Search

Two-dimensional (2D) halide perovskites represent the natural semiconductor quantum wells (QWs), which hold great promise for optoelectronics. However, due to the hybrid structure of Ruddlesden-Popper 2D perovskites, the intrinsic nature of hot-carrier kinetics remains shielded within. Herein, we adopt CsPbBr

Ni3Al-based alloys have drawn much attention as candidates for high-temperature structural materials due to their excellent comprehensive properties. The microstructure and corresponding mechanical properties of Ni3Al-based alloys are known to be susceptible to heat treatment. Thus, a significant step is to employ various heat treatments to derive the desirable mechanical properties of the alloys. This paper briefly summarizes the recent advances in the microstructure evolution that occurs during the heat treatment of Ni3Al-based alloys. Aside from γ′ phase and γ phase, the precipitations of β phase, α-Cr precipitates, and carbides are also found in Ni3Al-based alloys with the addition of various alloying elements. The evolution in morphology, size, and volume fraction of various types of secondary phases during heat treatment are reviewed, involving γ′ phase, β phase, α-Cr precipitate, and carbides. The kinetics of the growth of precipitates are also analyzed. Furthermore, the influences of heat treatment on the mechanical properties of Ni3Al-based alloys are discussed.

Recently, the γ′-strengthened superalloys are of great interests in high temperature applications due to their excellent high temperature strength which is derived from the γ′ strengthening phase. For these γ′-strengthened superalloys, the changes in morphology, size and distribution of γ′ precipitates due to coarsening during thermal exposure have a significant impact on the properties of alloys. This article briefly summarizes the recent advances on the coarsening behavior of gamma prime precipitates in the recently-developed γ′-strengthened superalloys and its effects on the hot deformation behavior of superalloys, drawing specific examples on Allvac® 718PlusTM and Ni3Al-based intermetallic superalloys. It is found that the particle size plays an important role in morphological evolution of γ′ precipitates. For instance, the morphology of γ' precipitates evolves from cuboidal to strip-like or other complex structures in Ni3Al-based intermetallic alloys, while the γ' precipitates in Allvac® 718Plus alloy always present near-spherical morphology due to the relatively small initial particle size. The Lifshitz-Slyozof-Wagner (LSW) theory and its modifications, as well as Trans-Interface Diffusion Controlled (TIDC) theory have been applied to describing the coarsening kinetics of γ' precipitates. Additionally, the hot deformation behavior of γ′-strengthened superalloy is found to be greatly influenced by the coarsening of γ′ precipitates.

Carbon nanofiber (CNF) is a promising nanomaterial to prepare the strain sensor due to the simple preparation and high controllability. Despite the sensors have been developed based on CNFs, it is still a challenge to detect the full deformation with high sensitivity. In this study, we prepare the aligned semitransparent graphene-reinforced CNF membrane (G-CNFM) by electrospinning. The anisotropy of sensing performance of the ultrathin sensor was demonstrated. The sensor along parallel direction shows high sensitivity in the wide strain range of 0.1–38%. Moreover, the high durability can be obtained for over 1000 cycles at the subtle strain of 0.1% and high strain of 30%. The high linearity was also obtained under the low strain. The low sensitivity was exhibited along perpendicular direction, and the sensor was still working for 1000 cycles at 60% strain. The sensing mechanism was analyzed according to the microstructures of cracks. The thickness, the aligned degree and the width of G-CNFM and the thickness of TPU substrate show effects on the strain levels and sensitivity. The strain sensors can detect the full deformation caused by personal physiological movements and body motions. The sensor made using aligned G-CNFM may be used for various smart wearable electronic applications.

The single screw compressor (SSC) is widely used in air compression and refrigeration systems due to its many advantages. The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance. In this paper, mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights. The refrigerating capacity, volume efficiency and adiabatic efficiency of the SSC are calculated and discussed. Three prototypes, with different meshing clearance heights, were manufactured to study the internal influence mechanisms. The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results. Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%–7.98% and 5.92%–9.4%, respectively. Based on the models, analysis under varying meshing clearance heights and working conditions was performed. Taking into account working performance, actual manufacturing conditions and manufacturing cost limitations, a meshing clearance height range from 0.01 mm to 0.08 mm is suggested. This study can provide important theoretical data and experimental support for the design, manufacturing and optimization of single screw compressors.

Influence of solidification rate on the interdendritic microstructure evolution of a multiphase Ni3Al-based superalloy was investigated. Compared to the original as cast sample, rapid solidification rate leads to high nucleation burst of α-Cr precipitates in spray casting alloy, which promotes the transformation from b.c.c. B2 β phase to f.c.t. L10 martensite plates with high density of stacking faults and microtwins in interdendritic regions.

