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To explore the potential for further enhancing the gas mixing uniformity of natural gas (NG) engines, this paper identifies turbulent kinetic energy (TKE), which has an essential impact on gas mixing, as the entry point of the research. After establishing a computational fluid dynamics (CFD) model for NG engines' direct injection and mixing processes, the inlet pressure is selected as the experimental variable to investigate the influence of TKE on gas mixing uniformity. In particular, by proposing the theoretical concept of the core mixing stage, the numerical variation rule between the best mixture concentration region (BMCR) percentage and the mean turbulent kinetic energy (MTKE) of the core mixing stage is analyzed under certain injection timing conditions. The results indicate that, with identical intake pressures, an advanced gas injection timing elevates the total turbulence kinetic energy (TTKE) during the core mixing stage, thereby amplifying the uniformity of the gas mixture at the ignition. In specific scenarios, as the intake pressure increases, the decreasing trend in the BMCR proportion closely resembles the diminishing trend in the MTKE during the core mixing stage. Scrutinizing the variation trend in either parameter allows for an approximate prediction of the variation trend in the other parameter. When the intake pressure is gradually raised from the naturally aspirated state, the adequacy of the gas jet development is progressively reduced by the increasing back pressure in the cylinder. [ABSTRACT FROM AUTHOR]

Cavitation is a common issue in pumps, causing a decrease in pump head, a fall in volumetric efficiency, and an intensification of outlet flow pulsation. It is one of the main hazards that affect the regular operation of the pump. Research on pump cavitation mainly focuses on mixed flow pumps, jet pumps, external spur gear pumps, etc. However, there are few cavitation studies on external herringbone gear pumps. In addition, pumps with different working principles significantly differ in the flow and complexity of the internal flow field. Therefore, it is urgent to study the cavitation characteristics of external herringbone gear pumps. Compared with experimentalmethods, visual research and cavitation area identification are achieved through computation fluid dynamic (CFD), and changing the boundary conditions and shape of the gear rotor is easier. The simulation yields a head error of only 0.003% under different grid numbers, and the deviation between experimental and simulation results is less than 5%. The study revealed that cavitation causes flow pulsation at the outlet, and the cavitation serious area is mainly distributed in the meshing gap and meshing area. Cavitation can be inhibited by reducing the speed, increasing the inlet pressure, and changing the helix angle can be achieved. For example, when the inlet pressure is 5 bar, the maximumgas volume fraction in themeshing area is less than 50%. These results provide a reference for optimizing the design and finding the optimal design parameters to reduce or eliminate cavitation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Multi-outlet pipes can be used to distribute and collect fluids and have applications in various engineering fields, especially in the water supply system. The hydraulic design of a submain unit pipeline with multiple outlets is a very important concern for the proper hydraulic performance of irrigation water distribution systems. The operating inlet pressure head, H0I, is a main hydraulic component for the proper hydraulically efficient design and evaluation of pressure head distribution along the line. The energy-gradient ratio (EGR) approach is a useful tool to identify first which type of pressure profile occurs for a given uniform design slope with other hydraulic variables initially known and then, comprehensively evaluate its definite hydraulic characteristics along the line. Knowing the hydraulic properties of any type of pressure profile regarded enables the design engineer to evaluate pressure parameters through the line sections in a simple way. The procedure is simplified by regarding the localized head loss along the pipe but neglecting the change in kinetic head. The present analytical technique performs sufficiently accurately in comparison with the computer-aided software design technique, for all performed simulations. HIGHLIGHTS This paper presents a new analytical procedure based on the energy-gradient ratio (EGR) approach, identifying different types of energy head profiles.; The present technique is simple, direct, and sufficiently accurate for a wide range of water application uniformity.; The proposed method offers considerable flexibility by directly computing values of the required hydraulic variables along the energy profile, incorporating different uniformity patterns and without requiring any additional hydraulic variables, such as pipe diameter, total inlet discharge, required average outflow, downstream end pressure head, total friction drop or outlet characteristics.;

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, an a typical domestic cooker-burner was investigated numerically using parametrical research to observe the effects of four different fuels. Propane, natural gas, hydrogen, and biogas (three different compositions) were used in the simulations. Sixteen design parameters were examined for comparison, including four different fuel inlet pressures and four different fuel channel diameters. Simulation results were validated with experimental results and compared to each other. The comparison among all cases was given visually and graphically as emissions, temperatures, and efficiencies. In the mentioned pressure range, propane cases have shown almost independent behavior concerning the change in diameters, except for 0.25-mmdiameter cases. Furthermore, the temperature drop on the cooker’s bottom surface was observed at all pressure levels for natural gas and propane, with an increasing supportive fuel channel diameter after 0.30 mm in general. As predicted for the biogas cases, lower flame temperatures have been observed from visual Computational Fluid Dynamics results compared to the other gases due to their low calorific value. While unburnt hydrocarbons and CO emission levels were observed to be the highest for natural gas, NO appeared to be the highest, approximately three times higher than the average NO emissions of all fuel types for hydrogen among those of other fuels. Also, a higher average cooker bottom temperature, approximately 8% higher than the average surface temperature of all fuel types, was obtained for natural gas. Higher efficiency, about 50% higher than the average efficiency of all fuel types, was obtained for hydrogen fuel. Moreover, results showed that supportive fuel channel diameter was the most effective parameter for NO emissions. [ABSTRACT FROM AUTHOR]

