Large Pressure Research Articles

Simulation Analysis of Pipeline Detection Robot Motion State

Pipeline transportation has the advantages of safety, reliability and low energy consumption in transporting natural gas, and is an important transportation route for transporting natural gas. Due to the characteristics of natural gas pipelines with large internal pressure fluctuations, plenty of pipeline bending sections and complex pipeline deformation characteristics, pipeline detection robots are required to have higher detection capabilities, and the study of the motion state of natural gas pipeline detection robots in pipeline detection is of practical significance. This paper adopts the CFD numerical simulation method and establishes the model of DN800 pipeline deformation detection robot. Next, by simulating the natural gas pipeline detection robot under different media and different pipeline types respectively, the motion state of the detection robot is analyzed under different conditions. The simulation results verify the reliability of the detection robot working inside the pipeline, which can fully guarantee the safe transportation of natural gas pipeline.

Study on Flow Characteristics of Francis Turbine Based on Large-Eddy Simulation

The research object was a Francis turbine, and the working conditions at 100%, 75%, 50%, 25%, and 1% opening were determined by the opening size of the guide vane. Large-Eddy Simulation (LES) was adopted as a turbulence model method to conduct three-dimensional unsteady turbulent numerical simulation of the entire flow channel of a Francis turbine, and the flow situation of various parts of the turbine under different working conditions was obtained. The flow characteristics of each component under different working conditions were analyzed, and the hydraulic performance of each part was evaluated. The factors that affected the stability of hydraulic turbines were identified, and their formation mechanisms and evolution laws were explored. The results show that the guide vane placement angle was reasonable in the guide vane area, and the hydraulic performance was fine. The impact on the stability of the hydraulic turbine was small. Further research showed that the hydraulic performance was poor in the runner area, and there were flow separation and detachment phenomena in the flow field. This created a channel vortex in the runner blade channel. The channel vortex promoted the lateral flow of water and had a significant impact on the stability of the hydraulic turbine. The diffusion section of the draft tube can dissipate most of the kinetic energy of the water flow in the draft tube area, and it had a good energy dissipation effect. However, the was a large pressure difference between the upper and lower regions of the diffusion section, and it generated a backflow phenomenon. It created vortex structures in the draft tube, and the stability of the hydraulic turbine was greatly affected.

Dimensionless plate height is unsuitable for comparing chromatographic columns

Dimensionless plate height (h) is differently defined for the columns with different type of internal filling (internal support structure). It is h = H/d for open columns (d is the internal diameter), h = H/dp for packed columns (dp is the particle size), h = H/ddom (ddom is the domain size) for columns with other filling (e.g., monolithic, pillar array). The plate height (H) and the column kinetic performance in general depend on the flow channels through the column filling – on their cross-sectional dimensions (dchan), shape, and wall porosity. Other than through their effect on the flow channels, the dimensions of skeleton of the filling and the ddom do not affect H. Parameters d, dp and ddom cannot be found from external measurements of a column as a ”black box” separation device and, therefore, are unmeasurable subjective metrics, and, therefore, so is h. Moreover, in some fillings (e.g., monolithic, pillar array) ddom can be chosen independently of dchan. By increasing ddom without changing dchan, one can make h as small as desired with no effect on H and on the column kinetic performance in general. This implies that h does not represent column performance and cannot be used for comparing differently structured column.In this report, previously introduced measurable (objective) performance metrics – the kinetic performance factor (q) and the quality factor (qmax) are described and evaluated. The latter is suitable for comparing differently structured columns. A column practically achievable performance depends not only on qmax, but on the largest pressure that a column can tolerate, the narrowest flow channels that can be manufactured and other practical factors. Practically achievable performance of several column types is compared in this report.

