Surface Of Tube Research Articles

Experimental and Numerical Study of Parallel Flow Evacuated U-Tube Solar Collector with Parabolic Reflector: Impact of Particulate Matter

Abstract The paper explores the performance of an evacuated U-tube solar collector integrated with a parabolic reflector under extreme hot tropical conditions, both with and without the presence of particulate matter, using experimental and simulation approaches. Experimental results showed that at peak conditions of 1017 W/m2 solar intensity and 42 °C ambient temperature, the heat transfer fluid (HF) exhibited a temperature increase of 11.5 °C, accompanied by a heat gain of 1100 W, with a flow rate ranging from 0.028 to 0.03 L/s and a U-tube contact area of nearly 0.18 m2. In these tropical conditions, the maximum thermal efficiency achieved was 66% without particulate matter and 61% with particulate matter treatment (PMT), which simulated the accumulation of particles on the evacuated tube's surface. The introduction of PMT on the evacuated tube's outer surface led to slight deteriorations, including a 2 °C reduction in HF temperature increase, a 200 W decrease in heat gain, and a 17% drop in thermal efficiency compared to the scenario without PMT. The study also includes case studies using two numerical models to assess the time required to reach steady state and to understand the system’s thermal behaviour throughout the day, both with and without PMT. The analyses reveal that under peak solar conditions, steady state is achieved in 117 seconds with PMT and 131 seconds without, at a flow rate between 0.026 and 0.028 L/s. Additionally, the impact of HF flow rate, solar intensity, and HF inlet temperature on thermal performance is examined, revealing intricate temperature patterns along the U-tube’s radial and axial directions. Detailed 3D temperature contours for hourly variations on sunny days and transient analyses along the collector length are presented. These findings offer valuable insights for optimizing solar collector systems for extreme hot tropical climates.

Damage response analysis combined with machine learning to investigate the effect of frequency on the impact-sliding fretting corrosion behavior of Inconel 690 alloy

Abstract Inconel 690 alloys have been widely applied in the manufacturing of steam generator tubes for pressurized water reactors at nuclear power station. However, complicated impact-sliding fretting corrosion behavior always accompanies its entire service period. This study, which is based on experimental research and numerical analysis methods, investigates the effect of impact frequency on the impact-sliding fretting corrosion behavior of Inconel 690 alloy tubes. Then, machine learning is applied to predict the evolution law of the degree of damage. The results show that different impact frequencies do not affect the damage failure mechanism of the impact-sliding fretted alloy tube surface. However, an increase in impact frequency will lead to a more severe degree of damage. The corresponding maximum wear depths of the 5, 10, and 15 Hz impact frequencies caused by the impact-sliding fretting wear scars were approximately 6.630, 11.105, and 14.485 µm, respectively. The corresponding wear volume increased from approximately 3.626×104 µm3 to 6.325×104 µm3 and 8.395×104 µm3. Furthermore, machine learning modeling demonstrates perfect robustness and precision in predicting the damage evolution rule of the impact-sliding fretting corrosion behavior of an alloy tube.

In situ atmospheric cold micro-PECVD of uniform superhydrophobic silica on internal surface of tubes for improving anti-corrosion and anti-impact behaviors

In situ atmospheric cold micro-PECVD of uniform superhydrophobic silica on internal surface of tubes for improving anti-corrosion and anti-impact behaviors

Mass and heat transfer at spiral tube internal used as a heat exchanger and catalyst support in a continuous bubble column reactor

