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Flow-sensitive four-dimensional Cardiovascular Magnetic Resonance Imaging (4D Flow CMR) has increasingly been utilised to characterise patients’ blood flow, in association with patiens’ state of health and disease, even though spatial and temporal resolutions still constitute a limit. Computational fluid dynamics (CFD) is a powerful tool that could expand these information and, if integrated with experimentally-obtained velocity fields, would enable to derive a large variety of the flow descriptors of interest. However, the accuracy of the flow parameters is highly influenced by the quality of the input data such as the anatomical model and boundary conditions typically derived from medical images including 4D Flow CMR. We previously proposed a novel approach in which 4D Flow CMR and CFD velocity fields are integrated to obtain an Enhanced 4D Flow CMR (EMRI), allowing to overcome the spatial-resolution limitation of 4D Flow CMR, and enable an accurate quantification of flow. In this paper, the proposed approach is validated in a U bend channel, an idealised model of the human aortic arch. The flow patterns were studied with 4D Flow CMR, CFD and EMRI, and compared with high resolution 2D PIV experiments obtained in pulsatile conditions. The main strengths and limitations of 4D Flow CMR and CFD were illustrated by exploiting the accuracy of PIV by comparing against PIV velocity fields. EMRI flow patterns showed a better qualitative and quantitative agreement with PIV results than the other techniques. EMRI enables to overcome the experimental limitations of MRI-based velocity measurements and the modelling simplifications of CFD, allowing an accurate prediction of complex flow patterns observed experimentally, while satisfying mass and momentum balance equations.

According to self-determination theory, individual well-being is universally dependent upon the satisfaction of three basic psychological needs: autonomy, competence and relatedness. This study set out to further elucidate the relationship between basic psychological need satisfaction (BPNS) and well-being across age by (i) more closely examining the age distribution of BPNS, and (ii) investigating whether BPNS is comparably associated with well-being across all ages, as predicted by the universality assumption, while taking into account variability in other demographic factors. A general population sample of Dutch speaking adults from The Netherlands and Belgium (N = 1709; Mage = 48.6 years, SD = 19.0, range 18–97) filled out a cross-sectional online or paper-and-pencil survey questionnaire, providing self-reports of BPNS and well-being, using the Basic Psychological Need Satisfaction and Frustration Scale and Mental Health Continuum-Short Form, respectively. Data analyses consisted of initial visual inspection using LOESS smoothed curve plotting, and subsequent model testing using multiple regression analyses. When correcting for other demographic factors, results showed a positive linear relationship between age and autonomy satisfaction, no significant relationship between age and competence satisfaction, and a slight positive cubic relationship between age and relatedness satisfaction (initial ‘peak’, followed by a slight decline and ‘dip’, and steady rise for later ages). All basic psychological needs factors were positively linked to well-being in all domains, with associations generally comparable between adults of different ages, thus lending support to the universality assumption of self-determination theory. Despite distinct age distributions, all three basic psychological needs seem important for maintaining a sense of well-being throughout life.

The parametrisation of the geometry in shape optimisation has an important influence on the quality of the optimum and the rate of convergence of the optimiser. Refinement studies for the parametrisation are not shown in the literature, as most methods use non-orthogonal parametrisations, which cause issues with convergence when the parametrisation is refined. The NURBS-based parametrisation with complex constraints (NSPCC) is the only CAD-based parametrisation method that guarantees orthogonal shape modes by constructing an optimal basis. We conduct a parametrisation refinement study for the benchmark turbomachinery cooling bend (U-bend) geometry, an intially symmetric geometry. Using an adjoint RANS solver, we optimise for mininmal total pressure drop. The results show significant effects of the control net density on the final shape, with the finest control net producing an asymmetric optimal shape resembling strakes that induces swirl ahead of the bend. These asymmetric modes have not been reported in the literature so far. We also demonstrate that the convergence rate of the optimiser is not significantly affected by the refinement of the parametrisation. The effectiveness of these shape features obtained with single-point optimisation is evaluated for a range of Reynolds numbers. It is shown that total pressure drop reduction is not sensitive to Reynolds number.