Extreme thermodynamics in nanolitre volumes through stimulated Brillouin–Mandelstam scattering

Examining the physical properties of materials—particularly of toxic liquids—under a wide range of thermodynamic states is a challenging problem due to the extreme conditions the material has to experience. Such temperature and pressure regimes, which result in a change in the refractive index and sound velocity, can be accessed by optoacoustic interactions such as Brillouin–Mandelstam scattering. Here we demonstrate the Brillouin–Mandelstam measurements of nanolitre volumes of liquids in extreme thermodynamic regimes. This is enabled by a fully sealed liquid-core optical fibre containing carbon disulfide. Within this waveguide, which exhibits tight optoacoustic confinement and a high Brillouin gain, we are able to conduct spatially resolved measurements of the local Brillouin response, giving us access to a resolved image of the temperature and pressure values along the liquid channel. We measure the material properties of the liquid core at very large positive pressures (above 1,000 bar) and substantial negative pressures (below –300 bar), as well as explore the isobaric and isochoric regimes. The extensive thermodynamic control allows the tunability of the Brillouin frequency shift of more than 40% using only minute volumes of liquid.

Soft capacitive tactile sensing array with high-robustness for three-axis pressure measurement

Tactile sensing with capability to measure and differentiate synergistic normal and shear pressures real-timely is crucial for possible dexterous manipulation of objects in robotic applications. Here in this paper, the measuring principle, as well as fabrication and testing of a soft tactile sensing array for three-axis pressure measurement are proposed. It is enabled by a floating electrode structure rather than a typical electrode-dielectric-electrode sandwiched prototype that the interconnects and sensing electrodes are realized using flexible printed circuit (FPC) meanwhile the floating electrodes are easily fabricated on a soft polyethylene terephthalate (PET) film. The transformation of embedding fragile interconnects into soft PDMS sensor body under excessive bending and deformation to a FPC layer of increased robustness and less compression drastically reduce the possibility of loss of function, and guarantee the robustness of the designed tactile sensing array. Moreover, hierarchically porous PDMS composite as the dielectric inlaid between floating electrode layer and sensing electrode layer results in a soft tactile sensing array with enhanced sensitivity (0.04 kPa−1 under normal pressure and 0.10 kPa−1 under shear pressures), large pressure sensing range (>300 kPa under normal pressure and > 62 kPa under shear pressures), minimal hysteresis, excellent repeatability, and fast response time (less than 60 ms) attributing to the synergistic effect of uniformly distributed macro and micro pores. The constructed soft tactile sensing array would provide essential sensing feedback for controlling an artificial arm in various tasks, illustrating its great potential application in robotics.

Influence of focusing intensity on optically pumped metastable rare gas based on laser-induced ionization

When traditional optically pumped metastable rare gas laser (OPRGL) operating in high power output, a potential issue may arise: electromagnetic interference (EMI) caused by large volume atmospheric pressure discharge. This EMI problem imposes limitations on the application of OPRGL. We propose a new idea of preparing metastable atoms by 532 nm laser-induced preionization, which has the potential to circumvent the EMI problem. An 811.5 nm laser was used to excite the metastable (4s[3/2]2) Ar atoms in Ar-He mixture, resulting in the generation of a prominent amplified spontaneous emission (ASE) signal at 912.3 nm (4p[1/2]1→4s[3/2]2). By investigating intensities of the 912.3 nm fluorescence and ASE as a function of the delay time between 811.5 nm and 532 nm lasers, the influence of the 532 nm laser's focusing intensity on the evolution of prepared metastable atomic concentration was unveiled, as well as the amplification mechanism of 912.3 nm signal. Furthermore, the competition mechanism between ASE and the fluorescence channels originating from the 4p[1/2]1 level was studied. Considering the influence of plasma expansion on metastable atomic concentration, as well as the influences of threshold, gain and gain length on ASE, at the “photoexcitation + radiation + collisional relaxation” stage, we obtained a reliable effective lifetime of the metastable 4s[3/2]2 level through analysis of the decay curve of the 912.3 nm ASE intensity. Similarly, in the “ion-electron recombination” stage, a reliable effective lifetime of the metastable 4s[3/2]2 level was obtained by analyzing the decay curve of the 912.3 nm fluorescence intensity. Additionally, the 912.3 nm ASE pulse width was influenced by various factors, including the effective lifetime of the 4p[1/2]1 level, the concentration of metastable Ar, the plasma expansion rate, and the gain length, etc. This work demonstrates that OPRGL based on laser-induced preionization offers a promising alternative for the future advancement of OPRGL.

