Pressure P0 Research Articles

Validation of prediction capability of operating space for plasma initiation in MAST-U

Abstract DYON is a plasma initiation modelling code that solves the differential equation system of the full circuit equations (plasma current, active coil currents and eddy currents in full passive structures) and 0D global energy and particle balance equations[1]. In order to test the capability of the full electromagnetic plasma initiation model to predict individual discharges in experiments and thus the operating space in the device, a dedicated experimental database was built in MAST-U by scanning the prefilled gas pressure p0 and the induced loop voltage Vloop . In the experimental operating space of p0 and Vloop the lower and the upper limits of p0 are determined by the plasma breakdown failure and the plasma burn-through failure, respectively. The lower limit of Vloop is determined by the plasma burn-through failure. By directly reading the control room data used in each discharge (i.e. currents in the solenoid, poloidal field coils, and toroidal field coils, p0 , and gas puffing rate), the full electromagnetic DYON consistently predicted the failed breakdown, failed burn-through, and successful plasma initiation discharges in the experimental database, demonstrating its capability to predict the operating space for inductive plasma initiation. The Paschen curve calculated with the effective connection length in MAST-U indicates a much higher p0 required for plasma breakdown than the experimental data, indicating that individual field line evaluation is necessary to calculate the quantitative requirements for Townsend breakdown. The demonstration in this paper shows that the full electromagnetic DYON could be a useful simulation tool to assess the feasibility of inductive plasma initiation and to optimise operating scenarios in future devices. [1] Hyun-Tae Kim 2022 Nuclear Fusion 62 126012

On an isotropic porous solid cylinder: the analytical solution and sensitivity analysis of the pressure

Within this work, we perform a sensitivity analysis to determine the influence of the material input parameters on the pressure in an isotropic porous solid cylinder. We provide a step-by-step guide to obtain the analytical solution for a porous isotropic elastic cylinder in terms of the pressure, stresses, and elastic displacement. We obtain the solution by performing a Laplace transform on the governing equations, which are those of Biot’s poroelasticity in cylindrical polar coordinates. We enforce radial boundary conditions and obtain the solution in the Laplace transformed domain before reverting back to the time domain. The sensitivity analysis is then carried out, considering only the derived pressure solution. This analysis finds that the time t, Biot’s modulus M, and Poisson’s ratio v have the highest influence on the pressure whereas the initial value of pressure P0 plays a very little role.

Improved forming height and reduced energy consumption through an optimized hybrid quasi-static and high-speed forming strategy

It is widely accepted that aluminum alloy-based materials exhibit improved formability and enhanced ductility under high-speed impact. However, in this study, the experimental results were not entirely similar to the traditional theoretical results. Thus, this study once again confirms the conclusion that high-rate forming can increase the forming limit of materials, and simultaneously supplements the conclusion. Herein, a hybrid process combining quasi-static hydraulic forming and electromagnetic hydraulic forming was proposed. The effects of the forming sequence and pre-deformation amount on sheet bulging and fracture morphology were analyzed via experiments and simulation. It was found that when the electromagnetic hydraulic forming is pre-deformation and the quasi-static hydraulic forming is post-deformation, the forming height of aluminum alloy does not improve significantly. Conversely, when the quasi-static hydraulic forming is pre-deformation and the electromagnetic hydraulic forming is post-deformation, the forming height of aluminum alloy improves significantly. In case of pre-deformation quasi-static liquid pressure P0 = 2 MPa, and post-deformation electromagnetic hydraulic forming, the limit forming height is 22.4 % higher than that under quasi-static hydraulic forming. Moreover, the limiting voltage decreases with increasing pre-deformation quasi-static liquid pressure P0, and the energy consumption reduces by 42.9 %. The deformation behavior and damage characteristics of quasi-static hydraulic forming, electromagnetic hydraulic forming, and hybrid forming were accurately predicted by multi-physics coupling analysis. Compared with quasi-static hydraulic forming, void nucleation and growth are inhibited due to high-speed impact. In particular, when the sheet is about to crack during high-speed forming, the voids that should have grown sharply are significantly inhibited. Therefore, the improved formability mainly acts at the post-deformation stage during high-speed forming, with the analytical results corroborating the experimental and simulation ones.

Assessment of Hydrophilicity/Hydrophobicity in Mesoporous Silica by Combining Adsorption, Liquid Intrusion, and Solid-State NMR Spectroscopy.

