Straight Tube Research Articles

Numerical and experimental investigations on coiled resonance tube of a duplex Stirling cryocooler

Duplex Stirling cryocooler is promising in mitigating methane emission due to its environmentally-friendly working gas, high thermal efficiency and high adaptivity to varying methane concentration. In this work, a coiled resonance tube is introduced to supplant the conventional straight tube in a resonance tube coupled duplex free-piston Stirling cryocooler (RT-DFPSC) to reduce footprint and elevate power density. At first, an experimental setup was built employing resistance-compliance acoustic load to produce the analogical acoustic field. It was observed from experiments that on a coiled resonance tube, an acoustic power transfer efficiency of 35% was obtained. Based on the experiments, a three-dimensional computational fluid dynamics (CFD) model was subsequently developed to pinpoint the loss mechanism. Due to the interaction of centrifugal, viscous and inertial force, there are two secondary flow vortices in the cross-section of the coiled resonance tube during the reversing flow, accounting for the primary loss. Furthermore, the acoustic loss of the coiled resonance tube increases with the decrease of the coiled diameter, while the spiral pitch has minimal effect on the acoustic and flow field. Typically, the acoustic loss of a coiled resonance tube with a diameter of 0.8 m increases by approximately 9% compared to that of a straight tube. Finally, a one-dimensional equivalent model of the coiled resonance tube was established and integrated into a one-dimensional system-level model. Compared to the straight RT-DFPSC, a system with a coiled tube resonance tube demonstrates a cooling capacity and overall exergy efficiency reduction by 465.2 W and 2.4%, respectively.

Energy absorption characteristics of aluminum foam-filled corrugated tube under axial compression loading

To improve the energy absorption characteristics of thin-walled structures and reduce the initial peak compression force and load fluctuation, a novel aluminum foam-filled corrugated tube was proposed in this study. Finite element model validated by quasi-static compression experiments was adopted to investigate the crashworthiness performances of aluminum foam-filled corrugated tubes and their combined energy-absorbing structures. The effects of structure parameters including corrugation radius, wall thickness, corrugation length and corrugation radius increments on axial compression characteristics were investigated through finite element analysis. The results showed that compared with aluminum foam-filled straight tubes, the initial peak compression force of aluminum foam filled corrugated tube was reduced by 22.87 %, the compression force efficiency was increased by 6.69 % and the load fluctuation was reduced by 17.94 %. The smaller the values of corrugation radius, wall thickness and corrugation length, the smaller the initial peak compression force; Because the corrugation radius had a great effect on the peak compression force, the order that the corrugations were compressed into folds can be controlled by designing the corrugation radius; In view of the peak and valley values of compression force, an innovative combination of single tubes with different △H was obtained, which had better energy absorption performance. Compared with a single aluminum foam-filled corrugated tube, the compression force efficiency of the combined structure (△H: 0–5–10) was increased by 18.15 % and the load fluctuation was reduced by 33.60 %. The research results can provide a reference for the design and optimization of energy-absorbing devices.

The artificial roughness effect on the thermal performance of a submerged combustion vaporizer

The submerged combustion vaporizer (SCV) is a popular vaporizer used for the peak regulation of liquefied natural gas (LNG) in large cities or as a primary vaporizer in cold regions. Due to the consumption of produced natural gas as a heat source for gasification during SCV operation, the thermal efficiency and gasification rate of SCV must be improved urgently. One of the effective methods to improve the heat transfer of a heating tube is adding artificial roughness inside the tube. Hence, this paper establishes a 3D numerical model of the serpentine heating tube with artificial roughness cubes in SCV and explores the impact of artificial roughness on the heat transfer and thermal performance of SCV. To strengthen the heat transfer between the LNG heating tube and the water bath in the straight tube section and avoid the water freezing outside the tube due to the supercooling at the bend section simultaneously, critical factors, such as the arrangement of artificial roughness, especially on the bend region, and the heat flux obtained from the water bath, are discussed. The results indicate that the artificial roughness positively affects the heat transfer of the LNG heating tube. However, it is better to add the artificial roughness only in the straight section of the serpentine tube to suppress the ice formation on the bend regions. The LNG flow becomes chaotic, and the region of forced convection increases due to artificial roughness and centrifugal force. The serpentine tube with artificial roughness exhibits similar thermal behaviour under different heat fluxes, and its influence on the friction factor and irreversible energy loss is more significant than that of smooth tube. Moreover, the comprehensive evaluation coefficient of the heating tube is enhanced obviously by the artificial roughness, and the outlet temperature of LNG is larger by 17.63% and 16.34% respectively with different configurations of artificial roughness than that of the smooth one under the same heated condition, and the gasification rate is improved significantly.

