Cross Section Of Tube Research Articles

Secondary ultrasonic atomisation mechanisms

Liquid atomisation is the basis for various practical applications such as pharmaceuticals, cosmetics, food industry, etc. In this case, the main challenge is the development of high-performance, highly dispersed atomisation systems. Generally, high-throughput atomisation systems form aerosol with large droplet sizes, and high-disperse atomisation systems have low performance. Secondary ultrasonic atomisation can solve this problem by allowing non-contact crushing of already formed aerosol droplets with large droplet sizes by means of a high-intensity ultrasonic field. For this purpose, a pre-generated stream of liquid droplets is directed into a cylindrical region formed by an emitter in which a high-intensity ultrasonic field is generated. Ultrasonic radiator, is a tube of stepped-variable cross-section, providing the formation of bending-diametral or diametral oscillations at a frequency above 20 kHz. At sufficiently high ultrasound intensity, conditions for further crushing of liquid droplets are realised, which leads to the formation of a highly dispersed aerosol. This paper describes the proposed mathematical model of the atomisation process and finds the regularities of the process depending on the determining parameters of the ultrasonic field and physical and chemical properties of the liquid. Two mechanisms of jet destruction are revealed: direct destruction of droplets when they hit the ultrasonic wave front and cavitation mechanism of droplet and jet destruction. The dominant crushing mechanism depends on the problem parameters and, in turn, determines the minimum size of the resulting droplets. The results of this work will help to optimise the secondary ultrasonic atomisation process and improve liquid atomisation technologies in various applications.

コンクリート充填角形鋼管断面の単純累加強度時の応力状態

The purpose of this study is to clarify the stress distribution of the cross-section at the simple superposed strength of concrete filled square steel tubular section. The moment-axial force relationships correspond to the simple superposed strength are calculated based on the Navier’s hypothesis. Analytical parameters are strength of concrete and steel tube and the width-to-thickness ratio. The stress or strain at the outermost edges of concrete and steel tube cross section with the stress or strain at allowable stress of the respective materials are compared and the relationship between the stress or strain of the cross-section at the simple superposed strength and the analytical variables are discussed.

THE FRACTAL MATHEMATICAL MODELS FOR SPONTANEOUS AND FORCED IMBIBITION WITH DIFFERENT CROSS-SECTION SHAPES IN SHALE OIL RESERVOIR

Large-scale hydraulic fracturing is the critical technology for effective shale oil production. However, the imbibition flow mechanisms of fracturing fluid in shale micropores and the influence of shale microstructure and physical properties are still indistinct, which makes the optimization goal of fracturing flowback unclear and restricts the enhancement of shale oil recovery. Therefore, based on SEM and XRD experiments, it is analyzed that shale has the characteristics of multiple pores, which are divided into organic pores, brittle mineral pores, and clay pores. Nonetheless, how the tube cross-section controls the interface displacement is not well discussed in the available literature, especially in irregular triangles, rectangles and other non-circular shapes. This paper studies the influence of cross-section shapes on the capillary force by considering the corner flow of the wetting phase, and it analyzes the imbibition dynamics of different types of pores. Using the shale multi-pores physical model and fractal theory, the shale semi-analytical solution models of SI and FI are established. Theoretical analysis of the water imbibition mechanisms shows that the key factors controlling SI and FI volume include imbibition time, fluid properties, pore cross-section shapes, tortuosity, and forced pressure.

On the crashworthiness optimisation of a new multi-corner tube under axial loading

ABSTRACT In this paper, multi-objective crashworthiness optimisation of the new multi-corner cross-section tubes has been studied. The experimental validated Abaqus/ExplicitTM finite element simulations have been utilised to analyse the force and energy absorption–displacement of the different cross-section specimens. The results of the crashworthiness performances of the tubes for the metaheuristic optimisation algorithm of non-dominated sorting genetic algorithm II (NSGA-II) have been extracted from the machine learning process of the neural network-type group method of data handling (GMDH). The results show that the optimisation of these sections may lead to higher crashworthiness abilities without any increase in cost and difficulties in production. The comparison of the crashworthiness results between the 12 and 20-cornered cross-sections have shown that the higher the design parameters, the more the capability of the energy absorption by multi-objective optimisation. Finally, the crashworthiness performances of the optimised and the best SEA of the 12, 20-cornered specimens with the square section have been compared. It has been demonstrated that in the same IPF, the specific energy absorption in the optimised and the best SEA of the 12, 20 multi-cornered sections are about 27%, 40% and 67%, 78% higher than the square one, respectively.

