Small Diameter Tubes Research Articles

Fluid Dynamics of Small Diameter Tubes Used in Membrane-tube Type Glaucoma Shunt Devices

PurposeTo investigate the outflow characteristics of silicone tubes with intraluminal stents used in membrane-tube (MT) type glaucoma shunt devices.MethodsThe silicone tubes used in MicroMT (internal diameter of 100 µm with a 7-0 nylon intraluminal stent) and Finetube MT (internal diameter of 200 µm with a 5-0 nylon intraluminal stent) were connected to a syringe-pump that delivered a continuous flow of distilled water at flow rates of 2, 5, 10, and 25 µL/min. The pressures and resistances of tubes were measured at a steady flow rate with full-length, half-length, and absence of intraluminal stents.ResultsThe mean outflow resistance of the two types of tubes ranged from 3.0 ± 1.9 to 3.8 ± 1.7 mmHg/µL/min with a full-length intraluminal stent, 1.8 ± 1.1 to 2.2 ± 1.1 mmHg/µL/min with a half-length intraluminal stent, and 0.1 ± 0.0 to 0.2 ± 0.0 mmHg/µL/min without an intraluminal stent. Theoretically, for a physiologic state with a flow rate of 2 µL/min and episcleral venous pressure of 6 mmHg, the mean pressures of tubes were expected to be 13.2 ± 3.0, 10.5 ± 2.4, and 6.4 ± 0.2 mmHg in MicroMT with full-length, half-length, and absence of intraluminal stents, respectively, and 12.5 ± 3.9, 9.6 ± 2.4, and 6.2 ± 0.2 mmHg in Finetube MT with full-length, half-length, and absence of intraluminal stents, respectively. The pressure variance also decreased with intraluminal stent retraction (p < 0.01).ConclusionsThe small diameter tubes of 100 and 200 µm internal diameters, with 7-0 and 5-0 nylon intraluminal stents, respectively, used in the MT-type glaucoma shunt device showed safe and effective outflow characteristics.

Simulation and theory of open-tube dispersion in short and long capillaries with slip boundaries and retention

Using random walk techniques, high resolution simulations of zone shape are conducted in open capillary tubes for short and long tube conditions. Finite size solutes are used as tracers in this treatment. Slip flow boundary conditions and wall retention are utilized as needed. These simulations are able to reproduce previous work in short and long tubes. For the short tube case where dispersion does not asymptotically approach the classic Taylor-Aris and Golay solutions, the effect of slip flow boundaries in the transient region shows zone shapes with abbreviated tails where the larger slip flow values cause zone compression. The use of slip flow to lower dispersion in capillary-based, wall-coated separations is shown to favor long tube behavior. This is because slip flow is relevant for cases where slip lengths are fractions of small capillary tube diameters. Incorporating slip flow into transport in capillaries favors a very small capillary radius where the cross-sectional diffusion length is very small and sampling times are fast. The purely convective zone shape with slip flow boundaries is derived analytically. Applications for this type of separation, guided by both analytical theory and simulation, show the potential for nano-sized capillary tubes less than 1 μm in diameter and favor very fast isocratic separations. Using long tube retention theory with slip boundaries shows that the dispersion-reducing region is most important in the range 0 ≤ k′ ≤ 1, a relatively small retention window. Further discussion of the gradient elution technique and dispersion in packed beds suggests that the general usage of slip flow boundaries is restricted in liquid phase separation systems.

Concentric annular heat pipe characterisation analysis for a drying application

We present a new configuration of concentric annular heat pipe (CAHP). A CAHP consists of two concentric tubes, with the smaller diameter tube positioned inside the larger one so that an annular space is created by sealing the ends whilst the inner space of the smaller tube is open to the surroundings. Evaporation and condensation take place along the length of the annular space. Unique to our CAHP design, the entire inner space of the central tube was designated as the condenser where wet ceramic slurries were to be conveyed through for moisture reduction. A 515 mm-long stainless steel CAHP was constructed for the present study with 76.2 and 38.1 mm outer and inner tube diameters, respectively. A screen wick was attached only to the inner wall of the outer tube. Several experimental parameters were investigated for their effects on axial temperature profile and thermal resistance: 11–43% filling ratios (a measure of fluid inventory inside the annular space), 0–90° angular orientations and 272–302 W heat inputs. An 11% filling ratio was found to be optimum, giving sufficient fluid inventory for wick saturation and compatible with all orientations and heat inputs. For the 11% filling ratio, vapour temperature differentials between heat pipe extremities were 0.4–1.3 K, showing an excellent isothermal condition. Global thermal resistances were calculated to be 0.08–0.31 K/W. As the wet loads were conveyed through the inner tube, vapour was condensed all along the outside surface of the inner tube, releasing thermal energy to the loads through radial heat transfer. The moisture content of the ceramic slurries was reduced from 33 wt% to 21 wt%, at the highest CAHP heat input of 302 W within 35 s residence time, demonstrating the promising potential of the CAHP as an efficient moisture removal technology.

