Concentric Tube Research Articles

Effect of shot peening on augmenting the thermo-fluid characteristic of a concentric tube water-to-air counter flow heat exchanger

The current work focuses on heat transfer and pressure drop performance and determines the thermal enhancement factor in a concentric tube heat exchanger (HEX), whereby the external profile of the copper inner tube is modified via shot peening. The Reynolds number of the water-side varied from 6000 to 12,000 and the water temperature varied from 60 to 80 °C. The cold air mass flow rate was maintained at approximately 0.01 kg/s. The Nusselt number of a shot-peened surface HEX was improved by nearly 25.78%, compared with the normal copper tube HEX, where the water inlet temperature and Re were 80 °C and 10,000, respectively. The test outcomes displayed that the increase in surface roughness induces the rise in HTFs turbulence and, successively, an augmentation of Nusselt number. The shot peening process breaks the thickness of the viscid sublayer and it creates the local wall turbulence owing to flow separation and reattachment between the grain particles, which enhances the heat transfer to a considerable amount. The friction factor increased up to 26.82% when Re was 6000 and reduced as Re increased. The thermal enhancement factors were in the range 1.007–1.19 for surface roughness of 6.41 μm.

Estimation of heat transfer coefficient for intermediate fluid stream in triple concentric tube heat exchanger

The design of triple concentric tube heat exchanger (TCTHE) requires heat transfer coefficient (HTC) values for all three fluid streams as input parameters. The fluid through intermediate tube transfers heat to other fluids simultaneously. The present study applies a concept of thermal resistance network and quadratic equation is developed for computing HTC of intermediate fluid for TCTHE under adiabatic condition. ‘Oil ISO VG 22’ is taken as intermediate fluid and is cooled by using water as inner and outer cooling fluid in the present work. The HTCs of inner and outer cooling fluids are calculated from the well-established empirical correlations available in the literature. CAD modelling is done using Catia V5 and simulation is carried out using STAR CCM+ CFD software. The results of the method are compared with those obtained from mathematical models in the literature as well as results from CFD analysis are validated.

Experimental and numerical investigation on the thermal performance of triple tube heat exchanger equipped with different inserts with WO3/water nanofluid under turbulent condition

A novel curve tube design called Triple Tube Heat Exchanger was investigated to identify the thermofluidic characteristics in the current paper. This research analysis comprises of both computational fluid dynamics and experimental results. A three-dimensional computational fluid dynamics model was developed using Ansys R19.1 (fluent) research package, and the k-epsilon model is used to realize the thermofluidic characteristics. In this new design, an additional tube is introduced between a double concentric tube heat exchanger. The complete analysis is done under consideration of turbulent fluid to fluid heat transfer conditions. The influence of different thermal parameters such as overall heat transfer and effectiveness were the main points of research interest by using WO3/water nanofluid with different novel inserts like twisted tape, rib, and porous plate. The thermodynamic effect of nanofluid was considered under the concentration range of 0.5%–3.0%. The computational fluid dynamics method is used to simulate the process, and experimental data is used to validate it. The result shows that the maximum overall heat transfer rate and effectiveness were 1767.91 W/m2K, 1702.71 W/m2K, and 1.86, 1.79, respectively, at 1% optimized volume concentration with WO3/water nanofluid by using rib type insert during experimental and computational fluid dynamics methods, respectively. The maximum thermal performance factor by using nanofluid in the rib type insert was observed at 0.75. The study shows an enhancement of 11.84%, 12.38%, and 14.56%, 14.30% in overall heat transfer and effectiveness by using a rib-type insert for both experimental and computational fluid dynamics methods, respectively, in comparison to without using inserts. There was also a progressive decrement in friction factor during the increment in mass flow rates.

