Stainless Steel Microtubes Research Articles

Multiscale framework-based crystal plasticity modeling and texture evolution of the deformation behavior of AISI 304 stainless steel microtubes manufactured through 3D-FBF technology

The grain size often influences the precision and quality of products manufactured by microforming at the microscale. Macroscale finite element modeling (FEM) cannot accurately predict nonuniform deformation and microstructural evolution at the microscale. In addition, the microscale FEM is challenging for forming processes with complex loading boundary conditions. Thus, in this study, a multiscale framework-based CPFEM is proposed to study the deformation behavior of microtubes manufactured through the 3D-FBF process. The acquired results show that significant nonuniform deformation is caused by greater geometric dimensions and smaller grain sizes, which increase the bending radius of microtubes at the macro level. In addition, a larger offset leads to higher flow stress, larger lattice rotation angles, and consequently, a larger bending radius for the microtube, and grain orientation also influences bending deformation, with easily deformable grain orientations leading to greater stress distribution within the grains.

Variations in gas temperature and average velocity during laminar-turbulent transition in high-speed gas flow through microtubes

The primary objective of this study is to investigate variations in gas temperature and average velocity during the laminar-turbulent transition of compressible flow. This investigation encompasses an exploration of the effect of Mach number on transitional Reynolds number. Experiments were conducted utilizing a pair of adiabatic stainless steel microtubes with a diameter (D) of 131.6 μm. The first microtube was dedicated to measuring local pressure to obtain friction factor, local Mach number, and bulk temperature. The second microtube was employed for measuring local wall temperature. Additionally, a stainless steel microtube with a diameter (D) of 124 μm and a rectangular microchannel with a hydraulic diameter (Dh) of 99.36 μm were incorporated in the study. Friction factor, Mach number, and bulk temperature were determined by measuring mass flow rate and local pressure near the outlet. The measured mass flow rate exhibited a slight increase that plateaued during the laminar-turbulent transition as the Reynolds number increased. In laminar flow, an increase in the Reynolds number resulted in an increase of the Mach number and a reduction in bulk temperature. Conversely, during the laminar-turbulent transition, the Mach number either remained constant or decreased, and the bulk temperature increased due to the conversion of kinetic energy to thermal energy. Experimental validation of this phenomenon was achieved by measuring the wall temperature of an adiabatic microtube.

Temperature recovery factor for gaseous nitrogen flow in a microtube

For gas flow over a flat plate, the temperature recovery factor is defined as a fraction of free-stream total temperature rise recovered at the wall or is the ratio of the actual temperature rise at the wall to the maximum possible temperature rise in the free-stream. Its value depends on Prandtl number and is independent of Mach number. The gas velocity and temperature are determined by the temperature recovery factor using the adiabatic wall temperature. It is an important parameter to be used to evaluate the gas velocity and temperature indirectly. In the present study, for internal flow, a methodology was introduced to estimate the temperature recovery factor numerically based on the total and bulk temperature for both laminar and turbulent flow regions in a microtube. The numerical simulations are based on the arbitrary Lagrangian-Eulerian method. The compressible momentum and energy equations for an ideal gas were solved to obtain the temperature recovery factor. To further validate the temperature recovery factor from numerical results, experiments were conducted using stainless steel microtubes. Although it is not a direct comparison, the gas bulk temperature and Mach number that were determined by the temperature recovery factor were compared with the experimental results and they were in good agreement.

Heat Transfer of Turbulent Gaseous Flow in Microtubes With Constant Wall Temperature

Abstract In this paper, we report on experimental results to measure the total temperature of nitrogen gas at the inlet and outlet of microtubes with constant wall temperature and to quantitatively determine the heat transfer rates. Experiments were conducted with nitrogen gas flowing in a stainless steel microtube with a diameter of 524 μm and a copper microtube with a diameter of 537 μm. The temperature differences between the inlet and the wall were maintained at 3, 5, and 10 K by circulating water around the inlet and the wall. The stagnation pressures were also controlled so that the flow, with atmospheric back pressure, could reach Reynolds numbers as high as 26,000. To measure the total temperature, a polystyrene tube with a thermally insulated exterior wall containing six plastic baffles was attached to the outlet. Heat transfer rates were obtained from the gas enthalpy difference by using the pressures and the total temperatures measured at the inlet and outlet. Heat transfer rates were also compared with those obtained from the ideal gas enthalpy using the measured total temperatures and from the Nusselt number of incompressible flows. It was found that the measured total temperature at the microtube outlet was higher than the wall temperature. Also, the heat transfer rates calculated from the total temperature difference were higher than the values obtained from the incompressible flow theory.