In present work, a multiphase Ni3Al-based intermetallic alloy with complex components of γ'+γ dendrite comprising extremely high volume fraction (81 vol %) of γ′ phase and interdendritic β phase is investigated, the microstructure evolution and phase transformation behavior tailored by different solution cooling rates are studied by applying different cooling methods of water cooling (WC, 138 °C/s), air cooling (AC, 72 °C/s), and furnace cooling (FC, 0.05 °C/s) after solution treatment at 1200 °C for 10 h. Results show that the cubic degree, size and volume fraction of cuboidal primary γ′ as well as size of spherical secondary γ′ particles in the γ'+γ dendrite are improved by decreasing cooling rates, and the average sizes of the primary and secondary γ′ particles are found to meet logarithmic relationships with cooling rates. There are three kinds of precipitates in the interdendritic β phase resulted from different cooling methods, i.e., the rod-like Cr3C2 carbides, the semi-spherical α-Cr particles, and the long acicular γ′ precipitates. The lower cooling rate decreases the number of rod-like Cr3C2 carbides, increases the number and size of the semi-spherical α-Cr particles, and promotes the formation of long acicular γ′ precipitates in the interdendritic β-matrix. The semi-spherical α-Cr particles play the role of pinning dislocations in the β-matrix and have the orientation relationship of [‾110]α-Cr//[‾110]β-matrix. In addition, the precipitation of semi-spherical α-Cr particles in β-matrix is observed to accomplish in two sequential stages and grow in an onion-like ordered way. Stacking faults existed in partial of α-Cr particles due to the nanotwins in β-matrix. Microtwins are observed in the interdendritic β-matrix after water cooling, which have a bimodal configuration of nanotwins at the microtwinning boundaries and interior stacking faults. Besides, γ′-envelope formed between the γ'+γ dendrite and interdendritic β phase dependent on the solution cooling processes.

Thermal performance of molten salts can be enhanced by nanostructured materials, which can enhance the heat transfer capacity of heat pipes and further improve the global efficiency of Concentrated Solar Power plants. In this work, a eutectic mixture of sodium bromide, potassium bromide, lithium bromide and calcium bromide acted as the base salt, into which nine SiO2 nanoparticles in three diameters were dispersed to form twenty-two nano-bromides in total. The thermodynamic properties of the base salt and nano-bromides, e.g. the thermal stability and the phase change performance were investigated experimentally and analytically. It was observed that the size and the mass concentration of the SiO2 nanoparticles exhibited significant influence on the heat of fusion and the decomposing temperature but little on the melting point. By adding 0.7 wt% of 10 nm SiO2 particles, the heat of fusion and the decomposing point of the base salt were increased by maximum 99.19% and 68.4 °C respectively. In addition, densely dendritic-like networks were observed with Scanning Electron Microscopy in the nano-bromides and considered to be responsible for the improvement of the heat of fusion and the decomposing point. The authors believed these findings would contribute to enhance the heat transfer performance of heat pipes furtherly.

The morphological evolution and coarsening kinetics of γ′ precipitates in the γ'+γ area of a Ni3Al-based alloy during isothermal aging at temperature range of 800 °C to 1000 °C have been investigated. For the aging temperature above 900 °C, the average size of γ′ precipitates increases and the morphology of γ′ precipitates gradually changes from cuboidal to strip-like and L-shaped with increasing aging time up to 50 h. The temporal evolution of the average size of γ′ precipitates is evaluated by the experimentally measured data and it suggests that the cube rate law fits better for experimental data at the early stage coarsening, while the square rate law fits better for the later stage coarsening. Moreover, using these determined values of coarsening rate constants which determined by using a coarsening rate equation based on the LSEM model, the activation energy of the early stage and later stage coarsening have been calculated as 174.2 kJ/mol and 186.3 kJ/mol, respectively.

The MXenes with excellent chemical and physical properties are novel and promising electrode materials for supercapacitors. However, aggregation and restacking of MXene sheets limit material’s electrochemical performance. Here, we report a method to prevent MXene sheets from restacking and significantly improved electrochemical capability of Ti3C2Tx MXene by intercalating with N-doped carbon (NC) introduced from ZIF-8. Ti3C2Tx MXene sheets were prepared by etching Ti3AlC2 powder in HF, then ZIF-8/Ti3C2Tx composite was prepared, followed by annealing in H2/Ar atmosphere. Benefited from higher specific surface area and electron conductivity, the obtained NC-Ti3C2Tx hybrid shows the quick charge/discharge rate up to 3.0 V s−1, little IR drop at 50.0 A g−1, higher specific capacitance of 82.8 F g−1 at 1.0 A g−1 (about 210% of the origin), and 100% retention in capacitance after 5000 cycles. This new and effective approach efficiently enhanced the electrochemical performance of Ti3C2Tx MXenes and improved them as one of auspicious electrode materials in future energy storage devices.

