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A 1+1-dimensional(1+1D) multiphase model of proton exchange membrane fuel cell (PEMFC) is developed to simulate the dynamic behaviors of the fuel cell under various operating conditions. Electrochemical, fluidic, and thermal physical phenomena are taken into account, and the model can accurately describe the multi-physical processes inside the PEMFC. Meanwhile, the water phase change and nitrogen crossover are also considered in this model. The developed model can simulate the fuel cell behaviors in both normal temperature and cold start conditions. Selection of the time step size is discussed, and the solution method of the real-time model is proposed. Computational efficiency is greatly improved by simplifying the multicomponent diffusion inside the membrane electrode assembly (MEA), which results in the shorter calculation time than the simulated physical time. The proposed model is suitable for embedded applications, such as real-time simulation or online diagnostic control. The comprehensive model validation is carried out by comparing the simulation results, including polarization curves, ohmic resistance, local current density distribution, and voltage evolution, under various working conditions of steady state, load change, and cold start, and a good agreement is achieved. Finally, some simulation cases are studied to further demonstrate the simulation ability of the model.

In this paper, numerical simulations of Diffusion Absorption Refrigeration – DAR cycle were conducted in order to study the performance of two configurations in steady state mode and use ammonia, water, hydrogen as working fluids. The two configurations were numerically simulated using models developed with the commercial flow sheet Aspen HYSYS V10 software. The first configuration where the main simple DAR cycle components were simulated and validated the experimental results. The second configuration where the modified DAR cycle was simulated which has an auxiliary heat exchanger added to the main simple DAR cycle as a modification. It was found that for the same input assumptions and heat applied, the modified DAR cycle shows higher cooling load. Therefore, higher COP than the simple DAR cycle. The optimal operation of the modified cycle is 36 W applied to the generator to achieve a COP of 0.235 instead of 0.209 for simple DAR cycle. The Simulation results show that by using the modified cycle, the COP improves by 12.4%.

A two-stage vacuum pressure swing adsorption (VPSA) process that coupled kinetically controlled and equilibrium controlled separation process with reflux has been investigated for capturing carbon dioxide from dry flue gas (85% N2/15% CO2). In the first enriching stage, carbon molecular sieve (CMS), which shows kinetic selectivity for CO2/N2, is adopted as the adsorbent to remove most N2 in feed gas, thereby upgrading CO2 and significantly reducing the amount for further refinement. The second stage loads zeolite 13X as adsorbent to purify the CO2-rich flow from the first stage for meeting the requirements of National Energy Technology Laboratory. Series of experiments have been conducted for adsorption isotherms measuring and lab-scale experimental validation as well as analysis. The effect of feed composition on the separation performance of the PSA system was studied experimentally and theoretically here. The optimal results achieved 95.1% purity and 92.9% recovery with a high CO2 productivity (1.89 mol CO2·h−1·kg−1) and an appropriate energy consumption of 1.07 MJ·(kg CO2)−1. Further analysis has been carried out by simulation for explicating the temperature, pressure, and concentration distribution at cyclic steady state.

Sterilizing filtration is a common unit operation for the manufacture of parenteral drug products. However, filter performance can be impacted by properties of both the membrane material and the solution being filtered, requiring extensive multi-factor studies to optimize the filtration process for a given drug product. Here, we report the use of a modified bundle of capillaries approximation to predict filter performance. The model is directly applicable for both Newtonian and non-Newtonian solutions and does not require assumptions of steady state. Using a hydrophilic polyvinylidene difluoride (PVDF) filter as a test case, we show that the model fitting parameters align with expected values and both flux and shear are well predicted. Moreover, two case studies are presented to demonstrate the model's utility for filtration process optimization: 1) protein adsorption of an antibody formulation and 2) filter fouling of a 1% (w/v) carboxymethylcellulose (CMC) solution. In both cases, the model was able to accurately identify optimal filtration parameters to reduce the amount of adsorption or improve the filter capacity, respectively. This methodology can be easily extended to alternate filter types and provides an additional predictive tool to speed process development and minimize trial and error during filtration process design.

In this article, coupled electromagnetic-thermal simulations of inductive power transfer (IPT) pads using finite-element simulations are discussed. Derivation of each electrical and thermal parameters required for the modeling process is outlined. Simulation models are used to predict the power loss and the temperature rise of an IPT pad at different ambient temperatures at steady state. Using these simulation methods, the power loss within an IPT pad operating at 50 ${^\circ }$ C ambient temperature is predicted. A 10-KW IPT system is set up within an environmental chamber to validate the predicted losses within the system.

Ammonia synthesis is a crucial section of ammonia and urea plant. Many industries are facing a challenge of efficient ammonia production every day. In this study, steady state one dimensional pseudo-homogeneous models of an axial flow industrial catalytic packed bed ammonia converter have been developed. The converter is a vertical two catalytic bed reactor with varying volumes of catalysts. Required industrial data for the design were collected from a real fertilizer industry in Bangladesh (RFIB) and the Halder Topsoe process was followed. Differential equations of the the developed mathematical model was solved using Runge-Kutta-Fehlberg (RKF45) method by Polymath solver software. For a 23.8% single-pass conversion total 22.5 (15 + 7.5) m catalyst bed required. Pressure vessel wall and head thickness were found 112 mm and 62 mm respectively. Skirt support was selected and the thickness was calculated 12 mm. Pressure drop along the length of the bed was calculated and the value was found 2.55 atm. Finally, parameters of the optimized model were compared with the real plant data and quite satisfactory result were obtained.

This paper presents the study of binary component analysis subjected to distillation process using Aspen Plus. Binary components namely Isopropyle alcohol and water were considered for the study and their characteristics are analyzed at certain temperature and pressure. Aspen Plus provides virtual exposure of physical process, gives quantitative measure of mole fraction of liquid phase, vapor phase with changes in temperature, pressure and activity coefficients. Steady state and dynamic simulation results depicts the behavior of the system and enables the user to understand how the system reacts in virtual environment, to realize the system behavior in real-time environment.