We have developed a comprehensive strategy for quantitatively assessing the hydrophilicity/hydrophobicity of nanoporous materials by combining advanced adsorption studies, novel liquid intrusion techniques, and solid-state NMR spectroscopy. For this, we have chosen a well-defined system of model materials, i.e., the highly ordered mesoporous silica molecular sieve SBA-15 in its pristine state and functionalized with different amounts of trimethylsilyl (TMS) groups, allowing one to accurately tailor the surface chemistry while maintaining the well-defined pore structure. For an absolute quantification of the trimethylsilyl group density, quantitative 1H solid-state NMR spectroscopy under magic angle spinning was employed. A full textural characterization of the materials was obtained by high-resolution argon 87 K adsorption, coupled with the application of dedicated methods based on nonlocal-density functional theory (NLDFT). Based on the known texture of the model materials, we developed a novel methodology allowing one to determine the effective contact angle of water adsorbed on the pore surfaces from complete wetting to nonwetting, constituting a powerful parameter for the characterization of the surface chemistry inside porous materials. The surface chemistry was found to vary from hydrophilic to hydrophobic as the TMS functionalization content was increased. For wetting and partially wetting surfaces, pore condensation of water is observed at pressures P smaller than the bulk saturation pressure p0 (i.e., at p/p0 < 1) and the effective contact angle of water on the pore walls could be derived from the water sorption isotherms. However, for nonwetting surfaces, pore condensation occurs at pressures above the saturation pressure (i.e., at p/p0 > 1). In this case, we investigated the pore filling of water (i.e., the vapor-liquid phase transition) by the application of a novel, liquid water intrusion/extrusion methodology, allowing one to derive the effective contact angle of water on the pore walls even in the case of nonwetting. Complementary molecular simulations provide density profiles of water on pristine and TMS-grafted silica surfaces (mimicking the tailored, functionalized experimental silica surfaces), which allow for a molecular view on the water adsorbate structure. Summarizing, we present a comprehensive and reliable methodology for quantitatively assessing the hydrophilicity/hydrophobicity of siliceous nanoporous materials, which has the potential to optimize applications in heterogeneous catalysis and separation (e.g., chromatography).

Comparative study of different layouts in the closed-Brayton-cycle-based segmented cooling thermal management system for scramjets

The segmented cooling thermal management system based on the closed-Brayton-cycle (CBC) is an excellent technology for thermal protection and power generation of scramjets. In this paper, a comparative study is conducted to investigate the system performance under different supercritical carbon dioxide CBC layouts. A zero-dimensional thermodynamic model was established to analyze the effects of compressor inlet temperature (T1), turbine inlet temperature (T3), and compressor outlet pressure (p2) on fuel mass flow rate for cooling (mf) and net power (Pnet). A quasi-one-dimensional flow and heat transfer model was developed to study the cooling effectiveness. Results indicate that higher T3 and p2 reduce mf while increasing Pnet in the simple layout (SL) and simple recuperated layout (SRL). However, in the recompressing layout (RCL), the effects of T1, T3, and p2 on mf are more complex due to the split ratio. Moreover, RCL has the lowest maximum wall temperature among the three layouts. Finally, after optimization, RCL has the lowest mf about 0.332 kg/s, which is a 19.8 % reduction compared to the regenerative cooling system. Correspondingly, RCL achieves the highest Pnet, reaching 109.89 kW. In general, the recompressing layout is most suitable for the CBC-based segmented cooling thermal management system for scramjets.

Rozwiązanie problemu tworzenia się zatorów w rurociągach podczas transportu gazu poprzez proces automatycznego strumieniowania

The article presents the application of autoejection process to ensure efficient operation of pipeline systems and gas separation installations when it is impossible to remove and utilize the condensate from the pipelines. Thus, in the suggested ejector, a single common stream is separated into two streams, i.e., an active and a passive stream, as opposed to two separate independent streams in existing ejection devices. As a result, we refer to such an ejection process as autoejection, or a self-ejection process. Such a procedure is run in the pipeline with the goal of blowing and dusting the liquid phase through the central high-velocity nozzle in circumstances of mass blocking and coating rather than expelling the liquid from the pipes. On the cross-sectional area of the belts, the velocity profiles of flows in laminar and turbulent regimes are known to differ greatly from one another. The adhesion forces acting from the tube's central axis outwards, towards its walls cause the flow rate to decrease. There is a cross-sectional interaction of flows in this mode, according to experimental studies of turbulent flows. As a result, compared to the laminar domain, the flow velocities in this regime are more equally distributed across the cross-section of the flow, and their values are roughly equal to the flow's average value. In this case, based on the dependences of the flow ∆p = f(W), it is known from the calculations and the table that at such velocity limits of the flows, the “braking” pressure (p0) of the liquid coating on the pipe walls corresponds to the maximum velocity of the central gas flow. The autoejection process can occur due to the difference between the static pressures. Unsaturated absorbent coatings can be blasted off the tube absorber's walls using this technique and blended back into the main gas stream. Gas-liquid autoejectors installed along the pipe absorber's length make it possible to use this method. The purpose and principles of autoejectors’ operation are considered and a perspective of their application in tube absorbers is noted.

