ID Tube Research Articles

CODE BLUE in a patient with tracheal stent: Are we fully equipped?

Sir, Airway stents have long been used to maintain luminal integrity of compromised airway in case of obstruction and malignancy.[1] The complications associated with airway stent placement are malposition, haemorrhage, airway rupture during placement, migration, impaction, formation of granulation tissue, and stent fracture.[2] We present here a challenging case of an airway emergency in a patient with a tracheal stent inserted for a malignancy. A 29-year-old woman diagnosed with adenoid cystic carcinoma of trachea 2 years back had undergone debulking of tumor, tracheal stenting with a metallic stent, and chemo-radiotherapy elsewhere. On the second day of admission, CODE BLUE was activated in view of acute onset biphasic stridor, with air hunger and low oxygen saturation. Despite resuscitation measures, the patient had persistent tachycardia, tachypnea, and hypoxia with non-rebreathing mask (15 L/min of O2). A review of Computed Tomography (CT) neck revealed a tracheal narrowing 1.7 cm distal to vocal cords with narrowest diameter of 6 mm [Figure 1a], complicating an imminent intubation for the patient. She was pre-oxygenated with a non-invasive ventilation mask. Intravenous boluses of fentanyl 75 mcg, muscle relaxant (suxamethonium 100 mg) was given and intubated with a 5.0 mm ID cuffed endotracheal (ET) tube through direct laryngoscopy. A chest x-ray confirmed the position of the ET tube but it fell short of bypassing the tracheal stent, which was reflected in decreased tidal volumes and increased peak pressure. As the length of the 5.0 mm ET tube (23 cm) was not enough to bypass the stent, we had to increase the length by rail roading another 6.5 mm ID tube at the distal end, after removing the connector [Figure 1b]. This step significantly improved the tidal volumes (350-400 ml) without much rise in peak pressure with marked improvement in the oxygenation of patient in the blood gas analysis. Patient underwent bronchoscopic biopsy and excision of mass around the stent after putting on veno-venous extracorporeal membrane oxygenation for oxygenation. Post-procedure ET tube was removed after suctioning and intubated with 7.0 mm ID ET tube for postoperative ventilation and eventually extubated.Figure 1: (a) image showing CECT neck with tracheal stent in situ. (b) image showing the proximal end of 6.5 mm ID tube is cut and railroaded over 5.0 mm ID tube to increase the lengthSecuring airway in an in-hospital CODE blue needs quick thinking and swift action. This case highlights a unique situation where a tracheal stent precluded a “conventional intubation.” A tracheostomy could damage the stent and a supraglottic airway device risked aspiration.[3] A fibre-optic bronchoscope is essential and the best available option to ensure correct position of the tube within the stent or just above the stent. It can also avoid stent-related complications but is not readily available everywhere.[4] No formal guidelines are available in terms of airway management with tracheal stents in situ. A literature search also revealed paucity of data with regard to management in similar case scenarios. Microlaryngeal surgery (MLS) tubes can be made available in the CODE BLUE kits anticipating such scenarios, as they are longer than conventional ET tubes with same internal diameter.[5] This case though uncommon highlights the need to incorporate airway management in cases of tracheal stents as part of our teaching curriculum. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Categorization of liquid-liquid counter-current two-phase flow-structures in 11 mm ID tube at different conduit-orientations

Attempts are made to identify, characterize, and automatically categorize the liquid-liquid counter-current two-phase flow-structures in a circular-conduit of 11 mm diameter by varying the flow-orientation. Rigorous experimentations are performed for a wide range of superficial kerosene and water velocities at seven conduit-orientations. Some unique liquid-liquid counter-current two-phase flow-structures, not reported in the literature to date, are found in the present investigation. Interfacial distributions and the highly time-varying nonlinear attributes of the flow-structures corresponding to different combinations of the superficial water and kerosene velocities at each conduit-orientation are detected and recognized through high-resolution photography and high-speed videography. Objective descriptions of the flow-structures are accumulated in the form of time-series current and voltage signals using a differential-pressure-transmitter and in-house fabricated conductivity-probes, respectively. Statistical analyses are performed to parameterize the time-series repetitive objective signatures. The non-parametric probability distribution plot and statistical parameters extracted from the signals are found to be very effective in detecting and distinguishing the individual flow-structures. Flow-structures are parameterized using those statistical parameters. A computational intelligence-based categorization methodology is developed to automatically categorize the obtained flow-structures considering these statistical parameters as the inputs. A good agreement is found for each orientation between the flow-regime groups based on visual observation and those obtained through the categorization methodology. It simply establishes that the flow-structures are perfectly characterized by the statistical parameters extracted from their objective-signatures.

