Increasing Tube Diameter Research Articles

Small Particle Driven Chain Disentanglements in Polymer Nanocomposites.

Using neutron spin-echo spectroscopy, x-ray photon correlation spectroscopy, and bulk rheology, we studied the effect of particle size on the single-chain dynamics, particle mobility, and bulk viscosity in athermal polyethylene oxide-gold nanoparticle composites. The results reveal a ≈25% increase in the reptation tube diameter with the addition of nanoparticles smaller than the entanglement mesh size (≈5 nm), at a volume fraction of 20%. The tube diameter remains unchanged in the composite with larger (20nm) nanoparticles at the same loading. In both cases, the Rouse dynamics is insensitive to particle size. These results provide a direct experimental observation of particle-size-driven disentanglements that can cause non-Einstein-like viscosity trends often observed in polymer nanocomposites.

Characterization of basket-forceps-type micro-flow-sensor for breathing measurements in small airway

We previously proposed a basket-forceps-type flow sensor, in which a flexible thermal flow sensor is mounted onto basket forceps to fix the flow sensor onto the inside surface of the airway. The basket-forceps-type flow sensor has an asymmetrical structure to prevent reciprocating airflow; thus, we investigated the characteristics of the basket-forceps-type flow sensor under both expired- and inspired-airflow conditions in this study. The thermal flow sensor was fabricated on a flexible polyimide film and mounted onto a guide tube of a basket-forceps. Two heaters and their electrical wiring patterns were designed to produce symmetric heat distribution over the heaters. The effects of the basket structure and guide tube on flow-rate measurement were experimentally evaluated, and it was confirmed that they did not affect sensor output. Conversely, sensor output decreased with the increase in tube diameter due to the reduction in the average flow velocity with the diameter increase. Thus, we carried out a procedure to construct a calibration curve under an arbitrary tube diameter. Finally, we applied the basket-forceps-type flow sensor in an animal experiment in which it successfully detected the breathing properties in the airway of a rat.

Healing of a carbon-vacancy defect in silicon carbide nanotubes by CO molecules: A DFT study

DFT calculations are performed to investigate the healing process of C-vacancy defective silicon carbide nanotubes (SiCNTs) by CO molecules. The healing process consists of the CO-vacancy recombination, followed by extra O removal by another CO molecule. It is found that the removal of the extra O atom on SiCNTs is the rate-limiting step, for which the energy barrier decreases with an increase of tube diameter. Nevertheless, the healing of SiCNTs is nearly independent on the tube chirality. Our results can be useful not only in the purification of SiCNTs, as well as in the removal of CO gas.

APPLICATION OF ENTROPY GENERATION MINIMIZATION FOR OPTIMIZING THE GEOMETRY OF A DOUBLE-TUBE HEAT EXCHANGER

The paper presents an analysis of entropy generation for a double-tube heat exchanger with water as heat transferring fluids. Four heat exchanger configurations were considered: with the heating fluid in the inner and outer tubes, and with parallel and counter flows. The aim of the analysis was to determine the tube inner [inner tube] diameter for which entropy generation is minimum. The entropy generation resulting from heat flow and from resistance to flow (pressure losses) of heat transferring fluids were taken into account. The minimum of entropy generation as a function of the inner tube diameter was found for two cases: for the counter and parallel flows when the cold fluid flows through the inner tube and the hot fluid passes through the space between the tubes. For two other cases of the counter and parallel flows when the hot fluid flows through the inner tube and the cold fluid passes through the space between the tubes, entropy generation is approximately linearly decreasing with the increase in the inner tube diameter, and there is no entropy generation extremum (minimum) in the range of dimensions analyzed in the study.

Critical heat flux in helical coils at low pressure

The work presents the study on flow boiling crisis in helical coils at low pressure with water as working medium. Published correlations of critical heat flux in helical coils are collated. The characteristics of boiling crisis in helical coils are studied. The experiments are performed with six helical coils made of SS 304 tubes having inner diameters varying from 6 to 10mm. The coil diameter to the tube diameter ratio ranges from 14 to 58. The critical heat flux data are collected in complete saturated region for the quality range of 0–1. The wall temperature distribution is measured in the axial direction using infrared thermal imaging technique. The results concluded that, the wall temperature in inner half surface is higher than outer half surface of helical coils. Increase in mass flux increases the critical heat flux. Critical heat flux decreases with increase in quality. For the same quality, the critical heat flux decreases with increase in tube diameter and coil diameter. In a high quality region, the critical heat flux in helical coils is higher than vertical straight tubes. A correlation is suggested for critical heat flux in helical coils.

