Main Deposition Mechanisms Research Articles

Sulfate sources, biologic cycling, and mobility in Atacama Desert soils revealed by isotope signatures

A set of 55 surface samples from Atacama Desert gypsisols was collected along four altitude transects and analyzed for ∆17OSO4, δ18OSO4, δ34SSO4, and 87Sr/86Sr in order to identify the main depositional mechanisms and quantify the proportional contribution of sulfate sources across the desert's main topographic units – the Coastal Cordillera, the Central Depression, and the Precordillera. Sulfate deposited at any location in the Atacama Desert may derive from up to five different source and process endmembers that can principally be identified by their isotopic composition. Three aerosol sources dominate sulfate deposition and accumulation in gypsisols throughout the Atacama. These are secondary atmospheric Ca- and Na-sulfate derived from global volcanic SO2 oxidized by ozone and its derivates, and a marine sulfate aerosol that is roughly a 9:1 mixture of sea salt (primary) sulfate from evaporated sea spray, and secondary non-sea salt sulfate, i.e., dimethyl sulfide (DMS) mainly oxidized by ozone. These marine sources dominate sulfate deposition in the Coastal Cordillera. Unlike in most places on Earth, the positive mass-independent ∆17OSO4 signature of secondary atmospheric sulfate is ubiquitous in Atacama Desert soils and is never completely erased by biologic cycling. Hence, biologic cycling of the sulfate inventory – i.e., the reduction of sulfate, subsequent oxygen isotope exchange with water, and re-oxidation – is apparently not quantitative in any of the Atacama Desert environments sampled here, including the most biologically active permanent salt lakes. The preservation of highest ∆17OSO4 values (∼ 1.0‰) at altitudes of the Coastal Cordillera above the 1200 m altitude cut-off level of fog advection suggest that episodic rainfall events are insufficient for significant in situ biologic sulfate turnover. At lower altitudes and regular fog advection, moisture supply appears to be sufficient for limited in situ biologic sulfate turnover. Overall, biologically recycled sulfate constitutes a fourth major contributor to the desert's gypsisol sulfate inventory. This may comprise fluvially redeposited sulfate from older sediments, particularly on the debris fans protruding from the Precordillera into the Central Depression. In the Central Depression, Sr-isotopes may allow for a further distinction between redeposition-dominated and aerosol-dominated sedimentation environments. On the Precordillera, rainfall and run-off provide sufficient moisture for significant but still incomplete in situ biologic sulfate cycling. Hydrothermal non-evaporitic Na-sulfate – the fifth potential source – likely originates from larger outflow events or mobilization from rock veins over the course of the Atacama's geologic history may contribute locally to the sulfate inventory. The degree of bio-cycling and mobility of sulfate likely reflects a balance between overall water availability and the mixing proportion of very soluble (mobile) Na-sulfate and less soluble Ca-sulfate inherent in the various sulfate sources.

Characteristics of the gold-bearing and barren quartz veins at the Zaylik-Sarilar epithermal deposit, Ahar-Arasbaran Zone, NW Iran: Evidence from mineralogy, alteration, texture and fluid inclusion

