Energy Release Process Research Articles

Study on design optimization of new liquified air energy storage (LAES) system coupled with solar energy

In view of the low round trip efficiency of the liquified air energy storage (LAES) system, the thermodynamic model is established by Ebsilon professional soft. Different solar energy coupled LAES systems are proposed to reduce the impact of the energy storage temperature on the energy release process. And their performances under design/off-design conditions are investigated and compared. The results show that after coupling with the solar energy, under the design conditions, the round trip efficiencies of three solar energy coupled LAES systems, which have 3 stages compressors and 3 stages turbines (3C + 3 T), 4 stages compressors and 4 stages turbines (4C + 4 T), 5 stages compressors and 5 stages turbines (5C + 5 T), respectively, are improved from 59.46%, 57.67%, 56.46% to 73.6%, 81.9%, 87.17%, respectively. The performance of the solar energy coupled 5C + 5 T system is the best. Under the off-design conditions, with the increase of the solar energy, the solar power is increased, the LAES power is increased, and the power generations of these three systems are increased. On this basis, the solar energy coupled isothermal compression-liquid air energy storage (IC-LAES) systems are proposed. The thermal performance and the variable conditions of these three IC-LAES systems are analyzed. Under the design conditions, the round trip efficiencies of the IC + 3 T, IC + 4 T, IC + 5 T systems are significantly improved to 112.73%, 117.53%, 120.71%, respectively. Under the off-design conditions, when the solar energy decreases, the power generations of these three IC-LAES systems decrease rapidly. It can be seen that the solar energy has great influence on the solar energy coupled IC-LAES systems. It is necessary to ensure that the solar energy is always at a high value.

Effect of spherical Al-Mg-Zr on the combustion characteristics of composite propellants

In this work, spherical Al-Mg-Zr alloy with intensive heat release were characterized and compared to neat Al powders. The morphology, element distribution and thermal performance were characterized by TEM, SEM, Mapping and TG-DSC. The laser-induced ignition and combustion characteristics of Al-Mg-Zr alloy powders were performed by microscopic high-speed video-recording. The effect of Al-Mg-Zr on the combustion process of HTPB-based solid propellants were carried out as well. It was observed that, the energy release process of Al-Mg-Zr is accompanied by the phenomena of gas emission and microexplosion, which is useful for improving the combustion efficiency of the alloy and reducing the combustion product particles of solid propellants. The findings in this work validate the potential of Al-Mg-Zr as an additional fuel for high aluminum content solid propellants.

Resolving Two Distinct Thermal X-Ray Components in a Compound Solar Flare

Abstract X-ray emission provides the most direct diagnostics of the energy release process in solar flares. Occasionally, a superhot X-ray source is found to be above hot flare loops of ∼10 MK temperature. While the origin of the superhot plasma is still elusive, it has conjured up an intriguing image of in situ plasma heating near the reconnection site high above the flare loops, in contrast to the conventional picture of chromospheric evaporation. Here we investigate an extremely long duration solar flare, in which EUV images show two distinct flare loop systems that appear successively along a Γ-shaped polarity inversion line (PIL). When both flare loop systems are present, the hard X-ray spectrum is found to be well fitted by combining a hot component (T e ∼ 12 MK) and a superhot component (T e ∼ 30 MK). Associated with a fast coronal mass ejection (CME), the superhot X-ray source is located at the top of the flare arcade that appears earlier, straddling and extending along the long “arm” of the Γ-shaped PIL. Associated with a slow CME, the hot X-ray source is located at the top of the flare arcade that appears later and sits astride the short “arm” of the Γ-shaped PIL. Aided by observations from a different viewing angle, we are able to verify that the superhot X-ray source is above the hot one in projection, but the two sources belong to different flare loop systems. Thus, this case study provides a stereoscopic observation explaining the coexistence of superhot and hot X-ray-emitting plasmas in solar flares.

