Cross Section Of Tube Research Articles

Experimental study on flow boiling and circumferential non-uniform heat transfer characteristics in helically-coiled tube under coupled heat transfer conditions

Helically-coiled tube steam generator has been widely used in nuclear reactor, energy power, petrochemical and other systems. In the liquid metal reactor, the liquid metal on the primary side of the helically-coiled tube steam generator exchanges heat with the water on the secondary side. Due to the coupled heat transfer between liquid metal and water, the distribution of the wall temperature or heat transfer coefficient of helically-coiled tube are significant different in the circumferential direction of the tube cross-section. An experimental system of helically-coiled tube steam generator was set up in this paper. The non-uniform heat transfer characteristics of secondary side fluid of helically-coiled tube steam generator were studied under the coupled heat transfer conditions between the heat transfer of primary side and secondary sides fluid. It was found that the wall temperature or heat transfer coefficient in the circumferential direction of tube cross-section were significantly different, the maximum and minimum wall temperature appeared on the inside and bottom of the tube cross-section, respectively, the maximum and minimum heat transfer coefficient appeared on the outside and top of the tube cross-section, respectively. The effect of secondary side refrigerant pressure, secondary side refrigerant supercooling degree, mass flux of secondary side refrigerant, primary side heating water temperature and mass flux of primary side heating water on the maximum wall temperature, minimum wall temperature, maximum heat transfer coefficient, minimum heat transfer coefficient were obtained. Beside, The local and overall non-uniformity of the wall temperature and heat transfer coefficient in the circumferential direction of tube cross-section were obtained and the influence of each parameter on the local and overall non-uniformity were revealed, respectively. Finally, it was concluded that the non-uniformity of heat transfer coefficient in the circumferential direction of tube cross-section under coupled heat transfer conditions was more obvious than that under constant heat flux conditions. And the the overall non-uniformity of heat transfer coefficient (δh) obtained in our experimental were larger than the δh of Chang et al. [33], Zheng et al. [38], Kong et al. [34], Yao et al. [36] and Niu et al. [37] by 130.67%, 48.10%, 289.48%, 151.28% and 271.67%, respectively.

Crashworthiness study of polyamide bi-tubular thin-walled tubes using hybrid lattice filling

Thin-Walled Tubes (TWT) are widely used as crashworthiness elements to absorb and dissipate kinetic energy during collision through plastic deformation. Various design strategies, including nested tubes, triggers, and filling with lattices, are commonly used to enhance the crashworthiness of TWT. Additive Manufacturing (AM) offers unique opportunities to produce complex lattice-filled TWT with higher precision, but challenges persist in the design and fabrication of bi-tubular TWT to enhance crashworthiness. The aim of this study is to propose an approach for hybrid lattice filling in bi-tubular structures. In the preliminary phase, the parametric study was conducted to understand the influence of tube cross-section geometry, thickness, and trigger hole diameter on the crashworthiness of empty TWT using Taguchi’s L9 orthogonal array. Empty TWTs were fabricated using Selective Laser Sintering (SLS) with PA12 material and compressed uni-axially at 8 mm/min speed. In the second phase, bi-tubular TWT was filled with three different unit cells such as Cube, Kelvin, and Octet Truss (OT) having 30% relative density. In the lattice filling approach, two different strategies were followed such as uniform and hybrid lattice filling. Designed TWTs were fabricated and tested under uni-axial compression at two different speeds such as 8 mm/min and 8 mm/sec. Based on the results of the preliminary study, it has been observed that cross-section geometry and tube thickness significantly enhance SEA through an increase in the stiffness and number of folding. With the help of the Signal to Noise (S/N) ratio graph, appropriate levels were selected as input for the hybrid lattice-filling approach. The results of the second phase revealed that hybrid lattice filling significantly enhances the deformation modes, energy absorption, and crashworthiness properties of TWTs. Hybrid lattice-filled TWT offers better Specific Energy Absorption (SEA) as 18.32 kJ/kg at 8 mm/sec compression speed, which is 113.9% higher than empty and 42.8% higher than uniform lattice-filled TWT. This work demonstrated that adopting the hybrid lattice-filling approach is one of the potential ways to enhance the crashworthiness of protective equipment such as crash boxes and frames.