A COMPREHENSIVE REVIEW STUDY ON HEAT TRANSFER IMPROVEMENT TECHNIQUES WITHIN TWISTED TUBES

Heat transfer equipment has been used in many different domestic and industrial applications. There has been a concentrated effort to create a heat exchanger design that will reduce energy requirements while saving materials and other costs. Increasing the effective heat transfer surface area or creating turbulence are two common ways to improve heat transfer and hence lower thermal resistance. The thermal Performance Factor is the ratio of the difference in heat transfer rate to the difference in friction factor and serves as a metric to assess the efficiency of heat transfer enhancement technologies. Different types of twisted tubes are used in many heat transfer improvement devices. geometrical parameters of the twisted tube encompassing the aspect ratio, twist ratio, twist direction, twist length, etc. impact the heat transfer. For Instance, oval pipes with unequal twist pitches have a thermal performance factor (1.75) and equal twist pitches have a thermal performance factor (1.98). furthermore, the thermal performance factor of the twisted tube with oval dimples is equal to 1.19 compared with the twisted tube without dimples. The thermal performance factor of the twisted tube with oval dimples is equal to 1.38 compared with the straight tube, with another improvement to the twisted tube that improves the heat transfer properties by disrupting the thermal boundary layer and destabilizing it. This paper presents a comprehensive investigation of passive heat transfer devices (twisted tubes) and their relative merits in a myriad of commercial applications.

Abstract 244: Effect of Actuation Frequency on Clot Integration with the Tigertriever Device: An In Vitro Study

Introduction Mechanical thrombectomy has been widely recognized as the preferred treatment for large vessel occlusion strokes. The Tigertriever stent‐retriever (Rapid Medical, Yokneam, Israel) is a novel operator‐adjustable device that can be actively expanded and contracted by the operator [1], which allows for several actuation‐related parameters to be optimized to potentially improve device efficacy. These parameters – such as amplitude and frequency of the actuation cycle, and rate of expansion and contraction – have not yet been evaluated in correlation with device success. We conducted a benchtop study to evaluate the effect of actuation frequency on clot integration within the stent. Methods A Tigertriever 17 device was deployed within a biological thrombus analog (2.5 cm length) placed in a straight silicone tube (2.4 mm diameter). The device was actuated between the maximally contracted and maximally expanded states with three different frequencies: Passive (one‐time opening, n=6), Slow (20 seconds/cycle, n=6), and Fast (5 seconds/cycle, n=7). A flat‐detector CT scan was acquired, the clot and stent wires were segmented, and the boundaries of the clot and stent wires were calculated on each axial slice (Figure 1A). The intersection between the stent and clot boundaries throughout the volume was defined as the volume of clot integrated within the stent. The clot integration factor (CIF, ratio of integrated clot volume to total clot volume) was then statistically compared between the three frequencies as an estimate of clot capture efficiency. Results The CIF was significantly higher (23% increase, p=0.01) with the Fast actuation as compared to the Passive and Slow actuations, with a post‐hoc test showing no difference (p>0.05) between the Passive and Slow actuation frequency (Figure 1B). Conclusion The unique malleability of the Tigertriever stent‐retriever (Rapid Medical) presents an opportunity to better understand actuation parameters that can maximize thrombus capture. Results indicate that faster actuation frequencies may result in improved clot integration with the Tigertriever device. These results are concordant with a previous clinical study [1] that found repetitive‐expansion‐contraction was more successful than single unsheathing (which corresponds to our Passive group). It is possible that the greater acceleration of the stent mesh wires in the Fast actuation frequency resulted in increased radial forces that improved clot integration. This effect must be further validated in an in vitro setting more representative of physiological conditions, as well as eventual clinical evaluation.

