Tube Height Research Articles

Enhancement of Condensation Heat Transfer Rate of the Air-Steam Mixture on a Passive Condenser System Using Annular Fins

This paper presents an experimental investigation on the enhancement of the heat transfer rate of steam condensation on the external surfaces of a vertical tube with annular fins. A cylindrical condenser tube, which is 40 mm in outer diameter and 1000 mm in length, with annular disks of uniform cross-sectional area is fabricated in the manner of ensuring perfect contact between the base surface and fins. A total of 13 annular fins of 80 mm diameter were installed along the tube height in order to increase the effective heat transfer area by 85%. Through a series of condensation tests for the air-steam mixture under natural convection conditions, the heat transfer data was measured in the pressure range of between 2 and 5 bar, and the air mass fraction from 0.3 to 0.7. The rates of heat transfer of the finned tube are compared to those that are measured on a bare tube to demonstrate the enhanced performance by extended surfaces. In addition, based on the experimental results and the characteristics of steam condensation, the applicability of finned tubes to a large condenser system with a bundle layout is evaluated.

Evaluation of interfacial shear stress in active steel tube-confined concrete columns

This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.

Compressive characteristics of damaged circular hollow section (CHS) steel columns repaired by CFRP or grout jacketing

An experimental study was conducted to evaluate the compressive behavior of damaged circular hollow section (CHS) steel columns repaired by carbon fiber-reinforced polymer (CFRP) or high-strength grout. A total of 22 specimens, including bare steel specimens, CFRP repaired specimens and grout repaired specimens were tested under axial compression loading. The design parameters are the amount of loss in wall thickness, extent of damage along tube height, and the damage angle around the circumference. Two promising retrofit techniques, external wrapping of CFRP and grouted jacket, were adopted here. The repairing efficiency was assessed in terms of the above-mentioned retrofit techniques and design parameters. A finite element (FE) analysis was also performed and analyzed with test results. The failure modes are presented together with load-shortening and load-strain behavior of specimens. The results indicate that the behavior of damaged CHS steel columns can be effectively rehabilitated by either CFRP or grout jacketing. The local buckling of the internal steel tube was either delayed by fibers or suppressed by the surrounding grout, leading to an improvement both in compressive strength and deformation capacity. It was also found that grouted jacket repair generally shows an overwhelming strength enhancement over the CFRP wrapping method except for specimens with 90° damage around circumference, which shows a delay of the restraining effect. A parametric study was eventually undertaken to fully understand the influences of design parameters on columns' compressive characteristics.

(Invited) Enhanced Self-Assembly of Crystalline, Large-Area and Periodicity-Tunable TiO2 Nanotube Arrays on Various Substrates for Technological Applications

Due to their superior physical properties, titanium dioxide (TiO2) nanotube arrays are one of the most investigated nanostructure systems in materials science until now. However, it is still a great challenge to achieve damage-free techniques to realize controllable, cost-effective and high-performance TiO2 nanotube arrays on both rigid and flexible substrates for different technological applications. In this work, we demonstrate a unique strategy to achieve self-assemble crystalline, large-area and regular TiO2 nanotube arrays on various substrates via hybrid combination of conventional semiconductor processes. Besides the usual applications of TiO2 as carrier transport layers in thin film electronic devices, we demonstrate that the periodic TiO2 nanotube arrays can show the effect of optical grating with large-area uniformity. Specifically, the fabricated nanotube geometries, such as the tube height, pitch, diameter and wall thickness, as well as the crystallinity can be reliably controlled by varying the processing conditions. More importantly, utilizing these nanotube arrays in perovskite solar cells can further enhance the optical absorption leading to the improved power conversion efficiency. In contrast to other typical template-assisted fabrication approaches, we employ the soft template here, which would enable the construction of nanotube arrays without any significant damage associated with the template removal. Furthermore, without the thermal restriction of underlying substrates, these crystalline nanotube arrays can be transferred to mechanically flexible substrates by using the simple one-step method, which can expedite these nanotubes for potential utilizations in other application domains.