High resolution surface temperature maps of a slotted surface grating laser operating at approx. 1550 nm are obtained by means of CCD-thermoreflectance imaging. The resolution is such that the temperature of the 2 µm wide ridge can be determined. Experimental temperature profiles along the ridge and in the lateral direction are provided. A 2D numerical model is developed to simulate the steady state thermal distributions in the laser. There is good agreement between the experiment and simulation. This technique allows for high-resolution imaging and will be useful where hot spots occur on laser devices.

The dynamics of the interaction between immiscible fluids is relevant to numerous complex flows in nature and industry, including lubrication and coating processes, oil extraction, physicochemical separation techniques, etc. One of the most essential components of immiscible flow is the fluid interface, which must be consistently monitored. In this article, the unsteady flow of two immiscible fluids i.e., an Eringen micropolar and Newtonian liquid is considered in a horizontal channel. Despite the no-slip and hyper-stick shear stress condition at the channel edge, it is accepted that the liquid interface is dynamic, migrating from one position to the next and possibly get absolute change; as a result, The CS (continuum surface) model is integrated with the single moment equation based on the VOF (volume of fluid) approach to trace the interface. The immiscible fluids are considered to flow under three applied pressure gradients (constant, decaying, and periodic) and flow is analyzed under seamless shear stress over the entire interface. The modified cubic b-spline differential quadrature method (MCB-DQM) is used to solve the modeled coupled partial differential equations for the fluid interface evolution. The advection and tracking of the interface with time, wave number, and amplitude are illustrated through graphs. It is observed that the presence of micropolar parameters affects the interface with time. The novelty of the current study is that previous studies (which considered the smooth and unstable movement of the micropolar fluid, the steady stream of two immiscible fluids, and interface monitoring through different modes) are extended and generalized to consider the time-dependent flow of two immiscible fluids namely Eringen micropolar and Newtonian with a moving interface in a horizontal channel. For the decaying pressure gradient case, which requires more time to achieve the steady-state, the peak of the waves resembles those for the constant pressure gradient case. The interface becomes steady for a more extensive time when a constant pressure gradient is applied. The interface becomes stable quickly with time as the micropolar parameter is decreased for the constant pressure gradient case i.e., weaker micropolar fluids encourage faster stabilization of the interface. With periodic pressure gradient, the interface takes more time to stabilize, and the crest of the waves is significantly higher in amplitude compared to the constant and decaying pressure cases. The simulations demonstrate the excellent ability of MCB-DQM to analyze complex interfacial immiscible flows.

We present experiments and theory relating to transpiration through unrestrained hydrogel beads in contact with a water reservoir below and air above. Experimentally, we find that saturated hydrogel beads shrink until a steady state is reached in which water flows continuously through the beads. The size of the bead in steady state is sensitive to the evaporation rate, which depends on the relative humidity and speed of the surrounding air, and to the pressure head imposed by the fluid reservoir. Specifically, the bead size decreases with increasing pressure head or evaporation rate. Our one-dimensional model proposes that transport in the hydrogel is driven by gradients in osmotic pressure, caused by gradients in polymer concentration in the hydrogel that correspond to gradients in swelling. If the evaporation rate or the pressure head changes, the adjustment of this gradient requires the bead to change shape and size. Smaller beads have larger gradients of osmotic pressure, which drive higher transpiration rates and can draw water against larger pressure heads.

A UVC-LED is a deep ultraviolet LED with a wavelength of 200–280 nm, which has a wide range of applications in disinfection, water purification and other fields. However, UVC-LED chips have limitations of high heat and poor heat dissipation, so it is necessary to test and analyze the thermal and optical properties of UVC-LEDs. This paper studies the photothermal characteristics of a UVC-LED under different driving currents. By measuring and analyzing the radiation flux, radiation intensity, junction temperature and thermal resistance of the UVC-LED under different driving currents, it is found that the junction temperature of the UVC-LED under the transient and steady state increases with the increase in the driving current, while the thermal resistance decreases. The radiation flux and intensity of the UVC-LED increase with the increase in driving current. The peak wavelength appears as a redshift with the increase in current, and the half-wave width also increases with the increase in current.

This article is to study the ramping loss of no-insulation (NI) high temperature superconducting (HTS) racetrack coil under different external magnetic fields during the charging process. An improved equivalent circuit electromagnetic coupling model for the HTS racetrack coil is introduced with good computational speed and accuracy. The simulation results show that the turn-to-turn loss and the change of the lowest critical current position are obviously influenced by the external field that have not been mentioned from our knowledge base. During the rising time of the power supply current, there is little difference in current distribution under different external fields. But after that, steady state of charging process is deeply influenced by the external field. A larger external field will lead to a lower charging current and the external bypass phenomenon. Another result is that the relationship between direction of external field and orientation of coils will influence the lowest critical current amount and position. The relationship between turn-to-turn resistivity of co-winding materials and ramping loss is also discussed in the paper. The distributed unevenness and value of the turn-to-turn loss change with the increase of turn-to-turn resistivity.

