Dynamic simulation of steam generation system in solar tower power plant

Concentrated solar power (CSP) plant with thermal energy storage can be operated as a peak load regulation plant. The steam generation system (SGS) is the central hub between the heat transfer fluid and the working fluid, of which the dynamic characteristics need to be further investigated. The SGS of Solar Two power tower plant was selected as the object. The mathematical model with lumped parameter method was developed and verified to analyze its dynamic characteristics. Five simulation tests were carried out under the disturbances that the solar tower power plant may encounter under various solar irradiations and output electrical loads. Both dynamic and static characteristics of SGS were analyzed with the response curves of the system state parameters. The dynamic response and time constants of the working fluids out of SGS was obtained when the step disturbances are imposed. It was indicated that the disturbances imposed to both working fluids lead to heat load reassignment to the preheater, evaporator and superheater. The proposed step-by-step disturbance method could reduce the fluid temperature and pressure fluctuations by 1.5 °C and 0.03 MPa, respectively. The results could be references for control strategies as well as the safe operation of and SGS.Peer reviewe

Influence of Structure Parameters of Flux Diverters on Performance of Superconducting Energy Storage Coil

This article studies the influence of flux diverters (FDs) on energy storage magnets using high-temperature superconducting (HTS) coils. Based on the simulation calculation of the H equation finite-element model, FDs are placed at both ends of HTS coils, and the position and structure are optimized. The impact of the diverter structural parameters on the energy storage of the HTS energy storage magnet is explored, and an optimized diverter structure is designed. The rectangle is the most basic structure of FDs, so this article first optimizes the structure of the rectangular FDs and then performs various slotting treatments on the optimized FDs. By comparison, it is concluded that the concave FDs have the best energy storage effect. Then, based on the optimization of the concave FDs, a Γ-shaped structure is obtained, further improving the magnet's energy storage effect. The conclusion of the influence factors can be applied to the optimization design of diverter structures and provide a new perspective for improving energy storage.</p

Valley Bosonic Stimulation of Exciton-Polaritons in a Monolayer Semiconductor

The newly discovered valley degree of freedom (DOF) in atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) offers a promising platform to explore rich nonlinear physics, such as spinor Bose-Einstein condensate (BEC) and novel valleytronics applications. However, the critical nonlinear effect, such as valley polariton bosonic stimulation (BS), has long remained an unresolved challenge due to the generation of limited polariton ground state densities necessary to induce the stimulated scattering of polaritons in specific valleys. Here, we report, for the first time, the valley bosonic stimulation of exciton-polaritons via spin-valley locking in a WS2 monolayer microcavity. This is achieved by the resonant injection of valley polaritons at specific energy and wavevector, which allows spin-polarized polaritons to efficiently populate their ground state and induce a valley-dependent bosonic stimulation. As a result, we observe the nonlinear self-amplification of polariton emission from the valley-dependent ground state. Our finding paves the way for both fundamental study of valley polariton BEC physics and non-linear optoelectronic devices such as spin-dependent parametric oscillators and spin-lasers.Comment: Article + Supplementary Information (tot. 21 pages

Structure basis for the unique specificity of medaka enteropeptidase light chain

Thermal stresses concern not renewed type of stresses, that is once having liberated, they cannot accumulate more. The estimation of purely thermoelastic contribution to a lithosphere stress state gives the additional information, allowing to predict the danger connected with such natural factors, as seismic and volcanic activity. Some theoretical thermoelastic problems for the geological environment of a difficult outline with non-uniform thermophysical characteristics are considered. The decision is received on the basis of a numerical finite elements method. Influence of the model fixation, the geometrical factor and boundary conditions on distribution of thermal stresses and dislocation is investigated. Computing experiments have shown, that the size of the maximum thermal stresses reaches 500 bar. The maximum values of vertical dislocation are reached by 90 m, and horizontal — 50 m. Neutral plane position are precisely defined. Термоупругие напряжения относятся к невозобновляемому типу напряжений, то есть, однажды высвободившись, напряжения не могут накапливаться вновь. Расчет термоупругого вклада в напряженное состояние литосферы дает дополнительную информацию, позволяющую оценить опасность, связанную с такими природными явлениями, как сейсмичность и вулканическая активность. Рассмотрено несколько теоретических моделей для геологической среды сложного очертания с неоднородными теплофизическими характеристиками. Решение получено на основе численного метода конечных элементов. Исследовано влияние «закрепления» модели, геометрического фактора, неоднородных граничных условий на распределение термоупругих напряжений и перемещений. Вычислительные эксперименты показали, что величина максимальных термоупругих напряжений достигает 500 б. Максимальные величины вертикальных перемещений не превышают 90 м, горизонтальных — 50 м. Положение нейтральной плоскости определяется точно. На основі методу скінченних елементів отримано детальний розподіл термопружних напружень і переміщень для неоднорідного геологічного середовища. Досліджено взаємний вплив геометрії середовища й неоднорідних граничних умов на розподіл термопружних напружень та переміщень

Effect of Arc Chute on DC Current Interruption by Liquid Nitrogen in HTS Electrical System of Distributed Propulsion Aircraft

