Tube Geometry Research Articles

Effect of right-angled ribbed geometry on the performance of a Ranque–Hilsch vortex tube: A numerical study

The working principle for the energy separation observed in a Ranque–Hilsch Vortex Tube (RHVT) is a matter that is widely debated and unsettled. It is, however, indisputable that modifications to the tube geometry can substantially affect the performance of the tube. In this paper, a three-dimensional computational fluid dynamic study is performed to investigate the enhanced performance of a geometrically modified vortex tube by studying the flow structure, heat transfer, and energy separation. The novel vortex tube is modeled in ANSYS FLUENT, similar to the original device: 3D Steady-state flow analysis using the standard k-ϵ turbulence model on a hybrid mesh. The results acquired are compared and found to demonstrate the increase in the observed energy separation in the novel geometry. The total increase in thermal separation for the novel design is observed to be 15.1 K at 0.9 Cold Mass Fraction, with an increase of 10 W in overall energy transfer. Compared to the nominal design, a maximum of 13.74 percent improvement in thermal separation. Furthermore, the flow structures are compared to understand the reason behind the increased performance. It is found that the factors responsible for the extent of separation of energy in the tube are: Higher Radial Pressure Gradient, Higher Circumferential, and Axial Shear Work, and Conductive Heat Transfer. Finally, an energy balance is carried out on the peripheral hot control volume to study the fundamental modes of energy transfer. The energy balance verifies that these factors are the prominent factors responsible for the observed increase in separation.

Comparative Study of Different Tube Geometries of Evacuated Tube Solar Collector

Abstract This study investigates the thermal performance of an evacuated U-tube solar collector (ETSC) using different tube geometrical configurations. The effect of tube geometry on the overall collector efficiency is numerically analyzed and compared with experimental results. Three different ETSC configurations made of copper viz., Model 1 (M1) having one inlet and two outlets, Model 2 (M2) having one inlet and three outlets, and Model 3 (M3) having one inlet and four outlets are considered. An overall rise in temperature of heat transfer fluid at the outlets for each model is predicted and compared with a conventional U-tube (CT) for different mass flowrates and solar insolations to evaluate the collector performance. In comparison with the CT, the outlet temperature of the M3 and M1 is higher by 46.2% and 40.3%, respectively. M2 gives a nearly similar fluid outlet temperature as M1. A maximum of 35.4% enhancement in heat gain compared to the CT is observed for M3 (which is best among modified configurations) under similar operating conditions. However, at 788 W/m2 solar insolation and a constant mass flowrate of 0.0167 kg/s, the estimated thermal efficiency of M1 is higher among the three models which is 33.5% higher than the CT. The experimental results closely approximate the numerical predictions with a deviation of ± 1.1 °C. From the economic evaluation of the modified collectors, a minimum payback period of 2.5 years was observed for Model 1 which is the shortest among the investigated ETSC systems.

Flow and thermal performance of a multi-jet twisted square microchannel heat sink using CuO-water nanofluid

Due to the rapid development in micro manufacturing and 3D printing technology, the complex shape of microchannel heat sink (MCHS) can be realized, instead of just the traditional rectangular channels. It is recognized that twisted square channels which are similar to a kind of internal thread channel have favorable effects on heat transfer because of its enhancement of turbulence intensity. In this work, a geometry of twisted tube is applied to the microchannel and the thermal and hydrodynamic performance of twisted square microchannels with jet impingement are investigated. The arrangement of the jet channels is the research focus and one-jet and multi-jet microchannel heat sinks are compared by discussing the temperature profile, pressure drop and heat transfer characteristics. By applying the twisted geometry to the microchannel, the Nusselt number can be increased by 16.48% with little increase in pressure drop. However, with the increase in torsion angle of the twisted microchannel (from 90° to 720°), the thermal performance changes little for the limited effect on the temperature uniformity of the cross section. Integration of jet impingement further improves the thermal-hydrodynamic performance of MCHS. Specifically, the thermal resistance of MCHS was reduced by 41% at most. Finally, by comparing the comprehensive performance of the cases with varied jet arrangement, it is concluded that jets distributed at the cross section with the torsion angle of 45°, 135°, and 225° can induce better performance. The present investigation combines the twisted geometry and jet impingement into microchannel, quantitatively characterizes the performance of MCHS and gives the guidance for the jet arrangement design.