Complex systems often exhibit shear banding—the coexistence of two different states characterized by their internal structuring and local shear rates. For some of them, the heterogeneous flow corresponds to the final steady-state response, while for others, shear banding can only be transient, the banding structure healing back to a homogeneous flow in the ultimate steady state after long-lived periods. In order to explain the diversity of observations, Moorcroft and Fielding have established general criteria for the onset of banding in time-dependent flows of complex systems, ranging from polymeric fluids to soft glassy materials [Moorcroft et al., Phys. Rev. Lett. 110, 086001 (2013)]. The proposed criteria are based on the time evolution of the bulk rheological response function of the system to a given time-dependent flow protocol and are associated with a specific signature in the mechanical response. In this contribution, we test the validity of these criteria in the case of two common time-dependent flow protocols: a step stress and a shear startup. Two types of fluids are examined. On the one hand, a wormlike micelles system exhibiting steady shear banding is studied experimentally, using rheometry coupled with direct visualizations and particle image velocimetry. On the other hand, we analyze previous literature on yield stress fluids exhibiting transient shear banding. Under conditions of a constant imposed stress, for both types of fluids, the onset of banding arises in a time window compatible with the Moorcroft–Fielding criterion. However, the mechanical signature, i.e., the shape of the bulk mechanical signal as a function of time, is not the one expected within some of the specific models with which the general Moorcroft–Fielding criteria were tested numerically. Under shear startup, both types of fluids behave differently. The criterion holds for yield stress fluids, the onset of banding arising just after the stress overshoot, as expected. On the contrary, for wormlike micelles, the window of instability is delayed, even if the overshoot clearly plays a crucial role in the nucleation of shear-induced structures. Regardless of the flow protocol or the system, wall slip seems to go hand in hand with banding indicating that it is a key ingredient to take into account.

The present paper studies the thermal-hydraulic behaviour of the rectangular supercritical natural circulation loop (SCNCL) using numerical model of one dimensional. Then the results of this model is confirmed with experimental and benchmark results. Variations with several geometric parameters like loop diameter, riser length, and heater length and operating conditions like heater inlet enthalpy, pressure, friction factor, and inlet and exit loss coefficient on steady-state performance are investigated for various orientations like HHHC , HHVC, VHVC and VHHC of the heater and cooler. The chances of existing static instability (Ledinegg excursion) has been investigated, which reveals that it can arise only in a low inlet enthalpy condition, far from the suggested various orientations of heater and cooler.

Joining heterogeneous ceramic oxides (e.g., zirconia (ZrO2), alumina (Al2O3)) is important to widen their application horizon. Unfortunately, the joining of heterogeneous ceramics is hindered by dissimilar microstructures. Herein, a composite of 3 mol.% Y2O3-stabilized ZrO2 (3YSZ) and Al2O3 was used as interlayer (ZrO2-Al2O3, ZA) to form 3YSZ-ZA-Al2O3 joint under the influence of an electric field, which reduced the joining temperature and joining time. The joint strength attained steady state with current and joining time being beyond the threshold. The strength of the 3YSZ-ZA interface decreased and that of ZA-Al2O3 interface increased with increasing Al2O3 content in ZA. The strength of the 3YSZ-ZA interface is higher than that of the ZA-Al2O3 interface under the same joining parameters, and this was ascribed to the higher oxygen vacancies diffusion rate in 3YSZ than in Al2O3. The joint was formed by the connection of 3YSZ and Al2O3 ceramics to the respective grains in ZA.

We study the transient and steady shear rheology of rigid particle suspensions in Boger fluids via complete 3D numerical simulations and experiments. We calculate the transient per-particle extra viscosity and primary stress coefficients for suspensions at different particle volume fractions ϕ for a range of Weissenberg numbers (Wi). The per-particle viscosity ( ηp) and the primary normal coefficient ( ψ1p) increase monotonically to steady state in body-fitted (BF) simulations (for dilute suspensions) and immersed boundary (IB) simulations (for nondilute suspensions). We also present experimental measurements including small amplitude oscillatory shear, steady shear, and transient shear measurements at different particle volume fraction suspensions in a Boger fluid. The simulations and experiments suggest that longer strains are needed to achieve steady state at higher ϕ and Wi. We also show the comparison of the BF and the IB simulations with experimental data for the per-particle viscosity and find excellent quantitative agreement between simulations and experiments at Wi=3 but the IB simulations underpredict the steady values at higher Wi=6. Nevertheless, the IB simulations show an increase in the per-particle viscosity with ϕ as witnessed in the experiments. To understand this behavior, we examine the particle-induced fluid stress (PIFS) and the stresslet contributions using a novel method developed for the IB simulations in this work. We find that the PIFS is independent of ϕ but the stresslet values increase with ϕ. Thus, the particle-particle hydrodynamic interactions in nondilute suspensions affect the stresslet and, in turn, the per-particle viscosity at a given Wi.

Friction extrusion is a thermomechanical process that combines conventional extrusion with the action of a rotating die. The plastic deformation of the material being sheared and extruded is the primary source of process heat and it produces strain distributions unlike those resulting from conventional extrusion. This paper proposes an improved strain analysis that evaluates three main strain components in a series of rate-controlled friction extrusions in which the steady state was achieved. Cylindrical AA1100 extrusion billets with two embedded markers were extruded to wire with a 10:1 diametral reduction. The shape change of the embedded markers was determined via serial, transverse sectioning and quantitative metallography of the extruded wires. Three mutually orthogonal strain components (longitudinal, circumferential, and radial) were calculated at different positions along each extruded wire from the marker's shape change. The development of strain from the initial transient to the steady state is discussed. The variation of the steady-state strain with different process parameters is correlated with the die advance per revolution.

Temperature differences between the surrounding ground and the tunnel lining will cause a variation of the tunnel lining forces. The hyperstatic reaction method (HRM) could be efficiently and simply used to investigate the impact of thermal load on tunnel linings. First, the steady state numerical solution is derived for a shallow circular tunnel to estimate the internal forces and displacements of tunnel lining caused by thermal load. The effective strain coefficient βTl is deduced to calculate the thermal stresses in tunnel lining. Secondly, the influence of the temperature difference on the internal forces of tunnel lining is investigated using the HRM method considering different lining elastic modulus, lining thickness and ground coefficient of thermal expansion. Lastly, the impact of fires which will be able to modify the elastic modulus of tunnel lining is investigated, which makes it possible to predict the damage of tunnel lining caused by fires.