Effect of running-in on the low-pressure tribological performance of valve plate pair in axial piston pumps

Axial piston pumps are widely used in tunnel boring machines with compact structures and high efficiency. The efficiency and lifetime heavily depend on the tribological performance of the pump's valve plate pair. The running-in process is crucial to the steady-state tribological performance of the valve plate pair and directly influences its friction coefficient and wear rate, etc. Axial piston pumps always run-in with different pressure and speed gradients, starting from low-pressure. However, the initial running-in conditions significantly affect the running-in process of the valve plate pair and their effects on tribological performance are unclear. In this paper, ring-on-block testing is conducted. Effects of the speed (500 r/min and 1500 r/min) and pressure (2 MPa, 5 MPa, and 7 MPa) at different initial roughness (Ra = 0.4 μm and 0.05 μm) on the running-in are investigated. The friction coefficient, running-in time, wear rate, and worn surface are compared. Results show that a higher speed and initial roughness can reduce the running-in time, while the larger pressure will increase the friction coefficient and its fluctuation amplitude. The wear mechanism during the running-in process is mainly abrasive wear, while the plastic deformation wear appears with low initial roughness.

Letter to the Editor: Longitudinal Assessment of Retinal Nerve Fiber Layer and Ganglion Cell Complex Thicknesses in Patients With Large Optic Disc Cups and Normal Intraocular Pressure and Visual Fields.

Letter to the Editor: Longitudinal Assessment of Retinal Nerve Fiber Layer and Ganglion Cell Complex Thicknesses in Patients With Large Optic Disc Cups and Normal Intraocular Pressure and Visual Fields.

Response to Letter to the Editor: Longitudinal Assessment of Retinal Nerve Fiber Layer and Ganglion Cell Complex Thicknesses in Patients With Large Optic Disc Cups and Normal Intraocular Pressure and Visual Fields.

Response to Letter to the Editor: Longitudinal Assessment of Retinal Nerve Fiber Layer and Ganglion Cell Complex Thicknesses in Patients With Large Optic Disc Cups and Normal Intraocular Pressure and Visual Fields.

EXPERIMENTAL INVESTIGATION OF DENSITY EFFECT ON TSUNAMI BORE FORCES ON VERTICAL WALLS

In the tsunami generated by the 2011 Great East Japan Earthquake, black tsunamis were identified in many locations. According to Kise and Arikawa (2020), in the areas where samples were obtained, the seawater was found to be mixed with silt components by about 10 percent. They also reported that a large impulsive wave pressure might be generated when the silt-mixed seawater acted on a vertical wall as a bore. Although there have been many studies on the mechanism of impulsive wave pressure in bore-shaped tsunamis (e.g., Co and Yeh, 2018), the effects of sand and silt mixing have rarely been investigated. Therefore, in this research, bore-shaped tsunami pressure experiments with sand and silt in various states of density were conducted to clarify the mechanism of impulsive pressure on a vertical wall and to verify the effect of density on impulsive pressures.

NUMERICAL EXPERIMENTS ON OVERHANGING PARAPETS UNDER NON-BREAKING WAVE CONDITIONS

Sea-wall and storm-wall structures aim to protect coastal areas and harbours from wave attacks. They are often located in the neighbours of city centres, that in turn impose rather severe visual limits affecting the maximum height of the structure. To combine the architectonical visual restrictions and the overtopping safety limits, imposed by different national standards, alternative solutions such as recurved parapet are often applied. Even for non-breaking wave conditions, these structures are subjected to large impulsive pressure that has been recently described and named as Confined-Crest impact, (C-CI, Castellino et al., 2018). The C-CI has been the cause of recent failures such as in the Civitavecchia harbour (Italy, Castellino et al., 2021 and Dermentzoglou et al., 2020). Accordingly, this phenomenon raised the attention of researchers and professionals who require an additional tool to design these curvilinear structures by considering the overtopping reduction performance, the structure complexity and the C-CI.