Critical heat flux correlations for tube and annulus geometries under inclination and rolling conditions

In floating nuclear reactors, critical heat flux (CHF) prediction is crucial because the CHF can be influenced under heaving, rolling, and inclination conditions, unlike in land-based reactors. Hence, the existing land-based empirical correlations of the CHF can be invalid under some conditions in marine reactors. Therefore, empirical correlations of the flow boiling CHF were developed in this study to predict the CHF under inclination and rolling motions in tubes and annuli. Available experimental CHF data (616 points) were collected including our previous experimental data (405 points) and their trends under marine conditions were analyzed. The CHF variation was expressed using two types of modified Froude numbers depending on the CHF regime—departure from nucleate boiling and dryout. These parameters were used in correlations for the CHF under inclination. CHF correlations under rolling conditions were developed. Rolling was found to attenuate the CHF variation through the inclination. This observation was reflected in the newly developed rolling CHF correlation. The proposed correlations adequately described the existing CHF experimental data under inclination and rolling within an uncertainty of 9.5%. The developed CHF correlations can be used for the safety analysis and reactor core thermal–hydraulic design of marine reactors.

Technical note: Water-equivalent thickness of Superflab bolus material at diagnostic x-ray energies.

The purpose of this work was to determine the water-equivalent thickness of Superflab bolus material for narrow and broad field-of-view (FOV) x-ray geometries at diagnostic x-ray energies. Transmission measurements were performed for incremental thicknesses of Superflab bolus material and water in narrow and broad FOV x-ray geometries. The transmission data was fit to a non-linear model for x-ray transmission - the Archer model. Water-equivalent thickness of Superflab was calculated based upon fitting parameters to transmission curves for 75, 95, and 115kV x-ray tube voltages. Measured x-ray transmission factors for water and Superflab were used to determine the water equivalence of Superflab. For all x-ray tube voltages and geometries, the water equivalence of Superflab was greater than one, indicating that Superflab is more attenuating than water. This effect was stronger for broad FOV geometries. At 95kV, 30cm of Superflab corresponded to 32.0cm of water in the narrow FOV geometry, and 34.3cm of water in the broad FOV geometry. The Archer model fitting parameters and Superflab water equivalence are reported for all x-ray beam conditions explored in this work. Superflab bolus material is more attenuating than water at diagnostic x-ray energies. The Archer model and its respective fitting parameters reported in this work may be used to estimate the water-equivalent thickness of Superflab for diagnostic x-ray spectra.

HEAT-TRANSFER ENHANCEMENT OF A SOLAR PARABOLIC TROUGH COLLECTOR USING TURBULATORS AND NANOPARTICLES: A NUMERICAL STUDY

Solar energy harnessing devices exhibit promising potential for providing a significant portion of the energy requirement. Among these devices, the solar parabolic trough collector (PTC) is a well-renowned and effective technology. In recent times, a great deal of research has been done further improving the thermal performance of PTC systems. The current numerical study investigates the effect of modifications to the geometry of the absorber tube and the effect of nanoparticles on the thermal performance of PTC. A corrugated tube (CT), sinusoidal corrugated tube (SCT), the corrugated tube having a cylindrical insert (CI), star insert (SI), and increasing diameter rod insert (IDRI) are used to modify the geometry of the absorber tube. The corrugated tube is also analyzed with water-Al<sub>2</sub>O<sub>3</sub> and water-TiO<sub>2</sub> nanofluids at volume concentrations of 2%, 4%, and 6%. The results showed that the sinusoidal corrugated tube produced the best results with a value of Nusselt number (Nu) being 15.2% greater than simple corrugated absorber tube without incurring any significant increase in pressure. Moreover, the performance evaluation criterion (PEC) value is also found to be greater than that of simple corrugated geometry. The use of nanofluids as the heat-transfer fluid (HTF) led to an overall enhancement in the heat transfer coefficient h by as much as 20%.

