Energy Conversion Characteristics Research Articles

Dynamic damage evolution of double-block ballastless track structure under train derailment impact

Train derailment is a rare event, which seriously threatens the safety of personnel and the service status of track structures along the line. Aiming at the impact damage of high-speed train on ballastless track structure, a nonlinear dynamic analysis model of vehicle-ballastless track-bridge was established based on the theory of concrete plastic damage and impact dynamics. Based on the energy conversion characteristics, the damage evolution and energy dissipation characteristics of ballastless track are studied by using the plastic damage and failure constitutive model. The results show that the contact force during sleeper collision is mainly composed of longitudinal resistance and vertical pressure. At this time, the tensile damage of ballastless track develops rapidly and the shoulder is almost destroyed. When the track bed is collided, the contact force is characterized by a single peak. At this time, the edge of the track bed is seriously damaged by tension, and the shoulder falls off due to tensile damage. At the peak position of the collision contact force, the damage of the sleeper and the track slab is the largest. Compared with the collision track bed, the ballastless track has a larger damage volume when colliding with the sleeper, and can dissipate the kinetic energy of the train faster, and the dissipated energy is 5.07 times that of the former. The research results can provide help for the repair and protection design of the early structure of the accident.

Study on gasification reaction and energy conversion characteristics of the entrained flow coal gasification based on chemical kinetics simulation

Coal gasification that converts coal into syngas is a promising technology for efficient and clean utilization of coal. Current simulations of coal gasification are mostly based on equilibrium reactions, which cannot reflect the residence time and carbon conversion rate. In this paper, the reliable chemical kinetics simulation of the coal gasification is carried out considering the solid residence time and the effects of the main parameters on the gasification performance are analyzed. The results show that the higher the O2/coal ratio, the higher the carbon conversion rate until it reaches 100 %. However, an excessively high O2/coal ratio will reduce the cold gas efficiency. Therefore, the ideal cold gas efficiency is further proposed, revealing the energy saving potential of the system by reusing the ungasified coal. Based on this, the energy conversion characteristics of the combined cycle system were analyzed, showing that the effective conversion of coal to synthetic gas is the key to improving efficiency.

Study on the energy conversion characteristics in the impeller of ultra-low specific speed pump as turbine

Study on the energy conversion characteristics in the impeller of ultra-low specific speed pump as turbine

Simulation and structural design of 2–2 PIMNT/epoxy piezoelectric composites

Piezoelectric materials are commonly used in transducers to convert electromechanical signals due to their energy conversion characteristics. We designed a PIMNT/epoxy 2–2 composite to take full advantage of the excellent beam-mode piezoelectric and acoustic features of PIMNT single crystals. Following the approach used for piezoelectric ceramic composites, we selected PIMNT piezoelectric single crystal and EPO-TEK301-2 epoxy resin for the composite, and combined finite element analysis with experimental preparation. We prepared, tested and analyzed 2–2 piezoelectric single crystal composites with varying volume fractions, which showed high electromechanical coupling properties ([Formula: see text]%) and low acoustic impedance ([Formula: see text][Formula: see text]MRayl). These encouraging findings suggest the possibility of devising high-performance ultrasonic transducers utilizing the PIMNT/epoxy 2–2 composite.

Proposal design and thermodynamic analysis of a coal-fired sCO2 power system integrated with thermal energy storage

