Large Length Diameter Research Articles

Research and application of roll bending method for welded pipe with large length and small diameter to thickness ratio

Research and application of roll bending method for welded pipe with large length and small diameter to thickness ratio

Startup characteristics of the large length–diameter ratio high-temperature heat pipe

Large length–diameter ratio high-temperature sodium heat pipes (HTSHPs) are uniquely structured heat-transfer devices with significant application potential in high-temperature solar thermal power and small-scale nuclear systems. This study tested HTSHPs' startup characteristics examining various parameters. Results indicate that the transition temperature for flow transition is 564 K, and the continuous flow transition temperature is 722 K. Heat pipes at 15 % fill ratio are adaptable across various inclination angles, whereas those at 25 % and 35 % fill ratios show optimal startup at smaller angles (15°, 30°), with decreasing startup time as angle increases, notably significant at 45°.The start-up time refers to the duration from the initiation of heating to the point when all the normal operational temperature points of the HTSHP reach the continuous flow transition temperature during the condensation section. During the experiments, heat pipes with a large length–diameter ratio exhibit heat transfer instability, temperature oscillation and local overheating. Reducing the fill ratio and inclination angle effectively reduces the probability of temperature oscillation and local overheating. This study proposes a novel method for optimizing temperature oscillations in heat pipe design, offering pioneering insights and experimental data crucial for specialized high-temperature heat pipe research.

Numerical analysis and experimental comparison of temperature-compensation method for large length–diameter ratio thermal mass flowmeter

Thermal mass flowmeters (TMFs) are inherently sensitive to temperature fluctuations, which can result in inaccurate measurements. This study focuses on a novel TMF named the large length–diameter ratio thermal mass flowmeter (LLRTMF), which was previously proposed for its insensitivity to the distribution of radial flow velocity and implemented via a variable-speed, variable-temperature experimental setup. The power characteristics of the LLRTMF are investigated over velocity and temperature ranges of 1.00–6.00 m/s and 283.0–319.0 K, respectively. The experimental results indicate that the maximum relative error of the experimental power consumption is 21.96 %. Additionally, a full-size numerical model of the LLRTMF is developed to simulate its power characteristics across wider velocity and temperature ranges of 0.25–16.00 m/s and 283.0–353.0 K, respectively. Experimental data are used to verify the accuracy of the simulation model. Using the numerical model, an empirical correlation equation between power and velocity is derived and polynomially fitted to establish a temperature-compensation equation. The results of the temperature compensation equations and experiment were compared. The maximum relative error of the absolute value was 20.84 %, i.e., less than the maximum error in the results of the experiment due to temperature change, confirming the validity of the formula.

Numerical modeling and experimental verification for anisotropic heat conduction process in velocity probe of the thermal mass flowmeter

Traditional models ignore the temperature gradients caused by anisotropic heat conduction process in the axial and radial directions of the velocity probe of a thermal mass flowmeter (TMF), essentially assuming constant wall temperature. Recently, a novel TMF with a large length–diameter ratio of the velocity probe and more evident temperature gradient was proposed; although this novel TMF is insensitive to the radial velocity profile, it leads to significant calculation errors. To reduce the error of this TMF, this study proposes a numerical model of pipeline flow heat transfer that considers the axial and radial heat conduction of the velocity probe. The velocity probe axial heat conduction numerical model is proposed, and the results of apparent thermal conductivity are verified using empirical formulas. A feedback adjustment convergence program is performed to maintain the average temperature of the velocity probe at 10 K above the temperature of the observed fluid. The simulation results showed that a temperature gradient forms in both the axial and radial directions of the velocity probe of the improved model. Moreover, the higher the flow velocity and the farther it is from its central axis, the lower the temperature. Experimental results revealed that, at a velocity rang of 1.0–7.0 m/s, the average relative error between the improved simulated results and current experimental data is 2.92 % and the maximum relative error is 10.91 %, whereas the average relative error between the traditional simulated results and original experimental data is 7.44 % and the maximum relative error is 19.45 %. Thus, the improved model better simulates the real process.

Simulation of Internal Defects in TKX-50 Crystals.