ABSTRACT Slurry bubble columns find extensive applications in three-phase reactions, including biological wastewater treatment, fermentation, and hydrotreating, among others. Despite their merits, these reactors suffer from drawbacks such as high back mixing and challenges in product-catalyst separation. This study introduces a novel approach to address these issues by employing a horizontally placed spiral tube within the column, serving as both a catalyst support and a heat exchanger. The study investigates the impact of two-phase flow on mass transfer at the outer surface of the spiral tube using the limiting current based electrochemical technique. The experimental setup involves varying spiral tube diameter and pitch, as well as distances between successive spiral tubes. The results showed that the mass transfer coefficient increases with increasing superficial gas and solution velocities but decreases with increasing spiral tube diameter and pitch. An array of three separated horizontal spiral tubes was also tested, and the mass transfer coefficient was found to be slightly lower than that of a single spiral tube by an amount ranged from 4 to 19%. The study provides valuable insights into optimizing reactor design for improved efficiency, offering a potential solution to challenges in slurry bubble column reactors.

Thermal-Fluid study of curved tubes in cross-flow

Three-dimensional simulations have been performed to investigate thermal performance by the external surface of curved circular tubes provided with concave and convex curvatures. The simulations were performed in Ansys-fluent software and results has been validated against the available results. The tubes were placed in a uni-directional free stream of air at a Reynolds number of 35000 which is within subcritical range for circular tube. The heat transfer capabilities of curved tubes have been compared with that of a straight tube of same diameter and height. A constant-heat-flux condition over the external surface has been used. The curved tubes have been designed such that it has vertical extensions at the end and curvatures at the middle section with curvature ratios of 0.075, 0.15, 0.225 and 0.3. Plots of coefficients of pressure, drag and lift, Nusselt number, heat transfer ratio and contours of pathlines were utilized to investigate the thermal behaviour around the tube surface. Results show the highest augmenting thermal performance exhibited by convex curved tube with curvature ratio 0.15 followed by curvature ratio of 0.225. Other reasonably better augmented heat transfer exhibited by concave curved tube with curvature ratio of 0.3. The present study also identifies augmenting, mitigating and insignificant zones around the tubes based on heat transfer rates. The results show an improvement in heat transfer when curved tube is used instead of straight tube which can be utilised in waste heat recovery recuperators.

Latent Thermal Energy Storage for Cooling Demands in Battery Electric Vehicles: Development of a Dimensionless Model for the Identification of Effective Heat-Transferring Structures

Thermal energy storage (TES) systems open up alternative paths for air conditioning to increase the range of battery electric vehicles (BEVs) by reducing power consumption. The central prerequisites for this purpose are high storage densities: high-temperature TES systems are being focused on for heat demands, while effective solutions for cooling are missing. Due to their lower temperature potentials, concepts with high storage capacities and heat transports between the storage and cold transferring medium are needed. Latent TES systems based on water enable these capacities but require adequate internal structures for effective heat transfer. Due to the large number of geometric options, high simulation efforts must be conducted to identify favored structures, or the possible design space must be limited for investigations. For this purpose and for the first time, an alternative way is presented using newly developed dimensionless models in a top-down methodology for time-efficient design studies and evaluations. These models were successfully validated and used as a design tool to identify effective structures in latent TES systems for cooling demands in BEVs. A wide array of variation studies on tube, finned plate and novel Triply Periodic Minimal Surface (TPMS) structures were performed and uniformly evaluated with regard to storage densities, cooling efficiencies and geometry. The results show high storage densities for novel TPMS structures, including the enclosure of 100 Wh/kg or 102.2 kWh/m3 with average cooling capacities of 1 kW over 30 min, confirming the usability of latent TES systems in terms of compactness and efficiency for cooling demands in BEVs.

Disease management of malignant struma ovarii.