Constitutive relationship for high temperature deformation is generally based on the presence of stable microstructure and constant flow stress or strain rate, independent of strain. However, prior to and subsequent to steady state there appears, respectively, the transient and accelerated flow of materials both in strain rate and stress-controlled plastic deformation tests as shown by different stages of stress–strain and creep curves. In this work, an attempt is made to explain the transient flow behavior by continued variation in work hardening and dynamic recovery whereas the accelerated flow is explained by concurrent deformation-induced microstructure and damage evolution. For this purpose, the stress–strain curves, creep curves, microstructural and substructural evolution in a range of metallic systems are analyzed and the relationships between transient flow in strain rate and stress-controlled deformation are established. A similar approach was extended to analyze the accelerated flow in the two cases. There appear wide variations in morphology and length scale of micro/substructure, which result in strain-dependent flow stress. This leads to obeying a self-organized concurrent structure-flow property correlation during deformation.

Pulverized coal injection is widely used for the sustainability of ironmaking blast furnace process. However, the quantification of unburnt pulverized coal in the blast furnace is not well understood. The gas-powder flow in a packed bed in the raceway presence is studied using a two-dimensional cold model to understand the static and dynamic holdups of powder. Due to the lack of clarity in the existing literature about the procedures for estimating the powder holdups, it is proposed in the present work that the steady state and dynamic holdup can be quantified based on the mass balance concept and elutriation velocity, respectively, to get reproducible results. The application of these concepts across both rectangular and cylindrical geometries helped to validate and reproduce the results. The different parameters, such as powder flux, powder size, and gas flowrate, helped to evaluate the powder holdups in the blast furnace’s cold model with the raceway presence.

The linear–nonlinear step load control is proposed to meet the requirements of the pulse load. The nonlinear optimal step control from absolute no-load to full-load is able to force the converter to reach the full-load steady-state operation point with the minimum output voltage drop and minimum settling time. The key is to calculate the initial switching frequency and the duty cycle of the first switching period depending on the load condition. The proposed method is realized by analytic geometry analysis on the state trajectory and confirmed in a 6.6-kW 1-kV/48-V SiC LLC converter. From no-load to full-load, the output voltage drops by 2.24 V and the settling time is 0.76 ms, which reduce by 18.8% and 79.3% compared with the conventional linear control, respectively. Under 100-Hz pulse load with the duty cycle of 30%, the output voltage drop is limited within 2.30 V and overshoot by 1.68 V.

Single and multi-stage Joule-Thompson refrigerators operating with natural nitrogen-hydrocarbon mixtures are marketable for creating refrigeration equipment for freezing and cryopreservation of biomedical materials, liquefaction of certain gases, high-temperature superconductors cooling, conducting climate tests without using cryogenic liquids. One of the main objectives of the development of such refrigerators is to determine the optimal weight of mixed-refrigerant charge with the known geometry of the refrigeration circuit and to ensure the optimal “circulating” composition in the steady-state mode. This article proposes an analytical method for solving this problem and presents the experimental results. The accuracy of the method is determined by the validity of calculating thermodynamic properties of the mixed refrigerants forming solutions with limited solubility in the liquid phase and by taking into account the shift of the “circulating” working body composition relative to the “charge” composition in the steady-state mode due to structural specifics of real refrigerators. The application of the method will allow reducing the time and cost of experimental development of new refrigeration equipment.

A mechanical switch can be used instead of a power electronic load commutation switch in orderto reduce the losses during normal power flow in standard hybrid DC circuit breakers. The success of current commutation in such hybrid breakers depends on the arc voltage formed across the contacts in the mechanical switch. The behaviour of rapidly elongated, wall constricted arcsgenerated during the opening of an ultra-fast mechanical switch in the air is studied here. The voltage-current characteristics of the generated arcs are obtained for steady state contact opening velocities of 6, 11 and 21 m/s. It is found that the arc voltage at a given current and contact separation increases with the contact opening velocity. It is shown that stationary,zero-contact-velocity characteristics can not be used to accurately quantify the voltage build-up in fast elongating arcs in hybrid breakers. A best-fitting black-box equation for the dynamic arc characteristics is presented for the tested velocities. The obtained voltage-current characteristics are used as input to simulate the current commutation process in a 12 kV hybridDC circuit breaker case-study. Different scenarios of current commutation failure related to the arc voltage build up are identified. It is shown that these failures scenarios can be avoided by increasing the contact opening velocity.

The operational performance of small-scale refrigeration systems is mainly decided by their capillary tubes outlet parameters, wherein an accurate determination of the pressure and vapour quality is a prerequisite. Experiments have been performed for a capillary tube (CT) with specified geometry consisting of a straight, a helical and a suction line heat exchanger (SLHX) section. The capillary tube is incorporated in a small refrigeration system operated with R600a. In addition, a model was developed to determine the steady-state operation of the capillary tubes (activated with R134a, R1234yf, R1234ze(E), R600, R600a, R152a and R513A refrigerants) and validated. The highest and lowest value of the vapour quality was discerned to be 0.3132 (for R1234yf) and 0.2124 (for R600), respectively. The relative errors between the experimental and model results for the CT outlet pressure and temperature were ranged from 1.16 to 5.35% and 0.12–0.81%, respectively. It is asserted that the present strategy may contribute towards the precise estimation of the pressure and vapour quality to customize the working performance of small scale refrigeration systems.