In this paper, a free piston expander-linear generator (FPE-LG) experiment rig equipped with different linear generator (LG) is established. A comparison study on the performance of FPE-LG with different LGs is conducted. Then the operation characteristics and output characteristics of FPE-LG are investigated. The results show that the selection and design of LG has significant influence on FPE-LG performance. The displacement and velocity with LG-1 are higher than that LG-2’s, but the operation stability and output performance with LG-2’s are better. Considering the high pressure and temperature operation conditions in ORC system, LG-2 is suitable for this experiment rig. Both actual stroke and velocity increase with intake pressure and external load resistance. The variations of actual stroke, velocity, indicated efficiency, voltage and power output are more sensitive to intake pressure than external load resistance. The maximum power output can reach up to 111 W. The voltage output is in agreement with that of velocity. The peak voltage output is usually obtained when the velocity reaches peak value. The energy conversion efficiency shows first increases and then decreases with external load resistance and intake pressure. The maximum energy conversion efficiency of 74% can be obtained.

The microstructure evolution and creep behavior of a novelly designed as-cast Ni3Al-based superalloy with multiphase configuration are investigated by high-temperature annealing treatments. The as-cast microstructure comprises dominant γ′+γ dendritic and less (~19.37 vol%) interdendritic β areas, annealing treatments at 1160–1280 °C promoted the growth of γ'Ⅰ phase in the γ'+γ dendrite, during which the interdendritic β phase aggregated and coarsened rapidly in width with keeping its relatively constant volume fraction. Meanwhile, the annealing treatments significantly promoted the precipitation of quasi-spherical α-Cr phase particles within the β phase. The original as-cast microstructure exhibited inferior creep resistance at 800 °C/200 MPa with the shortest creep rupture life of 194 h, however, the annealing treatments at 1160–1280 °C prolonged the creep rupture life to beyond 611 h. Although the steady-state creep rate was gradually reduced with increasing annealing temperatures, the creep ductility was degraded by higher-temperature annealing at 1240 and 1280 °C compared with original as-cast microstructure. The 1160 °C annealed microstructure exhibited the longest creep rupture life of 665 h and the maximum creep strain to fracture of 3.21%, while the minimum steady-state creep rate was obtained on account of the largest γ'Ⅰ phase sized 0.91 µm after annealing at 1280 °C. Despite its positive role in the castability, thermoplasticity and weldability of the explored multiphase Ni3Al-based superalloy, interdendritic β phase has negative effects on the creep properties due to its incoherent existence with the dominant γ′+γ dendrite.

The present paper experimentally investigates the thermal performances of an Organic Rankine Cycle (ORC) using a self-developed single screw expander. Experiments were conducted to study the net efficiency of the ORC under different cooling water flows in different seasons. Taking the power consumed by the circulation pump, cooling water pump, cooling tower fan and lubricant oil pump into account, the experimental results showed that the maximum value of produced net power and net efficiency achieved 3.27 kW and 3.04%, respectively, obtained at a cooling water flow of 12 m3 h−1 in winter. The experimental results also reported that the shaft power and shaft efficiency of the expander increased gradually with growth of cooling water flow. Under the same evaporating temperature, the performances of the ORC system deteriorated with the increase of ambient temperature, and the net efficiency of the system in summer was decreased by more than 16.45% than that in winter. In addition, the power consumption by the cooling system was the largest factor restricting the net efficiency than the power consumption by other auxiliary machines. Therefore, reducing the power consumption by the cooling system can effectively enhance the net efficiency of the ORC system.

The two-phase (liquid and gas) flow distribution in the header of a plate-fin heat exchanger was experimentally investigated. Small mass fractions of the liquid phase in the liquefaction process of natural gas were considered in this study. The liquid and gas flow velocity were measured using optical methods such as PIV/PTV/LIF. The flow maldistribution of liquid and gas flows was quantified and addressing this problem by attaching a porous baffle or modifying the inlet nozzle configuration was studied. The results showed that a vane swirler with a diffuser enhanced the flow distribution of both the liquid and gas phases fluid.

A single-screw expander (SSE) is a type of volumetric expander that can be applied to low-grade heat and waste heat recovery utilizing the organic Rankine cycle system. In this paper, a new thermodynamic modeling of SSEs considering the friction power consumption is carried out to examine the performance. The mathematical model was verified by experimental results, and the calculation results have a good agreement with the experimental results. The clearance height has great influence on the expander performance. The influence of clearance height on the leakage flow rate, friction power consumption, volumetric and isentropic efficiency were investigated. Results show that path L 8 , L 7 and L 2+4 are the three main leakage paths, and path L 8 , L 7 and L 9 are the three main friction power consumption. Compared with the meshing clearance height, the fitting clearance has a more significant effect on the performance of SSEs. Setting a higher fitting clearance and meshing clearance is an effective measure to reduce friction power consumption and prevent gaterotor wear, respectively. It would be favorable if the fitting and meshing clearance height is no less than 0.04 mm and 0.02 mm, respectively.

