Transient Behavior Research Articles

Influence of Electronic and Melting Fuses on the Transient Behavior of Automotive Power Supply Systems

Influence of Electronic and Melting Fuses on the Transient Behavior of Automotive Power Supply Systems

Study on acoustic characteristics of bubble interaction

Abstract Bubble flow exists widely in various hydraulic systems. The shape and size of the initial bubble deformed from a nozzle/orifice have a significant effect on the dynamic characteristics of the rising processes. In the monitoring of the sound signal of the bubble flow, it is found that the bubble will produce the sound signal when it detaches and rises, and the bubble flow pattern is related to the acoustic signal. In order to better understand the physical mechanism of passive acoustic emission, the acoustic characteristics of different nozzle arrays and gas flow rates were studied. The bubble acoustic statistical characteristics are obtained by filtering. The spectrogram based on time-frequency analysis is used to count the formation of individual bubbles and also to show the transient behaviour of bubble acoustics. Synchronous analysis is applied to study the image information and acoustic signal characteristics, the corresponding relationship between the flow pattern and the acoustic texture feature is established. This will provide a reference for predicting flow patterns through acoustic signals, and is significant for improving work efficiency and detecting faults.

Spatiotemporal characteristics of flow in the bend and return channel perturbed by rotor–stator interaction

The flows in turbomachinery systems are strongly perturbed by the rotor–stator interaction (RSI) between the rotating and stationary through-flow components, generating the fluctuating flows. This work presents a numerical investigation of a flow in a test centrifugal pump system consisting of an impeller, diffuser, bend, and return channel at the designed and low flow rates. Both vaneless and vaned diffuser models are considered to determine the perturbation of the diffuser vanes on the flow. The objective is to quantitatively assess the impacts of two influential factors, i.e., the diffuser type and the flow rate, on the spatiotemporal characteristics of the transient flow in the various through-flow components. Particular attention is paid to the generation of the reversed flow, circulating vortices, and temporal fluctuations of the velocity field. It is found from the numerical data that both the flow rate and the diffuser type affect the temporal fluctuations of the flow, primarily via the impact of the RSI-induced large-scale vortices generated in the passages of the impeller and the vaned diffuser. The flow in the bend experiences the streamline curvature on the solid walls; thus, the peak values of the fluctuating amplitude of the streamwise and transverse velocities and the reversed flow may shift between the two halves of the channel close to the inner and outer wall. The boundary layer flow patterns are mainly determined by the flow rate at the low flow rate and by the diffuser vanes at the designed flow rate. This work comprehensively reveals the transient behaviors and unsteadiness of the flow which was not provided in the experimental investigation for the test centrifugal pump system which was widely studied since the essential flow physics are included. The numerical data in the stationary bend and return channel are first provided, which are of engineering significance for this type of centrifugal turbomachinery.

Experimental, computational, and analytical investigation of cooktop thermosyphon heat transport device for its feasibility in indoor solar cooking system

Cooking is a key contributor to worldwide energy usage and subsequent greenhouse gas emissions. Given this, clean and green energy-based cooking technologies are being explored globally. Though many solar cooker designs are being researched, the social acceptance rate is low due to operational, financial, and accessibility aspects. Hence in the present study, an indoor solar cooking system has been proposed, which has a cooktop Thermosyphon heat transport device (THTD) as an integral part. It transports heat from the outdoor receiver to the indoor kitchen through natural circulation (buoyancy-driven flow) of a heat transfer fluid (HTF). For the first time, different aspects of cooktop THTD are explored through experimental, analytical, and computational approaches. Based on the recommendations from a previous study, the flat design of cooktop THTD was constructed and tested with Therminol-VP1 as the HTF for both steady-state and transient performance. The steady-state results predicted by analytical and computational models were in good agreement with the experimental outcome. The HTF flow in the system is unidirectional, except in the cooktop region, where a combination of radial flow maldistribution and localized recirculation loops are seen (from velcoty contours and vectors) due to a larger flow passage. However, such flow anomalies vanish once the flow gap is reduced. Further, the transient tests witnessed a longer time for boiling (41–68 min) one litre of water in the first trial, which was reduced to 18–27 min with subsequent refills. An important observation is the increment in boiling time with increase in hot leg length. The rise in HTF flow rate (due to increased center-line elevation) and subsequent reduction in the bulk average temperature of HTF in the THTD was the reason for it. Further, the cooktop THTD could cook 315 g of rice in 40–45 min against 35–40 min using an electric induction stove, which justifies the proposed system’s efficacy. The study also demonstrated the criticality of thermal contact resistance between the cooktop surface and the surface of the cooking vessel. Hence devising an efficient and practically viable method (other than thermal paste) is essential. Also, due diligence is required while selecting the HTF as viscous fluid leads to a poor transient performance due to reduced flow rate. Hence, the transient behavior (practically the boiling time) of cooktop THTD is a trade-off between the bulk average temperature of the HTF and its flow rate.