Effects of structure parameters of tube outlet on the performance of a hydrogen-fueled micro planar combustor for thermophotovoltaic applications

In order to obtain high energy output power and energy conversion efficiency for micro-thermophotovoltaic system, in this work, a hydrogen-fueled micro planar combustor with tube outlet is designed. Effects of structure parameters of tube outlet (tube distance, tube cross section and tube number) on the performance of micro planar combustor are numerically investigated for thermophotovoltaic applications. Results suggest that the energy output and energy conversion efficiency of MTPV system is slightly increased with the increment of tube distance, and the pressure loss is slightly reduced. Moreover, compare with the micro planar combustor with the circular tube, the micro planar combustor with square tube is more suitable for MTPV system. Furthermore, with the tube number increasing from two to three, the energy output and energy conversion efficiency of MTPV system is increased by about 8.49%–9.38%, and the pressure loss is significantly reduced by about 44.54%–46.78%.

Influence of tube cross-section geometry on high-pressure hydrogen-flow-induced self-ignition

Self-ignition within a cylindrical tube that discharges high-pressure hydrogen results in flame formation. Because rectangular tubes are used to visualize fuel-flow dynamics, the influence of the tube cross-section on the self-ignition characteristics is investigated. As experimental investigation of the mechanisms underlying the self-ignition phenomenon in cylindrical tubes is difficult, three-dimensional numerical simulation is employed. Following the bursting of diaphragm by high-pressure hydrogen with a storage pressure of 9.0 MPa and a temperature of 300 K, initial self-ignition occurs at the center of the rectangular tube sidewall. This is because of the mixing of air and hydrogen induced by the bow-shock reflection-generated jet flow and resulting adiabatic shock compression-induced temperature increase. This temperature rise induces a secondary self-ignition at the tube corners. In the cylindrical tube, a solitary ring-shaped self-ignition occurs near the sidewall. The flame evolutions in rectangular and cylindrical tubes reveal similar flame-spreading trends, which indicates similar bow-shock reflection-induced self-ignition mechanisms.

Eliminating flooding by phase separation in condenser tube

Flooding may take place for in-tube condensation, causing unstable flow and deteriorated heat transfer. Here, the phase separation principle is proposed to eliminate flooding. Comparative experiments of condensation were performed in both bare tube (BT) and modulated heat transfer tube (MHTT) with a mesh membrane tube (MMT) insert. The working fluid is water-steam under a sub-atmospheric pressure. It was observed that slug flow exists at small mass fluxes and vapor mass qualities in BT. Due to the periodic formation of liquid column over the tube cross section, flooding indeed takes place, causing unstable flow, deteriorated heat transfer, and large pressure drop. The MHTT completely eliminated flooding, converting the unstable flow into a stable flow. Heat transfer coefficients are 7.47 times of those in BT, maximally, accompanying reduced pressure drops. High-speed visualization and theoretical analysis indicated that smaller pore size provides larger capability to prevent the vapor phase penetrating the mesh screen, resulting in larger driving force for liquid suction toward the MMT inside. The MMT provided a tunnel for liquid transportation in the upward direction, which is the mechanism to eliminate flooding. The modulation of the annular flow pattern was also performed and analyzed by using the phase separation principle, and the results indicated the effectiveness of MMT in the annular flow regime. This work is benefit for applications, such as air-cooled condenser, whose performance is important to influence the whole system performance for power generation.

Nanofluids in Zigzag Elliptical Tube Heat Exchanger: A Design Perspective

Abstract Nanofluids contain nanometer-sized particles in suspension to enhance heat transfer by increasing the thermal conductivity. This paper provides an overview of particle size and volume fraction of nanofluids, and their roles in enhancing the heat transfer. Often, the transfer of heat is enhanced by dispersed particles with small diameter and high concentration despite some debate about the governing effects. The design of elliptical cross-section and zigzag tube also sheds insight into augmenting heat transfer for future research directions and applications.

Novel ensemble approach to predict the ultimate axial load of CFST columns with different cross-sections

Concrete-filled steel tubes (CFST) have been widely used in construction due to their numerous benefits over traditional structural components made of steel or reinforced concrete. The ultimate axial load (UAL) of the CFST column, regarded as the most critical mechanical property, is determined by several constitutive elements, including the material’s mechanical properties and tube cross-sections. Due to the complexity introduced by the interaction of steel tubes and the filling concrete, it is challenging to conduct an analysis of CFST columns using design codes and empirical formulas. As a consequence of this, the principal objective of this study is to use machine learning (ML) methods to predict the UAL of CFST columns. This study mentions six ML models, divided into two groups: the single (or individual) and ensemble ML models. The considered models include Decision Tree, Gradient Boosting, Light Gradient Boosting, Adaptive-Gradient Boosting, Voting Ensemble, and Stacking Ensemble. A database containing 349 test results defining the UAL of rectangular and elliptical CFST columns is compiled to construct the ML models. For model assessment purposes, common quality evaluation criteria, a 10-fold cross-validation approach, and Monte Carlo simulations are utilized. The observed results demonstrate that ensemble ML models outperform single ML models in terms of performance and stability, with the Adaptive-Gradient Boosting model being the best predictive model. In the last step, a partial dependence plot (PDP) analysis is carried out to assess the impact of each input variable and the correlation between variables on the UAL of the CFST columns.