Investigation of the Thermo-hydraulic performance of a roughened Parabolic trough collector

Parabolic trough collectors (PTC) are an already established technology set to prove its competitiveness. Recently, a lot of research is ongoing to further enhance the thermal performance of PTC systems. Computational Fluid Dynamics (CFD) can help in the design and development of PTCs with optimized thermal efficiency. In the current work, a combined enhancement in the performance of a PTC is evaluated, involving modifications to the geometry of the absorber tube and the use of a heat transfer fluid (HTF) (Syltherm800). Absorber tube geometries involving dimpled protrusions (d-PTC) and circumferential inclined ribs (IR-PTC) are used. The performance of PTC with and without turbulators is compared with that of a smooth absorber tube by calculating the Nusselt number (Nu), friction factor (f) and performance evaluation criterion (PEC). PEC values of 1.46 and 1.18 are observed by using inclined ribs and dimpled protrusions, respectively at an absorber tube inlet temperature (Tin) of 500 K and mass flow rate (ṁ) of 0.5 kg s−1. Thus, a significant enhancement in thermo-hydraulic performance of PTC is observed with inclined rib turbulators.

Tube geometry controls protein cluster conformation and stability on the endoplasmic reticulum surface.

The endoplasmic reticulum (ER), a cellular organelle that forms a cell-spanning network of tubes and sheets, is an important location of protein synthesis and folding. When the ER experiences sustained unfolded protein stress, IRE1 proteins embedded in the ER membrane activate and assemble into clusters as part of the unfolded protein response (UPR). We use kinetic Monte Carlo simulations to explore IRE1 clustering dynamics on the surface of ER tubes. While initially growing clusters are approximately round, once a cluster is sufficiently large a shorter interface length can be achieved by 'wrapping' around the ER tube. A wrapped cluster can grow without further interface length increases. Relative to wide tubes, narrower tubes enable cluster wrapping at smaller cluster sizes. Our simulations show that wrapped clusters on narrower tubes grow more rapidly, evaporate more slowly, and require a lower protein concentration to grow compared to equal-area round clusters on wider tubes. These results suggest that cluster wrapping, facilitated by narrower tubes, could be an important factor in the growth and stability of IRE1 clusters and thus impact the persistence of the UPR, connecting geometry to signaling behavior. This work is consistent with recent experimental observations of IRE1 clusters wrapped around narrow tubes in the ER network.

Tube wall deformation behaviour of tensile-loaded blind-bolted connections in octagonal hollow section tubes

The structural behaviour of octagonal hollow section (OctHS) tubes under lateral tensile loads applied through blind-bolted T-stubs were experimentally and numerically investigated in this study. Two series of T-stub connections – single-side and double-side bolted T-stub connections, were tested to investigate the influence of the tube geometry and boundary conditions on the failure modes, deformation, and strength. Finite element (FE) models were developed and validated against the test results. Based on the validated FE models, parametric studies were conducted to further assess the influence of width-to-thickness ratios, tube length-to-width ratios and boundary conditions on the tube deformation and strength. Furthermore, the applicability of the tube deformation of 3% of a tube width to be the ultimate state criterion for OctHS tubes was evaluated using tube-face component shell FE models. A simplified two-dimensional analytical model was developed, and the calculation equations were proposed based on either small deformation assumption or large deformation assumption. The comparison of the strengths obtained from the proposed equations, numerical simulations and tests demonstrated that the proposed equations are able to give reasonable predictions on the yield and ultimate strengths of blind-bolted OctHS tube connections under tensile loading.