Characterization of R134a two-phase flow regimes in horizontal and vertical smooth tubes with capacitive sensors

This paper presents the identification of slug/stratified-wavy, stratified-wavy and annular regimes for horizontal flow (in the range of mass fluxes 40 – 150 kg m−2 s−1), and slug, churn, and annular flow regimes for vertical upward flow (in the range 65 – 115 kg m−2 s−1) for R134a flow through 7 mm ID tube. Flow regimes are characterized based on time plot of normalized capacitive signals, kernel density estimation (KDE), power spectral density (PSD), and visualization results from a high-speed camera. Sensors with different axial lengths (D, 2D/3, and D/2) are also tested to study the adequacy of shorter sensors for the characterization of flow regimes. Results show that all three sensors have a similar capability of characterizing flow regimes, justifying the use of the shorter sensors in many applications with limited space.

Diffusion and Dispersion in Tubes in Supercritical Fluid Chromatography Using Sub-2 µm Packings

Detailed plots of diffusion coefficients, Dm, versus % methanol in CO2 and pressure, P, are presented. Using sub-2 µm particle columns with small ID connector tubing make for large pressure drops, ∆P, across both the system and the column. This creates low average Dm, and large gradients in Dm, slowing the chromatography. The ∆P with 75 µm ID tubing varies non-linearly with flow creating U shaped plots of reduced plate height versus flow rate. Plumbing does but should never change h versus F plots. Using larger ID tubes to estimate the extra-column variance $$\sigma_{e - c}^{2}$$ of smaller tubes, by keeping the aspect ratio (L/r) constant, assumes the same constant Dm in both tubes, which is not true in SFC. Contrary to prediction, calculated tube plate count, N, indicates connector tubing is more dispersive in SFC compared to high performance liquid chromatography (HPLC). Current supercritical fluid chromatographs (SFC) have up to 20 × higher variance than appropriate for use with 2.1 and 3 mm columns ≤ 100 mm long, packed with sub-2 µm particles. Lower volume UV detector flow cells are needed for use with sub-2 µm particles. The modular nature of instruments makes it difficult to further minimize tube lengths while retaining column temperature control. Very small ID tubes, like 75 µm should probably be avoided. It remains difficult to characterize and minimize $$\sigma_{e - c}^{2}$$ .

Flow boiling heat transfer of R134a in a 500 µm ID tube

The present paper presents experimental results for the heat transfer coefficient during flow boiling of refrigerant R134a in a circular channel with internal diameter of 500 µm. The experimental database covers mass velocities ranging from 200 to 800 kg/m2 s, heat fluxes up to 100 kW/m2 and vapor qualities from 0.02 to 0.75 for a saturation temperature of 40 °C. The experimental data were parametrically analyzed and the effects of the experimental parameters (heat flux, mass velocity and vapor quality) identified. Additionally, images of two-phase flow were obtained through a high-speed camera and employed to identify the flow patterns. A flow pattern map was built and compared to prediction methods from the literature. In general, the heat transfer coefficient increased with increasing mass velocity and heat flux. The experimental data were compared against seven flow boiling predictive methods from the literature. Sun and Mishima (Int J Heat Mass Transf 52(23):5323–5329, 2009. https://doi.org/10.1016/j.ijheatmasstransfer.2009.06.041 ) and Kanizawa et al. (Int J Heat Mass Transf 93:566–583, 2016. https://doi.org/10.1016/j.ijheatmasstransfer.2015.09.083 ) methods provided the best prediction of the experimental results with only Kanizawa et al. (2016) capturing the experimental heat transfer trends.

