Argon Layer Research Articles

Optimization of coupling phase-change materials and thermal screens in façade-integrated hybrid photovoltaic collectors for optimal energy production and thermal comfort in buildings

The operation of building-integrated photovoltaic (BIPV) systems gives rise to a significant proportion of the solar radiation absorbed by the cells being unable to be converted into electricity. This phenomenon consequently increases the temperature. This temperature increase impacts the cells' electrical efficiency, leading to a reduction in their performance and accelerating their degradation. The combination of phase-change materials with insulating fluid blades, situated behind photovoltaic cells, represents a passive cooling solution that optimizes the performance of hybrid photovoltaic systems when incorporated into facades. The present study assesses a system that incorporates paraffin as a PCM and an argon layer in a PV-PCM-argon layer physical model (PVT/ArPCM), in comparison with a PV-PCM system (PVT/PCM), to enhance the thermoelectric performance of photovoltaic systems mounted on façades while ensuring optimal thermal comfort within buildings. The discrete heat transfer equations were solved using the Thomas algorithm and the iterative Gauss-Seidel method in conjunction with the implicit finite difference method. The findings illustrate that the electrical efficiency experienced only a slight increase, estimated at 0.01%, while there was a notable enhancement in the indoor thermal comfort experienced by occupants, with a 65% improvement observed due to the incorporation of an argon-filled thermal screen. The incorporation of an argon layer led to a minor reduction in temperature of 0.01°C in the photovoltaic cells, resulting in a minimal improvement of 0.014% in electrical power production. The phase-changing material incorporated into PVT/ArPCM demonstrated superior thermal management capabilities in comparison to the same material employed in PVT/PCM.

EMPRESS. XIII. Chemical Enrichment of Young Galaxies Near and Far at z ∼ 0 and 4–10: Fe/O, Ar/O, S/O, and N/O Measurements with a Comparison of Chemical Evolution Models

We present gas-phase elemental abundance ratios of thirteen local extremely metal-poor galaxies (EMPGs), including our new Keck/LRIS spectroscopy determinations together with 33 James Webb Space Telescope z ∼ 4–10 star-forming galaxies in the literature, and compare chemical evolution models. We develop chemical evolution models with the yields of core-collapse supernovae (CCSNe), Type Ia SNe, hypernovae (HNe), and pair-instability supernovae (PISNe), and compare the EMPGs and high-z galaxies in conjunction with dust depletion contributions. We find that high Fe/O values of EMPGs can (cannot) be explained by PISN metal enrichments (CCSN/HN enrichments even with the mixing-and-fallback mechanism enhancing iron abundance), while the observed Ar/O and S/O values are much smaller than the predictions of the PISN models. The abundance ratios of EMPGs can be explained by the combination of Type Ia SNe and CCSNe/HNe whose inner layers of argon and sulfur mostly fallback, which are comparable to the Sculptor stellar chemical abundance distribution, suggesting that early chemical enrichment has taken place in the EMPGs. Comparing our chemical evolution models with the star-forming galaxies at z ∼ 4–10, we find that the Ar/O and S/O ratios of the high-z galaxies are comparable to those of the CCSN/HN models, while the majority of high-z galaxies do not have constraints good enough to rule out contributions from PISNe. The high N/O ratio recently reported in GN-z11 cannot be explained even by rotating PISNe, but could be reproduced by the winds of rotating Wolf–Rayet stars that end up as a direct collapse.