Energy absorption of self-similar inspired multi-cell hexagonal tubes

Self-similar inspired multi-cell tubes have been widely used in energy absorbing devices due to their flexible and feasible design strategy. In this paper, a novel multi-cell hexagonal tube is constructed by space-filling and cross-section topological design of self-similar inspired multi-cell tubes. A user-friendly plug-in tool is developed in Abaqus/CAE to rapidly estimate the crashworthiness of these multi-cell tubes by taking as input the geometry of these multi-cell tubes. The discrete robust optimization algorithm and multi-object decision-making method (COPRAS) are used to select the optimal cross-section topology of the self-similar inspired multi-cell hexagonal tubes. In addition, the effect of different space-filling strategies and the number and layout of ribs on the crashworthiness of these multi-cell tubes are studied. The results show that the crashworthiness of these multi-cell structures can be further improved by double space-filling. Hence, these design strategies and optimization methods proposed in this paper can be used in the topology optimization of the multi-cell tubes.

A precise measurement method for tube endpoints based on spatial geometry and perspective projection model

Tubes are widely used in the aerospace field for such things as engines, fuel pipelines, cooling systems, etc. To improve manufacturing efficiency and accuracy, researchers develop multi-camera vision methods for measuring tube geometry parameters. However, these methods cannot measure the exact position of the endpoints of the tube, because the projection points of the tube endpoints have no obvious texture features in the image. To solve the above problem, a precise measurement method for tube endpoints based on spatial geometry and perspective projection model is proposed in this paper. First, we establish a Plücker coordinate system, which treats the end of the tube as a cylinder. Then, several line equations parallel to the center line are calculated on the surface of the cylinder and their intersections with the end face are obtained on these lines, which refers to the optical center of the camera, the radius of the tube, and etc. These intersections are projected onto the centerline and optimized to get the endpoint. Finally, we build a multi-camera vision measurement system consisting of ten industrial cameras to verify the effectiveness of the proposed method. Extensive experiments have shown that the average error of this method is within 0.1 mm, and the standard deviation is within 0.08 mm, which proves the superiority of our proposed method.

Effects of support type and geometric shape of steel tube on concrete-encased concrete-filled steel tube beam under low velocity impact

Concrete-encased concrete-filled steel tube (CEFST) beams prepared by placing steel tube in RC beam is a beam type that has widespread use. The current study examines the effects of steel tube geometry and support conditions on the behavior of CEFST beams under low velocity impact loading. First, CEFST beam specimens with different lengths and different tube section geometries (circular and square) were produced in the laboratory. These four test specimens with two different support conditions were exposed to low velocity impact load tests. Finite element models of the test specimens were created using Abaqus\\Explicit software. In the next stage, 4 finite element models were verified by the experimentally obtained damage conditions, maximum displacements, and support reaction forces. In the final stage, as parametric study 12 finite element models were prepared in addition to 4 verified models and analyzed under low velocity impact loading. In addition to experimental values, Von Mises stresses, Equivalent plastic strain, Friction energy, and Damage energy values were also obtained by the numerical study and thus the effects of steel tube geometry and support conditions were comparatively examined. The obtained results showed that CEFST beams with a square tube section exhibited better performance under a sudden load such as impact compared to the beams with a circular tube section. Moreover, both numerical and experimental results pointed out that the beam length beyond support has a positive impact on the performance of beam under impact loading.

