Mixed Tube Research Articles

Comprehensive evaluation on deposition and heat transfer performance of the mixed tube bundle based on orthogonal experimental study

Deposition on heat exchange surfaces is an urgent problem to be solved to achieve efficient utilization of energy in thermal equipment. To mitigate deposition and the resultant heat attenuation, this work proposes a mixed tube bundle strategy of inserting attached cylinders behind the tube bundle, which can effectively meet the design requirements of high anti-deposition performance, high heat transfer efficiency, and low flow resistance. An integrated dynamic model for deposition is developed to elucidate the effect of ash particles on deposition, flow, and heat transfer characteristics. Based on the inverse distance weighting interpolation, a dynamic mesh smoothing technique is employed to simulate the evolving deposition layer on the heat transfer surface. In addition, the L16(43) orthogonal experimental design method is adopted to study the influence of the arrangement angle, diameter, and distance to the primary bundle of the attached cylinder on the overall performance, and determine the optimal scheme. The results show that deposition in the cases using the mixed tube bundle strategy has significantly decreased. The weakening effects of the attached cylinder on the deposition of small-medium particles and large-sized particles are due to the inhibition of vortex development in the gap of tube bundle and the deviation of the motion trajectory, respectively. The novel design exhibits the lowest deposition mass Mdep = 1.12 g and the best comprehensive performance PEC = 1.14 under the condition of the arrangement angle of 50°, the diameter of 10 mm, and the distance between the primary bundle of 5 mm. The obtained results can provide reference schemes and guidance for the optimization of the design of heat exchange equipment and accessory devices.

A strategy of mixed tube bundle to improve anti-deposition performance and heat transfer

Ash deposition is a key issue that limits the energy utilization and safety operation of high-energy-consuming equipment in industrial applications, and the clarification of the heat and mass transfer process under ash deposition is vital. To improve the anti-deposition performance of tube bundles and mitigate heat transfer deterioration, a mixed strategy with attached small cylinders arranged behind the tube has been proposed, which overcomes the difficulties faced by irregular and extended surface tube bundles in manufacturing, cleaning, maintenance, and energy consumption. A CFD model incorporating multiple deposition mechanisms is established to investigate the dynamic deposition behavior, heat transfer characteristics, and comprehensive performance of the tube bundles. In particular, the dynamic growth process of the deposition layer on heat transfer surface in this work is achieved through a dynamic mesh smoothing method based on inverse distance weighting interpolation. Parametric studies are conducted on different arrangements and angles (α = 15° - 65°) of the attached cylinders to obtain the optimal comprehensive performance design. The results show that the attached cylinders suppress the formation and development of the wake vortex caused by the primary tube bundle, significantly enhancing the anti-deposition performance of the tube bundles. The length of vortex evolution increases and the separation point of the boundary layer extends with the angles, leading to a transition of the vortex shedding regime between tube bundles. Compared to the benchmark case, Case 1 exhibits a higher anti-deposition and heat transfer performance, where the deposition mass decreases by 43.98% and the PEC reaches the maximum value of 1.11 at α = 45°, which delivers the best comprehensive performance. The results can provide more realistic predictions for the practical design, operation, and maintenance of thermal equipment.

Correlations and numerical analysis of thermal-hydraulic performance of staggered mixed tube bundle composed of circular and drop-shaped tubes

Flow and heat transfer across six-row staggered mixed tube bundles composing of circular and drop-shaped tubes have been investigated numerically. The Reynolds number Re was within the range of 1.78 × 103–18.72 × 103. Six cases of the mixed tube bundle were discussed. The streamlines, velocity, turbulent kinetic energy, temperature, and static pressure contours for the studied cases were predicted using Ansys Fluent software package. The results of the mixed tube bundles were compared with those of the circular and drop-shaped ones. The best thermal performance was obtained for case IV (circular tubes in the 1st, 3rd, 5th rows, and drop-shaped tubes in the 2nd, 4th, 6th rows). However, it was found that case VII (drop-shaped tubes in the 1st, 2nd, 4th, 6th rows, and circular tubes in the 3rd, 4th rows) has the best hydraulic performance compared to the other cases of circular and mixed tube bundles. Besides, the average Nusselt number Nu¯, friction factor f, and efficiency ε were observed to be positively correlated to the Reynolds number. As the Re increased, both Nu¯ and ε increased, while f decreased. Results showed that the maximum values of the thermal-hydraulic performance were achieved for case IV at Re = 1.78 × 103 and case VII at Re>1.78 × 103, which were about 14.55% and (2.08–4.49)%, respectively, higher than those obtained for the drop-shaped tube bundle. Finally, generalized correlations of Nu¯, f, and ε (in terms of Re) were developed, offering a useful reference for the design of such heat exchangers.