1,1'-Dihydroxy-5,5'-bi-tetrazolium dihydroxylamine salt (TKX-50) is a new type of high-energy low-sense explosive with great application value, but TKX-50 made directly from the reaction has problems such as irregular crystal morphology and relatively large length-diameter, and these factors seriously affect the sensitivity of TKX-50 and limit its large-scale application. The internal defects of TKX-50 crystals have a great influence on their weakness, and studying its related properties is of great theoretical significance and application value. To further investigate the microscopic properties of TKX-50 crystals and to explore the connection between microscopic parameters and macroscopic susceptibility, this paper reports the use of molecular dynamics simulations to construct TKX-50 crystal scaling models with three types of defects-vacancy, dislocation and doping-and conducts molecular dynamics simulations. The influence of TKX-50 crystal defects on the initiation bond length, density, bonding diatomic interaction energy, and cohesive energy density of the crystal was obtained. The simulation results show that the models with a higher bond length of the initiator bond and higher percentage activated the initiator's N-N bond and lowered the bond-linked diatomic energy, cohesive energy density, and density corresponding to higher crystal sensitivities. This led to a preliminary connection between TKX-50 microscopic model parameters and macroscopic susceptibility. The results of the study can provide a reference for the design of subsequent experiments, and the research method can be extended to the research work on other energy-containing materials.

DSMC Simulation of the Effect of Needle Valve Opening Ratio on the Rarefied Gas Flows inside a Micronozzle with a Large Length-to-Diameter Ratio

The cold gas micro-propulsion system can provide low noise and ultra-high accuracy thrust for satellite platforms for space gravitational wave detection, high-precision earth gravity field measurement. In this study, the effect of different needle valve opening ratios on the rarefied flow characteristics of a micro-nozzle in a cold gas micro-propulsion system was investigated based on DSMC method. The special feature of the currently studied micro-nozzle is that it has a section of micro-channel with a large length–diameter ratio up to 4.5. Due to the extremely small needle valve displacement of the nozzle (minimum needle valve displacement up to 1.7 μm), a finely structured mesh was used. The molecular particle and macro flow characteristics inside the micro-nozzle were calculated for the conditions of a needle valve opening ratio from 5% to 98%. The throttling effect of the throat has a significant effect on the rarefied flow in the micro-nozzle; especially under the tiny opening, this effect is more significant. The spatial distribution of continuous flow, transition flow, and free molecular flow in the micro-nozzle varies at different needle valve opening ratios. As the needle valve opening ratio increases, the continuous flow will gradually fill the microfluidic region.

Simulation of fiber arrangement in slub strands and twisting on the slub yarn with the finite element method

Slub yarn is a popular yarn because of its distinctive appearance. In this paper, the simulation of the fiber arrangement in the slub strand is proposed. After twisting, the slub strand is converted into slub yarn. A cylinder with a large length–diameter ratio is used to simulate the fiber, and the random arrangement of the fibers forms the slub strand. Spring-damper-mass models are established to prevent cross-embedding among fibers and gather fibers along the slub strand axis. The slub strand is twisted by the roller-collet twisting model in ABAQUS software. By comparing the twisting effect, it can be seen that the twist distribution of the slub yarn simulated by the finite element method is consistent with the real slub yarn spun on a ring-spinning frame. The work can predict the twist change of slub yarn by the established model. The established model provides the basis for future research work on the properties of slub yarn.

Mullite Reinforced SiC/Al2O3 Composites Prepared by Microwave Sintering Based on Green Manufacturing