Cross-sectional zero-dimension temperature model for thin-walled circular tubes in space environment

A sufficiently accurate, yet computationally efficient prediction of temperature field is essential for design of spacecraft structures. This paper presents a model dimension reduction method for thermal analysis of thin-walled circular tubes in space environment, which takes into account radiation heat transfer among the internal surfaces besides heat conduction along the circumferential direction and radiative emission from the external surface. Temperature distribution on the tube cross section is approximated by a series of harmonic functions, so that a one-dimensional problem is reduced to that of zero dimension. The relation between average and perturbation temperatures that depend only on time is broadened to fully coupled one. By comparison to the previous model and the plane finite element model, the accuracy and economy of the new model are illustrated. The results show that internal radiation exchange plays an important role in thermal analysis of thin-walled circular tubes used extensively in spacecraft appendages. Furthermore, differences between present and previous models are analyzed and a two-way analysis of variance is performed to determine the effect of various physical and geometric parameters on the temperature distribution and response of the tubes. The work can be further developed to analyze thermally induced deformation and vibration of spacecraft structures.

Redesign of Heat Transfer Pipes in Radiators, Air-Conditioners and Refrigerators for Higher Efficiency

Heat transfer is a surface phenomenon. Instead of straight hollow rectangular cross section tubes with heat transfer liquid passing through it, a triangular cross section tubes having the tip of the triangle facing front to receive the flow of air is the proposed new geometrical design. With minimum material maximum heat transfer as a whole is the aim of the new Radiator design.

Numerical Simulation Study of an Artificial Percolation Riverbed and Its Hydraulic Characteristics under Different Reynolds Numbers

The direct extraction of clear water from a sandy river is a difficult task and can only be achieved through specific engineering measures. This paper proposes an artificial percolation riverbed structure for extracting clean water from sandy rivers, using a numerical simulation to study the flow field distribution characteristics of the structure under clean water conditions. The main conclusions are as follows: When the percolation vortex tube opening rate is 1.4%, the vortex tube with or without opening the percolation hole has little influence on the distribution characteristics of the flow field in the artificial riverbed, and the purpose of water extraction can be achieved while constructing a helical flow field. The axial flow velocity and circumferential flow velocity of the vortex tube cross-section under different Reynolds numbers show the distribution of a low-flow velocity close to the center of the vortex tube, and a high-flow velocity close to the vortex tube side-wall area. The average axial flow velocity and average circumferential flow velocity of the vortex tube show a trend of increasing and then decreasing distribution along the axial axis of the vortex tube in the direction of the sediment transport flume. The mean axial flow velocity of the vortex tube along the axis of the vortex tube toward the sediment transport flume and the mean circumferential flow velocity both show a distribution trend of increasing and then decreasing. At the junction of the vortex tube and the sediment transport flume, there are obvious pressure changes, and the pressure changes drastically under the same horizontal line. Along the direction of the bottom line of the vortex tube, the pressure at the vortex tube is obviously greater than that at the sediment transport flume. The vortex of the artificial percolation riverbed is mainly concentrated in the vicinity of the vortex tube, and the maximum value of the vortex intensity generally occurs at the junction of the vortex tube and the sediment transport flume. With the increase in the Reynolds number, the vortex intensity has an overall increasing trend, and the distribution of the vortex is more complex. This study helps to elucidate the distribution characteristics of the flow field in the artificial percolation riverbed, and it provides a reference basis for the future study of the flow field of artificial percolation riverbeds of sandy rivers.

