Small Diameter Tubes Research Articles

Two-phase heat transfer in horizontal dimpled/protruded surface tubes with petal-shaped background patterns

Experimental investigations were carried out to measure the average heat transfer coefficient and frictional pressure loss of R410A during condensation and evaporation in five newly-developed dimpled tubes and two smooth tubes. These dimpled tubes were called EHT series tubes enhanced by dimple or protrusion arrays and staggered petal-shaped background patterns on their inner surface. Tests were conducted at three condensation temperatures and two evaporation temperatures; over a mass flux range of 60–450 kg/(m2·s); with an inlet vapor quality of 0.8/0.2 and outlet vapor quality of 0.2/0.8. Among the copper test tubes having the same outer diameter, the 1EHTa tube (dimpled surface tube) showed the highest condensing coefficient and pressure drop under the same test conditions. On the contrary, the superior evaporation heat transfer performance was given by the 1EHTb tube (protruded surface tube). In addition, the positive effects of small tube diameter and low saturation temperature on thermal performance have been confirmed. It was also observed that measured heat transfer coefficient and pressure drop of the copper 1EHTa tube were higher in comparison with the stainless steel one. The main reason could be the low thermal conductivity of stainless steel material. A comparison of heat transfer enhancement in these enhanced tubes has been done. Results indicated that both the copper 1EHTa and 1EHTb tubes provided the satisfactory surface thermal efficiency.

Custom-built light-pipe cell for high-resolution infrared absorption spectroscopy of tritiated water vapor and other hazardous gases.

We present a new custom-built cell for high-resolution absorption spectroscopy of hazardous gases. The use of an aluminum light-pipe enables sensitive detection due to the small tube diameter and an increased particle density in the interaction volume for a limited analyte amount in the cell, while avoiding additional surfaces such as mirrors. To demonstrate this, we have used the cell to measure tritiated water isotopologues (HTO and traces of T2O) for which spectroscopic data is scarce, due to the challenge of performing spectroscopy of these highly radio-chemical aggressive substances. For this purpose, the new cell also features the efficient inline-production of tritiated water. In this paper we present the concept of the light-pipe cell and demonstrate its performance with a high-resolution absorption spectrum of gaseous HTO generated inside of this cell.

Nasopharyngeal Tube Effects on Breathing during Sedation for Dental Procedures: A Randomized Controlled Trial.

Dental procedures under sedation can cause hypoxic events and even death. However, the mechanism of such hypoxic events is not well understood. Apnea and hypopnea occur frequently during dental procedures under sedation. The majority of the events are not detectable with pulse oximetry. Insertion of a nasal tube with small diameter does not reduce the incidence of apnea/hypopnea. Intravenous sedation is effective in patients undergoing dental procedures, but fatal hypoxemic events have been documented. It was hypothesized that abnormal breathing events occur frequently and are underdetected by pulse oximetry during sedation for dental procedures (primary hypothesis) and that insertion of a small-diameter nasopharyngeal tube reduces the frequency of the abnormal breathing events (secondary hypothesis). In this nonblinded randomized control study, frequency of abnormal breathing episodes per hour (abnormal breathing index) of the patients under sedation for dental procedures was determined and used as a primary outcome to test the hypotheses. Abnormal breathing indexes were measured by a portable sleep monitor. Of the 46 participants, 43 were randomly allocated to the control group (n = 23, no nasopharyngeal tube) and the nasopharyngeal tube group (n = 20). In the control group, nondesaturated abnormal breathing index was higher than the desaturated abnormal breathing index (35.2 [20.6, 48.0] vs. 7.2 [4.1, 18.5] h, difference: 25.1 [95% CI, 13.8 to 36.4], P < 0.001). The obstructive abnormal breathing index was greater than central abnormal breathing index (P < 0.001), and half of abnormal breathing indexes were followed by irregular breathing. Despite the obstructive nature of abnormal breathing, the nasopharyngeal tube did not significantly reduce the abnormal breathing index (48.0 [33.8, 64.4] h vs. 50.5 [36.4, 63.9] h, difference: -2.0 [95% CI, -15.2 to 11.2], P = 0.846), not supporting the secondary hypothesis. Patients under sedation for dental procedure frequently encounter obstructive apnea/hypopnea events. The majority of the obstructive apnea/hypopnea events were not detectable by pulse oximetry. The effectiveness of a small-diameter nasopharyngeal tube to mitigate the events is limited.