Portable natural gas liquefaction devices are widely used to exploit unconventional natural gas resources and one of key components is a compressor. In this paper, a new natural gas liquefaction process is simulated and optimized and a single-screw compressor with 200 mm diameter is designed to be applied in this process. To verify the performance of the single-screw compressor, an experimental system was set up and performance parameters were studied, including volumetric efficiency, specific power rate, shaft efficiency, irreversible loss rate and cooling efficiency of the lubricating oil. The influence of the lubricating oil on the volumetric efficiency was also observed. Furthermore, the impact of actual compressor performance on the liquefaction process was also analyzed. The results indicate that the performance of the compressor changes greatly when it operates deviating from its design condition. The maximum volumetric efficiency, shaft efficiency, irreversible loss rate and cooling efficiency of the lubricating oil are 0.91, 0.64, 0.56 and 0.22, respectively. The minimum specific power rate is 6.5 kW·(m3·min−1)−1. In addition, the lubricating oil has a good effect of sealing so that the volumetric efficiency can be improved by 10.5%. Considering the actual performance of the single-screw compressor, specific power consumption of the process increases by 43.3%.

To recover high pressure energy in a letdown station, a high pressure single screw expander (HPSSE) with 117 mm diameter is developed in our laboratory recently. This study presents the results of an experimental survey on the performance of HPSSE under varied inlet pressure and rotational speed. The inlet pressure of HPSSE ranges from 1.0 MPa to 5.0 MPa and the rotational speed is from 1500 rpm to 3000 rpm. The experimental results show that when the inlet pressure is 5.0 MPa, the maximum power output, volumetric efficiency, isentropic efficiency and shaft efficiency of HPSSE are 56.55 kW, 80.57%, 62.55% and 50.96%, respectively. The volumetric efficiency is immensely affected by inlet pressure under fairly slow rotational speed and a slight change in volumetric efficiency is observed under considerably high rotational speed. A high rotational speed is an effective method to reduce leakage in large pressure difference working conditions.

A single-screw expander (SSE) is a type of volumetric expander that can be applied to power generation, which is beneficial for energy conservation and environment protection. Investigating the SSE leakage characteristics is necessary because leakage has a significant influence on the SSE performance. This study provides theoretical and experimental analyses of the SSE internal leakage with compressed air as the working fluid. Both mathematical model of different leakage paths and leakage model have been established. The simulation model was verified by experimental data at internal volume ratios of 2.95 and shows a maximum deviation of 3.63%. Results show that fitting clearance height and rotational speed could clearly influence the volumetric efficiency and power output. The diameters of both the screw and the gate rotor could also significantly influence the volumetric efficiency. The volumetric efficiency decreased with the increase in internal volume ratio.

Microalgae gasification in the presence of Fe2O3 oxygen carrier and CaO additive was investigated in a fixed bed reactor to simulate the reactions in direct chemical looping gasification, focusing on the thermal behavior of CaO in synthesis gas production and multiple redox cycles. The results showed that Fe2O3 as oxygen carrier improved the synthesis gas but brought much more CO2 generation, lowering the gas LHV. Introducing CaO efficiently inhibited CO2 release and improved CO and H2 production, and gasification efficiency and gas LHV elevated from 55.2% and 13.27 MJ/N m3 to 66.2% and 14.85 MJ/N m3 at 850 °C. CaO mainly played as CO2 absorbent and hardly had catalytic effects on tar crack for synthesis gas production at 650 °C. At 850 °C, CaO mainly played as catalyst and still had a great selectivity for synthesis gas production. The CaO/C molar ratio of 0.5 was sufficient for achieving its function. The multiple redox experiments showed that the gas efficiency and carbon conversion declined in the second reduction and kept at 60.1 ± 1.2% and 77.4 ± 1.5% respectively in 2–10 cycles. XRD and SEM-EDX results showed the coverage of CaO, the formation of calcium ferrites and CaO deactivation accounted for the variation of oxygen carrier reactivity in multiple cycles.