It is essential to develop supercritical carbon dioxide (sCO2) power systems integrated with thermal energy storage (TES) to achieve efficient and flexible operation of thermal power plants. This study proposes a novel integrated configuration of the sCO2 coal-fired power system and TES. The extracted sCO2 from the high-pressure turbine inlet is utilized as the source of the stored heat, and the extracted heat is used for storage, work, and recovery in steps to decrease the feasible lowest power load ratio. While in the discharging process, the stored energy is used to heat the branched sCO2 to increase the output power. Thermodynamic models for both design and off-design conditions are developed, and the multi-parameter optimization is carried out by genetic algorithm aiming at the highest energy efficiency. The energy conversion characteristics of the heat storage/release process are obtained, and the impacts of variations in the sCO2 extraction ratio and the initial temperature of the molten salt on the performance are analyzed. The results indicate that the adjustable power load range of the integrated system widens with an increase in the sCO2 extraction ratio. When the extraction ratio reaches its maximum value of 0.2749, the minimum power load of the charging process can reduce from 30 % of the rated load to 10.47 %, and the load of the discharging process can increase from 75 % of the rated load to 88.20 %, thus enhancing the operational flexibility. At this point, the round-trip efficiency of the TES system is 67.56 %, which is mainly limited by the performance of the charging process, especially the throttling loss of the turbine. Furthermore, as the temperature of the molten salt cold tank increases, the heat storage capacity decreases, while the minimum power load of the unit increases, thereby reducing the system's flexibility.

Effect of Flow on the Energy Conversion Characteristics of Multiphase Pumps Based on Energy Transport Theory

Multiphase pumps operate under different flow conditions with different work performance. In order to reveal the energy conversion regulations in multiphase pumps under different flows, this paper presents an analysis of the effects of different flows on the pressure propulsion power, Lamb vector dispersion, and vortex enstrophy dissipation in the pressurization unit of a multiphase pump based on energy transport theory. It is found that at different flows, the pressure propulsion power near the impeller inlet decreases sharply, the pressure propulsion power is mainly located in the first half of the impeller near the suction side of the blade, and with the increase in the flow, the pressure propulsion power in the pressurization unit increases gradually, as well as its energy loss, while the Lamb vector dispersion gradually increases and the area of scattering region tends to be narrow under the small impeller tip clearance, while the Lamb vector dispersion region area slowly decreases with the flow rate when the impeller tip clearance is larger. The effect of flow on the vortex enstrophy dissipation in the multiphase pump is mainly located in the middle of the impeller near the blade pressure surface, and as the flow increases, the value of the vortex enstrophy dissipation in the impeller pressurization unit increases accordingly, and the vortex enstrophy dissipation in the first half of the impeller is even more chaotic. The investigation results have significant theoretical meaning for the deep mastery of the energy conversion characteristics in multiphase pumps.

Research on gas–liquid separation characteristics in the helico-axial multiphase pump

Due to the fact that it serves as both a pump and a compressor, the helico-axial multiphase pump is better suited for mixed-transport oil-gas two-phase flow and is frequently used for deep-sea oil extraction. The gas–liquid separation caused by the asynchrony of the gas–liquid two-phase medium is the primary cause of the damage or failure of the helico-axial multiphase pump in the project, resulting in the pump's damage or inability to operate. To investigate the variation of phase separation in the helico-axial multiphase pump under diverse operating conditions, a test system was designed and the theory of fluid flow mechanics was applied. The effects of different flow fields on the energy conversion characteristics of the pump were investigated. The results indicate that the gas–liquid separation position in the impeller occurs near the 2/3 of the airfoil bone line. After the gas–liquid separation, gas mass will be formed, pocket flow will be readily induced, and the gas block-up phenomenon will result in energy loss in the compression unit. Simulations indicate that the static pressure recovery and total pressure loss in a diffuser fluctuate over time. The static pressure recovery efficacy of the diffuser is highest when the imported gas volume fraction is 10% and lowest when the imported gas volume fraction is 60%. On the surface of the impeller blade, perpendicular to the flow direction, the separation phenomenon near the hub side is more severe than that near the rim. Along the flow direction, the pattern of phase separation is comparable.