Luminal Plasma Treatment for Small Diameter Polyvinyl Alcohol Tubular Scaffolds.

Plasma-based surface modification is recognized as an effective way to activate biomaterial surfaces, and modulate their interactions with cells, extracellular matrix proteins, and other materials. However, treatment of a luminal surface of a tubular scaffold remains non-trivial to perform in small diameter tubes. Polyvinyl alcohol (PVA) hydrogel, which has been widely used for medical applications, lacks functional groups to mediate cell attachment. This poses an issue for vascular applications, as endothelialization in a vascular graft lumen is crucial to maintain long term graft patency. In this study, a Radio Frequency Glow Discharges (RFGD) treatment in the presence of NH3 was used to modify the luminal surface of 3-mm diameter dehydrated PVA vascular grafts. The grafted nitrogen containing functional groups demonstrated stability, and in vitro endothelialization was successfully maintained for at least 30 days. The plasma-modified PVA displayed a higher percentage of carbonyl groups over the untreated PVA control. Plasma treatment on PVA patterned with microtopographies was also studied, with only the concave microlenses topography demonstrating a significant increase in platelet adhesion. Thus, the study has shown the possibility of modifying a small diameter hydrogel tubular scaffold with the RFGD plasma treatment technique and demonstrated stability in ambient storage conditions for up to 30 days.

Effect of infiltration head on soil water movement of small-diameter tube outflow furrow irrigation under mulch film

PurposeThe purpose of this study is to investigate the effect of different infiltration heads on soil water movement using a free infiltration test for small-diameter tube outflow furrow irrigation under mulch film.Design/methodology/approachThe test consisted of small-diameter tube outflow furrow irrigation under mulch film with three different infiltration heads (3, 4 and 5 cm) and furrow drip irrigation under mulch film using an infiltration head of 4 cm (CK).FindingsDuring irrigation, the accumulated infiltration and migration distance of the wetting front increased with time. During the same infiltration time, both the accumulated infiltration and horizontal migration distance of the wetting front increased with the larger infiltration head, whereas the vertical migration distance of the wetting front gradually decreased. With increasing distance from the furrow center, soil moisture content declined, but the uniformity of its distribution increased as the infiltration head increased.Originality/valueThis study can provide scientific basis for the use of small-diameter tube outflow furrow irrigation under mulch film.

Hierarchical design, manufacture and crushing behaviors of CFRP tubular energy absorbers

Hierarchical topology is introduced to construct weight-efficient carbon fiber reinforced polymer (CFRP) tubular energy absorbers through filling small-diameter tubes into large-sized tubes. Crushing behaviors of the thin-walled tubes and the hierarchical tubes are investigated through quasi-static compression experiments and compared with each other. Large-diameter and long thin-walled tubes always fail at brittle modes with limited energy absorption (EA). The hierarchical tubes are crushed progressively and have excellent EA, for the mean crushing force (MCF) exceeds half of the peak force (PF) and the crushing distance is larger than half of the tube length. The improvement in the EA is attributed to the interactions among substructures at different levels which induce a ductile crushing mode. Taking into account the priority of low density, the hierarchical CFRP tubes are weight-efficient absorbers.

Design and development of miniature free piston free displacer dual opposed Stirling cryocooler

A miniature Free Piston Free Displacer (FPFD) Dual Opposed Stirling Cryocooler is designed for the applications in Infrared Imaging. Helium is used as a working gas, providing cooling effect at 80K operating under ambient conditions. A moving magnet linear motor drives the Cryocooler. Compressor and Expander are separate units connected via small diameter tube for minimum vibration export. The Cryocooler is modelled in Sage Software. Variation of the design parameters on the performance of the Cryocooler is studied. An optimization is done to maximize heat lift with frequency, displacer spring stiffness and negative facing area as optimization variables and work input as the constraint. Flexure spring is designed and analysed using Ansys. The variable features are the spiral angle, the number of arms and the gap width for the required stiffness and safe stress. Analysis of the moving magnet linear motor is done using Ansys Maxwell.