CANDU6 single channel CCP analysis on pressure tube deformation effects with multi-physics coupled calculation

Though pressure tube deformation rigorously and simultaneously affects channel coolability and neutronics behavior, the two effects have never been coupled with each other. In this study, the CUPID code is coupled with the SHAFE code to obtain the Critical Channel Power (CCP) of a designated channel which has high nominal power, a high void fraction, a high flow rate, and high pressure deformation. Even though appendage modeling is not included in this study, adequate cell-wise uniform artificial form loss was sought through iteration and imposed to conserve the header to header pressure drop by considering the inlet & outlet feeder and end fitting pressure drop. Nested loops are included in CCP calculation logic; they are the channel power loop, pin power distribution update loop and flow rate optimization loop from outer loop to inner loop, in sequence. Both CUPID and SHAFE are based on the Fortran computer language; the CUPID code is converted to the Dynamic Link Library (DLL) and the SHAFE code can load the CUPID library whenever it is required. Finally, we found that a CCP decrement for a channel with large pressure tube deformation is not that much, even for a complex deformation case. In addition, the sagging effect for a CCP decrement is significantly different from the expectation before an analysis is completed.

(Invited) Regenerative Fuel Cell System Utilizing a High Differential Pressure Water Electrolysis Technology

The expansion of manned activities in space requires energy system technology that utilizes sunlight, and hydrogen fuel cells are one such means. By electrolyzing water with sunlight, energy is stored with oxygen and hydrogen, and electricity is generated by fuel cells. The generated water can be recycled, and energy can be stored and supplied without external replenishment. This is commonly called a regenerative fuel cell. In the space domain, such energy systems must be compact and lightweight, and gas must be stored under high pressure. However, mechanical compressors that are generally used for compressing are heavy, and there are also issues of vibration and noise.Since the 1990s, Honda has worked on the development of high-differential-pressure water electrolysis technology that generate hydrogen from renewable energy and compress without a mechanical compressor, in parallel with the development of fuel cell technology. High-differential-pressure water electrolysis is a technology that generates high pressure hydrogen by moving the protons generated by electrolysis to the cathode through the Proton exchange membrane (PEM) . The energy required is only the potential generated by the difference in hydrogen concentration, which is superior to small mechanical compressors whose efficiency is reduced by friction loss. However, a large differential pressure is generated across the PEM because only one side is at a high pressure. Honda has achieved a maximum pressure increase of 70 MPa by using its own structure. Moreover, this principle can be applied not only to the generation and pressurization of hydrogen, but also to oxygen. Honda is working on the development of RFC technology that integrates these hydrogen technologies with the aim of applying them not only to sustainability on Earth, but also to the space domain. Currently, we are undertaking a JAXA project and are promoting the production of a breadboard model.The feature of Honda's RFC technology is that it applies high-differential-pressure water electrolysis technology, not only to generate oxygen and hydrogen, but also to pressurize each gas. By not using a mechanical compressor, it is possible to downsize the system, and it is also no vibration or noise. Utilizing the characteristics of this technology, we are planning to build an energy system that can store energy at high density and apply it to various manned missions.Honda's RFC consists of the high-differential-pressure water electrolysis system that simultaneously electrolyzes water and pressurizes oxygen, a Electrochemical hydrogen compressor system (EHC system) that electrochemically pressurizes the hydrogen and a fuel cell system. In the electrolysis stack, oxygen is generated and compressed to the target pressure by the differential pressure water electrolysis. The generated hydrogen is sent to the EHC stack that also applies the technology of high-differential pressure water electrolysis, where the hydrogen is pressurized. As a result, both oxygen and hydrogen gases were generated and compressed without a mechanical compressor. For the fuel cell system, the compact and highly efficient fuel cell technology that has been developed for FCVs is applied. When the fuel cell is used on the ground, oxygen is supplied from the atmosphere, but in space RFC it is necessary to generate electricity using pure oxygen and to circulate the system. A dedicated circulating FC system was constructed to achieve stable power generation. The water produced by power generation is used in the next water electrolysis cycle, and the proof of principle as RFC has been completed. In addition to these basic functions, for space application, we must address issues not found on Earth, such as heat management in a vacuum, radiation, and vibrations during launch. Starting with the lunar exploration mission scheduled for 2030, Honda will develop this technology for the spread of manned activities. Figure 1

Self-pressurized rapid freezing at arbitrary cryoprotectant concentrations.