Energy Conversion and Combustion Characteristics of Diesel and N-Alcohol Blends (N-Propanol to N-Hexanol) Under Low Ambient Temperature and Different Injection Pressures

ABSTRACT To reveal the effects of different alcohols addition to diesel on the energy conversion characteristics and combustion characteristics under low ambient temperature, diesel and four sets of blends (the volume ratio of n-propanol/diesel, n-butanol/diesel, n-pentanol/diesel, and n-hexanol/diesel being 20%/80%) were formulated. To explore the possibility of compensating for the decrease in heat value of alcohol blended fuel by increasing injection pressure, the experiments were also carried out under injection pressure of 80–160 MPa. It was discovered that the blending of alcohols into diesel significantly improved the energy conversion efficiency, and n-propanol was the most significant. In addition, the energy conversion efficiency was increased the most when the injection pressure was 120 MPa, and the energy conversion efficiency of n-propanol/diesel blend fuel was increased by 6% compared to pure diesel. However, as the carbon chain length of the alcohols increased, energy conversion efficiency gradually decreased. In addition, the impact of alcohol additives on the ignition process depends on the balance between two opposing effects, the dilution promotion effect, and the cooling inhibition effect. Both n-propanol and n-butanol blended with diesel fuel led to increased ignition delay time and combustion durations, which negatively impacted the cold start success rate and energy conversion efficiency of compression ignition engines. However, n-hexanol was found to reduce ignition delay time and combustion duration while simultaneously reducing soot radiance, making it a favorable choice as an alcohol additive for diesel fuel.

Macro- and micromechanical properties of flawed sandstone and their degradation mechanisms under hydrodynamic scouring

To reveal the degradation mechanisms of the mechanical properties of a rock mass in a reservoir bank slope under hydrodynamic scouring, a hydrodynamic scour test device was developed in this study. Sandstone specimens containing prefabricated flaws were used as the research objects. Three conditions, namely, natural conditions, hydrostatic immersion, and hydrodynamic scouring, were considered. By considering the results of laboratory testing, digital image correlation (DIC), scanning electron microscopy (SEM), and thermodynamic analysis and fractal theory, the effects of different flow states on the mechanical properties of the flawed rock mass were systematically investigated in terms of the macromechanical parameters, strain field, strain energy, and microstructure. A crack initiation stress identification method based on the differentiation rate of the effective variance of strain fields was proposed. The energy conversion in the rock loading process was quantitatively characterized using three strain energy characteristic indicators. The internal microstructure of the rock was quantitatively characterized using a combination of SEM image characteristics and the fractal dimension. It was found that the uniaxial compressive strength, elastic modulus, crack initiation stress, energy storage limit, elastic strain energy conversion rate, and dissipated strain energy conversion rate of the hydrodynamically scoured specimen were the smallest, while the fractal dimension was the largest. There was a strong correlation among the mechanical parameters, energy characteristic indicators, and fractal dimensions of differently treated sandstone specimens because the macromechanical response and energy conversion characteristics of a rock mass are closely correlated with changes in its internal structure.

Energy Conversion Characteristics of an In-Line Mixing Pump in Solid–Liquid Two-Phase Dynamic Mixing

Energy Conversion Characteristics of an In-Line Mixing Pump in Solid–Liquid Two-Phase Dynamic Mixing

Electro-mechanical-thermal energy coupling characteristics analysis and EFMM-based energy modelling for machine tools considering dynamic thermal environment

Machine tool is an isolated thermodynamic and inefficient energy-consuming system, whose energy consumption is increasingly influenced by its internal thermal environment. While the thermal environment changes dynamically due to the complex electro-mechanical-thermal (EMT) energy conversion characteristics. Therefore, it is urgent to expound the multi-energy coupling mechanism to establish an accurate energy model for machine tool. However, the existing studies merely emphasize the electro-mechanical conversion that related to the material-removal (MR) process and fail to reveal the dynamic characteristics of energy caused by EMT, which results in inaccurate energy models. In light of this, the energy flow matrix modelling (EFMM) method, which can model the multi-energy flows automatically and accurately, is introduced to construct a generic energy balance matrix equation for machine tool, where the coupling relationship between electrical, mechanical and thermal energy are taken into consideration. Subsequently, the dynamic mechanical and thermal energy are analyzed, respectively. Based on this, the total energy consumption and cutting energy efficiency models for machine tool in a dynamic thermal environment are established. The reliability and accuracy of the constructed models are demonstrated by the case study and comparative analysis. The results indicate that the average relative errors of the proposed energy models are mostly within 5 %. The presented approach is conducive to understanding the multi-energy coupling characteristics and providing a feasible way for energy-efficient machine tools.