Rubber pad tube straining as a new severe plastic deformation method for thin-walled cylindrical tubes

A novel severe plastic deformation technique entitled rubber pad tube straining is proposed suitable for manufacturing of high-strength ultrafine-grained and nanostructured thin-walled cylindrical tubes. A punch with a convex portion in the middle is pressed down into a tube constrained with a hollow cylindrical rubber supported by a rigid cylinder. Tube diameter increases and decreases incrementally when the punch is pressed down, and the rubber pressure pressed back the tube diameter to its initial size. This process was performed on a commercially pure aluminum tube. Finite element results revealed that the equivalent plastic strain of about 1 could be reached at the end of the first cycle of rubber pad tube straining while having a good strain homogeneity along the thickness and length. Experimental results showed that the yield and ultimate strengths were increased to about 172 and 182 MPa from the initial values of about 80 and 128 MPa, respectively. Also, the hardness was increased to ∼55 HV from ∼44 HV.

Boiling pressure drop and local heat transfer distribution of water in horizontal straight tubes at low pressure

The objective of the present work is to investigate the heat transfer and pressure drop in flow boiling at low pressure with water as the working medium. The effect of pipe diameter, heat flux and mass flux on boiling pressure drop and local heat transfer coefficient is studied. In the present work, the available correlations are revisited for low pressure flow boiling. Comparison of local heat transfer coefficient with the existing correlation is carried out to identify an appropriate correlation which performs well in complete flow boiling range (subcooled regions and saturated regions) for water at low system pressure.Experiments are performed with eight test sections made of thin walled stainless steel (SS 304) tubes having inner diameters from 5.5 mm to 12 mm and length varying from 550 mm to 1000 mm. The system pressure is varying form 1 bar to 3 bar. No change in slope of heat transfer curve is found for subcooled regions. Heat transfer in all the three regions of subcooled boiling namely partial subcooled boiling, fully developed subcooled and net vapour generation are predicted by a single correlation. Tube diameter has no effect on boiling heat transfer distribution. However, tube diameter affects two phase pressure drop. Increase in mass flux increases the convective heat transfer coefficient. However, mass flux has no influence on subcooled and nucleate boiling heat transfer coefficient. Heat flux increases the boiling heat transfer coefficient. Increase in tube diameter and mass flux decreases the two-phase pressure drop. Most of all the correlations in the subcooled region predict heat transfer coefficient with reasonable accuracy. Kandlikar and Shah correlations perform well in the low pressure saturated boiling i.e. nucleate and convective. None of the available two-phase pressure drop correlations are able to predict the pressure drop in a low pressure system. A correlation is developed to predict two-phase pressure drop in low pressure flow boiling system with a reasonably good accuracy.

Research on variation of static contact angle in incomplete wetting system and modeling method

The solid-liquid contact angle which reflects the wettability of solid-liquid system is determined by the physical nature of solid-liquid medium and environmental factors. Through experiments we discovered that the value of contact angle in capillary is generally greater than 0° and multivalued. In addition, the experiments show that as the tube diameter increases, the equivalent height of liquid meniscus increases; as the liquid column height increases, the equivalent height of liquid meniscus decreases. In order to build the solid-liquid static contact angle model of incomplete wetting system, we established the equivalent height function with the capillary diameter as the independent variable. Furthermore, the contact angle model was constructed based on the Jurin formula. The experiments indicated that the model was coincident with the experimental data, what is more, the forecast errors of the contact angle were less than 3%. The model had higher prediction precision compared with that of Jurin or Rayleigh formula. Meanwhile, the reasonability of the modeling method and the practicability of the model are also verified by the paper.

