Wall Coupling Research Articles

Enhancing energy efficiency of PCM wall in winter with novel PCM-DLCB coupling design

In order to enhance the thermal performance of the phase change material (PCM) wall during winter, a novel PCM and double-layer capillary bundles (PCM-DLCB) coupling wall is proposed. The PCM-DLCB wall utilizes the capillary bundle near the outer surface to capture solar energy during sunny winter days. The heat is then transferred to the capillary bundle near the inner surface through a circulating pump, promoting the melting of the PCM. Optimization and long-term operation comparison research were conducted using numerical simulation to investigate the potential of the PCM-DLCB wall to improve energy efficiency during winter. Five structural parameters, including the type of PCM, the position of the capillary bundle, the position and thickness of the PCM layer, the spacing of the capillary bundles, and the flow velocity in the capillary bundle, were selected as variables for structural and operation optimization. The optimization target was the accumulated heat gain from the inner surface of the wall. The research results indicate that: (1) The most suitable PCM is RT-18HC; (2) Placing the PCM layer between the double-layer capillary bundle yields better results compared to other arrangements; (3) Optimal energy saving is achieved when the outer capillary bundle is positioned 6 mm away from the outer surface and the inner capillary bundle is positioned 8 mm away from the inner surface; (4) The optimal thickness of the PCM layer is 10 mm; (5) The optimal flow velocity in the capillary bundle is approximately 0.04 m/s. Furthermore, long-term operation results based on a typical hot summer and cold winter climate zone reveal that the optimized PCM-DLCB wall provides a 7.80 % increase in indoor heat gain compared to an ordinary PCM wall during winter, and an 18.4 % increase compared to a wall without PCM.

Investigation of MHD flow balancing in electrically conductive manifolds of liquid metal blankets

In the liquid metal (LM) blanket design for magnetic confinement fusion reactors, manifolds including main and branch ducts are commonly used to direct fluids to various locations of the blanket to cool its components. The primary objective of this structural configuration is to achieve flow balancing within each branch duct. However, magnetohydrodynamic effects will cause uneven flow distribution, consequently, uncontrollable overheating phenomena in certain blanket segments may be caused by this flow distribution. To assess its impact, the influences of external magnetic fields, inlet velocities and coupling wall thicknesses on the flow partitioning in conductive manifolds are investigated in this study. The results indicate that the flow distribution among the branch ducts becomes less uniform as the external magnetic field strength increases, while varying the inlet velocity has minimal impact. In addition, increasing the coupling wall thickness leads to more even flow distribution when the rectangular branch ducts are perpendicular with the magnetic field direction. Based on above physical understanding, three controlling methods for the flow partitioning in conductive manifolds are proposed to achieve flow balancing in each branch duct and then validated through numerical simulations. The results indicate that flow balancing can be achieved by adjusting the coupling wall thickness when the rectangular branch ducts are aligned with the magnetic field direction, however, it is challenging when they are perpendicular. Furthermore, the flow balancing can be realized by a symmetrical design of the manifold with circular branch pipes and it is independent of external magnetic fields and inlet velocities. These findings will enhance the physical understanding of flow distribution patterns in conductive manifolds under strong magnetic fields, which is important for the flow control and design of manifolds in LM blankets.

EFFECT OF DEFECTIVE MICROSTRUCTURE ON THE VALUE AND NATURE OF DISTRIBUTION OF RESIDUAL MACRO-STRESSES ON THE STEEL COUPLING OF THE TUBING