In this work, we report a high-performance strain sensor with ultra-sensitivity under the subtle strain and large sensing strain range based on Ecoflex rubber and carbonized natural yarns. The flexible strain sensor based on wrapping yarn with carbon nanofiber yarn as sheath and natural silk yarn as core can capture ultralow detection limit ( cotton yarn as sheath and silk yarn as core endowed the sensor with wide strain range from 0.1% to 130%, high sensitivity for the subtle deformation, quick response time (

The compressed air-powered system is widely studied as a promising, environment-friendly, and high-efficiency technology. The influences of centrifugal and filter oil-gas separator on the performance of single screw expanders for compressed air-powered systems are experimentally investigated. Results show that the intake volume flow rate using the centrifugal oil-gas separator is lower than that of the filter oil-gas separator. Meanwhile, the temperature difference between the inlet and outlet of a single screw expander, the average output power, and the average shaft efficiency by using the centrifugal oil-gas separator is 1.88, 1.67, and 1.42 times higher than that of the filter oil-gas separator under the same working condition in this study. The maximum expansion ratio in this work is 8.5 by using the centrifugal oil-gas separator. The actual total output power, effective working time, and exergy efficiency by using the centrifugal oil-gas separator are respectively 56.67%, 4.51%, and 92.52% substantially higher than that of the filter oil-gas separator. The performance of single screw expanders in compressed air-powered systems can be improved by using the centrifugal oil-gas separator.

Precipitation and growth behavior of mushroom-like Ni 3 Al phase along the dual phase (γ + γ′) and eutectic γ − γ′ area interfaces of as-cast JG4246A Ni 3 Al-based alloy were investigated by using short time cyclic heat treatment. Results showed that vacancies, small angle grain boundaries and dislocations formed along the dual phase (γ + γ′) and eutectic γ − γ′ area interfaces during the cyclic heat treatment, which promoted the precipitation of Ni 3 Al phase along this location. In addition, concentration gradient of Al elements between the eutectic γ − γ′ area and dual phase (γ + γ′) areas and the more rapid pipe diffusion provided by dislocations contributed to growth of directional mushroom-like Ni 3 Al phase.

Glucose oxidase-mediated starvation therapy that effectively cuts off energy supply holds great promise in cancer treatment. However, high glutathione (GSH) contents and anoxic conditions severely reduce therapy efficiency and cannot fully kill cancer cells. Herein, to resolve the above problem, this study constructed a biomimetic nanosystem based on nanreproo-MnO2 with porous craspedia globose-like structure and high specific surface area, and it was further modified with dopamine and folic acid to guarantee good biocompatibility and selectivity toward cancer cells. This nanosystem responsively degraded and reacted with GSH and acid to regenerate O2, which significantly increased intracellular O2 levels, accelerated glucose consumption, and improved starvation therapy efficiency. Moreover, anticancer drug of camptothecin was further loaded, and notably enhanced cancer growth inhibition was obtained at very low drug concentrations. Most importantly, this novel therapy could unprecedentedly inhibit cancer cell migration to a very low ratio of 19%, and detailed cell apoptosis analyses revealed late stage apoptosis contributed most to the good therapeutic effect. This work reported a new train of thought to improve starvation therapy in biomedicine, and provided a new strategy to design targeted nanocarrier to delivery mixed drugs to overcome the restriction of starvation therapy and develop new therapy patterns.

At present, the most prominent technical problems of small and medium capacity expanders are low internal efficiency and small expansion ratio. In order to promote the practical application of small and medium capacity Organic Rankine Cycle (ORC) system, improving the thermodynamic performance of the expander was a remarkable issue, and the systematic research on the irreversibility of expander's working process is the fundamental work to achieve this goal. Summarizing the related research on various small capacity volumetric expanders, the research on flow problem is lacked. For an atypical volumetric expander, the flow mechanism of single screw expanders (SSEs) is more complex. In this paper, we discussed the effect of the pressure loss in the inlet and exhaust passages on the performance of SSEs. We selected two SSE prototypes developed by our laboratory to carry out the experiment under variable working conditions. The internal volume ratios are 2.95 and 3.98 respectively. The pressure differences of inlet and exhaust passages were measured. In order to evaluate the effect of the flow losses on the performance, we defined two indexes: pressure loss rate (PLR) and pressure energy loss influence rate of shaft efficiency (PELRe). From the results, the pressure losses of inlet and exhaust passages for each SSE increase gradually, PLRin increases slightly and PLRout increases gradually. At the maximum point of shaft efficiency, the losses of the SSE with 2.95 are 28.06 kPa and 46.09 kPa, and the values of the SSE with 3.98 are 37.58 kPa and 33.79 kPa, respectively. It shows that the pressure losses are relatively high. The maximum values of internal and external expansion ratio for the SSE with 2.95 are 4.8 and 6 respectively, and the values of the SSE with 3.98 are 5.7 and 7 respectively. For ideal volume expansion, the internal expansion ratio of two prototypes should be 4.55 and 6.9, respectively. Summarizing the above results, how to enhance the pressure drop effect of leakage and reduce the flow resistance loss of inlet and exhaust passages simultaneously is an important technical premise to improve the expansion ratio by structural optimization. Meanwhile, PELRe of two prototypes are 16.01% and 13.59% respectively at the point. It shows that the flow losses of inlet and exhaust passages could significantly influence the performance of SSEs.