Estimation of surface roughness from friction loss of gaseous flow though stainless steel microtubes

Effects of surface roughness on microchannel gas flow are significant since the surface roughness of a microchnnel is relatively large compared to conventional size tubes. Therefore, in this study, the effects of surface roughness on friction factors of nitrogen gas flow through stainless steel microtubes experimentally investigated under atmospheric back pressure and variable inlet pressure. The experiments were carried out with six different diameters stainless steel microtubes whose diameters range from 256 to 867 μm. The average values of Mach number and Fanning & Darcy friction factors between the inlet and outlet considering decrease in gas temperature were obtained from measured stagnation temperatures & pressures and mass flow rates. The effects of surface roughness on the compressibility effect were described with Fanning and Darcy friction factor correlations as a function of Mach number. The arithmetic mean height of the surface (Ra) of the microtube was also measured with a 3D laser scanning confocal microscope for profilometry. Comparing the measured Ra and the equivalent sand grain surface roughness (Ks) determined from Colebrook-White correlation, a correlation between Ra and Ks was obtained.

乱流域におけるマイクロチューブを流れるガスの温度回復係数の推定

In this paper, a temperature recovery factor defined as the ratio of the actual temperature rise at the wall to the maximum possible temperature rise were estimated from experimentally measured wall temperatures and pressures to determine the velocity and temperature of gas through an adiabatic microtube. The experiments were carried out using two pairs of stainless steel microtubes with D=528.4 and 754.2 μm. One of a pair was tested for measurements of local pressures to obtain local Mach numbers and bulk temperatures. And the other of a pair was tested for measurements of local wall temperatures. The stagnation pressure with the atmospheric back pressure was chosen in such a way that the outlet flow reached sufficiently choked. Local total and bulk temperatures were obtained with total and static enthalpies determined with the measured stagnation & local pressures, stagnation temperatures, mass flow rates by real gas manner. In order to estimate the temperature recovery factor, the measured wall temperature and the obtained total temperature were normalized by bulk temperature and represented as Mach numbers. The estimated values of the temperature recovery factor were independent of the Mach number. The present estimated temperature recovery factor was compared with numerical and experimental ones obtained with the assumption of an ideal gas.

Introduction of a new method for bending of AISI 304L stainless steel micro-tubes with micro-wire mandrel

Abstract The purpose of this study is presenting a new method for bending metal micro-tubes in a critical bending ratio. At first, using the fluid pressure and bending die in the bending ratio of 1.6, the micro-tube has been bent, which is caused wrinkling on the intrados of the micro-tube. Then, using a micro-wire mandrel, a new method for micro-tube bending has been proposed. Two parameters of micro-wire clearance and micro-wire arrangements have been investigated to generalize this method. The results have shown that the clearance of micro-wire with micro-tube should not be less than 50 μm because it will not be possible to insert micro-wire into the micro-tube. Also, the arrangement that has less clearance will have less cross-section distortion because they cause more filling within the micro-tube. In general, the results have shown that micro-tube bending with micro-wire mandrel did not have defects such as wrinkling and rupture. It also allows the micro-tube to bend at room temperature in a critical bending ratio.