Research on electromagnetic tube compression of small diameter aluminum alloy tube and efficiency of field shaper

The electromagnetic tube compression is a high-speed electromagnetic pulse-forming process. The process can be used for connecting metal tube with other tube and bar, and the traditional forming method can be partially replaced. At present, the development and application of the electromagnetic forming technology are restricted, and the main problems are the control of the forming process, the precise forming, and accurate measurement of small diameter tubes. Through the electromagnetic tube compression experiment and optical strain measurement of 6063 aluminum alloy, small diameter tubes were carried out; the numerical simulation analysis of electromagnetic field under different field shaper parameters was carried out and combined with theoretical derivation. In this paper, the theoretical relationship between the electromagnetic force and the process parameters was determined, the influence of the discharge voltage and the process parameters of the field shaper on forming was analyzed, and the reasons for the difficult forming of the small diameter tubes were discussed. The result shows that, the smaller the tube diameter, the harder it is to form. The greater the angle of inner slope of the field shaper, the higher the forming efficiency, and the angle is 40°, which is more reasonable. The higher the discharge voltage, the greater the deformation. The combination of traditional measurement and optical measurement is efficient and accurate to measure tube strain. The uneven distribution of the electromagnetic force along the circumferential direction is caused by the gap of field shaper, which is the main reason for the uneven deformation of the aluminum tube.

A hybrid small-diameter tube fabricated from decellularized aortic intima-media and electrospun fiber for artificial small-diameter blood vessel.

Hybrid small-diameter tubes were fabricated by wrapping decellularized aortic intima-media sheets around a tubular stainless steel mandrel with diameter 4 mm, and then by coating with electrospun segmented polyurethane. The synthetic coat was deposited uniformly to a thickness of about 0.5-3.5 μm depending on the duration of electrospinning. Resistance to luminal pressure, burst strength, and stiffness increased with the thickness of the electrospun coat, suggesting that the synthetic fabric reinforces the reconstructed acellular aortic intima-media. Human umbilical vein endothelial cells seeded on the inner surface acquired flagstone morphology, while normal human dermal fibroblasts seeded on the outer surface proliferated well and partly migrated into deeper layers. Collectively, the data suggest that reinforcing decellularized aortic intima-media with electrospun fibers generates a small-diameter hybrid blood vessel with good biocompatibility and suitable mechanical properties. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1064-1070, 2019.

Enhanced tube performance evaluation and economic analysis for small diameter tube replacement

In this article, eight enhanced single tubes and two smooth single tubes are selected for condensing and evaporating experiments with R134a. Heat transfer performance is compared under different test conditions. The heat transfer coefficients of small diameter enhanced tube are greater than those of large diameter tube in condensing test, while in evaporating test, the coefficients are approximately the same. The pressure drop of small diameter enhanced tube is greater than that of large diameter enhanced tube under same water flow velocity inside tube. Based on the experimental study result, a simulation model is proposed to evaluate small diameter tube replacement. The limit values of the theoretical simulation of STRPE (small tube replacement performance evaluation) are 1.257, 1.304, 1.286, 1.292 and 1.295 for tubes 1#, 2#, 3#, 4#, and 5#, respectively, for which replacement by a small diameter tube with the same enhanced fin configuration yields the same pressure drop and material consumption. According to the simulation model, the material reduction can be achieved directly for selected tubes. The study provides a reference for heat exchanger design in terms of cost reduction.

An optimization study into thermally activated wall system with latent heat thermal energy storage

Thermally activated building structures with latent heat thermal energy storage (LHTES) are relatively new elements of building thermal energy systems. The system considered in the present study involved lightweight wall panels with a plaster containing a microencapsulated phase change material (PCM). The polyethylene tubes of small diameter for heat transfer fluid were embedded in the plaster. The wall panel system could be used for both heating and cooling. The PCM provided short-term thermal energy storage in case of intermittent supply of heat and cold (e.g. in case of a PV powered heat pump). A 1D computer model of the wall system was developed and implemented as a TRNSYS type. Consequently, an optimization model based on the 1D model of the system was developed. The optimization model employed a metaheuristic particle swarm optimization method. The aim of the optimization was to determine the position of the tubes for HTF, relative to the surface of the panel, that would provide fast thermal response and, at the same time, high amount of stored heat. The optimization was performed for heating operation.

Investigations of heat transfer and hydrodynamics in heat exchangers with compact arrangements of tubes

The paper presents the main results of theoretical and experimental investigation of hydrodynamics and heat transfer processes in heat exchangers with a compact arrangement of small diameter tubes. A new design of heat exchangers is proposed, in which there are no gaps and shifting in the direction of transverse to the flow between adjacent tubes.Numerical modeling of heat transfer processes and hydrodynamics for turbulent flow of heat-carrier and experimental investigations of hydrodynamic and heat transfer characteristics of new designs of heat exchangers with compact bundles of small diameter tubes are carried out. The analysis results demonstrated that the proposed designs of shell-and-tube heat exchangers have dimensions of 1.7–2 times smaller and mass is 10–15% lower compared to heat exchangers of traditional designs with the same heat power. The findings in this work may provide a theoretical basis for the selection of optimal designs of shell-and-tube heat exchangers with tube bundles.