Numerical analysis of coupled flow and heat transfer in primary and secondary sides of double-side heating once-through steam generator with helical tubes

The inner tubes of double-side heating once-through steam generator (OTSG) with helical tubes are spiral channels, and the secondary fluid is heated on both sides, effectively improving the heat transfer efficiency. The spiral structure makes its flow heat transfer characteristics different from straight tube type OTSG. This article establishes a numerical model of Euler two-phase flow in double-side heating OTSG with helical tubes to analyze its velocity distribution, volume fraction distribution, and temperature distribution. The results show that the fluid spirally rises in the secondary flow passage, the velocity of two phases increases rapidly after vaporization, the slip ratio is greater than 1, the steam volume fraction on the wide side is higher than that on the narrow side, and the steam volume fraction presents a spiral distribution on the wall. The non-uniform circumferential steam volume fraction leads to the wall dryout first at the wide edge, and the wall temperature also presents a spiral distribution. The dryout position temperature rises 40.13 K along the Z direction, and the temperature gradient is 5.26 K/mm. The circumferential temperature rises 44.46 K, and the temperature gradient is 15.11 K/mm.

Experimental and numerical study of an innovative twined tube HX design

An innovative twined tube heat exchanger (HX) design is proposed, which is simple, robust, and efficient for use in advanced nuclear reactors. The heat exchanger is designed with two tubes twined around each other. Multiple modules can be assembled within a shell to meet the necessary heat load. Thermal-hydraulic investigations of the novel design are performed through experiments and numerical simulation. The experimental investigations of the twined tube HX are carried out on a laboratory-scale thermal–hydraulic rig commissioned at the Pakistan Institute of Engineering & Applied Sciences (PIEAS). The primary loop contains water at a high temperature and a pressure of 4.0 bar pressure, while the secondary loop operates at atmospheric pressure. Single-phase forced convection heat transfer characteristics of the twined tube HX are investigated experimentally. Pressure drop is measured for mass fluxes ranging from 350 kg/m2s to 1376 kg/m2s. A correlation for the estimation of friction factor is developed based on the experimental studies. Heat transfer measurements are carried out for mass fluxes ranging from 244 kg/m2s to 419 kg/m2s. Based on these experiments, the Nusselt number is evaluated for the mass flux range mentioned above. The numerical simulations of a twined tube HX are performed on a full-scale STAR-CCM + model. The model is validated against the experimental results. The performance factor of the twined tube HX is higher than that of straight tube HX, with a maximum performance enhancement of 60%. The thermal–hydraulic performance of the twined tube HX is comparable with helical coil HX designs. However, the proposed HX design is easier to fabricate and maintain than the helical coiled HX. Overall, the study provides valuable insights into the thermal–hydraulic performance of the twined tube HX, which could be useful in the design of compact and efficient heat exchangers for small modular reactors.

Versatile, elastomeric and degradable polyHIPEs of poly(glycerol sebacate)-methacrylate and their application in vascular graft tissue-engineering

Polymer scaffolds are an important enabling technology in tissue engineering. A wide range of manufacturing techniques have been developed to produce these scaffolds, including porogen leaching, phase separation, gas foaming, electrospinning and 3D printing. However, all of these techniques have limitations. Delivering suitable scaffold porosity, small feature sizes and macroscopic geometry remain challenging.Here, we present the development of a highly versatile scaffold fabrication method utilising emulsion templating to produce polymerised high internal phase emulsions (polyHIPEs) of the polymer poly(glycerol sebacate) methacrylate (PGS-M). PGS-M is biocompatible, degradable and highly elastic, with tunable mechanical properties. PGS-M was formulated into an emulsion using solvents and surfactants and then photocured into polyHIPE structures. The porosity, degradation behaviour, mechanical properties and biocompatibility of the PGS-M polyHIPEs was investigated.The versatility of the PGS-M polyHIPEs was demonstrated with the production of various complex tubular scaffold shapes, using injection moulding. These shapes were designed for applications in vascular graft tissue engineering and included straight tubes, bends, branches, functioning valves, and a representative aortic arch. The PGS-M polyHIPE scaffolds supported vascular smooth muscle cells (SMCs) in 3D cell culture in a bioreactor.