Spontaneous boiling-up of gas-saturated liquids: Attainable superheating of ethane–helium and ethane–hydrogen solutions

The fluctuation growth of a vapor-gas bubble is described as a diffusion process in the space of three variables: the bubble volume V and the partial pressures P1 and P2 of the mixture components in the bubble. The dynamics of the nucleus growth takes into account the viscosity, the solvent volatility and the diffusion supply of the substance dissolved. An equation has been obtained for nucleation rate J expressed as a function of temperature, pressure, and solution concentration. Nucleation in superheated ethane–helium and ethane–hydrogen solutions was studied by the lifetime measurement method. Temperature and pressure dependencies of the nucleation rate have been established at pressures p = 1.6 and 2.0 MPa in solutions containing up to 0.05 mol% of helium and up to 0.31 mol% of hydrogen. The range of nucleation rates studied was J = (2.3·106 – 1.4·108) m−3s−1. The experimental results were compared to classical nucleation theory (CNT). Similarly to pure ethane, there is systematic “underheating” of the solutions as compared to the temperatures predicted by the CNT. The discrepancy found between theory and experiment is explained by the size-dependence of the surface tension of critical bubbles. It is noted that although, unlike hydrogen, helium in ethane acts as a surface-inactive component, this does not lead to an excess of the attainable superheating temperature of the ethane–helium solution over the superheating temperature of the ethane–hydrogen solution.

Transient Flow Evolution of a Hypersonic Inlet/Isolator with Incoming Windshear

In this paper, a novel flow perturbation model meant to investigate the effects of incoming wind shear on a hypersonic inlet/isolator is presented. This research focuses on the transient shock/boundary layer interaction and shock train flow evolution in a hypersonic inlet/isolator with an on-design Mach number of 6.0 under incoming wind shear at high altitudes, precisely at an altitude of 30 km with a magnitude speed of 80 m/s. Despite the low intensity of wind shear at high altitudes, the results reveal that wind shear significantly disrupts the inlet/isolator flowfield, affecting the shock wave/boundary layer interaction in the unthrottled state, which drives the separation bubble at the throat to move downstream and then upstream. Moreover, the flowfield behaves as a hysteresis phenomenon under the effect of wind shear, and the total pressure recovery coefficients at the throat and exit of the inlet/isolator increase by approximately 10% to 12%. Furthermore, this research focuses on investigating the impact of wind shear on the behavior of the shock train. Once the inlet/isolator is in a throttled state, wind shear severely impacts the motion of the shock train. When the downstream backpressure is 135 times the incoming pressure (p0), the shock train first moves upstream and gradually couples with a cowl shock wave/boundary layer interaction, resulting in a more significant separation at the throat, and then moves downstream and decouples from the separation bubble at the throat. However, if the downstream backpressure increases to 140 p0, the shock train enlarges the separation bubble, forcing the inlet/isolator to fall into the unstart state, and it cannot be restarted. These findings emphasize the need to consider wind shear effects in the design and operation of hypersonic inlet/isolator.

