Small Diameter Tubes Research Articles

Influence of Cold-Rolling Processes on the Dimensional Accuracy and Roughness of Small-Diameter Thick-Walled Seamless Tubes

Cold pilgering is widely utilized in high-end applications for the precise shaping of seamless tubes due to its capacity for large deformation, which reduces the number of deformation processes and shortens production cycles. However, there is a gap in the research on the cold pilgering of small-diameter, thick-walled seamless tubes, specifically those with an outer diameter–wall thickness ratio of ≤3. In this study, cold pilgering tests were performed on Cr-Mo-V hot-working die steel small-diameter thick-walled tubes. It was discovered that increasing the feed rate results in greater deviations in both inner diameter and wall thickness, although it has little effect on inner wall roughness. In contrast, increasing wall thickness reduction leads to higher wall thickness deviation but reduces inner surface roughness without significantly affecting inner diameter deviation. The study also found that a decrease in the initial inner wall roughness before pilgering results in improved final roughness. Under optimal conditions, the average inner surface roughness Sa can reach 0.177 μm, and small-diameter thick-walled seamless tubes with deviations in the inner diameter and wall thickness of 0.05 mm and 0.03 mm, respectively, are obtained. After tempering at 600 °C, the tensile strength (Rm) and yield strength (Rp0.2) of the cold-pilgered tube reach 1092 MPa and 947 MPa, respectively, and the elongation (δ5%) and impact energy (AkU) increase to 20.4% and 61.5 J, respectively.

Safety of Small-Diameter Endotracheal Tubes in Microlaryngeal Surgery.

Microlaryngeal surgeries require unique considerations for airway management to facilitate patient safety and adequate surgical exposure. Small-diameter endotracheal tubes (ETTs) are widely used but have raised concerns regarding patient safety, including questions about the potential for barotrauma, effective ventilation, and adequate oxygenation. We hypothesize that small ETTs will prove to be safe in a variety of cases. We conducted a case series analyzing the safety of 5.0 ETTs in microlaryngeal surgeries at Washington University School of Medicine from November 2020 to November 2023. Outcome measures included intraoperative desaturations (SpO2 < 90% for >2 min), high peak inspiratory pressures (PIPs) (>40 cm H2O), and prolonged extubation times (>15 min). Univariate regression models were used to analyze associations of sociodemographic and clinical variables with these outcome measures. This study included 76 small-ETT microlaryngeal surgeries. There were 5 instances of desaturations, no reported incidents of barotrauma, and no cases in which intraoperative tube exchange was required due to issues with oxygenation or ventilation. Median PIP was 38 cm H2O, with a range of 17-78 cm H2O. 46% of patients had a PIP above 40 cm H2O. There were prolonged extubation times in 14% of procedures. No association was shown between sociodemographic and clinical variables with risk of desaturations, high PIPs, or prolonged extubation times. Our study suggests that 5.0 ETTs are safe for microlaryngeal surgery in a variety of patients. Otolaryngologists and anesthesiologists should consider this information when choosing between the multiple available options for airway management during microlaryngeal surgery. Level 4 Laryngoscope, 2024.

A New "Tube-in-tube" Method to Extend Glaucoma Drainage Devices Using Paul Glaucoma Implant.

