Tube Geometry Research Articles

Impact of Eccentric Tube Shapes and Heat Pipes on Phase Change Material’s Thermal Charging

The thermal charging performance of phase change material (PCM) in an eccentric tube and shell system is investigated through numerical analysis. Various shapes of eccentric tubes, including circular, semi-circular, triangular, inverted triangular, square, and C-shape, are considered. The PCM mass and shell diameter remain consistent across all tube geometries. Moreover, vertical heat pipes (HPs) are utilized to connect the heat source eccentric tube wall and the PCM stored in the shell. The examination evaluates the consequences of the tube shape and HPs using liquid fraction, temperature time history and contours, enhancement ratio, total energy storage, and mean power as performance indicators. The findings demonstrate that non-circular cases exhibit a shorter melting time than circular tube cases. The C-shape tube has the (Largest) 30.3% less thermal charging time than the circular tube, and the mean power is 39% higher. Moreover, adding HPs increases the mean power by up to 241% more than the circular tube, and reduces thermal charging time by about 72.2%. The inverted triangular tube exhibits the highest energy charge capability within the selected options.

Strategies for multi-case physics-informed neural networks for tube flows: a study using 2D flow scenarios

Fluid dynamics computations for tube-like geometries are crucial in biomedical evaluations of vascular and airways fluid dynamics. Physics-Informed Neural Networks (PINNs) have emerged as a promising alternative to traditional computational fluid dynamics (CFD) methods. However, vanilla PINNs often demand longer training times than conventional CFD methods for each specific flow scenario, limiting their widespread use. To address this, multi-case PINN approach has been proposed, where varied geometry cases are parameterized and pre-trained on the PINN. This allows for quick generation of flow results in unseen geometries. In this study, we compare three network architectures to optimize the multi-case PINN through experiments on a series of idealized 2D stenotic tube flows. The evaluated architectures include the ‘Mixed Network’, treating case parameters as additional dimensions in the vanilla PINN architecture; the “Hypernetwork”, incorporating case parameters into a side network that computes weights in the main PINN network; and the “Modes” network, where case parameters input into a side network contribute to the final output via an inner product, similar to DeepONet. Results confirm the viability of the multi-case parametric PINN approach, with the Modes network exhibiting superior performance in terms of accuracy, convergence efficiency, and computational speed. To further enhance the multi-case PINN, we explored two strategies. First, incorporating coordinate parameters relevant to tube geometry, such as distance to wall and centerline distance, as inputs to PINN, significantly enhanced accuracy and reduced computational burden. Second, the addition of extra loss terms, enforcing zero derivatives of existing physics constraints in the PINN (similar to gPINN), improved the performance of the Mixed Network and Hypernetwork, but not that of the Modes network. In conclusion, our work identified strategies crucial for future scaling up to 3D, wider geometry ranges, and additional flow conditions, ultimately aiming towards clinical utility.

Optimization of Elbow Draft Tubes for Variable Speed Propeller Turbine

The design of the elbow draft tubes is challenging due to the complexity of the flow. The whole turbine unit’s power output strongly depends on the draft tube function, especially for the low-head turbines. The article presents a novel approach to optimizing elbow draft tubes for a variable-speed propeller turbine designed for low-head applications. First, the study addresses the specifics of the propeller variable speed turbine by comparing the classical Kaplan turbine. Then, the grid scaling test is conducted to evaluate the uncertainty of the pressure regeneration. Further, a new approach to parameterising the elbow draft tube geometry is introduced. The study employs ANSYS CFX 2021 R1 software for numerical simulation to optimise the elbow draft tube geometry in the CAESES environment. After the sensitivity test and deselecting the non-sensitive parameters, we perform multi-objective genetic algorithm (MOGA) optimization. The optimization process results in a Pareto front of optimised elbow draft tube shapes with the best pressure regeneration for different draft tube construction heights, enabling the selection of suitable candidates for various locations. Minimal difference in the performance of the selected elbow draft tube shapes with the simple straight draft tube confirms a high-quality draft tube optimization achievement.