Self-pressurized rapid freezing (SPRF) has been proposed as a simple alternative to traditional high pressure freezing (HPF) protocols for vitrification of biological samples in electron microscopy and cryopreservation applications. Both methods exploit the circumstance that the melting point of ice reaches a minimum when subjected to pressure of around 210 [MPa], however, in SPRF its precise quantity depends on sample properties and hence, is generally unknown. In particular, cryoprotective agents (CPAs) are expected to be a factor; though eschewed by many SPRF experiments, vitrification of larger samples notably cannot be envisaged without them. Thus, in this study, we address the question of how CPA concentration affects pressure inside sealed capillaries, and how to design SPRF experiments accordingly. By embedding a fiber-optic probe in samples and performing Raman spectroscopy after freezing, we first present a direct assessment of pressure buildup during SPRF, enabled by the large pressure sensitivity of the Raman shift of hexagonal ice. Choosing dimethyl sulfoxide (DMSO) as a model CPA, this approach allows us to demonstrate that average pressure drops to zero when DMSO concentrations of 15 wt % are exceeded. Since a trade-off between pressure and DMSO concentration represents an impasse with regards to vitrification of larger samples, we introduce a sample architecture with two chambers, separated by a partition that allows for equilibration of pressure but not DMSO concentrations. We show that pressure and concentration in the fiber-facing chamber can be tuned independently, and present differential scanning calorimetry (DSC) data supporting the improved vitrification performance of two-chamber designs. Lay version of abstract for "Self-pressurized rapid freezing at arbitrary cryoprotectant concentrations" Anyone is familiar with pipes bursting in winter because the volume of ice is greater than that of liquid water. Less well known is the fact that inside a thick-walled container, sealed and devoid of air bubbles, this pressure buildup will allow a fraction of water to remain unfrozen if the sample is also cooled sufficiently rapidly far below the freezing point. This phenomenon has already been harnessed for specimen preparation in microscopy, where low temperatures are useful to immobilize the sample, but harmful if ice-formation occurs. However, specimen preparation cannot always rely on this pressure-based effect alone, but sometimes requires addition of chemicals to inhibit ice-formation. Not enough is known directly about how these chemicals affect pressure buildup: Indeed, rapid cooling below the freezing point is only possible for small sample volumes, typically placed inside sealed capillaries, so that space is generally insufficient to accommodate a pressure sensor. By means of a compact sensor, based on an optical fiber, laser and spectrometer, we present the first direct assessment of pressure inside sealed capillaries. We show that addition of chemicals reduces pressure build-up and present a two-chambered capillary to circumvent the resulting trade-off. Also, we present evidence showing that the two-chambered capillary design can avoid ice-formation more readily than a single-chambered one. This article is protected by copyright. All rights reserved.

Machine learning assisted hybrid transduction nanocomposite based flexible pressure sensor matrix for human gait analysis

Human gait analysis strongly correlates with critical health metrics and provides significant information about physiological well-being. Therefore, accurate, fast, and cost-effective gait monitoring is required for intelligent healthcare systems. This paper reports the development of a flexible hybrid transduction Barium Titanate (BTO)/SU-8 nanocomposite-based, individually addressable pressure sensor matrix. The proposed sensor is highly suitable for wearables compared to the conventional pressure sensors due to its speedy and cost-effective design flow and ease of operation. The hybrid (piezoelectric/triboelectric), photo-patternable active layer enables strain and contact electrification-based sensing that convolves into a highly sensitive, lower cross talk and large area pressure sensing. The reported sensor is incorporated with a solder-free modular data acquisition setup for a straightforward design integration. A pressure sensitivity of 34 mV kPa-1 for the deep linear region and 2.7 mV kPa-1 for the linear region over a pressure range of 0–170 kPa is reported. The sensor shows excellent reliability and negligible hysteresis with an average deviation of 2.7 %. Furthermore, the 36 pressure cells with hybrid transduction deliver rich feature extraction to machine learning algorithms compared to single transducer-based systems for an accurate gait and grip strength monitoring. The developed convolution neural network (CNN)-2D model gives a model accuracy of 98.5 % and 98.3 % for two different gait characterizations, while delivering a model accuracy of 93.75 % for grip strength assessment. The combination of hybrid sensor design, development, and use of machine learning offers a novel approach to tackle the issues associated with sensors that are incompatible with rapidly developing smart healthcare technology.