Discovering two general characteristic times of transient responses in solid oxide cells

A comprehensive understanding of the transient characteristics in solid oxide cells (SOCs) is crucial for advancing SOC technology in renewable energy storage and conversion. However, general formulas describing the relationship between SOC transients and multiple parameters remain elusive. Through comprehensive numerical analysis, we find that the thermal and gaseous response times of SOCs upon rapid electrical variations are on the order of two characteristic times (τh and τm), respectively. The gaseous response time is approximately 1τm, and the thermal response time aligns with roughly 2τh. These characteristic times represent the overall heat and mass transfer rates within the cell, and their mathematical relationships with various SOC design and operating parameters are revealed. Validation of τh and τm is achieved through comparison with an in-house experiment and existing literature data, achieving the same order of magnitude for a wide range of electrochemical cells, showcasing their potential use for characterizing transient behaviors in a wide range of electrochemical cells. Moreover, two examples are presented to demonstrate how these characteristic times can streamline SOC design and control without the need for complex numerical simulations, thus offering valuable insights and tools for enhancing the efficiency and durability of electrochemical cells.

Thermal effect on the transient behavior of a piezomagnetic half-space subjected to dynamic anti-plane load

Considering the importance of understanding the propagation of transient waves in the piezomagnetic solids, the thermal effect on the transient behavior of a piezomagnetic half-space subjected to dynamic anti-plane load is investigated analytically in this paper. Using one-sided, two-sided Laplace transformation and Cagniard–de Hoop (CH) technique, an efficient and accurate analytical derivation for the solution of the anti-plane displacement, shear stress, magnetic potential, and induction in Laplace domain is presented. The study shows that the thermal stresses developed in x-axis and y-axis directions have significant influence on the transient response of the half-space. The magnetic induction B x increases obviously when the thermal stress is applied in x-axis direction, while it decreases when the thermal stress is applied in y-axis direction. Approaching time of magnetic induction B x and B y will become longer with higher thermal stress in x-axis direction. With the growth of the thermal stress in x-direction, contribution from the electromagnetic–elastic head (EH) wave increases, while the contribution from the shear elastic (SE) wave and the static value of shear stress decrease.

Recent Developments in Halide Perovskite Nanocrystals for Indirect X‐ray Detection

AbstractMetal halide perovskites are revolutionizing X‐ray detection through a combination of low cost, solution processing, favorable optoelectronic properties, and high stopping power for high‐energy ionizing radiation. While perovskite single crystals and polycrystalline wafers are considered direct X‐ray converters, most medical X‐ray applications are based on scintillators that shift high‐energy radiation into the visible. Several materials are on the market, but demonstrations based on CsPbBr3 nanocrystals, possibly embedded in a matrix material or combined with organic molecules as luminescent species, highlight their competitiveness with established scintillators in terms of radioluminescence yield and transient behavior. Major hurdles that perovskite nanocrystal scintillators must overcome are environmental stability and toxicity. While there are still few examples of high‐performance lead‐free perovskite nanocrystal scintillators, microcrystalline perovskites are emerging with promising properties, reduced toxicity, and significant Stokes shifts to avoid reabsorption of emission in thick films. Thus, the near future of perovskite nanocrystal scintillator materials will primarily be the adoption of recipes for materials with proven properties in microcrystalline form. The nanocrystal colloidal solutions will facilitate the large‐scale printing of homogeneous and scattering‐free films to obtain high contrast and spatial resolution X‐ray images by scintillation.

Investigation of a flexible triple-evaporator domestic refrigerator/freezer with R600a with integrated economization