Proposal and parametric investigations of square steel tubes as post-tensioned connectors for linear-shaped precast concrete elements

Given the pivotal role of connections in the progress of the precast building industry, issues such as costs, chain collapse, and low robustness in all degrees of freedom are critical considerations. This study draws inspiration from Concrete Filled Steel Tube Elements to design and investigate using simple steel tubes as joints for precast linear-shaped elements. The study proposes and examines uncomplicated joints where two precast reinforced concrete beams are positioned within the tube. The encompassment of the beams by the tube, combined with the application of post-tensioning forces, creates a sturdy integrity between the beams, resembling a head-to-head joint. Through 48 experimental tests, various connection parameters such as beam and tube cross-section height, re-bar quantity, tube thickness, and length were systematically investigated. The experimental setup utilized a three-point bending-shear testing configuration, and the results were compared with monolithic references. The findings demonstrate that these adaptive and ductile connections rapidly exhibit a capacity similar to that of monolithic exact beams. All studied parameters exhibited their influences on the capacity of the connection; however, the primary determinant is the length of the tube. Within the discussed range, the tube length should be at least twice as long as the height of the beam. Failing to meet this criterion would prevent the complete manifestation of the desired failure mechanism.

Influence of inhomogeneous magnetic field source location on the intensity of thermomagnetic convection in a closed loop

Purpose. Obtaining information on the influence of the location of the inhomogeneous magnetic field source relative to the heated section of a vertical hydrodynamic loop filled with magnetic fluid on the intensity of convective heat transfer along the loop.Methods. Experiments were carried out using a hydrodynamic loop made of a thin tube of circular cross-section and placed in a vertical plane. Heat source was carried out by a heater on a short vertical section of the loop, and heat removal was implement out by blowing the entire surface of the tube with thermostated air. The source of the magnetic field was the flat pole tips of the ferrite magnetic core, in the gap between which the heater was located. The position of the pole tips relative to the heater varied vertically in the experiments. In the control experiments, the source of the magnetic field was deleted. The circuit was filled with medium concentrated magnetic liquid of the type "magnetite - kerosene - oleic acid". The intensity of steady-state convective heat flow along the tube was calculated from the results of measuring the tube surface temperature by copper-constantane thermocouples. The measurement results were presented in dimensionless form - the relationship between the Nusselt number and Rayleigh number.Results. The unfluctuating mixed, thermomagnetic and gravitational, convection of the magnetic fluid in the loop was observed at any location of the pole tips of the magnetic core relative to the heater. At location of pole tips above the heater, competition of gravitational and thermomagnetic convection was observed, and the heat flux was weak. When the pole tips were placed below the heater, the Nusselt number was 2 - 4 times higher than in the control tests (only gravitational convection) with equal Rayleigh numbers. The highest Nusselt numbers were obtained when the field source was placed in center of the heater.Conclusion. Information on the influence of the relative location of the magnetic field source and the heater on convective heat transfer by magnetic fluid in a hydrodynamic loop is obtained experimentally. The optimal concerning of heat transfer intensity position of the field source was found.

Tube cross-section flatness optimization to enhance the cooling performance of nanofluid-based photovoltaic thermal systems combined with nano-enhanced phase change material

Photovoltaic (PV) systems have emerged as a crucial technology in transitioning to sustainable energy. Despite their growing prominence, PV panels face challenges related to temperature-induced that can lead to reduced energy output. By considering this, the utilization of cooling systems is useful. In the quest to design the active cooling system for PV panels, a key challenge remains in optimizing tube cross-section configurations. In this study, a validated CFD simulation investigates the impact of the tube cross-section flatness (tube flattening) on the cooling performance of the nanofluid-based photovoltaic thermal system combined with nano-enhanced Phase Change Material (PCM). Evaluation parameters for cooling performance are PV surface temperature (T_s), PCM liquid Fraction (LF), tube pressure drop (ΔP), and the PV temperature uniformity (ΔT). Aluminum Oxide (Al2O3) and Silver (Ag) nanoparticles are used in different concentrations (0 %, 1 %, 5 %, 10 %). Also, using the Response Surface Method (RSM), a multi-objective optimization determines the optimal tube flattening percentage for achieving the best cooling performance. The ideal state entails minimizing T_s, maximizing LF, minimizing ΔP, and minimizing ΔT. The findings indicate that increasing tube flattening leads to a decrease in T_s, a decrease in LF, an increase in ΔP, and a reduction in ΔT. Reducing the T_s and ΔT is a favorable effect but increasing the ΔP and reducing the LF is unfavorable to the system's cooling performance. After evaluating different parameters in the optimized scenarios, the most optimal mode is determined when the system uses Ag nanofluid in 10 % concentration, PCM without nanoparticles, and tube with 44 % flattening. In this scenario T_s, LF, ΔP, and ΔT are respectively 54.04 °C, 37.7 %, 117.67 Pa, and 34.74 °C.

