Short-circuiting Effect Research Articles

Heat transfer performance and optimal design of shallow coaxial ground heat exchangers

The heat transfer performance of coaxial ground heat exchangers (GHEs) can be strongly influenced by their structure parameters and improved by the optimal design. To improve the heat transfer efficiency, this study proposed a coaxial GHE with large pipe diameters and thick inner pipe insulation for shallow ground source heat pump systems, which had heat transfer rates of more than 120 W/m in 12 h during both heat injection and extraction experiments. The validated three-dimensional CFD model was used to numerically investigate the influence of various structural parameters on the heat transfer efficiency considering the thermal short-circuiting effect. The thermal short-circuiting effect could be alleviated with thicker inner pipe insulation, while the decreasing annular space occupied by the insulation would reduce the borehole heat transfer rates, thus, an inner pipe with a 35 mm-thick insulation obtained the optimal heat transfer rate. The inner pipe diameter increase contributed to a more severe thermal short-circuiting and poor heat transfer performance. Increasing the outer pipe diameter improved the heat transfer efficiency and an optimal outer pipe diameter of 155 mm existed when considering the heat transfer performance and its efficiency. Therefore, increasing the inner pipe insulation thickness and outer pipe diameters can be regarded as an efficient method to improve the thermal performance of coaxial GHEs.

Airflow and heat transfer characteristics for different cargo pallet arrangements in a heat transfer enhanced refrigerated container

Improving the performance of a refrigerated container is crucial in effectively preserving thermal-sensitive cargo. The combined effect of vertical airflow resistance and airflow short-circuiting in air gaps play a vital role in cargo cooling. This study numerically investigates the effects of cargo vertical airflow resistance and air gaps between cargo pallets using two commonly used apple packaging boxes, each stacked in six different cargo pallet arrangements. A heat transfer enhanced refrigerated container design and a numerical model developed from the present authors’ previous studies are used. The numerical model uses the porous medium model to incorporate the refrigeration unit and cargo within the refrigerated container. Additionally, the numerical domain includes the T-bar floor in the refrigerated container. Initially, the airflow characteristics based on vertical airflow resistance and air gaps are discussed. Then, the corresponding effects on cargo cooling are addressed. Results show that the air gaps between the cargo pallets have positive and negative effects on cargo cooling. In cargos with lower vertical airflow resistance, an increase in air gaps leads to reduced cargo cooling and elevated temperature non-uniformity. Conversely, cargos with higher vertical airflow resistance experience increased cooling rates and reduced temperature non-uniformity with the increase in air gaps. However, avoiding airflow short-circuiting through the air gaps between the cargo pallets and improving the vertical airflow inside the cargo pallets can provide better cargo cooling, which outweighs the positive cooling effect of the air gap.

An investigation into the short-circuit characteristics of Sic MOSFET power devices

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) devices exhibit substantial prospects for application under extreme operational conditions, including elevated temperatures, high voltages, and high frequencies. Nevertheless, owing to their distinctive material and structural attributes, SiC MOSFET devices are not devoid of challenges, with the short-circuit phenomenon constituting a pivotal avenue of inquiry. The short-circuit effect pertains to the abrupt escalation of leakage current that these devices might undergo under elevated voltage conditions, thereby exerting a perturbing influence on their stability and reliability. Investigations into the short-circuit effect predominantly revolve around two dimensions: one involves comprehending its underlying physical mechanisms, while the other centers on identifying commensurate remedial approaches.With respect to the underlying physical mechanisms, researchers have discerned that the elevated breakdown field strength and augmented carrier mobility intrinsic to SiC materials engender an augmentation in leakage current, consequently giving rise to the short-circuit effect. Furthermore, factors such as oxide layer anomalies and surface states are also conceivable catalysts for the surge in leakage current. To rectify this predicament, scholars have proffered a panoply of stratagems, encompassing the optimization of material synthesis processes, enhancement of oxide layer quality, refinement of device structural designs, and incorporation of protective circuitry, among others. In summation, the investigation of the short-circuit effect in silicon carbide MOSFET devices is fundamentally aimed at attaining an in-depth comprehension of its causative mechanisms. Moreover, it endeavors to proffer efficacious resolutions conducive to augmenting the reliability and steadfastness of these devices within high-temperature and high-voltage environments, thereby facilitating their widespread integration within the ambit of high-performance power electronics.

Residence time and the concentration of microorganism in the ozone contactor: a CFD simulation on chamber deflectors.

