Non-uniform Diameter Research Articles

Experiments on Enhanced Heat Transfer of Self-Exciting Mode Oscillating-Flow Heat Pipe with Non-Uniform Structure

Experiments were performed on a closed loop self-exciting mode oscillating flow heat pipe (SEMOS HP) with uniform and non-uniform structures under the same tested conditions. The heat transfer characteristics are analyzed by comparing the temperature of wall of the heat pipe and output power when the heat input of the electric heating board and heating position are changed. The result shows that the heat transfer rate could be improved by using a non-uniform structure under low or middle heat input, and it gives the highest heat transfer performance when the non-uniform diameter section is at the bottom of the heat pipe and the heating source located below the non-uniform section.

Natural convection heat transfer of nanofluids in a vertical cavity: Effects of non-uniform particle diameter and temperature on thermal conductivity

This paper analyzes the heat transfer and fluid flow of natural convection in a cavity filled with Al 2O 3/water nanofluid that operates under differentially heated walls. The Navier–Stokes and energy equations are solved numerically, coupling Xu’s model ( Xu et al., 2006) for calculating the effective thermal conductivity and Jang’s model ( Jang et al., 2007) for determining the effective dynamic viscosity, with the slip mechanism in nanofluids. The heat transfer rates are examined for parameters of non-uniform nanoparticle size, mean nanoparticle diameter, nanoparticle volume fraction, Prandtl number, and Grashof number. Enhanced and mitigated heat transfer effects due to the presence of nanoparticles are identified and highlighted. Based on these insights, we determine the impact of fluid temperature on the heat transfer of nanofluids. Decreasing the Prandtl number results in amplifying the effects of nanoparticles due to increased effective thermal diffusivity. The results highlight the range where the heat transfer uncertainties can be affected by the size of the nanoparticles.

Effect of Length Ratios on Heat Transfer Characteristics of Closed-Loop Oscillating Heat Pipe with Non-Uniform Diameter

Problem statement: Closed-loop oscillating heat pipe is a high performance heat exchanger especially as this heat exchanger has one direction flow of working fluid inside tube. Approach: This research studies the effect of length ratios on heat transfer characteristic of Closed Loop Oscillating Heat Pipe with Non-Uniform Diameter (CLOHP/NUD). The 2.03 and 1.06 mm inner diameter of capillary tube were alternated connection and bent into 16 turns and both ends were connected to form of loop. Length ratio of 3, 1, 0.33 and 0.2 were studied. Evaporator, adiabatic and condenser length were 100 mm. R123, ethanol and water were used as the working fluid and filling ratio 50% by total inner volume of CLOHP/NUD was used. The evaporator and condenser temperatures were controlled at 100 and 20 °C CLOHP/NUD operated at vertical plane. Results: It was found that, the CLOHP/NUD transferred higher heat than the conventional Closed Loop Oscillating Heat Pipe (CLOHP) with the same heat transfer area because the working fluid flowed in only one direction. Working fluid moved to condenser section in larger inner diameter and returned to evaporator section in smaller inner diameter. The heat flux of the CLOHP/NUD with R123 as working fluid increased from 15.49-20.85 kW m-2 when length ratio decreased from 1-0.2, respectively. This is due to the head loss from the sudden enlargement resulted in well circulation of working fluid. Furthermore, higher heat flux was obtained by using water as working fluid. Conclusion: The heat transfer performance of CLOHP/NUD can be improved if one directional circulation of working fluid can be induced.