Experimental study on ice breaking by a cavitating water jet in a Venturi structure

Ice breaking by a cavitating water jet based on Venturi structure is studied experimentally. Systematic researches of cavitating water jet interacting with ice are carried out by doing indoor experiments, where the cavitating jet is generated by a tailor-made device through Venturi nozzle and the circular fresh-water ice plates are made of boiled water in a cryostat. The whole evolution of cavitating jets and ice plates is recorded by two high-speed cameras from two views simultaneously. Pressure loads on the rigid wall of cavitating water jet is compared with that of conventional non-cavitating water jet and the change is analyzed. Among two typical structural parameters of Venturi cavitating nozzles selected in this paper, the ratios of throat length to diameter ε (1; 1.5; 2) and the diverging angles α (8°; 10°; 12°), the nozzle withε = 1 andα = 12° is found to be the best in terms of loads on wall. On this basis, the responses of ice plate, including crack generation, crack development and fracture, are studied under the cavitating jet loads, mainly involving the compressible pressure P1 and cavitation pressure Pc. According to the main cause and propagation sequence of cracks, the failure mechanisms of ice under Venturi cavitating jet can mainly be divided into three types: shock waves failure, overall strength failure and local strength failure, along with six damage patterns roughly. Furthermore, the effects of ice plate thickness, cavitating water jet strength and boundary conditions are also investigated.

Numerical studies on the ignition and propagation for spherically expanding premixed cool flames under gravitational conditions

Cool flame speed is a fundamental parameter, which requires special consideration in terrestrial measurement due to the slow propagation of the cool flame, the intrusion of gravity, and multiple flame regimes (cool, hot, and double flames). The current study employs multiscale numerical simulations with and without gravity to investigate premixed spherical cool flame ignition and propagation. One-dimensional simulations without gravity are adopted to study the effects of initial ambient temperature T0, pressure P0, equivalence ratio ϕ, and ignition kernel temperature TH on feasible conditions for an isolated cool flame measurement, emphasizing the intrinsic couplings among the cool flame, hot flame, and autoignition. Besides considering the minimum and maximum ignition energies for low-temperature ignition (LTI), the results highlight the impacts of the auto-ignition upstream and hot flame downstream of the cool flame on speed measurement. Comprehensive effects of T0, P0, and ϕ are evaluated in order to obtain accurate flame speed versus stretch rate data for extrapolation. Two-dimensional simulations focus on the cool flame deformation with buoyancy. Buoyancy induces a toroidal vortex, causing the spherical cool flame to be mushroom-like at high Richardson numbers, a non-dimensional metric used to evaluate the relative importance of buoyancy. The flame deformation at different ambient temperatures and equivalence ratios are observed. Detailed analyses of the flow field, the deformed flame structure, and the effects of stretch and diffusion are performed. In addition, three equivalent flame radius definitions are proposed and compared to extrapolate cool flame speed. Different from the previous studies on the gravitational hot flames, the current results identify the flame volume-based radius (i.e., Req,V) to be the best one for extrapolating non-spherical cool flame speed, with which cool flames faster than 8 cm/s can be measured within 5% uncertainty. Finally, a systematic strategy is proposed to guide the experimental design. The current work reveals unique cool flame dynamics under gravity conditions and helps to measure the cool flame speed in a terrestrial environment.

Large-Strain Nonlinear Consolidation of Sand-Drained Foundations Considering Vacuum Preloading and the Variation in Radial Permeability Coefficient

The vacuum preloading method effectively strengthens soft soil foundations with vertical drainage, which produces a smear effect when laying sand drains. Meanwhile, the seepage of pore water and soil deformation during consolidation exhibit nonlinear characteristics. Therefore, based on Gibson’s 1D large-strain consolidation theory, this paper developed a more generalized large-strain radical consolidation model of sand-drained soft foundations under free-strain assumptions. In this system, the double logarithmic compression permeability relationships for soft soils with large-strain properties, the variation in the radical permeability coefficient in the smear zone, and the effect of the non-Darcy flow were all included. Then, the partial differential control equations were numerically solved by the finite difference method and validated with existing radical consolidation test results and derived analytical solutions. Finally, the influences of relevant model parameters on consolidation are discussed. The analysis shows that the greater the maximum dimensionless vacuum negative pressure P0, the faster the consolidation rate of sand-drained foundations. Meanwhile, the decrease in the negative pressure transfer coefficient k1 will result in a decreasing final settlement amount. Moreover, the consolidation rate of sand-drained foundations is slower considering the non-Darcy flow, but the final settlement is unaffected.