The Zaylik-Sarilar epithermal deposit is located 35 km southeast of Ahar in the Ahar-Arasbaran Zone in the Alborz-Azerbaijan Magmatic Belt, NW Iran. Exposed rocks in the Zaylik-Sarilar deposit are mainly composed of Eocene volcanic rocks and Miocene dacite-rhyodacite that are intruded by younger intrusions. The deposit occurs within a sequence of Eocene porphyritic andesite and andesitic lithic tuff. Mineralization occurs as open space filling, taking place as irregular veins, veinlets, and hydrothermal breccias. The mineralization zones can be categorized into two main groups according to sulfides and sulfosalts mineralogy, alteration assemblages, ore textures, and fluid inclusion data. The first group consists of gold-bearing quartz-sulfide ± breccia veins, silicified-phyllic ± argillic zones, and a few quartz-calcite veins. The second group is composed of barren milky (or white) quartz veins, silicified lithocaps, and argillic-kaolinite ± silicic zones. Pyrite, chalcopyrite, bornite, galena, sphalerite, and Au-Ag sulfosalts were identified in ore paragenesis of the gold-bearing veins. Pyrite is the main sulfide mineral in the barren quartz veins and silicified lithocaps. Gold and silver were enriched during oxidation and supergene alteration of the gold-bearing veins. Textural evidences from the gold-bearing veins, such as mosaic breccia monomicts, floating clast breccias, hydrothermal breccias, colloform-crustiform textures, ginguro bands, dendrite textures, and rarely lattice- and parallel-bladed calcite replacement textures, suggest that boiling occurred in the veins. Comb, cockade, reed molds, zonal, and feathery textures are common in the barren veins and silicified lithocaps. Fluid inclusion data show a decreasing trend in salinity and homogenization temperature (Th) from the gold-bearing quartz veins to the barren ones. The average salinity and homogenization temperature (Th) of fluid inclusions from the gold-bearing veins are 1.05 wt% NaCl equiv. and 297 °C, respectively; higher than the average salinity (0.68 wt% NaCl equiv.) and homogenization temperature (192 °C) of fluid inclusions from the barren quartz veins. Th versus salinity diagram suggests that boiling was the main mechanism of ore deposition in the gold-bearing quartz veins and silicified zones. These data propose that the barren quartz veins and silicified lithocaps were formed by cooling. A combination of the geologic, mineralogic, alteration, and fluid inclusion data from the Zaylik-Sarilar deposit represents an epithermal system of low-sulfidation type. Structurally, mineralization has been controlled through the NW-trending strike-slip principal displacement zone and it’s subsidiary Riedel fractures in response to a N-trending compression in the Arabia-Eurasia collision zone.

Aerosol Therapy in Intensive Care Unit

Inhalation therapy is a cornerstone especially in pulmonary diseases or comorbidities, either in invasive or noninvasive mechanical ventilation. In pediatric patients, mainly in respiratory failure of the premature born child inhalation of surfactant is crucial in the therapy. Additional drugs given by inhalation are antibiotics, mucoactive substances and drugs that treat pulmonary hypertension. This article describes main deposition mechanisms of inhalation therapies and presents recommendations for correct performance of inhalation therapy in invasively as well as noninvasively ventilated patients in ICU. Also safety aspects for patients and medical staff during aerosol therapy in the Corona pandemic era are discussed.

A Simple Method for Aerosol Transport Efficiency Tests in Sampling Tubes

To obtain representative data, particle loss in sampling tubes must be minimal; otherwise, the magnitude of the losses must be known so it can be corrected. Since particle loss in sample tubes occurs through various mechanisms and depends on particle size, airflow velocity, and Reynolds number, there is no simple method to predict the particle loss of multitudinous configurations of sampling tubes. This study aims to present a simple method for experimentally determining particle loss as a function of particle sizes. Moreover, the applicability of existing models is verified experimentally. An ultrasonic atomizing nozzle was used to generate micrometer-sized polydispersed particles as challenge aerosols. Following charge neutralization, the particle size distribution and number concentration upstream and downstream of the sampling tubes are measured by an Aerodynamic Particle Sizer. The particle loss in the sampling tubes with inner diameters of 4.5, 7.7, and 10 mm are measured at various values of Re (500~5000) and the tube orientations (horizontal and vertical). Both the horizontal and vertical tubes have the lowest loss at a Re of approximately 2100. Gravitational settling and turbulent-induced inertial impaction are the main deposition mechanisms in aerosol transport for particles large than 1 μm. Gravity plays a significant role when the Re is less than 5000, then its dominant position is gradually replaced by turbulence with the Re continuing to increase. Further, the transport efficiency increased with increasing tube diameter. Consequently, each sampling tube needs to be tested according to the methods mentioned in this study to fully grasp the transport efficiency of particles through the sampling tube.