To study the hot deformation behavior of Ni3Al-based alloy, hot compression tests were conducted in the temperature range of 1050–1250 °C with the strain rates from 0.01 to 10 s−1. With the increase in deformation temperature and the decrease in strain rate, flow stress of the Ni3Al-based alloy would be decreased. Based on the obtained constitutive equation, the calculated values of peak flow stress are in good agreement with the experimental ones, and the activation deformation energy is determined as 802.71 kJ/mol. Moreover, by dynamic material model (DMM), processing maps of the hot-deformed Ni3Al-based alloys are established. It is indicated that the optimum processing parameters for the studied alloy correspond to deformation temperature of 1250 °C and strain rates from 0.01 to 0.1 s−1. Specimens deformed under the optimum processing conditions exhibit fine and uniform grains, which is a typical dynamic recrystallization (DRX) microstructure. The DRX degree could be effectively enhanced with the increase of deformation temperature and the decrease of strain rate.

This paper reports a fundamental experimental investigation of the start-up characteristics of heat pipes using a dedicated molten-salt mixture as the working fluid. Based on four single salt, i.e. NaNO3(AR), KNO3(AR), LiNO3(AR) and Ca(NO3)2(AR), a quaternary molten-salt working fluid was developed and charged at different masses into four heat pipes with the same dimensions of 980 mm in length and 22 mm in diameter. A parallel comparison on the start-up performance of these heat pipes was then conducted to observe the influence of the charging mass and the inclination angle under the consistent lab-controlled conditions. The experimental results showed the heat pipe with molten-salt charge of 40 g responded much quicker than those with molten salt charge of 60 g, 70 g and 80 g respectively; meanwhile, the molten-salt heat pipe achieved the maximum condensation temperature at inclination angle of 50°. Comparing to the conventional naphthalene heat pipe, the dedicated molten-salt heat pipe had a much shorter start-up time when they were charged with the same amount of 40 g. The overall research result is expected to provide certain guidance for further design and operation of molten-salt heat pipe in high-and-medium-temperature heat transfer and storage scenarios.

Computational fluid dynamics (CFD) methods have been widely used in simulating internal flow of rotary positive displacement type compressors and expanders, especially for twin screw, scroll and rolling piston machines. But it is still lack of CFD research on single screw compressors and expanders due to the difficulty of spacial screw curved surface of single screw structure and the working principle of symmetrical intake and six screw groove simultaneous discharge in single screw machines. In order to investigate internal unsteady flow characteristics and improve the performance of single screw machines, CFD analysis in a single screw expander has been given in this paper. The STAR-CCM+ commercial software and its dynamic mesh technology have been applied to simulate the single screw expanders. The air has been selected as the working fluid of single screw expander and the ideal gas equation of state has been used to analyze its properties. The simulation results show that the periodic variation in pressure and velocity of single screw expander have been carried out, the pressure cloudy chart of internal flow field of single screw expander has been obtained.

As a thermal control system for space applications, the vapor compression heat pump is crucial for the future development of aerospace technology. The evaporator in the heat pump is significantly affected by the space environment. Lubricant is present in the system during the operation, and the gas-liquid separation is difficult to achieve in a microgravity environment. The oil-containing refrigerant may form an oil film on the evaporator wall, and deposition may occur. A mixed flow and heat transfer model of the refrigerant and lubricating oil in the evaporator of the vapor compression heat pump was established to investigate the gas-liquid separation and lubricating oil deposition of the vapor compression heat pump in microgravity. The heat flux effects on the flow and heat transfer characteristics were simulated in normal gravity and microgravity using FLUENT. The simulation and experimental results of the evaporator outlet temperature in normal gravity were compared, and the simulation results of the heat transfer coefficient of the refrigerant R134a were compared with experimental data obtained from the literature. The results demonstrate that the velocity field exhibits a large gradient and an asymmetric distribution in normal gravity and an asymmetric distribution with lower values in the lower and upper right positions in microgravity. The heat transfer performance of the evaporator is lower in microgravity than in normal gravity for the same heat flux. For the same heat flux (100000 W/m2), the vapor phase volume ratio of the evaporator outlet is 0.95-1 in normal gravity and 0.6-0.7 in microgravity. After the phase change of the refrigerant and lubricant mixture in the evaporator, the lubricant deposition is not affected by the heat flux in normal gravity and microgravity, and normal oil return occurs. A maximum deviation of 14.9% is observed between the simulated and experimental values of the evaporator outlet temperature in normal gravity. The heat transfer coefficient of the R134a obtained from the simulation is within the range of the experimental values in the literature. This work expands our understanding of microgravity two-phase flow heat transfer and provides theoretical guidance for the development of the evaporator in vapor compression heat pumps for aerospace applications.