The self-excited oscillating cavitation jet nozzle (SEOCJN) serves as a crucial component for converting hydrostatic energy into dynamic pressure energy and ensuring optimal hydraulic and cavitation performance of cavitating jets. Thus, it is of crucial significance to understand the cavitation characteristics and the influence law of SEOCJN for its extensive industrial applications. This paper utilizes numerical simulation methods to analyze the dynamic process of cavitation initiation, development, and outlet cavitation performance of SEOCJN. It explores the effects of inlet pressure and flow rate on the frequency characteristics of SEOCJN, and establishes a mathematical relationship between self-excited oscillation frequency and outlet flow frequency. The results indicate that the self-excited oscillation nozzle has an inlet diameter (D1) of 4.7 mm, an outlet diameter (D2) of 12.2 mm, a length (L) of 52 mm, a chamber diameter (D) of 83 mm, an oscillation angle of 120°, and an inlet pressure (Pin) of 4.8 MPa. At these parameters, the frequency of the pulse jet reaches 830.01 Hz, with an internal flow period of approximately 0.0024 s. The maximum vapor volume fraction is found to be located 0.28 m from the outlet of the SEOCJN. Furthermore, the frequency of self-excited oscillation pulse increases with an increase in inlet pressure. These findings provide a theoretical basis for the industrial application of self-excited oscillation cavitation jet nozzles.

To explore the potential for further enhancing the gas mixing uniformity of natural gas (NG) engines, this paper identifies turbulent kinetic energy (TKE), which has an essential impact on gas mixing, as the entry point of the research. After establishing a computational fluid dynamics (CFD) model for NG engines’ direct injection and mixing processes, the inlet pressure is selected as the experimental variable to investigate the influence of TKE on gas mixing uniformity. In particular, by proposing the theoretical concept of the core mixing stage, the numerical variation rule between the best mixture concentration region (BMCR) percentage and the mean turbulent kinetic energy (MTKE) of the core mixing stage is analyzed under certain injection timing conditions. The results indicate that, with identical intake pressures, an advanced gas injection timing elevates the total turbulence kinetic energy (TTKE) during the core mixing stage, thereby amplifying the uniformity of the gas mixture at the ignition. In specific scenarios, as the intake pressure increases, the decreasing trend in the BMCR proportion closely resembles the diminishing trend in the MTKE during the core mixing stage. Scrutinizing the variation trend in either parameter allows for an approximate prediction of the variation trend in the other parameter. When the intake pressure is gradually raised from the naturally aspirated state, the adequacy of the gas jet development is progressively reduced by the increasing back pressure in the cylinder.

The self-excited oscillating cavitation jet nozzle (SEOCJN) serves as a crucial component for converting hydrostatic energy into dynamic pressure energy and ensuring optimal hydraulic and cavitation performance of cavitating jets. Thus, it is of crucial significance to understand the cavitation characteristics and the influence law of SEOCJN for its extensive industrial applications. This paper utilizes numerical simulation methods to analyze the dynamic process of cavitation initiation, development, and outlet cavitation performance of SEOCJN. It explores the effects of inlet pressure and flow rate on the frequency characteristics of SEOCJN, and establishes a mathematical relationship between self-excited oscillation frequency and outlet flow frequency. The results indicate that the self-excited oscillation nozzle has an inlet diameter (D1) of 4.7 mm, an outlet diameter (D2) of 12.2 mm, a length (L) of 52 mm, a chamber diameter (D) of 83 mm, an oscillation angle of 120°, and an inlet pressure (Pin) of 4.8 MPa. At these parameters, the frequency of the pulse jet reaches 830.01 Hz, with an internal flow period of approximately 0.0024 s. The maximum vapor volume fraction is found to be located 0.28 m from the outlet of the SEOCJN. Furthermore, the frequency of self-excited oscillation pulse increases with an increase in inlet pressure. These findings provide a theoretical basis for the industrial application of self-excited oscillation cavitation jet nozzles. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhengzhou University: Engineering Science is the property of Editorial Office of Journal of Zhengzhou University: Engineering Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Methane which can be produced from biogas has a great potential to be used as an alternative renewable fuel for spark-ignition engines. However, engines need to be optimized for methane use. The aim of this study was to numerically optimize a spark-ignition engine fueled with methane and operated at a constant speed of 1,500 rpm via using a validated two-zone combustion model. The model was able to predict engine performance parameters, NO emission, and engine knock at different engine operating conditions including inlet pressure, compression ratio, and excess air factor. Engine knock was prevented by increasing the excess air factor up to 1.2 when the engine operated with higher inlet pressure and compression ratio. It was found that a maximum inlet pressure of only 120 kPa could be used with an engine compression ratio of 14 and excess air factor of 1.2 for knock free operation. The peak engine power was produced when the engine operated with an inlet pressure of 200 kPa and compression ratio of 8 or 9. It was also found that the optimum operating condition which resulted in high engine power accompanied with low fuel consumption and high efficiency was obtained when the engine operated with an inlet pressure of 180 kPa and a compression ratio of 11. This condition required the engine to operate with an excess air factor of 1.19 to prevent engine knock. However, operating the engine at this optimum condition would be accompanied with high NO emission.