THE EFFECT OF MECHANOACTIVATION AND MICROWAVE EFFECTS ON THE SURFACE PROPERTIES OF WATER AND AQUEOUS SOLUTIONS

Most food mixtures, where the liquid acts as a dispersion medium, are formed with the participation of water and aqueous solutions,. The formation of stable surface interactions in disperse systems with the participation of water is based on overcoming the forces of surface tension at the interface between the phases. The aim of the research is to analyze the effect of mechanical activation during stirring and microwave exposure on the surface properties of water and aqueous solutions. The object of the research is distilled water, bottled “Berdovskaya taiga” drinking water, an aqueous solution of NaCl (3.33%), an aqueous solution of NaCl (3.33%) with the addition of 1% flour with stirring. The main research method is the method of capillary rise of liquid in a tube of small cross section, partially immersed in liquid. It has been established that both mechanical and electromagnetic effects change the surface energy of water and aqueous solutions. But their influence is ambiguous. Surface tension during mechanical activation by stirring decreases to a certain minimum for different time intervals for different solutions, and then increases to a certain level. The retention time of the reduced surface energy of distilled water after stirring at a frequency of 100 rpm is 60–80 s. There is a tendency for a noticeable effect of impurities on the surface tension. The more complex the solution and the higher the concentration of impurities, the lower its surface energy. According to the results of the research, for technological purposes, for example, dough kneading, it is recommended to mechanically process (mix) solutions for dough kneading for 60–70 s or microwave treatment for no more than 20 s.

Numerical analysis of a developing turbulent flow and conjugate heat transfer for molten salt and liquid sodium in a solar receiver

• Temperature uniformity within a solar receiver using guide vanes was investigated. • Friction coefficient and Nu number were reported for liquid sodium and molten salt. • The effect of wall heat flux on fluid flow and heat transfer was studied. A numerical analysis of the developing flow and conjugate heat transfer in a solar receiver tube with a three-blade guide vane at the tube inlet was performed to investigate the effect of guide vane and working fluid on the flow and temperature distribution in a solar receiver tube subjected to the boundary condition of the non-uniform wall heat flux. Three dimensional Navier-Stokes, energy, and Laplace equations were solved numerically using Fluent code for the molten solar salt and liquid sodium as the working fluids. The SST k-ω turbulence model was used to predict the flow behavior inside the tube. The values of the friction coefficient and Nu number predicted by the numerical analysis were compared to and validated against experimental correlations from the literature. The numerical results show that a significantly lower pressure drop, and more uniform temperature distribution in the receiver tube are achievable by using the liquid sodium, compared to the molten solar salt. Application of a three-blade guide vane improves temperature uniformity across the receiver tube cross-section, but increases pressure drop in the developing flow region and, thus the overall pressure drop in the tube. The increase in the pressure drop is attributed to the swirling flow and higher friction coefficient compared to the fully developed flow for both working fluids studied in this work.

Evaporation in a single channel in the presence of particles

Liquid corner films in channels or pores of polygonal cross-section are known to have a strong impact on evaporation with a much faster evaporation compared to a tube of circular cross section. The aim of this work is to study the interplay between colloidal particles, development of the corner films and evaporation in a micro channel from a combination of visualization experiments with fluorescent particles and numerical simulations. It is shown that the triple line pinning along the corner films due to particle accumulation in the films leads to the thinning of the corner films. As a result of the film thinning, evaporation is slower in the presence of particles compared to pure water. The identification of such an evaporation reduction mechanism at pore scale shed new light on the phenomenon of reduced evaporation in porous media due to the presence of colloidal particles reported in previous works.