Diaphragm-Induced Attenuation in Shock Tubes

This is a numerical and experimental study on shock attenuation in shock tubes. Tube geometry, boundary layer, and reduction in cross-sectional area induced by burst diaphragms are often considered the main causes of shock speed reduction (or shock attenuation) observed during the experiments. In order to distinguish how each single phenomenon contributes toward shock attenuation, the National Cheng Kung University shock tube is simulated for driver and test (driver–test) gas pairs involving air–air and He–air. For low pressure ratios, the diaphragm effect was found to be negligible. For a pressure ratio of 200 and helium as driver gas, the shock speed was found to decrease linearly with the size of the diaphragm orifice. In general, wall viscous effects caused a 2.5% decrease in shock speed, while an additional 7% reduction was caused by the presence of the diaphragm. The gradual opening of the diaphragm mainly contributed to a decrease in shock oscillations.

Spatio-temporal relationship between three-dimensional deformations of a collapsible tube and the downstream flowfield

The interactions between fluid flow and structural components of collapsible tubes are representative of those in several physiological systems. Although extensively studied, there exists a lack of characterization of the three-dimensionality in the structural deformations of the tube and its influence on the flow field. This experimental study investigates the spatio-temporal relationship between 3D tube geometry and the downstream flow field under conditions of fully open, closed, and slamming-type oscillating regimes. A methodology is implemented to simultaneously measure three-dimensional surface deformations in a collapsible tube and the corresponding downstream flow field. Stereophotogrammetry was used to measure tube deformations, and simultaneous flow field measurements included pressure and planar Particle Image Velocimetry (PIV) data downstream of the collapsible tube. The results indicate that the location of the largest collapse in the tube occurs close to the downstream end. In the oscillating regime, sections of the tube downstream of the largest mean collapse experience the largest oscillations in the entire tube that are completely coherent and in phase. At a certain streamwise distance upstream of the largest collapse, a switch in the direction of oscillations occurs with respect to those downstream. Physically, when the tube experiences constriction downstream of the location of the largest mean collapse, this causes the accumulation of fluid and build-up of pressure in the upstream regions and an expansion of these sections. Fluctuations in the downstream flow field are significantly influenced by tube fluctuations along the minor axes. The fluctuations in the downstream flowfield are influenced by the propagation of disturbances due to oscillations in tube geometry, through the advection of fluid through the tube. Further, the manifestation of the LU-type pressure fluctuations is found to be due to the variation in the propagation speed of the disturbances during the different stages within a period of oscillation of the tube.

The motion of Brownian particles suspended in a non-uniform fluid flow

The effect of the type of fluid flow velocity profile on the motion of a Brownian particle in a circular tube has been studied using a Monte Carlo technique to simulate particle trajectories. Three types of fluid flow were studied: uniform (UF), parabolic (PF), and an initial uniform flow which evolves and may eventually attain the parabolic velocity profile, i.e. transient flow (TF). For UF and PF, radial and axial particle diffusion were simultaneously considered in some cases; for TF, where fluid dynamics equations had to be solved in addition to the Monte Carlo simulations, axial diffusion was neglected for fluid and particles, so that calculations had to be restricted to tube aspect ratios (radius/length) smaller than 0.1, a common scenario in most practical aerosol applications. A first series of simulations were performed to determine the overall particle penetration through the tube. For fixed tube geometry and particle diffusion coefficient, penetration in TF lied between those in PF (highest) and UF (lowest), in such a manner that, for a given value of the diffusion coefficient, the larger the degree of flow development (i.e., the smaller the values of the tube aspect ratio and the Reynolds number), the larger the penetration. These findings are coherent with those found in a former investigation dealing with the particle residence time in the tube. In a second series of simulation runs, calculations were done for selected initial locations of the particle within the tube entrance cross section, to examine the effect that the proximity of the particle starting position to the tube wall or to the tube axis has on variables such as penetration, mean first hitting time and length, mean first exit time, and mean axial velocity of lost and survived particles. When the fluid flow is not uniform but varies from place to place, the mean particle axial velocity is larger than that of the fluid. This counterintuitive fundamental result allows interpretation of the trends observed in penetration and residence time.