Numerical investigation of the effect of tracheostomy on flow and particle transport characteristics in human airways

Tracheostomy is a typical surgical procedure that has been widely practiced to address airway-related difficulties, such as airway obstruction or chronic conditions, that require long-term supportive ventilation. However, it may result in symptoms that detrimental to respiratory system. Computational fluid dynamics (CFD) is a noninvasive and efficient approach for observing the effects of tracheostomy. In this study, we introduced a CFD framework that can reveal the effects of tracheostomy tube insertion based on a comparison with the airflow of a normal airways. An automatic transformation method was developed using a patient's anatomical information to combine subject-specific airways with an artificial tracheostomy tube geometry and an idealized upper airway geometry for later comparison of characteristics of airflow and particle transport. The CFD scheme used for flow simulation in lungs was employed to achieve the behaviors of airflow. The tracheostomy tube generates a jet flow, resulting in twice greater wall shear stress (WSS) and 30 times greater viscous dissipation in the trachea compared to normal airway. The tracheostomized airway induces an intense turbulent jet, which enhances chaotic motion of the particles therein and allows particles to deposit more frequently on the surface. Subsequently, an increase in particle deposition is observed on the central airway's surface. The variation of pressure between inspiration and expiration phase was twice greater and the airflow resistance was also significantly higher compared to normal airway, implying the greater work of breathing. The novel framework could evaluate the efficiency and potential complications in performing tracheostomy beforehand by observing airflow behaviors.

Printing Hollow Tubes Using Digital Glass Forming

Abstract This article investigates printing hollow tubes using the digital glass-forming process. A CO2 laser locally heats continuously fed glass tube feedstock so that it can be plastically deformed. This allows it to be bent and deposited onto a workpiece. The workpiece is positioned relative to the laser using precision four-axis computer numerical control stages. The loading on the laser-heated region is controlled by the stages as well as pneumatic pressure in the tube, which allows the printing complex shapes without the tube collapsing. The bending behavior of freestanding glass structures is examined, focusing on the geometric accuracy and temperature profile of the deformation zone as a function of the process parameters. The application of pneumatic pressure allows the control of the printed tube diameter. Several complex tube geometries deposited on the planar substrates as well as freestanding structures are demonstrated.

Three-dimensional detonation structure and its response to confinement

Three-dimensional (3D) detonation simulations solving the compressible Navier-Stokes equations with detailed chemistry are performed in both square channel and round tube geometries. The simulations are compared with each other and with two-dimensional (2D) channel simulations and round tube experiments of identical mixture and conditions (stoichiometric hydrogen-oxygen with 3000 PPMv ozone at 300 K and 15 kPa) with the goal of understanding the effect of confinement and boundaries on detonation structure. Results show that 3D detonations propagate with highly inhomogeneous blast dynamics, where blasts emerge not only from intersections of two transverse waves (similar to 2D propagation) but also from intersections of many transverse waves (unique to 3D detonations in the confinements tested). Intersections of many transverse waves lead to extreme thermodynamic states and highly overdriven wave velocities, well in excess of those seen in the ZND model and in 2D simulations. 3D simulations in the square tube show highly regular blast latticing, smaller detonation cells, and highly oscillatory velocities when compared to the round tube simulations. Round tube simulations show more spatially non-uniform blast dynamics. The conclusions reached in the current work are found irrespective of numerical grid resolution.

Numerical analysis of conjugate heat transfer within internally channeled tubes

A novel heat exchanger design concept to enhance heat transfer is presented. The exchanger geometry includes six channels arranged inside an insulated circular tube along its axis and forming the so-called internally channeled tube (ICT). The ICT concept offers an increase in the heat transfer surface area between cold and hot fluids. Two original channeled tube geometries are proposed and studied. Single-phase flow and conjugate heat transfer are captured by steady-state CFD simulations utilizing a new approach based on the fluid domain splitting. Heat transfer coefficients and pressure drop are determined under laminar and turbulent flow conditions using water as working fluid. The possibility to apply existing correlations to determine friction factors and Nusselt number in ICTs was explored based on the numerical results. Furthermore, an evaluation of the ICT designs is given in comparison with a traditional double-pipe heat exchanger (DPHE). The heat transfer rate in ICT heat exchangers was found to be up to 50% higher than that in the DPHE, yet with a pressure drop penalty of up to 70%.