Visit-to-visit blood pressure variability and the risk of cardiovascular disease: a prospective cohort analysis.

Large blood pressure (BP) variability contributed to subclinical brain disease thus may be implicated in the development of cardiovascular disease (CVD). This study included 64,810 CVD-free participants who attended the first two examinations from the Kailuan study to investigate the association of BP variation, considering its magnitude, direction, and time interval prior to CVD diagnosis, with the risk of CVD in Chinese population. Magnitude and directional BP variability was calculated as absolute BP difference or BP difference value divided by mean BP over 2 sequential visits, respectively. During a median follow-up of 10.91 years, a total of 4129 cases of CVD. A large SBP variability (the highest vs the lowest tertile) was associated with a higher risk of CVD (adjusted HR, 1.31; 95% CI, 1.22-1.41). The associations were stronger with longer time intervals, the hazard ratio (HR) with 95% confidence interval (CI) for CVD was 1.30 (95% CI, 1.20-1.39) at 1 years, 1.32 (1.18-1.40) at 3 years, and 1.34 (1.20-1.45) at 5 years. For directional SBP variability, rise in SBP was associated with an increased risk of CVD (HR, 6.17; 95% CI, 5.65-6.75), while fall in SBP was associated with a decreased risk of CVD (HR, 0.52; 95% CI, 0.46-0.59). Subgroup analysis showed the significant associations were only observed in men (Pint = 0.0010). Similar patterns were observed for DBP variability and CVD subtypes. The results indicated that a large SBP variation in rise direction was associated with an increased risk of incident CVD, especially in men.

A systematic non-equilibrium thermodynamics approach for assessing transport mechanisms in membrane distillation

Membrane distillation (MD) is a promising technique for purifying volatile liquids at temperatures below their boiling points. This study presents a systematic non-equilibrium thermodynamics (NET) approach for analysis of transport mechanisms in direct-contact membrane distillation (DCMD). By incorporating the transport properties of the membrane, membrane interfaces, and temperature polarization layers, a unified framework is established to assess mass and heat transfer, including coupling effects in the composite membrane system. Explicit expressions for the transport properties are derived, and a numerical solution procedure is used to obtain temperature and partial pressure profiles through the system. The NET approach reveals that the temperature difference across the membrane is the true driving force of mass transfer, which after suitable approximations is equivalent to the saturation pressure difference. The commonly employed formula for distillate flux in MD literature was found to agree with the comprehensive NET approach within 3% when predicting the water flux through a DuraPore GVHP membrane. Incorporating a correction factor that accounts for kinetic heat-mass coupling effects improves the agreement to 0.5%. The simplified model disregards interfacial transport phenomena and mass-heat coupling. These effects are shown to be insignificant for the DuraPore GVHP membrane. However, it is crucial to account for temperature polarization to obtain agreement with experimental results. The resistance of the vapor-liquid interface is shown to be more important if the membrane has a Cassie-Baxter wetting state than a Wenzel wetting state, and this can enhance the water flux. When the pore-sizes approach the nanometer scale, we show that direct interactions between the molecules and the pore walls must be accounted for due to sorption effects. In applications where nanometer scale pores are important, such as in systems where the membrane must maintain a large pressure difference, it may be important to take such corrections into consideration. The presented NET approach provides a comprehensive toolkit for assessing and analyzing transport properties in membrane systems, which can be used to better understand how the properties of MD systems can be tailored to enhance performance.