To describe a novel and uncomplicated technique of elongating the tubing of a glaucoma drainage device (GDD) sourced from a segment of the tube from a Paul® Glaucoma Implant (PGI). Conjunctival and Tenon's peritomy are performed with relaxing incisions to expose the original tube. The original tube is then removed from the anterior chamber, and the original entry site is closed. The tip of the original Baerveldt/Ahmed tubing is shortened to near the plate, and the lumen is stretched open using Burke's forceps (nontoothed to avoid damage to the tubing) while the appropriate length of the Paul tube was being pushed inside and is secure without the need for any suturing. The new smaller Paul tube is then inserted back into the anterior chamber using a 26-gauge tract. An 8-0 Ethilon® was then used to secure the tube to the sclera, and TISSEL® was used to secure it (Baxter, United States). Depending on the positioning, either the original Tutoplast® pericardium or new double-layered Tutoplast® can be placed over the tube to prevent erosion. The Tenon's and conjunctiva were then closed to secure the conjunctival and Tenon's back in their original position at the limbus, and the radial conjunctival incisions can be closed using TISSEL® fibrin glue or further sutures if required. This method offers several benefits over previously documented techniques; it avoids significant bulkiness, and the elongated tube conforms to the curvature of the globe owing to the suitable rigidity of the extended section. The additional tubing segment fits securely without the need for sutures. Introducing a smaller diameter tube into the anterior chamber in comparison to other GDDs minimizes the surface area between the tube and corneal endothelium, therefore decreasing the rate of potential endothelium cell loss. This novel "tube-in-tube" technique is efficient, safe, and straightforward to perform. It eliminates the need for alterations in glaucoma medication since the PGI is not thought to offer any flow resistance. Berman T, Au L. A New "Tube-in-tube" Method to Extend Glaucoma Drainage Devices Using Paul Glaucoma Implant. J Curr Glaucoma Pract 2024;18(3):130-133.

Development of a highly stable IrO2-RuO2-Ta2O5/Ti with fluorine doped nanotube interlayer

Fluorine-doped titanium oxide nanotubes were studied as a coating interlayer for IrO2-RuO2-Ta2O5/Ti to retard the passivation of titanium substrates and enhance anode life and corrosion characteristics. Nanotubes were produced by anodizing the substrate at 10, 20, and 40 V in HF, and their effect on the microstructure of the coating was assessed using FE-SEM. Additionally, EIS and ALT measurements were conducted to investigate this coating's electrochemical behavior. Results showed that titanium oxide nanotubes with a smaller diameter would improve the performance and increase the life of the anode (IrO2-RuO2-Ta2O5/Ti). Likewise, the diameter of the nanotubes demonstrates a direct relationship with anodizing voltage. Furthermore, high voltages during anodizing resulted in an etched surface that was not ideal for an interlayer. All an all, it was concluded that the layer anodized at 10 V, with smaller-diameter tubes and a higher number of walls, could result in a product with high corrosion resistance and 80 % excess lifetime compared to a bare titanium substrate. This study provides valuable insights for engineering applications, demonstrating the potential for enhanced anode design in corrosion-sensitive environments in electrochemical engineering, water treatment, or fuel cells and electrolyzers where durability of the anodes are crucial.

Image restoration of reflectors by the method of digital aperture focusing in thick-walled pipes of small diameter

In ultrasonic inspection of pipes of various diameters using antenna arrays and arrays, two technologies of reflector image reconstruction are widely used: antenna array focusing technology (PAUT) and digital aperture focusing (DAF) technology. If the tube diameter is larger than a hundred wavelengths, the DAF method can be used to reconstruct the reflector image by taking into account several reflections from the boundaries, assuming that the object of inspection is flat. In this case, the errors in the formation of DAF-image of reflectors will be insignificant. However, if the pipe diameter is several tens of wavelengths and the wall thickness is about half of the pipe diameter, then in this case the geometry of the inspection object must be taken into account to obtain a high-quality DAF-image of the reflectors. The paper considers the peculiarities of image formation at registration of echo signals by an antenna array or matrix, when scanning both on the external and internal surfaces of the object of control. In numerical and modeling experiments it is shown that both antenna array and antenna array can be used to obtain high-quality DAF-image of reflectors when scanning along the outer surface of a thick-walled pipe of small diameter. This is due to the presence of the effect of physical focusing of the ultrasonic field. But when scanning along the inner surface of a thick-walled tube of small diameter, because of the defocusing effect, it is necessary to register echoes with an antenna array to restore the image of reflectors.