Neonatal Pierre Robin sequence: An airway challenge addressed with retrograde intubation

We report the case of a 25-day-old neonate posted for glossopexy. The child born at 35 weeks of gestation was diagnosed to have Pierre Robin sequence. The neonate was underweight (2.2 kg), had difficulty in feeding and had respiratory distress needing respiratory assistance and prone position to maintain saturation. Anticipating difficulty in intubation with respect to physiology, age and mismatch of equipment size, we planned retrograde intubation through a laryngeal mask airway with a 2.5 mm ID tube using a needle cricotracheotomy and a flexible-tipped paediatric urological guidewire. Based on our experience, we propose that neonatal difficult airway can be managed using the retrograde intubation technique.

Experimental investigation of gravity and channel size effects on flow boiling heat transfer under hypergravity

Abstract Understanding of flow boiling heat transfer under hypergravity is needed due to its applications to modern flight vehicles. Few investigations on this issue have been reported. The present paper presents the experimental results of R134a flow boiling heat transfer in 1.002 and 2.168 mm ID tubes under hypergravity up to 3.16 g. The results reveal effects of gravity, channel size, heat flux, mass flux, quality, and pressure on and their interrelations in flow boiling heat transfer. Gravity has strong effects on flow boiling heat transfer. The heat transfer coefficients (HTCs) under hypergravity levels up to 3.16 g are normally greater than those under Earth's gravity. The heat transfer characteristics in the 1.002 and 2.168 mm tubes are very different, indicating that gravity effects on flow boiling heat transfer strongly interrelate with channel size. Also, gravity effects on flow boiling heat transfer are influenced by heat flux, mass flux, and pressure, and somewhat related to quality.

Reduced Plate Height of 1.65 on a 20 × 3 mm Column Packed with 1.8 µm Particles in Supercritical Fluid Chromatography (SFC)

The plumbing of a commercial supercritical fluid chromatograph was modified by replacing all the connector tubing with the shortest possible lengths (65 cm) of 75 µm ID tubes. Heat exchangers controlling column temperatures and column outlet temperature were bypassed. The UV detector flow cell was replaced with an experimental cell with a 75 µm inlet tube, and a 2 µL internal volume. All these steps were taken to minimize extra-column dispersion. The extra-column dispersion was decreased from ≈ 80 µL2 in the commercial instrument to roughly 2 µL2 with the modifications. Reduced plate heights as low as 1.65 were obtained using a 20 × 3 mm column packed with 1.8 µm particles. This is a remarkably low value for such a short column. The optimum flow was ≈ 2.5 mL min−1. The system pressure drop at optimum was 220 bar (320 bar pump pressure), but increased rapidly with flow rate, to 450 bar (550 at pump) at 3.5 mL min−1.

An investigation of the effect of nanoparticle composition and dimension on the heat transfer coefficient during flow boiling of aqueous nanofluids in small diameter channels (1.1 mm)

The present paper concerns an experimental investigation of the effect of adding nanoparticles to DI-water on the heat transfer coefficient during flow boiling in a 1.1mm ID tube. Results were obtained for DI-water and solutions of Al2O3 (20–30nm)/DI-water, Al2O3 (40–80nm)/DI-water, SiO2 (80nm)/DI-water, SiO2 (15nm)/DI-water and Cu (25nm)/DI-water for nanoparticles volumetric concentrations of 0.001, 0.01 and 0.1%. Additional results were obtained for pure DI-water before and after performing tests with nanofluids in order to evaluate the effect of nanoparticles deposition due to the boiling process on the heat transfer coefficient. Experiments were carried out for heat fluxes up to 350kW/m2, mass velocities ranging from 200 to 600kg/m2s, vapor qualities up to 0.5 and saturation temperatures at the test section outlet of 102°C. An analysis of the surface roughness and a characterization of its texture using an optical profiler were also performed before and after the experiments with nanofluids. According to most of the results, the heat transfer coefficient for flow boiling of nanofluids is lower than for DI-water in a tube without nanoparticles deposition. The data analyses revealed that the nanoparticles dimension affects the heat transfer behavior. This fact is associate to the nanoparticles deposition on the surface and its effect on the density of active nucleation sites. This hypothesis is corroborated by the fact that the deposition characteristics depends on the nanoparticles size.

