Small Tube Research Articles

Heat Transfer in Double Pipe Heat Exchangers with Small Tube Spacing

Abstract In this current work, the heat transfer in double pipe heat exchangers with small tube spacing is analysed. This type of heat transfer is generally described in many literary sources, however, in laminar flow, the resulting values of the theoretical equations differ. Moreover, the small spacing of the pipes can affect the fluid flow and subsequent heat transfer. The suitability of using available theoretical methods for the design of double pipe heat exchangers (the Stephan, VDI and Baehr methods) was evaluated. A series of experiments was carried out on a double pipe heat exchanger with a tube spacing of 1.4 mm. The experimentally determined value of the heat transfer coefficient was up to two times higher in comparison with the values calculated according to theoretical methods. The relative increase was more significant for the lower Reynolds number values. At the same time, the difference of the wall temperature along the circumference of the outer tube was detected. This phenomenon was theoretically analysed and can be explained by tube misalignment in the small tube spacing. The procedure of quantification of this effect was proposed. This effect may cause an inhomogeneity of the media flow and temperature distribution and, as a result, increase the performance of the heat exchanger by tens of percent.

Freeform 3D deposition of small diameter copper tubes using a powder-binder feedstock

AbstractCopper is an interesting material for many applications including thermal management devices, which make often use of copper piping. This study proposes a method for the freeform deposition of a copper-binder feedstock, extruded through an additive manufacturing machine. Several tubes have been printed using a special nozzle and varying process parameters. The dimensional results of the deposited specimens at the green state and the physical properties of the tubes after debinding and sintering have been measured. The results demonstrate that piping in serpentine layout can be deposited by extrusion and sintered, even with sharp bends without significant ovalization of the cross-section.

The universal gaseous detonation dynamics

The present communication proposes a new scaling approach to unify the dynamics of gaseous detonations subject to wall losses in both the narrow channels and small tubes, by compiling the published experimental data of detonations in 23 different mixtures with a very large range of cellular instabilities. A kinetic induction length Δi,loss can be determined from the detonation velocity deficit and detailed chemistry. In order to take into account the sensitivity of the latter length to post-shock temperature fluctuations (through the reduced activation energy θ), which is a partial and indirect marker of the cellular structure, and to bring out energetics (through the Chapman–Jouguet detonation Mach number MCJ), an effective kinetic length of Δi,loss(MCJ4/θ3) was built and has been shown to collapse the different detonation dynamics of various gaseous mixtures, subjected to wall losses, into a single universal curve for detonation velocity deficits.Novelty and Significance: Scaling analysis of large sets of published data of gaseous detonation experiments in narrow channels and small tubes has been made for 23 different mixtures with varied cellular instabilities and activation energies. The universal dynamics of gaseous detonations subject to wall losses in different mixtures has been achieved, for the first time, by adopting an effective kinetic length by taking into account the effect of both the activation energy and the energetics.

Hydrodynamic performance characteristics of small-scale in-situ buoys with critical motion requirements

As the accuracy of high-precision oceanographic measurement instruments increases, the operational requirements for buoy motion become critical. This study focuses on the small-scale in-situ buoy, optimizing buoy configuration to ensure stability and performance. Aiming at the special structure which consists of a large floating column and several small tube connectors, a method for evaluating the hydrodynamic performance is proposed which combines potential flow theory with Morison equation. And the method validity is confirmed using experimental data. The performances analysis of different type buoy with catenary or taut mooring system are developed. According to the critical motion requirements for the long-term stability, the cylindrical type buoy equipped with a catenary mooring system is regarded as the most stable and economical choice, exhibiting a surge motion response of 4.07 m, a heave motion response of 2.89 m, and a pitch motion response of 9.37°. Furthermore, the anchor chain acts as an elastic damper which can mitigate the transient impact of the environmental loads, greatly limiting the amplitude of the longitudinal and heaving motions. And the maximum mooring line tension is 249.28 kN, which is significantly lower than other schemes. The evaluation method offers a technical support for engineering applications.

Biocompatibility and Haemocompatibility Assessments of RBC with Polymeric Coated Cardiac Stent.