The current a conductor can carry for short durations can be significantly greater than under steady state conditions. In power system applications short duration events are usually associated with faults, typically lasting for 100 ms up to a few seconds. Power systems use these differences in current levels to discriminate between normal and abnormal operational conditions. High magnitude short duration currents, such as those which occur during power system faults, can significantly heat conductors, potentially resulting in damage or destruction. Specifying minimum conductor sizes potentially subject to these conditions requires an understanding of the physical effects resulting from the consequential stresses, particularly the heating. This paper investigates the established approach to rating these conductors, which uses an equation based on an adiabatic system. This equation, Onderdonk's equation, is demonstrated to have four identifiable limitations. Novel analytical solutions are proposed for two of the four limitations, being skin effect and cooling resulting in an improved equation for rating conductors for high magnitude short duration currents.

In this study, we performed a computational fluid dynamics (CFD) modeling of tetracycline photocatalytic degradation using rGO/ZnO/Cu as the photocatalyst. The photoreactor was an unbaffled dished bottom tank with a backswept impeller and four lamp tubes. The CFD equations were solved for light intensity, velocity, pressure, and concentration fields in time-dependent modes of the fluid regime. Our model was more complex than the previous studies in several ways: we modeled the system is 3D instead of 2D, allowed variation of light intensity and pressure throughout the photoreactor, and traced the change of key parameters over time during the initiation phase until the steady state was reached. The flow pattern was solved and visualized in the presence of mixer in vertical and horizontal cuts. Experimentally measured concentrations over time matched model predictions well but also indicated the need for yet more complex models incorporating more factors that affect reaction rates.

The article presents the results of the calculation analysis of the criticality of the reactor pool compartment for VVER-1000 reactors at different stages of a severe accident. The criticality analysis of fuel-containing systems formed during the development of a severe accident is considered on the example of several discrete configurations that can be described by certain models. In reality, the course of a severe accident will be a continuous process of transition from the initial stage of the accident to its steady state at the end. However, depending on the fuel characteristics and conditions of development of a severe accident, any considered configuration of fuel assemblies and reactor pool materials may become final. The article presents a criticality analysis of the reactor pool compartment of the VVER-1000 reactor unit at the severe accident stages following the deformation of fuel rods and fuel assemblies at the initial stage of the accident due to water boil-off and temperature increase. On the basis of the models developed, the multiplication properties of the reactor pool compartment in the conditions of degradation of hexagonal tubes were investigated. Supercriticality (i.e. multiplication factor was greater than 1) was achieved in all two considered configurations of the water-uranium mixture. That is, under such conditions, the required level of subcriticality can be provided by a boron solution in water. The considered homogeneous single-layer and two-layer model of corium spreading on the support plate is safe in terms of criticality. However, the support plate has holes for the passage of the coolant to the fuel assembly. In the case when the melt or fuel debris enters the space under the support plate through these holes, they can form a uranium-water mixture with the remaining water, which at certain fuel and water ratios can become supercritical. In this case, the multiplication properties of the reactor pool compartment will depend on the ratio of impurities of the reactor pool and fuel assembly structural elements in the material under the support plate and/or the concentration of boric acid in the water. After damage of the reactor pool compartment floor, the melting of concrete begins. The considered configurations and material composition of the mixture of corium, concrete and water allow us to make a conclusion about the safety of this phase of a severe accident in terms of criticality.

Heat recirculating (HR) geometries have been studied in the literature for their use in energy generation applications. This work investigates the ignition and cold-start behavior of lean propane-air combustion in a U-bend catalytic microreactor through computational fluid dynamics (CFD) study. Although several studies have focused on stability and combustion behavior, the role of heat recirculation on catalytic and homogeneous ignition from the cold-start conditions has not been analyzed so far. The U-bend microreactor is a typical example of HR geometry, where the hot exhaust gases in the recirculation channel transfer heat to the cold incoming fluid. Significance of heat recirculation across the dividing wall on the ignition temperature, as well as transient evolution of temperature, propane conversion and reaction are presented. Ignition temperature is found to be 20 K lower in the U-bend microreactor than straight channel microreactor. However, transient ignition study revealed that at nominal conditions, U-bend microreactor takes about 35 s longer than straight channel for ignition and to reach steady state, owing to heat distribution internally within the U-bend microreactor. The effect of flowrate is analyzed, which shows that at higher flowrates, the ignition and steady-state times are also lower for the U-bend microreactor. Finally, the effect of solid wall material is investigated, which shows that lower conductivity material (such as ceramic) showed faster ignition with low thermal inputs.

The parametric identification of the tribosystem as an object of modeling the functioning of tribosystems in the conditions of boundary lubrication is performed in the work. Using the analysis of the dimensions of significant factors, expressions are obtained to calculate the gain and time constants. It is established that the coefficient takes into account the degree of influence of the load, sliding speed, tribological characteristics of the lubricating medium on the quality factor of the tribosystem. It is shown that the increase in the coefficient will have a positive effect on the processes inherent in tribosystems during operation. Coefficient – characterizes the magnitude of the change in volumetric wear rate and friction coefficient when changing the magnitude of the load, sliding speed, quality factor of the tribosystem. Coefficient – characterizes the ability of the tribosystem to self-organize when changing the values of the input parameters by rearranging the surface layers of materials from which the triboelements are made during secondary running-in. It is shown that the value of the coefficient is large will contribute to the rapid change in the roughness of the friction surfaces, the restructuring of the structure of the surface layers, the appearance of oxidizing films on the friction surfaces (secondary structures). It is proved that the time constant – this is the time required to change the roughness of the friction surfaces and rearrange the structure of the materials of the surface layers when changing external conditions. Time constant characterizes the time during which there is a stabilization of the temperature gradient by volume of triboelements, taking into account the thermal conductivity of materials when changing external conditions. Time constant characterizes the time during which the tribosystem returns to a steady state of operation after the cessation of the outrageous force, or the time to stabilize the parameters in the new mode of operation. It is proved that the value will be optimal for the process of self-organization. It is shown that one of the factors that can control the value , this is the sliding speed