In the preparation process of composites, the implementation of green manufacturing technology has an important impact on improving material properties and preparation efficiency. The adopting of green manufacturing technology not only greatly reduces the energy consumption but also effectively avoids the environmental pollution. Compared with the traditional material preparation process, the material preparation process for green manufacturing is a new concept and idea. Microwave sintering is such an efficient, clean, and pollution-free preparation process, so it is widely used in the field of material preparation. By microwave sintering, the mullite reinforced SiC/Al2O3 composites with different SiC particle size were prepared from the composite powders composed of SiC particles coated with SiO2, by a sol-gel method and Al2O3 particles. The effect of SiC particle size on the microstructure, bulk density, fracture toughness, flexural strength, and thermal shock resistance of SiC/Al2O3 composites was studied. The bulk density, fracture toughness, and flexural strength were evaluated by the Archimedes method, single-side notched beam method, and three-point bending method, respectively. The thermal shock resistance of samples was investigated through the combination of water quenching and three-point bending methods. The results showed that with the increase of SiC particle size, the bulk density, fracture toughness, and flexural strength of samples all increased first and then decreased. The bulk density, fracture toughness, flexural strength, and flexural strength retention of SiC(5 μm)/Al2O3 composites were better than those of other samples, which were 2.06 g/cm3, 1.98 MPa·m1/2, 63 MPa, and 60%, respectively. The better mechanical properties and thermal shock resistance of SiC(5 μm)/Al2O3 composites are due to the formation of bridging mullite whiskers between SiC and Al2O3 particles with large length diameter ratio. Therefore, the unique sintering mechanisms of size coupling effect and local thermal aggregation effect in microwave sintering were discussed. The research results can not only provide reference for the preparation process of mullite reinforced SiC/Al2O3 composites but also for the wide application of microwave sintering technology.

РАСЧЕТ ЭФФЕКТИВНОЙ ДЛИНЫ БУРОНАБИВНЫХ ВИСЯЧИХ СВАЙ ПРИ СЖАТИИ ПО НЕСУЩЕЙ СПОСОБНОСТИ ДВУХСЛОЙНОГО ГРУНТА ОСНОВАНИЯ

The article discusses a new method for calculating the effective length of bored hanging piles based on the bearing capacity of a two-layer foundation soil. This calculation problem is of particular importance when it is necessary to use piles of large length and large diameter. The calculation of a hanging pile according to the bearing capacity of the foundation soil adopted in regulatory documents is based on the occurrence of friction forces on the surface of the pile because of its movement (“disruption”) in the ground environment. It does not correspond to the behavior of the pile during operation. In practice, the disruption of the pile is unacceptable, therefore, for the safe operation of the pile, the coefficients of the working conditions are entered into the calculation. A new approach to the calculation of hanging piles by bearing capacity in multilayer foundation soils based on the account of friction-adhesion forces on the surface of the pile is proposed. The friction-coupling forces are caused by micro-displacements of the surface layers of the pile material because of its general deformation from the compressive load on the pile. The effective length of the pile is understood to be such a length at which the bearing capacity of the soil on its surface and under the lower end of the pile is effectively used. Due to this length of the pile, an economic effect is achieved in pile foundations. The above method of calculating the bored pile can be used in the calculations of other piles by material, method of immersion and the number of layers of the foundation soil.

A Study on Temperature Distribution within HVDC Bushing Influenced by Accelerator Content during the Curing Process

Power transmission technology plays an important role in energy sustainability. Bushing is an indispensable type of equipment in power transmission. In production, the accelerator changes the temperature distribution during the curing process, influencing the formation of defects and thus the safety output of renewable energy. In this study, uncured epoxy resin samples with different accelerator contents were prepared and measured by differential scanning calorimetry (DSC). The obtained heat flow curves were analyzed for curing kinetics. Then, the curing process of large length–diameter ratio bushings was simulated by using the finite element method combined with a curing kinetics model, transient Fourier heat transfer model, and stress–strain model. The study reveals that the curing system can be established by the Sestak–Berggren autocatalytic model with different accelerator contents. The overall curing degree and the maximum radial temperature difference of the capacitor core tend to increase and then decrease with the accelerator content. This is mainly attributable to the rapid exotherm excluding the participation of some molecular chains in the reaction, resulting in permanent under-curing. As the accelerator content increases, the strain peak decreases and then increases. This paper provides guidance for the comprehensive evaluation and manufacturing of the low-defect capacitor cores of large-size high voltage direct current (HVDC) bushings.