The Effect of Fiber Diameter Distribution on the Elasticity of a Fiber Mass

A random mass of loose fibers interacting by fiber-fiber contact is considered. As proposed in a previous paper, the elastic response is modeled based on the statistical mechanics of bending and torsion of fiber segments between fiber-fiber contact points. Presently we show how the statistical approach can be used to account for a distribution of fiber diameters rather than just a single diameter. The resulting expression has the same form and the same set of parameters as its single-diameter counterpart, except for two dimensionless reduction factors, which depend on the fiber diameter distribution only and reduce to unity for monodisperse fibers. Uniaxial compressibility experiments are performed on several materials with different bimodal fiber diameter distributions and are compared to model predictions. Even though no additional parameters were introduced to model the effect of mixed fiber diameters, the behavior is accurately predicted. Notably, the effect of the nonuniform fiber diameter is strong: A mixture of two fiber diameters differing by a factor of 2 can reduce the response by an order of magnitude, compared to the case of uniform diameter.

Granular phase change materials for thermal energy storage: Experiments and numerical simulations

The present paper reports on the utilization of granular phase change composites (GPCC) of small particle diameter (1–3 mm) in latent heat thermal energy storage (LHTES) systems. The phase changing parameters (phase change temperature, latent heat, and energy storage capacity) of GPCC have been determined using differential scanning calorimeter (DSC) and temperature-history methods. Further analysis of measurement results has been conducted to describe the evolution of latent heat with temperature during phase change in terms of liquid fraction–temperature relationships. Charging and discharging packed bed column experiments have been also carried out for different operating conditions to analyze the potential of GPCC for packed bed thermal energy storage. The present column results clearly demonstrate the dependence of temperature variation along the packed bed and the overall performance of the storage unit on the phase change characteristics of GPCC. Small and non-uniform particles diameters of GPCC and heterogeneity of the bed material complicate the phenomena of heat transfer and evolution of latent heat in the packed bed. Mathematical modeling of the packed bed that considers the GPCC and air as two separate phases with inter-phase heat transfer is presented. Comparisons between experimental and numerical results are used to evaluate the sensitivity of numerical simulations to different model parameters.

Recovery of used cork stoppers

Cork is a natural cellular material. As fabricated cork stoppers for wine bottles are cylindrical with a uniform cross-sectional diameter. Upon removal from a bottle, the stopper shows a smaller and slightly non-uniform diameter. If a used cork stopper is immersed in water or water vapour at a sufficiently high temperature, the original dimensions can be recovered in a time interval of a few minutes. The kinetics of dimensional recovery in air and water (liquid and vapour) at different temperatures were experimentally determined. Water absorption is determinant of a fast recovery rate. A simple viscoelastic model is used to explain the experimental results. Since the mechanical properties are also restored, the stopper can be re-used, provided the damage due to the cork-screw used to remove the stopper is confined to its bulk.

Winter Wheat Blends (Mixtures) Produce a Yield Advantage in North Carolina

Seed mixtures, or blends, of small grain cultivars are unknown in eastern U.S. wheat production, where numerous diseases and abiotic stresses often reduce yield and quality. In 2004–2005 and 2005–2006, a field experiment was conducted at Kinston, Plymouth, and Salisbury, NC, to compare performance of eight soft red winter wheat (Triticum aestivum L.) cultivars having a range of maturities with that of 13 blends, each consisting of equal proportions of two or three of the cultivars. The blends were composed to have complementary disease resistance traits. Disease pressure was at most moderate in any environment. Blends significantly outyielded the means of their respective components (midcomponents) in Plymouth in 2005 (P = 0.042) and across all environments (P = 0.039), with a mean overall blend advantage of 0.13 Mg ha−1. Averaged across environments, two blends significantly outyielded their midcomponents (P ≤ 0.011). Yield stability of blends exceeded that of pure cultivars by the stability variance model and principal component analysis. In general, blends did not differ significantly from midcomponents for test weight (P = 0.37), protein content (P = 0.10), hardness (P = 0.68), or falling number (sprouting tolerance, P = 0.89), but seed diameter nonuniformity of blends exceeded that of midcomponents (P = 0.0002). Wheat blends may offer a small yield advantage to North Carolina growers even in the absence of severe disease.