An experimental investigation was conducted to investigate the effects of different cold orifice diameters and operating pressures of the vortex tube. A vortex tube test rig was employed to conduct the experiments for various cold orifice diameters and operating pressures. Cold orifice diameters range from 1 mm to 6 mm, whereas the pressure condition ranges from 2 to 5 bar. The vortex generators were made up of brass material having six inlet nozzles. It was found that the temperature separation of the vortex tube significantly depends on the cold orifice diameter of the vortex tube and operating pressure. The study demonstrates the deviation of cold temperature separation with respect to the cold orifice diameters and inlet pressure for different cold mass fractions. In addition, present experimental results are used to determine the optimum cold orifice diameter, which is 5 mm at 5 bar inlet pressure. The percentage improvement in average cold temperature separation for 5 mm cold orifice diameter is 66.18% compared to rest of the cold orifice diameters at an inlet pressure of 5 bar. The maximum cooling power separation is 0.08 kW at 0.3 cold mass fraction and inlet pressure of 5 bar. The CFD technique was approached to discuss the complex fluid flow inside the tube at various radial distances. A three-dimensional numerical study was done and validated with the present experimental work. It was found that the numerical results are in good agreement with the present experimental data.

Laser diode pumped solid-state lasers (DPSSLs) have been widely used in many fields, and their thermal effects have attracted more and more attention. The laser diode (LD) side-pumped amplifier, as a key component of DPSSLs, is necessary for effective heat dissipation. In this paper, instead of the common thermal analysis based only on a crystal rod model, a fluid–structure interaction model including a glass tube, cooling channel, coolant and crystal rod is established in numerical simulation using ANSYS FLUENT for the configuration of an LD array side-pumped laser amplifier. The relationships between cooling layer thickness, coolant velocity and maximum temperature, maximum equivalent stress, inlet pressure and the convective heat transfer coefficient are analyzed. The results show that the maximum temperature (or maximum equivalent stress) decreases with the increase in the coolant velocity; at low velocity, a larger cooling layer thickness with more coolant is not conductive enough for improved heat dissipation of the crystal rod; at high velocity, when the cooling layer thickness is above or below 1.5 mm, the influence of the cooling layer thickness on the maximum temperature can be ignored; and the effect of the cooling layer thickness on the maximum equivalent stress at high velocity is not very significant. The comprehensive influence of various factors should be fully considered in the design process, and this study provides an important reference for the design and optimization of a laser amplifier and DPSSL system. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted to investigate the effects of different cold orifice diameters and operating pressures of the vortex tube. A vortex tube test rig was employed to conduct the experiments for various cold orifice diameters and operating pressures. Cold orifice diameters range from 1 mm to 6 mm, whereas the pressure condition ranges from 2 to 5 bar. The vortex generators were made up of brass material having six inlet nozzles. It was found that the temperature separation of the vortex tube significantly depends on the cold orifice diameter of the vortex tube and operating pressure. The study demonstrates the deviation of cold temperature separation with respect to the cold orifice diameters and inlet pressure for different cold mass fractions. In addition, present experimental results are used to determine the optimum cold orifice diameter, which is 5 mm at 5 bar inlet pressure. The percentage improvement in average cold temperature separation for 5 mm cold orifice diameter is 66.18% compared to rest of the cold orifice diameters at an inlet pressure of 5 bar. The maximum cooling power separation is 0.08 kW at 0.3 cold mass fraction and inlet pressure of 5 bar. The CFD technique was approached to discuss the complex fluid flow inside the tube at various radial distances. A three-dimensional numerical study was done and validated with the present experimental work. It was found that the numerical results are in good agreement with the present experimental data. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, an experimental test rig has been developed by utilising the free-piston linear generator (FPLG) principle of a dual-piston air-driven system. The mechanical energy of the FPLG is converted into electric power through a linear generator. The piston motion, root mean square (RMS) power output, operating frequency, system stability and the conversion efficiency of the FPLG at various inlet pressure and valve opening duration (VOD) are duly discussed in the paper. It is noticed that the piston displacement (stroke) is associated with the VOD and inlet pressure, which have the greatest effect on the FPLG motion characteristics. A long VOD leads to a high piston speed, causing high peak power output. However, the RMS power shows an approximately linear decline with the increase in VOD due to the free-piston dwelling for a certain time at the dead centre position before the exhaust process starts. The FPLG can be achieved a maximum RMS power of 120 W when the inlet pressure is 8 bar and VOD is 30 ms. When the inlet pressure changed from 8 bar to 5 bar, the FPLG operating frequency shows a similar trend and values because it is associated with the piston velocity and stroke. The FPLG Cycle-to-Cycle variation (COV) is low when the inlet pressure is high, and the system stability increases with decreases in VOD. As the VOD increases, the indicated efficiency and work to electrical efficiency increase, whereas the thermal to work efficiency decreases. The maximum indicated efficiency, work to electrical efficiency and thermal to work efficiency achieved are 59.9%, 14.7% and 14.6 %, respectively.