Analysis on Heat Transfer Characteristics of Constant‐Temperature Heat Pipe in Waste Heat Utilization for Semi‐Coke

In the coal chemical industry, an internal heating retort furnace is applied to the processing of low‐temperature coal pyrolysis so as to produce semi‐coke. Because the cooling water is used to reduce the temperature of semi‐coke from 500 °C to 60 °C, the waste heat carried by the semi‐coke is released. Meanwhile, the waste water of higher temperature involved with the hazardous substances is discharged into rivers or lakes, causing serious environmental pollution. In the present work, a constant temperature heat pipe is used to recover the waste heat. An iterative method is adopted to numerically solve the thermal resistances and the overall heat transfer coefficients. Results show that the conductivity thermal resistance decreases as the tube diameter increases. In the heating section, the main factors affecting the heat transfer are the thermal resistances of both the radiation heat transfer and the convective heat transfer. As the pressure climbs, the thermal resistance of radiation heat transfer increases, while the thermal resistance of convective heat transfer decreases. In addition, the overall heat transfer coefficients increase with the pressure. The heat transfer efficiency of the heat pipe is about 30%, and a higher economic benefit can be obtained.

Lattice Boltzmann Simulation of Healthy and Defective Red Blood Cell Settling in Blood Plasma.

In this paper, an attempt has been made to study sedimentation of a red blood cell (RBC) in a plasma-filled tube numerically. Such behaviors are studied for a healthy and a defective cell which might be created due to human diseases, such as diabetes, sickle-cell anemia, and hereditary spherocytosis. Flow-induced deformation of RBC is obtained using finite-element method (FEM), while flow and fluid-membrane interaction are handled using lattice Boltzmann (LB) and immersed boundary methods (IBMs), respectively. The effects of RBC properties as well as its geometry and orientation on its sedimentation rate are investigated and discussed. The results show that decreasing frontal area of an RBC and/or increasing tube diameter results in a faster settling. Comparison of healthy and diabetic cells reveals that less cell deformability leads to slower settling. The simulation results show that the sicklelike and spherelike RBCs have lower settling velocity as compared with a biconcave discoid cell.

Diameter monodispersity of imogolite-like nanotube: a density functional theory study

The diameter monodispersity and the surface charge distribution of three imogolite-like nanotubes (not substituted (IMO), substituted by NH2 (IMO-NH2), substituted by F (IMO-F) are investigated using self-consistent periodic density functional theory, and the phenomenon of the monodispersity is explained qualitatively in terms of bond length. We assume that the axial length of the nanotube is constant and confirm it; the energetic minimum axial lengths of the three nanotubes increase in the sequence IMO_NH2 IMO IMO_F, and are respectively 8.61, 8.62 and 8.66 . Then the energies for different nanotubes and lamellar structures are calculated. A series of strain energy curves of IMO, IMO_NH2 and IMO_F are plotted based on calculations, and the results show that the energetic minimum diameters of these three nanotubes increase in the sequence of IMO IMO_NH2 IMO_F, and are respectively N= 9, 10 and 11. In order to explain the diameter monodispersity, we have calculated the bond lengths of SiO, AlO and AlOH three nanotubes and plotted the curves of length against diameter. Results show that the monodispersity can be attributed to the interaction between the energy increase resulting from the stretching of the SiO, AlO bonds in the inner wall, and the energy decreases caused by the shortening of the AlOH bond in the outer wall. In a word, with the increase of tube diameter, the SiO and AlO bonds increase while the AlOH bond decreases monotonically. Additionally, we have also calculated the Mulliken charge distributions of the three nanotubes with different diameter and analysed their surface charges. On this basis, we summarize the effect of diameter on surface charge. Results show that the main positive charges are accumulating on the outer surface while the negative charges are located on the inner region, and the outer surface charge increases gradually with the increase of the diameter of the nanotubes. The study indicates that the internal surface functional group has an effect on the axial length, diameter and surface charge of the imogolite-like nanotubes. We can control the nanotube diameter and surface charge distribution by changing different functional substitutes in the inner surface; it is significant in the molecular design and application of imogolite-like materials.

