High-pressure Test Research Articles

Experimental investigation of stress corrosion on supercritical CO2 transportation pipelines against leakage for CCUS applications

Carbon Capture, Utilization and Storage (CCUS) is one of the key technologies that will determine how humans address global climate change. For captured CO2, in order to avoid the complications associated with two-phase flow, most carbon steel pipelines are operated in the supercritical state on a large scale. A pipeline has clear Stress Corrosion Cracking (SCC) sensitivity under the action of stress and corrosion medium, which will generally cause serious consequences. In this study, X70 steel was selected to simulate an environment in the process of supercritical CO2 transportation by using high-temperature high-pressure Slow Strain Rate Tensile (SSRT) tests and high-temperature high-pressure electrochemical test devices, with different O2 and SO2 contents. Studies have shown that 200 ppm SO2 shows a clear SCC sensitivity tendency, which is obvious when the SO2 content reaches 600 ppm. The SCC sensitivity increases with the increase of SO2 concentration, but the increase amplitude decreases. With the help of advanced microscopic characterization techniques such as scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), through the analysis of fracture and side morphology, the stress corrosion mechanism of a supercritical CO2 pipeline containing SO2 and O2 impurities was obtained by hydrogen embrittlement fracture characteristics. With the increase of SO2 content, the content of Fe element decreases and the corrosion increases, demonstrating that SO2 plays a leading role in electrochemical corrosion. This study further strengthens the theoretical basis of stress corrosion of supercritical CO2 pipelines, plays an important role in preventing leakage of supercritical CO2 pipelines, and will provide guidance for the industrial application of CCUS.

Effect of High-Pressure Tests on the Mechanical Properties of Kh70 Steel and the Stress Corrosion Cracking Resistance

Effect of High-Pressure Tests on the Mechanical Properties of Kh70 Steel and the Stress Corrosion Cracking Resistance

Lessons Learned from a Prematurely Ended High-Pressure Air Injection Test in a Light Oil Naturally Fractured Reservoir

Summary Sixty billion barrels of oil still reside in the matrix of mature onshore and offshore Mexican reservoirs located in the southeast basins after primary and secondary recovery. Capillary and viscous forces are responsible for this amount of oil retained within the pore structure of the matrix (immobile oil). Gravitational forces are not enough to counterattack these forces due to the high fracturing intensity. On the other hand, laboratory testing demonstrates that oil residing in the matrix could be mobilized by the exothermic reaction that takes place with air injection. Air injection in homogeneous heavy and light oil sandstones and nonfractured limestones, at small or large scales during short and long periods of time, is feasible for producing resources technically and economically nonrecoverable by other means. However, to the best of our knowledge, the published literature does not report any application of an air injection project in naturally fractured reservoirs. During 2015, an air injection pilot test was performed in a light oil naturally fractured reservoir in Mexico, referred to as “A” field. The implementation of the pilot test was preceded by its corresponding laboratory study, which consisted of five accelerating rate calorimeter (ARC) tests and two combustion tube (CT) experiments. The analysis of the aforementioned experimental work led us to corroborate that air and oil react at reservoir conditions. Based on the above finding, the pilot test was conducted by injecting air at a rate of 10 MMscf/D with a wellhead pressure of 4,500 psia for 1.5 years, which was followed by a 1.5-year production period giving a total of 3 years for the pilot test. The results indicate that combustion was successfully applied in the reservoir. However, no oil was produced. This paper discusses the results of a prematurely ended air injection pilot test in “A” field and the main lessons learned from it, which could help in the design and its subsequent implementation in other naturally fractured reservoirs.