Study on energy release characteristics and penetration effects to concrete targets of Hf-based amorphous alloys

In this paper, the energy release characteristics and penetration effects of Hf-based amorphous alloys subjected to high velocity impact were investigated. The quasi-sealed test chamber system was used to record the impact energy release process of Hf-based amorphous alloy fragments shotted by 14.5 mm ballistic gun at elevated impact velocities. The reaction behaviors were observed by the high-speed camera and measured by the history curves of the impact reaction pressure using a piezoresistive pressure sensor. The penetration experiments of jacketed long rod projectiles (LRPs) of Hf-based amorphous alloys launching into concrete targets were carried out by 30 mm ballistic gun with velocities about 1400 m/s, where the experiments with inert steel jacketed LRPs were taken as a contrast. The video frames from the impact events were recorded by the high-speed camera. The results demonstrated that obviously shock-induced chemical reactions took place in Hf-based amorphous alloy fragments during the impact process, where the impact velocity played a significant role. Compared with the traditional steel jacketed LRPs, both the penetration depth and the crater of Hf-based amorphous alloy jacketed LRPs to concrete targets were significantly increased, which indicated that Hf-based amorphous alloy could be used to increase the damage effects of warheads.

A Robust Operation Method with Advanced Adiabatic Compressed Air Energy Storage for Integrated Energy System under Failure Conditions

Integrated energy system (IES) is an important direction for the future development of the energy industry, and the stable operation of the IES can ensure heat and power supply. This study established an integrated system composed of an IES and advanced adiabatic compressed air energy storage (AA-CAES) to guarantee the robust operation of the IES under failure conditions. Firstly, a robust operation method using the AA-CAES is formulated to ensure the stable operation of the IES. The method splits the energy release process of the AA-CAES into two parts: a heat-ensuring part and a power-ensuring part. The heat-ensuring part uses the high-temp tank to maintain the balance of the heat subnet of the IES, and the power-ensuring part uses the air turbine of the first stage to maintain the balance of the power subnet. Moreover, another operation method using a spare gas boiler is formulated to compare the income of the IES with two different methods under failure conditions. The results showed that the AA-CAES could guarantee the balance of heat subnet and power subnet under steady conditions, and the dynamic operation income of the IES with the AA-CAES method was a bit higher than the income of the IES with the spare gas boiler method.

Coronal Magnetic Field Measurements along a Partially Erupting Filament in a Solar Flare

Abstract Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare that occurred on 2017 September 6, using data obtained by the Expanded Owens Valley Solar Array. This flare event is associated with a partial eruption of a twisted filament observed in Hα by the Goode Solar Telescope at the Big Bear Solar Observatory. The extreme ultraviolet (EUV) and X-ray signatures of the event are generally consistent with the standard scenario of eruptive flares, with the presence of double flare ribbons connected by a bright flare arcade. Intriguingly, this partial eruption event features a microwave counterpart, whose spatial and temporal evolution closely follow the filament seen in Hα and EUV. The spectral properties of the microwave source are consistent with nonthermal gyrosynchrotron radiation. Using spatially resolved microwave spectral analysis, we derive the magnetic field strength along the filament spine, which ranges from 600 to 1400 Gauss from its apex to the legs. The results agree well with the nonlinear force-free magnetic model extrapolated from the preflare photospheric magnetogram. We conclude that the microwave counterpart of the erupting filament is likely due to flare-accelerated electrons injected into the filament-hosting magnetic flux rope cavity following the newly reconnected magnetic field lines.

On the fractal analysis of the serration behavior of a bulk metallic glass composite

In this work, the plastic-flow dynamics of a Zr48Cu47.5Al4Co0.5 (at.%) bulk metallic glass composite (BMGC) under varying strain rates and stress gradients were investigated. Statistical analysis on the distributions of the elastic energy accumulation rates (Ep) and L' values (L' = |d(load)/d(t)|) was conducted. A self-similar structure was observed in the distribution of the plastic-flow serrations, including the serration shape and the L' value. The three-parameter Weibull moduli of both Ep and L' values of the plastic flows have shown that the Ep values can have a relatively high uniformity while the L' values demonstrate intrinsic large variations. The fractal dimensions of both the Ep and L' values are dependent on applied strain rates and stress gradients. During the evolution of plastic flows, the Weibull moduli of both Ep and L' values decreased with the increasing of plastic strains, regardless of varying strain rates and stress gradients. Moreover, the relationships between the elastic energy accumulation and release processes were also discussed. The present findings not only shed more light on the plastic-flow dynamics of BMGCs, but also open up a window for uncovering the underlying mechanisms of the serration behavior of related solid materials.