Piecewise constant strain kinematic model of externally loaded concentric tube robots

This paper presents a piecewise constant strain kinematic model for concentric tube robots (CTR) in externally loaded conditions. It discretizes the pre-curved tubes comprising the robot into a finite number of pieces and involves external effects as a set of wrench vectors exerted along the robot backbone. Constant strain lets us describe the pieces with helices in which shear deformation and elongation are neglected. The resulting piecewise helix is the simplest curve that can catch the torsion of tubes that play a crucial role in kinematic behavior. This approximation transforms the conventional boundary value problem (BVP) of CTRs models into a set of nonlinear equations that drastically decreases the model resolution time. The present method uses a Lyapunov function and torsional Jacobian to ensure the distal torsion constraint consistently and, as a result, the solution’s convergence. The paper’s primary purpose is to present a fast, numerically stable, and relatively accurate kinematic model not reliant on measurement data. Experimental results on a two-tube prototype and provided for different tip loading conditions reveal maintaining a balance between adequate accuracy and reasonable running time, about 7 ms for five pieces per section, for real-time applications in the presence of external load.

A modular, multi-arm concentric tube robot system with application to transnasal surgery for orbital tumors

In the development of telemanipulated surgical robots, a class of continuum robots known as concentric tube robots has drawn particular interest for clinical applications in which space is a major limitation. One such application is transnasal surgery, which is used to access surgical sites in the sinuses and at the skull base. Current techniques for performing these procedures require surgeons to maneuver multiple rigid tools through the narrow confines of the nasal passages, leaving them with limited dexterity at the surgical site. In this article, we present a complete robotic system for transnasal surgery featuring concentric tube manipulators. It illustrates a bagging concept for sterility, and intraoperatively interchangeable instruments that work in conjunction with it, which were developed with operating room workflow compatibility in mind. The system also includes a new modular, portable surgeon console, a variable view-angle endoscope to facilitate surgical field visualization, and custom motor control electronics. Furthermore, we demonstrate elastic instability avoidance for the first time on a physical prototype in a geometrically accurate surgical scenario, which facilitates use of higher curvature tubes than could otherwise be used safely in this application. From a surgical application perspective, this article presents the first robotic approach to removing tumors growing behind the eyes in the orbital apex region, which has not been attempted previously with a surgical robot.

Characterization of heat transfer on concentric tube heat exchanger using ethylene glycol/TiO2 nanofluid

This study aims to determine the effect of temperature and volume fraction on heat transfer rate and heat transfer coefficient on concentric tube heat exhanger with nano ethylene glycol / TiO2 fluid. From the results of tests and analyzes that have been done, it is obtained the best temperature and volume fraction that supports the rate of heat transfer. The best heat transfer rate of 22,430.25 W is done at the condition of the 0.03% TiO2 Volume Fraction and at a temperature of 100 ° C. The best heat transfer coefficient occurs at a volume fraction of 0.03% and at a temperature of 100 ° C. It can be concluded that, TiO2 will increase the heat capacity and heat conductivity of the base fluid which will optimize the performance of the fluid.

An experimentation on gravity influence in concentric tube heat pipe heat exchanger using various working fluids

In present work the experimentation is carried out in the heat pipe introduce inside concentric-tube heat exchanger. Methanol, Acetone as working fluids, and water as heat transport fluid. The investigation is done by different mass flow rates and temperatures of the fluids. The effect of gravitational angles for 0° and 90° are experimented. The maximum heat transfer performance is obtained at angle is 0°. In this investigation for acetone as working fluid there is an increment of 30.42% for effectiveness, 2.5% for Reynolds number and 21.57% decrease in thermal resistance than with methanol. This experimentation clearly shows that heat pipe heat exchanger with acetone exhibits enhanced performance when related with methanol.

Thermohydraulic behavior of concentric tube heat exchanger inserted with conical wire coil using mono/hybrid nanofluids

The experimental studies with a new type of enhancer, conical wire coil insertion in the concentric tube heat exchanger using water-based mono (Al2O3 and CNT) and hybrid (Al2O3 + CNT) nanofluids, flowing in the inner tube, are conducted to examine the effect on thermohydraulic performance. The thermohydraulic performances are studied with various conical wire coil configurations (converging, diverging and converging-diverging coils). The outcomes indicate that the diverging wire coil insert exhibits better thermohydraulic performance as compared to other wire coil arrangements. In comparison to DI water in the plain tube (without insert), the maximum Nusselt number enhancements for diverging, converging-diverging and converging wire coil inserts are 171%, 152% and 139%, respectively. Similarly, the friction factor is increased up to 106%, 92% and 72%, respectively, for diverging, converging-diverging and converging wire coil inserts. In all conditions, it is found that the entropy generation of DI water is higher than that of mono/hybrid nanofluids. The thermal performance factor is observed more than one with all mono/hybrid nanofluids and wire coil inserts, indicating a promising combination.