The current investigation was conducted to evaluate the biocompatibility and hemocompatibility of polymeric-coated cardiac stents. Coronary stents are typically small wire mesh tubes that are used to open arteries that are obstructed over time as a result of the buildup of fat, cholesterol, or other materials. A 10 milliliter isolated blood red blood cell was obtained using the Prozeta cobalt chromium coronary stent, which had the following specifications: stent length = 18 mm, strut thickness = 0.065 mm, expansion range = 2.25 mm to 4.00 mm, and burst pressure = 6ATM. Using an R&D coating equipment, polyethylene glycol (PEG) polymers were applied to the coronary stent. Assessments of the polymeric-coated cardiac stent’s biocompatibility and hemocompatibility were conducted using various evaluation criteria. CAD software has been used to help with the stent’s modeling. According to the supplied catalog, the strut’s thickness and width are calculated to be 0.065 mm and its length is 18 mm. The histology of RBC in an isolated sample (polymer coated on stent) found at 2000 Rx was examined using a motic microscope. Using a UV-visible spectrophotometer set to 414 wave length, a 10µg/ml solution of RBC in distilled water was scanned at 200–500 nm to measure the UV absorption maximum. The absorbance was found to be 0.8312 nm. An FTIR analysis of RBC reveals absorptions that include bending and stretching vibrations. Peak Position was discovered at wave numbers 3661.76, 1684.62, 1547.98, 1472.07, 1278.06, and 841.98. Using SEM the surface morphology of RBC was study and it was found the measurements 6.1, 4.2, 3.3, 3.2, 3.1, and 2.2 µm in diameter with standard error 0.548584. It has been determined that PEG-coated material demonstrated significant outcomes that resulted in coronary stent that was both biocompatible and hemocompatible of polymeric-coated cardiac stent, which is a step towards altering the treatment regimen.

Experimental study of two-phase pressure-drop in horizontal return bends with ammonia

In evaporators and condensers of refrigeration and air conditioning systems, various straight tubes are joined via U-bends. These U-bends result in higher pressure drops due to flow disturbances and centrifugal effects. Accurate prediction of pressure drops in these bends is essential for reliable design and operation. This study investigates the two-phase flow pressure-drop in horizontal U-bends with ammonia under wide range of experimental conditions. Three pipes with nominal outer diameter between 22.2, 15.9, and 9.5 mm were used, each with three bend radii (R/do ratio) between 1.2 and 2.5 in horizontal configuration. Tests were conducted at saturation temperature of +10 and -15 °C, with mass flux varying between 10 and 50 kg m−2 s−1, and vapor quality between 0.1 and 0.9. The pressure-drop increased with mass flux and vapor quality while decreased with saturation temperature, pipe diameter and R/do ratio of the bend.Large tubes exhibited a greater increase in pressure drop with rising mass flux and decreasing bend ratio compared to small tubes, which showed higher absolute values and more consistent performance across the vapor quality range at both saturation temperatures. The tube diameter had a less significant effect at high saturation temperature and high mass flux, while the bend curvature ratio predominantly influenced the pressure drop performance for large diameter tubes. One correlation from the literature predicted the data well only if the vapor quality was below 0.5. For wider range of quality, the existing models in the literature were not well-suited for predicting pressure drops in ammonia U-bends.

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.

An acoustic bellows-type round window transducer for middle-ear implants

BackgroundThis study describes the development of output devices for round window middle-ear. To overcome the problems of output devices that apply sound pressure directly to the round window, an acoustic bellows-type round window transducer was implemented by combining a small bellows, acoustic tube, and balanced armature driver. MethodsThe output characteristics of the proposed acoustic bellows-type round window transducer were confirmed through bench tests and distortion measurements. To compare the vibration transmission characteristics of the proposed transducer with those of sound pressure stimulation devices, an experiment was performed using four human temporal bones. FindingsThe average output magnitude of the acoustic bellows-type round window transducer was equivalent to sound pressure levels of 92, 96, and 108 dB for frequency ranges of <1, 1–2, and > 2 kHz, respectively. The results showed that the proposed transducer delivered vibration consistently without reducing the sound pressure level due to leakage, unlike the sound pressure stimulation device. InterpretationTherefore, the acoustic bellows-type round window transducer is a more stable and suitable output device for round window middle-ear implants than a sound pressure stimulation device. It is expected to overcome the limitations of sound pressure stimulation devices and to contribute to new technical solutions in the field of round window middle-ear implants development.