Ovarian goiter that meets the diagnostic criteria for malignant thyroid tumors or has invasive distant metastasis is called malignant struma ovarii (MSO). The incidence of MSO is very low. The level of serum thyroglobulin (Tg) is helpful to differentiate MSO with highly differentiated pathological type from other ovarian malignancies. But its therapeutic method is currently debated. Herein, we present a case of 54 years old woman, who was admitted to hospital due to frequent abdominal pain for 9 months and with normal serum Tg. Postoperative pathological examination revealed highly differentiated follicular thyroid carcinoma of bilateral ovarian origin, which penetrated bilateral ovarian cortex, involved the serosal surface of left fallopian tube and disseminated to sigmoid mesentery, small intestinal mesentery and pelvic cavity. The disseminated lesions were considered to originate from right ovary. After the total thyroidectomy, iodine-131(131I) treatment was performed with a dose of 150mCi. The 131I whole-body scintigraphy (WBS) 2 days after treatment showed residual thyroid tissue in the neck and implantation metastasis in mesentery. After 1-year regular follow-up, no significant abnormalities were found in tumor indicators, Tg, thyroid function, neck ultrasound and abdominopelvic enhanced computed tomography (CT). This MSO case with normal Tg and multiple implantation metastasis aimed to discuss its clinical management especially for Tg and 131I and to improve its prognosis.

Does the TruBlue Laser Set Microlaryngoscopy Equipment on Fire? A Systematic Evaluation.

The risk of fire during laser microlaryngoscopy is well known. However, limited information is available about fire risk with the novel TruBlue laser. This study systematically evaluates its interactions with common surgical supplies, offering valuable insights into safety considerations for surgeons. We used experimental conditions to test the extent to which TruBlue laser energy produces smoke, perforation, or fire in Rüsch®, Medtronic™ and microlaryngeal endotracheal tubes and in surgical pledgets. Only the Microlaryngeal Tube (MLT) caught fire. Notably, it happened only when the laser fiber shifted on the tube's surface. Smoke emerged solely from the laser fiber applied to the Medtronic™ shaft and only during continuous contact mode. Cuff perforation and smoke emanating from the shaft occurred in three-quarters of the Rüsch® trials. The pledgets' radiopaque segment exhibited a greater combustibility than other segments (p < 0.01). In many of the pledget trials, faster smoke emission occurred with shorter laser-to-target distances (p < 0.05). Water-soaked pledgets displayed a reduced rate of smoke production (p < 0.01) and string division. The Medtronic™ tube assures remarkable safety with a nonignitable shaft and low cuff ignition. The MLT poses the highest ignition risk. Cuff perforation risk is mitigated by maintaining a 0.3-cm distance from the laser fiber tip. Pledget fire risk is mitigated by positioning the radiopaque part away from the laser beam and by soaking the pledget with water. Laser division of the pledgets' string was common. NA Laryngoscope, 2024.

Research on thermohydraulic performance of the petal-type vortex generator inserted tube heat exchanger

The petal-type vortex generator inserted tube was proposed in this paper to explore higher heat transfer performance. The k-ω model was selected and a good agreement can be obtained. Basically, the influences of the interval distance t, the angle α and the pitch P were meticulously examined within a Reynolds number spectrum ranging from 5000 to 15,000. The analysis of the internal flow dynamics revealed that the petal-type vortex generator effectively transformed the longitudinal velocity of the fluid into radial velocity, leading to the formation of vortices within the tube. The petal-shaped vortex generators led a portion of the fluid toward the tube surface, facilitating boundary layer weakening and redevelopment near the wall, while also allowing another portion of the fluid to pass through the slits, which enhanced the generation of vortices and significantly improved heat transfer performance. The numerical results indicated that the tube equipped with petal-type vortex generator insert achieved a 196–347 % increase in the Nusselt number (Nu) and a 244–1149 % increase in the friction factor (f), relative to a smooth tube. The maximum performance evaluation criterion (PEC) obtained in this study reached 2.01.