Improvement of a Closed Mixed Injection Tube to Prevent Accidental Opening to the Atmosphere of a Central Venous Catheter

【背景】中心静脈ルートに接続した三連型混注管（セーフタッチ®）が大気に開放された経験に基づき予防策を策定したので報告する．

Flow and heat transfer characteristics of staggered mixed circular and drop-shaped tube bundle

The purpose of this study is to clarify heat transfer and fluid flow behavior across six-row mixed tube bundles. The tube bundle consists of circular and drop-shaped cross sections in a staggered arrangement. The Reynolds number Re for the flow is varied from 1.78 × 103 to 18.72 × 103. Six cases of the mixed tube bundle were considered. The results of the mixed tube bundles were compared with those of the circular (case I) and drop-shaped ones (case II). The Ansys Fluent software package was utilized to predict the flow pattern over the tube bundles. The results of the numerical simulation showed that the cross-sectional shape of the tubes and their location in the bundle significantly affect the heat transfer and pressure drop in the bundle. Case IV (circular tubes in the first, third, and fifth rows and drop-shaped tubes in the second, fourth, and sixth rows) increases the average Nusselt number Nu¯ by about 1.11%–8.10% and 47.86%–49.04% compared to that of the circular and drop-shaped tube bundles, respectively. Case VII (drop-shaped tubes in the first, second, fourth, and sixth rows and circular tubes in the third and fourth rows) has the lowest friction factor f compared to the other cases of circular and mixed tube bundles. Moreover, the maximum values of the thermal–hydraulic performance ε were achieved for case IV at Re = 1.78 × 103 and the case VII at Re >1.78 × 103, which were about 14.55% and (2.08–4.49)%, respectively, higher than those obtained for the drop-shaped tube bundle. Generalized correlations of Nu¯, f, and ε for the studied mixed tube bundles were predicted.

Numerical simulation of heat transfer performance of different heat exchange tubes in heat recovery steam generator

For the purpose of reducing the cost of hydrogen production in process engineering and practice and enhancing the heat exchange efficiency of heat recovery steam generator, a new spring-blade mixed heat exchange tube was creatively put forward, and the performance evaluation criterion (PEC) was used as evaluation index of comprehensive heat transfer performance. To explore the heat transfer performance, the velocity distribution, temperature distribution, pressure distribution and comprehensive heat transfer performance were analyzed, and heat transfer coefficient and the value of PEC were obtained. The addition of spring and blade in the mixed heat exchange tube has obvious positive impacts on the velocity, temperature and pressure drop. In the Reynolds number range of 20000–40000, the heat exchange coefficient increment of the mixed heat exchange tube is increased by 35% and 45% than that of the spring and blade heat exchange tube respectively. The pressure drop is positively correlated with the heat exchange coefficient, and its increase leads to the decrease of PEC value.

Effect of time and storage temperature on canine and feline erythrocyte sedimentation rate

We aimed to test the influence of storage temperature and time for canine and feline ESR. Forty dogs and 12 cats were included and randomly allocated in “room temperature” and “refrigerated” groups. Both groups had the T0 ESR measures few minutes after complete blood count. Afterwards, room temperature group had ESR measured at 2, 4, 6 and 8h after T0, whereas the “refrigerated” group had the blood sample stored at 4-6°C for 24 and then T24h ESR was measured. In each ESR measurement, [1] blood samples were put on a tube rocker waiting for ESR analysis; [2] before inserting the blood tube in the MINI-PET ESR instrument, samples were gently mixed again by complete inversion 10 times; (3) each mixed blood tube was inserted in the one of the four MINI-PET tubes position; (4) on the machine display, patient's species has to be chosen and the 14 minutes countdown started; (5) after the 14 minutes optical reading, the ESR result (mm/h) is displayed on the machine. ESR of canine samples at room temperature were significantly stable until T6, while feline samples remained stable at T8. After 24h at refrigerated temperature, both canine and feline samples were stable.• MINI-PET is an ESR automatic continuous-loading instrument that can analyze up to four EDTA blood samples simultaneously using an optical system that measures the erythrocytes sedimentation level• We aimed to test influence of storage temperature and time for canine and feline ESR• At room temperature, dogs’ samples were stable within 6 hours from collection, and cats’ samples were stable until 8h. At refrigerated temperature, there was no difference in T0-T24 ESR in both canine and feline samples

