorption. On the contrary, increasing temperature reduces the affinity of hydrogen with the quartz surface causing a decrease in adsorption capacity and Henry coefficients. Furthermore, a weak single hydrogen adsorption layer is developed at all pressure and temperature conditions, while most of the hydrogen remains as a free gas in the pore. In addition, the hydroxyl group controls most of the adsorption of hydrogen in the hydroxylated quartz. Furthermore, the addition of water film (approximately 1 wt%) reduces the hydrogen adsorption by around 3 %. The H2 adsorption values further experience a notable decrease with the introduction of CO2 and CH4, primarily due to the establishment of a strong adsorption layer caused by the high electrostatic attraction between these gases and the quartz mineral. The study offers crucial microscopic details regarding H2 adsorption alongside CO2 and CH4 gases within hydroxylated quartz pores. These insights support efficient hydrogen geo-storage and larger-scale simulation research.

Revisiting the wetting behavior of solid surfaces by water-like models within a density functional theory

We perform the analysis of predictions of a classical density functional theory for associating fluids with different association strength concerned with wetting of solid surfaces. The four associating sites water-like models with non-associative square-well attraction parametrized by Clark et al. [Mol. Phys., 2006, 104, 3561] are considered. The fluid-solid potential is assumed to have a 10-4-3 functional form. The growth of water film on the substrate upon changing the chemical potential is described. The wetting and prewetting critical temperatures, as well as the prewetting phase diagram are evaluated for different fluid-solid attraction strength from the analysis of the adsorption isotherms. Moreover, the temperature dependence of the contact angle is obtained from the Young equation. It yields estimates for the wetting temperature as well. Theoretical findings are compared with experimental results and in a few cases with data from computer simulations. The theory is successful and quite accurate in describing the wetting temperature and contact angle changes with temperature for different values of fluid-substrate attraction. Moreover, the method provides an easy tool to study other associating fluids on solids of importance for chemical engineering, in comparison with laboratory experiments and computer simulations.

Understanding the filling effect of ice on the mechanical properties of calcium silicate hydrate gel

Ice exhibits good mechanical performance at low temperatures, and when it replaces the weakest pores in cement-based materials, it can noticeably enhance the overall mechanical properties of the material. However, the specific micro-mechanisms that contribute to the improvement of tensile mechanical properties in gel pores at low temperatures are still not fully understood. Based on the results of molecular dynamics simulations, significant roles have been attributed to pore size and temperature in the mechanical performance of gel pores at low temperatures. A thorough investigation was conducted on the process of tensile failure in saturated gel pores, as well as the changes in bonding interactions between calcium silicate hydrate (CSH)-ice and the unfrozen water film (UWF) at different pore sizes and temperatures. The results indicate that increasing pore size and decreasing temperature can improve the mechanical properties of saturated gel pores. With the decrease in temperature, the mechanical properties of the three gel pore systems with heights of 100 Å, 68 Å, and 54 Å were significantly enhanced. Under an engineering strain rate of 8×10−4/ps, the tensile strength and elastic modulus of gel pores increased from 0.57 GPa and 17.81 GPa at 250 K, to 0.97 GPa and 20.87 GPa at 150 K, respectively. To explain this phenomenon, further studies were conducted on the radial distribution function and dynamic hydrogen bonding behavior. The critical contribution of the hydrogen bond network to the mechanical performance of gel pores was discovered. The hydrogen bond structure which experienced the earliest damage, was investigated. As the strain increased, the hydrogen bonds continuously broke and reformed. This research provides a theoretical understanding of the mechanical properties of gel pores under low-temperature conditions.