12.06: Numerical analysis of stainless steel, concrete encased and carbon steel double skin tubular stub columns

ABSTRACTThe use of stainless steel as formwork for concrete columns provides several benefits for the structure, including the high corrosion resistance, durability, fire resistance, ease of maintenance and high aesthetic value. The use of composite systems in columns has been a major breakthrough in bridges and viaducts. A particular advantage of the composite columns is the reduction of cross sectional area, speed of construction, easy maintenance and material saving when compared to conventional reinforced concrete structures. These advantages are related to the idea that the columns are concrete filled eliminating the use of forms and the need for extra steel reinforcing bars. The investigated system adopts a second carbon steel tube inside the primary stainless steel tube composing the structural system made of concrete‐filled double skin composite tube columns (CFDSCT). This study aims to develop numerical models, using the finite element method and considering geometric imperfections. The structural behaviour was assessed through a nonlinear analysis and was later compared to compressive tests performed in the laboratory. After the completion of the numerical models calibration, a parametric analysis was performed to investigate the influence of parameters like the diameter, thickness and height of the stainless steel tube (outer) while its results were also compared to predictions made by traditional design equations.

Dimension‐Controllable Microtube Arrays by Dynamic Holographic Processing as 3D Yeast Culture Scaffolds for Asymmetrical Growth Regulation

Transparent microtubes can function as unique cell culture scaffolds, because the tubular 3D microenvironment they provide is very similar to the narrow space of capillaries in vivo. However, how to realize the fabrication of microtube-arrays with variable cross-section dynamically remains challenging. Here, a dynamic holographic processing method for producing high aspect ratio (≈20) microtubes with tunable outside diameter (6-16 µm) and inside diameter (1-10 µm) as yeast culture scaffolds is reported. A ring-structure Bessel beam is modulated from a typical Gaussian-distributed femtosecond laser beam by a spatial light modulator. By combining the axial scanning of the focused beam and the dynamic display of holograms, dimension-controllable microtube arrays (straight, conical, and drum-shape) are rapidly produced by two-photon polymerization. The outside and inside diameters, tube heights, and spatial arrangements are readily tuned by loading different computer-generated holograms and changing the processing parameters. The transparent microtube array as a nontrivial tool for capturing and culturing the budding yeasts reveals the significant effect of tube diameter on budding characteristics. In particular, the conical tube with the inside diameter varying from 5 to 10 µm has remarkable asymmetrical regulation on the growth trend of captured yeasts.

An experimental study on the detonability of gaseous hydrocarbon fuel–oxygen mixtures in narrow channels

This study was performed to address the detonability related to gaseous hydrocarbon fuel–oxygen mixtures (i.e., CH4–2O2, C2H6–3.5O2 and C3H8–5O2) in different ducts (36-mm circular tube and annular channel heights with 2-mm, 4.5-mm and 7-mm gaps). The results show that detonation can achieve self-sustained propagation with a steady velocity because the conditions are within the detonability in C1–C3 alkanes/oxygen mixtures; the velocity decreases as the detonation transmits into the annular channel due to increased heat and momentum losses from the wall. A modified theoretical model is proposed to predict the detonation velocity deficit for different size channels. Through a comparison with the experimental results, this model was determined to be suitable for predicting the velocity deficit in C1–C3 alkane fuel with oxygen mixtures within reasonable accuracy. Both experimental and theoretical predicted data indicate that velocity deficit is more significant in the smaller channel gap, which verifies that losses are more prominent in the narrower channel. Furthermore, the detonation cellular structure from the smoked foil was measured to analyze the propagation mechanism. The results show detonation has a single-headed spinning structure when detonability is approached. The onset of single-headed spinning detonation of CH4–2O2, C2H6–3.5O2 and C3H8–5O2 in a 36-mm circular tube occurs from p0=3–7 kPa, 4.2–5 kPa and 3.5–3.6 kPa, respectively. This suggests the pressure range of the single-headed spinning phenomenon is narrower for hydrocarbon fuels with more carbon atoms.

Enhanced Self-Assembly of Crystalline, Large-Area, and Periodicity-Tunable TiO2 Nanotube Arrays on Various Substrates.

Due to their superior physical properties, titanium dioxide (TiO2) nanotube arrays are one of the most investigated nanostructure systems in materials science until now. However, it is still a great challenge to achieve damage-free techniques to realize controllable, cost-effective, and high-performance TiO2 nanotube arrays on both rigid and flexible substrates for different technological applications. In this work, we demonstrate a unique strategy to achieve self-assemble crystalline, large-area, and regular TiO2 nanotube arrays on various substrates via hybrid combination of conventional semiconductor processes. Besides the usual applications of TiO2 as carrier transport layers in thin-film electronic devices, we demonstrate that the periodic TiO2 nanotube arrays can show the effect of optical grating with large-area uniformity. Specifically, the fabricated nanotube geometries, such as the tube height, pitch, diameter, and wall thickness, as well as the crystallinity can be reliably controlled by varying the processing conditions. More importantly, utilizing these nanotube arrays in perovskite solar cells can further enhance the optical absorption, leading to improved power conversion efficiency. In contrast to other typical template-assisted fabrication approaches, we employ a soft template here, which would enable the construction of nanotube arrays without any significant damage associated with template removal. Furthermore, without the thermal restriction of underlying substrates, these crystalline nanotube arrays can be transferred to mechanically flexible substrates by a simple one-step method, which can expedite these nanotubes for potential utilization in other application domains.