Physical, microstructure and leaching assessments for pavement road base containing mixed steel slag and cathode ray tube glass

Physical, microstructure and leaching assessments for pavement road base containing mixed steel slag and cathode ray tube glass

Enteral tube feeding for people with severe dementia.

Enteral tube feeding for people with severe dementia.

VLSI based Implementation of Channel oriented ICA Processor for Biomedical systems

The remarkable developments in neural engineering in collecting and analyzing big data have made it possible to further recognize the patient’s brain conditions through their neural recovery, reconstruction, identification, and diagnosis. As a recent science field, the convergence of signal processing and neural processing begins to emerge to work with a major amount of neuronal information for easy, long, but powerful purposes. With complex neuroscience uses, mass spectroscopy indications for brain-computer connections have proved very exciting. We concentrated on EEG-based methods in this analysis from Solutions in getting high and power solutions. Specifically, in Ecg signals’ growing field, we discuss the latest practices, scientific prospects, and CS threats. We stressed that big CS imaging techniques summarise the minimum foundation and the calculation function being used CS to interpret electrical signals. The whole researcher noted selecting an efficient recovery method, imperfect base, and measuring matrix; it will increase current Adc Brain imaging assessments’ efficiency. Finally, the possibilities and issues emerging from promoting the implementation of its application domain architecture are discussed. Research article presents 4-channel Ica in Eeg data differentiation for treated patients and studies brain functionality. A modern ICA process is developed using a mixed linear, tube, and concurrent processing elements and using alternating and triangular Systems in the brain to achieve a device design and manufactured with UMC 90nm Strong Conventional technologies.

Experimental study on flow around a tube in mixed tube bundles comprising cam-shaped and circular cylinders in in-line arrangement

Flow and heat transfer around a tube in mixed tube bundles composing of cam-shaped and circular tubes were investigated in an experimental study. The tube bundle is consisting of three tubes with equal circumferential length, and with pitch ratios = 1.5, 2, and 2.5 in in-line configuration. Also, the Reynolds number is within the range of 24000–38500. Results showed that in all mixed tube banks, increasing the pitch ratio from 1.5 to 2.5 leads to the increment in Nusselt number. The best thermal performance in all pitch ratios was obtained for case 2 (the cam-shaped tube with aspect ratio 1.35 is located between two circular tubes) and case 3 (the cam-shaped tube with aspect ratio 3.13 is located between two circular tubes). However, it was found that case 5 (the circular tube between two cam shaped tubes with aspect ratio 3.13) has the lowest Nusselt number compared to other cases. Besides, in all the cases, since the test tube was affected by the wake region of the upstream cylinder, the average coefficient of drag was significantly reduced. Moreover, by increasing the pitch ratio, the coefficient of drag also increases. Case 1 (three circular tubes) in pitch ratio = 1.5 had the lowest value of average drag coefficient, and case 5 in pitch ratio = 2.5, which its upstream cylinder had streamlined shape, indicated the highest coefficient of drag. The cam-shaped tube in mixed bundles has better performance in order that the thermal-hydraulic performance of case 2 and case 3 was about 2–24% and 4–34% greater than case 1, respectively.

Feeding during High-Flow Nasal Cannula for Bronchiolitis: Associations with Time to Discharge.