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Numerical simulations are performed to study the effect of backpressure disturbances on a shock train. The basic problem consists of a shock train within a constant-area channel with an M=2 inflow and backpressure applied to the outlet. By subjecting the shock train to different fixed backpressures, it is shown that the shock train length varies linearly with backpressure, while the shock spacing is conserved. Through backpressure step forcing, it is shown that the response of the shocks, after an initial lag, is largely determined by the magnitude of the step change. Step increases in backpressure cause upstream shock movements with higher shock pressures. The opposite response occurs with backpressure decreases. With sinusoidal backpressure forcing, the shock train oscillates at the applied forcing frequency. The forcing propagates disturbances upstream, and therefore there is a noticeable forcing-response lag. Higher frequency disturbances are filtered as they travel upstream through the shock train while lower frequencies induce larger shock oscillations and produce upstream offsets in the shock positions. Further examination of the flow reveals a region of low-frequency motion below the leading shock, which becomes strongly amplified by the lowest backpressure forcing frequency. [ABSTRACT FROM AUTHOR]

• The distribution of the reverse flow boundary is analyzed under four different inlet conditions. • The parameters at the reverse flow boundary of the vortex tube were obtained and discussed. • Cold fluid flow from inside to outside at Z = 0.1 ∼ 0.3; reverses at Z > 0.6 with flow oscillations. • Three energy transfer processes were obtained, including momentum transfer, heat transfer and turbulent heat transfer. The performance of the vortex tube (also known as the Ranque-Hilsch tube) is significantly influenced by the inlet pressure and the internal flow processes, which can be categorized into two distinct flows: the center and the outer flow. The reverse flow boundary, acting as the interface between the two flows, plays a crucial role in energy separation. However, the research on the location of the reverse flow boundary and the associated flow parameters and energy transfer at this boundary are still insufficient. Therefore, this research employs the measurement method of interpolation probe to analyze the distribution of the reverse flow boundary and the specific flow parameters at this boundary. These parameters include static pressure gradient, angular velocity, and static temperature gradient, which substantially impact energy separation. A qualitative analysis of the energy transfer process in the vortex tube by examining mass flow in the reverse area and tangential and axial velocities are further delved. This analysis covers momentum transfer, heat transfer, and turbulent heat transfer processes resulting from the compression and expansion processes. The findings provide a research direction for exploring the energy separation performance of vortex tubes. [ABSTRACT FROM AUTHOR]

A jet pump operates under the Venturi effect, where a fluid enters through a primary nozzle and, when passing through a convergent-divergent nozzle, it reaches supersonic conditions, originating a vacuum pressure in a secondary fluid. Fluid-dynamics simulations of jet pumps are performed here using standard k-ε turbulence model. Numerical results are compared to those obtained with an analytical model previously developed, concluding that both approaches predict a similar behavior of Match number, fluid pressure and fluid velocity. A parametric study is done to determine the influence of inlet pressure and primary nozzle position in jet pump performance, Mach number field and total pressure profile. Both parameters have an important influence in those variables, but this is not monotonic in all cases.

In order to determine the optimal inlet pressure during permeability test of municipal solid waste, the gas permeability test of fresh waste and old landfilled waste under different compaction density was carried out by means of the self-developed gas permeability test device. The effect of gas compressibility on gas permeability and the optimum inlet pressure of gas permeation test were determined. The test results show that when 1～10 kPa is used for the gas permeability test, the pressure difference and the pressure squared difference have a good linear relationship with the gas flow, and the gas compressibility has negligible influence on the gas permeability. The best inlet pressure of fresh waste is 3 kPa, and the best inlet pressure of old landfilled waste is 4 kPa. [ABSTRACT FROM AUTHOR]

The cavitation development process in regulating valve under different inlet pressures is investigated experimentally and numerically in our paper. The influence of inlet pressure Pin on cavitation location, shape, area and intensity is studied in axial and radial directions, and the axial and radial pressure distributions are also analyzed. The cavitation is generally annular in shape radially and irregular polygon in shape axially. Cavitation bubbles occur at the throat entrance when the inlet pressure increases. The bubbles then accumulate, and a bubble ring is formed. The cavitation development process under different inlet pressures is separated into three stages, no-cavitation, initial cavitation and steady-cavitation stages. During the no-cavitation stage, no bubbles exist. During the initial cavitation stage, bubbles occur and the area and intensity of cavitation increase in the radial and axial directions with increasing inlet pressure. During the steady-cavitation stage, the calculation area and intensity of bubble rings reach their maximum values and then remain stable. The cavitation bubbles extend downstream, and the area of cavitation ring and cavitation intensity increase with increasing inlet pressure. A slit exists between the upper and lower parts of bubbles in the cavitation process, both parts touch each other forming a whole.

Laser diode pumped solid-state lasers (DPSSLs) have been widely used in many fields, and their thermal effects have attracted more and more attention. The laser diode (LD) side-pumped amplifier, as a key component of DPSSLs, is necessary for effective heat dissipation. In this paper, instead of the common thermal analysis based only on a crystal rod model, a fluid–structure interaction model including a glass tube, cooling channel, coolant and crystal rod is established in numerical simulation using ANSYS FLUENT for the configuration of an LD array side-pumped laser amplifier. The relationships between cooling layer thickness, coolant velocity and maximum temperature, maximum equivalent stress, inlet pressure and the convective heat transfer coefficient are analyzed. The results show that the maximum temperature (or maximum equivalent stress) decreases with the increase in the coolant velocity; at low velocity, a larger cooling layer thickness with more coolant is not conductive enough for improved heat dissipation of the crystal rod; at high velocity, when the cooling layer thickness is above or below 1.5 mm, the influence of the cooling layer thickness on the maximum temperature can be ignored; and the effect of the cooling layer thickness on the maximum equivalent stress at high velocity is not very significant. The comprehensive influence of various factors should be fully considered in the design process, and this study provides an important reference for the design and optimization of a laser amplifier and DPSSL system.