Machine and deep learning driven models for the design of heat exchangers with micro-finned tubes

The design of micro-finned tube heat exchangers is a complex task due to intricate geometry, heat transfer goals, material selection, and manufacturing challenges. Nowadays, mathematical models provide valuable insights, aid in optimization, and allow us to explore various design parameters efficiently. However, existing empirical models often fall short in facilitating an optimal design because of their limited accuracy, sensitivity to assumption, and context dependency. In this scenario, the use of Machine and Deep Learning (ML and DL) methods can enhance accuracy, manage nonlinearity, adjust to varying conditions, decrease dependence on assumptions, automatically extract pertinent features, and provide scalability. Indeed, ML and DL techniques can derive valuable insights from datasets, contributing to a comprehensive understanding. By means of multiple ML and DL methods, this paper addresses the challenge of estimating key parameters in micro-finned tube heat exchangers such as the heat transfer coefficient (HTC) and frictional pressure drop (FPD). The methods have been trained and tested using an experimental dataset consisting of over a thousand data points associated with flow condensation, involving various tube geometries. In this context, the Artificial Neural Network (ANN) demonstrates superior performance in accurately estimating parameters with MAEs in the range below 4.5% for both HTC and FPD. Finally, recognizing the importance of comprehending the internal mechanisms of the black-box ANN model, the paper explores its interpretability aspects.

Semi-empirical model for abrasive particle velocity prediction in abrasive waterjet based on momentum transfer efficiency

Abrasive waterjet (AWJ) is a technology that removes a target material with an abrasive accelerated by ultra-high-pressure water. Recently, its application for rock excavations in civil and geotechnical engineering has increased. AWJ excavation performance is affected by the abrasive velocity formed by momentum transfer during mixing and acceleration. The abrasive velocity varies owing to changes in the abrasive flow rate, focusing tube diameter, and focusing tube length. In this study, the momentum transfer efficiency (MTE) according to the abrasive flow rate and focusing tube geometry was investigated by a numerical analysis to better understand the multiphase flow inside the AWJ system. The MTE was defined based on the theoretical relationship between the abrasive velocity ratio and focusing tube factor, and evaluated through the empirical relationship between the water stiffness and focusing tube length. The optimal abrasive flow rate for generating efficient MTE was approximately 15 g/s, which enabled economical and effective acceleration of abrasive particles. Accordingly, a prediction model based on the derived MTE was developed for the final abrasive velocity generated at the tip of the focusing tube. Using the prediction model, it is possible to evaluate the comprehensive relationship between various AWJ parameters. Based on the prediction model, the abrasive–water flow ratio to generate the optimal abrasive velocity was 0.83. The developed prediction model provides guidelines for selecting the optimal focusing tube geometry and applying an economical abrasive flow rate when designing an AWJ system.

Cryogenic Failure Behaviors of Al–Mg–Si Alloy Tubes in Bulging Process

Abstract Cryogenic medium pressure forming has been developed to form the complex-shaped tubular components, in which the needed shape and tube diameter directly determine the complex evolution of biaxial stress in bulging process. The superposition of biaxial stress and cryogenic temperature complicates the deformation behaviors, especially for the final fracture and bulging limit, which determine the forming quality of components. Therefore, the effects of tube geometry on failure orientation and fracture strain of Al–Mg–Si alloy tubes under cryogenic biaxial stress were elucidated, by utilizing cryogenic free bulging with different length–diameter ratios. The failure orientations and corresponding damage modes under different bulging geometric conditions were revealed. The influence mechanism of tube geometry and temperature on the failure mode was analyzed theoretically. A fracture model was established to predict the fracture strain in cryogenic bulging. The failure mode changes from circumferential cracking to axial cracking with the decreasing length–diameter ratio, owing to the stress sequence reversal induced by the significant nonlinearity of the stress path under a small length–diameter ratio. The failure mode can inverse under a larger length–diameter ratio of 1.0 at −196 °C because of the enhanced nonlinearity, which is promoted by the improved plasticity at cryogenic temperature. The established model based on the more accurate assessment of hardening ability during deformation can accurately predict the fracture strain with an average deviation of 10.6% at different temperatures. The study can guide deformation analysis and failure prediction in the cryogenic forming of aluminum alloy tubular parts.