High-flow nasal cannula (HFNC) is increasingly used to treat children hospitalized with bronchiolitis; however, the best practices for feeding during HFNC and the impact of feeding on time to discharge and adverse events are unknown. The study objective was to assess whether feeding exposure during HFNC was associated with time to discharge or feeding-related adverse events. This retrospective cohort study included inpatients aged 1-24 months receiving HFNC for bronchiolitis at an academic children's hospital from January 1, 2015 to March 1, 2017. Feeding exposures during HFNC were categorized as fed or not fed. Among fed children, we further evaluated mixed (oral and tube) or exclusive oral feeding. The primary outcome was time to discharge after HFNC cessation. Secondary outcomes were aspiration, intubation after HFNC, and seven-day readmission. Of 123 children treated with HFNC, 45 (37 %) were never fed. A total of 78 children (63%) were fed; 50 (41%) were exclusively orally fed and 28 (23 %) had mixed feeding. Median (interquartile range) time to discharge after HFNC was 29.5 hours (23.5-47.9) and 39.8 hours (26.4-61.5) hours in the fed and not fed groups, respectively. In adjusted models, time to discharge was shorter with any feeding (hazard ratio [HR] 2.17; 95% CI: 1.34-3.50) and with exclusive oral feeding (HR 2.13; 95% CI: 1.31-3.45) compared with no feeding. Time to discharge from HFNC initiation was shorter for exclusive oral feeding versus not feeding (propensity weighted HR 1.97 [95% CI: 1.13-3.43]). Adverse events (one intubation, one aspiration pneumonia, one readmission) occurred in both groups. Assessment of feeding exposure did not account for quantity and duration. Children fed while receiving HFNC for bronchiolitis may have shorter time to discharge than those not fed. Feeding-related adverse events were rare regardless of the feeding method. Controlled prospective studies addressing residual confounding are needed to justify a change in the current practice.

Study of mixed materials heat exchanger using optimization techniques

PurposeThis paper aims to examine total annual cost from economic view mixed materials heat exchangers based on three optimization algorithms. This study compares the use of three optimization algorithms in the design of economic optimization shell and tube mixed material heat exchangers.Design/methodology/approachA shell and tube mixed materials heat exchanger optimization design approach is expanded based on the total annual cost measured by dividing the costs of the heat exchanger to area of surface and power consumption. In this study, optimization and minimization of the total annual cost is considered as the objective function. There are three types of exchangers: cheap, expensive and mixed. Mixed materials are used in corrosive flows in the heat exchanger network. The present study explores the use of three optimization techniques, namely, hybrid genetic-particle swarm optimization, shuffled frog leaping algorithm techniques and ant colony optimization.FindingsThere are three parameters as decision variables such as tube outer diameter, shell diameter and central baffle spacing considered for optimization. Results have been compared with the findings of previous studies to demonstrate the accuracy of algorithms.Originality/valueThe present study explores the use of three optimization techniques, namely, hybrid genetic-particle swarm optimization, shuffled frog leaping algorithm techniques and ant colony optimization. This study has demonstrated successful application of each technique for the optimal design of a mixed material shell and tube heat exchanger from the economic view point.

Mixed stochastic-deterministic tube MPC for offset-free tracking in the presence of plant-model mismatch

This paper presents a stochastic-tube model predictive control (MPC) strategy that systematically handles plant-model mismatch, guarantees stability in the presence of changing operating conditions, and ensures offset-free tracking for all reachable operating conditions. The key notion of this work is to separate the system uncertainty into two distinct sources of additive bounded state error. The first source is a non-random uncertainty that represents mismatch between the linear model of the controller and the true plant (as well as other types of persistent disturbances). The second source represents random fluctuations due to either the intrinsic stochastic variability of the system, or exogenous disturbances. Recursive feasibility and stability of the stochastic-tube MPC strategy is guaranteed by defining the terminal invariant set to include the effect of changes in the steady-state operating conditions. Offset-free tracking is achieved with a disturbance estimator that can be tuned independently of the controller. To reduce the conservatism inherent to robust control performance, a new filter model for deterministic disturbances is proposed that predicts uncertainty in the future evolution of the disturbances based on a bound on how quickly the plant-model mismatch can vary. The stochastic-tube MPC strategy is demonstrated on two simulation case studies—a benchmark DC-DC converter and an industrially-motivated fluidized-bed catalytic cracking unit.