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.

The Detailed Axial Compression Behavior of CFST Columns Infilled by Lightweight Concrete

The utilization of lightweight aggregate concrete (LWC) plays a major role in reducing the self-weight of CFST (concrete-filled steel tube) columns, which is reflected in the behavior of the structural system. This paper aims to investigate the characteristics of lightweight concrete-filled steel tubular (LWCFST) columns under an axial compressive load, using a total of (48) LWCFST column models. The simulated models were divided into four groups with different concrete compressive strength, length-to-diameter ratios (L/D), and diameter-to-thickness ratios (D/t). Four concrete compressive values were examined (30, 40, 50, and 60) MPa, three length-to-diameter ratios short (L/D = 3), medium (L/D = 6), and long (L/D = 9), and four diameter-to-thickness ratios (36, 31, 26, and 21). The method of nonlinear finite element analysis (NLFEA) was used to fulfill the objective of this study where results were presented as graphical plots between the compressive loading versus the axial and lateral strains along with the failure modes. In addition, the results were compared with the AISC360-16 and EC4 codes predictions to examine their applicability on the LWCFST columns where the AISC was overpredicted in most cases with higher percentages under lower (L/D) values, whereas the EC2 was underestimated in most cases with high percentages up to 28%, which become closer to the NLFEA predictions at higher (L/D) values. It has been revealed that the utilization of steel tubes significantly improves the LWCFST column’s mechanical performance, ductility, compressive strength, and toughness. Moreover, the structural behavior of the LWCFST columns and their associated failure modes was found to be highly affected by the geometrical properties of the CFST column (i.e., L/D ratio and D/t ratio) where specimens with small tube thickness show bad behavior. Finally, the utilization of high-strength concrete has a favorable performance compared to the utilization of thick steel tubes.

Late Ordovician cornulitid tubeworms from high-latitude peri-Gondwana (Sardinia and the Pyrenees) and their palaeobiogeographic significance

Seven Cornulites species, including a new one — Cornulites leonei n. sp., are described from the Upper Ordovician Portixeddu Formation (Katian, stage slices Ka2–3) of Sardinia and the Cavá (lower Katian, stage slice Ka2) and Estana (upper Katian, stage slices Ka3–4) formations of the Pyrenees. The Sardinian and Pyrenean cornulitids represent an adaptation to live in environments with high sedimentation rates and limited hard substrates availability. Their prominent annuli could have had a stabilizing function in the soft sediment that helped cornulitids to keep a favourable position in the sediment to enable suspension feeding. The known Late Ordovician cornulitid diversity in different Gondwana areas is low, usually ranging from one to three taxa, being higher (seven) in Sardinia. Like other benthic groups during the Late Ordovician, the cornulitid tubeworm faunas within the high-latitude peri-Gondwana Province indicate a certain endemism and share morphological and ecological affinities, such as a small body size and tubes with a strikingly small apical angle. Although essentially endemic, some links with cornulitids from the Late Ordovician of Scotland are revealed.

A Reconfigurable Proangiogenic Hydrogel Patch Enabling Minimally Invasive Drug Delivery.

Hydrogel is widely used for the sustained delivery of bioactive molecules that can treat various injuries, diseases, and tissue defects. However, inserting hydrogel implants without disrupting their functionality and microstructure often requires a large incision, leading to potential complications, such as infection, scarring, and pain. The gel implant is often manually rolled and inserted through a catheter for a minimally invasive delivery. However, success heavily depends on the user's skills, which can inadvertently damage the implant. To address this issue, we developed a reconfigurable hydrogel patch that can self-fold into a small tube and unfold spontaneously after implantation through a catheter. The hydrogel path was assembled by layering a drug-releasing poly(ethylene glycol) diacrylate (PEGDA) hydrogel sheet onto a PEGDA and polyethylenimine (PEI) hydrogel sheet, which rapidly swells and degrades homogeneously at controlled rates. The dynamics of the self-folding and unfolding process could be controlled by differences in the expansion ratio and elastic modulus between the two gel layers according to a mathematical model that closely matched experimental results. The unfolding process triggered a sustained release of the protein cargo. Specifically, the reconfigurable gel loaded with angiopoietin 1 significantly enhanced neovascularization, nearly doubling the vascular density compared to the control group following implantation through a tube with 15% smaller diameter than the original shape of the gel patch. This gel biopatch will be broadly useful for the minimally invasive delivery of a wide array of therapeutic molecules, potentially enhancing therapeutic outcomes.