Temperature controlled interval contact design for ultrasound assisted liquid–liquid extraction

This work aims at constructing a design which integrates a direct (solid) contact method with temperature control for chemical process applications. To realise this integration a two-step approach is proposed. Firstly, temperature control is achieved by suspending the tubing in a temperature controlled and sonicated liquid medium (indirect contact). Secondly, direct contact elements are introduced at regular intervals along the tubing. Therefore, this design is termed the hybrid contact reactor, as it incorporates both direct and indirect approaches of ultrasound transfer. Furthermore, two possible configurations, open and closed interval connection to the tubing, were assessed. Both hybrid reactors performed better than the indirect contact reactor (20–27% increase in yield) for residence times of less than 45s and similar for residence times above. Even though the performance of the two hybrid designs was similar the closed interval resulted in more reproducible and distinct yields. This configuration was then scaled up 10 times in internal volume using a 2mm ID tube. This design showed a relative performance similar to the interval contact design which gave the highest yields thus far for the same operating conditions.

Convective heat transfer at high subcritical pressures in tubes with and without flow obstacles

Heat transfer measurements to CO2-cooled tubes with and without flow obstacles at high subcritical pressures were obtained at the University of Ottawa’s supercritical test facility. Tests were performed for vertical upward flow in a directly heated 8mm ID tube for a pressure range from 6.6 to 7.2MPa, a mass flux range from 115 to 1000kgm−2s−1, and a wall heat flux range from 1 to 122kWm−2. Cases with spacing between obstacles equal to 250, 500 and 1000mm were investigated. The results are presented in plots of wall temperature and heat transfer coefficient vs. bulk fluid enthalpy. The effects of flow conditions and obstacle geometry and spacing on high subcritical heat transfer have been discussed. Obstacles were found to suppress nucleate boiling, increase the CHF and lower the maximum post-CHF temperature. The maximum increases in CHF and in post-dryout heat transfer coefficient were observed for the obstacles having a spacing of 250mm. Comparisons of the experimental data with prediction methods for single-phase heat transfer, CHF and post-dryout heat transfer are also presented.

Convective heat transfer in supercritical flows of CO2 in tubes with and without flow obstacles

Heat transfer measurements to CO2-cooled tubes with and without flow obstacles at supercritical pressures were obtained at the University of Ottawa’s supercritical pressure test facility. The effects of obstacle geometry (obstacle pitch, obstacle shape, flow blockage) on the wall temperature and heat transfer coefficient were investigated. Tests were performed for vertical upward flow in a directly heated 8mm ID tube for a pressure range from 7.69 to 8.36MPa, a mass flux range from 200 to 1184kg/m2s, and a heat flux range from 1 to 175kW/m2. The results are presented graphically in plots of wall temperature and heat transfer coefficient vs. bulk specific enthalpy of the fluid. The effects of flow parameters and flow obstacle geometry on supercritical heat transfer for both normal and deteriorated heat transfer are discussed. A comparison of the measurements with leading prediction methods for supercritical heat transfer in bare tubes and for spacer effects is also presented. The optimum increase in heat transfer coefficient was found to be for blunt obstacles, having a large flow blockage, and a short obstacle pitch.