Flow boiling heat transfer and pressure drop of R32 inside 2.1 mm, 2.6 mm and 3.1 mm microfin tubes

The flow boiling heat transfer and frictional pressure drop of R32 were experimentally investigated inside three horizontal small-diameter microfin tubes of equivalent diameters of 2.1 mm, 2.6 mm, and 3.1 mm. These microfin tubes of the same fin height, helix angle, and number of fins, but different tube diameters were used to resolve the effect of tube diameter. Furthermore, the effects of the mass velocity, heat flux, vapor quality, and channel size on the flow boiling characteristics were investigated. It was found that under high-mass velocities and high-heat flux conditions, the well-known heat transfer characteristics, forced convection and nucleate boiling, were dominant. On the contrary, under intermediate mass velocities and low-heat fluxes, the heat transfer through a thin liquid film formed in spirally grooves was dominant. The heat transfer coefficients increased and the dryout inception quality decreased with a decrease in channel size, under almost all conditions. Moreover, the frictional pressure drop increased with an increase in mass velocity and vapor quality and a decrease in channel size.

Numerical modeling and parametric study of a vertical earth-to-air heat exchanger system

A numerical model of a vertical earth-to-air heat exchanger (VEAHE) system was developed for the first time. Compared to conventional EAHE system models, the developed model considered the vertical distribution of soil temperature and thermal conductivity. The model validation against experimental data showed a good agreement. A parametric study was then conducted to investigate the effects of tube parameters, insulation parameters, mass flow rates and soil types. Results indicate that a system with a smaller tube diameter provides more thermal capacity with a fixed air mass flow rate, while a larger tube diameter can enhance the system's COP. An increase in tube depths causes the outlet air temperatures to decrease/increase in summer/winter, with a smaller daily oscillation. Compared to PVC and PE, stainless steel can be recommended as the most appropriate tube material, taking into account both heat exchange and soil pressure. Polyurethane, rubber or rock wool as insulation materials can be used as thermal barriers to shield the undesirable heat gains from the shallow soil with the almost same insulation effects. A thickness of 30 mm and a length of from 4 to 5 m can be recommended as the most appropriate insulation parameters for this proposed system.

Simulation of natural convection boiling heat transfer for refrigerant R-134a flow in a metal foam filled vertical tube

Natural convection boiling heat transfer for Refrigerant R-134a flow in a metal foam filled vertical tube is numerically investigated in the present work by using the Multiphase Mixture Model MMM at constant heat flux for both transient and steady state behavior under different parameters. The effect of changing imposed heat flux, porosity, PPI (pore per inch), and tube diameter was analyzed. It is found that liquid saturation will reach its minimum value at the exit, and the dry out point will be seen always at the 2nd half of the tube length. Results also show that smaller tube diameter and higher porosity for the same PPI caused a higher temperature variation over the entire metal foam tube. Comparisons with previous works show good agreement.

Replacement of Rat Tracheas by Layered, Trachea-Like, Scaffold-Free Structures of Human Cells Using a Bio-3D Printing System.

Current scaffold-based tissue engineering approaches are subject to several limitations, such as design inflexibility, poor cytocompatibility, toxicity, and post-transplant degradation. Thus, scaffold-free tissue-engineered structures can be a promising solution to overcome the issues associated with classical scaffold-based materials in clinical transplantation. The present study seeks to optimize the culture conditions and cell combinations used to generate scaffold-free structures using a Bio-3D printing system. Human cartilage cells, human fibroblasts, human umbilical vein endothelial cells, and human mesenchymal stem cells from bone marrow are aggregated into spheroids and placed into a Bio-3D printing system with dedicated needles positioned according to 3D configuration data, to develop scaffold-free trachea-like tubes. Culturing the Bio-3D-printed structures with proper flow of specific medium in a bioreactor facilitates the rearrangement and self-organization of cells, improving physical strength and tissue function. The Bio-3D-printed tissue forms small-diameter trachea-like tubes that are implanted into rats with the support of catheters. It is confirmed that the tubes are viable in vivo and that the tracheal epithelium and capillaries proliferate. This tissue-engineered, scaffold-free, tubular structure can represent a significant step toward clinical application of bioengineered organs.