Design of a slender turning cutting tool via a vibration absorber equipped with piezoelectric ceramic

Turning cutting tool with large length–diameter ratio has been essential when machining structural part with deep cavity and in-depth hole features. However, chatter vibration is apt to occur with the increase of tool overhang. A slender turning cutting tool with a length–diameter ratio of 7 is developed by using a vibration absorber equipped with piezoelectric ceramic. The vibration absorber has dual functions of vibration transfer to the absorber mass and vibration conversion to the electrical energy via the piezoelectric effect. Equations of motion are established considering the dual damping from the piezoelectric ceramic and rubber gasket. The equivalent damping of piezoelectric ceramic is derived, and the geometries are optimized to achieve optimal vibration suppression. The modal analysis demonstrates that the cutting tool with the vibration absorber can reach 80.1% magnitude reduction. Machining tests are carried out in the end. The machining acceleration and machined surface roughness validate the vibration suppression of the VA, and the output voltage by the piezoelectric ceramic demonstrates the ability of vibration sensing.

Optimization and Tuning of Passive Tuned Mass Damper Embedded in Milling Tool for Chatter Mitigation

Milling tools with a large length–diameter ratio are widely applied in machining structural features with deep depth. However, their high dynamic flexibility gives rise to chatter vibrations, which results in poor surface finish, reduced productivity, and even tool damage. With a passive tuned mass damper (TMD) embedded inside the arbor, a large length–diameter ratio milling tool with chatter-resistance ability was developed. By modeling the milling tool as a continuous beam, the tool-tip frequency response function (FRF) of the milling tool with TMD was derived using receptance coupling substructure analysis (RCSA), and the gyroscopic effect of the rotating tool was incorporated. The TMD parameters were optimized numerically with the consideration of mounting position based on the maximum cutting stability criterion, followed by the simulation of the effectiveness of the optimized and detuned TMD. With the tool-tip FRF obtained, the chatter stability of the milling process was predicted. Tap tests showed that the TMD was able to increase the minimum real part of the FRF by 79.3%. The stability lobe diagram (SLD) was predicted, and the minimum critical depth of cut in milling operations was enhanced from 0.10 to 0.46 mm.

Room temperature multiferroic properties of electrospun gallium ferrite nanofibers

Gallium ferrite (GaFeO3) is a promising multiferroic material for multifunctional device applications. Compared with bulk and thin film materials, nanofibers are possible to magnify the magnetostriction or piezoelectric effect due to their large length–diameter ratio, thus improving the performance of the material. In this work, GaxFe2 – xO3 (GFO) nanofibers have been synthesized by sol-gel based electrospinning. With the increasing Fe ion content, the room-temperature antiferromagnetic to ferromagnetic transition of GFO nanofibers has been confirmed by magnetic hysteresis loops; and the corresponding temperature dependent magnetization curves show that the ferromagnetic–paramagnetic transition temperature (Tc) is above room temperature and increases from around 292 K to above 400 K. Ferroelectricity of GFO nanofibers has been confirmed by second harmonic generation and piezoresponse force microscopy. Magnetoelectric (ME) coupling has been further measured by dual amplitude resonance tracking piezoresponse force microscopy and sequential excitation piezoresponse force microscopy under an in-plane external magnetic field. The newly developed SE-PFM method reduces the crosstalk of morphology, confirming that no obvious intrinsic ME coupling appears in the GFO nanofibers.

Second Law Analysis for the Experimental Performances of a Cold Heat Exchanger of a Stirling Refrigeration Machine.

The second law of thermodynamics is applied to evaluate the influence of entropy generation on the performances of a cold heat exchanger of an experimental Stirling refrigeration machine by means of three factors: the entropy generation rate , the irreversibility distribution ratio ϕ and the Bejan number based on a dimensionless entropy ratio that we introduced. These factors are investigated as functions of characteristic dimensions of the heat exchanger (hydraulic diameter and length), coolant mass flow and cold gas temperature. We have demonstrated the role of these factors on the thermal and fluid friction irreversibilities. The conclusions are derived from the behavior of the entropy generation factors concerning the heat transfer and fluid friction characteristics of a double-pipe type heat exchanger crossed by a coolant liquid (55/45 by mass ethylene glycol/water mixture) in the temperature range 240 K < TC < 300 K. The mathematical model of entropy generation includes experimental measurements of pressures, temperatures and coolant mass flow, and the characteristic dimensions of the heat exchanger. A large characteristic length and small hydraulic diameter generate large entropy production, especially at a low mean temperature, because the high value of the coolant liquid viscosity increases the fluid frictions. The model and experiments showed the dominance of heat transfer over viscous friction in the cold heat exchanger and and ϕ → 0 for mass flow rates kg.s−1.