Posterior pericardial window: a simple and reproducible technique in order to prevent pericardial tamponade in paediatric cardiac surgery.

Pericardial tamponade, which increases postoperative mortality and morbidity, is still not uncommon after paediatric cardiac surgery. We considered that posterior pericardiotomy may be a useful and safe technique in order to reduce the incidence of early and late pericardial tamponade. Herein, we present our experience with creation of posterior pericardial window following congenital cardiac surgical procedures. This retrospective study evaluated 229 patients who underwent paediatric cardiac surgical procedures between June 2021 and January 2023. A posterior pericardial window was created in all of the patients. In neonates and infants, pericardial window was performed at a size of 2x2 cm, whereas a 3x3 cm connection was established in elder children and young adults. A curved chest tube was placed and positioned at the posterolateral pericardiophrenic sinus. An additional straight anterior mediastinal chest tube was also inserted in every patient. Transthoracic echocardiographic evaluations were performed daily to assess postoperative pericardial effusion. A total of 229 (135 male, 94 female) patients were operated. Mean age and body weight were 24.2 ± 26.7 months and 10.2 ± 6.7 kg, respectively. Eight (3.5%) of the patients were neonates where 109 (47.6%) were infants and 112 (48.9%) were in childhood. Fifty-two (22.7%) re-do operations were performed. Six (2.6%) patients underwent postoperative surgical re-exploration due to surgical site bleeding. Any early or late pericardial tamponade was not encountered in the study group. Posterior pericardial window is an effective and safe technique in order to prevent both the early and late pericardial tamponade after congenital cardiac surgery.

Turbulent flow-driven liquid-solid mass transfer in serpentine tube heat exchanger/reactors: applications and implications

ABSTRACT This study examines liquid-solid mass and heat transfer rates in serpentine tube heat exchangers/reactors under turbulent flow using the copper dissolution technique. Key factors include solution flow rate, properties, tube diameter, U-bend curvature, and drag-reducing polymers. An empirical correlation predicts mass transfer coefficients, which are 4.12–5.36 times higher than straight tubes. Serpentine tubes show potential for economically viable diffusion-controlled reactions. Drag-reducing polymer (Polyox WSR-301) reduces corrosion rates by up to 23.3%. The study highlights serpentine tubes’ applicability in catalytic continuous reactors and membrane processes, emphasizing their significance in heat exchanger design and corrosion allowance prediction.

Studying the Effects of Wave Dissipation Structure and Multiple Size Diffusion Chambers on Explosion Shock Wave Propagation

Explosion chambers are crucial to the technology used to prevent coal mine gas explosions. Investigating the shock wave propagation law at various coal mine tunnel cross-sections helps ensure mine safety. A self-built, highly explosive experimental setup was used to conduct empirical research on straight tubes, eight sizes of single-stage explosion chambers, and multi-stage tandem explosion chambers. Ansys Fluent numerical simulation software constructed five different tandem explosion chamber models. The wave dissipation efficiency of various types of explosion chambers was calculated, the propagation law and process of shock waves across multiple explosion chambers were examined, and the best size and type of explosion chambers were summarized to increase the wave dissipation efficiency of single-stage explosion chambers. Gun silencers inspired these models. The findings indicate that the three-stage tandem explosion chamber is the best diffusion tandem combination form, the 60° silencer-type explosion chamber is the best single-stage explosion chamber modification program, and the 500 mm × 500 mm × 200 mm explosion chamber is the best single-stage explosion chamber.