A filling lattice with actively controlled size/shape for energy absorption

This study unveils a groundbreaking development: the chain lattice structure (CLS), a unique lattice with the capability to actively adjust its size and shape for filling diverse thin-walled structures, thereby enhancing their energy absorption characteristics. Traditional lattice structures, known for excellent energy absorption, are constrained by fixed sizes and shapes post-fabrication, limiting their adaptability to various energy-absorbing structures. The CLS introduces a revolutionary lattice structure dynamically modifying dimensions and shape. Employing selective laser sintering (SLS), we craft CLS prototypes using nylon 11 material, followed by rigorous quasi-static compression experiments. The congruence between experimental and simulation analyses validates our model's accuracy. CLS actively adjusts within varying cross-sectional thin-walled square tubes, demonstrating substantial improvements in energy absorption and compression stability compared to empty tubes (ETs). Additionally, CLS adapts to diverse cross-sectional shapes, including circular, hexagonal, and triangular tubes. Comparative assessments reveal significant enhancements in energy absorption and compression stability for CLS-filled tubes. Moreover, the pre-deformed CLS model was filled with different shapes of front rails, and its axial crashworthiness and deformation pattern stability were significantly improved compared with the unfilled front rails. In summary, CLS's flexibility in adjusting to thin-walled structures of varying dimensions and shapes holds immense promise for enhancing their performance across a wide range of applications.

Data-driven axial bearing capacity analysis of steel tubes infilled with rubberized alkali-activated concrete

This study aims to employ machine learning algorithms to analyze the axial bearing capacity of rubberized alkali-activated concrete filled steel tubes. A dataset encompassing 327 synthesized instances and seven input features is adopted for training and testing six machine learning models, including Decision Tree, Random Forest, Extremely Randomized Trees, Adaptive Boosting, Gradient Boosting Decision Trees (GBDT), and eXtreme Gradient Boosting Trees (XGBoost). The SHapley Additive exPlanation algorithm is employed to elucidate the prediction process of machine learning models and to analyze the influence of each parameter on axial bearing capacity. Comparison of evaluating metrics shows that GBDT and XGBoost models achieve highest accuracy and generalization capabilities when their Coefficient of Determination values surpassing 0.98 and Mean Absolute Percent Error remaining below 3%. Moreover, the explanation analysis of machine learning models reveals that diameter/width of the cross section, rubber content, yielding strength and thickness of steel tubes are critical variables that affect the axial bearing capacity, while compressive strength of alkali-activated concrete, specimen height, and shape of cross section show negligible impact. Besides, GBDT model overemphasizes the effect of specimen height and might lead a conservative prediction for specimens with smaller heights. Finally, compressive strength of alkali-activated concrete and diameter/width, thickness, and yielding strength of steel tubes are positively correlated with axial bearing capacity, and the increase of rubber content in alkali-activated concrete leads to the decrease of capacity.