Insight into the tribological performances of coconut shells as a potential natural water lubrication material

To better understand the tribological performance of coconut shell and to demonstrate its potential as a wear-resistant material for use in a water-lubricated environment, the microstructure of coconut shell was hereby characterized, and its hardness and water absorption properties were correspondingly measured. The tribological characteristics of coconut shells rubbing against a ZrO2 ceramic ball in dry and wet environments were studied, and the wear mechanism was revealed. The measurement characterization and experimental results indicate that the long axis of coconut shell ellipsoid cells grows along the direction of the long axis pointing towards the coconut shell ellipsoid, but this directionality has a relatively small impact on the tribological properties. The average sliding friction coefficient of coconut shell rubbing against ZrO2 ceramic balls is about 0.52 and 0.095, respectively under dry and wet friction conditions. Under dry friction conditions, the wear of coconut shells is mainly because of cell tearing, detachment and abrasive wear caused by alternating friction forces. Mainly considering the combined effects of the high hardness, high strength and good water absorption of coconut shells, as well as the water film at the friction interface, the friction force significantly reduces and makes it difficult to damage the cell structure, leading to a wear rate decrease by more than 100 times under wet friction conditions, much lower than that of lignum vitae. Overall, this study indicates the potential of coconut shell as a water lubricated friction pair material featuring excellent performance.

Microscopic occurrence of primary water in carbonate gas reservoirs with fractures and vugs and its effect on water invasion mechanism

The structure of carbonate gas reservoirs has multiple pore-fracture cave media, and the gas–water flow mechanism is complex. Computed tomography (CT) and nuclear magnetic resonance (NMR) were used to explore the pore structure differences and collocation relationships of different small-scale carbonate cores with fractures and holes in the Longwangmiao Formation. Based on the concept of fractal dimensions, a quantitative method for water film occurrence was established, combined with surface wetting physics and mechanics. The formation of primary irreducible water and the influence mechanism of the water film on water invasion flow were clarified, the mechanical control mechanism of gas–water flow was analysed from the microelement structure, and the difference in water invasion in different pore structures was proven. This study showed that the bound water in carbonate rocks is controlled by micromechanics and occurs in the reservoir space through four mechanisms. Under the action of intermolecular forces and linear tension, a small amount of water film is formed as a movable pore surface, a small amount of pore edge space exists in the form of a corner because of the uneven rough pore surface, and a small amount exists in pores with pore diameters less than the critical pore diameter to form filling. Numerous pores occurred in isolated pores coordinated only by pores smaller than the critical pore size. Furthermore, the flow of the intrusive water phase is controlled by micromechanics such as the displacement force, viscous force of the water film layer on the pore wall, and the capillary force, which mainly occurs in connected pores and fractures larger than the “critical pore diameter of water invasion.” The “critical pore diameter” of the Longwangmiao formation ranges from 2.2 μm to 3.4 μm, and only the pores coordinated by small pores below the “critical pore diameter of water invasion” cannot be affected by the intrusive water phase due to the action of “pore resistance.” To form residual gas.

Influence of slug flow on sand dune transport in a 3.6° upward inclined pipeline

AbstractThis study presents an experimental investigation of sand conveying from a stationary flatbed through two‐phase liquid–gas flows as a function of the fluids flow rates and pipeline orientation (α = 0°, and α = +3.6°). The characteristics of sand particle transportation by saltation, sand dune formation process and morphologies are visualized using a transparent cylindrical acrylic pipeline and digital photography. It was observed that slug flow regime was the dominant mechanism to lift the sand particles for both horizontal and upward inclinations. It was also found that sand dunes deconstructed more quickly at an upward inclination than horizontal position. For the upward inclination, the conveying phenomenon is characterized by sand bed lifting, suspension, and backward entrainment below the air bubble in the water film. Due to the increased liquid flow rates, higher dune velocity is recorded for the inclined condition. The dune pitch length grew for the horizontal configuration after the transient phase, as a result of the gravitational force effect, while it remained constant for the inclined orientation. In both conditions the slip face angle decreased with time; however, for the inclined configuration, this angle was lower because of the higher upstream liquid flow rate. These results provide important insights into the effect of pipe inclination on bed‐load mode solid transport by two‐phase flow inside a closed circular conduit. The obtained experimental data can be used to validate future numerical investigations.