The work analyzes the influence of certain types of metal microstructure defects on the value and nature of distribution of the active residual macro-stresses of the σ in the tubing sleeve. The tubing coupling was made of pre-eutectoid steel, and to improve corrosion resistance, a bainite structure was formed in it. As defects of the metal microstructure, the most common cases in the manufacture of a coupling were considered, such as the structural gradient of the formation of constituent phases (upper and lower bainite, martensite tempering, martensite, etc.) along the thickness of the tubing wall, as well as non-metallic inclusions and pores in the material wall. To assess the residual macrostresses on the selected coupling surface, a non-destructive X-ray scattering method modified by the authors was used. At the same time, the modernization of this method consisted in the use of a micro-X-ray parallel beam (diameter 0.5 mm) in estimating the σ value, in measuring the spectrum of reflexes at inclined surveys at given coordinates (pitch 1.0 mm) for different directions of the φ plane, in determining the value of macro-stresses at each point and constructing their surface distribution with superimposed power lines. In order to take into account the anisotropy of the acting residual macro-stresses of the σφ on the analyzed surface of the coupling, in the measurements of the reflex (222), the sample was rotated about an axis perpendicular to the analysis plane. As a result of applying the modified macro stress estimation approach for the initial tubing sleeve having no process defects, it is found that the distribution of residual macro stresses in the longitudinal section of the wall is symmetrical. It is shown that residual compressive-type macro stresses of minus 341 MPa are formed in the inner part of the tubing coupling wall, and the tensile type — with the value of plus 347 MPa acts on the outer side of the coupling wall, the absence of macro stresses is detected in the middle part of the material wall. It has been shown that the presence of a structural gradient, i.e. the presence of martensitic plates in the near-surface layers of the coupling with a content of about 12 %, increases the active residual macro-stresses in these areas by more than 1.3 times. It was found that the presence of pores and non-metallic inclusions in the near-surface layers concentrated on the thickness of 170 μm of the coupling wall increases the residual macro stresses 1.6 times from the outside and 1.4 times from the inside of the wall. It has been shown that increased pore size and increased pore content, which are analyzed by raster electron microscopy, are factors in the increase of macro stresses from the outside of the coupling wall.

Analysis of Fluid-Solid Coupling Radial Heat Transfer Characteristics in a Normal Hexagonal Bundle Regenerator under Oscillating Flow

The main purpose of this paper is to analyze the heat transfer mechanism of a new type of regenerator with a low temperature difference and low current resistance under oscillatory flow at room temperature. Taking the single tube of the regenerator as the research object, the exact analytical solution of the radial heat transfer characteristics of the regenerator is obtained by studying its analytical model. The factors affecting the heat transfer characteristics are analyzed, and then the regenerator is optimized to improve the performance and efficiency of the regenerator system. In this study, we systematically analyzed the radial heat transfer characteristics of a regenerator under isochoric process conditions. A closed-system physical model of the incompressible isochoric process under oscillating flow was established. Then, the radial analytical solutions of pressure fluctuation, fluid velocity, fluid-solid temperature, and heat were derived in the complex number field. Furthermore, the fluid velocity, fluid-solid coupling wall temperature, heat, and equivalent heat transfer coefficient were assessed. Furthermore, the influences of frequency, inner diameter R1 of the regenerator, and different working medium and materials on the above parameters were discussed. It was found that the analysis and evaluation of fluid velocity, fluid-structure coupling wall temperature, heat, and equivalent heat transfer coefficient are helpful in understanding the dynamic characteristics of radial heat transfer in a regenerator system. Through the study of radial heat transfer under oscillating flow, it was found that the working medium, frequency, inner diameter of the regenerator, and material quality of the regenerator are helpful for the design optimization of the regenerator. Furthermore, our investigations established that the variation law of wall fluid-solid coupling temperature amplitude could be divided into three parts: the unidirectional flow part; the low-frequency part, where the temperature amplitude falls rapidly with increasing frequency; and the high-frequency part, where the temperature amplitude increases with the frequency. In addition, the variation of radial heat transfer of the fluid-solid coupling surface is similar to the changes in the temperature amplitude. We also discovered that the equivalent heat transfer coefficient of the fluid-solid surface is related to thermal conductivity of the material. Specifically, larger thermal conductivity values result in greater equivalent heat transfer coefficients. Based on the research into the radial heat transfer characteristics, the new regenerator has great application potential in the Stirling air conditioning system at room temperature.

