Diameter Of Microtubes Research Articles

Determinação do diâmetro de microtubos em irrigação localizada

A microtube is a simple type of drip emitter which has been used since the 70’s. In microtubes, small differences in the diameter can cause errors in estimating discharge, reducing the irrigation project efficiency, even if the real values are close to those specified by the manufacturer. This worked aimed at comparing diameter values, determined by using an optic measuring projector and hydraulic determination, with the data provided by themanufacturer. The microtubes used had internal diameters of 0.6; 0.7; 0.8; 1.0 and 1.5 mm, according to the manufacturer. The optical projector manufactured by Starrett Precision Optical was used in thirty rings of each microtube, of 5 mm in length. Hydraulic determination of diameter was calculated with data obtained in assays under laminar flow, applied using the basic equation for energy drop by friction and Bernoulli’s equation. Basedon our results, we suggest that optimum irrigation project design should be based on microtube diameters determined from hydraulically determination, as well as from optic measuring projectors, not only from the diameter supplied by manufacturer. Hydraulic determination of the diameter is the most simple and viable way, as it doesn’t present differences when compared to standard optical projector.

Experimental Investigation of Turbulent Heat Transfer in the Entrance Region of Microchannels

Within the entrance region of a closed channel, the effects on flowfield and heat transfer mechanisms are significant. Where microchannels and microdevices are concerned, there are limited heat transfer studies into this region, and those available are for laminar flows. In the turbulent regime, where the hydraulic resistance is conventionally increased, higher pumping powers are required. However, future microscale applications may have a need for turbulent flow data in microchannels. There is currently no heat transfer data available on the turbulent entrance region of microchannels. An experimental investigation has been carried out to explore turbulent convection heat transfer in the entrance region of uniformly heated microtubes. The measurement of local wall temperatures is achieved through the use of unencapsulated thermochromic liquid crystals, a state-of-the-art, nonintrusive thermal-measurement technique. Heat transfer data was obtained for two stainless steel microtubes, with nominal inner diameters of 1.067 and 0.508 mm, over a Reynolds number range of 4000 to 9000. The working fluid is FC-72, and adequate tube entry length is provided for hydrodynamic flow development before heating. Local temperature data and Nusselt values are obtained in the thermal entrance region of the microchannels. The thermal turbulent entrance length is found to remain relatively constant for the Reynolds number range considered for both microtube diameters. This is in good agreement with conventional thermal turbulent entrance studies for pipes.

G402 90°の曲りを有するマイクロチューブ内の圧縮性流れに関する研究(GS4 閉空間内の流れ,一般セッション)

Experimental and numerical investigations are performed to obtain the fluid flow characteristics of gaseous flow in micro-tube with 90° bend. Especially, attention is put on the influence of compressibility in micro-tube. In numerical calculation, the diameter of micro-tube is changed 50, 75, 100 and 150μm, and Dean number ranges from 50 to 200. The results show that the friction factor is increase with increasing Dean number, and this trend becomes pronounced at the micro-tube with smaller diameter. The friction factor at the bend is expressed as the Mach number at the entrance of bend.

Investigation of laminar flow in microtubes with random rough surfaces

A new approach of numerically generating a microtube with three-dimensional random surface roughness is presented. In this approach, we combined a bi-cubic Coons patch with Gaussian distributed roughness heights. Two random roughness generation methods are studied. A computational fluid dynamic solver is used to solve the 3-D N–S equations for the flow through the generated rough microtubes with D = 50 μm and L = 100 μm. The effects of the peak roughness height, H, asperities spacing in the θ direction, S θ , and Z direction, S Z , standard deviation of the Gaussian distribution, σ, arithmetical mean roughness, R a, on the Poiseuille number, Po are investigated. It is found that when H/D < 5% the Po number can still be predicted by the conventional flow theory if the mean diameter of rough microtubes, D m, is used to be the hydraulic diameter D h. When H/D = 10%, the main flow is strongly affected by the roughness at Reynolds number Re = 1,500. The Po number increases with Re and deviates from the prediction up to 11.9%. The Po number does not change a lot with S θ and S Z because D m almost keeps constant when the spacing is changed. For the rough microtubes with different R a values, the Po numbers can be almost the same, which prove that only with the R a value we can not determine the friction in the rough microtube. The mean value μ, the maximum and minimum values of the random roughness are found to be critical to determine the Po number.