In this work, the cavitation water jet technique was used to clean the inner walls of oil pipes after tertiary oil recovery. The surface morphology, depth of impinging pits, and corrosion resistance of aluminum samples after impingement with the cavitation water jet were examined using scanning electron microscopy (SEM), 3D microscopy, and an electrochemical workstation. When the inlet pressure was higher than 3 MPa, the number of cavitation bubbles generated by the cavitation nozzle increased with an increase in inlet pressure. Moreover, the cleaning effect that the cavitation water jet had on the aluminum samples was higher than that of general water jet technology. There were no obvious changes to the surface of the aluminum samples when the inlet pressure was decreased to 13 MPa. Meanwhile, the mass loss of aluminum samples also increased. However, the internal corrosion resistance of the pipe wall after impact was relatively low. These results indicate that the impinging efficiency of the cavitation water jet was obviously enhanced and the degree of damage to the oil pipe wall was low at an inlet pressure of 15 MPa. The best target distance was 8–12 mm, and at this point, the jet flushing effect was the best. Moreover, the jet velocity at the outlet cavity was 184 m/s, and the jet strike area was 250 mm2. [ABSTRACT FROM AUTHOR]

In view of the extensive application of swirl flow pipes (vortex tubes) in refrigeration systems, the parameters of swirl flow pipes were investigated to provide optimal cooling and heating conditions. Three-dimensional numerical simulations were carried out using available experimental data and models. The analysis verified that the heat pipe with a length of 175 mm performed better than the swirl flow pipe with a length of 125 mm, confirming experiments by Agrawal. Meanwhile, by comparing different pressures, it was found that in the single-nozzle swirl flow pipe, the greater the increase of pressure (0.1–1.0 MPa), the greater the burden on the vortex chamber and the more serious the wear is, which can be seen in the higher inlet pressure. In order to improve the durability of the swirl flow pipe, we suggest using a swirl flow pipe with more nozzles. Finally, according to the simulation results, with the rise of carbon dioxide pressure potential energy at the inlet, the cooling effect of the swirl flow is first increasing and then decreasing. When the swirl flow pipe is used as a refrigeration device to determine the minimum cooling temperature under the maximum pressure, the lowest temperature of the 125 mm swirl flow pipe was 252.4 K at 0.8 MPa, while the lowest temperature of the 175 mm swirl flow pipe was 246.0 K. Secondly, the distance from the inlet to the hot outlet of the swirl flow pipe had little effect on the cooling temperature and radial velocity, but increasing its distance increased the wall temperature of the swirl flow pipe because it increases the contact time between the airflow and the hot end of the tube wall. When the swirl flow pipe is used as a heat-producing device, increasing the tube length of the swirl flow pipe appropriately increases its maximum heat-producing temperature. [ABSTRACT FROM AUTHOR]

Abrasive flow precision machining technology is an effective technology for precision machining special-shaped curved surface products in the mechanical field. In order to explore the vortex formation mechanism of special inner curved surface machined by abrasive flow precision machining, taking the polygonal spiral curved surface tube as the research object, the large eddy simulation method is used to analyze the precision machining behavior of abrasive flow and the effect of vortex cluster on the wall under different inlet pressure. The motion law of abrasive is expounded, the formation mechanism of the fluid vortex is revealed, and the mechanism of abrasive micro-cutting is discussed. The results show that the inlet pressure of abrasive flow plays an important role in the machining quality of abrasive flow. With the increase of inlet pressure, the precision machining quality of abrasive flow is improved accordingly. Properly increasing the inlet pressure of the abrasive flow can effectively improve the inner surface machining quality of the polygonal spiral curved surface tube, and the abrasive flow precision machining technology can obtain the ideal surface quality and improve the surface accuracy of the machined workpiece. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When tubing is in a high-temperature and high-pressure environment, it will be affected by the impact of non-constant fluid and other dynamic loads, which will easily cause the tubing to vibrate or even resonate, affecting the integrity of the wellbore and safe production. In the structural modal analysis of the tubing, the coupling effect of the fluid and the tubing needs to be considered at the same time. In this paper, a single tubing is taken as an example to simulate and analyze the modal changes of the tubing under dry mode and wet mode respectively, and the effects of fluid solid coupling effect, inlet pressure, and ambient temperature on the modal of the tubing are discussed. After considering the fluid–structure interaction effect, the natural frequency of tubing decreases, but the displacement is slightly larger. The greater the pressure in the tubing, the greater the equivalent stress on the tubing body, so the natural frequency is lower. Furthermore, after considering the fluid–solid coupling effect, the pressure in the tubing is the true pulsating pressure of the fluid. The prestress applied to the tubing wall changes with time, and the pressures at different parts are different. At this time, the tubing is changed at different frequencies. Vibration is prone to occur, that is, the natural frequency is smaller than the dry mode. The higher the temperature, the lower the rigidity of the tubing and the faster the strength attenuation, so the natural frequency is lower, and tubing is more prone to vibration. Both the stress intensity and the elastic strain increase with the increase of temperature, so the displacement of the tubing also increases.