Electromagnetic attenuation displayed by La-Co substituted Ba-Sr hexaferrite nanoparticles and multiwall carbon nanotubes in polyaniline and polythiophene matrix

Our presented research aims to provide a systematic study of electrical, magnetic and microwave absorption properties of La-Co substituted Ba-Sr hexaferrite nanoparticles and MWCNTs, encapsulated in conductive polymer matrix. La-Co substituted Ba-Sr hexaferrite nanoparticles were produced using Sol-Gel auto combustion, whereas carrier fluid ultrasonication dispersion and in-situ polymerization were used to synthesize their composites with multiwall carbon nanotubes (MWCNTs) and conductive polymers. Structural investigations were accomplished using X-rays diffraction, secondary electron microscopy, Infrared and Raman Spectroscopy. The dielectric measurements revealed increased dielectric losses (4.86 at 1 GHz for pure nanoparticles, which increases up to 11.59 and 13.36 for ternary composites within PANI and PTh matrix), indicating good energy dissipation behavior. The decrease in magnetism was observed due to the weakening of exchange coupling or domain wall pinning at the interface of Ferrite-MWCNTs and Ferrite-Polymer, resulting in lowered saturation magnetization, remanence and coercivity values. The microwave absorption of our samples was evaluated as a function of frequency and thickness, revealing its dependence on the quarter wavelength phenomenon with maximum reflection loss of − 40.4 dB observed for ternary composite with Polythiophene matrix at 7.54 GHz resonance frequency. The dependence of reflection loss peaks on matching thickness was analyzed using calculated thickness profiles, revealing their close agreement with simulated thickness. The study highlighted the potential of synthesized samples for electromagnetic signature reduction, in both commercial and military applications. The resonance bands were found to coincide with the operating frequency of military radars for shipborne and airborne surveillance and navigation in the X band (8–12 GHz).

Echocardiographic indices of right ventricular function differentiate pre- and post-capillary pulmonary hypertension

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Heart and Lung foundation Background The importance of assessing right ventricular (RV) function in heart failure is well established. Methods evaluating intrinsic RV function using Doppler echocardiography estimating RV -pulmonary coupling assessment might improve the understanding of RV response due to increase in RV afterload in different conditions. Aim To investigate RV function and RV-pulmonary coupling in patients with pre- and postcapillary pulmonary hypertension. Material and Methods We investigated 85 patients with pulmonary hypertension (PH) defined as mPAP >20mmHg from right heart catheterization (RHC). Those having PH with PCWP≤15mmHg and PVR ≥ 3WU were categorized as pre-capillary PH (preCPH, n=60) and those with PCWP>15mmHg and PVR <3WU as post-capillary PH (postCPH, n=25). Of those 25 having postCPH, 16 had HFrEF (LVEF<50%) and 9 HFpEF )LVEF≥50%). Doppler echocardiography and RHC were done simultaneously. Results Pulmonary artery acceleration time (<0.01), sPAP (<0.01) and regional RV strain ( p<0.05) differed between pre- and postCPH, whereas RV -pulmonary coupling did not, table 1. The indirect echocardiographic measure demonstrating strongest association with Ees/Ea (volume method= SVrhc/ESVecho) in patients with preCPH was mPAP/CO (r=0.61, fig 1A), RV s’/sPAP and RVGLS/sPAP (r=0.62, fig 1B, and 0.57 respectively). RV e’, RV segmental and global strain were lower in HFrEF compared with HFpEF but RV-pulmonary coupling did not differ between groups. Conclusion Right ventricular-pulmonary coupling and RV free wall strain had low accuracy to differentiate pre- from post CPH which was not the case for PAAt, sPAP and RV regional strain. mPAP/CO and RVs’/sPAP suggests promise as markers for right ventricular- pulmonary coupling, especially in pre CPH.

Encapsulation of Ba–Sr hexaferrite nanoparticlesand MWCNTs in conductive polymer matrix for improved dielectric spectroscopy, electromagnetic shielding and microwave absorption applications