Annular two-phase flow in a small diameter tube: OpenFOAM simulations with turbulence damping vs optical measurements

In this work, numerical simulations are performed to predict two-phase annular flow of refrigerant R245fa inside a 3.4 mm diameter vertical channel. The VOF (Volume of Fluid) method implemented in an OpenFOAM solver is used to accurately track the vapor-liquid interface. A 2D axisymmetric domain is considered and the Adaptive Mesh Refinement (AMR) method is applied to the cells near the liquid/vapor interface. The Reynolds-Averaged Navier Stokes (RANS) equations are solved and the k-ω SST model is adopted for turbulence modelling in both the liquid and vapor phase. Simulations are used to calculate instantaneous and mean values of the liquid film thickness at mass flux G = 100 kg m-2 s-1 and vapor quality ranging between 0.2 and 0.85. Numerical results are compared against measurements of the liquid film thickness taken during vertical annular downflow. Previous works from the literature and the deviations observed between present numerical and experimental results suggest the need for turbulence damping at the vapor-liquid interface by adding a source term in the ω equation. The simulations show that a low value of the turbulence damping parameter (e.g. 1) causes the average liquid film thickness to increase by 25 %–52 % compared to the non-damped scenario. The interface presents large amplitude disturbance waves in the non-damped case, whereas small ripple waves are predicted when turbulence damping is introduced. Furthermore, the difference between the application of a symmetric and asymmetric treatment for the source term is analysed. From the comparison between experimental data and numerical simulations, it emerges that the value of the correct damping source term to be applied is strictly dependent on the vapor quality.

Electropolishing of 316L Stainless Steel Small-Diameter Tubes: Reduced Surface Roughness and Enhanced Corrosion Resistance

Electropolishing of 316L Stainless Steel Small-Diameter Tubes: Reduced Surface Roughness and Enhanced Corrosion Resistance

Thermo-hydrodynamic characterization and mapping of the two-phase flow in a capillary tube

The study presents an experimental investigation on the behavior of condensate film and liquid–vapor meniscus in the unit cell of a pulsating heat pipe (PHP) at different operating boundary conditions, and their respective roles in determining PHP’s performance. The orientation and the temperatures of evaporator and condenser sections are taken as the variable operating boundary conditions whereas the amplitude of oscillations influences the performance of the PHP. The entire thermo-hydrodynamic phenomenon is captured using high-speed imaging. By tracking the interface of liquid film and vapor, different regimes for film flow in the condenser section are observed and characterized. Also, the oscillation amplitude has been quantified at different operating boundary conditions. Despite a quite small tube diameter, gravity plays a key role in determining the liquid and vapor phase distributions in the tube. The variation of oscillation amplitude is intimately linked with the nuances of film flow regimes and inter-regime transitions. The optimum inclination angle, and evaporator and condenser temperatures are found to exist for the PHP unit cell which maximize the oscillation amplitude. The dependence of optimum inclination angle on condenser temperature has also been understood along with. Further, the associated film flow regime in condenser which facilitates these optima has also been recognized. All variable operating boundary conditions are observed to have a peculiarly mixed influence on the flow regimes and thus oscillation amplitude. The study would help to achieve a better elementary understanding of the role of condensate film flow in determining PHP’s performance and develop a flow regime map particularly for PHPs.

Construction and performance of the precision tracking chambers for the ATLAS muon spectrometer upgrade for high-luminosity LHC

For the operation at the High-Luminosity (HL) LHC, the Monitored Drift Tube (MDT) chambers of the inner barrel layer (BIS) of the ATLAS muon spectrometer will be replaced by small-diameter Muon Drift Tube (sMDT) chambers which will be integrated with triplets of thin-gap Resistive Plate Chambers (RPC) in order to improve the acceptance and robustness of the barrel muon trigger system. The sMDT chambers have half the drift tube diameter of the MDT chambers and about one order of magnitude higher background rate capability. The construction of the 96 new sMDT chambers was performed between January 2021 and September 2023 at two production sites at a continuous rate of one chamber every two weeks. The sense wire positioning accuracy guaranteed by precision assembly jigs was measured to be around 5μm over the whole construction period. Stringent performance tests had to be passed during the production which have been successfully repeated after delivery of the chambers to CERN. The chambers have been tested with the new MDT front-end ASICs developed for operation at HL-LHC which improve the spatial resolution of the drift tubes by 10% compared to readout with the legacy electronics.