Circular tube-in-tube dampers for seismic resilience of structures

A new brace-type slit damper, called ‘Circular Tube-in-Tube Damper (C-TTD), comprises two solid steel cylinders and one circular cross-section tube equipped with slotted holes, is proposed for seismic resilience of structures. In the proposed damper, a system of bolts was used to connect up various components of the damper, allowing inspection and replacement of the damaged components without any requirement for the replacement of the entire damper. Nonlinear finite element analyses using ABAQUS were carried out to verify the experimental results and to investigate the effect of damper geometric properties on the yield load capacity of the C-TTD dampers. The seismic performance characteristics of 4-storey, 8-storey, and 15-storey steel structures equipped with C-TTD dampers were determined by nonlinear time history analyses using three different earthquake excitations. The results indicated that when the structures were equipped with C-TTD dampers, the inter storey drift decreased in the range of 8%–55%, the base shear load decreased in the range of 27%–35%, and the input energy decreased in the range of 70%–80%, depending on the number of storeys and the earthquake type, compared to the counterpart structures without the damper.

Two-phase secondary flow characteristics and heat transfer mechanism during boiling in a vertical helically coiled tube

A VOF model was used to study the two-phase secondary flow characteristics and the heat transfer mechanism in a helically coiled tube. According to the vapor-phase volume fraction, the helically coiled tube was divided into four sections for analysis, considering the different heat transfer characteristics in various boiling states. The heat transfer coefficient, velocity vector, and circumferential temperature distribution of the tube cross-sections were studied during boiling. The numerical results reveal that the secondary flow plays different roles in heat transfer of the four boiling states. When water boils in a helically coiled tube, the secondary flow enhances heat transfer in the subcooled and convective boiling sections, and alleviates heat transfer deterioration in the dry-out section. However, due to the secondary flow, the heat transfer coefficient drops rapidly by about 36% in the nucleate boiling section.

Tubes of non-circular cross-section to destabilize liquid plugs in heat transfer devices

The stability of a liquid plug inside a vertical tube depends on the balance between the weight of the liquid and the capillary forces. Contact angle hysteresis is required for a liquid plug to be at equilibrium; it has a stabilizing effect. On the other hand, capillary drainage into corners or grooves destabilizes liquid plugs and may lead to their dislocation. Following a detailed literature review about the influence of the tube cross-section on plug stability, this paper provides original numerical and experimental results obtained in tubes of circular, regular polygonal and fluted cross-sections. The cross-section may affect stability either through direct modification of the menisci curvature, or through that of apparent contact angle hysteresis. The latter was characterized experimentally for the first time to our knowledge in tubes of non-circular cross-section. Among the studied shapes, the fluted and triangular ones are the most promising for destabilizing liquid plugs. They both promote capillary drainage. Besides, fluted tubes reduce stability by a direct effect on curvature, while triangular tubes decrease apparent contact angle hysteresis. These findings could help improve the performance of two-phase closed thermosyphons of small dimensions by mitigating liquid hold-up in the condenser section. Indeed, recent advances in additive manufacturing processes enable the fabrication of thermosyphons with very complex shapes. Other devices such as fuel cells could also benefit from the optimization of their geometry to prevent channel occlusion.

Experiments and Modeling of Machined Spring Rotary Actuators with Shape Memory Alloys.

This paper presents a novel rotary actuator using an NiTi shape memory alloy machined spring (SMAMS). An analytical model is put forward to describe the relationship between the twist angle and temperature of SMAMSs under different applied torques. Following that, a numerical model is developed to analyze the stress distributions and twist angle-torque responses of the SMAMS, tube, and spring of the circular cross-section. Thus, the advantages of the SMAMS over the other two rotary actuators are obtained. Moreover, experiments with SMAMSs are conducted to validate these models and study their mechanical responses. Results show that the SMAMS can be designed to have a larger twist angle than the cylindrical-type rotary actuators and to bear a larger torque than the wire-based-type rotary actuators, provided that the inner and outer diameter remains unchanged. Specifically, the maximum actuating twist angle of SMAMSs reaches 278.5°, and their maximum actuating torque is 0.312 N·m. The maximum two-way twist angle of SMAMSs reaches 171° at the pre-applied torque of 0.12 N·m. Moreover, the geometry is found to have a significant influence on the actuating capacity of SMAMSs. When the moments of inertia of SMAMS are 0.82 and 4.69, the corresponding torsion angles are 185.3° and 29.8°, respectively. In general, the SMAMSs with a larger moment of inertia can withstand a larger load. This work fills the gap between wire-based-type rotary actuators and cylindrical-type rotary actuators and is expected to expand the use for SMAs in the rotary actuator.