Multivariate and multi-interface insights into carbon and energy recovery and conversion characteristics of hydrothermal carbonization of biomass waste from duck farm

High lipid, high nitrogen duck manure (DM) with high lipid, high lignocellulosic litter materials (LM) are the main wet biomass wastes from duck farms and both are naturally abundant carbon resources. The synthesis of duck farming biomass waste into carbon-rich materials for high value utilization by hydrothermal carbonization (HTC), which can directly treat wet biomass, has not been investigated. In this study, the physicochemical properties of hydrochar derived from co-HTC of DM and LM and its carbon and energy recovery patterns were systematically investigated under multivariate conditions of raw materials ratios, solids contents, temperatures and residence times. The application of synchrotron-based near-edge X-ray adsorption fine structure technique (C K-edge NEXAFS) combined with gas chromatography-mass spectrometry (GC–MS) to the hydrochar and hydrothermal liquid, respectively. At multiple interfaces provided an in-depth analysis of the important material transformations of the co-HTC process and the structure of the hydrochar. Extending residence time (180 min) and increasing LM ratio (M@4%) in co-HTC reaction of DM and LM is beneficial to achieve hydrochar containing higher carbon content (44.84%) at lower reaction temperatures (180 °C). The heating value (HHV) of the hydrochar ranges between 17.12 and 25.05 MJ/kg. The carbon recovery rate of the co-HTC of DM and LM all exceeded 55% and was more closely related to the carbon content of the hydrochar than to its yield. Additionally, the model ERR=0.97±0.01CRR+2.40±0.71 (R2 = 0.99, P < 0.01) was developed to predict energy recovery rate (ERR) based on carbon recovery rate (CRR). Esters were an important intermediate during co-HTC of DM and LM, and the derived hydrochar consisted of a wide range of polycyclic aromatic hydrocarbons, alkanes and N-aromatic heterocycles as well as polyfuran, pyrrole and pyridine structures.

A new design for thermophotovoltaic cell thermal management under high-flux irradiation

Efficient thermal management plays a significant role in a thermophotovoltaic system, especially in exploring the energy conversion characteristics of thermophotovoltaic cells (TPVC). If the cooling effect is insufficient, it is easy to cause temperature differences along the thickness direction of the cell. Meanwhile, temperature non-uniformity will cause electrical mismatch loss and reduce the reliability of cells. Therefore, a new design of a double-sided asymmetric cooling arrangement for testing the energy conversion performance of the TPVC at high-flux irradiation is proposed. This design consisted of a multi-channel water-cooling structure at the back (lower surface) of the TPVC, and the nitrogen is used to cool the TPVC radiation surface (upper surface). A three-dimensional structural computational model was created to examine the potential of the new design to lower cell temperature. According to the simulation results, compared with the conventional method, when the temperature of the radiation source is 2000 K, 2500 K, and 3000 K, the energy conversion efficiency has been improved by 7.23%, 17.97%, and 24.12%, respectively. Double-side cooling has a 30% higher uniformity at high-flux incident radiation than single-side cooling. Therefore, this new design model not only reduces the temperature difference between the upper and lower surfaces but also increases the temperature uniformity.