Отложение минеральных солей при использовании жидкостей глушения

Paper describes problems observed during clean-up & bean-up operations of one of the Western Siberia field wells. The problem consisted of an intensive mineral scale deposition in electrical submersible pump (ESP) impellers. This led to rapid ESP failure with “no flow” code. Main causes and mechanism of mineral scale deposition was determined, scale inhibitor and scale dissolver were selected based on laboratory tests, production chemicals application procedure was developed. It was shown that Zn2+ ions included in specific kill fluids compositioncould have significant impact on scale deposition rate. This shall be taken into account during scale management implementation in case of zinc-containing kill fluid use.

Plasma–wave interaction in helicon plasmas near the lower hybrid frequency

We study the characteristics of plasma–wave interaction in helicon plasmas near the lower hybrid frequency. The (0D) dispersion relation is derived to analyze the properties of the wave propagation and a 1D cylindrical plasma–wave interaction model is established to investigate the power deposition and to implement the parametric analysis. It is concluded that the lower hybrid resonance is the main mechanism of the power deposition in helicon plasmas when the RF frequency is near the lower hybrid frequency and the power deposition mainly concentrates on a very thin layer near the boundary. Therefore, it causes that the plasma resistance has a large local peak near the lower hybrid frequency and the variation of the plasma density and the parallel wavenumber lead to the frequency shifting of the local peaks. It is found that the magnetic field is still proportional to the plasma density for the local maximum plasma resistance and the slope changes due to the transition.

Inhalation and deposition of spherical and pollen particles after middle turbinate resection in a human nasal cavity

Middle turbinate resection significantly alters the anatomy and redistributes the inhaled air. The superior half of the main nasal cavity is opened up, increasing accessibility to the region. This is expected to increase inhalation dosimetry to the region during exposure to airborne particles. This study investigated the influence of middle turbinate resection on the deposition of inhaled pollutants that cover spherical and non-spherical particles (e.g. pollen). A computational model of the nasal cavity from CT scans, and its corresponding post-operative model with virtual surgery performed was created. Two constant flow rates of 5 L/min, and 15 L/min were simulated under a laminar flow field. Inhaled particles including pollen (non-spherical), and a spherical particle with reference density of 1000 kg/m3 were introduced in the surrounding atmosphere. The effect of surgery was most prominent in the less patent cavity side, since the change in anatomy was proportionally greater relative to the original airway space. The left cavity produced an increase in particle deposition at a flow rate of 15 L/min. The main particle deposition mechanisms were inertial impaction, and to a lesser degree gravitational sedimentation. The results are expected to provide insight into inhalation efficiency of different aerosol types, and the likelihood of deposition in different nasal cavity surfaces.

Using end-member analysis to determine sediment dispersal and depositional processes on the Heuksan mud belt, southwest Korean shelf

Due to the large volume of the Heuksan mud belt (HMB), the source of the mud and the depositional processes involved have been controversially discussed over the past two decades. To illuminate the issue, an end-member analysis (EMA) was applied to the grain-size data of 74 surficial samples in order to determine the sediment dispersal pattern on the HMB. In addition, a sedimentary facies analysis was carried out to serve an interpretation of depositional processes. Five grain-size end-members (EMs) were identified. Their dominant modes are 1.4 (EM1), 2.4 (EM2), 3.9 (EM3), 5.6 (EM4), and 7.3 ϕ (EΜ5). The EM3 and EM4 are mainly found on the inner shelf, their distribution decreasing from proximal to distal. On the middle shelf, where tidal rhythmites are found, the end-member scores show a mixture of EM4 and EM5, implying that these are good proxies for tidal influence. The distribution of EM4 decreases gradually from proximal to distal, whereas the finest end-member (EM5) increases toward the distal region. It indicates the outcome of progressive size-sorting with distance from the source area. As such, EM4 and EM5 can be interpreted to have been derived from Korean rivers. Previous geochemical and clay mineral studies suggested that sediments were partly supplied from Chinese rivers. The differences between the sedimentological and geochemical results suggest that the sediments may have been redistributed by tidal currents. Consequently, the end-member modeling of grain-size distributions of sediments from the western shelf of Korea has allowed the identification of the main sediment dispersal and depositional mechanisms.