A micropolar fluid model for hydrodynamics in the renal tubule

The creeping flow of an incompressible micropolar fluid in a small-diameter permeable tube is studied. The fluid absorption at the tube walls is taken as a function of wall permeability and the pressure gradient across the tube wall. Closed-form solutions of the governing equations for the pressure, velocity and micro-rotation fields are obtained. Expressions describing variations in the axial volume flow rate, mean pressure, wall leakage flux, wall shear stress and the fractional re-absorption are derived. Effects of the wall permeability coefficient K , the micropolar parameter m and the coupling number N on flow variables are graphically presented and implications of results are discussed briefly. The obtained solutions are applied to the flow problem in the proximal renal tubule and probable values of the wall permeability parameter and the mean pressure drop in the tubule are obtained. It is found that the mean pressure drop in the proximal tubule is higher for the micropolar fluid than for the Newtonian fluid. It is also found that the volume flow rate of the micropolar fluid decreases exponentially as a function of the axial distance. This is a biologically significant result which is well accepted and is reported in the literature by earlier researchers too. The derived solutions coincide well with the existing solutions for the Newtonian fluid flow in a permeable tube as a special case.

Experimental Investigation of Vibration Response of A Free-Hanging Flexible Riser Induced by Internal Gas-Liquid Slug Flow

The vibration response of a free-hanging flexible riser induced by internal gas-liquid slug flow was studied experimentally in a small-diameter tube model based on Froude number criterion. The flow regime in a curved riser model and the response displacements of the riser were simultaneously recorded by high speed cameras. The gas superficial velocity ranges from 0.1 m/s to 0.6 m/s while the liquid superficial velocity from 0.06 m/s to 0.3 m/s. Severe slugging type 3, unstable oscillation flow and relatively stable slug flow were observed in the considered flow rates. Severe slugging type 3 characterized by premature gas penetration occurs at relatively low flow rates. Both the cycle time and slug length become shorter as the gas flow rate increases. The pressure at the riser base undergoes a longer period and larger amplitude of fluctuation as compared with the other two flow regimes. Additionally, severe slugging leads to the most vigorous in-plane vibration. However, the responses in the vertical and horizontal directions are not synchronized. The vertical vibration is dominated by the second mode while the horizontal vibration is dominated by the first mode. Similar to the vortex-induced vibration, three branches are identified as initial branch, build-up branch and descending branch for the response versus the mixture velocity of gas-liquid flow.

Two-phase pressure drop of ammonia in horizontal small diameter tubes: Experiments and correlation

A series of experiments are conducted to investigate the two-phase pressure drop of ammonia in horizontal small diameter tube. The experiments are performed at saturation temperatures of −15.8–4.6 °C, and the mass flux range is from 20 to 100 kg m−2 s−1. This paper analyzes the influence mechanisms of vapor quality, mass flux, saturation temperature, and tube diameter on the two-phase frictional pressure gradient in detail. Meanwhile, several correlations are compared with all the experimental data and the results show that the Müller-Steinhagen and Heck (1986) correlation gives the best agreement. With the analysis of the major forces for ammonia two-phase flow under the tested experimental conditions, the Reynolds number and Bond number are introduced to modify the Müller-Steinhagen and Heck (1986) correlation. Lastly, a modified correlation is developed with the mean absolute deviation of only 13.5%, and 89.2% of the data are within the ± 30% error band. In addition, the modified correlation is evaluated based on a complied database which contains 951 experimental data points from 11 published literatures.