Identification of Gas Flow Regimes in Adiabatic Microtubes by means of Wall Temperature Measurements

There exists the laminar flow, transitional flow, turbulent flow and choked flow regimes in a microtube gas flow. Development of a non-invasive identification method of the flow regimes within a microdevice is expected. This paper demonstrated how the internal gas flow regimes can be identified by measuring the distribution of the external wall temperature of the microchannel along the flow direction. A series of experiments were conducted by using nitrogen as working fluid through a stainless steel micro-tube with an inner diameter of 523 µm and a fused silica micro-tube having a diameter of 320 µm. The experiments were performed by fixing the back pressure at the exit of the microchannel at the atmospheric value and by varying the inlet pressure in order to modify the gas flow regime. In order to measure the external wall temperature along the microtube, two or three bare type-K thermocouples with a diameter of 50 µm were attached to the micro-tube external surface by using a high conductivity epoxy. In the case of the microtube having a diameter of 523 µm, local pressures were measured at three local pressure ports along the microtube. The pressure ports were placed on the opposite side of the tube wall where three thermocouples were attached. The microtube external wall was thermally insulated with foamed polystyrene to prevent heat gain or loss from the surrounding. The experimental results show that the wall temperature decreases in the laminar flow regime, increases in the transitional flow regime, decreases in the turbulent flow regime and it stays nearly constants in the choked flow regime. The behavior of the average Fanning friction factor and the local Mach number can be explained by identifying the flow regime. It is clarified that the microtube external wall temperature is a reliable indicator of the flow regime.

Comparison of aqueous and non-aqueous alkanolamines solutions for carbon dioxide desorption in a microreactor

An experimental study of CO2 desorption from aqueous and non-aqueous saturated alkanolamine solutions carried out in a tubular microreactor, consisting of a stainless steel microtube with an internal diameter of 800 μm and a total length of 35 cm. We tested a total of six solvent mixtures of water or methanol with monoethanolamine, diethanolamine, or activated methyl diethanolamine in a broad range of operational conditions, including temperature (50–100 °C), rich solvent flow rate (0.5–4.5 ml/min), and amine concentration in the solvent (10 and 50% w/w). CO2 desorption was thoroughly characterized with respect to the mass transfer rate and energy consumption, and both were expected to improve with the use of a microreactor due to short diffusion distances and a larger surface-to-area ratio. An increase in the operating temperature or concentration of the amine resulted in a higher percentage of desorption and enhanced mass transfer rates, as shown by the local mass transfer coefficient based on the liquid phase values herein disclosed. Increasing the rich solvent flow rate also increased the local mass transfer coefficient values (80%–95%); however, the overall percentage of CO2 desorption reduced (25%–35%) due to shorter residence times in the microreactor. Similarly, the energetic desorption efficiency improved for all the solutions with increasing temperature (65–75% reduction) and concentration of amine in the solvent (20–35% reduction), yet again decreasing with an increasing flow rate of rich solvent (5–15%). Compared to the literature values for the packed columns and microreactors, our data showed the overall energy consumption up to an 88% reduction in specific CO2 desorption, demonstrating great potential for the intensification of solvent-mediated, energetically demanding CO2 desorption. In addition, the results showed that the energy consumption for CO2 desorption was reduced by 73% by choosing a non-aqueous in preference to an aqueous alkanolamine solvent.

Influence of Chemically Etched Roughness on Frictional Resistance of Micro-tubes

Chemical etching is a convenient process for enhancing three-dimensional (3D) roughness of internal surface of micro-tubes. The aim of this research work is to compare the frictional resistance and contact angle in smooth and rough stainless steel micro-tubes. At various inputs of Reynolds number in laminar regime (201.43 < Re < 1929.96), differential pressure has been measured for etched and unetched tubes with deionized water. In order to substantiate the effect of roughness on tube, contact angle is measured before and after etching to calculate roughness parameter. It is found that etching enlarges the inner diameter of the tube; hence new diameter should be considered for Poiseuille number (fRe) calculations. The role of etching on fRe is more significant on tube of inner diameter (ID) 0.932 mm, as compared to tube of ID 1.293 mm. Etching increases the contact angle of hydrophobic surface. This work would be applicable in design improvement of complex micro-devices when relative roughness plays a major role due to small scale.