Influence of the position and energy of local rapid heating of the supersonic gas flow on the position of the separation point on the surface of airfoil

Using numerical simulation, the study of the process of rapid local energy release in supersonic flow in a two-dimensional unsteady case and the process of separation point shift by a gas-dynamic perturbation caused by the energy input into the flow were carried out. The flow around the airfoil was modeled as laminar, and local heat release as a instantaneous isochoric process without changing the gas density. The value of energy input and the place of gas heating on the surface of the airfoil were varied. The cases of initiation of energy input at a certain distance before and after the initial position of the separation point, as well as immediately before the separation point, were considered. During obtained flow patterns processing, the displacement of the separation point position downstream, the time of this displacement, the position and size of the separation region with reattachment and the lifetime of this flow zone were determined. The obtained data can help to choose a strategy for initiating energy input in a repetitively pulsed regime, as well as in a regime of a variable position of energy release on the surface of a body, streamlined by compressible gas flow.

Detection of Flare Multiperiodic Pulsations in Mid-ultraviolet Balmer Continuum, Lyα, Hard X-Ray, and Radio Emissions Simultaneously

Abstract Quasi-periodic pulsations (QPPs), which usually appear as temporal pulsations of the total flux, are frequently detected in the light curves of solar/stellar flares. In this study, we present the investigation of nonstationary QPPs with multiple periods during the impulsive phase of a powerful flare on 2017 September 6, which were simultaneously measured by the Hard X-ray Modulation Telescope (Insight-HXMT), as well as the ground-based BLENSW. The multiple periods, detected by applying a wavelet transform and Lomb–Scargle periodogram to the detrended light curves, are found to be ∼20–55 s in the Lyα and mid-ultraviolet Balmer continuum emissions during the flare impulsive phase. Similar QPPs with multiple periods are also found in the hard X-ray emission and low-frequency radio emission. Our observations suggest that the flare QPPs could be related to nonthermal electrons accelerated by the repeated energy release process, i.e., triggering of repetitive magnetic reconnection, while the multiple periods might be modulated by the sausage oscillation of hot plasma loops. For the multiperiodic pulsations, other generation mechanisms could not be completely ruled out.

Ti3C2 MXene: A reactive combustion catalyst for efficient burning rate control of ammonium perchlorate based solid propellant

Achieving higher energy storage and controllable energy release processes is the major research goal in solid propellants. Combustion catalysts are applied to modify the energy release behavior of solid propellants but at the expense of lowering the total energy density of the propellants owing to their non-energetic feature. Here, with ammonium perchlorate (AP) based propellant as proof-of-concept material, we demonstrate a reactive combustion catalyst strategy based on the clever use of the novel structure of Ti3C2 MXene, including appropriate reactivity, high energy storage, and large specific surface area. It is found that the Ti3C2 MXene could first react with AP as fuel, releasing large amount of heat and in-situ generating TiOx/C nanosheets. The resulting TiOx/C nanosheets can further catalyze the thermal decomposition of AP by accelerating both electron and proton transfer during AP decomposition. As expected, the Ti3C2 MXene not only improves the pyrolysis reaction kinetics of AP based composites, but also increases the energy output of the propellants. The development of reactive catalysts with excellent catalytic activity and increased energy release provides a new strategy for the design of solid propellants.