Thermal Performance of Thermosyphons Intended for Evacuated Tube Solar Collector Using Graphene Oxide Nanofluids

Vacuum tube solar collectors are composed by two concentric glass tubes with the annular space evacuated. At the inner tube a thermosyphon is placed inside a metallic fin in order to absorb sun’s irradiation and heat running water placed at a manifold. Thermosyphons are passive heat transfer devices that absorb heat at the evaporator region, evaporating the working fluid that reaches the condenser in the form of steam. At the condenser, heat is dissipated to the environment, condensing the working fluid that returns to the evaporator, closing the thermodynamic cycle. In this study, thermosyphons with three different working fluids (5 and 10% graphene oxide nanofluids and distilled water) were built and experimentally tested. The evaporator and the adiabatic section have an outer diameter of 8.33mm and lengths of 1,600mm and 40mm, respectively. The condenser has an outer diameter of 13.40mm and a length of 35mm. The filling ratio used was 50% of the evaporator’s volume. A resistive tape wrapped at the evaporator and connected to a power supply was responsible for heating the working fluid by Joule effect, and water flow rates of 0.50, 0.75, and 1.00L/min were responsible for condensing the working fluid at the condenser. Heat loads of 35, 55, and 75W were applied to the devices and K-type thermocouples were responsible for acquiring temperature data from the thermosyphons, allowing the thermal analysis based in the temperature distribution and thermal resistance for each working fluid. The best working fluid for the conditions proposed, out of the three investigated, was 5% graphene oxide.

An experimental inquisition of waste heat recovery in electronic component system using concentric tube heat pipe heat exchanger with different working fluids under gravity assistance

In the utilizing of the waste heat in the electronic components meets the power demand and energy utilization for the industries and domestic applications. To meet out this by the understanding and optimization of the waste heat utilization by a compact and cost effective device using heat pipe heat exchanger. This paper states with the design, fabrication, development, and observation of an experimental investigation of the heat pipe introduce in the concentric tube heat exchanger. Working fluids like Methanol, Acetone and heat transport fluid as water. The investigation is further extended by varying the inclination angles, mass flow rates, and temperatures of hot and cold fluid at inlet conditions. The influence of gravitational effect on the heat pipe heat exchanger is conducted for inclination angle from 10° to 80° and the maximum performance is obtained at 60° inclination angle. It is observed while acetone as working fluid there is an increase in 29.75% for effectiveness, 79.81% as heat transfer coefficient, 39.53% as heat transfer rate, 6.70% for Reynold's number and 10.52% decrease in thermal resistance than with methanol. It is concluded that the acetone exhibits better performance when related with methanol as a working fluid. These observations show the suitability of the designed concentric tube heat pipe heat exchanger for the utilization of waste heat dissipation in electronic component system.

Steerable needles for radio-frequency ablation in cirrhotic livers

Accurate needle placement in deep-seated liver tumours can be difficult. In this work, we disclose two new manually controlled steerable needles for 17G radio-frequency ablation probe placement. The needles contain stylets with embedded compliant joints for active tip articulations, and concentric tubes for (curved-path) guidance. Needle steering was evaluated sequentially by intended users and in intended-use tissue types. Six interventional radiologists evaluated the needle in repeated ultrasound-guided steering tasks in liver-mimicking phantoms. Targets were located at a 100 mm depth and 20 mm lateral offset from the initial insertion line. The resulting mean absolute tip placement error was 1.0 ± 1.0 mm. Subsequently, steering-induced tissue damage was evaluated in fresh cirrhotic human liver explants. The surface area of puncture holes was estimated in scanned histology slides, using a connected-components analysis. The mean surface area was 0.26 ± 0.16 mm2 after steering with a median radius of curvature of 0.7 × 103 mm, versus 0.35 ± 0.15 mm2 after straight-path insertions with the steerable needle and 0.15 ± 0.09 mm2 after straight-path RFA probe insertions. The steering mechanisms proposed enable clinically relevant path corrections for 17G needles. Radiologists were quickly adept in curved-path RFA probe placement and the evaluation of histological tissue damage demonstrated a potentially safe use during liver interventions.