Flow Patterns of Tetraflouroethane Refrigerant in Different Small Diameter Tubes Used for Vaccine Delivery Boxes

This study aims to determine the flow patterns of tetrafluorethane refrigerant in different small diameter tubes. It attempts to establish a relationship among the temperature, pressure drop, volumetric flow of tetraflouroethane refrigerant in a 900 mm long small diameter tube. Tests are conducted to determine the effect of varying hydraulic tube diameter to the temperature and pressure drop of tetraflouroethane refrigerant in different flow rate. A copper tube with hydraulic diameter of 0.20 mm, 0.25 mm, 0.30 mm, 0.35 mm, 0.40 mm and 0.45 mm were used in this study. For every known hydraulic diameter, there are six (6) test points located in every 150 mm interval. The experimental rig is composed of six (6) pieces of 900 mm long copper tubes for the given hydraulic diameters. Each tube is marked with 150 mm, 300 mm, 450 mm, 600 mm, 750 mm and 900 mm. The markings represent the length of capillary tubes in millimeters where test points are located. A pressure transducer is attached to every test point and is used to measure the pressure drop at every length of the small diameter capillary tube. The result shows that pressure drop increases as the tube hydraulic diameter decreases and attained an evaporator temperature as low as -5 oC. The smaller the diameter of the tube, the more it is effective to give pressure drop for the design of a handy vaccine delivery box refrigeration system.

Aspiration tubing diameter is a key determinant of vacuum pressure and is associated with procedural outcome in mechanical thrombectomy for large vessel occlusion: An experimental and cohort study.

We (1) evaluated the effect of aspiration tubing diameter on intraluminal pressure and (2) compared thrombectomy outcomes in patients treated using small diameter tubing versus those treated using large diameter vacuum tubing. Intraluminal negative pressure was measured in a validated benchtop set up where consistency of negative pressure (inHg) was measured between static and dynamic aspiration. Static aspiration refers to activation of vacuum once the catheter is engaged with the clot. Dynamic aspiration refers to activation of vacuum when the catheter is slightly proximal to the clot. Four different sizes of vacuum tubing were trialed. We performed a retrospective analysis of consecutive patients who underwent mechanical thrombectomy. Procedural and functional outcomes were compared. The large diameter aspiration tubing held a consistent high negative pressure in static and dynamic aspiration (p = 0.152). Tubing types I to III were associated with a significant fall off in negative pressure between static and dynamic technique (p < 0.05). Two-hundred and five patients were included in the retrospective analysis; 124 (60%) underwent thrombectomy using small diameter vacuum tubing, and 81 (40%) using the large tubing. Mean thrombectomy time was shorter with the larger tubing [25.9 (17.9) minutes] versus the small tubing [37.5 (28.5) minutes, p = 0.002]. A greater proportion of patients had a thrombolysis in cerebral infarction score ≥2b in the group treated using the large tubing (78, 99%) than those with the small tubing (96, 78%, p < 0.001). Vacuum tubing diameter is linearly associated with intraluminal aspiration pressure. These findings have clinical significance as shown by increased recanalization rates and decreased thrombectomy times when large-diameter aspiration tubing is used. Shifting the paradigm toward a flow-based technique using large-bore vacuum tubing ought to be considered.

Investigation of Laminar Forced and Mixed Convection in Horizontal Mini Tubes with Uniform Wall Heat Flux Boundary Condition

In this study, a numerical model is established to study the forced and mixed convection heat transfer in the laminar region for horizontal mini tube with different diameters (1.2 mm to 3.0 mm) under the uniform wall heat flux boundary condition. The Reynolds number is set from 100 to 2,000 and the uniform wall heat flux boundary condition is set at 10 and 20 kW/m2. The model is verified with well-established correlation to guarantee good accuracy. The existence of mixed convection is examined by (1) the ratio between the heat transfer coefficients at the top and the bottom of the tube, and (2) the temperature contour plot. Based on the simulation results, the existence of buoyancy superimposed on the main flow is strongly related to the tube diameter, the dimensionless location, the Reynolds number, and the heat flux applied. Under the same heating condition, for small diameter tube with insufficient length, buoyancy effect can never establish. The existing flow regime maps for macro tube were used to predict the forced and mixed convection regimes from the simulated mini tube results and discrepancy was found. A new flow regime map is hence developed for mini tubes, and it classified the simulation results with good accuracy.