Rockburst Prediction From the Perspective of Energy Release: A Case Study of a Diversion Tunnel at Jinping II Hydropower Station

As a man-made engineering hazard, it is widely accepted that the rockbursts are the result of energy release. Previous studies have examined the unloading of in-situ stress resulting from deep tunnel excavation as a quasi-static process but the transient stress variation during excavation has received less attention. This research discusses rockbursts that happened during the construction of a diversion tunnel at Jinping II hydropower station. The brittle-ductile-plastic (BDP) transition property of Jinping marble was numerically described by the Hoek-Brown strength criterion, and the dynamic energy release process derived from the transient unloading of in-situ stress was studied using an index, local energy release rate. Studies have shown that, due to transient unloading, the strain energy of the surrounding rock mass goes through a dynamic process of decreasing at first, increasing second, then reducing before finally stabilizing. The first decrease of strain energy results from elastic unloading waves and does not cause brittle failure in rock masses, which is consistent with the elastic condition but the secondary reduction of strain energy is because the accumulated strain energy in rock masses exceeds the storage limit, which will inevitably trigger the brittle failure in the rock mass. Thus, the shorter the distance to the tunnel wall the bigger and more intense the energy release. Finally, a relationship between the average value of the local energy release rate and the rockburst intensity was established to assess the risk of rockburst induced by the blasting excavation of a deep tunnel.

Dynamic characteristics analysis for energy release process of liquid air energy storage system

In order to further research the dynamic characteristics of liquid air energy storage (LAES) system under typical operating conditions, a dynamic simulation model of energy release process of the 10 MW LAES system is established in this paper. The characteristic curves of expander are considered during modeling and simulation process. The dynamic changes of key parameters, such as temperature, pressure, mass flow rate, and so on, of energy storage system over time under the startup and grid connection are simulated. The sensitivity analyses of rotor speed rising rate and frequency disturbance on the key parameters are carried out. The results show that the outlet temperature and outlet pressure of 1st expander stabilized at 395.96K and 5.37 MPa, respectively, at 602s when the rotor starts up with a rising rate of 360 rpm/min. The actual rotor speed reaches the maximum value of 3010r/min at 504s, the overspeed ratio is 100.3%. During the grid connection, the outlet temperature and outlet pressure of 1st expander stabilized at 345.6K and 3.0 MPa, respectively, at 910s, and the mass flow rate of air rises from 11.25 kg/s of the no-load operation to 23.60 kg/s. In addition, the rotor speed rising rate and frequency disturbance have great influence on the key parameters of expander. The new startup scheme of changing rotor speed rising rate have been put forward to balance the relationship between maximum rotor speed and startup time. The fluctuation amplitudes of outlet temperature, outlet pressure, power and rotor speed increase with the frequency disturbance amplitude increasing. The analysis results of dynamic simulation can provide data reference for learning the dynamic characteristics of LAES system.

Evolvement of microwave spike bursts in a solar flare on 2006 December 13

Solar radio spikes are one of the most intriguing spectral types of radio bursts. Their very short lifetimes, small source size and super-high brightness temperature indicate that they should be involved in some strong energy release, particle acceleration and coherent emission processes closely related to solar flares. In particular, for the microwave spike bursts, their source regions are much close to the related flaring source region which may provide the fundamental information of the flaring process. In this work, we identify more than 600 millisecond microwave spikes which recorded by the Solar Broadband Radio Spectrometer in Huairou (SBRS/Huairou) during an X3.4 solar flare on 2006 December 13 and present a statistical analysis about their parametric evolution characteristic. We find that the spikes have nearly the same probability of positive and negative frequency drifting rates not only in the flare rising phase, but also in the peak and decay phases. So we suppose that the microwave spike bursts should be generated by shock-accelerated energetic electrons, just like the terminational shock (TS) wave produced by the reconnection outflows near the loop top. The spike bursts occurred around the peak phase have the highest central frequency and obviously weak emission intensity, which imply that their source region should have the lowest position with higher plasma density due to the weakened magnetic reconnection and the relaxation of TS during the peak phase. The right-handed polarization of the most spike bursts may be due to the TS lying on the top region of some very asymmetrical flare loops.

Ethylenediamine Catalyzes Nitromethane Shock-to-Detonation in Two Distinct Ways.