Thermal performance of mixed tube bundle composed of circular and elliptical tubes

A numerical study to determine forced convection heat transfer coefficient and pressure drop across mixed tube bundle (composed of circular and elliptical tubes) has been carried out in the present paper. The analysis is based on a 2-D computational domain consisting of five rows and three columns using commercial CFD package ANSYS 15-FLUENT module. The different configuration of mixed tube bundle for inline and staggered arrangement are considered for analysis. The variation of heat transfer coefficient and pressure drop across various configuration of mixed tube bundle has been investigated for different velocity input and variation in pitch to diameter ratio along vertical and horizontal direction. The Reynolds number and pitch to diameter ratio are varied from 100 to 2000 and 1.25 to 1.85 respectively. The study on convection over circular tube bundle is benchmarked with analytical solution and boiler design standard. The heat transfer coefficient and pressure drop of mixed tube bundle has been compared with circular and elliptical tube bundles. The heat transfer coefficient found to decrease from circular to mixed to elliptical tube bundle for given inlet velocity and pitch to diameter ratio. Similarly, for the same input parameters the pressure drop found to decrease from elliptical to mixed to circular tube bundle. The value of heat transfer coefficient and pressure drop are found to decrease with increase in pitch to diameter ratio and decrease in Reynolds number. The staggered mixed tube bundle has higher heat transfer coefficient and higher pressure drop as compared to inline arrangement. It is also observed that the variation of pitch to diameter ratio along horizontal direction affects heat transfer and pressure drop significantly as compared to the variation in vertical direction. It is concluded that the variation in heat transfer coefficient and pressure drop are not significant for mixed tube bundle arranged in inline and staggered manner.

Local entropy generation rate through convective heat transfer in tubes with wire coil inserts

Purpose – The purpose of this paper is to present a numerical analysis of the flow and heat transfer in a tube with a wire coil insert. A second law analysis of the results is accounted for, in order to assess the local and overall entropy generation in relation with the increased pressure drop and convective heat transfer. A wire coil with p/D=1.25 and e/D=0.076 is selected as insert device. A Reynolds number range between 100 and 1,000 is investigated, which corresponds to the typical operating regimes in the risers of liquid solar collectors. Different wall heat fluxes and inclination angles allow to analyze the potential impact of mixed convection in the presence of tube inserts. Design/methodology/approach – Three-dimensional numerical simulations are performed using a finite-volume solver, assuming laminar flow conditions. Pure water and a mixture of water and propylene-glycol (20 percent) are used as working fluids, with temperature-dependent properties. Fanning friction factor, Nusselt number and local entropy generation results are obtained in the fully developed region. Findings – The friction factor results are successfully compared with a well-known experimental correlation for wire coil inserts. The earlier onset of transition is devised at Re > 300. Nusselt number augmentations between 2.5- and 6-fold are reported with respect to the smooth tube. The mixed convection regime encountered in the smooth tube for the operating conditions investigated is canceled in the wire coiled tube, owing to the opposed effect of the swirl flow induced and the bouyancy forces. Frictional, heat transfer and overall entropy generation rates are computed locally in the fully developed region, allowing to relate these results with the flow structures in the mixed convection smooth tube and in the wire coiled tube. A threefold decrease in the entropy generation rate is reported for tubes with wire coil inserts. Originality/value – An holistic understanding of the heat transfer enhancement in tubes with wire coil inserts is provided through the analysis of the flow pattern, Fanning friction factor, Nusselt number and local entropy generation rates. The reduced entropy generation in the enhanced tube serves as a performance criteria to confirm the positive effect of wire coil inserts in heat transfer for the operating regime under investigation, in spite of the increased pressure drop.

Evaluation of image quality, radiation dose and diagnostic performance of dual-energy CT datasets in patients with hepatocellular carcinoma

To evaluate image quality and diagnostic accuracy of different dual-energy computed tomography (DECT) datasets for identification of hepatocellular carcinoma (HCC), assess the reliability of virtual unenhanced (VU) images in replacing standard unenhanced (SU) images, and quantify effective dose (ED) at different tube voltages. Thirty cirrhotic patients underwent liver contrast-enhanced DECT. Two blinded observers retrospectively evaluated conventional unenhanced and VU images, 140 kVp/80 kVp/mixed tube potential arterial datasets and conventional portal-venous/late phases in consensus. Final diagnosis was based on pathological proof or imaging criteria. Image quality, ED, sensitivity, and specificity of arterial datasets were calculated. Thirty-eight HCC and 18 benign lesions were detected at 80 kVp, 33 HCC and 22 benign lesions were detected at 140 kVp, and 36 HCC and 20 benign lesions were detected at mixed tube potentials. Final diagnosis confirmed 37 HCC and 20 benign lesions. There was no significant difference in diagnostic confidence between 80 kVp, 140 kVp, and mixed tube potential arterial datasets (p>0.05). Image quality was adequate for all datasets, with increased quality at higher tube potential (80 versus 140 kVp, p=0.001; mixed versus 140 kVp, p=0.001; 80 kVp versus mixed, p=0.0024). Significant ED reduction was observed between 140 and 80 kVp datasets (p<0.001). The 140 kVp dataset provided higher image quality. The 80 kVp images were more sensitive in detecting HCC. VU images are adequate in replacing SU images. The ED of the 80 kVp dataset was significantly lower.