In vitro maturation--n vitro fertilization--embryo transfer--frozen-thawed of human oocytes

To investigate the influence of different cycles, ovarian follicle size and IVM culture media on the number of retrieved immature oocytes, maturation rate, fertilization rate, embryo quality and implantation rate, pregnancy rate, delivery rate, survival and development of frozen-thawed embryos from IVM. The oocytes were obtained by follicular aspiration from 19 women undergoing oocyte retrieval for in vitro maturation due to the possible risk of ovarian hyperstimulation in IVF-ET program. One patient was in natural cycle, four patients were in ovulation induction cycles with gonadotropine and fourteen patients is controlled ovarian stimulated cycles. All the oocytes retrieved from follicles with 10.0 - 13.5 mm in maximumdiameter were allowed to culture in medium M-199 (TCM 199) or HTF supplemented with other substance. When there were nonuniform diameters of follicles and the diameter of largest oocyte exceeded 12 mm, the retrieval rate of oocytes, fertilization rate, and the number of high-quality embryos decreased. The high-quality embryos formation rate was higher for the oocytes cultured in TCM 199 medium than in HTF medium (P<0.01). After being frozen-thawed, the IVM embryos could achieve the same outcome when compared with the conventional IVF treatment. In addition, the offspring were healthy. When the nonuniform diameters of follicles and the diameter of largest oocyte exceeds 12 mm,the retrieval rate of oocytes, fertilization rate, and the number of high-quality embryos decreased. TCM199-based medium is better to improve the developmental potential and implantation rate of embryos derived from in vitro matured oocytes. After being frozen-thawed, the IVM embryos could achieve the same outcome when compared with the conventional IVF treatment. In addition, the offspring are healthy.

A gamma-ray irradiation reduction route to prepare rod-like Ag 2S nanocrystallines at room temperature

Rod-like Ag 2S nanocrystallines have successfully been synthesized by using Na 2S 2O 3 as a chalcogen source in an aqueous solution via gamma-ray irradiation at room temperature. The lattice constants of 0.41 nm, 0.68 nm, and 0.77 nm for the monoclinic Ag 2S phase were obtained from X-ray powder diffraction pattern. The nanorods have nonuniform diameters in the range of 200 to 500 nm and lengths of up to several ten micrometers. The band gap of Ag 2S nanorods calculated from the UV–Vis spectrum is 2.34 eV, showing an obvious blue shift in UV–Vis absorption.

In 2 O 3 nanowires grown from Au∕In film on glass

Two kinds of In2O3 nanowires (NWs), i.e., straight and tapered ones, are grown from 20-nm-thick Au∕300-nm-thick In and 20-nm-thick Au∕1-μm-thick In films on glass at 400°C by a one-step annealing method, respectively. All the NWs are single crystalline. The growth of the NWs is initiated by Au catalyst particles via vapor-liquid-solid growth mechanism, and an additional side growth might be responsible for the nonuniform diameters of the tapered NWs. It is revealed that a certain content of oxygen in the In film facilitates the large-scale growth of the In2O3 NWs. The field-emission studies show that the In2O3 NWs on glass have a low turn-on electric field of about 4.3V∕μm. Our growth method has potential applications in the in situ fabrication and integration of the In2O3 NWs-based devices, especially with glass as substrates.

Near hexagonal close-packed optical fiber array for parallel optical interconnection

In conventional optical fiber based two-dimensional (2-D) parallel optical interconnection (POI), optical fiber arrays are aligned to 2-D light sources and detectors using precisely fabricated hole-plate or stacked V-groove plates. All these structures have problems in making positioning components and assembly with high accuracy. For polymer optical fibers with large diameter, the whole dimension of the array will be too large if they are positioned using V-grooves or hole-plate. This paper proposes a 2-D near hexagonal close-packed (NHCP) optical fiber array for 2-D POI. NHCP array has a cross-sectional profile of near-hexagonal lattice and with fibers precisely positioned at each node of lattice. Compared with perfect HCP lattice, NHCP lattice is slightly stretched in one dimension and still have all fibers with nonuniform diameter packed tightly with high packing fraction. The position of fibers in NHCP array is very important when aligned to 2-D light sources and detectors. This paper deduce the analytically expression for the probability distribution of fiber position which is related to variance of fiber diameter and structure parameters of NHCP array, and verified it by computer simulation. Experiment samples of NHCP array have been made showing that NHCP array is easy to be fabricated.