Dielectric Screening inside Carbon Nanotubes.

Dielectric screening plays a vital role in determining physical properties at the nanoscale and affects our ability to detect and characterize nanomaterials using optical techniques. We study how dielectric screening changes electromagnetic fields and many-body effects in nanostructures encapsulated inside carbon nanotubes. First, we show that metallic outer walls reduce the scattering intensity of the inner tube by 2 orders of magnitude compared to that of air-suspended inner tubes, in line with our local field calculations. Second, we find that the dielectric shift of the optical transition energies in the inner walls is greater when the outer tube is metallic than when it is semiconducting. The magnitude of the shift suggests that the excitons in small-diameter inner metallic tubes are thermally dissociated at room temperature if the outer tube is also metallic, and in essence, we observe band-to-band transitions in thin metallic double-walled nanotubes.

A parametric optimization framework for fin-and-tube heat exchangers based on response surface methodology and artificial intelligence

This study presents a numerical investigation and provides a novel framework for the rapid parametric optimization of attack angles (α) and aspect ratios (e) in plate fin-and-tube heat exchangers (PFTHEs) featuring elliptical tubes. The methodology incorporates three-dimensional numerical simulations, response surface methodology (RSM), backpropagation neural network (BPNN), and Entropy-VIKOR. The study focuses on a PFTHE with a single elliptical tube, varying the attack angles (α) from −30° to 0° in 5° increments and the aspect ratios (e) from 0.4 to 1.0 in a step of 0.1. Air velocities (u) range from 0.4 to 3.2 m/s with an interval of 0.2 m/s, corresponding Reynolds number from 200 to 2200. The results indicate that using elliptical tubes reduces Δp and enhances heat transfer capacity, with the most significant improvements at an e of 0.4. Exponential relationships between dimensionless parameters Nu or f and Re are established for different range of α at specific e values. The synergistic effect of e, α, and Re or u on PFTHE performance is confirmed through RSM and BPNN analysis. Their R2 values are no less than 0.896 and reach a maximum of 0.998, indicating excellent predictive accuracy. Utilizing Entropy-VIKOR method, the framework identifies a suitable design solution with e = 0.6, α = -20°, and u = 3.2 m/s. This solution exhibits a 5 % increase in h and a 58 % reduction in Δp relative to the corresponding circular tube. The study provides specific expressions relating design variables to thermal–hydraulic behavior and indicates carefully selecting the α and e can improve the overall performance. In summary, these findings have significant implications for reducing optimization design period for PFTHEs with small tube diameters.

Compressive behavior of seawater and sea sand concrete-filled FRP-steel composite multi-tube hollow columns

To further explore sustainable development in high-performance marine engineering structures, this study introduced a new approach - a hybrid structural member called the seawater and sea sand concrete (SWSSC)-filled fiber-reinforced polymer (FRP)-steel composite multi-tube hollow column (S-MTHC). The S-MTHC consists of double-walled FRP-steel composite tubes filled with SWSSC, along with several small-diameter SWSSC-filled FRP tubes (known as SSFFTs). Monotonic axial compression tests were conducted on the S-MTHCs, and a bearing capacity model was established. The test results demonstrated that the presence of FRP-steel composite tubes and SSFFTs significantly improved the axial compressive behavior of S-MTHCs. Increasing the number of external FRP layers or SSFFTs enhanced the strength and ductility of the hybrid column. The influence of increasing concrete strength or FRP tube thickness in SSFFTs, however, was relatively negligible. Additionally, specimens with carbon FRP (CFRP) tubes in SSFFTs exhibited higher bearing capacity while maintaining similar ductility.