NaI gamma camera performance for high energies: Effects of crystal thickness, photomultiplier tube geometry and light guide thickness.

Gamma camera imaging, including single photon emission computed tomography (SPECT), is crucial for research, diagnostics, and radionuclide therapy. Gamma cameras are predominantly based on arrays of photon multipliers tubes (PMTs) that read out NaI(Tl) scintillation crystals. In this way, standard gamma cameras can localize ɣ-rays with energies typically ranging from 30 to 360keV. In the last decade, there has been an increasing interest towards gamma imaging outside this conventional clinical energy range, for example, for theragnostic applications and preclinical multi-isotope positron emission tomography (PET) and PET-SPECT. However, standard gamma cameras are typically equipped with 9.5mm thick NaI(Tl) crystals which can result in limited sensitivity for these higher energies. Here we investigate to what extent thicker scintillators can improve the photopeak sensitivity for higher energy isotopes while attempting to maintain spatial resolution. Using Monte Carlo simulations, we analyzed multiple PMT-based configurations of gamma detectors with monolithic NaI (Tl) crystals of 20 and 40mm thickness. Optimized light guide thickness together with 2-inch round, 3-inch round, 60×60 mm2 square, and 76×76 mm2 square PMTs were tested. For each setup, we assessed photopeak sensitivity, energy resolution, spatial, and depth-of-interaction (DoI) resolution for conventional (140keV) and high (511keV) energy ɣ using a maximum-likelihood algorithm. These metrics were compared to those of a "standard" 9.5mm-thick crystal detector with 3-inch round PMTs. Estimated photopeak sensitivities for 511keV were 27% and 53% for 20 and 40mm thick scintillators, which is respectively, 2.2 and 4.4 times higher than for 9.5mm thickness. In most cases, energy resolution benefits from using square PMTs instead of round ones, regardless of their size. Lateral and DoI spatial resolution are best for smaller PMTs (2-inch round and 60×60 mm2 square) which outperform the more cost-effective larger PMT setups (3-inch round and 76×76 mm2 square), while PMT layout and shape have negligible (<10%) effect on resolution. Best spatial resolution was obtained with 60×60 mm2 PMTs; for 140keV, lateral resolution was 3.5mm irrespective of scintillator thickness, improving to 2.8 and 2.9mm for 511keV with 20 and 40mm thick crystals, respectively. Using the 3-inch round PMTs, lateral resolutions of 4.5 and 3.9mm for 140keV and of 3.5 and 3.7mm for 511keV were obtained with 20 and 40mm thick crystals respectively, indicating a moderate performance degradation compared to the 3.5 and 2.9mm resolution obtained by the standard detector for 140 and 511keV. Additionally, DoI resolution for 511keV was 7.0 and 5.6mm with 20 and 40mm crystals using 60×60 mm2 square PMTs, while with 3-inch round PMTs 12.1 and 5.9mm were obtained. Depending on PMT size and shape, the use of thicker scintillator crystals can substantially improve detector sensitivity at high gamma energies, while spatial resolution is slightly improved or mildly degraded compared to standard crystals.

Multi-objective optimization of twisted tri-lobed tube geometry for enhanced heat transfer and reduced resistance in turbulent flow

This study presents a detailed multi-objective optimization analysis of turbulent flow and heat transfer within a twisted tri-lobed tube, employing an integrated approach that combines Central Composite Design (CCD), Response Surface Methodology (RSM), Non-dominated Sorting Genetic Algorithm II (NSGA-II), Pareto frontier analysis, Linear Programming Technique for Multidimensional Analysis of Preference (LINMAP), and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The investigation focuses on optimizing key design parameters: Reynolds number (Re), twist pitch (P), and minor circle radius (r), targeting Nusselt number (Nu), Poiseuille number (fRe), and Performance Evaluation Criterion (PEC) as optimization objectives. Our major findings reveal that the developed second-order regression model precisely predicts the influences of these parameters on Nu, fRe, and PEC, with sensitivity analysis showing Re's strong positive impact on Nu and fRe, P's negative effect on fRe, and r's minimal impact. The study notably highlights the significant Nu enhancement with Re increase. Utilizing multi-objective optimization, we identified a Pareto optimal set, and through LINMAP and TOPSIS methods, derived compromise solutions that optimally balance heat transfer efficiency, flow resistance, and overall performance. These outcomes underscore the critical importance of parameter selection to meet specific engineering needs, offering a strategic framework for enhancing twisted tri-lobed tube designs.