Inertial solution for high-pressure-difference pulse-decay measurement through microporous media

We present a theoretical asymptotic solution for high-speed transient flow through microporous media in this work by addressing the inertia effect in the high-pressure-difference pulse-decay process. The capillaric model is adopted, in which a bundle of straight circular tubes with a high length–radius ratio is used to represent the internal flow paths of microporous media so that the flow is described by a simplified incompressible Navier–Stokes equation based on the mean density, capturing the major characteristics of mass flow rate. By order-of-magnitude analysis and asymptotic perturbation, the inertial solution with its dimensionless criterion for the high-pressure-difference pulse-decay process is derived. To be compared with experimental data, the theoretical solution involves all three related effects, including the inertia effect, the slippage effect and the compressibility effect. A self-built experimental platform is therefore established to measure the permeability of microporous media by both pulse-decay and steady-state methods to validate the theoretical solution. The results indicate that the relative difference between two methods is less than 30 % even for permeability at as low as $48.2$ nD $(10^{-21}\,{\rm m}^2)$ , and the present theoretical solution can accurately capture the inertia effect in the high-pressure-difference pulse-decay process, which significantly accelerates the measurements for ultra-low-permeability samples.

Simulation Study on Thermal Performance of an Indirect Boiling Cooling Cylindrical Battery System with Two‐Phase Coolant R141b

In this study, a novel indirect boiling cooling battery thermal management system with two‐phase coolant R141b is proposed for the commercial cylindrical lithium‐ion battery pack. The heat conduction blocks are used to enlarge the heat transfer area between batteries and straight round tubes, and the R141b coolant flows and boils inside tubes to remove heat generated from batteries. Three‐dimensional simulation models are built and used to study the influence of partial structural parameters (height of heat conduction blocks, number and diameter of round tubes), the flow pattern layout, the coolant flow rate, and the battery discharge rate on the cooling performance of battery thermal management system (BTMS). The results show that the cross‐flow layout significantly improves the temperature uniformity of the batteries, with the maximum temperature difference reduced by 30% compared to the concurrent flow. Meanwhile, the appropriate geometrical parameters can further improve both cooling capacity of the BTMS and the temperature uniformity of the batteries. When the optimized structure with a coolant flow rate of 0.1 under the cross‐flow layout, the maximum temperature and maximum temperature difference of batteries discharged at 2 C reduced to 38.6 and 3.81 which are 97% and 64% of those in the concurrent flow, respectively.

Cellular Blood Flow Modeling with HemoCell.

Many of the intriguing properties of blood originate from its cellular nature. Bulk effects, such as viscosity, depend on the local shear rates and on the size of the vessels. While empirical descriptions of bulk rheology are available for decades, their validity is limited to the experimental conditions they were observed under. These are typically artificial scenarios (e.g., perfectly straight glass tube or in pure shear with no gradients). Such conditions make experimental measurements simpler; however, they do not exist in real systems (i.e., in a real human circulatory system). Therefore, as we strive to increase our understanding on the cardiovascular system and improve the accuracy of our computational predictions, we need to incorporate a more comprehensive description of the cellular nature of blood. This, however, presents several computational challenges that can only be addressed by high performance computing. In this chapter, we describe HemoCell ( https://www.hemocell.eu ), an open-source high-performance cellular blood flow simulation, which implements validated mechanical models for red blood cells and is capable of reproducing the emergent transport characteristics of such a complex cellular system. We discuss the accuracy and the range of validity, and demonstrate applications on a series of human diseases.

Experimental and numerical studies on characteristics of LPG-air premixed flames in curved tube

Liquefied Petroleum Gas (LPG) is the widely used fuel worldwide from residential to industrial applications, and thus largely meets the energy demand of various systems. The present study experimentally and numerically investigates the flame propagation behavior of LPG- air mixture in straight and curved tube with inner diameter 30 mm, a length of 500 mm for straight tube and a chord length of 500 mm for the curved tube. Numerical study has been carried out using ANSYS Fluent with FGM approach for modelling of combustion. The premixed reactant in the equivalence range of 0.3 ≤ φ ≤ 2.7 is supplied through the closed end of the tube and the mixture is ignited at the open end exposed to atmosphere. Different flame regimes are observed for 30 mm diameter combustor tube, like the self- repetitive extinction and re-ignition flame, forced repetitive extinction and re-ignition flames, cellular flames, blow out flames, stretched or slanted flames. The curvature of the tube was found to enhance the instabilities occurring in the flame, but rapid changing of flame speed towards the cold inlet is not observed in curved tubes. Cellular flames were formed in the curved combustor as a result of secondary flow and thermal-diffusive instability. Curvature in the combustor tubes induces cross stream vortices in the flow due to the secondary flow, which influence the flame structure in the fuel rich regime of the mixture.