Effect of vacancy defect on the structural and electrical properties of single-walled silicon nanotube

The effect of vacancy defects on zigzag and armchair single-walled silicon nanotubes (SiNTs) has been investigated using the self-consistent charge density functional tight-binding (SCC-DFTB) method. The findings indicate that the introduction of defects leads to the inability of the smaller-diameter tube to uphold its tubular structure and cluster. Conversely, the larger-diameter tube undergoes an elliptical transformation, yet retains tubular characteristics and hexagonal structures displaying specific symmetry. The double vacancy defect alters the atomic arrangement on the side opposite the defect. The stability of single-walled SiNTs is related to defect type and chiral index. In addition, the single vacancy defect increases the binding energy and stability of the zigzag tube, while causing a rapid decrease in stability of the armchair tube (7,7). The spin polarization phenomenon manifests within the defect tube, resulting in the splitting of the initial degenerate energy band and a significant decrease in its degeneracy. The existence of electronic interaction, results in a prominent manifestation of vacancy-induced magnetism in armchair and zigzag defect tubes. This phenomenon gives rise to localized spin-up bands situated below the Fermi level, as well as localized spin-down bands positioned above the Fermi level. In the energy band structure of most nanotubes, there are conduction bands or valence bands passing through the Fermi level, leading to a transition from semiconductor to semimetal or metal properties.

Experimental investigation of the supercritical heat transfer of the low GWP refrigerant R1234ze(E): calibration and validation of test rig

Heat transfer of supercritical refrigerants is applied in practical systems such as the transcritical organic Rankine cycle or supercritical heat pump. The concept of supercritical heat transfer is not new and has already been studied and applied for decades in several applications. However, results on one fluid cannot be directly translated to another one. This is because the thermohydraulic behavior of fluids is heavily influenced in the near-supercritical region due to sudden variations in the thermophysical properties when the fluid is heated or cooled close to its critical point. For refrigerants under horizontal flow, the research is limited. Most studies in literature are on small diameter tubes and on R134a, which has a high global warming potential. Therefore, an experimental test rig has been built to measure the supercritical heat transfer of low global warming potential refrigerants over a large temperature and pressure range in the supercritical region. In this work, the calibration and validation of this test rig is presented using the refrigerant R1234ze(E). The test section consists of a 4 m long horizontal tube with an inner diameter of 22.9 mm, equipped with thermocouples at both the tube wall and in the bulk of the flow, and is heated by resistance wires wrapped around the tube. For the calibration, the temperature profiles under both non-heating and heating conditions are evaluated. For the validation, the average Nusselt numbers obtained through experiments under subcritical conditions are compared to the average Nusselt numbers calculated based on the Dittus-Boelter and Gnielinski correlation.

Vibration-Free 40-80K Turbo-Brayton Cryocooler and its Very High Efficiency Recuperator for Earth Observation Instruments

Several studies have demonstrated that Reverse Turbo-Brayton cryocoolers could be the next space cryogenic revolution, thanks to their capability to provide vibration-free remote cooling in the temperature range of 4 to 150K and for medium to high cooling powers. With this motivation, Absolut System developed a very low vibration 40-80K Reversed Turbo-Brayton cooler, work performed under the ESA Technical Program Technical Research Program - 4000113495/15/NL/KML. The cooler is based on two turbo-compressor stages, a high efficiency recuperator and a cryogenic turbo-expander, for operation between 300 and 40K. Following the fabrication of the cooler, we performed tests on both individual components, compressors, expander and recuperator as well as on the complete cooler. The turbomachines use aerodynamic bearings, i.e. contactless bearings, generate very little vibrations and exhibit no wear over time. The characterizations performed during the project concern exported micro-vibration behaviors of the compressors and the expander, operating respectively up to 250,000RPM and 150,000RPM, and thermodynamic performance of the different elements. The cooler was tested down to its minimum temperature and required the development of specific operating procedures for the conditioning of the circuit. We report here in a first part the main results and observations stemming from the test campaigns carried out during the project. This work showed the necessity of putting additional effort into the recuperator, one of the most critical components of the cooler. Absolut System is thus also working in parallel on developing a very high efficiency and compact heat exchanger, which we report in a second part, for the specific needs of Turbo-Brayton Coolers in response to the ESA Proposal ESA-TDE-TECMTT-SOW-023649. The technology selected for this is based on the common tube and shell but using very thin tubes of small diameters (<1mm). The challenge of this exchanger is not only the manufacturing, but also the very stringent requirements. Obtaining an efficiency higher than 97.5% in a very small mass while maintaining very low pressure drops, makes for a very challenging project. We have performed the design phase, tested, and validated different aspects of the assembly. The design for the first breadboard model has been validated numerically and is in the fabrication process. Testing the exchanger will then take place to characterize the performances of the recuperator and allow for a comparison between experimental results and analytical and CFD models. This effort participates in placing the Turbo-Brayton cryocoolers at the forefront of space coolers and pushing Europe even further in State of Art advancements for space to bring us closer to fulfill future Space Explorations and Earth Observation missions.