Numerical analysis of laminar flow in micro-tubes with a slip boundary

Investigated numerically are the effects of slip and viscous heat dissipation on the friction number of thermally developing laminar water flow in micro-tubes. Also investigated are the effects of the micro-tube diameter, D, aspect ratio, L/ D, and Reynolds number on the friction number. The decrease in the dynamic viscosity slightly decreases the friction number below that of the Hagen–Poiseuille, determined from the solution of the Navier–Stokes equations assuming thermally and hydro-dynamically fully developed flow and constant fluid properties. A slip at the wall decreases the friction number with increased L/ D and decreased D. Results confirmed that the flow in micro-tubes is never thermally developed, significantly increasing the friction number with increased Reynolds number beyond critical values. Below the critical Reynolds numbers, the effect of the thermally developing flow is negligible and the friction numbers in micro-tubes is almost identical to those of the Hagen–Poiseuille, with and without slip at the wall. The comparison with reported experimental data confirmed the results of the present analysis.

Transesterification of Sunflower Oil with Methanol in a Microtube Reactor

Transesterification of sunflower oil with methanol to form fatty acid methyl esters (FAMEs) using a KOH catalyst was performed in a microtube reactor. Oil conversion was significantly affected by microtube length, microtube diameter, the methanol/oil molar ratio, and reaction temperature. Flow patterns were observed in the transparent microtube under different operating conditions and were characterized by optical measurements. The relationship between flow pattern and oil conversion was examined. The flow pattern at the entrance region of the microtube was segmented flow of the methanol and oil phases. As the reaction progressed, fine droplets composed of the produced glycerol and methanol were dispersed and circulated in the oil segments. At a methanol/oil molar ratio of 23.9 at 60 °C, a quasi-homogeneous phase formed approximately 300 mm from the reaction inlet where the oil was completely converted to FAMEs.

Characterization of the microtube emitters used in a novel micro-sprinkler

The microtube is a simple and cheap emitter that was widely used throughout the world in the early days of drip irrigation. Its length can be adjusted according to the pressure distribution along the lateral line and the discharge from the microtube can be adjusted by its length. This not only counters the pressure loss due to pipe friction but also makes it suitable for undulating and hilly conditions, where pressure in the lateral line varies considerably according to the differences in elevation. This is the major problem facing the designer, i.e., emitter flow changes as the acting pressure head changes. In this study, a novel micro-sprinkler system is proposed that uses microtube as the emitter and where the length of the microtube can be varied in response to pressure changes along the lateral to give uniformity of emitter discharges. The objective of this work is to develop and validate empirical and semi-theoretical equations for the emitter hydraulics. Laboratory testing of two microtube emitters of different diameter over a range of pressures and discharges was used in the development of the equations relating pressure and discharge, and pressure and length for these emitters. The equations proposed will be used in the design of the micro-sprinkler system, to determine the length of microtube required to give the nominal discharge for any given pressure. The semi-theoretical approach underlined the importance of accurate measurements of the microtube diameter and the uncertainty in the estimation of the friction factor for these tubes.

Monitoring of liquid flow through microtubes using a micropressure sensor

The pressure-driven liquid flow through microtubes was studied in a range of very low Reynolds numbers (<0.15) by monitoring the pressure change in situ. Cylindrical microtubes with diameters ranging from 50 μm to 500 μm were examined and two types of tube material, namely PEEK polymer and fused silica were compared. A good linear relation for the pressure drop versus flow rate was obtained. Apparent deviations between the measured slopes with those calculated using conventional theory were attributed to uncertainties in the calculated values which are dominated by the uncertainties in the microtube diameters. It was found that a period of stabilisation time was required for reaching a steady flow after the syringe pump was switched on/off or to a different flow rate. The stabilisation time was likely due to the compressibility of the fluid. Insignificant difference between PEEK polymer and fused silica microtubes in terms of flow resistance was observed. The in-situ measurement of pressure drops provides a convenient approach for monitoring fluid flow through microtubes and detecting dimensional changes within microchannels in Lab-on-a-Chip and microreactor systems.