Solvent‐free crystallization for fractionation of virgin coconut oil: Effect of process conditions on kinetics and crystal properties

AbstractThis research was aimed to conduct solvent‐free crystallization and fractionation of virgin coconut oil (VCO). This study investigated the effect of surface contact area‐to‐volume ratio and mixing conditions on crystal characteristics. Commercially available VCO samples, extracted by different methods, were analyzed for fatty acid and triacylglycerol composition using GC–MS and UPLC–ELSD. VCO extracted through enzyme and chilling–thawing cycles exhibited higher medium chain fatty acids and medium chain triacylglycerols, which was selected for crystallization studies. Isothermal crystallization of VCO at 21°C assessed the effect of scale of crystallizer tube on cooling rate using Newton's law of cooling equation. The smaller tube (20 mm diameter) with a higher surface contact area‐to‐volume ratio produced 4.1‐fold faster cooling and a higher crystallization yield (44%) compared to the 80 mm diameter tube when no agitation was applied. Whereas mixing with a magnetic stirrer produced a large number of nuclei, generating intense crystallization heat, and rendering the crystals inseparable from liquid fraction. The process of VCO crystallization was also studied for kinetics and crystal growth mechanism using the Avrami model employing angled rotation of sample tube during non‐isothermal crystallization. Angled rotary mixing produced stable crystals and significantly increased the crystallization rate (t1/2 = 26.86 min) with polyhedral or spherulitic crystal growth (n = 3.25) compared to non‐mixing condition (t1/2 = 161.87 min) with restricted linear growth (n = 1.64). DSC analysis of VCO and its fractions obtained after crystallization using the 20 mm tube with angled rotary mixing indicated shifts in their thermogram peaks, suggesting differences in triacylglycerol compositions.Practical applicationsVirgin coconut oil (VCO) is well recognized for its health‐beneficial properties, yet its application is limited due to its complex triglyceride composition. The solvent‐free crystallization method facilitates VCO fractionation into phases with different melting points without hazardous solvents. The efficacy of this process is highly dependent on temperature, cooling rate, and agitation, which affects crystal morphology and growth kinetics. This study addresses these challenges in the scarcely investigated area of VCO crystallization. The resulting fractions can be customized for specific applications based on their altered functional properties in producing baking and confectionery coatings, salad dressings, and so on. The olein fraction obtained in this study can be utilized in nutraceutical formulations targeting digestive and cognitive health, as it is reported to be rich in medium chain triglycerides. This research optimizes process conditions, suggesting an efficient method for dry‐fractionating VCO, which is significantly associated with the food and pharmaceutical industries.

Dispersion of a non-uniform solute slug in pulsatile viscoelastic fluid flow

Solute transport in pulsatile viscoelastic fluid flow is relevant in nutrient transport and drug delivery in blood flow. Previous studies have extensively analyzed the effect of the shear-thinning nature of the blood but neglected the elastic property. The present study aims to fill this lacuna by analyzing the role of blood viscoelasticity on solute transport. To accomplish this, we study solute transport for a non-uniformly distributed solute slug in the pulsatile flow of an Oldroyd-B fluid through a tube in the presence of wall absorption. We employ Gill's procedure and Aris' method of moments to compute the transport coefficients Km(t) (m≤4). We also numerically solve the species transport equation using a finite difference scheme to directly determine local solute concentration C(t,z,r). Consistent results for a non-viscoelastic fluid predict a negative convection coefficient K1 and a positive effective diffusivity K2 for realistic values of the parameters. However, the present analysis predicts positive K1 and negative K2 for small tubes due to flow reversal caused by the fluid elasticity. For high Λ1, the amplitude of oscillation for K1 and K2 exhibits scaling K1∼Λ11.5 and K2∼Λ12 indicating an enhancement in the dispersion due to fluid elasticity, where Λ1 is the dimensionless relaxation time. The analysis of the skewness and (excess) kurtosis coefficients reveals inconsistency in previous studies on Newtonian fluids. Thus, we present consistent results not only for a viscoelastic fluid but also for a Newtonian fluid subjected to a pulsatile pressure gradient. In addition, the solute dispersion is significantly influenced by the non-uniformity of a solute slug. As the radius of a slug increases, solute dispersion reduces in short and moderate times; however, at large times, it is independent of the radius of a slug.