Ba–Sr hexaferrite nanoparticles were produced using Sol-Gel auto combustion, whereas carrier fluid ultrasonication dispersion and in-situ polymerization were used to synthesize their composites with MWCNTs and conductive polymers. Structural investigations were accomplished using X-rays diffraction, secondary electron microscopy, Infrared and Raman Spectroscopy. The low frequency dielectric measurements revealed increased dielectric losses (304 at 100 Hz for pure nanoparticles, which increases up to 2721 and 7861 for ternary composites within polyaniline and Polythiophene matrix), indicating good energy dissipation behavior. The diminishing magnetism resulted from the weakening of exchange coupling or domain wall pinning at the interface of Ferrite-MWCNTs and Ferrite-Polymer, causing the shifting of magnetic resonance peak towards lower frequency in the shielding effectiveness (Absorption) plots. Increasing DC conductivity adds to the nominal increase of Shielding effectiveness (Reflection) values owing to the rise in charge carrier conduction. The maximum total shielding effectiveness, perceived for the composition of Ba0.5Sr0.5Fe12O19/MWCNTs/Polythiophene, was −34 dB and −33 dB at 8.1 GHz and 16.2 GHz, respectively. The microwave absorption of our samples was evaluated as a function of frequency and thickness, revealing its dependence on the quarter wavelength phenomenon with maximum reflection loss of −39 dB observed for ternary composite with Polythiophene matrix at 7.4 GHz resonance frequency. The resonance bands coincide with the operating frequency of military radars for shipborne and airborne surveillance and navigation in the X band.

Numerical study on the muck flow behavior in the screw conveyor during EPB shield tunneling

The muck flow behavior in the screw conveyor determines the pressure in the excavation chamber. The pressure in the chamber should be reduced to the atmospheric pressure at the outlet of the screw conveyor. Otherwise, the soil and water mixture would spew out form the screw conveyor, resulting in the pressure loss and face failure. In this study, three-dimensional numerical analyses of the muck transport performance of screw conveyor were performed using Computational Fluid Dynamics (CFD). The muck was assumed to behave as a Herschel-Bulkley (H-B) plastic fluid. A new model coupling rheological and wall slip models was developed and validated by a laboratory test. The error of the pressure transfer and the flow rate between simulation and test is around 3.8%. Through parametric analysis, the influence of the rheological parameters of muck and the working parameters of the screw conveyor on the muck flow behavior is further explored, and a spewing failure surface is given for the control of rheological parameters of the conditioned soil. The results in this study could provide some suggestions for soil conditioning and the optimization of screw conveyor performance.

Correlation between interlayer exchange coupling and domain wall velocity in multilayered magnetic wires

The effect of interlayer exchange coupling (IEC) in {Tb/Co}4/Rh/{Co/Tb}4/Pt multilayered wires on the domain wall (DW) structure and DW velocity was investigated. It was found that the stability of the Néel-type DWs was enhanced and the velocity of the current-induced DW movement increased with an increase in the antiferromagnetic IEC strength. The micromagnetic simulation based on the Landau–Lifshitz equation clarifies that the direction of the magnetic moment in the DWs depends on the antiferromagnetic IEC strength, and the stability of the Néel-type DW increases with an increase in the antiferromagnetic IEC strength. As a consequence of this stability, the spin-orbital torque affects effectively on the magnetic moment of the DWs and the DW velocity increases. These results imply that the DW velocity in magnetic domain-based memories can be controlled by the antiferromagnetic IEC strength.

Multi-scale modeling of the concrete SHPB test based on DEM-FDM coupling method

The split Hopkinson pressure bar (SHPB) test is the most commonly used method for testing the dynamic mechanical behavior of materials at high strain rates. In this paper, for the SHPB test of concrete, an efficient multi-scale mechanical calculation method based on coupling of discrete element method (DEM) and finite difference method (FDM) is proposed, and SHPB test system for analysis of the macroscopic and microscopic dynamic mechanical properties and damage evolution of concrete under impact loading is established by this coupling method. A three-phase mesoscopic scale model of concrete is constructed by DEM, and the crushability, real geometry-shape, and particle size distribution of aggregates are considered by combining 3D scanning technology and the “ball-clump-cluster” method. Meanwhile, FDM is adopted to simulate the SHPB model, and the “coupling wall” mechanism is applied to realize the signal transmission between the models. On this basis, the stress waves obtained by the direct monitoring method through numerical simulation are basically consistent with those obtained by the theoretical calculation method, which verifies the dynamic characteristics of the SHPB model. Finally, the different types of microcrack propagation are analyzed in the premise of examining the static and dynamic mechanical response of the concrete model. It was found that the distribution of mortar and aggregate microcracks on the outside of the concrete was significantly more than that on the inside due to transverse inertia force, and the superiority of the method in simulating the damage evolution behavior of concrete meso-structural is demonstrated.