CFD simulation of the hydrodynamic behavior in an internally circulating fluidized bed reactor for producing polysilicon granules

An internally circulating fluidized bed (ICFB) reactor with a central draft tube that was used for producing polysilicon granules was studied, with the focus on the inhibition of silicon deposition on the wall. The effects of gas velocity, particle diameter and reactor configuration on the solid circulation rate (Gs) and gas bypass fraction (γDA and γAD) were studied by two-dimensional CFD simulation. Among the commonly used drag models, the Syamlal and O'Brien drag model gave the best prediction. For the best heat transfer performance and inhibition of silicon deposition on the heated wall, the optimum gas velocities for the ICFB were UD/Umf=1.0–1.7 and UA/Umf=1.5–2.3. When UD/Umf<0.65 and UA/Umf>1.75, a reverse circulation pattern appeared and γDA increased significantly. The effects of particle diameter, orifice size and the parameters of the draft tube were studied. For good fluidization in the ICFB, the position and size of the orifices, area ratio of annulus to draft tube and height of draft tube should satisfy so<0.02m2, Ho<320mm, 1.5<sA/sD<3.2 and 700<Hd<900mm, respectively.

Modeling quorum sensing trade-offs between bacterial cell density and system extension from open boundaries.

Bacterial communities undergo collective behavioural switches upon producing and sensing diffusible signal molecules; a mechanism referred to as Quorum Sensing (QS). Exemplarily, biofilm organic matrices are built concertedly by bacteria in several environments. QS scope in bacterial ecology has been debated for over 20 years. Different perspectives counterpose the role of density reporter for populations to that of local environment diffusivity probe for individual cells. Here we devise a model system where tubes of different heights contain matrix-embedded producers and sensors. These tubes allow non-limiting signal diffusion from one open end, thereby showing that population spatial extension away from an open boundary can be a main critical factor in QS. Experimental data, successfully recapitulated by a comprehensive mathematical model, demonstrate how tube height can overtake the role of producer density in triggering sensor activation. The biotic degradation of the signal is found to play a major role and to be species-specific and entirely feedback-independent.

Pressure drop-flow rate curves for single-phase steam in Combustion Engineering type steam generator U-tubes during severe accidents

Characteristic pressure drop-flow rate curves are generated for all row numbers of the OPR1000 steam generators (SGs), representative of Combustion Engineering (CE) type SGs featuring square bend U-tubes. The pressure drop-flow rate curves are applicable to severe accident natural circulations of single-phase superheated steam during high pressure station blackout sequences with failed auxiliary feedwater and dry secondary side which are closely related to the thermally induced steam generator tube rupture event. The pressure drop-flow rate curves which determine the recirculation rate through the SG tubes are dependent on the tube bundle geometry and hydraulic diameter of the tubes. The larger CE type SGs have greater variation of tube length and height as a function of row number with forward flow of steam favored in the longer and taller high row number tubes and reverse flow favored in the short low row number tubes. Friction loss, natural convection heat transfer coefficients, and temperature differentials from the primary to secondary side are dominant parameters affecting the recirculation rate. The need for correlation development for natural convection heat transfer coefficients for external flow over tube bundles currently not modeled in system codes is discussed.