Analysis of energy and exergy of eutectic phase change material solidification for various configuration-based triplex tube

This study delves into the energy and exergy analysis of eutectic PCM solidification within a triplex tube latent heat storage unit featuring inner tubes of triangular, pentagonal, square, and circular configurations, analyzed numerically. Results encompassing the impacts of mean temperature, solidification temperature, melting fraction, exergetic efficiency, exergy destruction, heat transfer rate, entropy generation number, and system efficiency on solidification time are presented and compared using contour maps and figures. The research also scrutinizes the effects of Fourier numbers on Stefan, Rayleigh, and Nusselt numbers for TES systems based on inner configurations. Past studies primarily concentrated on cylindrical shapes for all three tubes within triplex-tube heat exchangers, disregarding varied internal tube configurations. This investigation introduces novelty by investigating diverse innermost tube geometries (triangular, square, pentagonal, circular) within a triplex tube heat exchanger. The tangible advantages encompass enhanced thermal efficiency relevant to industries such as oil and gas, chemical processing, food and beverage, and power generation. The inner triangular triplex tube thermal energy storage (TES) system exhibits superior performance over pentagonal topologies, boasting stronger Stefan and Rayleigh numbers by 22.52% and 22.86%, respectively, at Fo = 0.0023. Eutectic PCM solidifies 50%, 65%, and 66% faster within triangular configurations than the triplex tube's pentagonal, square, and circular interiors.However, the pentagonal inner tube topology outperforms the triangular one by 13.36 % at a solidification time of 300 seconds. Eutectic PCM solidifies faster in triangular TTTES systems due to their 0.3%, 1.02%, and 1.10% lower heat transfer temperatures than pentagonal, square, and circular systems. Furthermore, in 1800 seconds of solidification, the triangular inner tube discharges 20.16%, 4.92%, and 3.37% more than pentagonal, square, and circular TES systems. Pentagonal, square, and circular inner tube topologies are 13.36%, 3.01%, and 3.84% less efficient than triangular TTTES systems. TES systems with triangular shapes achieve rapid solidification of eutectic PCM at 305.24K, establishing their efficiency over pentagonal, square, and circular configurations.

A comparative study of latent heat thermal energy storage (LTES) system using cylindrical and elliptical tubes in a staggered tube arrangement

Numerical analysis was performed to compare the thermal and hydraulic performance of the elliptical and circular tube geometries in the prototype-scale latent heat thermal energy storage (LTES) system. A staggered tube array configuration was used for the analysis where the tubes were placed horizontally. Commercial grade hexahydrate calcium chloride (CC6) was selected as a phase change material (PCM) due to its phase change occurring at room temperature. The study included a numerical analysis of the melting and solidification processes of the PCM within the tube array for both tube shapes, employing transient two-dimensional Navier-Stokes equations and a Realizable k-ɛ turbulence model to predict fluid flow and heat transfer. The enthalpy-porosity technique was used to model PCM melting and solidification. Numerical predictions indicate that the thermal performance for both tube shapes is almost indistinguishable during the melting and freezing processes. However, due to the aerodynamic shape of the elliptical tube, the pressure drop across the horizontal elliptical tube array is approximately 80% lower compared to that of the circular geometry. This reduced pressure drop implies that less pumping power will be required to achieve the desired flow rate across the tube bank, leading to economic advantages for the horizontal elliptical tube array. The proposed design can be used as a dry cooling technique employing an Air Cooled Condenser (ACC) in a thermal power plant.