Disentangling UV photodesorption and photoconversion rates of H2O ice at 20 K

Context. The nondissociative ultraviolet photodesorption of water ice is a nonthermal desorption mechanism required to account for detected abundances of gas-phase water toward cold regions within the interstellar medium. Previous experimental and theoretical studies provide a range of photodesorption rates for H2O ice and point to a convoluted competition with other molecular processes following the absorption of a UV photon in the ice. Ultraviolet irradiation also induces photodissociation, resulting in the formation of radicals that may directly desorb triggering gas-phase reactions or recombine in surface reactions. Aims. In this work, we aim to quantify the effects of photodesorption and investigate photoconversion upon UV photolysis of an H2O ice. Methods. We irradiated a porous amorphous H2O ice at 20 K with UV photons in the 7–10.2 eV range and compared the measurements to a nearly identical experiment that included a layer of argon coating on top of the water ice. The purpose of the argon coating is to quench any type of photon-triggered desorption. To trace ice composition and thickness, laser desorption post ionization time-of-flight mass spectrometry was utilized. This method is independent of the (non)dissociative character of a process and provides a diagnostic tool different from earlier studies that allows an independent check. Results. The total photodesorption rate for a porous amorphous H2O ice at 20 K we derive is (1.0 ± 0.2) × 10−3 per incident UV photon (7–10.2 eV), which is in agreement with the available literature. This rate is based on the elemental balance of oxygen-bearing species. As a result, we placed an upper limit on the intact (H2O) and dissociative (OH) desorption rates equal to 1.0 × 10−3 per incident UV photon, while for the reactive desorption (O2), this limit is equal to 0.5 × 10−3 per incident UV photon. Photoconversion depletes the H2O ice at a rate of (2.3 ± 0.2) × 10−3 per incident UV photon. At low UV fluence (9.0 × 1017 photons cm−2), the loss of H2O is balanced by photoproduct formation (O2 and H2O2). At high UV fluence (4.5 × 1018 photons cm−2), about 50% of the initial H2O molecules are depleted. This amount is not matched by the registered O-bearing products, which points to an additional, unaccounted loss channel of H2O.

Molecular dynamics data-driven study of leidenfrost phenomena in context to liquid thin film phase transformation

In many micro and nanoscale applications of thin film phase transition, identifying the circumstances that allows stable liquid contact with a heated surface is critical. Using molecular dynamics (MD) simulations, our current data driven machine learning-based study attempts to examine the properties of liquid interaction with a solid surface at nanoscale. A few nanometer-thick liquid argon layer over a platinum surface has been used to simulate a liquid-solid contact system. The wall temperature is raised linearly after necessary initial equilibration of the entire system, with different boundary heating rates for various surface wetting conditions, namely hydrophobic, hydrophilic, and superhydrophilic. Our current investigation shows that the heating condition, liquid film thickness, and surface wetting condition all have a significant impact on the type of liquid wall contact that persists during the phase transition phenomena of thin liquid argon film (i.e., normal evaporation or explosive boiling). In the event of normal evaporation, a stable liquid contact with the solid surface continues, however in the case of explosive boiling, the liquid film is splashed away from the solid surface resembling the macroscopic Leidenfrost effect. For various system configurations in regard to liquid initial film thickness, liquid heating rate as well as solid-liquid interaction, a wide variation of the onset time as well as the wall temperature of boiling explosion have been found in the present study. An accurate mapping of the Leidenfrost conditions in context to nanoscale thin film liquid-vapor phase process has been generated using a predictive model based on deep neural networks that has been designed, trained and cross validated against molecular dynamics data of the present study.

Investigating the Thermal and Energy Performance of Advanced Glazing Systems in the Context of Hail City, KSA

Most new housing designs in Saudi Arabia are created to meet the client’s needs with minimal regard for environmental or energy-related considerations, resulting in buildings’ poor thermal performance and a growing reliance on artificial means. Polycarbonate windows have recently acquired popularity. Yet, there is a rising interest in combining polycarbonate windows with nanomaterials to reduce energy consumption, especially during the summer months when air conditioning use is at its peak. To improve building insulation, this research concentrated on the use of polycarbonate windows with nanogel, which has a low U-value. This study utilized polycarbonate windows with nanogel (two layers of polycarbonate panes filled with nanogel) in Hail City, Saudi Arabia, using DesignBuilder simulation software, resulting in a 14.3% reduction in annual energy consumption. The low U-value of nanogel compared to argon or air may be the cause of these savings, which are roughly double those gained by using double-paned polycarbonate windows. The incorporated nanogel layer between two layers of argon and two layers of polycarbonate panes decreased annual energy consumption by 29% compared to utilizing only one polycarbonate layer. Moreover, compared to a single 3 mm polycarbonate pane, the nanogel layer placed between two layers of argon and two layers of single polycarbonate panes demonstrated the lowest level of CO2 emissions, with an improvement of around 22.23%. This study reveals a method for insulating buildings that cuts energy use and CO2 emissions. This study’s conclusion supports the notion that sustainable design is the future. Sustainable construction can dramatically reduce building cooling costs and thermal loads.