Correlation for Condensation Heat Transfer in a 4.0 mm Smooth Tube and Relationship with R1234ze(E), R404A, and R290

In this study, the condensation heat transfer coefficient and pressure drop characteristics of a 4 mm outside diameter smooth tube, using R32, R152a, R410A, and R1234ze(E) refrigerants, were examined. Condensation heat transfer coefficients and pressure drops were measured at a saturation temperature of 35 °C, in the region of mass velocities from 100 to 400 kg m−2s−1. The frictional pressure drop, and the condensation heat transfer from the new measurements, using R1234ze(E) as a refrigerant, were compared with those of R32, R152a, and R410A, in the smooth tube. Experimental values of condensation heat transfer coefficient of smooth tube were also compared to the predicted values obtained using the previously established correlations. The previous correlation from Cavallini et al., for the condensation heat transfer coefficient of small-diameter smooth tube, was estimated to be within ±30%. However, the general correlation, which can be easily predicted, for condensation heat transfer inside small-diameter smooth tubes, was suggested, and the relationship of the general correlation was compared with data for R1234ze(E) obtained by us, and R404A and R290 obtained by other researchers.

Upgrades of the ATLAS muon spectrometer with new small-diameter drift tube chambers

Abstract Small diameter muon drift-tube (sMDT) chambers with 15 mm tube diameter provide excellent spatial resolution like the MDT chambers with 30 mm tube diameter used in the ATLAS muon spectrometer so far, but can be operated at ten times higher background rates and allow for the instrumentation of regions where MDT chambers do not fit in. In April 2014 two such chambers (called BME) have been installed at the bottom of the barrel middle layer of the muon spectrometer, followed in January 2016 by another 12 sMDT chambers (called BMG) inserted in the detector feet in the barrel middle layer. They are since then operational in ATLAS, increasing the acceptance for precision muon momentum measurement in all three chamber layers. An unprecedently high sense wire positioning accuracy of 5 μ m (rms) has been achieved. In the next long LHC shutdown 2019–2020, 16 new sMDT chambers (called BIS 78) will be installed in the barrel inner layer in the transition region to the endcaps in order to make room for the installation of new RPC muon trigger chambers which will reduce the accidental trigger rate in this region as required for operation at the high-luminosity upgrade of the LHC (HL-LHC). This is a pilot project for the complete replacement of the MDT chambers in the small azimuthal sectors of the barrel inner layer (called BIS 1-6) by integrated sMDT-RPC detectors in the long shutdown 2024–2026 for the upgrade to HL-LHC.

Influence of defect-induced deformations on electron transport in carbon nanotubes

We theoretically investigate the influence of defect-induced long-range deformations in carbon nanotubes on their electronic transport properties. To this end we perform numerical ab-initio calculations using a density-functional-based tight-binding model for various tubes with vacancies. The geometry optimization leads to a change of the atomic positions. There is a strong reconstruction of the atoms near the defect (called ‘distortion’) and there is an additional long-range deformation. The impact of both structural features on the conductance is systematically investigated. We compare short and long CNTs of different kinds with and without long-range deformation. We find for the very thin (9, 0)-CNT that the long-range deformation additionally affects the transmission spectrum and the conductance compared to the short-range lattice distortion. The conductance of the larger (11, 0)-or the (14, 0)-CNT is overall less affected implying that the influence of the long-range deformation decreases with increasing tube diameter. Furthermore, the effect can be either positive or negative depending on the CNT type and the defect type. Our results indicate that the long-range deformation must be included in order to reliably describe the electronic structure of defective, small-diameter zigzag tubes.

Design and construction of integrated small-diameter drift tube and thin-gap resistive plate chambers for the phase-1 upgrade of the ATLAS muon spectrometer

In the long shutdown for the Phase-1 upgrade of the Large Hadron Collider (LHC) in 2019–2020, 16 new integrated muon tracking and trigger chambers will be installed at the ends of the toroid magnet coils in the small azimuthal sectors of the inner barrel layer (BIS) of the ATLAS muon spectrometer in order to improve the trigger selectivity and fake trigger suppression in the transition region 1 . 0 < | η | < 1 . 3 between the barrel part and the endcaps. The new muon detectors consist of a small-diameter muon drift tube (sMDT) precision tracking chamber with 15 mm tube diameter and a pair of thin-gap RPC chambers with 1 mm gas gap width. The new integrated chamber modules (labeled BIS 78) are currently under construction and will replace the present BIS 7 and 8 MDT tracking chambers with 30 mm diameter drift tubes. The project is the pilot phase for the complete replacement of the small barrel inner layer MDT chambers with the new integrated tracking and trigger detectors in the ATLAS Phase-2 upgrade in 2024–2026 in order to increase the barrel first-level muon trigger coverage and efficiency at the high luminosities at HL-LHC. The sMDT chambers have been chosen to make room for the new trigger chambers and because of their eight times higher rate capability than MDT chambers. The new thin-gap RPC chambers have about 15 times lower avalanche charges and correspondingly increased lifetime and rate capability at HL-LHC and will be operated in coincidence with the endcap trigger chambers. They consist of a triplet of gas gaps which has to be very thin as well and which is supported by a light-weight aluminum structure which is interleaved with the sMDT chamber supports.