Theoretical and experimental studies for a transcritical CO2 heat pump with spirally fluted tube gas cooler

Transcritical CO2 system has been widely used in many fields to provide heating and cooling capabilities, and optimizing the structure of the gas cooler is an effective way to improve its performance. This paper presents a theoretical and experimental study of a spirally fluted tube-in-tube heat exchanger used as a gas cooler in a transcritical CO2 heat pump. The theoretical research uses numerical simulations to investigate the flow and heat transfer characteristics. The effect of the different CO2 mass flow rates, inlet pressure, and temperature on the performance of the spirally fluted gas cooler is evaluated and analyzed. The simulation results show that the spirally fluted structure can significantly improve the heat transfer performance of the CO2 side compared to the flat tube, which indicates that the spirally fluted gas cooler could be an effective way to enhance the operating performance of the transcritical CO2 system. Then experimental research is conducted in a transcritical CO2 heat pump prototype to validate the functional performance of the spirally fluted gas cooler. The effect of the different CO2 mass flow rates, inlet pressure and temperature, and the different water inlet and outlet temperatures on the performance of the spirally fluted gas cooler in the prototype are tested. The heat exchanger efficiency - number of transfer units (ε-NTU) method is employed to analyze the operating performance based on the experimental data. In addition, the exergy loss method is used to quantitatively evaluate the side-effect of the large pressure drop by the spirally fluted structure. Both the theoretical and experimental results show that the spirally fluted tube gas cooler can significantly improve the performance of the transcritical CO2 system. Besides, a heat transfer and friction coefficient correlation are established based on the experimental data for future research guidance.

Oxidative Damage during the Operation of Si(211)-Based Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) based on sliding metal–semiconductor junctions are an emerging technology that can efficiently convert mechanical into electrical energy. These miniature autonomous power sources can output large direct current (DC) densities, but often suffer from limited durability; hence, their practical scope remains uncertain. Herein, through a combination of conductive atomic force microscopy (C-AFM) and photocurrent decay (PCM) experiments, we explored the underlying cause of surface wear during the operation of DC-TENGs. Using monolayer-functionalized Si(211) surfaces as the model system, we demonstrate the extent to which surface damage develops during TENG operation. We reveal that the introduction of surface defects (oxide growth) during TENG operation is not caused by the passage of the rather large current densities (average output of ~2 × 106 A/m2); it is instead mainly caused by the large pressure (~GPa) required for the sliding Schottky diode to output a measurable zero-bias current. We also discovered that the drop in output during operation occurs with a delay in the friction/pressure event, which partially explains why such deterioration of DC-TENG performance is often underestimated or not reported.

An optical emission spectroscopy method for determining the electron temperature and density in low-temperature xenon plasma by using a collisional-radiative model considering the hyperfine structure of emission line into metastable state

Optical emission spectroscopy (OES) is an important technique for the diagnostics of plasma parameters in the development of plasma devices and material processing technology. OES depends on the collisional-radiative model which can accurately describe the kinetics of excited species in plasma. Metastable species usually have higher density (2–4 orders of magnitude) and longer lifetime (3–6 orders of magnitude) compared to other excited species, thus play important roles in the reaction kinetics. However, the kinetic of metastable species can be complex due to the transport and self-absorption processes, which may lead to coupling of the plasma reaction kinetics in the adjacent areas. Moreover, the line splitting of some elements make the description of metastable kinetics more complex. This work presents an OES method based on a collisional-radiative model considering the hyperfine splitting of emission lines into metastable levels. The density distribution of metastable state is determined by the self-absorption effect. It is then taken into the rate balance equations of other excited species to make an accurate description of metastable related kinetics. The electron density and temperature are determined based on this model. The OES method is demonstrated on a miniaturized electron-cyclotron-resonance ion thruster. The metastable density, electron density and electron temperature are determined along the radial direction of the ion thruster, which can be useful for revealing the physics of discharge phenomenon and optimizing the performance of the plasma source. This method can be used to determine electron parameters in a large pressure range.