Manufacturing Process Development and Rig Validation of Slurry Environmental Barrier Coatings for SiC Ceramic and SiC Composite Sub-Components

The process scale-up of fully oxide-based environmental barrier coatings (EBCs) on sintered SiC and chemical vapor infiltration (CVI) SiC/SiC ceramic matrix composite (CMC) sub-components was investigated using various slurry manufacturing processes (dip, spray, spin–dip). The performance of EBC-coated sub-components (SiC heating element, SiC/SiC ceramic matrix mini-composite, SiC airfoil, SiC/SiC CMC airfoil) was evaluated in steam oxidation and combustion rigs. Steam oxidation was conducted at 1427 °C in 90 vol.% H2O (g) + 10 vol.% O2 (g) with a 1 h hold at 1427 °C per cycle (1 h hot and 20 min cooling). For high-pressure combustion rig testing, the EBC surface temperature ranged between 1354 °C and 1538 °C with the temperature gradient through CMC + EBC ranging between 100 °C and 150 °C. Dip and spin–dip are non-line-of-sight processes, whereas spray is a line-of-sight process. The three processes, collectively, demonstrated the capability to manufacture slurry EBCs on sub-components with various shapes and sizes. There was no discernable disparity in the EBC steam oxidation performance between the coupons and sub-components in this study and coupons in a previous study. The dependence of steam oxidation rates on the substrate chemistry reported previously was confirmed. The steam oxidation rate of EBC-coated sintered SiC, compared with EBC-coated CVI CMC, was ~2 times and ~1.5 times higher after 100 h and 500 h, respectively, due to the boron sintering aid in sintered SiC. An EBC-coated CMC airfoil after 150 15-h-long cycles in a high-pressure combustion rig test showed only limited EBC spallation along the leading edge and more substantial spallation along the trailing edge, demonstrating the feasibility of an oxide-based bond coat to meet the extreme temperature requirements of next-generation EBCs.

One-step method to prepare coccinellaseptempunctate-like silver nanoparticles for high sensitivity SERS detection

The surface morphology of metal particles can be adjusted by the annealing process to enhance the activity of Raman substrate and achieve an ultra-low concentration detection limitation. In this study, a surface-enhanced Raman scattering (SERS) substrate of coccinellaseptempunctate-like silver nanospheres coated with a silver nanoisland structure (Ag NI@Ag NSs) was prepared using a simple annealing process. Numerous silver nanospheres were dispersed on the surface of the silver nanoislands, which exhibited a single crystal plane (111) orientation. The SERS substrate had an enhancement factor of 108 for Rhodamine B (Rh B) and was highly sensitive to phosphoethanolamine (PETA). The SERS response toward PETA showed excellent correlation during the range of 5 × 10−7 - 1 × 10−5 mol/L with the detection limitation as low as 5 × 10−7 mol/L, and the correlation coefficient is 0.9918. The simulated high-pressure test showed that the SERS response could be still observed at 1100 m sub ocean pressure even with a PETA concentration of 1 mM. The test results of selectivity, reproducibility, and accuracy indicated that the Ag NI@Ag NS sensor possessed potential applications in the deep-sea analytical and other related fields.

Experimental study on the evolution of mechanical properties of hot dry rocks under alternating temperature loads

Inspired by the physical process of thermal expansion and cold shrinkage, this study proposes a new idea to improve the capacity to form complex fractures (i.e., fracability) in hot dry rock (HDR) under alternating temperature loads. However, the evolution of the HDR mechanical properties under alternating temperature loads is rarely reported. This study analyzed the evolution mechanism of the HDR rock mechanics properties under alternating temperature loads by using the high-temperature high-pressure rock mechanics triaxial test system. The results show that mechanical parameters such as compressive strength, dilatancy stress, and elastic modulus are significantly reduced after alternating temperature loading, compared with those after simple heat treatment. After alternating temperature loading, compared with the case of simple heat treatment, the HDR rock samples reach the dilatancy stress earlier; its stress-strain curve features a visible concave arc at the micro-fracture closure segment; the axial loading ends up with the shear failure and enhanced complexity. The microstructural analysis shows that cyclic thermal stress occurs inside the HDR as the temperature increases and extensive mineral metasomatism is triggered, which is dominated by quartz penetrating plagioclase via metasomatism. Therefore, the decrease of quartz content and the HDR mineral metasomatism under alternating temperature loads are the fundamental causes for the great changes in the HDR mechanical properties.