The Effect of a Rigid Connection between the Slab and the Coupled Beam on the Seismic Performance of the Coupling Wall System

The evolution of the construction building is one of the urgent matters in the current era, especially for high and medium-rise buildings. The widely used frame shear wall system has the main sign for the resistance of the lateral load (seismic and wind loads), so adding the coupled shear wall system to the construction building can give sufficient lateral stability, which can be achieved by increasing stiffness, strength, and ductility of the system. However, much research had been studied the coupling beams in the shear wall system theoretically and experimental; the effectiveness of the slab performance on the system has a short thesis executed experimental with limiting factors. In other words, only a few studies have shown the effects of slabs on the behavior of the coupled beam, and these studies did not mention the representation of the model. This study aims to investigate the effect of the rigidity connection between the slab and coupled beam and to create a finite element model in 3D to get a full understanding of the behavior of the system with different cases and hence to get recommendations for constructing stability system, the interaction between the slab elements and the shear wall system can effect on the behavior of the building. Deformation, shear, and moment in the coupled beam consider as the main measurements of structure response; the measured responses with different models of building 4, 8, 12 stories have been investigated in 3D models to obtain the behavior of the interaction of the slab with the coupled wall system. Two cases have been created; one is made without slab between coupled beam, and the other with existence the slab. The results prove that the rigidity between the coupled beam and the slab diaphragm is more effective for stability versus the seismic load. It shows the response reduction in the coupled beam and hence the overall response of the structure modeling, which can be returned to the effects of interaction rigidity between elements of the coupled beam and slab.

Study on a new high-entropy alloy Nd20Pr20La20Fe20Co10Al10 with hard magnetic properties

High-entropy alloys (HEAs) are a new class of alloys that consist of at least five major elements in equimolar or near-equimolar ratios with atomic concentration between 5% and 35%. Many HEAs containing the ferromagnetic elements Fe, Co and Ni show soft magnetic properties, while few HEAs present hard magnetic properties. In this paper, we design and prepare the Nd20Pr20La20Fe20Co10Al10 HEA with hard magnetic property. The magnetic property and microstructure of this alloy have been investigated. The intrinsic coercivity (Hcj), saturation magnetization (Ms), and remanence (Mr) of Nd20Pr20La20Fe20Co10Al10 alloy is 280.0 kA/m, 14.0 Am2/kg and 8.9 Am2/kg, respectively, which is slightly lower than 301.0 kA/m, 14.9 Am2/kg and 9.6 Am2/kg of Nd60Fe20Co10Al10 bulk amorphous alloy. The elasticity modulus (Er) of Nd20Pr20La20Fe20Co10Al10 alloy is 58.7 GPa, 4.6% higher than that of Nd60Fe20Co10Al10 alloy. SEM results show that there are two kinds of amorphous phases with different chemical compositions. TEM results show that Nd (Pr) and La nanocrystals are embedded in the amorphous matrix. The high coercivity of the alloy may originate from the combined effect of exchange coupling and domain wall pinning. Our findings provide a new idea to design HEAs with hard magnetic property leading to widen their applications.

Heat transfer efficiency of hierarchical corrugated sandwich panels

As a kind of biomimetic materials, ultralight hierarchical porous structures possessing excellent mechanical properties such as load bearing, impact energy absorption, vibration reduction and noise attenuation have been exploited. Often, these porous structures exhibit continuous flow passages that allow for cooling fluids to pass through, thus enabling simultaneous load-bearing and active heat dissipation. This study investigated the convective cooling efficiency of a sandwich panel with hierarchical corrugated core subjected to heating from the face sheets and active cooling through the core. Built upon the classical fin approach, a theoretical model coupling wall heat conduction and fluid convection in the core was established for the hierarchical corrugated-core sandwich panel, covering the full range of fluid flow (from laminar, transition to turbulent). The theoretical model predictions were validated against full numerical simulations. Based on the theoretical model, an artificial intelligence optimization method (i.e., the ant colony algorithm) was adopted to find the optimal combination of key independent geometric parameters of the sandwich panel for maximized heat transfer performance. For the problem of multi-variables optimization, it was demonstrated that the ant colony algorithm is superior in terms of computational time to the traditional exhaustive search method. For a given pressure drop, a set of optimum geometric parameters corresponding to maximum cooling efficiency was found for the proposed hierarchical corrugated-core sandwich panel.