Experimental investigation on heat transfer and pressure drop of conical coil heat exchanger

The heat transfer and pressure drop analysis of conical coil heat exchanger with various tube diameters, fluid flow rates, and cone angles is presented in this paper. Fifteen coils of cone angles 180? (horizontal spiral), 135?, 90?, 45?, and 0? (vertical helical) are fabricated and analysed with, same average coil diameter, and tube length, with three different tube diameters. The experimentation is carried out with hot and cold water of flow rate 10 to 100 L per hour (Reynolds range 500 to 5000), and 30 to 90 L per hour, respectively. The temperatures and pressure drop across the heat exchanger are recorded at different mass flow rates of cold and hot fluid. The various parameters: heat transfer coefficient, Nusselt number, effectiveness, and friction factor, are estimated using the temperature, mass flow rate, and pressure drop across the heat exchanger. The analysis indicates that, Nusselt number and friction factor are function of flow rate, tube diameter, cone angle, and curvature ratio. Increase in tube side flow rate increases Nusselt number, whereas it reduces with increase in shell side flow rate. Increase in cone angle and tube diameter, reduces Nusselt number. The effects of cone angle, tube diameter, and fluid flow rates on heat transfer and pressure drop characteristics are detailed in this paper. The empirical correlations are proposed to bring out the physics of the thermal aspects of the conical coil heat exchangers.

Fabrication and Characterization of TiO<sub>2</sub> Nanotubes for Dye-Sensitized Solar Cells

TiO2nanotubes were successfully synthesized by anodization method of Ti foils. The electrolyte was composed of ethylene glycol (EG), ammonium fluoride (0.3%wt NH4F) and de-ionized water (2% vol H2O). A constant DC power supply of 50 V was used during anodization with anodizing times of 1 hour, 2 hours, 4 hours and 6 hours. The samples were annealed at 450 °C for 2 hours. The TiO2nanotubes were studied by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Structural analysis revealed the presence of pure Ti, and the crystalline anatase phase due to transformation of amorphous TiO2after annealing. The morphology of TiO2nanotube sizes showed an increase in tube diameter with anodizing time from approximately 50 nm to 200 nm. However, the efficiency of dye-sensitized solar cells increased with anodizing times up to a maximum of 5.74 % for anodizing time of 4 hours.

O41] Missing aspects in the structural phases of TMB4 tetraborides (TM = Cr and W): First-principles calculations and experimental verifications

The structural and electronic properties of nanotubes based on C2N sheet known as nitrogenated holey graphene are investigated using density functional theory. The cohesive and strain energies, electronic band structures, total and partial density of states of the armchair and zigzag nanotubes constructed by rolling up nitrogenated holey graphene are calculated. The calculated cohesive energies indicate that the zigzag nitrogenated holey nanotubes are more stable than the armchair ones. The energetic stability of the considered nanotubes increases with increasing tube diameter. It is found that both armchair and zigzag nitrogenated holey nanotubes show semiconducting properties similar to nitrogenated holey graphene sheet. The semiconducting properties of nitrogenated holey nanotubes are dependent on the tube size and chirality. The results provide new insight into nanomaterials for use in emerging nanoelectronic devices.

Properties of armchair ZnTe nanotubes: A density functional study

Using density functional theory we present the structural and electrical properties of various armchair ZnTe nanotubes. The structural and electrical properties studied include wall thickness, binding energy, curvature energy, band gap, work function, charge transfer etc. Curvature energy calculations show that the all the nanotubes follow classical elasticity theory. The study further reveals that the wall thickness, band gap as well as work function decreases with the increase of tube diameter. We believe that the results of this study will play a significant role in developing suitable band gap material for technological applications and for designing desirable field emission devices.

Molecular dynamics analysis on tensile properties of carbon nanotubes with different cracks

Molecular dynamics simulation is employed for the axial tension of single-walled carbon nanotubes (SWCNTs) with different cracks. The cracks of SWCNTs in this study actually are the crack-like defects. AIREBO potential is used to simulate the interactions among carbon atoms. The effects of the crack length, temperature, strain rate and tube diameter on the mechanical properties of SWCNTs are studied. It is found that the failure stress and failure strain decrease with the increase of crack length. And the results show that the failure stress and failure strain are related to the applied strain rate and affected by temperature especially by lower temperature. It is also revealed that the failure stress increases with the increase in tube diameter. The deformation behaviours of SWCNTs are also obtained.