Disinfection is an important step in deep drinking water treatment technology. This study applies computational fluid dynamics to investigate and optimize the hydrodynamics inside the ozone contactor. ANSYS Fluent was used to solve all the control equations. A step method is used to simulate the residence time distribution. The mean residence time is simulated under the Eulerian framework. The deflectors are installed in chambers to direct flow. The deflectors allow for a more uniform flow and a longer mean residence time within the contactor. The baffling factor showed that the deflectors could reduce the short-circuit effect in the contactor and improve the disinfection efficiency by 34.6% compared to the original reactor. The Morrill factor coefficient is improved by 22.8% compared to the original reactor. According to the Aral-Demirel index, contactors with deflectors are significantly better than other baffle-type contactors. The presence of the deflectors increased the microbial inactivation efficiency from 95.3 to 96.5%. The optimal deflector height should be controlled between 30 and 60 mm.

Short Circuit Effects on HV Feeders of Optimally Located Electric Vehicle Fast Charging Stations

Short Circuit Effects on HV Feeders of Optimally Located Electric Vehicle Fast Charging Stations

CO2 conversion improvement of solid-oxide electrolysis cells by inserting buffer layers between MFe2O4 (M = Ni, Cu, Co, Fe) cathode and electrolyte

This study investigated the potential of spinel-structured materials (MFe2O4; M = Ni, Cu, Co, and Fe) as cathodes of solid oxide electrolysis cells (SOECs); at the same time, it revealed that the La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) blocking layers would improve the performance of SOECs by interposing between MFe2O4 and the Sm0.2Ce0.8O2-δ (SDC) electrolytes. The fabricated SOECs were tested under 39% CO2-1% CO-60% He up to 800 °C. Our results showed that the Faradaic efficiency for CO2 reduction was significantly improved and approached the theoretical production rate after the insertion of LSGM blocking layers. In addition, the LSGM barrier layers effectively prevent the short-circuit effect between MFe2O4 and SDC, allowing the open-circuit voltage (OCV) to increase from ∼0.56 V to ∼0.77 V, which dramatically improved the gas generation efficiency of SOECs. According to our optimized SOEC structure, NiFe2O4 and CuFe2O4 exhibited superior electrolytic performance and maintained stable electrolysis after 10 h without degradation. In summary, the inserted LSGM layers would gently modify the interfacial contact and address the mismatch between the spinel-structured materials and SDC to avoid the performance degradation caused by electrode detachment and achieve higher durability than the SOECs without LSGM layers.

Research on Dynamic and Thermal Effects Based on the Calculation of the Short-Circuit Current in Low-Voltage DC Distribution Systems for Civil Buildings

The verification of short-circuit effects is very important for ensuring the safety of equipment and power systems. Compared with that in alternating current (AC) systems, research on this issue in direct current (DC) systems is scarce, and it is urgently necessary to develop an accurate verification method for applications in DC systems. This research establishes an equivalent model of a pole–pole cable short-circuit according to the characteristics of low-voltage DC distribution systems in civil buildings. Through theoretical analysis and numerical simulation, the development process of a short circuit is summarized, and the methods of verifying dynamic and thermal effects based on the time-domain characteristics of the short-circuit current are specified. By calculating the peak value and Joule integral of the short-circuit current, in comparison with those in the IEC 61660 (1997) standard, this research points out that the method in the IEC 61660 (1997) standard is insufficient. Finally, the short-circuit peak current is greatly affected by the DC-link capacitance, the steady-state current is directly related to the filter inductance of the AC-link; and the verification of the thermal effect requires the calculation of the Joule integral in the transient and steady state.

Corona: An effective polarization strategy of polymer composites with high-k filler for piezoelectric nanogenerators

Piezoelectric nanogenerators (PENGs) are mushrooming owing to demand of swift transformation of power supply from fossil fuel to green energy. Piezoelectric ceramics are enthusiastically chased because glorious PENGs demand for high piezoelectricity. Generally, brittleness of ceramics can be compensated by polymer, while the dielectric mismatch between low permittivity of polymer and high permittivity of ceramics plaguing researchers so long. Traditional contact poling is always interrupted by abrupt dielectric breakdown due to electric field concentration at interface between polymer and fillers. Here, we propose a strategy of using corona polarization instead of traditional contact polarization to insistently polarize large-area polymer composite films with high-k filler. The corona polarization technique can ignore the negative effect of local short circuit on polarization failure owing to prominent lateral insulation between deposited charges on surface of composites film, consequently obtaining well-performed piezoelectricity. Henceforth, polarization failure did not occur using corona even under poling voltage of 26 kV. The corona-poled PVDF/Y-ZnO PENG with only 15 wt% content of fillers generated output power density of ∼1064 μW/cm3. Our work will pilot the development of polymer composites with high-k filler and piezoelectric nanogenerators.