Experimental study on the heat transfer characteristics of saturated liquid nitrogen flow boiling in small-diameter horizontal tubes

Experiments were performed to investigate the heat transfer characteristics of the saturated liquid nitrogen flow boiling in a horizontal tube with an internal diameter of 1.98 mm. The heat transfer coefficients were obtained within a wide range of operation conditions, i.e. inlet pressure from 230 to 420 kPa, mass flux from 200 to 690 kg·m−2·s−1, heat flux from 1.5 to 67.1 kW·m−2, and vapor quality from 0 to 0.81. In the low vapor quality region, heat transfer coefficients showed strong dependence on heat flux and pressure but varied little with mass flux or vapor quality, indicating the dominant role of the nucleate boiling over the convective evaporation. The influence of convective evaporation became noticeable in the intermediate-to-high vapor quality region. A modified correlation was proposed by including both the influences of the nucleate boiling and the convective evaporation, which could predict the experimental data with MAD of 16.4%.

Experimental investigation of heat transfer coefficient with Al2O3 nanofluid in small diameter tubes

At present, heat transfer phenomena in the microscale and nanoscale systems have been strongly highlighted in the engineering applications of MEMS, NEMS, IC and IT. Since the electronic devices used in such applications involve a considerable amounts of heat generation in a service, a new type of cooling technology should be considered for the proper operation of them. In this study, the heat transfer coefficients of nanofluid, which is the mixture of nanosized alumina (Al2O3) particles and water, were studied with small copper tubes of three different sizes (0.8 mm, 1.6 mm and 2.0 mm) to identify the heat transfer coefficients according to the Reynolds number and the concentrations of alumina. For the even dispersion of the nanoparticles in the base liquid, ultrasound excitation was applied for 3.0 h and the degrees of nanoparticle dispersion with alumina concentrations were measured by using UV–VIS spectrophotometer. Additionally, the thermal conductivities of the nanofluids and the base fluid were measured by the transient hot-wire method. As the Al2O3 concentration of nanofluid was increased, it was confirmed that the thermal conductivity was also increased. According to the results of the heat transfer coefficient measurement, the heat transfer coefficient was increased as the Reynolds number or Al2O3 concentration was increased, and as the tube diameter gets smaller. When reducing the tube diameter at a constant flowrate, it was shown that the heat transfer coefficient was considerably increased. In the experimental ranges, the heat transfer coefficient at 0.8 mm diameter was averagely about 160% higher compared to 2.0 mm diameter at the Reynolds number of 1588.

Shear response of concrete filled tubes part 1: Experiments

Concrete-filled steel tubes (CFSTs) and internally-reinforced CFSTs (RCFSTs) are most commonly used as columns/piers or piles or shafts for deep foundations for buildings and transportation structures. Accurate engineering properties of CFSTs are needed but, in many cases, these expressions have been derived from reinforced concrete (RC) or structural steel design expressions and do not accurately capture the strength of CFSTs. In particular the steel tube without the concrete is prone to premature buckling and the shear reinforcement of RC components is discontinuous; clearly neither is an appropriate starting expression for CFTs with restrained and continuous steel. Although prior research has focused on the strength of CFSTs under axial and flexural loading, in comparison with flexural studies, very few research studies have evaluated the shear strength of CFSTs or RCFSTs. Most specifications compute the shear capacity of CFST by either assuming that either the steel alone contributes to the shear strength or by treating the CFST as a reinforced concrete member reinforced by the steel tube (analogous to spiral). Comparison of these existing provisions with prior test results performed on small-diameter tubes (approximately 150 mm (6 in.) in diameter) shows that these current expressions greatly underestimate the shear capacity of CFST. To develop a more accurate expression, a research program was undertaken to experimentally and analytically investigate the shear capacity of large-scale (508 mm or 20 in. diameter) tubes. A range of design parameters including shear-span aspect ratio, diameter-to-thickness ratio (D/t), concrete compressive strength, tube type, tail length and interface condition were studied. The tests were used to determine the response mode (flexure, shear or bond) and a simple numerical expression was developed to separate flexural and shear response modes. For specimens failing in shear, the effects of the parameters which impacted the behavior are described. The research experimental results are combined with prior research results and used to evaluate different shear expressions for CFST and RCFST. The final design expression is presented in the companion paper; this expression was validated using these results as well as those from the experimentally-validated parametric study conducted with high-resolution numerical models. The resulting shear strength is approximately twice current expressions.