An investigation on the falling film thickness of sheet flow over a completely wetted horizontal round tube surface

An investigation was performed to analyze the liquid film distributions of sheet flow on the surface of a horizontal round tube in a falling film evaporator using the commercial computational fluid dynamic code Fluent 6.3.26. A two-dimensional multi-phase flow model was developed under adiabatic condition. The temporal variation of flowing process of sheet flow and the steady film thickness distribution in the circumferential direction were analyzed in detail. The main objective has focused on the effects of multiple factors on the film thickness distribution. It was found that the whole process of liquid film flowing along the horizontal tube surface includes the transient sub-process and steady-state sub-process, and the former can be divided into five stages to be analyzed. The obviously asymmetric distribution of film thickness, which is contradictory to the Nusselt theory, is captured by the simulation results. Multiple factors have effects on the film thickness distribution. The film thickness increases with the increase in film Reynolds number. The big inter-tube spacing is capable of inducing high momentum and increasing the impact velocity of liquid film on the top of the tube, which results in the thinner distribution of liquid film layer around the perimeter of the horizontal tube. The film thickness becomes thinner as tube diameter increases. The effect of tube diameter is minor and the further increment of tube diameter shows few values to the improvement of heat and mass transfer.

Investigation on thermal analysis of conical coil heat exchanger

The experimental investigation on thermal analysis of conical coil heat exchanger is presented in this paper. Fifteen conical coils of different cone angles (0° (helical), 45°, 90°, 135°, 180° (spiral)), with three different tube sizes (ID×OD, 8×10, 10×12 and 12×15) are fabricated and analysed with, same average coil diameter (Dm=200mm) and tube length (L=3m). The experimentation is carried out with hot and cold water of flow rate 10–100lph (Re – 500 to 5000) and 30–90lph respectively. The observations recorded were leads to analysis the heat exchanger for heat transfer and pressure drop characteristics at different flow rate of cold and hot fluid. The various parameters (heat transfer coefficient (hi), Nusselt number (Nu) effectiveness (ε) and friction factor (f)) are estimated for the heat exchanger. The analysis indicates that, Nu and f are the functions of flow rates, tube diameter, curvature ratio and cone angle. Nu increase with increase in tube side flow rate whereas it reduces with increase in shell side flow rate, increase in cone angle and increase in tube diameter. The effects of cone angle, tube diameter and fluid flow rates on heat transfer and pressure drop characteristics are detailed in this paper. The empirical correlations are proposed to bring out the physics of the thermal aspects of the conical coil heat exchangers.

Influence of Inner Steel Tube Diameter on Compressive Behavior of Square FRP-HSC-Steel Double-Skin Tubular Columns

FRP-concrete-steel double-skin tubular columns (DSTCs) are a new form composite column system that effectively combines the advantages of the constituent materials. The performance of this column system has been experimentally investigated in a number of recent studies. However, apart from a single study reported on square DSTCs, all of the existing studies have been concerned with DSTCs with circular external tubes. This paper reports on part of an ongoing experimental program at the University of Adelaide on FRP-concrete-steel composite columns. The results from 12 square hollow and concrete-filled DSTCs and six companion hollow concrete-filled FRP tubes (H-CFFTs) that were tested under axial compression are presented. Results of the experimental study indicate that hollow DSTCs with larger inner steel tube diameters develop similar ultimate axial stresses to but significantly larger axial strains than companion DSTCs with smaller inner steel tubes. The results also show that, in concrete-filled DSTCs with similar Ds/ts ratios, an increase in the steel tube diameter leads to an increase in both axial stress and strain of concrete. It was observed that H-CFFTs perform significantly worse than both hollow and filled DSTCs under axial compression, and their behavior further degrades with an increase in the diameter of their inner voids.

The impact of nest tube dimensions on reproduction parameters in a cavity nesting solitary bee, Osmia bicornis (Hymenoptera: Megachilidae)

Recent declines of bee populations have led to great interest in preserving bee species and fuel efforts to develop solitary species for pollination purposes. Xylophilous solitary bees can be easily reared in artificial nests tubes for commercial agricultural as well as wild plant pollination. The impact of the dimensions of these artificial nest tubes on reproduction parameters was studied in the red mason bee, Osmia bicornis (L.), in a long-term study. Increasing tube diameter positively affected both progeny sex ratio and body size. Sex ratio, but not progeny body mass, was negatively affected by short tube length. Building costs rose with increasing diameter accompanied by deteriorated efficiency of tube space utilization. Although female bees used a wide spectrum of nest dimensions, artificial nest tubes of 8–10 mm internal diameter and a length of at least 150 mm were optimal.