An experimental test system for cryogenic high-speed hydrodynamic non-contact mechanical seals is developed. Based on this system, the performances of seals under different working conditions are studied in detail in this paper. With the experimental results, the main performances of the seals (such as inlet and outlet temperatures, separated speed, face temperature, friction force, friction coefficient, leakage rate) are obtained, and the relationships of the performances with the inlet fluid pressure, the closing force and the rotational speed are discussed. The results show that the difference between the outlet and inlet temperatures decreases with increasing inlet fluid pressure. As the speed increases, the friction force varies little and remains at a constant value. The friction coefficient of the seal is approximately 0.12 and basically does not change with the speed. The leakage rate is also maintained at approximately 190 g/s. With the increase in the closing force, the friction at the seal's face does not change greatly, which indicates that the friction at the face is always in a stable state with the seal's closing force. [ABSTRACT FROM AUTHOR]

In order to make a reasonable control strategy of Reactivity Controlled Compression Ignition (RCCI) combustion mode and to explore the influence of different combustion boundary conditions on the combustion and emission characteristics of RCCI, in this paper, a six-cylinder heavy-duty diesel engine was used to test the RCCI of gasoline / diesel dual fuel under the condition of constant engine speed and gasoline energy Premixing Ratio (PR). The effects and its degree of Start of Injection (SOI) and Inlet Pressure (IP) on gasoline/diesel RCCI combustion and emission characteristics were studied under different Cycle Energy (CE) operating conditions with a fixed gasoline energy PR of 65%. The results indicated that the effects of SOI and IP on all combustion characteristic parameters hardly changed with the increase of CE. For example, the ignition delay increased with the advancement of SOI under different CE. The effects degree of SOI and IP on some combustion characteristic parameters changed with the increase of CE. For example, with the same advancement of SOI (23 °CA), the maximum of cumulative heat release was average increased by about 150 J when CE was 885 J, while the maximum of cumulative heat release was average increased by about 250 J when CE was 1 700 J, the effects degree of SOI on maximum of cumulative heat release became greater with the increase of CE. What’s more, the adjustment range of IP on the peak average temperature in the cylinder was decreased by about 130 K, when CE increased from 885 to 1 700 J, the effects degree of IP on the peak average temperature in the cylinder became greater with the increase of CE, which indicated that the adjustment capacity of IP on the in-cylinder temperature became stronger. However, the effects degree of SOI and IP on some combustion parameters did not change with the increase of CE, such as the effects degree of SOI and IP on the ignition delay, the increase of the ignition delay was almost the same (about 10 °CA) with the advancement of SOI (23 °CA) under different CE. What’s more, the change of thermal efficiency was almost the same (about 5%) with the advancement of SOI (23 °CA) under different CE. Besides, the effects of SOI and IP on the gas emissions, except the CO emission, almost unchanged with the increase of CE. In fact, when CE increased from 885 to 1 700 J, the CO emission decreased continuously. However, the increase of CE changed the effects degree of SOI and IP on some gas emissions, for example, with the same increase of IP by 15 kPa, the HC emission was average increased by about 13.65 g/(kW·h) when CE was 885 J, it remained almost the same with the CE was 1 700 J, that was, the effects degree of IP on the HC emission was greatly reduced with the increase of CE, which indicated that the adjustment capacity of IP on the HC emission became weaker. What’s more, with the same increase of IP from 110 to 125 kPa, the NOx emission was average decreased by about 1 g/(kW·h) when CE was 885 J, while the NOx emission was average decreased by about 4 g/(kW·h) when CE was 1 700 J, that was, the effects degree of IP on the NOx emission was slightly increased with the increase of CE, which indicated that the adjustment capacity of IP on the NOx emission was slightly enhanced. In addition, the increase of CE changed the effects or its degree on some parameters of particles emission. For example, the effects degree of SOI and IP on the average particle size and number concentration of nuclear particles were both decreased with the increase of CE, which indicated that the adjustment capacity of SOI and IP on the nuclear particles became weaker. On the contrary, the effects or its degree of some parameters of particles emission did not change with the increase of CE. For instance, the impact of SOI on the total mass concentration of particles was almost the same under different CE. The research results can provide data support for making a reasonable control strategy of RCCI combustion mode. [ABSTRACT FROM AUTHOR]

The development of HCCI combustion technology has been drawing a great deal of attention from researchers. This survey explains ongoing research methodologies and results. HCCI combustion, other than conventional combustion, is purely based on chemical kinetics. At present the automobile sector faces the problem of emissions and needs to develop clean technologies. However, HCCI operation still has issues such as ignition control, combustion phasing control, operating range control, cold start, and UHC (unburned hydrocarbon) and CO (carbon monoxide) emissions. The challenge is to overcome these problems without compromising other engine parameters and performance. For HCCI, the mixture preparation is especially important, while the compression ratio, IVC (inlet valve closure) timing, inlet pressure, inlet temperature and EGR play a very prominent role in controlling it. This paper will go through a detailed discussion of all the above conditions. [ABSTRACT FROM AUTHOR]