Study on short circuit effect of silicon carbide power devices

SiC can provide better material properties when the performance of Si - based power devices is almost developed to the limit. But compared with Si material, the reliability of SiC device is poor under ultimate stress. The short circuit capability of SiC MOSFET has been the main area of attention in this papers study. Through the analysis of SiC MOSFET short-circuit capability, it is mainly represented by the time that the device can withstand short-circuit stress and the time it takes for the device to be safely turned off in the event of a short circuit fault. Secondly, the detection circuit and protection circuit under the SiC MOSFET short-circuit fault are briefly studied, and the optimization ideas and working principles are summarized.

Bilayer lattice structure integrated with phase change material for innovative thermal protection system design

In recent years, ceramic matrix composite (CMC) lattice structure has become a promising candidate for a new generation of integrated thermal protection systems (ITPSs) used in the ultrahigh-temperature environment. However, the thermal short circuit effect caused by lattice cores limits their application. In this work, we propose a bilayer CMC lattice structure filled with phase change material (PCM) and thermal insulation material for integrated thermal protection systems (ITPSs) to mitigate the thermal short circuit effect. The numerical simulation method is used to verify the effectiveness of the bilayer lattice structure in mitigating the thermal short circuit effect compared with one-layer ITPS. By inserting the middle face sheet, the thermal insulation effect enhances about 16%. Furthermore, the effects of thermal insulation materials, thermal conductivity and thickness of paraffin/expanded graphite composite PCM, and the diameter of the lattice core strut on the thermal insulation performance are discussed. The results show that the thickness of PCM has an optimal solution. Optimizing results show that when the aerogel insulation fiber is used as the thermal insulation material, the thermal conductivity k=0.82 W/(m⋅K) and the thickness t3=10 mm of PCM, the diameter of the core strut d=1.5 mm, the bilayer PCM-ITPS has the best thermal insulation performance. When the ultrahigh-temperature load is continuously loaded, the highest temperature of Top Face Sheet is more than 2300°C, but the highest temperature of Bottom Face Sheet is only 30.12°C, which thermal insulation effect is far better than the traditional ITPS. This work gives a novel scheme to solve the thermal short circuit effect, improving the thermal protection performance and accelerate the application of lattice structure in ITPS.

Case Study: Effect of mechanical short-circuiting of isolation pads on rooftop equipment noise and vibration transfer to spaces below.

The authors conducted investigations into noise from large rooftop air source heat pump (HP) equipment to student housing units below in a new concrete building. The investigation included both airborne noise and vibration measurements on the roof and in the dwelling units below. A total of five, 18-Ton devices were mounted on a foam-filled concrete housekeeping pad resting on an 8-inch thick PT structural slab and isolated by means of spring mounts fitted with neoprene isolation pads below their baseplate. The dwelling units below had exposed concrete at the ceiling, shear walls, and columns. Noise from the HPs were waking residents in the units directly below the equipment. After a number of adjustments to the spring isolation mounts to eliminate bindings and mechanical short-circuits, the investigation showed that vibration was also being transmitted to the building structure from the isolator base plates through the anchor bolts, bypassing the noise pads below the baseplate. Removal of this secondary short-circuit resulted in noticeable reductions in both noise and vibration at the spaces below, highlighting the need for careful adjustment and the provision of additional isolation elements in the installation.

Particle-in-cell modeling of electron beam generated plasma

Plasmas generated using energetic electron beams are well known for their low electron temperature (T e) and plasma potential, which makes them attractive for atomic-precision plasma processing applications such as atomic layer etch and deposition. A 2-dimensional particle-in-cell model for an electron beam-generated plasma in argon confined by a constant applied magnetic field is described in this article. Plasma production primarily occurs in the path of the beam electrons in the center of the chamber. The resulting plasma spreads out in the chamber through non-ambipolar diffusion with a short-circuiting effect allowing unequal electron and ion fluxes to different regions of the bounding conductive chamber walls. The cross-field transport of the electrons (and thus the steady-state characteristics of the plasma) are strongly impacted by the magnetic field. T e is anisotropic in the electron beam region, but low and isotropic away from the plasma production zone. The plasma density increases and the plasma becomes more confined near the region of production when the magnetic field strengthens. The magnetic field reduces both electron physical and energy transport perpendicular to the magnetic field. T e is uniform along the magnetic field lines and slowly decreases perpendicular to it. Electrons are less energetic in the sheath regions where the sheath electric field repels and confines the low-energy electrons from the bulk plasma. Even though electron and ion densities are similar in the bulk plasma due to quasi-neutrality, electron and ion fluxes on the grounded chamber walls are unequal at most locations. Electron confinement by the magnetic field weakens with increasing pressure, and the plasma spread out farther from the electron beam region.