АКТУАЛЬНОСТЬ МОДЕЛЕЙ ЗАГРЯЗНЕНИЯ ДЛЯ ДИАГНОСТИКИ СОСТОЯНИЯ ПЛАСТИНЧАТЫХ ТЕПЛООБМЕННИКОВ

The article analyzes various theoretical approaches to describing the processes of formation of scale layers on the working surfaces of heat exchangers. The main tasks include analyzing existing models of contamination of heat exchange channels, determining the main mechanism of salt deposition on the heating surface of plate heat exchangers of heat supply systems, determining the main factors that determine the intensity of salt deposition on the working plate in accordance with the dynamics of heat and hydraulic processes in heat exchange channels formed by corrugated plates, as well as forming trends for further research. The article presents the main results of research devoted to the study of contamination processes on heating surfaces. Inaccuracies in the proposed approaches to describing the nature of the formation of salt deposition layers are identified. By generalizing existing approaches to the mathematical description of pollution processes, the main assumptions are revealed when describing the processes of salt deposition on working plates. A hypothesis is proposed about the influence of the location of channels relative to the inlet pipe on the uniformity of the flow distribution between parallel channels in the device. There is a fairly large gap between the existing computational methods for modeling pollution processes and the actual distribution of scale layers during the operation of heat exchange equipment of heat supply systems

Quantitative characterization of the blockage effect from dispersed phase on wax molecular diffusion in water-in-oil emulsion

Molecular diffusion is the main mechanism of wax deposition, whereas the dispersed water droplets influence the wax diffusivity in water-in-oil (w/o) emulsion by restricting the diffusion path. In the present work, geometric analysis method was used to analyze the blockage effect from dispersed phase on the restricted diffusion path of wax molecules in w/o emulsion, and a correlation was proposed relating the blockage effect with water fraction, dispersed degree and nonuniformity of dispersed phase in real emulsions. Firstly, regarding water droplets as spherical particles with uniform size and arrangement pattern, the average tortuosity of different wax diffusion paths was deduced in two-dimensional (2D) and three-dimensional (3D) ideal conditions. The results showed that the blockage degree was enhanced with the increase in water fraction. Moreover, the droplet size distribution of different w/o emulsions was investigated by microscopic observation and a set of microstructure characterization parameters were summarized in statistics. A 3D microstructure model of real emulsion was established to derive the tortuosity, taking the effect of droplet size distribution into consideration. The blockage effect was enhanced by the increase in the dispersity and polydispersity of water droplets, but this influence was not significant and water fraction was still the main influencing factor. On this basis, a correlation of blockage coefficient with water fraction, number-averaged diameter and polydispersity was proposed and validated using the 1H/19F-NMR test results in literature with the average relative error being 3.17%. This will provide a support to the revealing of wax diffusion mechanism in w/o emulsions and the wax deposition prediction of multiphase flow pipelines.

Sediment transport mechanisms in altered depositional environments of the Anthropocene Nakdong Estuary: A numerical modeling study

The Nakdong Estuary, Korea, is a dramatic example of an Anthropocene estuary. Over the last century, the construction of two dams has divided the estuary into two discharge energy regimes with the East Nakdong Estuary receiving discharge and the West Nakdong Estuary receiving no discharge. The mean-flow sediment flux gradient during high discharge was the main mechanism for deposition in the East Nakdong Estuary. Because of limited observations, the sediment transport mechanisms for the entire estuary remained unclear. To complement previous observations that were limited to a high discharge event of the East Nakdong Estuary, this study aimed to better understand the spatiotemporal variation of sediment transport and the mechanisms of deposition throughout the Nakdong Estuary. Sediment fluxes and bed level changes were estimated by utilizing the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST). Results confirmed that the East and West Nakdong Estuaries had different depositional patterns. The East Nakdong Estuary was characterized as a river-dominated environment with a high influence of river discharge that experiences rapid deposition. The West Nakdong Estuary was characterized as an environment mainly influenced by tides and waves that contribute to gradual deposition throughout the year. The mean-flow sediment flux by river discharge was a main mechanism of deposition in the East Nakdong Estuary after the construction of dam. The continuous landward mean-flow flux by tides and waves through the inlets was the dominant mechanism for deposition in the West Nakdong Estuary. These model results suggest that the Nakdong Estuary may serve as an analogue for a microtidal estuary altered by an estuarine dam, particularly those for which there is a monsoonal climate or anthropogenically reduced river discharge.