Study on the energy conversion characteristics in the impeller of USSPAT based on velocity triangle space decomposition

With the development of micro-hydropower generation, traditional pump as turbine (PAT) is difficult to meet the needs of micro-hydropower for developing dispersed and small-flow water resources. Ultra-low specific speed pump turbine (USSPAT) has broad prospects in micro-hydropower generation in remote mountainous areas due to its advantages of larger output power at a small flow rate. In this paper, the dimensionless number ξ to measure the power output capacity of the fluid particle ξ is proposed based on the velocity triangle space decomposition. The impeller is the only energy conversion component in (USSPAT). The study of ξ in the impeller of USSPAT found that the area with the largest output power of the impeller is mainly concentrated in the area with a larger impeller radius, and the overall power output of the impeller increases with the increase of flow rate. The local high-speed jet formed by the rotor-stator interaction (RSI) between the impeller and the volute at the inlet of the region S is the fundamental reason for the NP and jet-wake phenomenon in the impeller. W* = 0.9 is the critical value of NP in region S. The jet wake formed in region A makes the critical value of the region decrease along the flow direction. Therefore, the region A is the core region of the NP inside the impeller. In addition, the secondary flow at the impeller outlet is the main reason for the NP in this region. In addition to 0.6Qd, the secondary flow intensity increases with the increase in flow rate, and WLF inhibits the secondary flow intensity in the wear ring area. However, at a small flow rate (0.6Qd), the WLF gradually enters the mainstream, which weakens the inhibition of the secondary flow in the wear ring region and promotes the secondary flow intensity in the downstream.

Investigation on the influence of bucket’s flow patterns on energy conversion characteristics of Pelton turbine

Efficient energy conversion can improve Pelton turbine unit efficiency and bring higher economic benefits. However, the reasons that influence the energy conversion characteristics of the Pelton turbine have not been effectively revealed. The main reason is the lack of systematic research on the change process of flow patterns in the bucket and its relationship with the energy conversion characteristics. Experimental and numerical simulation studies of a Pelton turbine were conducted. The change process of the flow patterns from when the jet enters the bucket to when it is completely discharged is analyzed and three main flow patterns in the buckets are summarized. Through energy characteristic analysis, it was found that during the power change process of the bucket, the flow rate entering the bucket and the velocity moment at the inlet of the bucket shows a trend of first increasing and then decreasing, while the velocity moment at the outlet of the bucket and flow loss show an opposite trend, resulting in the most sufficient energy conversion when the jet is perpendicular to the bucket. The basic topology of the bucket energy conversion process is constructed to effectively understand the Pelton turbine's energy conversion characteristics.

Multi-Time Interval Dynamic Optimization Model of New Energy Output Based on Multi-Energy Storage Coordination

In response to the problem of mismatch between new energy output and multi-energy load requirement in multi-energy power systems, this article proposes a dynamic optimization model for new energy output in multiple time intervals based on multi-energy storage coordination. First, considering the energy conversion characteristics of multi-energy storage, the dynamic optimization method of new energy output based on the discrete division of subinterval of scheduling time is studied. Then, considering the cost of adjusting various resources comprehensively, the optimization objective of new energy output is studied, and a model-solving method based on a directed graph topology distributed algorithm is proposed. Finally, simulation verification was conducted, and the simulation results showed that the method proposed in this paper can effectively suppress the new energy fluctuation and reduce peak-shaving costs.

Effect of relative chamber width on energy conversion and mechanical characteristics of the offshore OWC device: A numerical study

Effect of relative chamber width on energy conversion and mechanical characteristics of the offshore OWC device: A numerical study

Ductile–brittle quantitative evaluation of rock based on post-peak properties under true triaxial stress