Fabrication of Super-hydrophobic Surfaces and Studies of Water Flow in Super-hydrophobic Micro-tubes

Hierarchical alveolate structures of micro-nano scale were prepared on stainless steel substrates with chemical etching. Fine papillae stand on protuberances are found. After fluorination treatments, the surfaces exhibit super-hydrophobic properties, with water contact angles of 163°. Stainless-steel micro-tubes with super-hydrophilic and super-hydrophobic surface were fabricated with chemical etching and chemical etching-fluorination treatment respectively. The effect of surface wettability on the fluid flow in micro-tubes was investigated with water as the working fluid. The experimental setup was designed in such a way that the investigation of the pressure drop and friction factor was possible. It is found that friction factor in super-hydrophilic micro-tube is in good agreement with Hagen-Poiseuille theory at low Reynolds number (Re<600), while higher than classical values at higher Reynolds number. The pressure drop of water flowing in super-hydrophobic micro-tube decreases compared with that in super-hydrophilic micro-tube, with the maximal decrease of 39%, which indicates the prospective utilization in process industry.

A Simplified Model for Predicting Friction Factors of Laminar Blood Flow in Small-Caliber Vessels

The aim of this study was to provide scientists with a straightforward correlation that can be applied to the prediction of the Fanning friction factor and consequently the pressure drop that arises during blood flow in small-caliber vessels. Due to the small diameter of the conduit, the Reynolds numbers are low and thus the flow is laminar. This study has been conducted using Computational Fluid Dynamics (CFD) simulations validated with relevant experimental data, acquired using an appropriate experimental setup. The experiments relate to the pressure drop measurement during the flow of a blood analogue that follows the Casson model, i.e., an aqueous Glycerol solution that contains a small amount of Xanthan gum and exhibits similar behavior to blood, in a smooth, stainless steel microtube (L = 50 mm and D = 400 μm). The interpretation of the resulting numerical data led to the proposal of a simplified model that incorporates the effect of the blood flow rate, the hematocrit value (35–55%) and the vessel diameter (300–1800 μm) and predicts, with better than ±10% accuracy, the Fanning friction factor and consequently the pressure drop during laminar blood flow in healthy small-caliber vessels.

A time-dependent method for the measurement of mass flow rate of gases in microchannels

Accurate measurement methods are required in the analysis of thermodynamic non-equilibrium effects associated with rarefied gas flows. For example, for the specific case of accommodation coefficients measurements, the quantity of interest is often the mass flow rate along the channel. For this purpose, the following paper presents a new time-dependent version of the well-known constant volume method for the accurate measurement of mass flow rates of gases in microchannels. The technique proposed here is an improvement in respect to the classic technique since it can be used for transient experiments. Moreover, it can be applied to configurations with arbitrary upstream and downstream reservoirs dimensions. Particularly, the proposed method relies on the assumption that the flow conductance varies linearly during the experiments and thus the pressure variations in the reservoirs can be fitted by a well-defined exponential function. Then, the instantaneous mass flow rate through the channel can be determined directly from the pressure fitting coefficients. A great advantage of the time-dependent constant volume method is that the measurements can be obtained from a single experiment for a wide range of rarefaction conditions, since the mean pressure between the reservoirs is allowed to change with time. Moreover, this technique represents a convenient manner to provide raw data of pressure variation with time in the reservoirs and transient mass flow rate in the channel by simply providing the fitting coefficients of the theoretically derived functions. A clear geometric criterion is also presented to determine when such mass flow rate measurements can be considered as quasi-steady, corresponding closely to results obtained under steady conditions, when ideally the channel connects two infinite reservoirs at different pressures. Results for flows of nitrogen through a stainless steel microtube (L=92.22±0.01 mm and D=435.5±3.5 µm) were obtained from 118 independent experiments, provided in this work, using two different experimental setups and three different configurations of the system volumes. As expected, no deviation was observed between all experimental campaigns in terms of the reduced mass flow rate. In addition, all results indicate that nitrogen can be considered completely accommodated at the surface of the microtube used, with α=0.986±0.019 when the diffuse-specular gas-surface interaction model is adopted and αt=0.991±0.020 (αn=1) when the Cercignani-Lampis model is adopted.