Molecular dynamics simulations of unsteady evaporation of thin liquid argon layer into a vacuum

The unsteady evaporation of liquid argon layer into a vacuum was studied based on molecular dynamics technique using the LAMMPS package. The comparison of the mass flow rate with the known kinetic theory analytical equations was carried out for several temperatures of the liquid layer. It was obtained that after short relaxation time mass flow rate ceases to depend on time for some period. The relaxation time for mass flow rate was estimated. It turned out that this time depends on the temperature of the liquid layer and decreases with increase of its temperature. The mass flow rate values predicted by molecular dynamics simulation are found to be well described by some analytical formulas from kinetic theory. The temporal dynamics of the liquid layer was investigated. The linear dependence between film thinning rate and mass flow rate values was obtained both in the quasi-steady regime and out of it. It was found that liquid interface temperature depends on liquid thickness by power law with an exponent independent of initial liquid film temperature.

Molecular dynamics perspective of condensation over a hybrid wetting surface

ABSTRACT The aim of the present study is to investigate relative effect of philic/phobic fraction and philic–phobic patterning on nanoscale condensation over a hybrid wetting surface through molecular dynamics simulations. A three-phase Argon–Platinum system has been considered, where the argon atoms are bounded by the two Platinum (Pt) surfaces. Initially a liquid argon layer is placed on the bottom Platinum surface and the rest of the simulation domain is filled with argon vapour. Following necessary equilibration, the temperature of the bottom surface is rised to induce evaporation, while that of the top surface with hybrid wetting characteristics is maintained at equilibration temperature to tempt condensation. Variation in hybrid wetting condition of the condensing wall is assumed by changing the relative percentage of philic/phobic portion and the size of philic–phobic pattern strip. It has been found that a higher amount of argon atoms is condensed in cases with higher hydrophilic contents. Also, for a fixed philic–phobic fraction, a smaller strip size of philic–phobic patterning results in faster condensation. Early-stage condensation, i.e. nucleation and subsequent condensate growth mode has been distinctive and related to the distribution of local liquid–vapour interfacial surface tension near the condensing wall for different hybrid wetting conditions.

Use of Insulation Based on Nanomaterials to Improve Energy Efficiency of Residential Buildings in a Hot Desert Climate

Building insulation based on nanomaterials is considered one of the most effective means of reducing energy consumption in the hot desert climate. The application of an energy-efficient insulation system can significantly decrease the energy consumed via a building’s air-conditioning system during the summer. Hence, building insulation has become an interesting research topic, especially with regards to the use of insulation based on nanomaterials due to their low U-values. In the present study, the use of nano vacuum insulation panels (VIPs) or polystyrene foam in the walls enabled a significant reduction in the annual energy consumption, a savings of 23% compared to the uninsulated wall in a study in New Aswan City. The application of nanogel glazing to the windows (two layers of clear glass filled with the nanogel) achieved approximately 11% savings in annual energy. This savings, twice that obtained by using double-glazed windows, could be due to the low U-value of nanogel compared to the U-values of argon or air. The embedded nanogel layer between two layers of argon and two layers of single clear glass showed a significant reduction in annual energy consumption, saving 26% compared to the use of a single layer of glass. Moreover, the integration between this window and embedded walls with 50 mm of polystyrene foam exhibited a significant improvement of energy efficiency by 47.6% while presenting the lowest value of simple payback period (SPP). This research provides a way for buildings to be insulated to make them more energy efficient as well as attractive from the economic standpoint.