Field Tests and Behaviour Analysis of Saemangeum Inner Dike Construction with Geotextile Tube Method Applied

AbstractGeotextile tubes hydraulically or mechanically filled with dredged materials have been successfully applied to hydraulic and coastal engineering in recent years (e.g. shore protection structures, sea dikes, groins, jetties, detached breakwaters). This method is becoming popular and has been widely applied in the developed countries of the world. It is economical as well as useful, and enables us to store and isolate contaminated materials obtained from harbour dredging. In this study, a numerical analysis was performed to investigate the behaviour of geotextile tubes in terms of various properties of the material, shape condition and pumping pressure. The computer program GeoCoPS was employed for this analysis. Also, field tests were conducted in order to identify the construction workability of Saemangeum inner dike when the geotextile tube method is applied. In the field tests, geotextile tubes of 62 m in length and 4.0 m in diameter were used. The field tests found that geotextile tubes, when filled, did not have the same diameter as the unfilled theoretical one, but might reach approximately 55% of the theoretical diameter. At that time, the effective height of a geotextile tube was about 2.2 m. The behaviour during and after construction was measured to confirm the construction method and workability, which ended in successful identification. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Prediction of dryout and post-dryout wall temperature at different operating parameters for once-through steam generators

A three-dimensional “unit tube” physical model is established by simplifying the once-through steam generator (OTSG) designed by B&W and a three-dimensional two-fluid three-flow-field mathematical model that takes into account the interactions between liquid droplets and other flow-fields (steam and liquid film) and the interactions between liquid droplets and the wall in liquid deficient regions is introduced. The results of a numerical simulation using the developed OSTG model conducted at different operating parameters show that the three-dimensional two-fluid three-flow-field mathematical model used in this paper can accurately predict the dryout and post-dryout wall temperature distribution of the OTSG at different operating conditions. The simulations also show that the post-dryout wall temperature decreases along the height of the heat transfer tube at low mass fluxes while gradually increases at high mass fluxes, which is opposite to the changes in wall temperature seen in post-departure from the nucleate boiling region. Furthermore, dryout occurs later as pressure increases, with a smaller soaring maximum of the wall temperature. Dryout will occur when the wall temperature gradient reaches or exceeds 250K/m as the heat flux increases.

Hydrodynamic behaviors and mixing characteristics in an internal loop airlift reactor based on CFD simulation

This work aims to systematically study hydrodynamics and mixing characteristics in an internal airlift reactor using a computational approach. A 3D transient Eulerian–Eulerian multiphase model is carried out with the standard k–ɛ turbulence model, and the results are used to simulate a virtual tracer. Parameters of importance in the design of airlift reactors, such as the mixing time, circulation time, axial dispersion number, and axial dispersion coefficient, are presented in addition to basic hydrodynamic parameters, such as gas holdup and fluid velocities based on full 3D simulation. The effects of the superficial gas velocity, the downcomer diameter (Ar/Ad), Hl/dr ratio, and scaling up were investigated. The key observations were as follows. With increasing superficial gas velocity, the dispersion number increases, leading to more mixing. Increasing the downcomer area leads to lower dispersion number in the riser and consequently a more plug-flow-like behavior. A greater draft tube height causes a lower dispersion number but a higher dispersion coefficient due to a greater draft tube effect. Using a larger reactor with geometric similarity provides a higher dispersion number with more mixing because of reduced wall effect. In addition, correlations were proposed for gas holdup, circulation velocity, and dispersion coefficients for riser and downcomer.

SU‐F‐I‐72: Evaluation of the Ancillary Lead Shielding for Optimizing Radiation Protection in the Interventional Radiology Department

Purpose:The rising complexity of interventional fluoroscopic procedures has resulted in an increase of occupational radiation exposures in the interventional radiology (IR) department. This study assessed the impact of ancillary shielding on optimizing radiation protection for the IR staff.Methods:Scattered radiation measurements were performed in two IR suites equipped with Axiom Artis systems (Siemens Healthcare, Erlangen, Germany) installed in 2006 and 2010. Both rooms had suspended ceiling‐mounted lead‐acrylic shields of 75×60 cm (Mavig, Munich, Germany) with lead equivalency of 0.5 mm, and under‐table drapes of 70×116 cm and 65×70 cm in the newer and the older room respectively. The larger skirt can be wrapped around the table's corner and in addition the newer suite had two upper shields of 25×55 cm and 25×35 cm. The patient was simulated by 30 cm of acrylic, air kerma rate (AKR) was measured with the 180cc ionization chamber (AccuPro Radcal Corporation, Monrovia, CA, USA) at different positions. The ancillary shields, x‐ray tube, image detector, and table height were adjusted by the IR radiologist to simulate various clinical setups. The same exposure parameters were used for all acquisitions. AKR measurements were made at different positions relative to the operator.Results:The AKR measurements demonstrated 91–99% x‐ray attenuation by the drapes in both suites. The smaller size of the under‐table skirt and absence of the side‐drapes in the older room resulted in a 20–50 fold increase of scattered radiation to the operator. The mobile suspended lead‐acrylic shield reduced AKR by 90–94% measured at 150–170 cm height. The recommendations were made to replace the smaller under‐table skirt and to use the ceiling‐mounted shields for all IR procedures.Conclusion:The ancillary shielding may significantly affect radiation exposure to the IR staff. The use of suspended ceiling‐mounted shields is especially important for reduction of interventional radiologists’ cranial radiation.