Introduction: In the course of the study, we examined energy-efficient and environmentally friendly heat-insulating materials based on gypsum and gypsum-containing primary components. Purpose of the study: We aimed to assess the effectiveness of using gypsum materials in wall structures, by using the finite element method based on the ANSYS Steady State Thermal module. Porous materials of different densities (structural, structural and heat-insulating, and heatinsulating gypsum concrete) were used as wall materials. These materials were obtained as a result of the interaction between residual sulfuric acid adsorbed on the grains of “acidic” fluoroanhydrite and carbonate flour. Methods: The finite element method based on the ANSYS Steady State Thermal module was used. The thermal conductivity of the structures was evaluated in a three-dimensional coordinate system. The experimental values of thermal and physical characteristics were adopted for the walling fragments. Results: The problem was solved numerically, by using the finite element method based on the ANSYS Steady State Thermal module. We established that the developed structural and heat-insulating gypsum concrete is more effective since, under the set design conditions, the temperature of the inner surface of such a wall at the minimum (510 mm) and maximum (770 mm) structure thickness exceeds the temperature of the inner surface of walls made of different materials.

We theoretically investigated the effect of interface traps ( ${D}_{it}$ ) at the Si/SiO2 interface on the transient negative capacitance (NC) effect of the ferroelectric (FE) FETs. We used a metal/FE/interlayer/Si (MFIS) capacitor in series with a resistor to simulate the NC effect. Our simulation results show that appropriate ${D}_{it}$ can further improve the subthreshold swing (SS) by tuning the mismatch of the switching rate between free charges ( ${Q}_{f}$ ) and polarization charges ( ${P}$ ). In addition, we also analyzed the impact of different circuit parameters on the device performance. The following device design can improve the SS characteristics: thicker FE layer, thinner interlayer (DE), lower external resistance, and larger viscosity coefficient.

The hot strip method, as one typical transient method, is widely used to measure the effective thermal conductivity of thermal insulation materials at various temperatures. Since the test theory is based on solving the energy equation via heat conduction, the test result will be questionable when measuring thermal insulation materials, such as silica aerogel and photovoltaic glazing, in which the participating thermal radiation is a dominant heat transfer mode at high temperature. In this study, numerical investigation is employed to reveal the measurement reliability of hot strip method when applied to translucent thermal insulation materials. By reproducing the dynamic conduction-radiation coupled heat transfer process within the translucent materials numerically, the effective thermal conductivity of translucent materials with varying extinction coefficients are obtained at various temperatures. Comparisons are made for the effective thermal conductivity of translucent materials determined by the hot strip method, one-dimensional steady state method, transient plane source method and Rosseland model. Large discrepancies are found among the effective thermal conductivity determined by different methods for translucent materials with low extinction coefficient. The thermal conductivity obtained from the hot strip method is overestimated at elevated temperature when compared with that from one-dimensional steady state method. In order to measure the effective thermal conductivity of translucent materials accurately, the effect of thermal radiation should be considered for different transient methods.

This paper discusses a mathematical model of the diffusion and reaction in amperometric biosensor response with immobilized enzyme electrodes within a uniform film. This model contains a nonlinear differential equation related to Michaelis-Menten kinetics. In this paper, shifted Legendre wavelet method (SLWM) has been applied to obtain the mediator and substrate concentrations. The efficiency of the method is confirmed by means of the computational run time. The obtained approximate solutions are compared with the available results. Satisfactory agreement with homotopy perturbation method (HPM) and relaxation method (RM) is observed. Moreover, the shifted Legendre wavelet method is found to be simple, efficient and computationally attractive.

This study focuses on charge transport in epoxy bulk, an insulating spacer material. We discuss the relationship between the space charge behavior and the external current determined by conduction and displacement currents. One-dimensional space charge behavior in epoxy is simulated using a bipolar charge transport model that considers charge trapping, de-trapping and recombination. The simulated results show that the charge accumulation in epoxy is successfully modeled by considering high-density deep traps at the epoxy/electrode interface and optimizing the parameters, whereas the simulated external current is inconsistent with the experimental results where the external current decreases in power-law behavior. In the simulation, the external current gradually increases and reaches a steady state as the charge accumulation gets saturated. Charge accumulation does not contribute to the decrease in the external current, which is contrary to the prediction based on the experimental results. We then show that the power-law decrease of the external current is due to the presence of bipolar initial charges before voltage application and multi-depth traps in epoxy. The results strongly indicate that multi-depth trapping/de-trapping, like hopping transfer, rather than single-depth trapping/de-trapping should be taken into account when modeling charge transport in epoxy.

This article focuses on improving the control structure of electronic capacitor (EC), formed by a bidirectional dc–dc converter terminated with small auxiliary capacitance. Typical application of such a system is mimicking the dynamic behavior of a bulk dc-ink capacitor while actually employing a component with much lower capacitance value. It was previously revealed that EC may be treated as output-voltage regulated wide-input-range converter feeding a bidirectional power load. Dual-loop voltage-current linear cascaded regulator, typically employed for EC terminal voltage control, imposes slow unstable mode when absorbing power from the dc-link. This article demonstrates that performing a transformation from voltage–current to power-energy domain by feedback linearization-based nonlinear control simultaneously eliminates the unstable mode and increases control bandwidth. Revealed findings are well-supported by simulations and experiments.

Seoul National University and Hanmi Techwin Inc. have launched a program for the development of a large bore, low field, and low-cost high temperature superconductor (HTS) magnet for industrial applications. HTS coils exhibit defect-irrelevant behaviors when wound using no-insulation (NI) technique, i.e., wound without turn-to-turn insulation. Incorporation of defect-irrelevant winding (DIW) technique would be favorable to constructions of HTS magnets as it may drive the cost of production down and curtail construction time if used appropriately. An HTS magnet having a center magnetic field of 2 T and cold bore size of 230 mm has been designed, and charging simulation was performed using a turn distributed circuit model. Defect-irrelevant behaviors are examined stochastically, considering random occurrences of defective turns. Using the turn distributed circuit model indicates that the magnitudes of defects have limited effects on resistive heatings in both steady state and transient operations. The upper bounds of excess heat contributed by defective turns are numerically formulated using characteristic resistances and operating currents.