Domestic refrigerator/freezers account for approximately 6 % of all energy consumption around the globe and mainly rely on vapor compression cycles to operate. Researchers have investigated alternative cycle architectures such as dual-loop cycles and parallel circuit cycles to improve their efficiencies. Despite the demonstrated energy saving potential of these advanced cycles, additional implementation costs are often not justifiable. However, to meet forthcoming stricter energy standards while ensuring flexible multi-temperature operation of domestic refrigerator/freezers, advanced cycle architectures are needed. In this paper, a state-of-the-art bypass circuit cycle triple-evaporator domestic refrigerator freezer with R-600a and a reciprocating compressor has been used as the baseline cycle investigate an alternative cycle configuration. Specifically, this work presents a two-stage vapor-injected cycle with a multi-evaporator system to enable energy savings and cost-effectiveness. The cycle establishes two separate evaporation temperatures to better match the cabinet temperature of fresh food and freezer compartment. The reduced difference between cabinet temperature and its evaporation temperature decreases the irreversibilities in the heat exchanger and improves overall system efficiency. Moreover, the addition of the economization line from the medium temperature evaporator reduces the compressor work. To capture the complex transient behavior of both the baseline system and proposed cycle architecture with their control strategies, a dynamic model has been developed and validated with experimental data. The validated dynamic model with the baseline cycle was modified to consider the two-stage vapor-injected cycle and its control logic, and simulation results yielded up to 13 % energy consumption reduction with respect to the baseline system.

Synergistic tailoring of adsorption and vacancy enrichment in lamellar stacked layers of α-MoO3 nanorods by Mg2+ for NO2 gas sensor

Extremely toxic nitrogen dioxide (NO2) was detected using lamellar layered α-MoO3. The stable orthorhombic phase of MoO3 (α-MoO3) with preferential growth along (02k0) and the nano-rectangular rods (NRs) like morphology were observed. The incorporation of Mg2+ in α-MoO3 influenced the morphology and the oxygen vacancies (VO), which were analyzed through Raman, photoluminescence, and X-ray photoelectron spectroscopy. The core level spectra provided direct evidence for VO enrichment in 3 %Mg-α-MoO3 via emergence of peak at 531.02 eV with an area of 45.15 %. NO2 response was analyzed at 150–200 °C with various NO2 concentrations. 3 %Mg-α-MoO3 NRs provided maximum response of 133.9 % for 50 ppm with low limit of detection (LOD) of 250 ppb with good response (193 s) and recovery (260 s) transient behaviors. The fabricated sensor shows high selectivity to NO2 among H2S, SO2, N2O, and NH3, also good repeatability suggesting potential suitability for NO2 detection.

Experiment of electrothermal stress for different types of end turn grading in the inverter‐fed form‐wound windings

AbstractEnd turn grading with resistive–capacitive coupling experiences severe electrothermal stress when subjected to pulse width modulation (PWM) voltage. In this paper, several experiments and simulations were carried conducted for four types of end turn grading. First of all, the temperature rise in the end turn grading increased with a decrease in rise time. When the rise time was less than 500 ns, the temperature rise at the terminal was higher owing to the increased capacitive current coupled from the main wall insulation. Further, the current in the linear region exhibited minimal variation at different fundamental frequencies resulting in synchronized the temperature rise at the terminal and overlap. Furthermore, the jump voltage was the key factor influencing temperature rise in end turn grading, confirmed by comparing different voltage magnitudes. Finally, the transient behaviour of the maximum field in the stress grading material was determined at rise time. The experimental and simulation results indicate that balancing and interdependently addressing the electrical and thermal stress protection in end turn grading is crucial. The study aims to provide an experimental and theoretical foundation for an insulation system of inverter‐fed rotating machinery operating under PWM voltage.

Transient behavior of the freshwater-saltwater mixing zone after land reclamation in coastal aquifers

The interaction between freshwater and saltwater in the mixing zone governs regional groundwater flow and the exchange of water and salt between groundwater and the ocean. However, previous studies have overlooked the impact of land reclamation on the transient behavior of the mixing zone. This research investigated the dynamic influence of reclamation length, reclamation material properties, and recharge rate on the transient behavior of the mixing zone and timescale of mixing zone variation (TMV) through a series of field-scale numerical simulations. In general, the width of the mixing zone (WMZ) in the upper and center regions of the aquifer exhibited initial increase followed by subsequent decrease in various scenarios, displaying a consistent trend. For reclamation lengths less than 300 m, the mixing zone reached a steady-state condition within 8,000 days, while the corresponding TMV for a 500 m-length reclamation case increased to 20,000 days. The growth rates of the WMZ in the upper and center regions of the aquifer were notably slower, requiring more time to reach steady state in low-permeability scenarios. This observation underscored that reclamation with lower permeability could significantly extend the TMV. It was noteworthy that varying the longitudinal dispersion of the reclamation area between 0.5–10 m had only a slight effect on the TMV, ranging from 8,000 to 8,500 days. The peaks of the mixing zone width showed a proportional increase with longitudinal dispersion. Furthermore, increasing the recharge rate led to a substantial decrease in the TMV, from 10,000 days to 2,000 days. The WMZ exhibited faster growth with increasing recharge rate.