Development of Corrosion Diagnosis Method for Copper with Carbon Film by Potential Difference Measurement

Copper is widely used in the heat exchangers of air conditioning systems because of its high thermal conductivity and good workability. Although copper shows a good corrosion resistance in the fresh water, the occurrence of pitting corrosion is strongly related to the carbon films on copper 1,2. It has been reported that the pitting corrosion was observed in the inner surface of copper tubes due to the carbon films on copper 2,3. In this case, the carbon films were produced by the influence of undergoing an oil and heat treatment. Yamada et al.2 investigated the factor of the pitting corrosion on copper by field test of air conditioning systems in Japan. They indicated that the occurrence of type Ⅰ pitting corrosion was affected by the water quality and carbon films on copper. Iyasu et al.3 reported a method to estimate the residual amount of carbon on the inner surface of the carbon tube by electrochemical measurement. In this method, the corrosion potentials related to the inner and outer of copper tube were measured to estimate the corrosion potential difference from both corrosion potentials at arbitrary measurement time. They demonstrated that the residual amount of carbon on the inner surface of the carbon tube was correlated to the corrosion potential difference estimated from the corrosion potentials of the inner and outer of copper tube. Though they implied that their proposed method can be applied the corrosion diagnosis method for copper tubes, the dissolution mechanisms of copper with carbon films were still unclear.In the present study, we investigated the dissolution behavior of copper with carbon films in the fresh water based on the air conditioning systems. To estimate the corrosion potential difference, the corrosion potentials related to the inner and outer of copper tube were measured in the different compositions of electrolyte solution. The inner surface of copper tube with different residual carbon contents was employed for the measurement. To develop the corrosion diagnosis method of copper, the suitable conditions involving compositions of electrolyte solution for the corrosion potential measurements were discussed.References F. J. Cornwell, G. Wildsmith, P. T. Gilbert, ASTM STP (1976). Y. Yamada, K. Mizutani, and Y. Inoue, Zairyo-to-Kankyo, 63, 158-162 (2014).T. Iyasu, M. Kuratani, I. Ikeda, N. Tanaka, Y. Yamada, O. Sakurada, Open J. Compos. Mater., 11, 12-22 (2021).

(Invited) Near-Infrared Nanosensors Driven By Molecular Recognition at sp3 Defect Sites of Locally Functionalized Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) emit photoluminescence (PL) in the near-infrared (NIR) region. NIR PL is applicable to advanced biosensors and bioimaging because of its high transparency, low light scattering, and suppressed autofluorescence in biological tissues. Local chemical functionalization (slight amount of chemical modification) of SWCNTs forms luminescent sp3 carbon defects in the sp2 carbon lattice structures, producing locally functionalized SWCNTs (lf-SWCNTs) that are also called as organic color centers and luminescent quantum defects in SWCNTs [1-3]. Compared to original E 11 PL of pristine nanotubes, lf-SWCNTs show defect PL with red-shifted wavelengths and increased quantum yields from their defect sites. The chemical reactions used for the sp3 carbon formation in lf-SWCNTs are applicable to a technique for further functionalization such as the polymer gel coating layer formation around tube surfaces for their stable aqueous dispersibility [4] and the sensor function generation [5-10].Regarding selective sensing system fabrication, molecular recognition at the defect sites of lf-SWCNTs is a promising method. Therein, the selective binding of target molecules at the defect sites of lf-SWCNTs via the molecular recognition induces specific spectral shifts and intensity changes of defect PL as sensor responses. For example, sugar and ion sensors are produced by introducing phenyl boronic acid and azacrown ether groups at the defect sites of lf-SWCNTs, respectively [5,6]. Moreover, lf-SWCNT sensors for protein detection/recognition are created based on unique microenvironment response of defect PL. Namely, an avidin-biotin interaction at the defect sites of lf-SWCNTs is used to form different microenvironments around the defect sites based on the selective adsorption of the avidin derivatives with different amino acid sequences, by which the avidin derivatives are differentiated from the defect PL shift responses [9]. Serum albumin (SA) sensor using lf-SWCNTs is fabricated by introducing a long-chain fatty acid group at the defect site. Therein, the strong interaction between SA and the fatty acid group induced selective defect PL spectral shifts. Moreover, various SAs from bovine, mice, and human (BSA, MSA, and HAS, respectively) are detected by this sensor. The lf-SWCNT sensor works in body fluids such as fetal bovine serum for BSA detection and albuminuria of diabetes mice for MSA detection [10].Therefore, the molecular recognition systems in lf-SWCNTs have a high potential to develop advanced NIR sensors for biomolecule and protein detection/ recognition.