To understand the heat transfer performance of the middle-deep U-bend geothermal well, the 2500 m deep U-bend geothermal well was taken as the research object at the Hebei University of Engineering. This study established a mathematical and physical model of heat transfer in a U-bend geothermal, and the influence of geothermal gradient and lithologic changes on heat transfer performance was considered. The established model was verified based on the experimental data. Numerical simulation results show that a reasonable reduction of inlet temperature can increase thermal power. The thermal power of the geothermal well will increase by about 40 kW for every 1°C reduction of inlet temperature. The thermal power can be increased with a reasonable increase in the flow rate of the circulating fluid, but the increment of the thermal power decreases gradually. The simulation results show that the thermal power and outlet temperature of a deep U-bend geothermal well can be effectively improved by appropriately reducing the inlet temperature, increasing the flow rate, increasing the collection length, increasing the well depth, increasing the insulation length of the vertical well section and using low thermal conductivity insulation materials. The research results from this study could provide a reference for the heat transfer system optimization of the middle-deep U-bend geothermal well.

In this study, the influence of U-bends on the flow and pressure propagation characteristics of a gas–liquid two-phase flow in upstream and downstream straight pipes was investigated experimentally. The superficial velocities of the gas and liquid are 0.18–25.11 m/s and 0.20–1.98 m/s, respectively, covering plug flow, slug flow, and annular flow. The experiments were conducted in U-tubes with inner diameters of 9 mm and 12 mm and with a curvature ratio of 8.33. The U-tube was C-shaped. The pressure fluctuations at the axial measurement points of the straight tubes were measured. Flow images of the distal straight tubes and U-bends were obtained. The disturbance from U-bends in the two-phase flow in the vicinity of the bend is very obvious. The perturbation from U-bends in the fluid in the adjacent straight tubes is highly related to the incoming flow pattern. The slug flow has the most significant influence, whereas the effects of the plug and annular flows are small. Fundamentally, it mainly depends on the weight relationship between the gravity, centrifugal force, and inertial force of the gas–liquid two-phase fluid. The pressure fluctuation propagates in the form of a wave with the same dominant frequency in the straight pipes of the U-tube. The pressure pulsation energy in the straight tubes strengthens with decreasing distance from the 180° return bend. In addition, the pressure fluctuation energy downstream of the U-bend is greater than that upstream of the return bend.

304 stainless steels (SS) were considered as the materials for a dry storage canister. In this study, ER (Electrode Rod) 308L was utilized as the filler metal for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via a gas tungsten arc-welding process in multiple passes. The electron backscatter diffraction (EBSD) map was used to identify the inherent microstructures in distinct specimens. U-bend and weight-loss tests were conducted by testing the 304L substrates and welds in a salt spray containing 5 wt % NaCl at 80 °C to evaluate their susceptibility to stress corrosion cracking (SCC). Generally, the weight loss of the ER 308L deposit was higher than that of the 304L substrate in a salt spray in the same sample-prepared condition. The dissolution of the skeletal structure in the fusion zone (FZ) was responsible for a greater weight loss of the 308L deposit, especially for the cold-rolled and sensitized specimen. Cold rolling was detrimental and sensitization after cold rolling was very harmful to the SCC resistance of the 304L substrate and 308L deposit. Overall, the SCC susceptibility of each specimen was correlated with its weight loss in each group.

One of the major problems of using nanofluids in heat exchange applications is the forming and deposition of nanoparticles on the inner surface of the heat exchanger. In this paper, Water-Cmc fluid is used as a surfactant for nanoparticles to prevent deposition and congregation. The pressure drops and heat transfer in U-bend double pipe heat exchanger based on water-MgO-Cmc fluid, are examined. Nanoparticles of Magnesium Oxide (MgO) and Carboxymethyl Cellulose (Cmc) are used with pure water as a base fluid. The experimental rig and procedures are designed to facilitate various operational conditions such as flow rate, volume concentration of MgO particles and weight concentration of Cmc particles. Furthermore, convective heat transfer coefficient, heat exchanger effectiveness, pressure drop, friction factor, under different conditions, are measured. The results demonstrate convective heat transfer coefficient of U-bend double pipe heat exchangers is enhanced by 35% for 1 MgO vol.% and 0.2 Cmc wt.% compared to base fluid (Water-Cmc). It is concluded that pressure drops are directly proportion to the increase of MgO nanoparticles at same Cmc concentration by 23% at 0.2 wt.%. Whilst, friction factor of the system is inversely proportion to the increase of volumetric flow rate of water-MgO-Cmc fluid. An increase in MgO nanoparticle concentration increases the friction factor, hence maximum friction factor enhancement by 38% for MgO concentration of 1 vol.%. The effectiveness of heat exchanger is slightly increased by 8% with increase of MgO concentration and flow rate. Finally, thermo-physical characteristics of water-MgO-Cmc fluid at various temperatures, are measured