Full-Range Compressive Stress–Strain Curves for Cold-Formed 304 Stainless Steel Circular Hollow Sections After Exposure to Vacuum Brazing

With the rapid development of microscale cellular structures, the small-diameter cold-formed welded stainless steel tubes have recently been used for creating the metallic lattice topologies with high mechanical properties. In this paper, to obtain the accurate material properties of the circular hollow section (CHS) under pure compression, a series of concentric compression tests are conducted on the millimeter-scale cold-formed 304 stainless steel circular tubular stub columns after exposure to a vacuum brazing process. The tests cover a total of 18 small-diameter stub tubes with measured thickness-to-diameter ratios (t / D) from 0.023 to 0.201. A generalized three-stage nominal stress–strain model is developed for describing the compressive behavior of the post-brazing CHSs over the full strain range. This mechanical model is especially applicable to computer code implementation. Hence, an interactive computer program is developed to simultaneously optimize three strain hardening exponents $$(n_1 ,n_2 ,n_3 )$$ in the expression of the model to produce the stress–strain curve capable of accurately replicating the test data. To further reduce the number of the model and material parameters on which this model depends, this paper also develops five expressions for determining the 2.5% proof stress $$(\sigma _{p_2 } )$$ , $$n_2 $$ , the ultimate compressive strength $$(\sigma _{p_3 } )$$ , $$n_3 $$ , and the ultimate plastic strain $$(p_3 \% )$$ for given experimental values of three basic material parameters $$(E_0 ,\sigma _{0.01} ,\sigma _{0.2} )$$ . These expressions are validated to be effective for the CHSs with $$t{/}D\ge 0.027$$ . The analytically predicted full-range stress–strain curves have generally shown close agreement with the ones obtained experimentally.

The research and application of coiled tubing technology of horizontal well in drainage gas recovery

The Su 75 block is a typical low-permeability, low-pressure and low-abundance gas field, 89.6 percent of the gas wells are water-bearing, so it makes the drainage gas recovery become vital means for sustainable development. Recently, the main drainage gas recoveries are the foam drainage gas recovery, plunger drainage gas recovery, compressor/nitrogen gas lift and so on. These measures do not work in all water-bearing gas wells, especially for horizontal wells of big-size production string and gas wells of low entrainment capability. Based on the characteristics of drainage gas recovery and the applicable condition analysis, drainage gas recovery technology of downhole small diameter tubing of the horizontal wells without well killing is put forward. The feasibility was analyzed theoretically, and field experiment was carried out with remarkable effect.

Boiling heat transfer and flow characteristic of R32 inside a horizontal small-diameter microfin tube

This study experimentally investigated the flow boiling heat transfer and pressure drop characteristics of R32 inside a horizontal small-diameter microfin tube with an equivalent diameter of 3.48 mm. The boiling heat transfer coefficient and pressure drop were measured in a mass velocity range of 50–400 kgm−2 s−1, heat flux range of 5–20 kWm−2, and saturation temperature of 15 °C. The flow pattern at the outlet of the test microfin tube was observed and classified as wavy-slug flow and annular flow regime. The effects of quality, mass velocity, heat flux, and flow pattern on the flow boiling characteristics were clarified. The heat transfer mechanism was characterized by forced convection, nucleate boiling, and evaporation heat transfer through the thin liquid film inside the grooves. No difference in the frictional pressure drop on adiabatic and boiling flows was observed. The measured heat transfer and frictional pressure drop were compared with those in previous correlations.

Numerical study of a micro flow reactor at engine pressures: Flames with repetitive extinction and ignition and simulations with a reduced chemical model

Combustion in a narrow channel with an imposed temperature gradient is studied numerically at elevated pressure with engine-relevant fuels. The focus is placed on unsteady flames with repetitive extinction and ignition (FREI) to determine the potential of this regime for fuel testing and calibration of reduced chemical mechanisms. First, it is shown that the FREI regime does occur at elevated pressures for sufficiently small tube diameters. The sensitivity of the extinction and ignition temperatures to low-temperature chemistry is found to be significantly enhanced at 25 bar compared to atmospheric conditions. The ignition and extinction temperatures differ by up to 100 K between PRF mixtures with varying octane numbers. Ternary mixtures of iso-octane/n-heptane/toluene and iso-octane/n-heptane/ethanol at similar research and motor octane numbers are also studied. Second, the potential of using data from the micro flow reactor to infer reaction rates is assessed. A reduced chemical mechanism combining a small fuel-dependent submechanism with a detailed fuel-independent submechanism for the core species chemistry is used for that purpose. Only the most sensitive fuel-dependent reactions are inferred. the calibrated reduced model is compared to a detailed model and good agreement in ignition delay times and laminar flame speeds is observed. This illustrates the potential of a micro flow reactor with a controlled temperature profile to test fuels and infer kinetic data.