Effect of Outlet Boundary Condition on the Acoustic Modeshape and Flame Dynamics of a Partially Premixed Swirl Stabilized Combustor

Abstract Industrial gas turbines commonly use lean premixed swirl stabilized combustors that are prone to thermo-acoustic instabilities. Combustor testing involves several steps ranging from atmospheric to high-pressure conditions. An open outlet boundary condition is maintained for atmospheric tests commonly, whereas high-pressure testing involves complex exit boundary conditions, which change the reflection coefficient and can affect the nature of instability. Current work aims at studying how the change in outlet boundary affects the nature of instability due to changes in the exit reflection coefficient and acoustic mode shape inside the combustor. A laboratory-scale industrial swirl burner that uses partially premixed methane and air at atmospheric conditions is analyzed for this purpose. A constant area contraction ratio of 6.5:1 is maintained at the exit of the combustor while varying the inlet Reynolds number at a constant global equivalence ratio. Flame dynamics based on conditional phase averaged OH* chemiluminescence images and spatial Rayleigh index maps were used to compare different flow rate and exit boundary cases. The outlet contraction affects both the frequency and amplitude of the dominant thermoacoustic mode. The orifice plate at the exit reduces the outlet reflection coefficient leading to a change in acoustic mode shape inside the combustor. Overall, the instability amplitude is reduced considerably for cases with an orifice plates at the exit boundary compared to open exit boundary cases. The results show the importance of defining outlet boundary conditions as a parameter in combustion instability studies. Care should be taken while comparing and interpreting results from different facilities where outlet boundary condition is different.

Study on hydrogen embrittlement susceptibility of X80 steel through in-situ gaseous hydrogen permeation and slow strain rate tensile tests

Hydrogen embrittlement is a serious threat to the safety operation for hydrogen blended natural gas pipelines. To determine the critical safety hydrogen blending ratio, in-situ high-pressure gaseous hydrogen permeation tests and slow strain rate tensile tests of X80 pipeline steel were conducted in the simulated hydrogen blended natural gas environments with 0–20 vol% hydrogen. The permeability characteristics, mechanical properties and fracture morphologies were systematically analyzed, and the embrittlement mechanism was discussed. Results show that the subsurface hydrogen concentration, ductility loss and hydrogen embrittlement susceptibility increased significantly as hydrogen blending ratio increased from 10% to 15%. Moreover, a positive correlation between subsurface hydrogen concentration and hydrogen embrittlement index was revealed. Combining the gaseous hydrogen permeation, SSRT results and fracture analysis, the 10% hydrogen blending ratio was determined as the conservative critical value for the safety operation of X80 hydrogen blended natural gas pipelines.

Durability of EPDM geomembranes - Lifetime estimation by using high pressure autoclave test method

For determination of end of service life different accelerated ageing tests are available. However, ageing of modern polymers in conventional oven ageing tests takes many years. In high-pressure autoclave test (HPAT), thermo-oxidative ageing is caused by elevated temperature and by elevated oxygen availability. This results in significantly shorter test times of around 8 months. An EPDM geomembrane was submitted to thermo-oxidative ageing in high pressure autoclaves (HPA) at 3 temperatures (75 °C, 80 °C and 85 °C) and 3 elevated oxygen pressures (5 bar, 10 bar and 51 bar). During exposure in HPAT the oxidation progress was monitored via tensile tests and oxygen pressure measurements. Tensile strength decreases steadily with increasing exposure time, temperature and oxygen pressure. Based on 75% residual tensile strength as theoretical failure criteria and Arrhenius based 3D extrapolation model, time till failure for service temperature at atmospheric condition was calculated. As a result, service life of about 360 years at 40 °C and atmospheric pressure was estimated.