Distribution of trace elements between carbonaceous matter and sulfides in a sediment-hosted orogenic gold system

Carbonaceous matter (CM) plays a critical role in the formation of sediment-hosted ore deposits, but metal partitioning between CM and associated sulfides remains unclear. Here we use synchrotron X-ray fluorescence microscopy (SXRF), laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS), and nanoscale secondary ion mass spectrometry (NanoSIMS) to characterize the distribution and deportment of trace elements between CM and sulfides from the Daqiao orogenic gold deposit, China. Four types of CM co-existing with different generations of sulfides are recognized: sedimentary CM1 with pyrite polyframboids in black shale host; indigenous CM2 with early- to main-ore pyrite and marcasite; CM3 with main-ore pyrite; CM4 with pyrite porphyroblasts in underlying graphitic schists.The SXRF results reveal that As, Se, Ni, Pb, and Cu are enriched in pyrite polyframboids relative to CM1 in black shales, although a small proportion of As, Pb, Bi, and U is accommodated in the latter. NanoSIMS images show that Au and As are associated with the CM1 matrix within pyrite framboids that are overgrown by recrystallized pyrite rims. Most trace elements are enriched in the newly-formed aggregates of pyrite and marcasite relative to the CM2 rims that formed via the interactions between ore fluids and pre-existing CM2 cores. Gold, As, Tl, Se, and Hg are highly enriched in the main-ore pyrite relative to co-precipitated CM3 veinlets, and this deportment might reflect changes in fluid redox conditions in response to hydraulic fracturing that is the main mechanism of gold deposition. The pyrite porphyroblasts in the schists are enriched in As, Se, Ni, and Cu relative to CM4, but have lower Au, As, Co, Ni, and Pb than sedimentary pyrite framboids. Taken together, we suggest that biological activity causes accumulation of As and Au within CM interstitial to the framboidal pyrite, and that these elements are released during metamorphic recrystallization and hydrothermal replacement. Trace element deportment in hydrothermal CM and sulfides is controlled by a variety of factors such as the fluid chemistry and interaction between indigenous CM and fluids. Our quantitative results provide significant new insights into the complex processes that formed carbonaceous sediment-hosted ore systems worldwide.

Impact of cathode loss on plasma characteristics, microstructures and properties of 7YSZ coatings in PS-PVD

The slight changes in geometry and mass of the cathode of O3CP plasma torch during service life caused the variety of arc motion between the cathode and anode. The voltage appeared to rise first and then fall. In this experiment, the impact of cathode loss on plasma characteristics, microstructures and properties of 7YSZ coatings was investigated. Optical emission spectroscopy (OES) was used to characterize the plasma jet characteristics such as plasma temperature and electron number density. It is found that vapor deposition is the main deposition mechanism, and the microstructures of the coatings are mainly affected by the supersaturation and subcooling of the vapor phase, which determine the nucleation and growth of crystals. At the middle of cathode service life, the plasma temperature and electron number density are the highest and the powder is completely evaporated. High crystal growth rates and surface diffusion lead to large columnar crystals with large grain size. The best thermal shock resistance. The thermal shock resistance is the best in this case. When the cathode is in the beginning and end of service life, there are columnar grains with small size produced and many solid particles in the gaps due to diffusion difficulties generated by low temperature. Shadowing enhances to manufacture fine grains and few branches. The presence of solid particles prevents the release of thermal stress and reduces thermal shock resistance of coatings. Fine grains prevent cracks propagation to improve the bonding strength of coatings.