Measurements of the normal incidence sound absorption coefficient for Non-standard sized absorbers in impedance tubes

A measurement method is proposed for the normal incidence sound absorption coefficient of absorbers whose sizes are non-standard and distinctly smaller than inner dimensions of the impedance tube cross section, and the accuracy of the method is also evaluated. In this method, a type of parallel-arranged acoustic material (PAM) is to fill the non-standard sized absorber to be a flat inhomogeneous acoustic impedance boundary (IAIB) with the standard size. Then acoustic impedance of IAIB is measured in impedance tubes according to ISO 10534–2, and the acoustic impedance and absorption coefficient of the non-standard absorber is evaluated with the proposed method. Numerical simulations and experimental measurements were conducted to compare absorption coefficients of non-standard absorbers evaluated by the proposed method with those of the standard sized absorbers of same materials, where the influence from the IAIB parameters on accuracy of the proposed method are investigated as well. Numerical results show that, absorption coefficients measured by the proposed method for non-standard absorbers differ within 10% from the actual values if the area ratio of the absorber to the impedance tube cross section is larger than 43%, and acoustic impedance of PAM and the area ratio of the absorber mainly influence the evaluated results. Experimental results provided further validations on the proposed method.

A new serpulid species (Polychaeta) from the late Eocene lower part of the Lincoln Creek Formation in western Washington State (USA)

ABSTRACT A new species of serpulid tube worm, Metavermilia (Vepreculina) gollieti sp. nov., is based on tubes found in the late Eocene lower part of the Lincoln Creek Formation exposed along the Middle Fork of the Satsop River, Mason County, Washington State. Metavermilia (V.) gollieti differs from other species of the subgenus Metavermilia (Vepreculina) by its relatively large tube diameter, possession of 5 to 7 sharp longitudinal lines of granula, with a tube cross-section tunnel-shaped posteriorly and pentagonal at the aperture. Metavermilia (V.) gollieti extends the known geochronological range of the predominately Cretaceous subgenus Metavermilia (Vepreculina) from the Barremian to the late Eocene, only the second Cenozoic occurrence because there is the possiblity that ‘Serpula’ granosa from the Miocene (‘Tortonian’) may belong to Vepreculina. At the least, the new Eocene species fills a long gap in the geologic record of Vepreculina midway between Maastrichtian and Miocene as well as being the first record of the subgenus in North America.

Pressure fluctuation characteristics of a pump turbine in a draft tube: New insight into water column separation

The pumped-storage hydropower station is the most reliable, economic, long-term, large capacity, and mature energy storage technology in the power system, and it is an important component of renewable energy. Cavitation and water column separation of a pumped storage unit are important and widely researched factors in the safe and stable operation of a unit. This study focused on the evolution of water column separation of a pump turbine and its relationship with the pressure distribution of the cross section of a draft tube as well as the pressure pulsation characteristics of different measuring points in the cross section of the draft tube. A pumped storage experimental platform that can realize water column separation is established, and experiments with different opening angles are carried out. The results show that there are three factors that impact water column separation and cavitation: gas nucleus, vaporization pressure, and duration of vaporization pressure. Water column separation is the development and continuation of cavitation. The difference between the center pressure of the vortex rope and the wall pressure is large, reaching 2.23 m at a large opening. The pressure fluctuation amplitude of the wall measuring point is greater than that of the other measuring points in the same cross section, but the frequency characteristics are the same. In the transition process, the pressure pulsation amplitude of the liquid column bridging is the largest, and the largest pressure pulsation amplitude can reach 4.18 m at a small opening.

Behaviour of cold-formed steel-concrete composite columns under axial compression: Experimental and numerical study

Concrete filled cold-formed steel-concrete composite columns exhibit improved strength and ductility characteristics due to its ability to resist inward buckling as well as delay the outward buckling. Though concrete infill prevents inward buckling, outward buckling still limits the steel section from reaching its yield strength. From the past studies, it is observed that the introducing of web stiffeners in cross-section of steel section may improve its buckling resistance. The present study focuses on assessing the effect of longitudinal stiffeners on the behaviour of square cold-formed steel–concrete composite columns for the various slenderness range (0.01 to 0.4) through experimental and numerical studies. Conventionally, the integrity of hollow tube cross sections is ensured by welding or by rolling process during the manufacturing. Welding process cannot be adopted in thin-walled cold formed sections since it may lead to higher degree of imperfection. In this study, the desired square cross sections were formed from flat steel sheet and overlapped using self-tapping screws. An intensive numerical analysis was carried out by varying stiffener angle as 90°, 120°, and 141° and the buckling curves for plain and profiled sections were presented. It is concluded that the axial compressive strength of plain and stiffened composite sections is almost equal, attributed to the inability of concrete to reach its maximum stress due to stress concentration at the stiffeners’ edges. The buckling reduction factor of stiffened composite columns showed higher values in the higher slenderness range, indicating the positive effect of the stiffeners.