To quantitatively evaluate the influence of high true three-dimensional stresses on the ductile–brittle behaviours of rock in deep underground engineering, a series of true triaxial compression tests with different stress levels were carried out on marble and four kinds of granite. The influences of true triaxial stress states (σ2, σ3) on the post-peak characteristics were analysed, and a new normalized ductile–brittle evaluation index was proposed based on post-peak energy conversion characteristics of rock under true triaxial stresses. The ductile–brittle behaviours of rock were divided into four qualitative levels, namely, ductile-brittleness, transitional, brittleness and super-brittleness, and the influences of true triaxial stress states on the ductile–brittle behaviours of rock were quantitatively investigated. The research shows that as σ2 increases or σ3 decreases (that is, the differential stress between σ2 and σ3 increases), the brittleness of rock increases, and its increase rate gradually decreases and tends to be stable, transforming from ductile-brittleness to transitional, brittleness and super-brittleness and resulting in super-brittleness being easily induced by low-σ3 and high-σ2 conditions. When the differential stress between σ2 and σ3 is small, the intrinsic characteristics of rock itself have an obvious influence on ductile–brittle behaviours. When the differential stress between σ2 and σ3 is large, all kinds of rocks can exhibit super-brittle behaviour. The change of stress controls the evolution of rock ductile–brittle behaviours, and high-stress controls rock brittleness. The rock brittleness under true triaxial stress is significantly higher than that under conventional triaxial stress at the same σ3. σ2 induces an increase in rock brittleness and causes the decay rate of brittleness to decrease with increasing σ3, and σ2 increases the upper limit of σ3 for brittle failure of rock. The enhancement effect of σ2 on rock brittleness must be considered when evaluating the brittle failure of deep surrounding rock under high-stress conditions; otherwise, the risk of brittle failure may be underestimated.

Pore-scale evaluation on a volumetric solar receiver with different optical property control strategies

Pore-scale flow and heat transfer model is built for a volumetric solar receiver subjected to highly concentrated irradiation, in order to provide insight into the detailed thermal and hydrodynamic performance. Direct three-dimensional simulations on the coupled radiation-convection-conduction are performed based on the Weaire-Phelan structure which is used to represent the open-cell ceramic foam absorber. The energy conversion characteristics with two ceramic materials (SiC and Al2O3) are firstly predicted and compared. And then several cases focused on the control approaches for the optical property (absorption/reflection/emission) of the solar absorber are introduced and investigated, including gradient surface absorptivity, spectral selectivity, and combination design of semi-transparent and opaque configuration. The results show that a moderate volumetric effect can be achieved at very low inlet fluid velocity for both ceramic materials, however presenting low conversion efficiency. Increasing the inlet velocity could enlarge the thermal non-equilibrium between solid and fluid phases and lower the outlet temperature. SiC absorber shows improved performance compared to Al2O3 absorber, and the efficiency changes obviously with the inlet velocity, while a variation of 24% is found. The optical property of the absorber front region significantly affects the overall performance. Decreasing absorptivity design and spectral selective design both show positive impact, especially for the Al2O3 absorber with an increment by 33% in efficiency relative to the basic one. Among the different strategies, spectral selective improvement shows the best effectiveness. Besides, adding porous fused silica as the front absorber layer can effectively move the high-temperature area inward at a cost of small decrement in efficiency, herein, honeycomb structure shows preponderance compared to the foam silica.

Comparative life-cycle assessment of various harvesting strategies for biogas production from microalgae: Energy conversion characteristics and greenhouse gas emissions

Biogas production via anaerobic digestion is highly attractive in the realm of microalgae technology. However, the microalgae harvesting strategies for biogas production has yet to be comprehensively evaluated. Here, a comparative life-cycle assessment for microalgae harvesting scenarios of centrifugation (CT), sedimentation and centrifugation (SD-CT), flocculation and centrifugation (FC-CT), flocculation and electro-flotation (FC-EF) were conducted to evaluate the energy conversion characteristics and environmental impacts. The results showed that harvesting strategies significantly affected the net energy yield of the whole system. Only scenarios FC-CT and FC-EF achieved positive net energy yield of 0.17 and 0.04 MJ with 1 MJ net energy output. The net energy yield of scenarios SD-CT and CT were negative (−0.11 and −1.92 MJ) because of the low harvesting efficiency and high electricity consumption. The net GHG emissions of the four scenarios were all positive, and scenario FC-EF achieved the least GHG emissions (21.86 g CO2-eq MJ−1). According to the nutrient balance analysis of carbon, about 15 percent carbon from flue gas was fixed by microalgae in the form of soil fertilizer (9.32%) and biomethane product (5.63%–6.60%). Additionally, harvesting efficiency and biogas yield had the most profound impact on the parameters for two-step and one-step harvesting scenarios.