Study on Flow Model and Flow Equation of Shale Gas Based on Microflow Mechanism

Shale gas storage and permeability space is between nanometers and micrometers and has strong multiscale characteristics, resulting in highly complicated shale gas flow. Therefore, the development of shale gas needs to clarify the seepage mechanism of shale gas and establish a flow model and flow equation that can analyze shale gas flow. In this paper, based on the single nanotube model, combined with the Weiyuan-Changning shale gas demonstration zone of the target layer of the Longmaxi formation shale core high-pressure mercury pore throat test results, the contribution of seepage, diffusion, transition flow, and free molecular flow to shale gas flow was calculated. The contribution of seepage and diffusion is over 95%, and seepage and diffusion are the main flow pattern. Then, a shale gas seepage and diffusion coupled flow model and coupled flow equation were established. A method for calculating shale permeability and diffusion was proposed using the relationship between flow pressure and shale gas velocity. Finally, shale gas flow experiment analysis was carried out to verify that the established shale gas flow model and flow equation can describe the shale gas flow well. The result shows that the flow rate of shale gas is composed of seepage flow rate and diffusion flow rate. The seepage flow rate is proportional to the pseudopressure difference and proportionate to the low-pressure squared difference. The diffusion velocity is proportional to the difference in shale gas density, and the pressure difference in low pressure is proportional. As the pressure of a shale gas reservoir decreases, the proportion of diffusion flow increases. The research results enrich the understanding of shale gas flow; it also has particular reference significance to the development of shale gas reservoirs.

Inhibition of N-vinylpyrrolidone on hydrate in high-pressure flow system under the synergistic effect of ether compounds

Through the experimental tests as performed on a high-pressure flow loop test bench, the synergistic effect of diethylene glycol monoethyl ether (DEGEE), propylene glycol methyl ether (PM), and ethylene glycol phenyl ether (EPH) on the inhibition of inhibitors on hydrate growth was explored under the same initial temperature (285.15 K), pressure (5.0 MPa) and flow rate (230 L/h). The average particle size, relative inhibition performance factor (RIP), and initial formation rate of methane hydrate in the system with a single kinetic inhibitor (or monoalcohol ether synergistic agent) were obtained by experiments, and compared with the relevant parameters in the system with a kinetic inhibitor and a synergistic agent. The experimental results show that the presence of PVP in the system increases the average particle size, which may be due to the adsorption of kinetic inhibitors on hydrate crystals. When the relative inhibition performance factor was used as the index, all the three kinds of synergistic agents promoted the inhibition performance of PVP. DEGEE had the best promotion effect, EPH was the weaker, and PM was the weakest. The synergistic agents in the composite system had little effect on the initial formation rate of hydrate. The addition of kinetic inhibitors and synergistic agents would transform the hydrate formation medium from the wall to the gas–water interface, while the presence of the oil phase in the system significantly weakened the inhibition performance in the kinetic inhibitor-synergist system. The results and theories obtained in this experiment can provide a theoretical basis for the flow guarantee in actual pipelines.

Identification of ductile fracture design curve for hardened quasi-brittle AISI-D2 tool steel to predict shearing tool failure

Tool deformation and fracture during the shearing of ultra-high-strength steel has become a severe problem. Finite element (FE) simulations can help to solve this problem by evaluating improved tool edge designs, but they require the strain/stress range in which no fracture occurs. This study accordingly identified these properties for conventional and improved AISI-D2 tool steels by shearing them in sheet form using harder tools. First, the work-hardening parameters were fitted so that the FE simulation agreed with the measured punching force vs. stroke curves fitted using the Swift and Voce laws for the conventional and improved steels, respectively, at plastic strain levels exceeding 0.1. The plastic strain ε¯p vs. historically averaged stress triaxiality η¯ plots were derived from each element in the FE simulation at the punch stroke corresponding to fracture. The safe zone against ductile fracture was evaluated as a set of ε¯p — η¯ plots, and the exponential curves through the realms of these safe zones were drawn as the ductile fracture design curves. This evaluation suggested a drastically large fracture strain in the negative η¯ region compared with the fracture strain obtained using high-pressure tensile tests also conducted in this study. The effectiveness of the proposed method was confirmed as it clearly indicated the superiority of the improved AISI-D2 steel material.