Efficiency enhancement in solar energy storage: Impact of oval inner tube geometries on phase change material units

This comprehensive study systematically investigates the melting and solidification processes in phase change material (PCM) units, specifically comparing different inner tube geometries, including horizontal oval, inclined oval (45°), and vertical oval, against the circular inner tube. Through meticulous analysis, the study reveals that the vertical oval inner tube demonstrates superior efficiency, achieving complete melting and solidification in significantly shorter times compared to other geometries. In the melting process, the unit with a circular inner tube completes melting at 7560 s, the horizontal oval and inclined oval units complete at 7500 s, and the vertical oval unit completes at 7260 s. Notably, the reduction in melting time for horizontal oval and inclined oval units is approximately 0.8%, while for vertical oval unit, it is notably greater at 3.96%. Similarly, in the solidification process, the unit with the circular inner tube completes solidification at 17760 s; the horizontal oval completes at 17160 s, the inclined oval unit completes at 16080 s, whereas the vertical oval unit completes at 14400 s. The reduction in solidification time for the horizontal oval and inclined oval is 3.37% and 9.46%, respectively, whereas for the vertical oval, it is notably greater at 18.91%. These findings underscore the profound influence of inner tube design on heat absorption, temperature profiles, and overall PCM unit performance. The substantial reductions in both melting and solidification times, particularly for the unit with a vertical oval inner tube, highlight the critical role of inner tube geometry in optimizing PCM efficiency and responsiveness to thermal changes.

Dislocation Hardening in a New Manufacturing Route of Ferritic Oxide Dispersion-Strengthened Fe-14Cr Cladding Tube.

The microstructure evolution associated with the cold forming sequence of an Fe-14Cr-1W-0.3Ti-0.3Y2O3 grade ferritic stainless steel strengthened by dispersion of nano oxides (ODS) was investigated. The material, initially hot extruded at 1100 °C and then shaped into cladding tube geometry via HPTR cold pilgering, shows a high microstructure stability that affects stress release heat treatment efficiency. Each step of the process was analyzed to better understand the microstructure stability of the material. Despite high levels of stored energy, heat treatments, up to 1350 °C, do not allow for recrystallization of the material. The Vickers hardness shows significant variations along the manufacturing steps. Thanks to a combination of EBSD and X-ray diffraction measurements, this study gives a new insight into the contribution of statistically stored dislocation (SSD) recovery on the hardness evolution during an ODS steel cold forming sequence. SSD density, close to 4.1015 m-2 after cold rolling, drops by only an order of magnitude during heat treatment, while geometrically necessary dislocation (GND) density, close to 1.1015 m-2, remains stable. Hardness decrease during heat treatments appears to be controlled only by the evolution of SSD.

Analysis of the off-focal source in transmission geometry X-ray systems

For X-ray tubes in lab based computed micro-tomography systems, off-focal X rays are those emitted from the source but not produced at the primary focal spot of the electron beam. They can be attributed to both electron and photon scatter within the X-ray tube. Off-focal X rays can represent a significant fraction of the total X-ray flux and lead to artefacts in the radiographs, and reconstructed tomographic volumes, degrading contrast and resolution. Therefore, they are an undesirable feature in industrial and medical X-ray CT scanners. In this work, a general model of an X-ray tube with a transmission target has been developed in TOPAS, a Monte Carlo (MC) simulation extension to GEANT4. MC simulations enable: (1) the analysis of the origin of various types of off-focal X rays; (2) quantification of the prevalence of each type for a specific tube geometry and (3) replication and understanding of experimental results affected by off-focal X rays. Our MC analysis herein shows that the amount of off-focal X rays can represent up to 25% of total X-ray flux. The most prevalent off-focal X rays were found to be the X rays created by the electrons back-scattered from the target into the aperture and generating X rays.