Experimental Investigation of the Helical Condenser for Humidification Dehumidification Desalination Unit Powered by Solar Energy

In this paper, built the water desalination unit based on the humidification dehumidification (HDH) process powered by solar energy was examined. The unit uses a humidifier of the packing type (HPT) and the dehumidifier (condenser) made a concentric helically tube and shell heat exchanger was investigated. The dehumidifier was used to condensate water vapor from humid air. The Nusselt number (Nu) inside the helical tube was discussed in many studies before, although it is not mentioned before the Nusselt number outside the helical tube for a mixture fluid. In the current study cold water in passing inside a concentric helical tube, while a hot humid air passing over the external surface of the concentric helical tube. The concentric helical tube is positioned inside an insulated shell. Different air flowrates were used, and the experimental results were used to induce a new empirical equation for the shell’s Nusselt number. The water desalination unit was examined by using the solar collectors as a heating source for the saline feed water and the introduced air to the humidifier, and it is found that the freshwater productivity was 8.60 kg/day and to reduce the carbon dioxide released by 4600 g/day.

Conjugated heat transfer of power-law fluids in double-pass concentric circular heat exchangers with sinusoidal wall fluxes.

An analytical formulation, referred to as conjugated Graetz problems, is developed to predict the temperature distribution and Nusselt numbers for the power-law fluid flowing in a double-pass concentric circular heat exchanger under sinusoidal wall fluxes. A new design of inserting an impermeable sheet into a concentric tube, in parallel, to conduct recycling double-pass operations has been studied theoretically in the fully developed region, resulting in substantial improvements in the performance of heat exchanger device. The analytical solution was derived using the complex functions by transforming the boundary value problem into ordinary differential equations with the aid of the Frobenius method. The influences of power-law index and impermeable-sheet position on average Nusselt numbers with various designs and operating parameters are also delineated. The theoretical predictions show that the heat transfer efficiency is considerably improved through operating the double-pass device compared to via a single-pass circular heat exchanger (where an impermeable sheet is not inserted). The economic feasibility of operating double-pass concentric circular heat exchanger for power-law fluids is exemplified by the ratio of the heat-transfer efficiency enhancement and the increment in power consumption. The double-pass effect from increasing the convective heat-transfer coefficient can compensate for the rise in power consumption, which serves as important economic advantage of this design.

Comparative analysis of thermal and fluid flow behaviour of diverse nano fluid using Al2O3, ZnO, CuO nano materials in concentric spiral tube heat exchanger

Present paper based on computational and experimental study, in which diverse parameters have been investigated for observing the fluid flow, thermal and performance attributes like thermal performance factor, NTU, effectiveness and fluid flow attributes like Reynolds number, Nusselt number, Friction factor, HTR etc of diverse composition of nanofluids in spiral tube having insert, CTHE with insert diameter and pitch distance 2 mm and 20 mm. During present investigation water used as the base fluid associated with diverse additives or nano particles in single and combined form like Zinc Oxide, Aluminium Oxide and Cupric Oxide to form diverse composition of nano fluids with 10 nm particle size and 0.08% volume fraction like Zinc Oxide with water, Aluminium Oxide with Zinc Oxide with water, Aluminium Oxide with water and Aluminium Oxide with Cupric Oxide with water to improve the thermal conductivity. Experimentation has been performed for diverse nanofluids at 31 OC with flow range 0.721 to 2.941 L/min, which flows in the spiral tube whereas, the hot fluids as water flows at 4.02 L/min across the shell side of test set up at 50 OC. Here comparative investigation has been drawn for diverse nanofluids for observing its fluid flow, thermal and performance attributes at diverse flow rate with turbulent flow under counter flow condition with Reynolds Number 4236 to 18540. The result predicted that out of four diverse nano fluids Aluminium Oxide and Cupric Oxide with water as base fluid shows best results for fluid flow, thermal and performance attributes, for flow rate range 0.721 to 2.941 L/min and Reynolds Number 4236 to 18540. It has been evaluated that from minimum to maximum Reynolds Number, HTR, Nusselt number, Friction factor and effectiveness and NTU varies from 1228.3 to 3316.4, 88.28–160, 0.0438–0.0306, 0.84–0.55, 4.66–1.96 for Aluminium Oxide and Cupric Oxide nano fluid.