Adding amines to liquid nitromethane (NM) is known to lower the threshold for the shock-to-detonation transition because amines catalyze proton transfer reactions that are the initial steps in the energy release process. We studied NM with 1 wt % ethylenediamine (NM/EDA) with 4 ns input shocks using time and space resolved diagnostics: photon Doppler velocimetry (PDV), optical pyrometry, and nanosecond video imaging. The 4 ns shocks are fast enough to time-resolve the reaction kinetics and the shock-to-detonation transition. We find that it is possible to shock ignite the NM/EDA without producing a detonation, so there is more to amine sensitization of the shock-to-detonation process than simply lowering the barrier to initial reactions. We find that although 1 wt % EDA has little effect on the ambient properties of NM, it dramatically alters the Hugoniot. The shock speed in NM/EDA is reduced, indicating that shocked NM/EDA is significantly more compressible than NM. Higher compressibility is associated with greater adiabatic heating, so EDA both lowers the barrier to proton transfer reactions and increases shock energy absorption. To explain the enhanced compressibility, we propose that shocking NM/EDA produces a reactive flow that has a much higher ionic strength than in NM. The sudden transformation from a molecular liquid to an ionic liquid with stronger intermolecular interactions is responsible for enhanced compressibility and shock heating.

Evaluation of operation safety of energy release process of liquefied air energy storage system

In order to solve the safety problem caused by the abnormal load shedding of the liquefied air energy storage (LAES) system during expansion process, the dynamic simulation model of the 500 kW expansion unit was established. The model is used to simulate normal shutdown and emergency shutdown of the unit, and the changes of parameters such as unit load, valve opening, and rotor speed during the expansion process are analyzed. By studying the influence of valve closing time and rotor time constant on rotor speed and rotor downtime when the unit is shut down due to accident, the value range of valve closing time and rotor time constant which can meet the safety requirements of the unit was proposed. The simulation results show that during the process of shutdown, the highest rotor speed increases first and then decreases with the increase of valve closing time when the rotor time constant remains unchanged, and the valve closing time when the highest speed reaches the maximum value is related to the rotor time constant. When the valve closing time remains unchanged, the highest rotor speed decreases gradually with the increase of the rotor time constant, but the downtime increases. The rotor time constant should be set not less than 7s, and the closing time of the control valve should not exceed 1.5s to ensure the safe operation of the expansion process of the liquefied air energy storage system.

Numerical Simulation on Energy Concentration and Release Process of Strain Rockburst

Rockburst mechanism has been a hot topic in the stability analysis of underground carven excavation, and the accurate description of energy evolution process is very critical to rockburst prediction. To study the evolution process of rockburst, such as V-shaped rockburst pit, theoretical formula derivation and numerical simulation are adopted to research the dynamic response characteristics during the formation process of rockburst pits quantitatively. The results show that rockburst intensity distribution varies with failure depth. It can be divided into three zone: slow-increase, rapid-increase and slow-decrease. For a circular tunnel with radius R, the strain energy release rate and vibration response of surrounding rock increases gradually within (0–0.06) R; reaches the peak value around (0.06–0.1) R and drops to a balance beyond 0.1R. Due to the same law of them, the rockburst risk can be conveniently predicted by monitoring vibration of surrounding rock with a certain depth. This work is beneficial to provide a good reference for rockburst prediction.

Evolution of the toroidal flux of solar coronal mass ejections derived by tracing their on-disk footpoints

<p indent="0mm">As the most violent large-scale explosive phenomenon in the solar atmosphere, coronal mass ejections (CMEs) are the main source of disastrous space weather in our solar-terrestrial environment. Detailed evolution of the toroidal magnetic flux inside CME flux ropes is still poorly understood. Recently, researchers from Nanjing University developed a new method to achieve a better identification of the footpoint regions of erupting CME flux ropes. Applying this new method, they successfully obtained and further quantitatively investigated the evolution of toroidal flux of four erupting flux ropes. They found that the toroidal flux of CME flux ropes experiences a rapid increasing phase followed by a decreasing phase. Such a two-phase evolution of toroidal flux is generally synchronous with the energy release process in CME-associated solar flares. This study provides a quantitative assessment of the variation of the toroidal flux of CME flux ropes during their eruptions, which is of vital significance for understanding the three-dimensional nature of CMEs.