Study on the Construction Method and Effects of Ipsilateral, Multi-Nozzle, High-Pressure Jet Grouting Cut-Off Wall

High-pressure jet grouting is widely used in the construction of cut-off wall in hydraulic engineering. Compared to the high-pressure jet grouting used for foundation improvement, the high-pressure jet grouting cut-off wall of hydraulic engineering has lower requirements for the advance consolidation and provision of bearing capacity, and more focus on providing an anti-seepage effect and ensuring the continuous integrity of the wall. In the past, the research on high-pressure jet grouting focused more on the application to foundation treatments, and the research on the construction efficiency of cut-off wall is relatively insufficient. Therefore, in this study, a self-developed ipsilateral multi-nozzle jet grouting machine with a large drill diameter and construction method are proposed according to the construction characteristics of the embankment cut-off wall in hydraulic engineering. Based on the dyke protection projects, Jinggangshan navigation hydropower and Xingan navigation hydropower, the large-diameter, multi-nozzle, high-pressure jet cut-off wall test is carried out, and the wall forming effect of the cut-off wall is verified through the combination of indoor and outdoor tests. The results show that the proposed construction method can adapt to the formation conditions in which it is difficult to implement conventional high-pressure jet grouting, and obtains good construction efficiency. A favorable wall quality can be obtained by using more efficient large-diameter and ipsilateral multi-nozzle jet grouting in the construction of high-pressure jet cut-off wall.

Analysis of Flow Characteristics of Straight Conjugate Crescent Gear Pump at Variable Working Conditions

The working conditions (i.e., gas content, working pressure, and working temperature) of oil in the actual hydraulic system are always in a dynamic process, which will cause the basic properties of oil (i.e., density, absolute viscosity, and effective bulk modulus) to change and further generate changes of the flow characteristics in the straight conjugate crescent gear pump (SCCGP). However, no clear explanation has been given for the variation of the flow characteristics of the SCCGP with the working conditions in previous studies. This paper first expounds the gear pair profile equations used to draw the tooth profile curves and the equation applicable to the calculation of the geometric displacement at the given geometric parameters. Subsequently, the mathematical models of the oil’s basic properties are analyzed, and it is explained how the changing working conditions affect the changes in oil properties. After that, the paper designs an orthogonal test scheme and applies it to the study of the flow characteristics of the SCCGP for the first time to optimize its working conditions. Then, the paper performs simulations in commercial CFD numerical software, and the change laws of the internal flow field, flow pulsation, pressure pulsation, volumetric efficiency, and total efficiency of the SCCGP at different working conditions are analyzed in detail. The working conditions for decreasing pulse rate and improving total efficiency are summarized. Finally, for model validation purposes, the paper elucidates the construction process of a high-pressure positive displacement pump test system and carried out experimental research. The simulation and actual measurement results are compared under the same working conditions. The results validate the accuracy of the simulation model and the potential for future analytical studies.

Geotechnical characterization of deep Shanghai clays

To date, investigations of soils in Shanghai have mainly focused on upper clays, namely, Layer 2–6, generally within 30–40 m depth. Knowledge of the deep clays of Layer 8 and 10, at depths of approximately 50 m and 100 m, respectively, is very limited. In this study, the detailed geotechnical properties of the deep Shanghai clays of these two layers were investigated through a series of field and laboratory tests. Physical property tests showed that both clays can be classified as low-plasticity silty clay. For the first time in Shanghai, high-quality intact clay samples were retrieved from the deep soil using a double-tube rotary sampler. High-pressure oedometer tests and consolidated undrained (CU) triaxial tests were conducted to evaluate the compressibility and shear strength of intact samples. The oedometer tests indicate that Layer 8 is an overconsolidated clay with an overconsolidation ratio (OCR) of 2–3, and Layer 10 is a normally consolidated clay with a light degree of structure. CU triaxial tests further confirmed the above findings. The compressibility of the Layer 8 clay is lower, and its undrained shear strength and effective friction angle are larger than those of Layer 10, with the latter being deeper. The sensitivity framework, based on Burland's intrinsic compression line (ICL) and sedimentary compression line (SCL), can be used to characterize the overconsolidation/structure nature of the deep Shanghai clays. The strain energy method was found to be more suitable than the Casagrande method for determining the preconsolidation pressure of the deep Shanghai clays.