The distributed propulsion aircraft with HTS electrical system is a novel concept for future airliners, which can reduce by more than 70% fuel burn and NO x emissions. The circuit breakers ensure the security of this novel aircraft by isolating electrical faults timely. Solid-state circuit breakers (SSCBs) are preferred due to their fast response and high performance in the cryogenic circumstance. However, the high conduction loss of SSCBs impedes their further application. A mechanical switch using liquid nitrogen (LN 2 ) as an arc extinguishing medium shows excellent DC current interruption performance. The LN 2 switch is characterized with extremely low contact resistance, and the proper use may reduce the conduction loss of power switches significantly. Nevertheless, the effect of metal type arc chutes on the arcing process in the LN 2 is still not clear. Thus the objective of this paper is to understand the effect of metal type arc chutes on the current interruption performance of LN 2 . Silicon iron arc chutes are employed. Neodymium (NdFeB) magnets are used to stretch the arc into the arc chutes. The maximum interrupting current is 1 kV/ 2 kA when only magnets are applied. Further applying the arc chutes leads to a significant drop in the arc voltage and interruption performance. Since the high relative permeability of silicon iron weakens the magnetic field acting on the arc, metal type arc chutes are not recommended. 1 kV / 10 kA fault current is successfully cleared by the combination of resistance type superconducting fault current limiter (R-SFCL) and LN 2 switch with magnets, during which the R-SFCL responds to the fault within 420 μs, compensating the long clear time of the LN 2 switch

Integration of Superconducting Fault Current Limiter and DC Circuit Breaker for Electric Aircraft DC Network

Large-scale electric aircraft are a promising technology that could revolutionise air travel to reduce the environmental impact. Fault current limitation and interruption technology is crucial to realise the safety and reliability of the electric aircraft, in particular for large-scale electric aircraft using a DC distribution network. This paper proposes to integrate a resistive superconducting fault current limiter (SFCL) with a cryogenic DC solid-state circuit breaker (SSCB) so that the SFCL limits the fault current to acceptable levels in DC networks allowing the SSCB to operate quickly and reliably. A sub-cooled liquid nitrogen cryostat, which can be controlled from 65 K to 77 K, is designed and built for the integration of SFCL and DC SSCB. An SFCL and SSCB prototype is designed and experimentally tested at cryogenic temperatures, which successfully demonstrates the ability to limit and interrupt currents at cryogenic environment

Preliminary Design of DC Resistive Superconducting Fault Current Limiter for ASCEND

Airbus UpNext has launched an Advanced Superconducting and Cryogenic Experimental powertraiN Demonstrator (ASCEND) project in 2021 to develop a superconducting electric aircraft propulsion system. The demonstrator system power is rated at 500 kW with the dc voltage of 300 V. A dc networks can achieve smaller footprint and improved distribution efficiency. However, fault management in dc networks is much more challenging than ac systems because: firstly, there is no natural zero-crossing of the current to isolate the fault; and secondly, the rate of rise of fault currents is often significantly higher due to lower system impedances. Resistive superconducting fault current limiter (RSFCL) is a passive device that provides protection without requiring external input, making it inherently reliable. Non-inductive bifilar pancake RSFCL coils supported by G10 former are designed and built based on ASCEND system specification. This paper will present the design of RSFCL using 2G high temperature superconductor tapes for ASCEND demonstrator. A dc fault current testing circuit is built for testing of RSFCL. RSFCL is experimentally tested from 65 K to 77 K in the sub-cooled liquid nitrogen cryostat. The current limitation and recovery time are compared for different operating temperatures. In conclusion, RSFCL using HTS tapes demonstrates effective and fast current limitation within 1ms, which significantly improves the reliability of the system.</p

Application of Flux Diverters in High Temperature Superconducting Transformer Windings for AC Loss Reduction

Flux diverters (FDs) are used in High Temperature Superconducting (HTS) transformers for AC loss reduction and flux optimization. In this paper, a 2D axial symmetric superconducting winding model is proposed and two designs of flux diverters are applied to the windings. A homogenization approach is used to analyze the windings with large turn numbers. The key parameters including the number, width, height and the spatial positions of the FDs are adjusted for AC loss and magnetic flux analysis. The means of obtaining optimum designs of the FDs is provided and can be used to develop new winding designs with FDs, which contributes to better electromagnetic performance and higher efficiency of HTS transformers

Combined Y-configured stents for revising occluded transjugular intrahepatic portosystemic shunt

PURPOSEWe aimed to determine the technical feasibility, safety and prognosis of the transjugular intrahepatic portosystemic shunt (TIPS) revision by combined Y-configured stents placement.METHODSWe retrospectively evaluated 12 patients who received TIPS revision using Y-stenting technique between June 2015 and January 2019. The rates of technical success, complication, shunt patency, hepatic encephalopathy and mortality were described and analyzed.RESULTSThe combined Y-configured stents were successfully placed in 11 of 12 patients (92%) without major complications. The median portosystemic pressure gradient (PPG) decreased from 23 mmHg (interquartile range, IQR, 18.5–27.5 mmHg) to 10 mmHg (IQR, 9–14 mmHg). The left internal jugular vein approach was used in 5 patients. Four patients required a shunt extension with an extra stent to resolve the stenosis at the portal venous terminus. Two patients developed hepatic encephalopathy, which was medically controlled within 3 months after the procedure. The TIPS patency and survival rates were both 100% during a median follow-up period of 10 months (IQR, 5.5–14 months).CONCLUSIONTIPS revision by combined Y-configured stents placement was technically feasible and safe with favorable clinical outcomes