Stability limits of premixed microflames at elevated temperatures for portable fuel processing devices

In order to provide the database for designing microcombustors applicable to microfuel processing of portable power generation devices such as microfuel cells, the combustion characteristics of premixed hydrocarbon–air microflames at normal and elevated temperatures and atmospheric pressure generated on a microtube were studied experimentally and computationally. With methane and propane being the fuels, the stability limits of premixed microflames and the propensity of the microflames near the stability limits were experimentally determined, while the structure of the microflame at the fuel-leanest limit was obtained using a two-dimensional CFD simulation with a reduced kinetic mechanism. For all the microflames, the stability limits were observed only in the fuel-rich region. Results also show substantial extension of stability limits with elevated temperature that is realistic condition for microfuel processing and significant fuel dilution immediately near the tube exit due to a low Peclet number times Lewis number effect. The effects of microtube diameters on the stability limits were substantial only for the methane–air microflames of lower mixture temperature. Finally, the propane–air microflames generally showed extended stability limits compared to the methane–air microflames at similar conditions due to enhanced advection.

Evaluating asymbiotic seed culture methods and establishing Disa (Orchidaceae) germinability in vitro: relationships, requirements and first-time reports

The effects of 5-aminolevulinic acid (ALA), a key precursor in the biosynthesis of porphyrins such as chlorophyll and heme, on development and salt tolerance of microtubers of two potato (Solanum tuberosum L.) cultivars Jingshi-2 and Zihuabai were examined under in vitro conditions. ALA at 0.3–3 mg/l promoted microtuber formation by increasing the average number, diameter, and fresh weight of microtubers especially under 0.5% NaCl stress conditions, but further increase in ALA concentration resulted in a reduction of microtuber yield irrespective of NaCl stress. Under 1.0% NaCl stress conditions, microtuberization was seriously repressed and could not be restored by the addition of ALA. The accumulation of malondialdehyde in the microtubers treated with 30 mg/l ALA increased by 22% compared to the controls (no salinity), while only a 7% increase was observed when the microtubers were exposed to 0.5% NaCl, indicating that ALA functions as a protectant against oxidative damages of membranes. Under 0.5% NaCl stress conditions, the highest activities of peroxidase and polyphenoloxidase were detected in microtubers treated with ALA at 0.3 and 3 mg/l, being by 73% and by 28% greater than those in the untreated controls, respectively. These results demonstrate that ALA at lower concentrations of 0.3–3 mg/l promotes development and growth of potato microtubers in vitro and enhances protective functions against oxidative stresses, but ALA at 30 mg/l and higher concentrations seems to induce oxidative damage probably through formation and accumulation of photooxidative porphyrins.

Templated Assembly of Gold Nanoparticles into Microscale Tubules and Their Application in Surface-Enhanced Raman Scattering

We report a simple procedure to assemble gold nanoparticles into hollow tubular morphology with micrometer scale, wherein the citrate molecule is used not only as a reducing and capping agent, but also as an assembling template. The nanostructure and growth mechanism of microtubes are explored via SEM, TEM, FTIR spectra, and UV-vis spectra studies. The incorporation of larger gold nanoparticles by electroless plating results in an increase in the diameter of microtubes from 900 nm to about 1.2 microm. The application of the microtubes before and after electroless plating in surface-enhanced Raman scattering (SERS) is investigated by using 4-aminothiophenol (4-ATP) as probe molecules. The results indicate that the microtubes both before and after electroless plating can be used as SERS substrates. The microtubes after electroless plating exhibit excellent enhancement ability.