Subcooled flow boiling heat transfer of γ-Al2O3/water nanofluids in horizontal microtubes and the effect of surface characteristics and nanoparticle deposition

In this study, subcooled flow boiling heat transfer characteristics of nanofluids were investigated at micro scale. For this purpose, the effect of γ-Al2O3 (gamma-alumina) nanoparticles with an average solid diameter of 20nm was considered. In the experiments, various mass fractions were considered in horizontal smooth stainless steel microtubes with inner and outer diameters of ∼502µm and ∼717µm, respectively, at mass fluxes of 1200 and 3400kgm−2s−1. Nanoparticles were added to distilled water (base fluid) at five mass fractions (low mass fractions 0.05wt% and 0.2wt%; high mass fractions 0.5wt%, 1wt% and 1.5wt%). According to our results, subcooled flow boiling heat transfer coefficients for nanofluids with low mass fractions were nearly the same as those of the pure water. However, heat transfer deteriorated for nanofluids with high mass fractions. Observations of dynamic light scattering measurements for low and high mass fractions before and after the experiments revealed that agglomeration of nanoparticles is an important parameter in deterioration of heat transfer at higher concentrations. Besides, Scanning Electron Microscopy images of microtube inner surfaces showed that deposition of nanoparticles and agglomerated nanoparticles on the inner surface of the microtubes also contributed to the heat transfer deterioration at high mass fractions. Generally, the deterioration in heat transfer beyond a specific mass fraction value was linked to the disturbance in the stability of suspended nanoparticles and deposition of nanoparticles upon boiling.

EXPERIMENTAL VALIDATION OF LMTD METHOD FOR MICROSCALE HEAT TRANSFER

The s ingle phase fluid flow and heat transfer characteristic has been investigated experimentally. Experiments were conducted to cover transition zone for the Reynolds numbers ranging from 100 to 4800 by fused silica and stainless steel microtubes having diameters of 103-180 µm. The applicability of the Logarithmic Mean Temperature Difference (LMTD) method was revealed and an experimental method was developed to calculate the heat transfer coefficient. Moreover the scaling effects in micro scale such as axial conduction, viscous heating and entrance effects were discussed. The heat transfer coefficients were compared with data obtained by the correlations available in the literature in the study. The Nusselt numbers of microtube flows do not accord with the conventional results when the Reynolds number was lower than 1000. After that, the Nusselt number approaches the conventional theory prediction. On the aspect of fluid characteristics, the friction factor was well predicted with conventional theory and the conventional friction prediction was valid for water flow through microtube with a relative surface roughness less than about 4 %.

Experimental analysis of velocity slip at the wall for gas flows of nitrogen, R134a, and R600a through a metallic microtube

This paper reports measurements of mass flow rate of nitrogen, R134a, and R600a through a commercially available stainless steel microtube, which closely reproduces the case of gas leakage through micrometric clearances found in compressor valves. The accuracy of the measurements in the whole rarefaction range considered was verified through comparisons with predictions from the BGK kinetic model and results from the Navier–Stokes equations with modified boundary conditions. Furthermore, values of the tangential momentum accommodation coefficient (TMAC) were obtained by using an analytical approach derived from the solution of the Navier–Stokes equations with modified second-order boundary conditions. An incomplete accommodation is observed for all gases, with α = 0.933 ± 0.004 for nitrogen, 0.956 ± 0.004 for R134a, and 0.974 ± 0.008 for R600a. The results for all gases were very similar, indicating that the gas chemical composition does not significantly affect the flow through microtubes with rough internal surfaces, even when heavy polyatomic molecules are considered.

Multiaxial Deformation Apparatus for Testing of Microtubes Under Combined Axial-Force and Internal-Pressure