This study investigates the combined effect of catalyst placement and solid thermal conductivity on the stability of a U-bend catalytic heat-recirculating micro-combustor. The CFD code ANSYS Fluent 2020 R1 was used for two-dimensional simulations of lean premixed propane/air combustion by varying the inlet gas velocity, i.e., the input power. Three configurations were compared at low (3 W/(m K)) and high (30 W/(m K)) wall thermal conductivity: (A) the configuration in which both inner and outer walls are catalyst coated; (B) only the inner wall is catalyst coated; and (C) only the outer wall is catalyst coated. Numerical results show that, at low thermal conductivity, configuration (B) exhibits the same resistance to extinction as configuration (A), whereas at high thermal conductivity, configurations (B) and (C) exhibit much lower resistance to blowout than configuration (A). Accordingly, for low-power systems, which typically lose stability via extinction and thus require low-conductive materials, an optimal catalyst placement can be the partial coating of configuration (B). Conversely, for high-power systems, which are prone to blowout and thus require high-conductivity materials, a full coating of both the inner and outer walls is needed to guarantee higher stability. To elucidate these findings, a detailed analysis of the combustion behavior of the three configurations is presented.

This study aims to provide insights into the intricate interactions between gas and liquid phases within flow components, which are pivotal in various industrial sectors such as nuclear reactors, oil and gas pipelines, and thermal management systems. Employing the Eulerian–Eulerian approach, our computational model incorporates interphase relations, including drag and non-drag forces, to analyze phase distribution and velocities within a complex U-bend system. Comprising two horizontal-to-vertical bends and one vertical 180-degree elbow, the U-bend system’s behavior concerning bend geometry and airflow rates is scrutinized, highlighting their significant impact on multiphase flow dynamics. The study not only presents a detailed exposition of the numerical modeling techniques tailored for this complex geometry but also discusses the results obtained. Detailed analyses of local void fraction and phase velocities for each phase are provided. Furthermore, experimental validation enhances the reliability of our computational findings, with close agreement observed between computational and experimental results. Overall, the study underscores the efficacy of the Eulerian approach with interphase relations in capturing the complex behavior of the multiphase flow in U-bend systems, offering valuable insights for hydraulic system design and optimization in industrial applications.

Friction during contact between metals can be very complex under dynamic conditions. In this study, friction between 304 stainless steel and SKD11 steel with boundary lubrication was studied experimentally using a friction testing machine (MPX-2000). The friction coefficients at different sliding speeds and interface loads were determined, and a new friction coefficient model was established based on the experimental data. The sample surfaces were analyzed using a laser-scanning microscope, and it was found that the friction mechanism under boundary lubrication (where 0.1 < μ < 0.3) was mainly abrasive wear accompanied by slight adhesive wear. The new friction coefficient model developed was applied for a simulation of Axial Symmetric U-Bend parts using finite element methods, and the results were compared with stamping experiments. The prediction errors in the results of thickness and the springback angle showed that the new friction model had a good agreement of the thickness distribution to the experiments with less than 10% error, and the springback angles between the new friction model and the measurements with the errors of 6.86% and 5.13%. The experimental results show that the friction coefficient decreases with the rise of speed when the sliding speed is between 30 mm/s–50 mm/s; the friction coefficient decreases with the increase in interface load. A decreasing trend of friction coefficient gradually slows down when the interface load is between 2.0 MPa–4.0 MPa. This also agrees with the simulations using the new model.