Degassing Dissolved Oxygen through Bubbling: The Contribution and Control of Vapor Bubbles

An innovative yet sustainable approach for industrial deaeration is proposed, with demonstrated results and analyses, to contribute to finding solutions to improve energy efficiency in this field. Vacuum bubbling deaeration, sharing the same working principles of solubility control and the mass diffusion through vapor (or steam) with conventional thermal deaeration processes, works, however, at lower vacuum pressures. It neither resorts to heating nor requires any third-party materials such as membranes or gases, achieving orders of magnitude of reduction in the expected energy consumption in a simple and concrete way. In this study, the mechanisms of vapor bubble generation and retention were discussed by employing a vacuum bubbling model based on the experimental apparatus at Kongju National University, which uses a venturi-nozzle bubbler. The four parameters influencing vapor bubble generation and retention were identified as vessel pressure p1, nozzle depth Δh, nozzle performance p4−p3, and water temperature Tw. A series of deaeration experiments using the present approach for a tap water sample of 360~400 L were conducted under four different conditions to investigate the effects of the water temperature, vessel pressure, and bubbler nozzle depth. Final dissolved oxygen (DO) concentrations close to zero could be achieved with a vessel pressure of p1=1 kPa, with different bubbling times to reach a zero mg/L reading of DO concentration (case 2 and 3), which demonstrates the vital roles of the vapor bubble generation condition of (psat−p3) and retention condition of (p4−psat) in achieving the lowest DO concentration. Analysis of the test results, based on the discrete-bubble model with the measured DO concentrations and degassing rates, showed promising results in reproducing the experimental data. Though the potential of vacuum bubbling deaeration is demonstrated, for the first time, to its full extent, further research efforts are encouraged in many areas, including more case-specific validation test cases with optimum operating conditions along with the study of more detailed modeling for performance prediction, including energy analysis.

Effect of square-hole obstacle in a long pipe on methane/air premixed explosion characteristics

ABSTRACT This paper primarily studies the impact of the obstacle blocking ratios (BR) on the explosion characteristics of CH4 and Air premixed gases in cuboid pipes, a small plexiglass CH4 explosion pipe test platform of 50 mm × 50 mm × 600 mm was built independently. In this study, square-hole obstacles with different blocking ratios pressure peak set in a horizontal cuboid pipe to analyze the evolution of the explosion pressure, the shape and speed of the flame of propagation of the pre-mixed CH4/air in the pipeline. According to the results, the obstacle has a negligible impact on the initial and secondary pressure peaks, P1 and P2, However, it has a substantial impact on the P3, and the P3 only exists when there is an obstacle. As the BR increases, the time taken for the third pressure peak P3 to appear becomes shorter, the greater the pressure value. When BR = 0.75, the highest P3 recorded was 12.5 kPa and 30 kPa for methane equivalent ratios of 0.8 and 1, respectively. Compared with the non-obstacle, the square-hole obstacle in the pipe has a significant influence on the evolution of the flame shape. When there is an obstacle, after the hemispherical flame, the center position of the flame front is deformed and convex, and then the bundle flame is formed, and there is no tulip flame. Simultaneously, the presence of an obstruction results in a rise in the mean flame propagation velocity, the flame is the first to reach the location of the obstacle, when BR = 0.5. As the flame moves through the obstacle, its propagation velocity escalates with the blockage ratio’s progression.

Process analysis and optimization of high-N2 natural gas liquefaction

The demand for natural gas (NG) is increasing rapidly due to the world energy crisis. Liquefied Natural Gas (LNG) technology is one of the most flexible and reliable supply solutions, which has already been a major research hotpot in energy use. However, NG with high-N2 content lowers the gas calorific value and value of the gas and increases the energy consumption for production and transport. To address this issue, this study established nitrogen removal from the NG process using a single-column cryogenic distillation process based on Aspen HYSYS® in this study. An expanding refrigeration process using N2-CH4 was selected to provide the required cold energy for this plant, and the process power consumption and LNG specific power consumption was used as evaluation indicators. Results from sensitivity analysis showed that by the increase of natural gas feed temperature T1, the distillation column operation pressure Pc, and refrigerant high pressure P3, the LNG specific power consumption also demonstrated an increasing trend. The variables of natural gas inlet pressure P1, the outlet temperature of natural gas from pre-cooler T2, the ratio of return RR, the methane content ZCH4, the temperature of refrigerant after pre-cooler T4 and refrigerant low pressure P5 had a negative impact on the LNG specific power consumption. After conducting an optimization algorithm, the minimum LNG specific power consumption was determined to be 56.17 kJ/mol. Exergy analysis demonstrated that the total exergy destruction was 2076.13 kW. The compressor and expander components accounted for 31.57% and 26.29% of the total exergy losses respectively. This research provides valuable insights into optimizing LNG production processes by mitigating the impact of high nitrogen content, and it contributes to the advancement of LNG technology and energy efficiency in the industry.