Scaling laws for optimal power-law fluid flow within converging–diverging dendritic networks of tubes and rectangular channels

Flows in dendritic–fractal networks have garnered extensive research attention, but most studies assume a constant tube or channel cross section. In many applications, the cross section of the tube or channel changes as the flow progresses through it, such as the blood flow through the arterial system, which is a prime example of a deformable or non-uniform tree-like network. Heating, ventilation, and air conditioning ductwork also exemplify a tree-like network with varying cross sections. This research investigates power-law fluid flows in the converging–diverging tubes and rectangular channels, prevalent in engineered microfluidic devices, many industrial processes, and heat transfer applications. Power-law fluid flows through linear, parabolic, hyperbolic, hyperbolic cosine, and sinusoidal converging–diverging dendritic networks of tubes and rectangular channels are studied. The flow is assumed to be steady, incompressible, two-dimensional planar, and axisymmetric laminar flow without considering network losses. A theoretical model has been derived to evaluate the flow conductance under network volume and surface-area constraints. The flow conductance is highly sensitive to network geometry. The effective conductance of all networks increases with increasing daughter-to-parent radius ratio before eventually declining. The maximum conductance occurs when a specific radius or channel-height daughter–parent ratio β* is achieved. This value depends on the constraint and vessel geometry, such as tubes or rectangular channels. The optimal flow conditions for maximum conductance in a constrained tube volume network, βmax*=βmin*=N−1/3, while for a constrained tube's surface-area network, βmax*=βmin*=N−(n+1)/(3n+2). This scaling applies to all converging–diverging tube network profiles. Here, βmax*, βmin* are the radius ratios of the daughter–parent pair at the maximum divergent or minimum convergent part of the vessel. N represents the number of branches splitting at each junction, and n is the power-law index of the fluid. Furthermore, the optimal flow scaling for the height ratio in the rectangular channel, βmax*=βmin*=N−1/2α−1/2 for constrained channel volume and βmax*=βmin*=N−1/2α−n/(2n+2) for constrained surface area for all converging–diverging channel networks, respectively, where α is the channel-width ratio between parent and daughter branches. Additionally, at optimal conditions in both the channels and tube network, pressure drops are equally partitioned across each branching level. The results in this work are validated with experiments and existing theories for limiting conditions. This research expands existing design principles for efficient flow systems, previously in the literature developed for uniform vessels, to encompass non-uniform converging–diverging vessels. Additionally, it provides a valuable framework for studying non-Newtonian flows within complex, non-uniform tree-like networks.

The relationship between threshold power of wave mode transition and tube radius in argon helicon discharge

We report in this Letter a geometric similarity of threshold radio frequency (RF) power absorbed by the helicon wave coupled mode in argon helicon discharge. Helicon plasma was excited by a half-helical antenna in tubes of different radii at a pressure of 0.3 Pa. Plasma density was measured by using a Langmuir probe, and wave structure was measured by a B-dot probe. The results show that the threshold powers for triggering helicon wave mode are proportional to the tube cross sections, and the plasma densities at the transition point are the same, indicating a geometric scaling law between the RF power and the tube size. This similarity of threshold power might provide a comparison of results in different systems.

Torsion and Combined Torsion-Axial Load Behaviour of Concrete Filled Steel Tube Columns with and without ECC/CFRP Wrap

ABSTRACT Concrete-filled tube columns may experience coupled torsion and axial compression under seismic and wind loading. Fifteen square, rectangular, and circular concrete filled steel/aluminium tube (CFST/CFAT) are tested under pure torsion to understand the behaviour and develop/validate finite element (FE) models. Parametric studies under pure torsion are conducted using FE models to study the effect of geometric (tube cross-section, length, and thickness) and tube/concrete material parameters on torsional strength, stiffness, and tube-concrete composite interaction. FE models are used to study strength, stiffness, and failure modes of CFST columns under combined torsion and axial compression load at various preload levels of axial and torsion. Coupled torsional preloading and subsequent axial load reduce the axial load capacity significantly, while coupled axial preloading and subsequent torsional loading have shown no significant influence on the torsional strength of CFST columns. Implementation of FE models developed for CFST columns with engineered cementitious composite (ECC) and carbon fibre reinforced polymer (CFRP) wraps showed significant enhancement of axial strength and stiffness compared to control (without wrap) even under high torsional preload level. The energy absorption capacity and ductility of the CFRP wrapped CFST column are about 1.38 and 1.1 times higher than its counterpart with ECC wrap of same axial load capacity. Overall, the results suggest that use of both CFRP and ECC wrap is an effective approach to enhance the torsional behaviour and ductility of CFST columns under combined torsion and axial loading conditions. However, high crack resistance and better post-peak ductility of ECC wrapped CFST compared to sudden CFRP rupture failure in CFRP-wrapped counterpart should be taken into consideration for seismic applications.