Gas-liquid-soild triphasic continuous flow microreactor for improving homogeneous distribution of solid composites in heterogeneous photocatalytic degradation progress

The homogeneous distribution of solid composites in continuous flow photocatalytic progress is difficult due to the settle and clog in capillary. To overcome this challenge, a gas–liquid-soild triphasic continuous flow photoreactor was designed and used for heterogeneous photocatalytic degradation of antibiotics wastewater. In this work, take Bi2WO6 as photocatalyst, photocatalytic degradation of ofloxacin wastewater was studied systematically under different operational parameters and flow characteristics. The photocatalytic degradation performance of flow photoreactor was superior to batch counterpart, especially in later stage of reaction. The apparent reaction rate constants (k) of flow photoreactor was about 1.6 times that of batch counterpart. The gas–liquid mass transfer coefficient of flow photoreactor was more than 25 times that of batch photoreactor. Moreover, the influence mechanism of gas fraction, flow rate and tube diameter on photocatalytic degradation performance was investigated under various continuous flow conditions. Higher gas fraction, faster flow rate and smaller tube diameter were beneficial to improve photocatalytic degradation performance due to the enhancement of irradiation transmission and intensification of mass transfer. Therefore, the results of this work provided a guideline for the application of gas–liquid-soild triphasic continuous flow photocatalytic degradation technology in the future.

Airside heat transfer analysis using Wilson plot method of three analogous serpentine tube heat exchangers for aero-engine cooling

This research investigates the design, manufacture and heat transfer characteristic evaluation of three types of heat exchangers (HXs) serving for modern aero-engines. In the field of heat transfer system, previous research has concentrated on large-diameter tubes, whereas estimation for heat transfer in small-diameter tubes commonly relies on correction factors. However, small-diameter heat exchangers offer extensive applicaiton prospects in aero-engines utilizing cooled cooling air (CCA) technology, benefiting from their high heat transfer efficiency and lightweight. Hence, directly investigating compact small-diameter HXs is significant. In this paper, three analogous serpentine tube bundle HXs with different tube diameters (OD: 2.2/1.8/1.4 mm with 0.2 mm thickness) were designed by the Logarithmic Mean Temperature Difference method (LMTD). A series of comparative experiments were conducted to explore the effects of the tube diameter and flow rates on the airside heat transfer under different fuel flow conditions. The results indicate that in the case of turbulent fuel flow, decreasing the tube diameter assists in enhancing total heat transfer, whereas the trend is opposite in laminar fuel flow. In addition, during turbulent fuel flow, heat transfer capacity rises with the increase of flow rates on both sides, while variations in air flow rate have minimal impact on airside heat transfer in laminar fuel flow. Finally, the calculated heat transfer rate exceeds the experimentally measured value by no more than 15%, with this deviation escalating as the reduction of tube diameter. Subsequently, an airside Nu-Re correlation suitable for small-diameter HXs is fitted based on experimental data, with 94.1% of the data points locate in the 5% error band, providing guidance for the design and validation of aero-engine HXs in future.