A Molecular Dynamics Study of Heat Transfer Enhancement during Phase Change from a Nanoengineered Solid Surface

This study investigates the enhancement of the rate of evaporation from a nanoengineered solid surface using non-equilibrium molecular dynamics simulation. Four different types of surface modifications were introduced to examine the thermal transportation behavior. The surface modification includes: (1) transformation of surface wetting condition from hydrophobic to hydrophilic, (2) implementing nanostructures on the smooth surface, (3) cutting nano slots on the smooth surface and (4) introducing nano-level surface roughness. Evaporation behavior from the same effective surface area was also studied. The simulation domain consisted of three distinct zones: solid base wall made of copper, a few layers of liquid argon, and a vapor zone made of argon. All the nano-level surface modifications were introduced on the solid base surface. The few layers of liquid argon representing the liquid zone of the domain take heat from the solid surface and get evaporated. Outside this solid and liquid zone, there is argon vapor. The simulation began at the initial time t = 0 ns and then was allowed to reach equilibrium. Immediately after equilibrium was achieved on all three-phase systems, the temperature of the solid wall was raised to a higher value. In this way, thermal transportation from the solid wall to liquid argon was established. As the temperature of the solid wall was high enough, the liquid argon tended to evaporate. From the simulation results, it is observed that during the transformation from hydrophobic to hydrophilic conditions, enhancement of evaporation takes place due to the improvement of thermal transportation behavior. At the nanostructure surface, the active nucleation sites and effective surface area increase which results in evaporation enhancement. With nano slots and nano-level surface roughness, the rate of evaporation increases due to the increase of solid-liquid contact area and effective surface area.

2D modeling of fusion ignition conditions for a multilayer plasma liner magneto-inertial fusion target in a cylindrical configuration

A set of 2D time dependent simulations of an imploding cylindrical target and liner is presented. These simulations were performed using an ideal magnetohydrodynamic methodology that augmented the energy equation to account for fusion alpha particle deposition, thermal conduction, and Bremsstrahlung radiation. A reference case of a deuterium and tritium (DT) target compressed by a multilayer liner consisting of an inner layer of DT and an outer layer of argon was evaluated. The reference case was chosen to be within the region of positive fusion heating predicted by the Lindl–Widner power balance model. Analysis of the reference case determined fusion gains of three or greater can be achieved. A sensitivity analysis of four parameters was performed. These parameters were the target: radius, density, temperature, and inner/outer liner thickness ratio. It was found that the Lindl–Widner parameter space accurately predicts regions of positive fusion heating, but over-predicts the effects of mechanical work done by a plasma liner. It was determined that a plasma liner could be used as a confinement mechanism to contain a thermally conditioned target and allow it to ignite and burn. Thermal conduction from the hot fusing target was capable of heating the inner liner layer to fusion ignition conditions and increasing the fusion yield.

Molecular Dynamics of a Thin Liquid Argon Layer Squeezed between Diamond Surfaces with a Periodic Relief

The behavior of a liquid argon layer compressed between absolutely solid diamond surfaces with a periodic atomic relief has been studied by the method of molecular dynamics. The film consists of one or two layers of molecules for which the model of absolutely elastic spheres has been used. The equilibrium and dynamic properties of the film dependently on the load and shear force applied to surfaces and the number of argon layers have been investigated. The performed modeling allows us to compare the behavior of systems with smooth and rough plates. The results show that most of the properties of ultrathin argon films confined between surfaces of both types are similar.

Numerical Simulation, Design, and Construction of a Double Glazed Compound Parabolic Concentrators-Type Integrated Collector Storage Water Heater

The numerical simulation, design, and construction of a double glazed integrated collector storage (ICS) with compound parabolic concentrators (CPC) reflectors are presented. The design of the double glazing is optimized by means of numerical simulations under Tunisian climatic conditions. The numerical program used for the simulation consists on the transient resolution of the balance energy equations of each component of the solar water heater. Different proposed models of a double glazing are studied and compared with a reference case of a single glass ICS model. The simulation results have shown that the use of double glazing with argon layer and low-e coated lower glass instead of one glass cover significantly improves the thermal behavior of the ICS heater and visibly reduces its thermal losses during night. Taking into account these numerical results, a double-glazing ICS prototype-collector is constructed. The details of the construction, geometry, optical properties, and dimensions of the prototype are presented.