Stability capacity design of shuttle-shaped restrained-buckling braces with uniform cross-section at mid-span

This paper proposes a shuttle-shaped buckling restraint brace (SS-BRB) with the uniform core and the peripheral restraint system that consists of uniform cross-section tube at its mid span and tapering sections at its two ends. This type of BRB maned as SS-BRB-UCS adopts circular steel tubes in the core and the peripheral restraint system. An isolation system is strategically positioned between the core and the peripheral restraint system to effectively transmit lateral loads. Obviously, this type of the optimizing peripheral restraint system could reduce material utilization with an economic design and beautiful appearance. First, the finite element (FE) model of the SS-BRB-UCS is established, then the elastic buckling performance investigation is carried out to determine the elastic buckling load formula through fitting techniques of numerical results, so as to obtain the formula of the restraint ratio. Additionally, an elastic-plastic stability bearing capacity analysis is conducted for the SS-BRB-UCS to assess its load-bearing capabilities, and the corresponding relationships between stability coefficient (φ) and the restraint ratio (ζ) is established to determine the lower restraint ratio (namely threshold) for static load-bearing capacity BRB design. Finally, the hysteretic responses of SS-BRB-UCSs subjected to axial compressive-tensile cyclic loads are studied numerically, and the corresponding lower limit of restraining ratio of SS-BRB-UCSs is proposed for their energy-dissipation design. Those two lower limits of restraining ratios of the SS-BRB-UCSs obtained in this study provide fundamentals for preliminary static and seismic designs of SS-BRB-UCSs.

Numerical analysis of the fluid–structure interaction characteristics of a pontoon submerged floating tunnel

This study is intended to elucidate the mechanisms underlying fluid–structure interactions (FSIs) for a pontoon submerged floating tunnel (PSFT). To this end, a shear stress transport k-ω turbulence model was used to analyze the hydrodynamic force of the PSFT tube under the flow load. The finite element method was then used to predict the horizontal displacement of the PSFT tube under hydrodynamic action. In the calculation, the buoyancy of the PSFT pontoons was represented by an equivalent spring tension, and the fixed constraint was adopted at the shore wall of the tunnel tube. The FSI calculation results indicated that, when the flow load was larger, the pressure fluctuations of the flow field around the PSFT tube were stronger, resulting in greater dynamic effects on the horizontal direction of each tube segment. The smallest and largest deformations of the tunnel segment were observed at the mid-span and near the shore wall, respectively. It was also found that the barbell-shaped PSFT tube cross section may lead to intensify the pressure fluctuations near the tunnel tube as the flow load was increased. It is recommended that the appropriate number of pontoons and tunnel tube reinforcement can reduce the deformation of the PSFT.

Nerve Reconstruction Using ActiGraft Blood Clot in Rabbit Acute Peripheral Injury Model: Preliminary Study.

This preliminary study aimed to investigate an ActiGraft blood clot implant (RedDress Ltd., Pardes-Hanna, Israel) attempting to treat and induce the regeneration of a completely injured peripheral nerve with a massive loss defect. The tibial portion of the sciatic nerve in 11 rabbits was transected, and a 25 mm nerve gap was reconnected using a collagen tube. A comparison was performed between the treatment group (eight rabbits; reconnection using a tube filled with ActiGraft blood clot) and the control group (three rabbits; gap reconnection using an empty tube). The post-operative follow-up period lasted 18 weeks and included electrophysiological and histochemical assessments. The pathological severity score was high in the tube cross sections of the control group (1.33) compared to the ActiGraft blood clot treatment group (0.63). Morphometric analysis showed a higher percentage of the positive myelin basic protein (MBP) stained area in the ActiGraft blood clot group (19.57%) versus the control group (3.67%). These differences were not statistically significant due to the small group sizes and the large intra-group variability. The results of this preliminary study suggest that the application of an ActiGraft blood clot (into the collagen tube) can enable nerve recovery. However, a future study using a larger animal group is required to achieve objective statistical results.