A New Slip Length Model for Enhanced Water Flow Coupling Molecular Interaction, Pore Dimension, Wall Roughness, and Temperature

In this paper, a slip length model is proposed to analyze the enhanced flow based on the Hagen–Poiseuille equation. The model considers the multimechanisms including wall-water molecular interactions, pore dimensions, fractal roughness, and temperature. The increasing wall-water interactions result in the greater slip length and flow enhancement factor. The increased temperature enhances the kinetic energy of water molecules that leads to great surface diffusion coefficient and small work of adhesion. The wall roughness can decrease the slip length and flow enhancement factor in hydrophilic nanopores. This work studies the effects of multimechanisms on slip length and flow enhancement factor theoretically, which can accurately describe the liquid flow in nanopores.

INFLUENCE OF COUPLING DESIGN AND CONDITIONS OF ITS INSTALLATION ON PIPELINE SECTION STRENGTH

Background During operation to ensure the strength of pipeline sections of trunk oil and gas pipelines with external corrosion, couplings are widely used. The coupling installed on the corroded part of the pipeline takes up part of the load of the internal pressure, ensuring that this load is reduced by the reduced wall thickness due to corrosion. Coupling installation can be fulfilled with the tension of its wall and in the presence of internal pressure in the pipeline. Thereby, the efficiency of the corroded pipeline section is achieved. At the same time, coupling installation leads to a change in the stress-strain state of the pipeline sections adjacent to the coupling with the appearance of local bending stresses. With all this, the level of mechanical stresses in the walls of the corroded section of the pipeline and coupling during operation should not exceed the normative. In order to ensure the strength of the repaired sector, it is necessary to determine the maximal stresses in the walls of pipeline and coupling depending on their geometrical characteristics and installation conditions and after that to conduct a strength test in accordance with the requirements of SP 36.13330-2012. Aims and Objectives To obtain analytical dependences of the maximal stresses in the wall of the coupling and the pipeline arising from the action of internal pressure, depending on their geometrical characteristics and installation conditions of the coupling. Methods Theoretical research of pipeline corroded section and repair coupling stress-strain state during operation. Results The dependences of the stresses in the coupling wall and pipeline on their geometric characteristics, coupling installation conditions and internal pressure are obtained.

Coupled-Mode Theory of an Irregular Waveguide with Impedance Walls

The eigenvalue problem is solved for a longitudinally inhomogeneous waveguide with impedance walls. The cross-section method is applied to reduce the problem to an infinite set of ordinary differential equations for amplitudes of basis modes. As a numerical example, a tapered metallic cavity of currently available THz gyrotron is considered. The combined effect of mode coupling (conversion) and ohmic wall losses on electromagnetic properties of the gyrotron cavity is considered and discussed.

Reduced-scale experiments to evaluate performance of composite building envelopes containing phase change materials

This study presents a convenient approach to rapidly assess the thermal performance of building envelopes containing phase change materials (PCMs) or other building materials. It establishes that the transient thermal behavior of full-scale building test structures featuring envelopes with PCMs can be represented by a reduced-scale test cell conveniently placed inside an environmental chamber. Indeed, PCM-composite envelopes have been considered for reducing and time-shifting the thermal load on buildings thanks to the latent heat associated with reversible transition between liquid and solid phases. First, a thermal model coupling outdoor, wall, and indoor temperatures and accounting for PCM latent heat was developed. It was validated against experimental temperature measurements within a reduced-scale test cell enclosure placed in an environmental chamber and subjected to a series of sinusoidal temperature cycles. Then, scaling analysis of the experimentally-validated thermal model was performed. It identified eight dimensionless numbers governing the transient thermal behavior of building structures with envelopes containing PCMs. The scaling analysis was validated using detailed numerical simulations for different enclosure geometries and outside diurnal climate conditions. Finally, the method was demonstrated on full-scale experiments reported in the literature. It can be used to assess building envelope thermal performance by designing representative reduced-scale experiments without requiring a significant amount of material, time, or space.