Hydrothermal performance assessment of a parabolic trough with proposed conical solar receiver

Parabolic Trough Collectors (PTCs) are commonly employed in both industrial and residential settings for the purpose of harnessing solar energy. Several techniques have been implemented to improve performance, such as altering the geometry of the absorber tube, enhancing the selective coatings of the receiver envelope, and utilizing nanofluids. This study proposes a new method for enhancing the thermal-hydraulic efficiency of PTCs through the utilization of non-uniform heat flux distribution on conical solar receiver. The effectiveness of this approach is evaluated through numerical simulations conducted using Ansys Fluent with the aid of optical simulation performed using TracePro. The geometry under consideration is assessed at various diameter ratios (DR) spanning from 1.25 to 2 and Reynolds number (Re) ranging from 20000 to 100000, with increments of 20000. This evaluation is conducted at three distinct inlet temperatures: 150 °C, 250 °C, and 350 °C. The studied parameters include-the Nusselt number (Nu), friction coefficient (f), thermal efficiency (ηth), exergetic efficiency (ηex), and thermal enhancement factor (TEF). Furthermore, a comparative analysis is conducted between the newly proposed geometric design and a traditional straight absorber and glass structure. The findings indicated that a conical receiver generally enhances system heat transfer by a minimum of 7 % and up to 65 %, resulting in improved thermal and exergetic efficiencies. Decreasing the pipe outlet diameter from DR = 1.25 to DR = 2 led to a significant exponential rise in the friction coefficient. The TEF demonstrated that a diameter ratio of 1.25 and 1.5 resulted in maximum values of 1.19 and 1.11, respectively, at high Re and an inlet temperature of 350 °C. The results suggested that incorporating conical receivers in PTCs can greatly improve their performance. To minimize the friction coefficient and associated pumping power, it is crucial to carefully evaluate the reduction of the diameter of the absorber outlet. The results offered valuable insights for the development and improvement of PTCs in both industrial and power generation settings, promoting the adoption of renewable energy and supporting long-term sustainability.

Proposal of a control scheme for testing a centrifuge-based pellet injection system in DIPAK-PET

The envisaged Pellet Engineering Testbed (PET) in the framework of Direct Internal Recycling Integrated Development Platform Karlsruhe (DIPAK) will provide unique opportunities to advance pellet injection technology and its implementation in the fuel cycle as well as into plasma control of EU-DEMO. This work analyses the parameters for Pellet Launching System (PLS) control according to requirements from plasma control. Main parameter is the particle flux and the related accuracy with respect to amount of flux and arrival time of pellets. Others are addressed as well like dynamic response to setpoint changes and adaptivity of isotope composition of the hydrogen ice. The performance of the PLS is limited by the mass loss in the guiding tubes, both by erosion (applies to any pellet) and loss of an entire pellet, that may apply to only a few pellets, provided a suitable guiding tube geometry is selected depending on the required injection speed. DIPAK-PET has to provide data points in order to enable proper guiding tube design activities based on modelling. A short description of the proposed technical solution for the Pellet Launching System is provided and setup for the Programmable Logic Control (PLC) is suggested comprising a MasterPLC and a dedicated Human Machine Interface (operators’ desk). A non-exhaustive proposal of experiments to be performed in DIPAK-PET is listed in order to verify the estimated performance values for the relevant PLS parameters.

Structural stability of lunar lava tubes with consideration of variable cross-section geometry

This paper provides detailed numerical analyses of lunar lava tubes stability, where for the first time variability in cross-section geometries is considered. A novel approach included a dedicated procedure for extracting characteristics needed for random geometry generation together with the demonstration of its usage. Stability analyses were performed with finite element limit analysis (FELA) which is found to be very effective for analyzing tens of thousands of realizations. The FELA method provides collapse geometries that were examined to constrain the relations between the collapse size extent and width of the lava tube. New findings on types and sizes of lunar lava tube roof collapses were obtained, and they are the first step toward making stability analysis more realistic for future human and robotic exploration of lunar lava tubes. The results allow us to constrain the approximate widths of the lunar tube beneath skylights to be 300 m, as observed for the assumed rock parameters. In addition, the probabilistically based analyses allow to show that thin roofs (< 10 m) are very unlikely to be stable for the tubes of a few hundred meters in width under lunar conditions, and that the gravity trigger failures are more probable on the Moon when considering variations in lava tube geometry than for the previously considered cases of elliptical and circular shapes.

Numerical Characterization on the Influence of Flame Tube Geometry and Dump Gap in the Diffuser Performance at High Altitudes

Numerical Characterization on the Influence of Flame Tube Geometry and Dump Gap in the Diffuser Performance at High Altitudes