Positron study of surface tension reduction in liquid alkane at high pressure of argon

Surface tension σ of sub-nanometric bubbles in n-nonadecane + argon system as a function of pressure was estimated using the positron lifetime spectroscopy. The surface tension is higher than for flat surface (due to negative bubble curvature). The coefficient (∂σ/∂p)p=0 is negative but much smaller than for flat gas-liquid dividing surface. It can be explained by the lack of adsorbed argon layer on the bubble surface. In the narrow range of temperatures, where nonadecane melts by application of argon pressure, the concentration of argon in the liquid is found smaller than at higher temperatures and probably a kind of intermediate structure is formed.

Effective and accurate approach for modeling of commensurate-incommensurate transition in krypton monolayer on graphite.

Commensurate-incommensurate (C-IC) transition of krypton molecular layer on graphite received much attention in recent decades in theoretical and experimental researches. However, there still exists a possibility of generalization of the phenomenon from thermodynamic viewpoint on the basis of accurate molecular simulation. Recently, a new technique was developed for analysis of two-dimensional (2D) phase transitions in systems involving a crystalline phase, which is based on accounting for the effect of temperature and the chemical potential on the lattice constant of the 2D layer using the Gibbs-Duhem equation [E. A. Ustinov, J. Chem. Phys. 140, 074706 (2014)]. The technique has allowed for determination of phase diagrams of 2D argon layers on the uniform surface and in slit pores. This paper extends the developed methodology on systems accounting for the periodic modulation of the substrate potential. The main advantage of the developed approach is that it provides highly accurate evaluation of the chemical potential of crystalline layers, which allows reliable determination of temperature and other parameters of various 2D phase transitions. Applicability of the methodology is demonstrated on the krypton-graphite system. Analysis of phase diagram of the krypton molecular layer, thermodynamic functions of coexisting phases, and a method of prediction of adsorption isotherms is considered accounting for a compression of the graphite due to the krypton-carbon interaction. The temperature and heat of C-IC transition has been reliably determined for the gas-solid and solid-solid system.

Depolarised Rayleigh light scattering in argon layer confined between graphite plains: MD simulation

The interaction-induced light scattering many-body correlation functions and their spectra in a thin argon layer located between two parallel graphite walls have been investigated by molecular dynamics simulation method. The calculations have been performed for three different distances between graphite plates. Our simulations show the increased intensity of the interaction-induced light scattering spectra at low frequencies for argon atoms in confined space, in comparison to the bulk (unconfined) sample. Moreover, we show a substantial dependence of the interaction-induced light scattering correlation functions of argon on the distances between graphite walls, that is, on the density of argon layer. The mean square displacement and related diffusion coefficient of argon atom in the confined space has been also investigated. Moreover, the structural feature of the thin layer has been studied by calculating the argon density profile, perpendicular to the graphite walls. An interesting observation is the development of a fluid phase in the innermost region of the confined argon layer.

Structure, Energetic and Tribological Properties, and Possible Applications in Nanoelectromechanical Systems of Argon-Separated Double-Layer Graphene

The possibility to control the commensurability and distance between graphene layers separated by a dielectric spacer is considered by the example of a heterostructure consisting of double-layer graphene separated by atomic layers of argon. Van der Waals-corrected density functional theory (DFT-D) is applied to study structural, energetic, and tribological characteristics of this heterostructure. It is found that, in the ground state, monolayer and bilayer argon spacers are incommensurate with the graphene layers, whereas sub-monolayer argon spacers which are commensurate with the graphene layers can exist only as metastable states. The calculations show that this incommensurability provides negligibly small static friction for relative motion of argon-separated graphene layers; therefore, such a heterostructure holds great promise for use in nanoelectromechanical systems. A scheme and operational principles of the nanorelay based on the revealed tribological properties of the heterostructure are proposed.