Theoretical elements for the design of a small scale Linear Fresnel Reflector: Frontal and lateral views

This paper addresses the problem of the mathematical design of a Linear Fresnel Reflector, specifically the design of a reflector concentrator with flat mirrors and a single absorber tube. The mathematical aspects of the design, i.e., the number, width and position of the primary mirrors and the height, length and relative position of the single absorber tube, are analysed. The optimization of the relative position with respect to the primary reflectors and the size of the single absorber tube are both addressed, further analysing up to 12 different configurations. To do so, both the frontal and lateral view of the structure are taken into account. The lateral optical performance factor analysed here, has been overlooked until now, as it may be insignificant in large-scale concentrators. It is shown in this paper that it is a key aspect in medium- and small-scale concentrators, the most common in applications in the Household Sector like, for example, micro-cogeneration. Finally, a number of numerical simulations performed in a custom-designed program compiled using Mathematica® is presented. At the time of this writing, a prototype is being built at CIFP in La Felguera, Asturias, Spain.

The fertile physics of chemical gardens

Many a child has enjoyed watching the gardens grow; many a physicist has puzzled over the transformation of self-organized, nonequilibrium patterns into permanent structures.

New formulas for calculating mode II fracture energy of several typologies of GRP pipes under impact

Abstract The authors suggest a simple monomial formula to determine the delamination starting energy U0 under impact in GRP pipes with sand filled layer. By means of analytical procedures, deducted from the Mechanically Contaminated Layer Theory, a new equation in mode II of fracture, unique for all types and different manufacturers is developed. The shape of this equation adjusts in a 98.96% of the observed law and mainly depends on the square of the height of the tube and its resistance to internal hydraulic pressure, achieving numerical errors, using a general theoretical coefficient, of less than 10% for pipes of very different kinds, that can be improved using empirical coefficients customized for each manufacturer. Thus, it facilitates technicians with a practical design tool against the invisible effects of a blow and warrants seriously rethinking the current design criteria that does not take into account the brittleness of an impact.

Effect of Surface Active Pollutants on the Rate of Mass Transfer Controlled Corrosion of Reactors Used in Wastewater Treatment

The diffusion controlled corrosion of a cooling system composed of an array of vertical tubes attached to the inner wall of a fixed bed reactor containing plastic Raschig rings was studied by a rapid technique which involves the diffusion controlled dissolution of copper in acidified dichromate. Variables studied were solution velocity, Raschig rings diameter, vertical tube height and the presence of surface active agent. The present data were correlated by a dimensionless equation. The presence of surface active agents decreased the rate of mass transfer by an amount ranging from 7.5 to 36.2 depending on the operating conditions. Implications of the present results for the design and operation of built-in cooling systems of fixed bed reactors was highlighted. Also the possible use of the obtained equation in calculating the rate of heat transfer by analogy was discussed.

Numerical and field test verifications for the deformation behavior of geotextile tubes considering 1D and areal strain

Two-dimensional analytical and numerical solutions for determining the geometric dimensions and stresses of geotextile tubes are reviewed. Conventional one-dimensional (1D) approximation of the average drop in height (consolidated height) of geotextile tubes was also reviewed in this study. Densification modeling of the fill material based on areal-strain analysis is introduced. Leshchinky et al.'s approximation method considers only the vertical movement of the densifying material in the analysis. The areal-strain method offers an alternative analysis approach wherein both the vertical and lateral movements of the densifying fill material are considered. The geotextile tube is assumed to be resting on a rigid horizontal foundation and analyses for both filling and densified stages treats the internal material as liquid in order to apply normal pressure to the tube. Parametric cases for the densification of geotextile tube fill are presented. Results show that the degree of tube height reduction decreases as the density of the slurry fill is increased. Large-scale tests have been conducted on composite geotextile tubes made of outer woven and inner non-woven polyester (PET) material. The tubes were 10 m and 25 m long having theoretical diameters of 3.0 m and 5.0 m, respectively. The validity of the solution for densification analysis was demonstrated by comparing the numerical results to those of the field test. The agreement between the numerical results and field measurement data is fairly acceptable.