Neural network-based prescribed performance tracking control for a class of nonlinear systems with mismatched disturbances

This paper addresses the prescribed performance tracking control problem for a class of nonlinear systems subject to mismatched uncertainties. A novel disturbance observer-based control (DOBC) scheme is proposed through combining radial basis function neural network (RBFNN) and prescribed performance function (PPF). In contrast to traditional DOBC, the proposed approach employs RBFNN technology to approximate unknown nonlinear functions in the system, instead of treating them as part of lumped disturbances. A novel disturbance observer is developed to estimate disturbances characterised by a nonlinear exogenous system. To enhance control performance, a PPF that characterises both transient and steady-state behaviour is used for the transformation of tracking errors. It can be proved that all the states of the closed-loop system can be guaranteed to be uniformly ultimately bounded (UUB), and that the tracking error evolves within the prespecified boundaries. Theoretical results are validated and supported by two simulation examples.

CFD modelling of methane dispersion from buried pipeline leaks: Experimental validation and hazard distance estimation

The safe operation of buried pipelines necessitates an understanding of potential leak dynamics and the subsequent formation of flammable clouds defining hazard distances. This paper presents a computational fluid dynamics (CFD) model and its validation against experimental data on the dispersion of methane through a sand layer of 100 mm thickness to the atmosphere. A leak orifice diameter of 4 mm was considered for pipeline gauge pressures in the range of 10–300 kPa. This study describes the methane propagation in time through the sand and the development of the flammable cloud in the atmosphere. The simulations demonstrate a high degree of accuracy in capturing the transient behaviour of methane propagation in the sand and dispersion in the atmosphere when compared with a 60 s experiment. The model was applied to predict the development and maximum spread of the flammable cloud and hazard distances are presented. The simulations provide insight into the development of the flammable cloud. The validated CFD model can serve as a predictive tool for hazard distance estimation in case of buried leaks, inform safer pipeline design and improve emergency response strategies for gas leaks.

Wave packet enriched finite element for accurate modelling of thermoelectroelastic wave propagation in functionally graded solids

A wave packet enriched finite element (FE) formulation featuring electrothermomechanical coupling is presented for solving two-dimensional wave propagation problems in functionally graded elastic and piezoelectric media. The FE equations for the Lord-Shulman and Green-Lindsay theories of generalized piezothermoelasticity are derived, where the standard Lagrangian interpolation functions of the temperature, electric potential, and displacement field variables are extrinsically enriched with element-domain sinusoidal wave-packet functions and are solved using the Newmark–β direct time integration. The effective properties of the functionally graded material (FGM) are computed using the volume-fraction-based micromechanics models, the Mori-Tanaka model and Voigt's rule of mixture (ROM) model. A variety of wave propagation problems, including the mechanically and electrically excited high-frequency Lamb wave propagation in FGM plates, impact waves in FGM bars, and thermal shock waves in functionally graded piezoelectric cylinders, are solved using the present formulation, and results are validated with available solutions. The efficacy of the current solution in comparison with the conventional FE is evaluated for all the studied problems. The effect of the inhomogeneity parameter on the transient wave behaviour is also presented for all the problems. The results of the Mori–Tanaka model are compared with those of the widely used ROM.

Modeling of pulse and relaxation of high-rate Li/CFx-SVO batteries in implantable medical devices

We present a Hybrid Multiphase Porous Electrode Theory (Hybrid-MPET) model that accurately predicts the performance of Medtronic’s implantable medical device battery lithium/carbon monofluoride (CFx) - silver vanadium oxide (SVO) under both low-rate background monitoring and high-rate pulsing currents. The distinct properties of multiple active materials are reflected by parameterizing their thermodynamics, kinetics, and mass transport properties separately. Diffusion limitations of Li+ in SVO are used to explain cell voltage transient behavior during pulse and post-pulse relaxation. We also introduce change in cathode electronic conductivity, Li metal anode surface morphology, and film resistance buildup to capture evolution of cell internal resistance throughout multi-year electrical tests. We share our insights on how the Li+ redistribution process between active materials can restore pulse capability of the hybrid electrode, allow CFx to indirectly contribute to capacity release during pulsing, and affect the operation protocols and design principles of batteries with other hybrid electrodes. We also discuss additional complexities in porous electrode model parameterization and electrochemical characterization techniques due to parallel reactions and solid diffusion pathways across active materials. We hope our models can complement future experimental research and accelerate development of multi-active material electrodes with targeted performance.

Random walk on the Poincaré disk

We consider three interpretations of the standard random walk of [Formula: see text] on a hyperbolic space. We will consider the hyperbolic disk model, and we study properties such as transient behavior, synchronicity and properties of the stationary measure.