Effects of melting and ordering on the isosteric heat and monolayer density of argon adsorption on graphite

The aim of this paper is to study the effects of temperature on the state of the adsorbed argon on an uniform graphite surface. We applied the kinetic Monte Carlo scheme to simulate adsorption over a very wide range of temperature, which allows us to model the vapor–solid, the vapor–liquid and the order–disorder transition of the monolayer. The main distinction of our methodology is that it accounts for the lattice constant change with loading in the case of formation of an ordered molecular layer by appropriately changing the simulation box size. To do this we enforced the equality of the tangential pressures obtained by the virial and thermodynamic routes, which corresponds to the minimum Helmholtz free energy of a system at a given number of molecules and volume. This criterion is a consequence of the Gibbs–Duhem equation. A significant result obtained by application of the new simulation method was a sharp contraction of the monolayer just after its completion and the onset of the second layer. It manifests itself in an additional heat release. We re-determined the 2D-melting and 2D-critical temperatures of the molecular layer of argon. We also analyzed the order–disorder transition above the 2D-melting and showed that it could occur at some temperatures above the 2D-critical temperature. In this case, a hexagonal lattice appears at a sufficiently large tangential pressure. The effects of loading on the lattice constant, the 2D-critical temperature of the order–disorder transition and the differential heat of adsorption are thoroughly discussed.

Study of Hydrogen Pumping through Condensed Argon in Cryogenic pump

In ultra high vacuum (UHV) range, hydrogen is a dominant residual gas in vacuum chamber. Hydrogen, being light gas, pumping of hydrogen in this vacuum range is limited with widely used UHV pumps, viz. turbo molecular pump and cryogenic pump. Pre condensed argon layers in cryogenic pump create porous structure on the surface of the pump, which traps hydrogen gas at a temperature less than 20° K. Additional argon gas injection in the cryogenic pump, at lowest temperature, generates multiple layers of condensed argon as a porous frost with 10 to 100 A° diameters pores, which increase the pumping capacity of hydrogen gas. This pumping mechanism of hydrogen is more effective, to pump more hydrogen gas in UHV range applicable in accelerator, space simulation etc. and where hydrogen is used as fuel gas like tokamak. For this experiment, the cryogenic pump with a closed loop refrigerator using helium gas is used to produce the minimum cryogenic temperature as ~ 14° K. In this paper, effect of cryosorption of hydrogen is presented with different levels of argon gas and hydrogen gas in cryogenic pump chamber.

Computer simulation of two-step atomization in graphite furnaces for analytical atomic spectrometry

The processes of sample fractionation by two-step atomization with the intermediate condensation of the analyte on a cold surface in graphite furnaces were theoretically studied. The transfer equation was solved for the atoms, molecules, and condensed particles of the sample from a flow of argon directed along this surface. The spatial distributions of vapor and the condensate formed were calculated depending on the composition and flow rate. It was found that a cold surface section with a length of 6 mm is sufficient for the complete trapping of atomic analyte vapor from an argon layer having a velocity of about 1 m/sec and a thickness of 5 mm. In this case, the molecules and clusters condensation coefficients smaller than unity were deposited insignificantly; that is, they were fractionally separated. The results of the shadow spectral visualization of the process of sample fractionation on a cold probe surface of in commercial HGA and THGA atomizers were interpreted. The advantages of analytical signals upon the evaporation of a sample condensate from the probe in these atomizers and inductively coupled plasma were demonstrated.

Freezing behavior of argon layers confined in mesopores

Adsorbed layers of argon in mesoporous Vycor glass exhibit a peculiar phase behavior. We have studied their liquid-solid transition in pores with a mean pore diameter of 8 nm via ultrasonic measurements. An effective medium analysis reveals that during isothermal filling at low temperatures ($T<{T}_{\mathrm{fr},\mathrm{bulk}}$) frozen layers form on top of liquidlike surface layers. These frozen layers are bulklike (i.e., ${G}_{\mathrm{Ar},\mathrm{SL}}\ensuremath{\approx}{G}_{\mathrm{Ar},\mathrm{bulk}}$ holds for their intrinsic shear modulus). We detect that both the first and the second layer undergo a continuous phase transition in a broad temperature range of at least 40 K. A complete freezing is only achieved at very low temperatures of approximately 20 K (i.e., far below the bulk freezing temperature). Whereas those two adsorbed layers remain stable during cooling, the third one becomes unstable around 66 K, rearranges, and solid capillary condensate is formed (delayering transition).