Electromagnetic Vibration Characteristics of Inter-Turn Short Circuits in High Frequency Transformer

As a common fault of transformer winding, inter-turn short circuits cause severe consequences, such as excessive current and serious deformation of winding. Aiming to solve the problem of inter-turn short circuit at the end-winding and middle-winding of high frequency transformers (HFT), this paper considers the electromagnetic vibration characteristics of inter-turn short circuits (interleaved winding and continuous winding) at different positions, and the HFT is established by the multi-physical field coupling principle. Coupling equations for the inter-turn short circuit, as well as electromagnetic force and sound pressure level, are established to characterize the vibration noise mechanism of inter-turn short circuits. Furthermore, the HFT equivalent model is simulated in 3D finite element method (FEM) to emulate the real transformer operation and investigate the impact of interleaved winding and continuous winding under inter-turn short circuit faults. The short-circuit current and axial flux leakage, as well as the harmonic response of vibration acceleration and sound pressure level distribution, are obtained when inter-turn short circuits occur at different positions. Finally, the results show that the electromagnetic effect of the inter-turn short circuit in end-winding is worse than it is in middle-winding. Advantages in resisting impulse current make interleaved winding superior to continuous winding in terms of vibration and noise.

Research on cumulative effect and diagnosis method of transformer short-circuit impulse

After transformers suffer from short-circuit impact, their mechanical performance decreases significantly. This article establishes a two-wire vibration model to represent the coupling between forces and mechanics and analyzes the transient vibration signals of a 400 V transformer during 22 short-circuits impact. To illustrate the cumulative effect of short-circuits, the vibration entropy, and energy ratio of the main vibration frequency and half frequency are adopted. The results show that transient vibration signals of transformer in short-circuits contain half frequency components, such as 25 Hz and 75, etc., and with the increase of the number of short-circuits, plastic deformation exists in insulation material, which leads to the loss of winding clamping pressure, the reduction of natural frequency, and the upsurge of parametric resonance. With the increase of short circuits, the vibration entropy and half-frequency energy ratio increase, and the main frequency energy ratio decreases. After winding completely lose the axial stability, the vibration entropy and half frequency ratio decrease, and the main frequency ratio increases. The conclusion is of great significance to the analysis of the cumulative effect of short circuits on power transformers.

Reservoir Simulation Model Predicts EOR Performance on Alaska’s North Slope

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 206247, “History Matching and Performance Prediction of a Polymerflooding Pilot in a Heavy Oil Reservoir on Alaska’s North Slope,” by Xindan Wang, Cody Keith, SPE, and Yin Zhang, University of Alaska Fairbanks, et al. The paper has not been peer reviewed. _ The complete paper discusses the first polymerflooding pilot to enhance heavy oil recovery on the Alaskan North Slope. After more than 2.5 years of polymer injection, significant benefit has been observed from the decrease in water cut, from 65% to less than 15% in project producers. The primary objective of the study was to develop a robust history-matched reservoir simulation model capable of predicting future polymerflooding performance. Pilot Description The pilot program targets an isolated fault block in the Schrader Bluff NB sands with two horizontal injectors (J-23A and J-24A) and two horizontal producers (J-27 and J-28). The producing lengths of the horizontal wells range from 4,200 to 5,500 ft, and the average interwell distance is approximately 1,100 ft. The project wells were put on waterflooding in June 2016, recovering approximately 7.6% of the original oil in place with a cumulative water injection of 0.09 pore volumes (PV). In August 2018, polymer solution injection commenced. The polymer solution, with a target viscosity of 45 cp, was introduced to both injectors by means of a polymer injection unit. By the end of December 2020, a total of 1.7 million STB of polymer solution had been injected, representing 0.08 PV in the flood pattern. A significant benefit of polymerflooding has been observed in the decrease in water cut in both producers. The oil production rate of Producer J-27 (supported by both injectors) increased continuously from 500 to 800 BOPD in April 2019. The oil production rate of Producer J-28 (supported only by J-23A to the north) also increased to approximately 700 BOPD in late 2019 and stabilized at approximately 500 BOPD in 2020. Reservoir Modeling Base Reservoir Model. A 3D reservoir model was developed for the pilot fault block. The selected active reservoir simulation model, including 23,848 active gridblocks, covers the potential sweep area of the project wells. The 3D view of the selected active reservoir simulation model is shown in Fig. 1. The approximate dimensions of the active reservoir simulation model are 6,900, 4,100, and 15 ft in the x, y, and z directions, respectively. The reservoir simulation model consists of eight layers in the z direction. High-Transmissibility Strips. The early water breakthrough and high water cut during the pre-polymer/waterflooding period indicate strong communication and short-circuiting behavior between the injecting and producing wells. To simulate this short-circuiting effect, four high-transmissibility strips at different locations and with different widths were introduced to connect the injectors and producers in the reservoir simulation model. Each strip was present in all eight layers of the model such that the strips in each layer were identical.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Design and Application of Flexible Resistive Tactile Sensor Based on Short-Circuit Effect