Experimental study on the heat transfer characteristics of supercritical carbon dioxide in spiral tube with high pitch to spiral diameter ratio

Spiral tubes are compact and extremely heat-transfer-efficient that are suited for supercritical carbon dioxide (S-CO2) power cycles. Some existing experiments of S-CO2 heating in tubes are mainly conducted in spiral tubes with low ratio of pitch to spiral diameter (p/C<0.5) and straight tubes. In this study, experimental studies are conducted in a high p/C spiral tube with pitch (p) and spiral diameter (C) of 60 mm and 77 mm, diameter (d) and length (L) of 4.57 mm and 1000 mm, and compared with the straight tube of the same size. The results show that the spiral tube can alleviate heat transfer deterioration, with the maximum wall temperature dropping by 47 °C and the average heat transfer coefficient increasing by about 2.6 times from 1437 W·m−2·K − 1 to 3729 W·m−2·K−1 as compared to the straight tube. The wall temperature near the inlet of the spiral tube rises obviously at high q/G. The heat transfer coefficient and uniformity decrease with mass flux decreasing or heat flux increasing, and is little affected by pressure and inlet temperature. The buoyancy effect is analyzed using 1190 and 1260 experimental data points from spiral and straight tubes. The effect of buoyancy on heat transfer in the spiral tube is weakened as compared with the straight tube. A heat transfer correlation is proposed utilizing the experimental data.

Asymmetric PCM melting and thermal convection in a rectangular enclosure with straight and wavy heat transfer passages

Experimental and numerical investigations of thermal convection in the vicinity of a straight and wavy horizontal heat transfer fluid passage (HTF)s placed in a rectangular enclosure filled with phase change material (PCM) are presented. The enthalpy-porosity-based finite volume solver is used to simulate the spatiotemporal evolution of the thermal convection, which is well-complemented by experimental visualization and thermocouple measurements. Heat transfer from the horizontal HTF exhibits asymmetrical melting. Heat diffusion is the dominating energy transfer mechanism on the bottom part of the HTF passage and is compared with the Stefan problem. The temporal evolution of thermal convection on the top part of HTF passage involves three distinct phases of melting, viz. initial conduction phase, Rayleigh–Bénard (R-B) convection with linear convection, and vortex coalescence effects. The final stage of the melting process is influenced by the topography of a peninsula of unmelt PCM, which is influenced by specific top-boundary conditions. Thermal convection in PCM above the wavy HTF passage exhibits restricted plume development leading to an improved melting rate and a higher average melt height. Augmentation of internal convection characteristics of HTF with the evolution of melting is also explored. A systematic investigation of the convection plume development and heat transfer characteristics in PCM by varying the HTF Reynolds (1700<Re<2750) and Stefan numbers (0.4<Ste<0.6) has been carried out, and analyzed the nature of thermal plumes, melt fraction, and average penetration length with the Fourier number. Additionally, novel correlations are proposed between Nusselt and Rayleigh numbers for straight and wavy tubes in the intermediate melting stage (1.3×104<Ra<4.7×107).

Spatiotemporal frequency domain analysis for blood velocity measurement during embolization procedures.