High-Pressure PEMWE Stack and System Characterization

As the urgency to decarbonize the industry and transport sector intensifies, renewable energy-based hydrogen production via advanced low temperature water electrolysis is attracting increased interest. Proton exchange membrane water electrolysers (PEMWE) offer several benefits over the more mature alkaline water electrolysis technology, including its load-following capability and the ability to operate at higher pressures. The latter is important because significant benefits can be harvested by adopting systems operating at pressure-levels compatible with the end use applications and thereby render the mechanical compressor redundant. At IFE we have developed a methodology which encompasses detailed energy- and techno-economic calculations of high-pressure systems, and a comparison between high-pressure electrolysis and state-of-the-art electrolysis at 30 bar in combination with a compressor has been carried out. Here, direct pressurization to 80 and 200 bar (relevant for, e.g., methanol and ammonia production) was found to be economically viable.To realize high-pressure H2 generation systems, many challenges related to system operability, efficiency and safety needs to be addressed. As part of the national infrastructure “The Norwegian Fuel Cell and Hydrogen Centre”, Institute for Energy Technology (IFE) has installed a flexible PEM water electrolyzer system platform for testing of small-scale prototype electrolyzers up to 33 kW and 200 bar differential pressure. The test rig is integrated with a sophisticated power conditioning system which consists of three custom-built DC/DC-converters (for PEMWE, PEMFC, and Li-ion battery systems), all coupled to the same DC-bus. This configuration makes it possible to test different hybrid electric topologies and to emulate different loads (e.g., grid load profiles, wind generation). This one-of-a-kind high-pressure PEMWE test facility at IFE is well suited to study performances of next-generation PEMWE stacks and systems, and to tailor and test control strategies that safeguards the system and maximizes efficiency and durabilityThe test rig has been commissioned with a prototype high-pressure stack with a production capacity of 2 Nm3/h (Nel Hydrogen), and the identified economically viable pressure range of 80-200 bar has been the main target for an experimental test campaign. The experimental results are presented from stack testing including polarization curves and EIS data as a function of temperature, pressure and current density. The results are discussed in relation to the techno-economic model, in order to identify pathways towards more efficient hydrogen production. Figure 1

CO2 hydrate stability in oceanic sediments under brine conditions

Carbon capture and storage (CCS) is a critical approach to reducing atmospheric carbon emissions. The United Nations [UN] Climate Change Conference COP26 Glasgow [2021] emphasized setting execution plans to reach the goal of a zero-carbon economy by 2050 as per the Paris Agreement [2015]. CO2 sequestration in deep-sea sediments in the form of clathrate hydrates is a promising technique as it provides a significant capacity for CO2 storage. Deep-sea sediments contain high salinity water, which will impair the CO2 storage capacity and hydrate stability. Therefore, it's essential to examine the effect of salinity on CO2 hydrate stability in simulated deep-sea sediments to foster real-time field application.In this first-gen experimental work, the stability of CO2 hydrates across and inside the deep oceanic saline sediments has been evaluated for an extended period [14 days]. An artificial seabed, saturated with saline solution [3.5 wt% NaCl], was created using silica sand inside a high-pressure reactor system and stability tests were conducted at oceanic conditions (10 MPa, 4 °C). In phase 1, CO2 hydrates were formed across the seabed by pressurizing the system multiple times to 3.5 MPa using pure CO2 gas. In phase 2, the hydrates were immersed in a brine solution [3.5 wt% NaCl] and their stability was observed over 2 weeks [>14 days]. The experimental results indicate that CO2 hydrates are adequately stable when submerged inside the brine solution and layers of hydrates were visible at the end of 2 weeks of the stability experiment. In phase 3, a hybrid depressurization heating approach was used at the end of the stability test to confirm the presence of a good quantity of CO2 hydrates inside the sand bed.