Dynamic Tube Model Predictive Control for Powered-Descent Guidance

In this paper, a dynamic tube nonlinear model predictive control (NMPC) scheme is developed to solve the powered-descent guidance (PDG) problem in the presence of bounded disturbances and no-fly zones. First, owing to its simplicity and robustness, time-varying boundary layer sliding mode control (SMC) is used as an ancillary controller to compensate for external disturbances. Consequently, the tube geometry dynamics can be established as first-order differential equations to calculate the robust control invariant tube. Hence, the nominal trajectory and tube geometry are optimized simultaneously to improve the control performance by augmenting the tube geometry dynamics in open-loop MPC optimization. Moreover, the tube can be shrunk to reduce the conservativeness and enhance optimization feasibility by exploiting the tube geometry and tracking error dynamics. In addition, a constraint-tightening method is employed to ensure that the PDG problem satisfies all the constraints while accounting for the uncertainty caused by the disturbance. Finally, numerical case studies and Monte Carlo simulations validate the effectiveness and performance of the proposed strategy.

OPTIMIZING DIAMETER, LENGTH, AND WATER IMMERSION IN FLOW RESISTANT TUBE VOCALIZATION

The objective was to quantify the range of airflow resistance and oral pressure attainable with variation of length, diameter, and water immersion depth of tubes and straws. Pressure-flow equations for tubes, determined previously for variable tube geometries, were used to calculate oral pressure ranges. Human subjects were then recruited to use the variable tube geometries to produce oral pressures, which were quantified with commercial manometers. Nomograms for airflow resistances and oral pressures are plotted as a function of tube length, tube diameter, and water insertion depth. It is shown that tube diameters in the range of 2.5-3.0 mm with tube lengths of 10-40 cm produce oral pressures in the range of 10-40 cm H2O. Insertion of the distal end into water adds a pressure in the amount of the depth of insertion. Maximum power transfer with different tube geometries is discussed.

Investigation of Efficient Optimization Approach to the Modernization of Francis Turbine Draft Tube Geometry

The installation of new and revitalization of existing hydropower requires the optimal design of hydraulic turbine parts, which were previously mostly based on simplified analytical methods and engineering practices. With the increase in computational power, optimization methods now present an effective approach to the improvement of the geometry of turbine parts, thus enabling fine geometry-tuning adjustments of site specifics. However, despite continually increasing computational power, such numerical optimizations still require substantial resources and time. Therefore, in the proposed paper, extensive analysis of different numerical simplifications was conducted to determine the best trade-off between accuracy and the required computational resources for draft tube optimization. Additionally, the influence of geometry parametrization in terms of greater geometry flexibility, different goal functions, and optimization parameters was investigated. Within the considered constraints, a novel draft tube geometry was obtained, with the elbow displacements toward the draft tube exit, a shape that could not be obtained with the usual draft tube parametrization. It was also observed that geometry improvements for a single operating point did not provide improvements for other operating points. The obtained findings regarding the numerical and optimization setup can be used as guidelines for future optimization research, where multiobjective optimization for multiple operating points should be further investigated.

Chiral DNA Nanotubes Self-Assembled from Building Blocks with Tailorable Curvature and Twist.

DNA nanotubes with prescribed geometry could allow for nanomaterial organization with designed optical or electrical function. As one of the dominating driving forces for DNA nanotube assembly, intrinsic curvature and twist of building blocks can be induced by bending deformation and twisting deformation. However, it is still unknown that how bending and twisting design on nanoscale building blocks affects the geometry of DNA tubes with micrometer length. Here, through targeted base pair deletion or insertion, the amount of bending deformation in building blocks is modulated by length gradient and the amount of twisting deformation is modulated by average twist density. This work systematically explores the independent effect and synergistic effect of two types of deformation on tube geometry, including diameter, chirality, and helical angles, via a streptavidin-labeling technique. The design rules enable the construction of DNA nanotubes with prescribed chirality and tailored diameters.