Enhancement of Heat Transfer rate using Axially Interrupted Rectangular Fins in Double Pipe Heat Exchanger

The current investigates the thermo-fluid behavior of a double pipe heat exchanger (DPHE) featuring axially interrupted rectangular fins (AIRF) on the annulus part. The inner tube under this study with AIRF represents an interruption of straight longitudinal fins. This modification introduces periodic breaks along the tube's surface, effectively disrupting the boundary layer of the fluid flow. Consequently, it enables a non-continuous fluid passage along the length of the tube, potentially enhancing heat transfer. The experimentation employs standard liquid water, for investigations conducted under varying cold water mass flow rate 0.136 Kg/s to with 0.374 Kg/s keeping hot water at constant flow rate of 0.34 Kg/s with a fin split interval of four different lengths 7mm,27mm,55mm,100mm. A comprehensive investigation of the AIRF arrangements is carried out in contrast to the plain pipe arrangement, concentrating on fluid flow parameters such as Nusselt number (Nu), friction factor, heat transfer rate, and overall performance factor. The findings reveal that heat transfer rates in an annulus equipped with 7mm AIRF exceed those of a plain pipe by 59.31% under similar fluid flow conditions. The Nusselt number shows 1.5 times increase in the 0.007 m AIRF arrangement compared to the plain pipe. Thermal performance factor for 7mm interrupted length of AIRF outperforms other models.

High‐performance and flexible thermoelectric generator based on a robust carbon nanotube/BiSbTe foam

AbstractOrganic thermoelectric generators (TEGs) are flexible and lightweight, but they often have high electrical resistance, poor output power, and low mechanical durability, because of which their thermoelectric performance is poor. We used a facile and rapid solvent evaporation process to prepare a robust carbon nanotube/Bi0.45Sb1.55Te3 (CNT/BST) foam with a high thermoelectric figure of merit (zT). The BST sub‐micronparticles effectively create an electrically conductive network within the three‐dimensional porous CNT foam to greatly improve the electrical conductivity and the Seebeck coefficient and reinforce the mechanical strength of the composite against applied stresses. The CNT/BST foam had a zT value of 7.8 × 10−3 at 300 K, which was 5.7 times higher than that of pristine CNT foam. We used the CNT/BST foam to fabricate a flexible TEG with an internal resistance of 12.3 Ω and an output power of 15.7 µW at a temperature difference of 21.8 K. The flexible TEG showed excellent stability and durability even after 10,000 bending cycles. Finally, we demonstrate the shapeability of the CNT/BST foam by fabricating a concave TEG with conformal contact on the surface of a cylindrical glass tube, which suggests its practical applicability as a thermal sensor.

Pentameric Assembly Architecture of the Tail Tube Protein in SPR Phages

Abstract Most phages—viruses infecting prokaryotes—inject their genomes via a tail structure. The central tail tube, composed of tail tube protein (TTP), typically forms conserved hexameric or trimeric rings. In this paper, we report a novel pentameric TTP assembly, solved by cryo-electron microscopy (cryo-EM) at 3.5 Å and 3.7 Å resolution. Structural analysis reveals a highly negatively charged inner surface of this pentameric tube. Key residues in the loop connecting β3 and β4 strands are crucial for pentameric ring formation. Mismatches in interactions between stacked layers can induce curvature in the tube. The cryo-EM structure of the TTP polymer at the tube’s end shows that β-strands spanning amino acids 27–65 shift toward the central tunnel, potentially obstructing the passage of the phage genome. This study provides new structural insights into a unique TTP assembly, enhancing our understanding of phage assembly processes.