The cavitation development process in regulating valve under different inlet pressures is investigated experimentally and numerically in our paper. The influence of inlet pressure Pin on cavitation location, shape, area and intensity is studied in axial and radial directions, and the axial and radial pressure distributions are also analyzed. The cavitation is generally annular in shape radially and irregular polygon in shape axially. Cavitation bubbles occur at the throat entrance when the inlet pressure increases. The bubbles then accumulate, and a bubble ring is formed. The cavitation development process under different inlet pressures is separated into three stages, no-cavitation, initial cavitation and steady-cavitation stages. During the no-cavitation stage, no bubbles exist. During the initial cavitation stage, bubbles occur and the area and intensity of cavitation increase in the radial and axial directions with increasing inlet pressure. During the steady-cavitation stage, the calculation area and intensity of bubble rings reach their maximum values and then remain stable. The cavitation bubbles extend downstream, and the area of cavitation ring and cavitation intensity increase with increasing inlet pressure. A slit exists between the upper and lower parts of bubbles in the cavitation process, both parts touch each other forming a whole. [ABSTRACT FROM AUTHOR]

In view of the extensive application of swirl flow pipes (vortex tubes) in refrigeration systems, the parameters of swirl flow pipes were investigated to provide optimal cooling and heating conditions. Three-dimensional numerical simulations were carried out using available experimental data and models. The analysis verified that the heat pipe with a length of 175 mm performed better than the swirl flow pipe with a length of 125 mm, confirming experiments by Agrawal. Meanwhile, by comparing different pressures, it was found that in the single-nozzle swirl flow pipe, the greater the increase of pressure (0.1–1.0 MPa), the greater the burden on the vortex chamber and the more serious the wear is, which can be seen in the higher inlet pressure. In order to improve the durability of the swirl flow pipe, we suggest using a swirl flow pipe with more nozzles. Finally, according to the simulation results, with the rise of carbon dioxide pressure potential energy at the inlet, the cooling effect of the swirl flow is first increasing and then decreasing. When the swirl flow pipe is used as a refrigeration device to determine the minimum cooling temperature under the maximum pressure, the lowest temperature of the 125 mm swirl flow pipe was 252.4 K at 0.8 MPa, while the lowest temperature of the 175 mm swirl flow pipe was 246.0 K. Secondly, the distance from the inlet to the hot outlet of the swirl flow pipe had little effect on the cooling temperature and radial velocity, but increasing its distance increased the wall temperature of the swirl flow pipe because it increases the contact time between the airflow and the hot end of the tube wall. When the swirl flow pipe is used as a heat-producing device, increasing the tube length of the swirl flow pipe appropriately increases its maximum heat-producing temperature.

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Pipe cleaning is a common operation in the oil and gas industry. In this paper, the governing equation of the pipeline inspection gauge (PIG, lowercase pig is commonly used) speed is combined with the gas flow equations. The method of characteristics (MOC) is used to solve the transient equations of gas flow. And the process of a pig passing over an uphill section of a gas pipeline is simulated. The results indicate that a pig may get stuck in uphill gas pipeline, due to the coupling of the gas and the pig. Under these circumstances, a higher pressure of the upstream could be helpful for driving the pig in motion. Additionally, the ratio of inlet pressure rise during the pigging process is primarily determined by the inclination of the uphill section. In addition, a formula to predict the inlet pressure during pigging in an uphill pipe is presented. Furthermore, the proposed method and solution can be utilized to predict the speed and position of the pig, as well as the gas pressure and the stoppage of the pig in hilly gas pipelines. [ABSTRACT FROM AUTHOR]

Abstract Anode recirculation operation is one method to both achieve self-humidification and increase hydrogen utilization for proton exchange membrane fuel cells (PEMFCs) automotive application. In this study, effect of operating conditions, including cathode inlet relative humidity, anode and cathode inlet pressure, and anode stoichiometry on performance of PEMFC with anode recirculation are analyzed by simulation work. Generally, the performance variation when the PEMFC starts anode recirculation can be divided into two stages. The performance increases first due to the self-humidification effect and then decreases due to the nitrogen crossover. The results show that performance enhancement caused by self-humidification becomes less significant with increasing cathode inlet humidity. Increasing anode inlet pressure can retard the performance decline caused by nitrogen crossover and increasing cathode inlet pressure will exacerbate it. Increasing anode stoichiometry can enhance the self-humidification by anode recirculation. [ABSTRACT FROM AUTHOR]