Two-phase flow boiling pressure drop in small channels

Two-phase flow boiling in small channels finds a variety of applications in power and process industries. Heat transfer, boiling flow regimes, flow instabilities, pressure drop and dry out are some of the key issues related to two-phase flow boiling in channels. In this work, the focus is on pressure drop in two-phase flow boiling in tubes of 19mm diameter. These tubes are typically used in steam generators. Relatively limited experimental database is available on 19mm ID tube. Therefore, in the present work, the experimental set-up is designed for studying flow boiling in 19mm ID tube in such a way that any of the different flow regimes occurring in a steam generator tube (from pre-heating of sub-cooled water to dry-out) can be investigated by varying inlet conditions. The reported results cover a reasonable range of heat and mass flux conditions such as 9–27kW/m2 and 2.9–5.9kg/m2 s respectively. In this paper, various existing correlations are assessed against experimental data for the pressure drop in a single, vertical channel during flow boiling of water at near-atmospheric pressure. A special feature of these experiments is that time-dependent pressures are measured at four locations along the channel. The steady-state pressure drop is estimated and the identification of boiling flow regimes is done with transient characteristics using time series analysis. Experimental data and corresponding results are compared with the reported correlations. The results will be useful for understanding key aspects of flow boiling in small channels.

Two‐phase flow boiling in 19 mm tube: Experiments and CFD modelling

Boiling flows are encountered in a wide range of industrial applications such as boilers, nuclear reactors, electronic cooling, and various types of chemical reactors. Heat transfer coefficients, flow boiling regimes, flow instabilities, pressure drops, and conditions like dry‐out are some of the key issues in every boiling flow study. It is observed that a limited experimental database is available for the 19 mm ID channel diameter, i.e. a typical tube diameter of steam generator. Therefore, in the present work, the experimental setup was designed for studying boiling flows in a 19 mm ID tube in such a way that different flow regimes occurring in a steam generator tube (from pre‐heating of sub‐cooled water to dry‐out) could be investigated by varying inlet conditions. The reported results cover a reasonable range: 8–27 kW/m2 and 2.9–5.9 kg/m2 · s heat and mass flux conditions, respectively. A basic computational flow model was also developed to facilitate interpretation of the obtained data. The presented design of the experimental setup and the approach of mimicking different types of steam generator tubes as well as presented experimental and simulated results are useful for gaining insight into complex boiling flows in tubes, and provide a sound basis for further work in this area.

Liquid transport during gas flow transients applied to liquid loading in long vertical pipes

An experimental study was carried out to investigate the liquid distribution and transport in vertical gas–liquid flows in a 42m long, 0.048m ID tube system. Liquid loading in gas wells is generally defined as the inability of the produced gas to lift the co-produced liquid up the tubing, resulting in liquid accumulation in the wellbore. The characterization of the liquid loading phenomenon is often based on field monitoring, with limited measurements of pressure and liquid holdup profiles, and usually without visual observations of the phenomenon.The experimental observations obtained in this work show the liquid re-distribution during changes in gas flow rate. These observations revealed that, after a change in gas rate, the liquid film starts to flow downwards in the pipe, and subsequently, the liquid begins to steadily flow upward at a constant velocity. The experimental data were compared with a numerical model, showing an agreement of ±25%. A pseudo-steady state approach was used to model the vertical gas–liquid flows in this long pipe to describe liquid loading in vertical wellbores. The liquid droplets entrained in the gas core were observed and estimated to be flowing upwards in order to obtain a good agreement between experimental observations and model results, even though the gas velocities were lower than Turner critical velocities. The widely accepted droplet model of Turner says that below the critical velocity, the liquid droplets should be flowing downward and not upwards.

Experimental investigation on the prediction of liquid loading initiation in gas wells using a long vertical tube