In this study, a three-dimensional thermo-elastic model that considers the interaction of mechanical and thermal deformation is developed using a semi-analytic method for steady-state rolling contact. Creepage types in all directions are considered in this model. For verification, the numerical analysis results of shear traction and temperature increase are compared separately with existing numerical results, and the consistency is confirmed. The analysis results include heat flux, temperature increase, contact pressure, and shear traction. Under severe rolling conditions, the thermal effect changes the behavior of the contact interface significantly. Furthermore, the effects of creepage, rolling speed, and conformity under different rolling and creep conditions are investigated.

Experimental data on grain size in hypoeutectic alloys with various solute concentrations are collected and analyzed. Curves of grain size as functions of composition are plotted and compared with the relevant phase diagrams. These curves indicate that the minimum in grain size occurs at the solubility limit of the solute on a phase diagram, and the maxima occur at the pure metal and eutectic point where the solidification range of the alloy is zero. The grain size, d, is then plotted against phase diagram variables such as the growth restriction factor, Q, and the solidification range, ΔT. Two-parameter models are proposed to correlate grain size to phase diagram variables. Regression analysis of the experimental data with the two-parameter equations suggests that there is a clear correlation between grain size and the solidification range of the alloy. The linearity of d vs. ΔT is much better than that of d vs. Q. A grain refinement mechanism based on fragmentation and multiplication of dendrites is used to explain the dependence of d on ΔT when convection exists in the melt during solidification. Mathematical analysis indicates that the solidification range, ΔT, is actually the temperature depression of the planar solid–liquid interface under steady state growth conditions. The temperature depression at the root of a dendrite is proportional to ΔT. It is such a temperature depression that causes necking formation at the root of a dendrite. Remelting and fragmentation at the necks could occur due to local temperature fluctuations in the mushy zone in a casting where convection exists in the melt during its solidification.

This work presents solutions to Challenge 2 within the Air Force Research Laboratory Materials Inform Data-Driven Design for AM Structures (MID3AS) AM (Additive Manufacturing) Challenge. The solutions are for quasi-steady-state and transient Nth-track cross-sectional predictions as a function of scan paths. Tracks are deposited successively to produce a pad and overlap each other; their cross section is defined using four dimensions: total depth, remelt depth, half width, and width increment due to the addition of the latest (Nth) track. There are six pads for which the pad dimensions, build height, power, scan speed, hatch spacing, and number of tracks are varied. There also are two thin walls that consist of 10 single tracks deposited on top of each other. The track cross sections are to be reported at three measurement planes defined orthogonal to the scan path at varying distances from the start of a track in the quasi-steady-state and transient melt-pool regions. The predictions are generated using the Additive Manufacturing Parameter Predictor (AMP2) software that performed multi-scale simulations for the six pads and two thin walls. Two types of melt-pool simulations were performed: a quasi-steady-state, thermal-computational fluid dynamics simulation and a transient thermal simulation. The statistics of track dimensions were estimated using discrete element modeling to predict the local variation in recoat powder density and correcting for the additive mass consolidated by a track cross section accordingly. Applied Optimization, Inc. achieved third place for the accuracy of predictions required by Challenge 2 in the MID3AS AM Challenge.

The Molten Salt Reactor Experiment (MSRE), which operated at Oak Ridge National Laboratory from 1965 to 1969, was an experimental reactor that used UF4 fuel dissolved in molten fluoride salt. Criti...

In this study, we propose a centrifugation packaging (CP) structure to enhance the optical and thermal dissipation performance of LEDs, using SBA-15 particles to facilitate the sedimentation and dispersion of QDs. The results indicate that the EL spectra of the LEDs remains almost unchanged after the centrifugation time of 60 min and a CP structure can be obtained. The radiation power and luminous flux of LEDs with a CP structure improve by 9.1% and 10.4%, respectively, compared with the uniform distribution (UD) structure. The surface temperature of LED devices with the CP structure is reduced to 34.4 °C from 41.8 °C at a current of 100 mA. Furthermore, the simulation results show that the maximum temperature in the CP structure is 22.4% lower than that in the UD structure at a current of 500 mA. Thus, this study can provide a new perspective for designing settlement structures of QD–LEDs to enhance their optical and thermal performance.

The moisture ingression into photovoltaic module has significant impact on the reliability as it participates in multiple degradation pathways. Damp heat test is performed at a temperature 85°C and relative humidity of 85% for 1000 h to assess the ability of a photovoltaic module under humid conditions. In this paper, we have developed an analytical model to quantify the amount of moisture ingressing into a photovoltaic module with a breathable backsheet under damp heat testing condition. The analytical model is developed with the consideration that the vertical moisture diffusion in the ethylene vinyl acetate (EVA) layer is instantaneous. The comparison with numerical model validated the assumption. The analysis of the simulated profile with the developed analytical model showed that at 85°C, the moisture profile within the rear EVA and backsheet reaches a steady state value within 10 h. Considering that the damp heat test is performed for a span of 1000 h, to simplify we can consider that the moisture profile is temporally and spatially constant in the backsheet and rear EVA, with the moisture concentration being given by the product of moisture solubility (S) and permeability (P) for that particular material at 85°C. However, the moisture profile for top EVA in regions above the solar cell does not reach a steady state value even within a span of 1000 h. The non-uniformity of the moisture profile needs consideration for quantifying the degradation in the regions of top EVA that is directly above the solar cell.