Numerical Simulation on Vortex Bursting with Propagation in a Small Diameter Tube

Numerical Simulation on Vortex Bursting with Propagation in a Small Diameter Tube

Investigations of influence of epoxy composite coatings on hydrodynamics and heat transfer processes of compact small diameter tube bundles

Tube bundles with cross flow heat carrier chart are widely used in many power systems due to their relatively simple design, low cost, low pressure drops, high efficiency etc. In order to exploitation these tube bundles in dirty and aggressive applications, protective coatings can be applied to the heat transfer surface to enhance effectiveness and minimize pollutant deposits. Protective coatings generally using for improving wear resistance, corrosion resistance, thermal conductivity to heat transfer surface and thermal insulation of frame surfaces of heat exchangers. In this work physico-mechanical and thermophysical properties of heat conduct coating materials forheat transfer surface are investigated. Experimental and numerical investigations of hydrodynamics andheat transfer processes for compact small diameter tube bundles coated by epoxy composite with high thermal conductivity nanofillers are presented. Experimental investigations of investigated tube bundles were carried out in open circuit section type wind tunnel of subsonic speeds.

A Comparative Study of Standard PCNL vs Tubeless PCNL at a Tertiary Care Hospital

Introduction The role of percutaneous nephrostomy tube for drainage after percutaneous nephrolithotomy (PCNL) procedure has come under scrutiny in recent years. The procedure has been modified to use of small diameter tubes and tubeless PCNL. Aim & Objectives This study was done to evaluate perioperative characteristics, postoperative analgesic requirement, length of hospital stay and post-surgical complications between standard PCNL and tubeless PCNL. Methodology This prospective comparative study was conducted in department of surgery and radiodiagnosis of Rama Medical College, Hapur from June 2017 to September 2018 on 80 patients of nephrourolithiasis, who were randomly divided into two groups of 40 patients each, group A underwent standard PCNL while group B underwent tubeless PCNL. Post operatively, the efficacy of the operative procedure was analyzed based on the outcome of the procedure, duration of patient stay and post-operative complications. Result Majority of patient who had underwent PCNL were in age group of 21–60 years (mean age- 36.78 years) with a male predominance (M:F= 69:11). Operative time for tubeless PCNL (mean time ± SD = 59.97 ± 26.40 minutes) was shorter than for standard PCNL (mean time ± SD = 67.55 ± 28.00 minutes) but it was statistically insignificant (p value = 0.73462). 26 patients (65%) of tubeless PCNL were discharged within 48 hours while 33 patients (82.5%) of standard PCNL had to stay in hospital for a longer duration of 3–4 days. Post-operative analgesia requirement (Inj. Diclofenac) was significantly high in standard PCNL group (mean dose ± SD = 136.84 mg ± 39.12 mg) than in tubeless PCNL group (mean dose ± SD = 119.74 mg ± 36.13 mg, p value = 0.0026). Post-operative complications such as hematuria, urosepsis and leakage were also much less in tubeless PCNL (n=11, 27.5%) than in standard PCNL (n= 17, 42.5%). Conclusion Tubeless PCNL is a safe and effective technique and is associated with decreased pain, low analgesic requirement, less operating time and faster recovery. However it has its own limitation that precludes secondary procedure for the treatment, removal of internal stent, dysuria and need to visit hospital for subsequent removal of internal stent.

Summarizing of Nusselt numbers and Euler numbers in depending of Reynoldsnumber for the compact tube bundle of small diameter tubes by experimental and numerical methods of researches

The work reports on the experimental research on the determination of the number of Nusselt concerning the compact bundle of small diameter smooth tubes. Having an inline arrangement, it lacks the gapsbetween adjacent tubes of longitudinal rows. In comparison to the traditional inline arrangement, this type of bundle is noticed to have significant advantages such as an increased coefficient of heat transfer and reduced aerodynamic resistance of the tube bundle. At the same time, the use of the compact bundle of small diameter smooth tubes leads to the beneficial reduction of the size and mass of heat exchangers of the shell–and–tubes type. Several series of experimental investigations uponthe aforementioned kind of bundle in open circuit section type wind tunnel of subsonic speeds applyingvarious hydrodynamic flow conditions are ran. As a result of these investigations, the correlations and definite dependences of the Nusselt numbers Nu and Euler numbers Eu on the Reynolds number Re of tube bundle were revealed.