Liquid loading in gas wells is generally defined as the inability of the produced gas to lift the co-produced liquid up the tubing, resulting in liquid accumulation in the wellbore. This liquid accumulation is related to decrease in gas production and it can even cease production. The characterization of this phenomenon is often based on field monitoring, with limited measurements of pressure and liquid holdup profiles, and usually without visual observations of the phenomenon.This paper reveals there is still a significant discrepancy between the available models and the experimental data available in the literature. Besides reviewing the present state of research into this area, the current understanding about the mechanisms of liquid loading initiation is discussed in this paper and directions on how to use this understanding to model and provide solutions to liquid loading problems is also presented.An experimental investigation on the initiation of liquid loading in a gas well has been carried out using a vertical 42 m long, 0.0489 m (2 in) ID tube system. Vertical gas–liquid flows were analyzed with the aim of understanding how the liquid accumulates in a long vertical tube while decreasing the gas flow rate. This experimental study includes visual observations of the liquid transport and two-phase flow regimes, and measurements of pressure, temperature and liquid holdup along the vertical tube. The experimental observation of the liquid build-up was correlated to prediction criteria models available in the literature for liquid loading initiation.

Two Phase Flow Boiling Pressure Drop in Small Channels

Two-phase pressure drop, flow instability and boiling regime identifications are an essential step in the design of a variety of plant in the power and process industries. Despite the wide spread applications, significant experimental data on flow boiling in small channel is not available. In the present work, experimental set-up was designed for studying boiling flows in 19mm ID tube and identifies flow regimes at various mass and heat flux conditions by varying inlet fluid temperature. The steady-state pressure data was collected and flow regimes identified using pressure drop and pressure fluctuations inside the channel.

Developing air–water flow downstream of a vertical 180° return bend

The importance of developing two-phase flow downstream of return bends has been brought about by several authors wishing to quantify irreversible losses in singularities. In a recent work, a method for evaluating such losses in vertical return bends was proposed based on gas holdup and pressure drop measurements in the bend. In the present study, the nature of the developing flow upstream and downstream of a vertical 180° tube bend (curvature ratio of 8.7) is investigated by means of gas holdup and pressure drop measurements at several positions along the 26.4-mm ID tubes connected to the bend. The effect of the bend on the flow characteristics was evaluated for the plug, slug and annular flow regimes in the upward and downward flow directions. The results showed that, although the variations in gas holdup seemed to extend beyond the measuring limits, significant pressure changes were limited to 40 pipe diameters upstream and 60 diameters downstream of the bend.

Evaluation of the heat transfer enhancement and pressure drop penalty during flow boiling inside tubes containing twisted tape insert

This paper presents experimental data for pressure drop and heat transfer coefficient for two-phase flows in tubes containing twisted-tape inserts. Based on these data, an analysis of the heat transfer enhancement and pressure drop penalty due to the use of twisted-tapes is performed. Experimental results were obtained for horizontal 12.7 and 15.9 mm ID tubes without and with twisted-tape for twist-ratios of 3, 4, 9 and 14. The experiments were performed for R134a as working fluid covering mass velocities from 75 to 200 kg/m2 s, heat fluxes of 5 and 10 kW/m2 and saturation temperatures of 5 and 15 °C. The predictive methods available in the literature were compared against the experimental data obtained in the present study. In general, it was concluded that the use of reduced twist-ratios values provide higher overall heat transfer enhancement factors for intermediary vapor quality. Additionally, it was found that the pressure drop correlation proposed by Kanizawa and Ribatski (2012) is suitable to be used as a design tool because it predicted 99% of the present database within an error band of ±30%.

Axial development of annular, churn and slug flows in a long vertical tube

Experimental data are presented on the axial development of gas–liquid flows in a 42-m long, 0.048-m ID tube system. Different transitional models for slug, churn and annular flow regimes were compared with visual observations and showed reasonable agreement for locations L/D=560 and 820. The behavior of liquid holdup and frequency of flow structures (large waves, disturbance waves) were also analyzed for three different axial positions (L/D=102, 521 and 815), over a range of pressure between 1.4 and 5.2bar, liquid mass fluxes ranging from 17 to 319kg/m2-s and dimensionless gas velocities from 0.05 to 1.6. The liquid holdup showed significant axial variation at all monitoring locations for higher liquid mass fluxes, while it appeared that a kind of developed flow was reached at L/D=521 for lower liquid mass fluxes. The flow structure frequency did not exhibit significant axial variation for dimensionless gas velocities (Wallis parameter) between 0.2 and 1.6.