A Suspected Defect Screening-Guided Lightweight Network for Few-Shot Aviation Steel Tube Surface Defect Segmentation

A Suspected Defect Screening-Guided Lightweight Network for Few-Shot Aviation Steel Tube Surface Defect Segmentation

Numerical study on flow pattern transition, liquid film and heat transfer for R1233zd/FC72 mixtures across tube bundles

The non-azeotropic mixtures phase-change flow across tube bundles is widely used in the refrigeration industry. A simulation model of R1233zd/FC72 mixtures is presented to study flow pattern transition and heat transfer across tube bundles. Volume of Fluid (VOF) model is used to determine the flow pattern. An experiment is conducted to validate the simulation model with average deviation of 8.97%. The results showed that the flow pattern transition appears for various conditions. In addition, the liquid film thickness and heat transfer are analyzed, focusing particularly on the impact of various mixture components. With increasing vapor quality, the flow pattern transfers from sheet flow to semi-annular flow and then to droplet flow. Sheet to semi-annular flow transition occurs for a vapor quality of 0.4–0.6, and semi-annular flow transfers to droplet flow for a vapor quality of 0.7–0.8. For sheet flow, the local heat transfer coefficient on the tube surface is the highest at 90° (circumferential angle) from the summit point of the cross-sectional tube circle due to the thinnest liquid film. The liquid film turns thinner with increasing mass fraction of R1233zd and vapor quality. Increasing the mass fraction of R1233zd and vapor quality promotes heat transfer. However, the flow pattern transfers from sheet flow to the other ones, the heat transfer coefficient starts to decrease. The heat transfer coefficient is the highest for a vapor quality of around 0.4–0.5 and a mass fraction of R1233zd of around 0.7–0.9.

Study on stress concentration and fatigue life of tubing with slip indentation

The indentation caused by slip on the outer wall of tubing is a significant contributor to stress concentration and, consequently, fatigue failure in the tubing string. Through an analysis of the interaction between slips and tubing, a mathematical model to predict slip-tubing interaction and slip crushing load is formulated, accounting for external pressure, internal pressure, and axial forces. On this basis, the influence factors and influence rules of slip crushing load are studied, and three-dimensional yield surface and tri-axial stress ellipse of tubing are investigated, considering different transverse load factors and design factors. To accurately forecast the fatigue life of tubing subjected to slip indentation, two models are established: one for fatigue life prediction and the other for tubing string vibration. In order to quantitatively assess the stress concentration arising from slip indentation, a finite element model of tubing featuring slip indentation is established. Finite element analysis reveals that stress concentration and non-uniformity are evident in the vicinity of slip indentation, with their severity intensifying as the indentation depth grows. The initial step in assessing fatigue life involves fatigue life tests on tubing material subjected to varying stress levels. Subsequently, a case study is conducted and the variations of wellhead pressure and axial stress are evaluated. Fatigue life analysis reveals that the fatigue life is notably sensitive to variations in stress amplitude and slip indentation depth. An increase in the magnitude of alternating stress and the depth of slip indentation will result in a significant reduction in the fatigue lifespan. The methodologies employed in this research, along with the resulting findings, offer a robust theoretical framework and a solid practical basis for forecasting and managing stress concentration and fatigue durability in tubing affected by slip indentation.