Wax deposition mechanisms and the effect of emulsions and carbon dioxide injection on wax deposition: Critical review

Wax deposition inside the tubing walls endures being a critical operational challenge faced by the petroleum industry. The build-up of wax deposits may lead to the increase of pumping power, as well as the decrease of flow rate or, even, to the total blockage, with production losses and high operational costs. The current paper is a critical review of the main deposition mechanisms involved in wax deposition. Most of wax deposition models regard molecular diffusion as the dominant wax deposition mechanism. However, there are other deposition mechanisms which can also play a role. As most oil fields produce water along with crude oil, the deposition process for oil-water emulsions has also been investigated. Furthermore, carbon dioxide injection effects upon wax appearance temperature along its current applications onto wells have been reviewed. Having a total awareness of the wax deposition mechanisms background is the key factor to prevent the wax precipitation and control the deposition of solid wax crystals.

Numerical investigation of nanofluid particle migration and convective heat transfer in microchannels using an Eulerian–Lagrangian approach

An Eulerian–Lagrangian modelling approach was employed in order to investigate the flow field, heat transfer and particle distribution in nanofluid flow in a parallel-plate microchannel, with a focus on relatively low Reynolds numbers ($Re\leqslant 100$). Momentum and thermal interactions between fluid and particle phases were accounted for using a transient two-way coupling algorithm implemented within an in-house code that tracked the simultaneous evolution of the carrier and particulate phases while considering timescale differences between the two phases. The inaccuracy of assuming a homogeneous particle distribution in modelling nanofluid flow in microchannels was established. In particular, shear rate and thermophoresis were found to play a key role in the lateral migration of nanoparticles and in the formation of particle depletion and accumulation regions in the vicinity of the channel walls. At low Reynolds numbers, nanoparticle distribution near the walls was observed to gradually flatten in the streamwise direction. On the other hand, for relatively higher Reynolds numbers, higher particle non-uniformities were observed in the vicinity of the channel walls. Furthermore, it was established that convective heat transfer between channel walls and the bulk fluid can either improve or deteriorate with the addition of nanoparticles, depending on whether the flow exceeded a critical Reynolds number of enhancement. It was also established that Brownian motion and thermophoresis had a major role in nanoparticle deposition on the channel walls. In particular, Brownian motion was the main deposition mechanism for nano-sized particles, whereas due to thermophoresis, nanoparticles were repelled away from channel walls. The result of the competition between the two is that deposition gradually increased along the streamwise direction.

Geology, Alteration, and Mineralization of the Kay Tanda Epithermal Gold Deposit, Lobo, Batangas, Philippines