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.

Separate effect experimental test and theoretical investigate of pressure wave propagation and pressure rising process upon SGTR accident in advanced LFRs

Steam Generator Tube Rupture accident (SGTR) accident is one of the main safety events to the industrial application of Lead-cooled Fast Reactors (LFRs). This paper presents a separate effect test facility, called Lead-bismuth Eutectic Steam generator tube rupture Test facility (LEST), for testing high-pressure subcooled water jetting into a Lead Bismuth Eutectic (LBE) pool, and analyzes experimental data of maximum initial pressure peak, dynamic pressure attenuation together with the pressure rising process upon SGTR. The experimental analyses put forward a general equation form together with a dimensionless number of the initial pressure peak associated with a high-pressure Newtonian fluid injecting into another low-pressure Newtonian fluid, and the derivation of the general equation form is specifically applied to match a further semi-empirical equation for an initial maximum pressure peak with 5–10 MPa water injection in SGTR. The attenuation curve of dynamic pressure wave in each experiment is matched, and more weakening conditions can change the pressure peak from concentrated and non-period peak group to approximate period 1.4–3.7 s pulse group. The size relationship between pipe length L and nozzle diameter D, which L/D=12, is set to divide SGTR into small wall rupture and tube shear fracture, further three stages of pressure rising are distinguished in the tube shear fracture. This work provides experimental data to help determining the severity of SGTR and assessing the consequences of this event as part of the safety case for the industrial application of LFRs.

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.

Design and theoretical analysis of broadband bend-resistant low-loss hollow-core anti-resonant fiber

With the development of modern fiber-optic communication technology, bend-resistant low-loss fiber within the S+C+L bands is essential to meeting the requirements of dense wavelength division multiplexing (DWDM) systems, and a small-tube-added multi-nested hollow-core anti-resonant fiber (SM-HC-ARF) is proposed. In conventional double-nested HC-ARF, a pair of circular tubes are tangent to both the inner and outer tubes to form a multi-nested structure. A small tube is put in the gap between the nested structure to enhance the anti-resonance effect further. The influence of fiber structural parameters on transmission characteristics is analyzed by the finite element method combined with the perfect matching layer condition. The numerical results show that, in the range of 1460–1625 nm, the bending loss and the confinement loss are less than 1.17 (at a bending radius of 8 cm) and 0.80 dB/km, respectively. Specifically, at 1550 nm, the bending loss is 0.43 dB/km, and the confinement loss is 0.33 dB/km. The broadband anti-bending low-loss SM-HC-ARF can be expected to apply in the DWDM system and other optical communication technologies.

Field stability of an Alvarez-type drift tube linear accelerator with small drift tubes

This study presents theoretical, simulation and experimental investigations of the field stability of a 7 MeV Alvarez-type drift tube linear accelerator (DTL) with small drift tubes (DTs). Although technical advances in permanent magnet quadrupoles make smaller DTs possible, resulting in higher shunt impedance, it is widely recognized that the DT-to-wall spacing must lie between ∼0.90 and ∼1.03 times a quarter wavelength (λ/4) to achieve field stability through post couplers (PCs). To enhance the shunt impedance of a DTL cavity, we decrease the outer diameter of the DTs and increase the inner diameter of the cavity, resulting in a DT-to-wall spacing of 1.16 times λ/4. A low-power experiment confirms that when the global tilt sensitivity slope is zero, the PC-to-DT distance is larger and there exists a stronger coupling between the PCs, resulting in a disturbed distribution of PC modes, where the frequencies of lower-order modes are overwhelmed by higher-order modes. The observed result is consistent with the analysis result given by the equivalent circuit theory and three-dimensional simulation. After field tuning by the trial-and-error method, the relative error of the axial electric field is within ±1.9% and the tilt sensitivity is within ±70%/MHz.

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.