This paper presents a mathematical model of torque for Single screw expanders (SSEs). Instantaneous torque and torque ratio were analyzed and discussed. The periodic variation of instantaneous torque is the same for different inlet pressure levels. The torque ratio, with its value close to 1, is independent of the inlet pressure of SSE. An experimental system was established to measure the torque, power and shaft efficiency of the self-developed SSE prototype, and results were used to validate the model. Comparison shows that the difference between calculated and experimental torque values is small (6.58 N.m to 7.55 N.m). The calculated and experimental output power is similar, with a difference of 2.07 kW to 2.37 kW. Therefore, the proposed model can be used to estimate the torque and output power of SSEs.

The transition from fossil fuels to green renewable resources presents a key challenge: most renewables are intermittent and unpredictable in their nature. Energy storage has the potential to meet this challenge and enables large scale implementation of renewables. In this paper we investigated the dynamic performance of a specific Adiabatic Compressed Air Energy Storage (A-CAES) plant with packed bed thermal energy storage (TES). We developed for the first time a plant model that blends together algebraic and differential sub-models detailing the transient features of the thermal storage, the cavern, and the compression/expansion stages. The model allows us to link the performance of the components, in particular those of the thermal storage system, with the performance of the whole A-CAES plant. Our results indicate that an A-CAES efficiency in the range 60–70% is achievable when the TES system operates with a storage efficiency above 90%. Moreover, we show how the TES dynamic behaviour induces off-design conditions in the other components of the A-CAES plant. Such device-to-plant link of performance is crucial: only through integration of TES model in the whole A-CAES model is possible to assess the benefits and added value of thermal energy storage. To the authors’ knowledge the present study is the first of this kind for an A-CAES plant.

A test bench of a multistage centrifugal pump was constructed using R123 as working fluid in simulative organic Rankine cycle (ORC) conditions. Experimental results of the pump under various operating conditions were obtained based on controlled working frequency and mass flow rate. The effect of the key pump parameters on the ORC performance was analyzed in this study. In addition, the control strategy of the pump was presented. Results show that the overall pump efficiency was between 15% and 65.7%. The outlet pressure, pump efficiency, and ORC thermal efficiency increased with the working frequency of the pump. The mass flow rate needed to be regulated as the frequency became increasingly high. The maximum thermal efficiencies of the ORC system corresponding to various working frequencies of the pump were observed. Furthermore, back work ratio (BWR) can reach up to 0.45 with the increase of the evaporating temperature of the ORC system. Pumping power should not be neglected for small-scale ORC applications, and pump efficiency assumptions should be dependent on experiments. Low pump efficiency affected the increase of the thermal efficiency and net power of the ORC system. The superheat degree was also discussed.

Vapor compression refrigeration is considered as ideal miniature cooling system for miniature electronic systems and portable cooling systems. Many applications of the miniature refrigeration system are working under the situations (such as aviation field, individual combat system and automobile air conditioning, etc.) that exist bump, tilt, and even flip, which will severely degrade the performance of the miniature refrigeration system. In order to study the influence of compressor’s tilt angle on refrigeration system, a test bench was built and the performance experiments were made. The results show that the compressor’s tilt angle has a great impact on the refrigeration system performance. When the compressor worked at the maximum tilt angle of 60°, COP-c and COP-h of the system change periodically. When the compressor works in full load, the maximum tilt angle for compressor is 20°. When the compressor tilt angle is 15°, there is an optimal amount of refrigerant charge, and corresponding COP-c and COP-h reach the maximum of 2.9 and 3.9, respectively.

Expander is a key components in Organic Rankine Cycle (ORC) system. In order to improve the performances of single screw expander in large expansion ratio conditions and give consideration to normal conditions, a new idea called ‘increasing the built-in volume ratio appropriately and converting single screw expander into double-stage machine in large expansion conditions by utilizing the discharge velocity of screw grooves was proposed. By implementing this idea, a new prototype of single screw expander was designed and manufactured. Then the prototype was integrated into an experimental ORC system with R123. Experiments were carried out to analyze the characteristics of the developed single screw expander and the ORC system. The results show that the maximum expander shaft power, shaft efficiency, isentropic efficiency, volume efficiency and expansion ratio were 8.35 kW, 56%, 73%, 83% and 8.5, respectively. In addition, under expansion losses seem to be eliminated by the new structure of the expander. It was also found that 12–17% of the expander power was consumed by the circulation pump, of which the measured efficiency was between 20% and 31%. A maximum ORC efficiency of 7.98% was achieved.