The role of GaN/AlN double buffer layer in the crystal growth and photoluminescence of GaN nanowires

Vapor–liquid–solid (VLS) growth of GaN nanowires was performed and GaN/AlN double buffer layer was employed to minimize the lattice mismatch between GaN nanowires and Si substrates. GaN nanowires grown on GaN/AlN/Si substrates showed the formation of straight nanowires with ∼50–100 nm diameter, while those grown on bare Si wafers showed formation of tangled nanowires with non-uniform diameters. High-resolution transmission electron microscopy (HRTEM) analyses on the GaN nanowires grown on GaN/AlN/Si showed high crystallinity with [1 0 −1] crystal growth direction. Furthermore, GaN nanowires grown on GaN/AlN/Si showed high intensity blue emission and almost negligible yellow luminescence.

Measurement and analysis of effective thermal conductivities of lotus-type porous copper

Lotus-type porous copper is a porous medium made of copper that contains many straight pores. To effectively employ lotus-type porous copper as a heat sink, it is necessary to clarify the pore effect on the thermal conductivity of lotus copper. This article describes an experimental and analytical investigation on the effective thermal conductivities of lotus copper parallel and perpendicular to the pores. The lotus copper displayed anisotropy of the effective thermal conductivity. The effective thermal conductivity keff⊥ perpendicular to the pores was lower than that of the parallel ones keff∥ and was 40% that of lotus copper material ks with porosity ε of 0.4. Experimental data for keff∥ showed good agreement with analytical results derived from the assumption that heat flow through the cross-sectional area parallel to the pore axis is proportional to (1−ε). Experimental data for keff⊥ showed good agreement with the analytical results derived from the assumption of orthorhombic symmetry and with the numerical results under a uniform staggered array with a nonuniform pore diameter.

A new method for assessing arteriolar diameter and hemodynamic resistance using image analysis of vessel lumen.

To characterize the nonuniform diameter response in a blood vessel after a given stimulus (e.g., arteriolar conducted response), frequent serial diameter measurements along the vessel length are required. We used an advanced image analysis algorithm (the "discrete dynamic contour") to develop a quick, reliable method for serial luminal diameter measurements along the arteriole visualized by intravital video microscopy. With the use of digitized images of the arteriole and computer graphics, the method required an operator to mark the image of the two inner edges of the arteriole at several places along the arteriolar length. The algorithm then "filled in" these marks to generate two continuous contours that "hugged" these edges. A computer routine used these contours to determine luminal diameters every 20 microm. Based on these diameters and on Poiseuille's law, the routine also estimated the hemodynamic resistance of the blood vessel. To demonstrate the usefulness of the method, we examined the character of spatial decay of KCl-induced conducted constriction along approximately 500-microm-long arteriolar segments and the KCl-induced increase in hemodynamic resistance computed for these segments. The decay was only modestly fitted by a simple exponential, and the computed increase in resistance (i.e., 5- to 70-fold) was only modestly predicted by resistance increase based on our mathematical model involving measurements at two arteriolar sites (Tyml K, Wang X, Lidington D, and Oullette Y. Am J Physiol Heart Circ Physiol 281: H1397-H1406, 2001). We conclude that our method provides quick, reliable serial diameter measurements. Because the change in hemodynamic resistance could serve as a sensitive index of conducted response, use of this index in studies of conducted response may lead to new mechanistic insights on the response.