Exploring the effect of surface wettability on heterogeneous condensation of carbon Dioxide: A molecular dynamics study

The condensation characteristics of carbon dioxide (CO2) are critical for several engineering applications, including pressurized liquefied natural gas technology and carbon capture, utilization, and storage (CCUS). This study applies molecular dynamics simulations to investigate CO2 condensation on different solid surfaces by modulating the solid–liquid interaction coefficient, α, to alter wettability. The CO2 condensation process is categorized into three phases: nucleation, coalescence, and growth. Our findings suggest that increasing the α value not only enhances surface wettability but also alters the condensation of CO2 from a droplet to a film form. Higher α values are linked with increased condensation rate and liquefaction degree, thus leading to improved heat transfer performance. The effects of different initial system pressure (p0) and cooling temperatures (Tcold) on CO2 condensation are also examined. A reduction in Tcold and an increase in p0 both contribute to an enhanced liquefaction rate and degree of CO2 and improve heat transfer. For instance, when α = 0.10, decreasing Tcold from 200 K to 180 K increases the CO2 liquefaction rate from 46.68% to 72.95%, and when α = 0.24, the rate grows from 80.81% to 91.99%. This study provides pioneering insights into the heterogeneous condensation and heat transfer processes of CO2 at the microscopic level, potentially offering valuable knowledge for optimizing CO2 capture or removal in engineering applications.

R&amp;D of a Hydraulic Hydrogen Compression System for Refuelling Stations

Abstract The article presents a hydraulic hydrogen compression solution designed to serve as a booster compressor. It can be adapted to changing parameters of the inlet pressure of hydrogen and allows stabilising the hydrogen accumulation process in the high-pressure storage. The main results of this study were obtained using a numerical model developed to explore the thermodynamic processes that occur during the hydraulic compression of hydrogen. The modelling was carried out using COMSOL Multiphysics® 6.0 software with the CFD and heat transfer modules. The compression chamber in the form of a cylinder with a volume of 1.14 l and wall thickness of 5 mm was used in the computational model. The aim of these simulations was to investigate the temperature change limits of hydrogen, cylinder walls and working fluid, as well as to estimate the actual value of pressure inside the cylinder. The considered process of pressure increase in the cylinder chamber was modelled as a continuous change of volume filled with working fluid with discrete time step of 0.01 s, taking into account the increase of temperature inside the cylinder. The derived modelling results for different durations of compression stroke ts from 0.5 to 20.0 s were presented. The curves of energy consumption and temperature rise during the compression process were calculated for initial hydrogen pressures P1 = 3.0, 10.0, 15.0 and 20.0 MPa and compression ratio Kc = 5.0. The results of simulation of thermodynamic processes and their analysis allowed estimating energy consumption in the system of hydraulic compression and determining conditions which would lead to the increase in efficiency of hydrogen compression operation systems under consideration.

Water Vapor Adsorption on Desiccant Materials for Rotary Desiccant Air Conditioning Systems

In order to determine the water vapor adsorption performance of a rotary desiccant-based air conditioning system, the behavior of water adsorption on cylindrical pores of different sizes was studied by using classical density functional theory (CDFT) based on perturbated chain statistical associating fluid theory (PC-SAFT). Firstly, the structural parameters of the desiccant material were characterized by scanning electron microscopy (SEM), X-ray Energy Dispersive Spectrum (EDS), and N2 adsorption/desorption isotherms, as well as adsorption equilibrium measurements of water vapor at temperature range 293–308 K. Secondly, the potential energy equation of water molecules in cylindrical pores was determined, and contribution of various terms of PC-SAFT for simulating fluid in cylindrical pores were established. Finally, the pore size distribution (PSD) of the desiccant materials is determined by the PC-SAFT kernel. Moreover, water vapor condensation was investigated with the PC-SAFT model in micropores. The results indicate that the rotary desiccant materials have a large number of micropores with a volume of 0.3669 cm3/g and the amount of water adsorption is about 0.285 g/g. The condensation pressure and the pore width corresponding to the saturated pressure P0 grow with an increase in the temperature, signifying that adjusting the PSD of the material has a significant effect on improving the dehumidification performance. The research concludes that the PSD range of the oxide cylindrical pore between 1.09 and 1.53 nm is particularly beneficial for dehumidification. This study provides valuable theoretical guidance for optimizing dehumidification materials.