Abstract Reactivity controlled compression ignition (RCCI) is demonstrated as a controllable high efficiency and clean combustion strategy, which is confirmed to be affected by either inlet pressure (IP), total cycle energy (E total), or start of injection (SOI). This paper discussed their combined effect on low load RCCI combustion and emission characteristics in a multi-cylinder heavy-duty engine fueled with gasoline/diesel. Results show that low temperature heat release (LTHR) only occurs when SOI is sufficiently advanced. Combustion duration (CD) is lengthened, shortened and unchanged with SOI advance under different E total s, while lengthened with IP increase. NO X emission first increases and then decreases with SOI advance, and declines with IP increase or E total decrease. Trend CO changes with SOI or IP becomes opposite at the lowest E total , comparing with that at relatively high E total s. HC emission decreases with SOI advance or E total increase, while it is insensitive to IP. Trend number of nuclear particle (N u m n) changes with IP becomes opposite at the highest E total , comparing with that at relatively low E total s, while N u m n decreases with SOI advance or E total increase. Both number of aggregated particle (N u m a) and soot first decreases and then increases with SOI advance, and decreases with E total decrease or IP increase. Highlights • Low temperature heat release occurs when start of injection is sufficiently advanced. • Combustion duration is lengthened, shortened and unchanged under diverse conditions. • Opposite trends of carbon monoxide appear under the lowest total cycle energy. • Opposite trends of nuclear particle number appear under highest total cycle energy. • Trends of the rest emissions changes with the three parameters remains unchanged. [ABSTRACT FROM AUTHOR]

• Maximum COD reduction of 87.7 % was obtained at the optimized operation conditions of Hydrodynamic cavitation (HC) coupled with advanced oxidation. • Degradation of textile dye waste water followed pseudo first-order kinetics. • Potassium peroxymonosulfate was the most effective oxidant achieving almost 100 % decolorization of MTDW. • When cavitation and PPMS were combined, the synergetic effect was seen with a rate constant of 0.003448 min-1 as opposed to cavitation alone. In this paper, a detailed investigation of the treatment of model textile dye wastewater (MTDW) by applying a hybrid approach of hydrodynamic cavitation (HC) coupled with UV light and different oxidants is reported. A distinct hybrid strategy of HC combined with inline UV and different oxidants was employed to treat model textile dye wastewater comprising mixed dyes under neutral to alkaline conditions and in the presence of salt and detergent, which form significant components of textile wastewater. The model textile dye wastewater was made of three dyes: Reactive Yellow 84, Reactive Black 8, and Reactive Violet 5 with 100 ppm of total concentration. Effects of various operating conditions, such as feed pressure at the venturi inlet, initial pH, process time, and different oxidizing agents, on percentage COD reduction were investigated. The extent of dye decolourization using HC combined with different oxidizing agents, viz., hydrogen peroxide (H 2 O 2), sodium persulfate (NaPS), and potassium peroxymonosulfate (PPMS), were studied. HC coupled with UV and potassium peroxymonosulfate (PPMS) oxidant produced maximum decolourization of dyes to the extent of 100 % at pH 7. A maximum COD reduction of 87.7 % was obtained at the optimized operation conditions of hydrodynamic cavitation (HC) coupled with UV and PPMS. The treatment of model dye wastewater utilizing a hybrid strategy of HC+UV+PPMS achieved a synergetic index of 1.92, which was significantly better than standalone treatments. The current work contributes significantly to our understanding of the performance of cavitation-based systems for treating complicated textile effluent. [Display omitted] [ABSTRACT FROM AUTHOR]

Even a small axial vibration or an axis deflection vibration of the aerostatic bearing of DFC tool can be quite significant for ultra-precision machining. It is of great importance to obtain the accurate axial bearing characteristic（ bearing capacity and thrust stiffness） during its design,parameter optimization,machining and using process. However,there exists many error terms in the engineering practice to test the axial bearing capacity（ thrust bearing capacity） of T aerostatic bearing,such as, the machining error, effect of environment factors（ temperature, humidity, etc.） on the micro-displacement measurement device,deformation and deflection of the structure itself during the loading process,etc. All these lead to a large error between the measurement stiffness value and the actual value. Based on these problems,this article studied the axial bearing capacity（ thrust bearing capacity） of T aerostatic bearing by means of finite element simulation. Meanwhile,the influence of orifice number and air supply pressure on the axial bearing capacity（ thrust bearing capacity） of T aerostatic bearing is also studied and the accuracy of the simulation results has been validated by the carried out experiment.

The flow in a pipe having multiple outlets is considered as an advanced problem in hydraulic engineering; many discrepancies were found in the literature, in addition to the lack of experimental and field studies. The main goal of this study is to simulate the flow in a pipe with multiple outlets in order to examine the existing methodologies for estimation of the friction head losses, and to propose a methodology that is based on experimental data. The main physical model in this study consisted of a water supply tank, a pipe with multiple outlets having a piezometer at each outlet. Different pipe diameters were used in this study, the pipe diameters were 25.4 mm (1 in), 38.1 mm (1.5 in), 50.8 (2 in) and 76.2 mm (3 in). The inlet heads used were 1.7 m and 2.2 m. The data collected from different flow conditions were used to assess the variation in the coefficient of friction and friction head losses along the pipe length. It can be concluded that the spacing between any two successive outlets (S) and area ratio (AR = Area of outlet/Area of the main pipe) are the main factors affecting the friction head losses along the pipe. The ratio of total friction head losses along a pipe with outlets having the same properties (length (L), discharge (Q), diameter (d) and material) to a pipe without outlets and having the same properties is called the G factor. The G factor calculated using selected formulae was overestimated in comparison to the calculated G factor obtained from experimental data. For large values of S/d (spacing between outlets/diameter of main pipe), the difference between coefficient of friction in first segment (f1) and last segment (fn) of the multiple outlet pipe was noted to be minimal.