The crushing characteristics of reinforced Nomex honeycomb

A Nomex honeycomb core has been reinforced with small diameter composite rods and tubes in order to enhance its compression properties and energy-absorbing characteristics. The influence of the areal density of the rods and tubes on the strength and energy-absorbing properties of the reinforced honeycomb was investigated by introducing increasing numbers of rods/tubes in square samples with bonded composite skins. An initial series of crushing tests on arrangements of small tubes and rods resulted in a stable model of failure yielding specific energy absorption values of approximately 45 kJ/kg for the tube and rod-based structures. A subsequent observation of the failed tubes highlighted the similar failure processes to those observed previously following the tests on much larger composite cylinders. Mechanical tests on the Nomex cores have shown that the compression strength and energy-absorbing characteristics of the reinforced honeycombs increase rapidly with increasing composite reinforcement. At low and intermediate values of core density, the rod and tube-reinforced cores exhibited similar properties, in terms of their compression strengths and specific energy absorption, an effect that is likely to be due to the dominance of the heavier Nomex core in these samples. At higher densities, the rod-reinforced systems tended to out-perform their tube-reinforced counterparts. Tests at impact rates of strain have shown that the compression strength and energy-absorbing capabilities of the reinforced cores are higher under the dynamic conditions, with the rod-reinforced cores offering values of specific energy absorption as high as 78 kJ/kg.

Heat transfer and pressure drop characteristics of ammonia during flow boiling inside a horizontal small diameter tube

In this article, a series of experiments was conducted to investigate the flow boiling heat transfer and pressure drop characteristics of ammonia in a 4 mm horizontal plain tube. The experiments were performed for heat fluxes at 9 and 21 kW m−2 K−1, mass flux from 50 to 100 kg m−2 s−1, and saturation temperature from −15.8 to 5 °C. The experimental results show that with the increase of heat flux, the heat transfer coefficient increases. Meanwhile, it also increases with a rise in mass flux in the low vapor quality region, whereas reversed situation can take place in the high vapor quality region when the saturation temperature is decreased. The saturation temperature has little effect on the heat transfer coefficient in the low vapor quality region, however at higher mass fluxes, the heat transfer coefficient can decrease with decreasing saturation temperature in the high vapor quality region. The comparisons of the experimental data with existing correlations for flow boiling heat transfer coefficient show that Gungor and Winterton correlation can give good agreement with mean absolute deviation of 19.6% even though it is developed for turbulent flow. The adiabatic two-phase frictional pressure gradient increases with the increase of vapor quality and mass flux, while decreases with the increase of saturation temperature. The comparisons with existing correlations for two-phase frictional pressure gradient indicate that Müller-Steinhagen and Heck correlation can predict the experimental data well with mean absolute deviation of 16.1% and 93.4% of the data is within the ±30% error band.

Experimental study of vertical co-current slug flow in terms of flow regime transition in relatively small diameter tubes

In order to investigate the evolution characteristics of structure parameters during flow regime transition process in gas-liquid slug flow, the vertical upward slug flow in a wide range of liquid superficial velocity (0.03< jl<1.6m/s) are studied in a tubular test section with the inside diameter of 25.4mm. Impedance void meters are employed to measure the time series of cross-sectionally averaged void fraction of separated two parts corresponding to Taylor bubble and liquid slug. With increasing flow gas flow rates at constant liquid flow rate, the present research studies the evolution of length and void fraction of each part in slug unit. New structure of turbulent slug unit in strong relation with transition process is observed. It is found that such special structure plays an important role in transition from slug flow to churn-turbulent flow. It is also found that the flooding determines whether the flow regime evolves into churn-turbulent flow or directly into annular flow. By studying the evolution of flow regimes, two structure parameters, void fraction of liquid slug and length ratio of Taylor bubble to liquid slug, can be used as the transition criterion. New criterion for the transition from slug flow to churn-turbulent flow was also proposed based on these two parameters. It is found that the current results agree well with the existing flow regime map for relatively small diameter tubes in literature.