Simultaneous growth of silicon carbide nanorods and carbon nanotubes by chemical vapor deposition

Silicon carbide nanorods and carbon nanotubes are grown simultaneously on Ni-coated Si(001) substrates by chemical vapor deposition. The nanorods have a non-uniform diameter (average ≈100 nm) significantly larger than that of the nanotubes (<30 nm). Tips of the nanorods are decorated with catalyst particles. Both these features indicate that the SiC nanorods are not obtained through the chemical conversion of nanotubes. We demonstrate that the relative amounts of nanorods and nanotubes can be controlled by adjusting the Ni film thickness. Variants of our approach are potentially useful for creating hybrid architectures of high-aspect ratio nanostructures in one growth step.

Experimental observations on the general trends of the steady state and stability behaviour of single-phase natural circulation loops

The steady state flow in uniform or non-uniform diameter single-phase natural circulation loops (NCLs) can be expressed as Re ss= C[ Gr m/ N G] r where the constants C and r depend on the nature of the flow (i.e. laminar or turbulent). Testing these correlations with experimental data showed reasonable agreement. The above equation suggests that simulation of the steady state flow in single-phase NCLs can be achieved by simulating the non-dimensional parameter ( Gr m/ N G). The stability behaviour of a non-uniform diameter loop is found to depend on a large number of geometric parameters in addition to the modified Stanton number ( St m) and the ratio ( Gr m) b/(3− b) /( N G) 3/(3− b) . The transient and stability behaviour of a uniform diameter loop can be simulated by simulating the product ( Gr m) b/(3− b) ×( D ̄ / L ̄ t ) 3/(3− b) and St m if the length scales are preserved.

Analysis of vibration modes of a rod with nonuniform diameter

Analysis of vibration modes of a rod with nonuniform diameter

Synthesis of Carbon Tubes Using Microwave Plasma-assisted Chemical Vapor Deposition

Carbon tubes were successfully produced using microwave plasma-enhanced chemical vapor deposition on silicon, quartz, and ceramic substrates. The carbon tubes, about 80–100 nm in diameter and a few tens of microns in length, were formed under methane and hydrogen plasma at 720 °C with the aid of iron oxide particles. In this approach, an average tube density of about 109 cm−2 was obtained. The crooked and nonuniform diameters of some tubes suggested that they were composed of incompletely crystallized graphitic shells due to existing defects. The characteristic of the tubes grown upward on the silicon substrate accounted for a remarkably large electron field emission current of 0.1 mA/cm2 from the surface of the tube sample at a low turn-on field of 3 V/μm.

Increased thermal noise in nonuniform fiber suspensions

Fabrication techniques for fused silica fiber suspensions often result in nonuniform fiber diameters. We report the results of a model showing that the mechanical losses of a nonuniform fiber suspension can be twice those of the corresponding uniform fiber case, and suggest some techniques to reduce the level of nonuniformities.

Calibration in non-linear near infrared reflectance spectroscopy: a comparison of several methods

Principal component regression (PCR) and partial least-squares regression (PLSR) are the two calibration procedures most frequently used in quantitative applications of near infrared diffuse reflectance spectroscopy (NIRRS). Some systems, however, exhibit a non-linear relationship that neither methodology can model. Frequently, the main culprit of such non-linearity is the multiplicative effect arising from non-uniform particle sizes or diameters in the samples. In this work, we tested various approaches to minimizing the non-linearity resulting from the multiplicative effect of differences in particle size or sample thickness, using the determination of linear density in acrylic fibres as physical model. The approaches tested involve the prior linearizing of data by logarithmic conversion and/or the use of non-linear calibration systems; in this context, the results of applying stepwise polynomial PCR (SWP-PCR) and PLSR (SWP-PLSR), and those provided by a neural network based on the scores of the PCR model (PC-ANN), were compared. The PC-ANN approach was found to provide the best results with linear density data. On the other hand, the SWP-PLSR approach performed on par with the previous one when the variable was linearized by conversion of its values into decimal logarithms.