Design of a turning cutting tool with large length–diameter ratio based on three-element type vibration absorber

The vibration absorber has been effective in vibration control. From the demand of manufacturing structural parts with a deep hole, the design of a turning cutting tool with large length–diameter ratio is presented. An analytical approach of acquiring frequency response of primary structure equipped with typical single-degree-of-freedom vibration absorbers is formulated, and background modes are incorporated with the purpose of achieving an accurate tuning of vibration absorber. Specifically, the three-element type is investigated as the damping element of the vibration absorber embedded in the cutting tool contributes to the stiffness, although it demonstrates medium performance of vibration suppression according to non-dimensional analysis. The experimentally tuned frequency response function of the turning cutting tool with three-element vibration absorber achieves 87.1% reduction on the amplitude of the target mode. Finally, several configurations of internal turning operations are carried out to validate the design of the vibration absorber.

Technical exploration of horizontal screw centrifuge in solid-liquid separation of flowback liquid in offshore production

This paper introduces the structure and working principle of horizontal screw centrifuge with large length diameter ratio and its technological process in the separation of liquid-solid liquid in the flowback of offshore production. The effects of different water addition ratio, rotating speed and demulsifier content on the separation effect of centrifuge were investigated by indoor experiments. The orthogonal test was used to optimize the parameters, and the optimal combination of parameters was as follows: water ratio was 1.5/1, rotating speed was 3000r / min, demulsification was achieved The dosage was 400mg / L. The optimum rotating speed of the centrifuge is 2000r / min, and the field pilot test is carried out for 10 consecutive days with the best combination of parameters. The results are as follows: the average mechanical impurity rate of oil phase produced by horizontal screw centrifuge is 0.465%, and the average oil content in water phase is 183mg / L. The separation effect is stable.

Analysis of risk factors for lymph node meta-stasis in papillary thyroid microcarcinoma

Objective To investigate the clinical and pathological characteristics of cervical lymph node metastasis in papillary thyroid microcarcinoma (PTMC), and provide a basis for the individualized surgical procedure. Methods Retrospectively analyzed the clinical data of 940 PTMC patients admitted to the Department of Thyroid Surgery, the First Affiliated Hospital of Zhengzhou University, from January 2016 to June 2018, including 206 males and 734 females, with a gender ratio of 1.0∶3.6. Age ranged from 18 to 78, with an average of (45.5±10.6) years. The correlation between gender, age, cancer size, multifocality, BRAFV600E gene mutation, complicated with hashimoto′s thyroiditis, extrathyroidal extension and lymph node metastasis were analyzed. SPSS 21.0 software was used for statistical analysis. Chi-square test or rank sum test was adopted for comparison between groups, and logistic regression analysis was adopted for multivariate analysis. Results There were 397 (42.2%) patients with central lymph node metastasis (CLNM) and 104 (11.1%) patients with lateral lymph node metastasis (LLNM). Univariate analysis showed that male, age < 55 years old (χ2=24.485, P<0.001), bilateral cancer foci (χ2=8.100, P=0.004), larger length-diameter (Z=-0.016, P<0.001), and BRAFV600E gene mutation (χ2= 4.918, P=0.027) had a higher CLNM positive proportion, and LLNM positive proportion was higher in male (χ2=6.584, P=0.010), bilateral cancer foci (χ2=26.669, P<0.001), larger length-diameter (Z=-4.991, P<0.001), extra-glandular invasion (χ2=16.862, P<0.001) . Multivariate logistic regression analysis showed that gender (OR=2.091, P<0.001), age (OR=1.551, P=0.010), cancer lesion length (OR=5.285, P<0.001) and BRAFV600E gene mutation (OR=1.648, P=0.038) were independent risk factors for CLNM in PTMC patients. Gender (OR=1.657, P=0.032), bilateral lesion (OR=2.610, P<0.001), tumor length diameter (OR=7.420, P<0.001) and extrathyroidal extension (OR=2.611, P=0.005) were independent risk factors for LLNM. The optimal critical values of tumor lesion length-diameter for risk assessment in CLNM and LLNM were 0.6 cm and 0.8 cm, respectively. Conclusions For PTMC patients with negative cervical lymph node had risk factors for lymph node metastasis, preventive dissection of central lymph nodes was recommended, and preventive dissection of lateral lymph nodes should also be comprehensively considered, by evaluating the extrathyroidal extension. Key words: Surgical procedures, operative; Lymphatic metastasis; Neck dissection; Papillary thyroid microcarcinoma