The role of GA, IAA and BAP in the regulation of in vitro shoot growth and microtuberization in potato

The effect of auxin, GA and BAP on potato shoot growth and tuberization was investigated under in vitro condition. The shoot length of potato explants increased with the increasing of concentrations (0.5 – 10 mg dm−3) of IAA treatment especially with the addition of GA3 (0.5 mg dm−3), but was inhibited by BAP (5 mg dm−3). The root number and root fresh weight of potato explants increased with the increasing of IAA levels either in the presence of GA3 (treatment IAA+GA) or not (IAA alone). However, no root was observed in the treatment IAA+BAP, instead there were brown swollen calli formed around the basal cut surface of the explants. The addition of GA3 remarkably increased the fresh weight and diameter of calli. Microtubers were formed in the treatments of IAA+BAP and IAA + GA + BAP but not observed in the treatments of IAA alone or IAA + GA. IAA of higher concentrations (2.5 – 10 mg dm−3) was helpful to form sessile tubers. With the increasing of IAA levels, the fresh weight and diameter of microtubers increased progressively. At 10 mg/L IAA, the fresh weight and diameter of microtubers in the treatment of IAA + GA + BAP were 409.6 % and 184.4 % of that in the treatment of IAA + BAP respectively, indicating the interaction effect of GA and IAA in potato microtuberization.

Template synthesis of polyaniline/TiO 2 bilayer microtubes

In this article, highly ordered PANI/TiO 2 bilayer microtubes were prepared with two-step method. Firstly, anodic aluminum oxide (AAO) membrane with regular channel structure was chosen as the template, the PANI microtubes were synthesized in the channels of template by in situ polymerization. Secondly, the TiO 2 microtubes were synthesized with sol–gel method in the channels of PANI microtubes. The structure and morphology of PANI/TiO 2 bilayer microtubes were characterized by SEM, energy dispersive spectroscopy (EDS), TEM, and UV–vis. The results showed that the bilayer microtubes were successfully synthesized in the microchannels of template, the diameter and length of microtubes were closed to the pore diameter and thickness of AAO template, respectively, the arrangement of bilayer microtubes was very regular and uniform, also, a bilayer structure was found. UV–vis spectra confirmed that the photocatalysis property of PANI/TiO 2 bilayer microtubes in sunlight was better than that of TiO 2 microtubes, due to the existence of sensitizer, PANI.

The friction characteristics of gaseous slip flow in microtubes

The present work studies the friction characteristics of gaseous slip flow in microtubes. The reduced diameter of microtubes has significant influences on the flow. The degree of influence depends on the Knudsen number. If the Knudsen number is in the range of 10-3 to 0.1, the fluid can be assumed to be a continuum but a slip boundary condition at the tube wall has to be employed to account for the incomplete tangential momentum and energy exchanges between the gas molecules and the wall. Although slip flow in microtubes can be investigated by solving numerically the compressible Navier‐Stokes equations, the hyperbolic‐parabolic character of the equations makes it very inefficient. The very large length to diameter ratio of microtube flows suggests that they can be predicted accurately as well as efficiently by solving the compressible boundary‐layer equations. The parabolic character of the boundary‐layer equations renders the present method a very efficient and accurate tool in studying slip flows. The results confirm the findings of earlier investigators that the product off. Re is smaller for laminar microtube flows than that predicted by the conventional theory when the flow is in the slip region.

LAMINAR FORCED CONVECTION IN A CIRCULAR TUBE WITH CONSTANT HEAT FLUX AND SLIP FLOW

An analytical solution to the problem of laminar gas flow in microtubes with a constant heat flux boundary condition at the wall is presented. The microtube diameter is small enough that the Knudsen number becomes an important parameter; thus, both a slip flow hydrodynamic condition and a temperature jump thermal condition are assumed at the wall. The fluid is assumed to be hydrodynamically fully developed at the tube entrance. An indirect solution method utilizes the solution for a previously reported isothermal wall problem. The results indicate that the fully developed Nusselt number decreases with Knudsen number. For instance, with a Knudsen number of 0.04, the Nusselt number for fully developed flow is reduced 14 % over that obtained for a nonslip boundary condition.The reduction is strongly influenced by the increased temperature jump as Knudsen number increases.