Interface-induced spontaneous positive and conventional negative exchange bias effects in bilayer La0.7Sr0.3MnO3/Eu0.45Sr0.55MnO3 heterostructures

We report zero-field-cooled spontaneous-positive and field-cooled conventional-negative exchange bias effects in epitaxial bilayer composed of La0.7Sr0.3MnO3 (LSMO) with ferromagnetic (FM) and Eu0.45Sr0.55MnO3 (ESMO) with A-type antiferromagnetic (AF) heterostructures respectively. A temperature dependent magnetization study of LSMO/ESMO bilayers grown on SrTiO3 (001) manifest FM ordering (TC) of LSMO at ~320 K, charge/orbital ordering of ESMO at ~194 K and AF ordering (TN) of ESMO at ~150 K. The random field Ising model has demonstrated an interesting observation of inverse dependence of exchange bias effect on AF layer thickness due to the competition between FM-AF interface coupling and AF domain wall energy. The isothermally field induced unidirectional exchange anisotropy formed at the interface of FM-LSMO layer and the kinetically phase-arrested magnetic phase obtained from the metamagnetic AF-ESMO layer could be responsible for the spontaneous exchange bias effect. Importantly, no magnetic poling is needed, as necessary for the applications. The FM-AF interface exchange interaction has been ascribed to the AF coupling with sum {J}_{ex}vec{{S}_{{rm{FM}}}}cdot vec{{S}_{{rm{AF}}}} ({J}_{ex}approx {J}_{AF}, coupling constant between AF spins) for the spontaneous positive hysteresis loop shift, and the field-cooled conventional exchange bias has been attributed to the ferromagnetically exchanged interface with {J}_{ex}approx {J}_{F} (coupling constant between FM spins).

Investigation of Stiffness Effect of Coupling Beam on Boundary Element Detailing in Structures with Hybrid Coupled Shear Walls

Coupled walls are known to be efficient lateral load-bearing systems. Coupling beam and wall piers are two important and effective elements in the general response of these structures. In this paper, stiffness effect of steel coupling beams on boundary elements in coupled shear walls has been investigated. The provisions of Iranian National Building Code for concrete structure (INBC-No. 9) for evaluating detailing requirements at wall boundaries are based on studies on uncoupled continuous walls, in which stress distribution across sections is assumed to be linear and in un-cracked sections. Due to the fact that there have been severe axial forces on wall piers resulting in the creation of cracks in sections of tension walls, the applicability of these provisions in coupled walls should be evaluated. Several coupled wall structures with different geometrical specifications, representative of various ratios of stiffness of the coupling beam to stiffness of the wall (RSBW), under equivalent lateral force, were designed, and efficiency of the code provisions was investigated in comparison with the results of the numerical analysis in Abaqus software. In this analysis, nonlinear behavior of material was considered. Results show that for structures with large and medium RSBW, code provisions are not appropriate in evaluating detailing requirements of tension wall boundaries, and a nonlinear stress distribution on the section should be used. For compression walls and structures with low RSBW, code provision is reliable.

CFD for subcooled flow boiling: Coupling wall boiling and population balance models

In this work we investigate the present capabilities of CFD for wall boiling. The computational model used combines the Euler/Euler two-phase flow description with heat flux partitioning. Very similar modelling was previously applied to boiling water under high pressure conditions relevant to nuclear power systems. Similar conditions in terms of the relevant non-dimensional numbers have been realized in the DEBORA tests using dichlorodifluoromethane (R12) as the working fluid. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size.Essential for the momentum, mass and energy exchange between the phases is an adequate description of the interfacial area or respectively the bubble size. In a previous study (Krepper and Rzehak, 2011) it was shown that a monodisperse bubble size representation is not sufficient to this end. Therefore, in the present work a population balance approach is used, where bubbles are generated at the wall with a certain size that subsequently evolves due to both condensation/evaporation and coalescence/breakup processes. The results show the potential of this approach which is able to describe the observed bubble size increase after leaving the wall as well as the change of gas volume fraction profile from wall to core peaking with increasing inlet temperature.