The organic Rankine cycle is one of the most promising methods for converting low grade heat into power. However, the technology of small scale organic Rankine cycle is not as mature as that of large scale system. One of the limiting factors is the circulation pump. In the present work, a simulative organic Rankine cycle condition was created for performance testing of the circulation pump, and the results of a Roto-Jet pump were obtained for different rotational speeds. On this basis, an examination of small scale organic Rankine cycle system has been carried out. The results show that the efficiency of the pump is between 11% and 23%. Increasing the rotational speed of the pump or reducing the flow rate leads to a general decrease of pump efficiency in the parametric ranges under study. It is also found that the pump is suitable for the small scale organic Rankine cycle systems with evaporating temperature between 99.5 °C and 127 °C, and the organic Rankine cycle system is suitable for converting the heat with available thermal power between 66.2 kW and 92.7 kW into power. In addition, the optimal operation points were found to correspond to highest organic Rankine cycle efficiency for different rotational speeds of the pump. Based on the results of optimal operation points, the strategy of adjusting the pump rotation speed and the effects of superheat were investigated.

The evolution of η phase and its effect on the tensile properties at 700 °C in 718Plus superalloy after three solution (at 940 °C for 1 h) and single aging (at 870 °C for 25 h, 50 h and 100 h) heat treatments, were investigated. The results showed that there were several various morphologies of η phase in 718Plus samples. As aging time increased, the volume fraction of needle-like/plate-like increased continuously from 5.32%, 7.78% to 29.52%, while the volume of granular/short rod-like η phase firstly increased from 0.46% to 0.68% then decreased to 0.56%. The high temperature tensile properties were affected by η phases with various morphologies. With aging time increasing, the ultimate tensile strength was obviously improved from 797.11 MPa to 860.57 MPa, which could be attributed to a certain number of plate-like/needle-like η phases at the grain boundaries which could hinder the dislocations motion near the grain boundaries. And the elongation weakly increased firstly from 16.84% to 18.76% and then decreased to 18%, which was closely related to granular/short-rod η phases. Enhancing tensile strength and acceptable ductility could be obtained by morphology control of η phase applying SA heat treatments in the study: promoting the simultaneous precipitation of an appropriate amount of plate-like/needle-like η phases and a small amount of granular/short rod-like η phases.

Refrigerant injection is a good method for reducing the exhaust temperature of a single-screw refrigeration compressor (SSRC). In this paper, an accurate method is proposed to calculate the variation of the injection area for different initial positions and different sizes of injection holes. Furthermore, a mathematical model describing the internal working process of an SSRC with liquid refrigerant injection (LRI) is established to evaluate the performance of an SSRC and heat pump with a variety of injection hole geometries and working conditions. This theoretical model is verified by comparing the calculation results with experimental data. The results show that LRI can markedly reduce the exhaust temperature and improve the performance of the SSRC and heat pump to some extent. The injection-hole radius is the most important factor affecting the performance of the compressor and heat-pump system. The variations of different performance parameters of the SSRC and heat pump at low ambient temperature can be obtained. This work provides a theoretical method for optimizing the injection process in SSRCs.

The microstructure evolutions during 1000 °C-1000 h long-term aging and relevant 800 ~ 840 °C/220 ~ 300 MPa creep behaviors of a novelly designed multiphase Ni3Al-based intermetallic alloy were investigated. Results showed this alloy presented excellent intermediate temperature creep properties even after 1000 °C-1000 h long-term aging. A kind of bimodal R-type γ′ rafting structures were observed in the 800 °C/220 MPa creep process of the long-term aged alloy, and the creep resistance levels of three kinds of γ′ rafting structures were evaluated to be in the order of bimodal R-type γ′ rafting structures > R-type γ′ rafting structure > N-type γ′ rafting structure. The 1000 °C-1000 h long-term aging can promote the inhomogeneous precipitation of Cr4.6MoNi2.1 phase at the edge γ′+γ dendrite area, which can play the role of pinning dislocations and inhibiting the further rafting and coarsening of the R-type γ′ rafts during creep. Differed from Ni-based alloys and other Ni3Al-based alloys, this long-term aged alloy exhibited abnormal four-stage creep characteristics, which consisted of atypical short steady-state creep stage with step fluctuant feature and atypical long accelerated creep stage with creep rate increasing at a constant rate.

This paper focused on the intake and exhaust structure optimization of a single-screw expander (SSE) by using numerical method. The effects of internal volume ratio, the shape and clearance height of the intake port and exhaust area were numerically analyzed (R123 and HFO-1336mzz(Z) were selected as working fluids) to reduce the energy losses (more than 30%) caused by pressure loss and leakage in intake process and exhaust pressure loss. The suggestions of reducing the internal volume ratio and clearance height at intake port and removing the closed helix line were given based on the simulation results. Then, the optimized SSE was developed and experimentally tested in ORC system with R123 as working fluid. Results showed that the filling factor of the prototype was reduced from 125% to nearly 100% and the highest shaft efficiency was increased from 56% to 67.7% at 3000 rpm. The enhanced performance of the new prototype proves the correctness of the numerical optimization and this is expected to provide guidance for the design of SSE.