A control scheme implementation for a fixed-bed Fischer–Tropsch synthesis (FTS) reactor using the optimal initial operating conditions at steady-state is developed. The proposed approach consists of solving a nonlinear constrained optimization problem for a fixed-bed FTS reactor with incorporation of a control scheme in the cooling jacket in order to find the optimal values of the initial operating conditions of temperature, gas-hourly space velocity (GHSV), pressure and coolant flow velocity under a steady-state regime that maximizes CO conversion and $${\mathrm{C}}_{5+}$$ product selectivities. Such optimal operating conditions at steady-state are used to evaluate the dynamic behavior of the reactor under the proportional-integral control (PIC) scheme action that is implemented in the cooling jacket. An extended dynamic one-dimensional pseudohomogeneous model of a fixed-bed FTS reactor recently reported in the literature is used. The obtained results show the importance of the implementation of dynamic control strategies for the FTS carried out in a fixed-bed reactor, since they allow for ensuring the thermal control of such highly exothermic reactions and assure better reactor performance in terms of high CO conversion and liquid products selectivity (C5+).

In recent studies, the creep rate of Zircaloy-4, one of the basic property parameters of the nuclear fuel code, has been commonly used with the axial creep model proposed by Rosinger et al. However, in order to calculate the circumferential deformation of the fuel cladding, there is a limitation that a difference occurs depending on the anisotropic coefficients used in deriving the circumferential creep equation by using the axial creep equation. Therefore, in this study, the existing axial creep law and the derived circumferential creep results were analyzed through a circumferential creep test by the internal pressurization method in the isothermal conditions. The circumferential creep deformation was measured through the optical image analysis method, and the results of the experiment were investigated through constructed IDECA (In-situ DEformation Calculation Algorithm based on creep) code. First, preliminary tests were performed in the isotropic β–phase. Subsequently in the anisotropic α-phase, the correlations obtained from a series of circumferential creep tests were compared with the axial creep equation, and optimized anisotropic coefficients were proposed based on the performed circumferential creep results. Finally, the IDECA prediction results using optimized anisotropic coefficients based on creep tests were validated through tube burst tests in transient conditions.

The primary resonance and nonlinear vibrations of the functionally graded graphene platelet (FGGP) reinforced rotating pretwisted composite blade under combined the external and multiple parametric excitations are investigated with three different distribution patterns. The FGGP reinforced rotating pretwisted composite blade is simplified to the rotating pretwisted composite cantilever plate reinforced by the functionally graded graphene platelet. It is novel to simplify the leakage of the air flow in the tip clearance to the non-uniform axial excitation. The rotating speed of the steady-state adding a small periodic perturbation is considered. The aerodynamic load subjecting to the surface of the plate is simulated as the transverse excitation. Utilizing the first-order shear deformation theory, von-Karman nonlinear geometric relationship, Lagrange equation and mode functions satisfying the boundary conditions, three-degree-of-freedom nonlinear ordinary differential equations of motion are derived for the FGGP reinforced rotating pretwisted composite cantilever plate under combined the external and multiple parametric excitations. The primary resonance and nonlinear dynamic behaviors of the FGGP reinforced rotating pretwisted composite cantilever plate are analyzed by Runge-Kutta method. The amplitude-frequency response curves，force-frequency response curves, bifurcation diagrams, maximum Lyapunov exponent, phase portraits, waveforms and Poincare map are obtained to investigate the nonlinear dynamic responses of the FGGP reinforced rotating pretwisted composite cantilever plate under combined the external and multiple parametric excitations.

In this study, the plane steady state thermoelastic frictional contact problem between a rigid cylindrical punch and a homogenous piezoelectric layer bonded to the rigid base is considered. The pun...

To achieve the zero-waste goal as well as sustainability, the use of the raw materials, especially those from nature, and wood in particular, has to be smart, meaning that the resource has to be used to its full potential. Since wood-based industry is associated with high intensity and the generation of a relatively large amount of residues, those residues should be used for the production of useful products, otherwise they will easily be classified as waste and afterwards used as a source of energy. To present a possible solution for wood residues like wood chips, wood particles and bark, we investigated the possibility of using wood and bark residues as constituents for the production of single layer insulation panel with a target thickness of 40 mm and target density of 0.2 g·cm-3. Thermal conductivity was determined using the steady state principle at three different temperature settings. The average thermal conductivities were determined between 49 mW·m-1·K-1 and 74 mW·m-1·K-1. The highest values were determined at boards made from bark, which also had the highest density (0,291 g·cm-3), while the lowest thermal conductivity was observed for boards made from spruce wood particles.

In the process of continuous high-strength operation of the harvester, structure aging, surface hardening, brittle fracture, and other features appear on V-belt due to temperature rise, which seriously affects the service life of the belt and stability of the whole machine. To predict the temperature distribution of V-belt and improve its service life, an advanced calculation method of temperature field suitable for multiwheel is proposed. First, on the basis of analysing the heat source of the transmission belt, the values of internal friction and external friction are calculated based on AVL Excite Timing Drive (AVL Excite TD). Secondly, two-dimensional temperature field finite element calculation model is established by analysing the heat balance equation, determining the heat flow distribution coefficient and heat convection conditions. Then, to verify the calculation model of the temperature field, the experimental setup and instrumentation are built based on Controller Area Network-bus (CAN-bus) technology. At last, multi-condition tests are designed in this paper. The experiment results show that the maximum difference between the model calculated value and experiment is 4.77 ℃ in unsteady state, and 0.15 ℃ in steady state. Therefore, the multiwheel V-belt temperature field calculation model developed in this paper can realize the accurate calculation of the temperature field under steady state conditions. It has a very important guiding significance for reasonable selection of operating parameters and improvement of service lifetime of belt.