Research on the Ignition Height and Reaction Flame Temperature of PTFE/Al/Si/CuO with Different Mass Ratios of PTFE/Si

Recent studies have shown that the energy release capacity of Polytetrafluoroethylene (PTFE)/Al with Si, and CuO, respectively, is higher than that of PTFE/Al. PTFE/Al/Si/CuO reactive materials with four proportions of PTFE/Si were designed by the molding–sintering process to study the influence of different PTFE/Si mass ratios on energy release. A drop hammer was selected for igniting the specimens, and the high-speed camera and spectrometer systems were used to record the energy release process and the flame spectrum, respectively. The ignition height of the reactive material was obtained by fitting the relationship between the flame duration and the drop height. It was found that the ignition height of PTFE/Al/Si/CuO containing 20% PTFE/Si is 48.27 cm, which is the lowest compared to the ignition height of other Si/PTFE ratios of PTFE/Al/Si/CuO; the flame temperature was calculated from the flame spectrum. It was found that flame temperature changes little for the same reactive material at different drop heights. Compared with the flame temperature of PTFE/Al/Si/CuO with four mass ratios, it was found that the flame temperature of PTFE/Al/Si/CuO with 20% PTFE/Si is the highest, which is 2589 K. The results show that PTFE/Al/Si/CuO containing 20% PTFE/Si is easier to be ignited and has a stronger temperature destruction effect.

A study of the global magnetic activity of the star Kepler-17 using light curve inversion with bipartite regularization

A new method of light curve inversion with bipartite regularization (LIBR), which is complementary to the previous treatments by Bonomo and Lanza and Estrela and Valio, is used to reconstruct the physical properties of star spots on the solar-type star Kepler-17 by using the full Q1- Q17 data set. The Markov Chain Monte Carlo (MCMC) method was applied to find the best profile of the reconstructed surface. The known value of the rotation inclination of Kepler-17 allows the generation of a star spot model in a sequence of stellar rotation with a period of 12.26 d. Because of the nature of the light curve inversion, the spot model is limited to the equatorial region. We also investigated the starspot lifetimes of Kepler-17 utilizing the MCMC method. Combined with the LIBR inversion results, it was found that the star spots typically last from one to several stellar rotations. From the time evolution of the spot size, a magnetic cycle period of 437 d can be derived. This value is comparatively shorter than the solar cycle which might be a consequence of the younger age (∼ 1.78 Gyr) of Kepler-17. The light curve of Kepler-17 is characterized by the presence of large-amplitude variation caused by star spots but no superflare activity. An interesting possibility is that the magnetic energy stored in the star spot regions could have been constantly dissipated by electrodynamic interaction between the central star and the hot Jupiter, Kepler-17b, via a lower-level energy release process.

Relating the Properties of Chromospheric Condensation to Flare Energy Transported by Thermal Conduction

Abstract Chromospheric condensation is a brief episode of downflow often accompanying energy release and evaporation in a solar flare. While this component of a flare reflects the energy release process only indirectly, it can be observed at high spatial and temporal resolution, even from the ground. It appears in spectroscopic observations of cooler lines, formed below ∼105 K, as a redshift that peaks and decays after less than 1 minute. In order to use this signature to infer characteristics of solar flare energy release, it is important to establish quantitative relationships with properties of the condensation. The initial investigation reported here does so after restricting consideration to energy transport via thermal conduction into a simplified, stratified chromosphere. We develop an analytical expression for the decay of a condensation propagating into a stratified atmosphere. This model provides a relationship between shock velocity and preshock density structure. We also use one-dimensional gasdynamic simulations to explore the dynamics of these shocks as they penetrate into the stratified chromosphere. We find that the peak downflow speed primarily reflects the energy flux into the chromosphere, while the product of this velocity and the redshift duration is proportional to the preshock density scale height as H ≃ 0.6u 0 τ.