Resistive tactile sensor has excellent anti-interference characteristics in daily environment. Inspired by the short-circuit effect in electricity, a new design of flexible resistive tactile sensor was proposed in this study. We utilized conductive graphite paint and conductive silver paint as sensing materials to fabricate the high-impedance element (100–150 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega$ </tex-math></inline-formula> ) on the polyimide (PI) film and the low-impedance element (2– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\Omega$ </tex-math></inline-formula> ) on the silicone rubber, respectively. The output signal depends on the contact area between the high-impedance and the low-impedance elements caused by the applied pressure, which employs the short-circuit effect for the transduction mechanism. Besides, the spherical microstructure in silicone rubber layer was used to enlarge the measuring range of pressure. The experimental results show a wide range of pressure response up to above 3 MPa, and the resolution of the sensor with spherical structure is 79.6 kPa (0.25 N). The force sensing sensitivity of the sensor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S = - 5.733\times 10^{-4}$ </tex-math></inline-formula> kPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> (from 0 to 799.4 kPa) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S = - 1.744\times 10^{-4}$ </tex-math></inline-formula> kPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> (from 799.4 to 2834.4 kPa). Furthermore, an air gap between the high-impedance and the low-impedance elements was designed for restraining the interference of adjacent sensor arrays. Finally, we demonstrated the application in teleoperation and letter recognition, which implies that the proposed sensor has a great application potential in the field of robotics.

The Effect of Stator Inter-Turn Short-Circuit Fault on DFIG Performance Using FEM

Doubly-Fed Induction Generators (DFIG) are operated for wind energy production, and as their capacity is increasing, their safety and reliability become more important. Several faults affect the performance of DFIG. The stator winding Inter-Turn Short-Circuit Fault (ITSCF) is one of the most prevalent electric machine failures. This study examined the stator ITSCF effects on DFIG performance for different cases. The DFIG was designed and engineered using the Finite Element Method (FEM) and the Maxwell software, and was examined in healthy operation and four defective cases with various Numbers of Inter-Turn Short Circuit Faults (NITSCF): 4, 9, 19, and 29. These models allowed the examination of the effects and the comparison of each case separately from the healthy state. The comparison was plotted in Matlab to show the effects of the faults. The novelty of this study was that it investigated the effects of different NITSCF on the performance of DFIG and not only on their effect on the stator current and distribution of magnetic flux density. A better understanding of the short circuit effects on the performance of the DFIG can be exploited for subsequent implementations of early fault detection systems.

Federico Fellini (1920–2020), special issue of Journal of Italian Cinema and Media Studies, vol 9, no. 1, 2021

Federico Fellini (1920–2020), special issue of <i>Journal of Italian Cinema and Media Studies,</i> vol 9, no. 1, 2021

The effect of short circuits and flame temperature modes on the change in the microstructure of copper in automotive wiring

The purpose of the work is to investigate the causes of vehicle ignition by analyzing the microstructure of copper conductive elements of automotive wiring. This study considers the three most likely vehicle fire scenarios. According to the first scenario, a fire occurs due to overheating of the automotive wiring by short circuit currents. In the second scenario, car fires result from direct exposure to an open flame. In the third scenario, vehicle fires are due to the combined effects of short circuits and open flames. These three scenarios affect the microstructure of copper conductive automotive wiring elements in different ways. Microstructural analysis of copper wires exposed to the temperature conditions of these three fire scenarios was carried out using an optical microscope (OM) and a scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) spectrometer. It has been disclosed that when exposed to an open flame on a copper wire, the fine-grained microstructure of the original copper wire turns into a coarse-grained one. The impact of an electric arc caused by a short circuit can instantly melt copper wires. As a result, local spherical inclusions (beads and pits) appear on the surface of the copper wire, and grains of the dendritic structure are formed in its surface layer. The impact of an open flame on already short-circuited copper wires transforms their fine-grained microstructure containing local spherical inclusions into a kind of coarse-grained microstructure with clear boundaries between grains consisting of copper(II) oxide. The study of the microstructure of copper wires taken from a burned-out car should form the basis for studying the causes of car fires.