Experimental and numerical investigation on off-design performance of a high-pressure centrifugal compressor in compressed air energy storage system

In order to explore the off-design performance of a high-pressure centrifugal compressor (HPCC) applied in the compressed air energy storage (CAES) system, the author successfully built a high-pressure centrifugal compressor test rig for CAES, whose designed inlet pressure can reach 5.5 MPa, and carried out some experiments on adjustment of inlet guide vanes (AIGVs), adjustment of rotational speed (ARS) and adjustment of inlet pressure (AIP). Firstly, by analyzing the experimental data with the angle of AIGVs varying from −20° to +50°, it can be concluded that the mass flow range is widened by 41.18 %, the maximum efficiency is increased by 3.28 %, and the maximum pressure ratio can realize a slight increase. Then, the comprehensive performance map of the HPCC with AIGVs is obtained through interpolating the existing experimental data. Subsequently, the comparison between experimental and CFD results has been analyzed. Since the losses in the inlet expansion joint and outlet expansion joint, the aerodynamic performance obtained by experiments is slightly lower than CFD. Afterwards, the experiments on the ARS are carried out by three different speeds, and the change regulation of the performance by ARS is obtained. Lastly, the experiments on the AIP are carried out by seven different inlet pressure, when the inlet pressure of the HPCC is >50 % of the designed pressure, the results after simulated modeling are very close to the experiment results of the designed pressure. But once the inlet pressure is lower than 50 % of the designed pressure, the further the inlet pressure deviates from the designed pressure 5.5 MPa, the further the performance curve obtained by simulated modeling deviates from the design working condition. In this research, the experimental performance of a high-pressure centrifugal compressor applied in CAES under off-design conditions was obtained for the first time, which is of great significance to the research and development for the CAES system in the future.

Pore Structure Characteristics and Strength Variation of Red Sandstone under Freeze-Thaw Cycles.

To study pore structure characteristics and the strength of red sandstone under freeze–thaw cycles, the saturated red sandstone was studied by the combination of freeze–thaw cycle test, high-pressure mercury injection test, uniaxial compression test and theoretical analysis, and research shows that: with the increase of freeze–thaw cycles, the pores of red sandstone continue to expand and extend, macropore volume and the total pore volume increases gradually, and the pore size distribution curves become more continuous. Porosity of samples after 10, 30, 70 and 100 freeze–thaw cycles is 1.14 times, 1.17 times, 1.28 times and 1.44 times of that of 0 cycle, and the uniaxial compressive strength of samples is 0.68 times, 0.53 times, 0.26 times and 0.17 times of that of 0 cycle, respectively. With the increase of freeze–thaw cycles, freeze–thaw damage continues to accumulate, the crack propagation direction changes from axial through-through failure mode to transverse and axial simultaneous failure mode. Taken the change of porosity as a parameter, through the regression analysis of the test data, the functional relationship between uniaxial compressive strength and the change of porosity in red sandstone is established. The research results will provide a theoretical basis for stability research of slopes of railway subgrade in cold region.

Internal inflow study on a high-pressure centrifugal compressor with shroud and backside cavity in a compressed air energy storage system

The internal flow field and loss distributions are quite complicated in the high-pressure compressor with shroud and backside cavity applied in the compressed air energy storage (CAES) system. It’s necessary to develop physical understandings on the internal flow and losses inside the impeller, shroud cavity and backside cavity by the physical synergy relationship between some key quantities, which is innovatively applied to the internal flow of a high-pressure compressor used in CAES. First, the author successfully built a high-pressure centrifugal compressor test rig for CAES, and carried out the high pressure performance experiment for the first time. The aerodynamic performance of the high-pressure centrifugal compressor is compared by experiment and calculation. Then, the main flow characteristics and loss generation inside the impeller has been studied by analyzing the synergy between velocity and temperature gradient, and some other important quantities. And, the leakage flow characteristics inside the shroud cavity and backside cavity has been discussed by analyzing the synergy between velocity and pressure gradient, and some other key quantities. It is found that the regions where the high energy losses and entropy generation locate correspond to the relatively high synergy angle. At last, the interaction between leakage flow and main flow has been researched through clarifying the loss of temperature and radial velocity. It is found that there exit two boundary lines for leakage flow injecting into main flow.