AbstractThe Kay Tanda epithermal Au deposit in Lobo, Batangas is one of the Au deposits situated in the Batangas Mineral District in southern Luzon, Philippines. This study aims to document the geological, alteration, and mineralization characteristics and to determine the age of the mineralization, the mechanism of ore deposition, and the hydrothermal fluid characteristics of the Kay Tanda deposit. The geology of Kay Tanda consists of (i) the Talahib Volcanic Sequence, a Middle Miocene dacitic to andesitic volcaniclastic sequence that served as the host rock of the mineralization; (ii) the Balibago Diorite Complex, a cogenetic intrusive complex intruding the Talahib Volcanic Sequence; (iii) the Calatagan Formation, a Late Miocene to Early Pliocene volcanosedimentary formation unconformably overlying the Talahib Volcanic Sequence; (iv) the Dacite Porphyry Intrusives, which intruded the older lithological units; and (v) the Balibago Andesite, a Pliocene postmineralization volcaniclastic unit. K‐Ar dating on illite collected from the alteration haloes around quartz veins demonstrated that the age of mineralization is around 5.9 ± 0.2 to 5.5 ± 0.2 Ma (Late Miocene). Two main styles of mineralization are identified in Kay Tanda. The first style is an early‐stage extensive epithermal mineralization characterized by stratabound Au‐Ag‐bearing quartz stockworks hosted at the shallower levels of the Talahib Volcanic Sequence. The second style is a late‐stage base metal (Zn, Pb, and Cu) epithermal mineralization with local bonanza‐grade Au mineralization hosted in veins and hydrothermal breccias that are intersected at deeper levels of the Talahib Volcanic Sequence and at the shallower levels of the Balibago Intrusive Complex. Paragenetic studies on the mineralization in Kay Tanda defined six stages of mineralization; the first two belong to the first mineralization style, while the last four belong to the second mineralization style. Stage 1 is composed of quartz ± pyrophyllite ± dickite/kaolinite ± diaspore alteration, which is cut by quartz veins. Stage 2 is composed of Au‐Ag‐bearing quartz stockworks associated with pervasive illite ± quartz ± smectite ± kaolinite alteration. Stage 3 is composed of carbonate veins with minor base metal sulfides. Stage 4 is composed of quartz ± adularia ± calcite veins and hydrothermal breccias, hosting the main base metal and bonanza‐grade Au mineralization, and is associated with chlorite‐illite‐quartz alteration. Stage 5 is composed of epidote‐carbonate veins associated with epidote‐calcite‐chlorite alteration. Stage 6 is composed of anhydrite‐gypsum veins with minor base metal mineralization. The alteration assemblage of the deposit evolved from an acidic mineral assemblage caused by the condensation of magmatic volatiles from the Balibago Intrusive Complex into the groundwater to a slightly acidic mineral assemblage caused by the interaction of the host rocks and the circulating hydrothermal waters being heated up by the Dacite Porphyry Intrusives to a near‐neutral pH toward the later parts of the mineralization. Fluid inclusion microthermometry indicates that the temperature of the system started to increase during Stage 1 (T = 220–250°C) and remained at high temperatures (T = 250–290°C) toward Stage 6 due to the continuous intrusion of Dacite Porphyry Intrusives at depth. Salinity slightly decreased toward the later stages due to the contribution of more meteoric waters into the hydrothermal system. Boiling is considered the main mechanism of ore deposition based on the occurrence of rhombic adularia, the heterogeneous trapping of fluid inclusions of variable liquid–vapor ratios, the distribution of homogenization temperatures, and the gas ratios obtained from the quantitative fluid inclusion gas analysis of quartz. Ore mineral assemblage and sulfur fugacity determined from the FeS content of sphalerite at temperatures estimated by fluid inclusion microthermometry indicate that the base metal mineralization at Kay Tanda evolved from a high sulfidation to an intermediate sulfidation condition.

Four-way coupling of particle-wall and colloidal particle-particle interactions in direct absorption solar collectors

A novel model based on the Eulerian-Lagrangian approach was introduced in order to capture the physics of particle-fluid, particle-wall, and colloidal particle-particle interactions through four-way coupling in low-flux nanofluid-based direct absorption solar collectors (DASCs). This was accomplished by means of a computationally efficient particle-particle-interaction detection algorithm implemented within the frame of an in-house fluid-particle coupling algorithm that allowed for the simultaneous evolution of the carrier and particulate phases. The optical, thermal, and dispersion effects of particle-wall and colloidal particle-particle interactions were investigated over a range of particle volume fractions ϕp and flow Reynolds numbers (Re). It was found that the outcome of a particle-wall collision is either particle deposition or rebound, depending on the balance between kinetic energy of the incoming particle and particle-wall van der Waals potential energy. Brownian motion was established to be the main deposition mechanism for nanoparticles in the boundary layer. As Re decreased, Brownian motion of nanoparticles dominated over convection, which led to higher deposition rates. Deposited particles were found to cause greater attenuation of solar radiation near the collector upper surface, especially in the visible region of the solar spectrum. Whereas in the infrared region, radiation attenuation became less sensitive to particle deposition. The drop in collector efficiency when particles are allowed to deposit relative to the case when particles are not allowed to deposit was highest for low Re and ϕp. Yet, regardless of Re, an increase in particle surface potential led to a better dispersion of nanoparticles. Furthermore, colloidal interparticle interactions were found to have a negligible effect on collector performance. The results highlight the important effects of particle deposition and non-uniform particle distribution on the performance of DASC systems, which cannot be captured using conventional single-phase models.