Recycling Glass Cullet from Waste CRTs for the Production of High Strength Mortars

The present paper reports on the results of some experiments dealing with the recycling of mixed cathode ray tube (CRT) glass waste in the production of high-strength mortars. Waste CRT glass cullet was previously milled, and sieved, and the only fine fraction was added to the fresh mortar in order to replace part of the natural aggregate. The addition of superplasticizer was also investigated. All hydrated materials displayed high compressive strength after curing. Samples containing CRT mixed glass showed a more rapid increase of strength with respect to the reference compositions, and materials with a superplasticizer content of 1% showed the best overall performance due to the favourable influence of the small glass particles which increase the amount of silicate hydrated produced. The induced coupled plasma (ICP) analysis made on the solutions, obtained from the leaching tests, confirmed the low elution of hazardous elements from the monolithic materials produced and consequently their possible environmental compatibility.

Particle Size Distributions following Condensational Growth in Continuous Flow Aerosol Reactors as Derived from Residence Time Distributions: Theoretical Development and Application to Secondary Organic Aerosol

Condensational growth in continuous flow reactors, such as continuously mixed flow reactors (CMFRs) and flow tube reactors, is widely employed in the field of aerosol science and technology to produce particles for industrial use and scientific research. The development of analytical equations for the number-diameter distribution n(d) of the particles in the outflow from these reactors is advantageous both for the inversion of data sets to obtain thermodynamic and kinetic parameters as well as for the rational design of experiments. In this study, equations are derived that relate the number-diameter distribution n(d) to the probability density function p(t) of particle residence time. Specifically, the condensational growth rate is used to derive n(d) based on p(t). Analytical equations are developed for CMFRs, laminar-flow reactors, and dispersive plug-flow reactors, with a focus on CMFRs. The CMFR equation accurately describes data sets collected for α-pinene and β-caryophyllene ozonolysis in the Harva...

Persistent conductive or mixed hearing loss after the placement of tympanostomy tubes

ObjectiveDescribed is a case series of clinical findings in children with persistent conductive or mixed hearing loss following tympanostomy tube placement for serous otitis media. Study designRetrospective chart review. SettingTertiary pediatric hospital. Subjects/methodsMedical records of thirty-nine children who were referred for either conductive or mixed hearing loss post-tympanostomy tube placement were reviewed for clinical histories, physical examinations, audiological evaluations, diagnostic studies, consultations, and surgical findings. Approval was obtained from the Boston Children's Hospital Institutional Review Board. ResultsCauses of hearing loss included ossicular abnormalities, cochlear abnormalities, ‘third window’ effects, cholesteatomas, genetic syndromes, and unknown causes. In four patients with isolated mild low-frequency conductive hearing loss, the cause was the presence of functional tubes. All patients diagnosed with a genetic syndrome had bilateral hearing loss. Patients with mixed hearing loss were diagnosed with cochlear abnormalities, ‘third window’ effects, or genetic syndromes. Computed tomography led to diagnosis in sixteen of twenty-five patients. Vestibular-evoked myogenic potential testing suggested a diagnosis in three of four patients. ConclusionIn children with persistent hearing loss following tympanostomy tube placement, identifying the laterality and type of hearing loss appears to be of importance in diagnosis. Patients with bilateral hearing loss should be considered for genetic testing, given the possibility of a syndrome. Patients identified with a mixed hearing loss should be evaluated for inner ear anomalies. Patients with mild, low-frequency hearing losses should be monitored audiologically and investigated further only if the hearing loss progresses and/or there is no resolution following tube extrusion.