Axial Crushing Theory and Optimization of Lattice-Filled Multicellular Square Tubes.

A lattice-filled multicellular square tube features a regular cross-sectional shape, good energy consumption, and good crashworthiness, which is suitable for the design of energy absorbers in various protection fields such as automobiles, aerospace, bridges, etc. Based on the super folding theory, two reference planes are set to refine the energy consumption zone of the super folding element in this study. The energy consumption calculation of convex panel stretching is involved, and the critical crushing force formula is introduced in this study. Meanwhile, the calculation method from a single-cell square tube to a multicellular thin-walled square tube is extended and the structural optimization is investigated, in which the NSGAII algorithm is used to obtain the Pareto front (PF) of the crashworthiness performance index of the square multicellular tubes, the Normal Boundary Intersection (NBI) method is adopted to select knee points, and the influence of different cross-sectional widths on the number, as well as the thickness, of cells are discussed. This study's results indicate that the theoretical value is consistent with that obtained from the numerical simulation, meaning that the improved theoretical model can be applied to predict the crashworthiness of multicellular square cross-sectional tubes. Also, the optimization method and study results proposed in this study can provide a reference for the design of square lattice multicellular tubes.

Heat Transfer Enhancement in Circular Cross Section Tube Using Inserts

Convective heat transfer was empirically examined in tubes with ballooned flat perforated steel inserts under turbulent flow conditions, encompassing Reynolds numbers ranging above 15000. The primary objective of this study is to expand the existing dataset concerning inserts. The external surface of the tube received a uniform heat flux, with air serving as the chosen fluid. Correlations were derived for the mass flow rate and heat absorption, utilizing the gathered measurements within the explored range of geometrical parameters and Reynolds numbers.

Numerical and experimental analysis of thermal and flow operating conditions of waterwall tubes connected by fins

This paper presents a method for determining the temperature distribution in the cross-section of waterwall tubes connected by fins using an in-house numerical algorithm prepared in the MATLAB environment, based on differential equations with separable variables. In order to verify the correctness of the algorithm operation, the temperature values obtained from it, determined for the frontal area of the tubes, are compared with the temperatures found in the Ansys Fluent environment and those measured on the test stand. A system corresponding to a fragment of the combustion chamber wall of a supercritical steam boiler was selected to perform the analysis. The system consists of three tubes connected by fins. The temperature distributions in the cross-sections of the tubes were compared for the case when each of the tubes was heated on one side with the same heat flux and when the heat flux falling on the central tube was by 50% higher than the heat flux incident on the neighbouring tubes. Experimental verification was carried out on a stand equipped with three vertical tubes connected by fins, heated on one side by infrared radiators.

Rapid rehabilitation of damaged UHPC-NSC composite pier after earthquake

Resilience-oriented earthquake engineering requires that engineering structures can recover rapidly after earthquakes. However, the rehabilitation time of bridge piers is strongly dependent on the structure and retrofit plan. Although an ‘ultra-high-performance concrete (UHPC) – normal strength concrete (NSC)’ composite pier, with a cross-section of an outer UHPC tube and inner NSC core, can deliver satisfactory damage control, its post-earthquake rehabilitation has not been reported. This study investigated the rehabilitation performance of damaged UHPC-NSC composite piers. Six damaged composite piers were retrofitted, and cyclic tests were conducted to compare the performance of the retrofitted and original specimens. The actual compressive strength of the re-poured UHPC significantly affected the performance of the retrofitted composite piers. Parametric analysis was conducted based on the validated numerical model to investigate the impact of the rehabilitation time on the retrofitted performance quantitatively. The functions of the critical rehabilitation time were derived with respect to the strength and thickness of the re-poured UHPC, considering the full recovery of the initial stiffness and peak strength as the criteria.