Effects of low-molecular weight organic acids on the transport of graphene oxide nanoparticles in saturated sand columns

The impact of low-molecular weight organic acids (LMWOAs) on the transport of graphene oxide (GO) nanoparticles in saturated quartz sand was investigated. The different LMWOAs such as acetic acid, glycolic acid, malonic acid, and tartaric acid were used in experiments. The effects of LMWOAs on the transport of GO were markedly dependent upon organic acid species. In general, the transport enhancement effects followed the order of tartaric acid > malonic acid > glycolic acid > acetic acid, the regular pattern might be related to amount and type of functional groups of LMWOAs. Additionally, the different enhanced ability of LMWOAs was determined by their molecular weight. In the presence of Na+, the main deposition mechanism was ascribed to steric hindrance and competition between LMWOA and GO for deposition sites on grain surfaces under acidic conditions (i.e., pH 4.0 and 5.0). Batch adsorption experiments indicated the extents of competitive adsorption between LMWOAs and GO on quartz sand. In addition, the DLVO theory was not applicable to describe the transport of GO in the presence of LMWOAs at pH 5.0. Nevertheless, electrostatic and steric repulsion, existing between GO and sand grains, were the most important deposition mechanisms under the neutral condition (i.e., pH 7.0). When Ca2+ was the main cation in the background solution, the transport enhancement effects followed quite similar order to those of Na+, mainly due to different complexing strength of organic acids.

Influences of dust deposition on ground-mounted solar photovoltaic arrays: A CFD simulation study

Dust deposition processes and behaviors on ground-mounted solar photovoltaic (PV) arrays were investigated by shear stress transport k-ω turbulence model and the discrete particle model. Inlet velocity and turbulent kinetic energy distributions fitted from experimental data were imposed in the simulation to improve prediction accuracy. After mesh independent test and numerical verification, air flow fields over the solar PV array, dust deposition rates for different rows of PV panels and different dust diameters were investigated. It was found that dust deposition rates on solar PV panel array are declined from the front to the back row. Maximum deposition rate from the first to the fifth row of PV panels is 18.89%, 12.35%, 9.62%, 6.83% or 5.71% respectively. The corresponding dust diameter for the peak deposition rate is 350, 250, 200, 150 or 150 μm respectively. The main deposition mechanisms were investigated by analyzing dust motion trajectories on PV panel arrays. Furthermore, Maximum PV output reduction induced by dust can reach 79.77%, 18.16%, 5.88%, 2.66% or 1.89% from the first to the last row of PV panels, respectively. Therefore, the most degradation of PV efficiency appears for the first row of PV panels.

Effects of particle sizes and tilt angles on dust deposition characteristics of a ground-mounted solar photovoltaic system

The dust deposition behaviours of ground-mounted solar photovoltaic (PV) panels and their effects on the PV efficiency were numerically investigated. The shear stress transport k-ω turbulence model with the inlet user-defined function profiles and the discrete particle model were used to predict the wind flow fields and the dust deposition rates of a PV panel. A grid independence study was conducted, and the mean pressure coefficient was validated with the related experimental data. The effects of the different dust particle diameters and the different tilt angles of the PV panels on the dust deposition characteristics were investigated carefully. The results showed the dust deposition rates of a PV panel were considerably affected by the different tilt angles. The dust deposition rates were considerably higher for the upward PV installations than for the downward ones. Moreover, the dust deposition rates were greater when the solar PV panel was more horizontal with the ground. The peak deposition rates were observed for the 150-μm dust particles for all of the tilted PV panel angles. The maximum deposition rates were 14.28%, 13.53%, 6.79% and 9.78% for the tilted PV panel angles of 25°, 40°, 140° and 155°, respectively. Moreover, the main deposition mechanisms of the solar PV panel were analysed and discussed for the different dust particle sizes and PV panel installation angles. Finally, an empirical model was developed for estimating the PV output reductions caused by the dust deposition for different tilt angles, which could be applied in practical engineering applications.