Currently, determining procedural endpoints and treatment efficacy of vascular interventions is largely qualitative and relies on subjective visual assessment of digital subtraction angiography (DSA) images leading to large interobserver variabilities and poor reproducibility. Quantitative metrics such as the residual blood velocity in embolized vessel branches could help establish objective and reproducible endpoints. Recently, velocity quantification techniques based on a contrast enhanced X-ray sequence such as qDSA and 4D DSA have been proposed. These techniques must be robust, and, to avoid radiation dose concerns, they should be compatible with low dose per frame imageacquisition. To develop and evaluate a technique for robust blood velocity quantification from low dose contrast enhanced X-ray image sequences that leverages the oscillating signal created by pulsatile bloodflow. The proposed spatiotemporal frequency domain (STF) approach quantifies velocities from time attenuation maps (TAMs) representing the oscillating signal over time for all points along a vessel centerline. Due to the time it takes a contrast bolus to travel along the vessel centerline, the resulting TAM resembles a sheared sine wave. The shear angle is related to the velocity and can be determined in the spatiotemporal frequency domain after applying the 2D Fourier transform to the TAM. The approach was evaluated in a straight tube phantom using three different radiation dose levels and compared to ultrasound transit-time-based measurements. The STF velocity results were also compared to previously published approaches for the measurement of blood velocity from contrast enhanced X-ray sequences including shifted least squared (SLS) and phase shift (PHS). Additionally, an in vivo porcine study (n = 8) was performed where increasing amounts of embolic particles were injected into a hepatic or splenic artery with intermittent velocity measurements after each injection to monitor the resulting reduction invelocity. At the lowest evaluated dose level (average air kerma rate 1.3 mGy/s at the interventional reference point), the Pearson correlation between ultrasound and STF velocity measurements was . This was significantly higher ( ) than corresponding correlation results between ultrasound and the previously published SLS and PHS approaches ( and , respectively). In the in vivo study, a reduction in velocity was observed in of cases after injection of 1 mL, after 3 mL, and after 4 mL of embolicparticles. The results show good agreement of the spatiotemporal frequency domain approach with ultrasound even in low dose per frame image sequences. Additionally, the in vivo study demonstrates the ability to monitor the physiological changes due to embolization. This could provide quantitative metrics during vascular procedures to establish objective and reproducibleendpoints.

Development and validation of the helically coiled steam generator model of RELAP5/MOD3.4 code

The flow field and heat transfer characteristics in a helical coil tube-type once-through steam generator (HCOTSG) are more complex than those in a straight pipe-type steam generator owing to the complex geometry of the former and the secondary flow induced by the centrifugal force. Straight tube heat transfer correlations and pressure correlations unapplicable for helical coils. System analysis codes used in design and safety analysis of HCOTSG are still missing. In this study, a code called RELAP5/MOD3.4-HCOTSG was developed for a numerical simulation of an HCOTSG based on the RELAP5/MOD3.4 code, and on suitable empirical correlations of the heat transfer coefficients and pressure drop chosen for HCOTSG. The code is first validated through a comparison with the IRIS HCOTSG design parameters, and the results indicate that the chosen models can accurately simulate the wall heat transfer and achieve a higher accuracy in the wall friction pressure drop prediction. Based on this, an analysis of typical transients is conducted to evaluate the transient characteristics of IRIS HCOTSG. The results indicate that the RELAP5/MOD3.4-HCOTSG code has the ability to calculate the transient flow and heat transfer characteristics of an HCOTSG and can serve as an analysis tool for the system calculation of a small modular reactor.

Pressure drop in converging flows in three-dimensional printing of concrete

The additive manufacturing technology of extrusion of concrete mixtures through a nozzle and deposition layer-by-layer is commonly called three-dimensional concrete printing (3DCP). Such materials are rheologically characterized by yield stress and viscosity. The Bingham model is a good approximation of their rheological behavior. We have developed approximate expressions for determination of pressure for flow through slightly tapered tubes and wedge-shaped extrusion dies, starting from the Buckingham–Reiner equation for flow of a Bingham fluid in a straight tube. The predictions are compared to numerical simulations for convergence half-angles (taper) from 0° to 30° and to analytical solutions available in the literature. Good comparison has been obtained for taper angles up to 15° but the agreement deteriorates as the angle increases. Some experimental data available in the literature have been analyzed, and the challenges for prediction of pressure drop in flow of concrete mixtures through tubes and dies, including entry flow losses, are discussed.