An apparatus for multiaxial loading of microtubes with an outside diameter of less than a few millimeters is described. The apparatus is capable of applying axial-force and internal-pressure in a fully-coupled way, so that biaxial principal stresses along either proportional or non-proportional loading paths can be applied to the microtubes. The requirements of the apparatus for this fully-coupled loading and the resulting functional layout are described first. The hardware that was selected is then detailed. The maximum force and pressure capacities are 2000 N and 1034 bar, while the maximum available stroke and pressurized fluid volume are 50 mm and 68 ml, respectively. Since the apparatus is required to perform dynamic loading as well, with the stresses varying on the order of 1 Hz, the dynamic behavior of the pump used in the apparatus is established experimentally. It was determined that the dynamic response depends not only on the amplitude and frequency of the desired loading, but also, partially because of the minute dimensions of the apparatus, on the volume of fluid in the system and the compressibility of the fluid used for the inflation. The capabilities of the apparatus are demonstrated by proportional and non-proportional biaxial experiments on 304L stainless steel microtubes of 2.38 mm outside diameter and 0.15 mm nominal thickness. Two different strategies for performing these experiments, i.e., force- & volume-control and displacement- & pressure-control were implemented and are compared to each other. The former leads to a more stable system and thus is the preferred mode of operation of the apparatus, while the latter can allow better tracking of the microtube response past the observed limit-load instability. In the proportional loading experiments, the nominal stress paths are shown to be exactly linear, as desired. Although not pursued here, such experiments can be used to establish the plastic anisotropy of the microtube material. Two types of non-proportional experiments are performed: in both cases the microtube is loaded uniaxially (axial or hoop direction); then, by keeping that stress constant, the other principal stress (i.e., hoop or axial) is increased until failure. Digital Image Correlation is used to measure the full strain fields during the testing, establishing the strains at the limit of uniform deformation. Furthermore, comparison of the strain paths induced during the proportional and non-proportional experiments established the path-dependency of the failure strains. These successful experiments demonstrate that any complex loading path inside (or adjacent to) the first quadrant of the plane-stress space can be implemented with this apparatus.

Effects of oxidation and surface roughening on drawing limit in dieless drawing process of SUS304 stainless steel microtubes

In this study, we investigate the effects of surface roughening and oxidation, which are dependent on the heating temperature, on the drawing limit in the dieless drawing process of SUS304 stainless steel microtubes. The microtubes have an outer diameter of 0.5mm and a thickness of 0.13mm. Dieless drawing apparatus with a chamber filled with argon gas to prevent oxidation is used in the experiments. It was found that the limiting reduction in area increases to a maximum value and then decreases with increasing heating temperature in both argon gas and air. An appropriate heating temperature range from 950 to 1100°C with the maximum drawing limit is obtained from the dieless drawing experiment. In addition, the drawing limit in air is lower than that in argon gas at low temperatures of below 950°C owing to oxidization. In contrast, the drawing limit in air at high temperatures of over 1100°C is higher than that in argon gas, because the oxidation inhibits free surface roughening due to grain growth. Consequently, the drawing limit in dieless drawing strongly depends on the heating temperature. The roles of oxidation and surface roughening, which affect the drawing limit in the dieless drawing of microtubes, also vary widely depending on the heating temperature.

10512 レーザマルチパスダイレス引抜きにおけるステンレス微細管の表面平滑化の効果

10512 レーザマルチパスダイレス引抜きにおけるステンレス微細管の表面平滑化の効果

24-gauge ultrafine cryoprobe with diameter of 550 μm and its cooling performance

This paper describes the development of a novel cryoprobe with the same size as a 24-gauge injection needle and the evaluation of its cooling performance. This ultrafine cryoprobe was designed to reduce the invasiveness and extend application areas of cryosurgery. The ultrafine cryoprobe has a double-tube structure and consists of two stainless steel microtubes. The outer diameter of the cryoprobe is 550μm, and the inner tube has a 70-μm inner diameter to depressurize the high-pressure refrigerant. By solving the bioheat transfer equation and considering freezing phenomena, the relationship between the size of the frozen region and the heat transfer coefficient of the refrigerant flow in an ultrafine cryoprobe was derived analytically. The results showed that the size of the frozen region is strongly affected by the heat transfer coefficient. A high heat transfer coefficient such as that of phase change heat transfer is required to generate a frozen region of sufficient size. In the experiment, trifluoromethane (HFC-23) was used as the refrigerant, and the cooling effects of the gas and liquid phase states at the inlet were evaluated. When the ultrafine cryoprobe was cooled using a liquid refrigerant, the surface temperature was approximately −50°C, and the temperature distribution on the surface was uniform for a thermally insulated condition. However, for the case with vaporized refrigerant, the temperature distribution was not uniform. Therefore, it was concluded that the cooling mechanism using liquid refrigerant was suitable for ultrafine cryoprobes. Furthermore, to simulate cryosurgery, a cooling experiment using hydrogel was conducted. The results showed that the surface temperature of the ultrafine cryoprobe reached −35°C and formed a frozen region with a radius of 4mm in 4min. These results indicate that the ultrafine cryoprobe can be applied in actual cryosurgeries for small affected areas.