Experimental Investigation on Pyrolysis of n-Decane Initiated by Nitropropane under Supercritical Pressure in a Miniature Tube

Adding an initiator is an effective method of promoting hydrocarbon pyrolysis and improving the heat sink of fuels. Nitropropane was proposed as an initiator with good performance, owing to its lower reaction activation energy for C–N bond cleavage. To study the effects of this initiator on hydrocarbon pyrolysis, a miniature tube reactor that can simulate a real heating procedure in an aeroengine was used to investigate the n-decane pyrolysis with and without nitropropane under experimental supercritical conditions. The results demonstrate that the nitropropane initiator promotes the pyrolysis of fuel as it flows through a tube with a large length–diameter ratio within a certain temperature range. The initial decomposition temperature of n-decane is reduced by approximately 100 K, and the increase in the conversion leads to a higher heat sink for n-decane, which can result in decreases in the fuel and reactor temperatures under the same heating condition and within the effective temperature range. A stronger promoting effect can be achieved by increasing the concentration of the nitropropane initiator. The variation laws for the n-decane pyrolysis reaction rate along the flow reactor are changed by the initiator, the presence of nitropropane greatly accelerates the pyrolysis reaction of fuel at a lower temperature, and the opposite tendency appears as the fuel temperature increases, which is caused by the consumption of the initiator. In addition, the selectivity of methane, propane, and alkenes, especially ethylene, increases because of the propyl radical generated by the C–N dissociation of nitropropane before the initiator is consumed.

Effects of Inlet-Loss Coefficient on Dynamic Coefficients and Stability of Multistage Pump Annular Seal

In order to explore the influence of inlet-loss coefficient on dynamic coefficients and stability of finite-length annular seal, and then to provide theoretical basis for multistage pump rotor system vibration and stability, the bulk-flow model is taken into account to model the fluid control equations of clearance flow, and perturbation method is applied to calculate the first-order functions and dynamic coefficients. The calculated results are validated by comparing them with reference results, and the minimum and maximum error percentage are 1.4 and 5.6%, respectively. The dynamic coefficients change rule and stability of annular seal under the multifactor-coupled effects are researched in a detailed manner. The numerical results show that the inlet-loss coefficient plays an important role in dynamic coefficients of finite-length annular seal, especially for direct stiffness. All of the dynamic coefficients increase with the increase in inlet-loss coefficient, and the growth trends are the most distinct for large length–diameter ratio, small clearance or high rotating speed. Moreover, reducing the inlet-loss coefficient can improve the stability of annular seal. The research results and conclusions can provide references for the structure design of multistage pump and optimal design of rotor system.

Design of a milling cutter with large length–diameter ratio based on embedded passive damper

A milling cutter with large length–diameter ratio has been essential in machining structural parts with deep cavity and deep hole features. However, chatter vibration is apt to occur with the increase of tool overhang. A damped milling cutter is developed by employing a single-degree-of-freedom passive damper located inside the arbor. The stiffness and damping design of the embedded damper are carried out by following the equal peaks criterion. A novel design is fulfilled to avoid the disequilibrium of the cutter during high-speed rotation, and an accurate experimental tuning of the design parameters is required to achieve the optimum vibration suppression due to a low mass ratio of 2.5%. Modal analysis demonstrates that the damped cutter with an approximate length–diameter ratio of 8 can reach 75% magnitude reduction at all orientations, which is benefical to resist milling force excitation varying with the rotation angle. Chatter stability simulation demonstrates that the damped cutter is able to increase the stability limits based on the evaluation of undamped and Sandvik cutters. Three configurations of machining tests are carried out and the design of the damped cutter is validated by the machining audio signals and machined surface roughness in the end.