Characterisation and modelling of anisotropic hardening behaviour of cubic and hexagonal close packed polycrystalline metals

ABSTRACT In this study, anisotropic non-proportional hardening behaviour of the sheet metals with different crystalline structures is investigated. The investigated materials particularly exhibit the Bauschinger effect and complex transient hardening behaviour during loading path change. Furthermore, the finite element simulations are carried out to evaluate the performance of the distortional and multi-surface-kinematic hardening models in flow stress prediction under loading path change. Both models can well reproduce the measured anisotropic hardening, but the distortional hardening concept shows better predictive capability for flow stresses. The improved accuracy of the flow stress prediction with the distortional hardening model compared to the kinematic hardening is attributed to its flexibility in distortion of the yield surface following microstructure deviator independent on the initial yield surface. In contrast, the initial size of the yield surface in the kinematic hardening significantly affects the determination of the re-yielding stress at load reversal.

Method to determine instantaneous transient responses in pressurized pipes from transfer functions and state space for evaluation of leak signals

This article addresses the impact of transient pressure anomalies in hydraulic systems, triggered by the opening or closing of valves or pumps, instantly disturbing the line of hydraulic gradient (LGH). This variation in pressure has significant consequences both in hydraulic and structural terms for water networks. Most of the existing techniques to detect transients in water distribution systems use asynchronous methods, generating timeless information that limits the response capacity in critical situations. Therefore, an automatic transient detection system based on the Internet of Things (IoT) is proposed, capable of identifying overpressure or underpressure pulses in soft real-time, activating alarms to facilitate decision-making. This approach helps maintain the safety of the water distribution system and prevent leaks in the network. Furthermore, a model of the transient behavior of pressure and flow is presented by linearizing the water hammer equations from the Laplace transform, thus generating a transfer function that describes the algebraic relationship between the outlet and inlet of the hydraulic system.•The transient analysis of the hydraulic system prototype underscores its high sensitivity to initial conditions, attributed to turbulence. This observation suggests the possible presence of a dynamic strange attractor related to water hammer phenomena in pressure pipes.•The methodology involving transfer functions and state-space models enables the assessment of how leaks impact the transient responses of the system, including the magnitude, duration, and frequency of disturbances generated by them.•The proposed method introduces a dynamic transfer function capable of identifying instantaneous changes over time in terms of flow and pressure.

Modeling and experimental study of air-cooled finned-tube condenser using coupled distribution parameter method and air-side temperature distribution

The air-cooled finned tube condenser (ACFTC) plays a crucial role in refrigeration systems, profoundly influencing overall operational efficiency. Its intricate structure, connectivity, and phase change characteristics pose challenges for numerical simulation modeling. While traditional distribution parameter methods effectively capture flow and heat transfer within tube mediums, they overlook ACFTC’s air-side temperature distribution, resulting in discrepancies between simulated and experimental outcomes. This study enhances existing distribution parameter models by incorporating ACFTC’s air-side temperature distribution characteristics, yielding an improved predictive model for transient operational behavior of both Z-shaped and U-shaped configurations. Dynamic experiments and model analyses were performed on the Z-shaped configuration using a cold storage experimental setup. Results demonstrate the improved model’s accurate prediction of tubing medium outlet temperature and pressure, with maximum deviations of approximately 3 °C and 0.01 MPa, respectively. Notably, the improved model exhibits around a 30 % enhancement in predictive accuracy compared to the existing models for both Z-shaped and U-shaped ACFTCs.

Coal-derived conductive pavement for winter de-icing: prototype, modeling, and simulation

Existing pavement de-icing methods result in high installation and maintenance costs, traffic delays, excessive weariness and corrosion, and negative environmental and safety impacts. To overcome these challenges, this paper presents an innovative pathway to designing and constructing smart self-heating pavements using a low-cost coal-char bearing asphalt material. The conductive asphalt incorporates coal char, i.e., a key byproduct of the coal pyrolysis process, into the Stone Mastic Asphalt (SMA) mixture. This asphalt containing coal-derived solid carbon exhibits highly tailorable electrical conductivity, satisfactory mechanical and thermophysical properties, and superior cost-efficiency as compared to other conductive pavement materials. The de-icing performance was also demonstrated by laboratory experiments on a bench-scale prototype. Furthermore, an efficient thermal network model was developed and validated by experiments to investigate the transient thermal behavior and energy performance of the Ohmic heating pavement system. The whole-year energy simulation case studies were conducted on a bridge pavement with an annual energy use of 24.6–1444.8 kWh/m2, showcasing its potential in field applications across cool humid, cold humid, and subarctic/arctic climate zones.