MATHEMATICAL MODEL AND DYNAMICS OF A PILOT CONTROL PRESSURE-REDUCING VALVE

Energy consumption is currently on the rise. To control large energy flows, larger sizes of actuators and control mechanisms are required.One of the main control elements of the system is the pressure regulator. A pressure regulator or pressure reducing valve (RV) is a device designed to reduce and continuously maintain a certain, preconfigured, pressure level («after itself»), which is different from the nominal one. High requirements are imposed on the operation of the RV to maintain the set pressure value, such as: high speed, no overshoot and static error, since the presence of these dynamic properties in the RV can cause the «start of disasters». Modern methods for the development and analysis of technical systems are based on the widespread use of mathematical models based on detailed knowledge of the processes and phenomena occurring in the systems under consideration. The use of a mathematical model is of great and urgent importance – it allows not to carry out expensive and costly physical experiments both in terms of time and money. The results obtained in the course of computer simulation can be used to optimize systems, determine operating modes and causes of possible failures. The article describes the principle of operation and the scheme of the pressure reducing valve of indirect action. The developed mathematical model of an indirect pressure reducing valve is presented. With the help of the created mathematical model, the dynamic characteristics of the indirect pressure reducing valve were analyzed depending on the change in its design parameters. The limit of stability of the pressure reducing valve is determined, when the values of which are exceeded, self-oscillations are observed in the system of the pressure reducing valve. Recommendations are given for choosing and setting the value of pressure p2 at the outlet of the reducing controlled valve. The scientific novelty of the work should include the created mathematical model of a pressure reducing controlled valve of indirect action and the results of the analysis of its dynamic properties.

Mechanical Soil Resistance Influenced by Different Tillage Systems and Tractor Tire Pressures

Intensive agricultural practices affect soil compaction, and their indirect and direct effects on crop growth and development are an increasingly important focus of scientific research. The objective of this study was to determine the influence of different tillage systems on soil compaction and to observe the influence of tractor tire pressure on penetrometer resistance during sowing. The three-year study was conducted on the heavy pseudogley soil of Brod-Posavina County in the Republic of Croatia. During the research, crops were observed in the following cropping sequence: soybean (Glycine max L.) in the first year, maize (Zea mays L.) in the second year and winter wheat (Triticum aestivum L.) in the third year. The tillage systems as the main study factor were conventional tillage (CT) plowing to a depth of 35 cm, disc tillage (DH) to a depth of 15 cm, loosening (CH) to a depth of 30 cm, and undermining (SS) to a depth of 50 cm. The following pressures were used as a subfactor of this study, namely the pressure of the front and rear tires of the tractor during sowing: p1 (front 1.0 bar/rear 0.8 bar), p2 (front 2.0 bar/rear 1.6 bar), and p3 (front 3.0 bar/rear 2.4 bar). The tillage systems applied resulted in different soil compaction, thus the deepest tillage SS had the lowest resistance and the DH tillage had the highest resistance in all three experimental years. Penetrometer measurements showed the influence of tire pressure p1 on reducing compaction as early as the first year in 2017, while in the last year of research in 2019, tractor tire pressure p3 during sowing contributed to a significant increase in soil compaction.

Propagating characteristics of spherical flames in H2-N2O mixtures

The laminar burning velocity and cellular instabilities of premixed flame in H2-N2O mixtures were studied experimentally at various equivalence ratios (φ) and initial pressures (p0). High-speed schlieren was used to record the morphology of the spherical flame. Based on the spherical flame method, the laminar burning velocity and Markstein length were derived. In addition, the Lewis number, flame thickness, thermal expansion and Zel’dovich number were evaluated numerically. The results show that both the laminar burning velocity and Markstein length increase with the equivalence ratio. The Lewis number (less than unity) increases with the equivalence ratio while the flame thickness exhibits an inverse evolution. Hence, the most unstable flames were found to be at φ= 0.4–0.6 due to the combined effects of the thermal-diffusion and hydrodynamic instabilities. At lower initial pressure, the flame front is smooth in spite of the diffusion-thermal instability. With the increase of initial pressure, both the diffusion-thermal instability and hydrodynamic instability dominate the cellular structure of the flame front. The flames undergo self-acceleration at φ= 0.4–0.6 and p0= 40 kPa, with the acceleration exponents close to 1.5 (the value of self-turbulization). Due to the local oscillation of velocity, the flame propagation speed decreases after the self-similar regime.