USE OF TUBING COATINGS AND SCALE INHIBITORS TO PREVENT SCALING

The problem of formation of inorganic scaling in tubing is a common problem in oil production processes. The formation of salts on the inner surface of the tubing leads to a significant narrowing of the flow section of the pipe. An urgent task is to find methods, the use of which will either prevent or reduce the formation of inorganic scaling on the walls of pipes. Methods of removing scaling from the tubing are expensive, time consuming, and require shutdown of the oil production facility. Therefore, it is preferable to use methods for preventing salt formation in tubing. Methods of preventing the processes of scaling in the tubing include physical, chemical and technological. The most common method of preventing scaling is the use of scale inhibitors (chemical method). The use of internal protective pipe coatings (technological method) as a measure to prevent the formation of inorganic scaling on the walls of the tubing is a promising, but not fully studied method. The use of coatings is promising, since in addition to the potential reduction in the formation of scaling on the walls of pipes, their main function is corrosion protection.One of the methods of preventing salt formation in the tubing may be the integrated use of internal protective coatings of the tubing and scale inhibitors. But, since this method is not universal, an individual selection of the most effective coating-inhibitor combination will be required for each oil production facility. Selection of an effective coating-inhibitor combination using pilot field tests is an expensive and time-consuming procedure, therefore, it is necessary to develop a laboratory method to solve this problem. The article proposes a method that makes it possible to evaluate the effectiveness of the complex use of protective coatings and scale inhibitors to prevent the formation of inorganic salts on the inner surface of tubing in laboratory conditions. The results of bench tests for 9 grades of protective coatings and for 6 grades of scale inhibitors (in different dosages) are presented.

Liquid plugs in narrow tubes: application to airway occlusion

We study liquid plugs in the pulmonary airways based on the two-phase axisymmetric weighted residual integral boundary-layer model of Dietze et al. (J. Fluid Mech., vol. 894, 2020, A17), which was originally developed to study liquid films coating the inner surface of a cylindrical tube in interaction with a core gas flow. The augmented form of this model, which was never applied beyond a proof of concept, allows for the representation of liquid pseudo-plugs. Here, we demonstrate its predictive power vs experiments and direct numerical simulations, in terms of the dynamics of plug formation and the characteristics of developed liquid plugs, such as their shape, flow field, speed and length, as well as the associated wall stresses and their spatial derivatives. In particular, we show that the augmented model allows us to establish a direct continuation path from travelling-wave solutions (TWS) to travelling-plug solutions (TPS). We then apply the model to predict mucus plugs in the conducting zone of the tracheobronchial tree, based on the lung architecture model of Weibel. We proceed by numerical continuation of travelling-state solutions in terms of the airway generation, whereby we impose the wavelength of the linearly most-amplified convective instability (CI) mode or that of the absolute instability (AI) mode. We identify the critical airway generation for liquid-plug formation (TWS/TPS transition), maximum potential for wall-stress-induced epithelial cell damage and CI/AI transition, and investigate how these phenomena are affected by the main control parameters, i.e. airway orientation vs gravity, air flow rate, mucus properties and airway size.

Experimental study in steady-state for determining the coefficient of external heat transfer on the outer wall of rotating tubes during the quenching process by immersion in water tank

The quenching process by immersion is one of the steel tube industry's most commonly used heat treatment processes. For mathematical models to be reliably used as tools capable of simulating different geometries and cooling mechanisms, knowledge of the heat transfer coefficient between the surface of the tube and the water is essential. The present work's primary objective is the experimental determination of the heat transfer coefficient between the external surface of the tube and the water. For this purpose, an experimental apparatus capable of representing the conditions of a real process was built. The predominant heat transfer regime in the single-phase region was mixed convection for the conditions tested. Two correlations were proposed to represent the data obtained for this region. Based on existing correlations in the literature, the first one returned a mean absolute error of 13.97 %. The second one was proposed based on an optimization tool, returning a mean absolute error of 6.29 %. Concerning the two-phase region, the obtained data characterized a transition regime and the beginning of the nucleated boiling. In this region, it was possible to observe that the effect of increasing rotation on the external heat transfer coefficient decreases with increasing tube surface temperature, which follows studies in the literature. The repeatability test shows that the apparatus could replicate the heat transfer coefficient values for the free convection region, staying within the range of uncertainties. However, for the boiling region, the data showed more significant disagreement. This behavior is mainly due to the difficulty of keeping the surface under the same conditions, which have greatly influenced the formation of bubbles and heat transfer.