Non-linear analysis of double skinned composite hollow columns using geopolymer concrete

Abstract This paper investigates the behavior of Doubled skinned (DSCFT) composite hollow columns with steel tubes compressed under concentric axial loads. The DSCFT member is a new type of composite construction, which consists of two concentric steel tubes with geoploymer concrete sandwiched between them. Thus, DSCFT columns have a series of advantages, such as high strength, high bending stiffness, good seismic and fire performance, and also having favorable construction ability. The finite element analysis of the DSCFT circular column is conducted to validate the finite element model. The results obtained from the finite element investigation are compared with the strength values predicted using existing formulations in the analytical investigation. A good correlation was found between the values obtained.

High-Performance Fiber Optic Interferometric Hydrophone Based on Push–Pull Structure

A high-performance fiber optic interferometric hydrophone based on a push-pull mandrel structure, with high sensitivity and wide-frequency response, is designed and developed. Each arm of the Michelson interferometer is a fiber coil wrapped onto a separate but concentric thin elastic tube as the sensing arm to detect acoustic pressure wave. The fiber optic hydrophone is fabricated and examined experimentally, demonstrating its capacity to detect very low-frequency underwater acoustic pressure variation. The theoretical design is validated experimentally, with results showing that the push-pull fiber optic hydrophone has an average sensitivity of -134.39 dB re rad/ μPa within the frequency range of 1 Hz-2 kHz, which is 5.67 dB higher than that of the analogous one-sensing-arm fiber optic interferometric mandrel hydrophone that we made for comparison. The push-pull fiber optic hydrophone has a minimum detectable pressure (MDP) of 25.37 μPa/√{Hz} at 1 kHz, about 15 dB lower than the deep-sea state zero (DSS0) level. At 10 Hz, the MDP is ~1.71 mPa/ √{Hz}, which is nearly 7 dB lower than the acoustic ambient noise in the ocean at low frequency. The sensitivity and the MDP of the push-pull fiber optic hydrophone have been doubled and improved by about 20% at 1 kHz, respectively, compared to other state-of-the-art flat response fiber optic hydrophones.

Significant reduction of radiation dose and DNA damage in 18F- FDG whole-body PET/CT study without compromising diagnostic image quality

ABSTRACT Reduction of radiation dose from medical investigations still remains an important strategy. The combined effect of the reduced injected activity of 18F – FDG, low tube voltage & iodine concentration with iterative reconstruction on image quality, radiation dose, and DNA damage in patients undergoing PET/CT examination were examined. The study includes 16 patients who underwent PET/CT investigation twice using two different protocols; standard & new. A new protocol was followed during follow-up after 4–6 months. All acquisition and reconstruction parameters were the same in both protocols, except administered activity, iodine concentration and CT tube voltage which was reduced. Image quality was assessed using various parameters. Effective dose from PET/CT was assessed using CTDIvol and ICRP coefficients. DNA damage analysis was performed using comet and γ-H2AX assay. No significant difference was noted in quality parameters between two protocols (p > 0.05) except CT noise level (p < 0.05). Mean iodine dose, total radiation dose, mean foci and TM in the new protocol were found significantly lower than standard PET/CT (p < 0.05). There were 26.68% reduction in radiation dose, 10% reduction in contrast load, 20.31% reduction in the number of foci and 17.67% reduction in TM was noted with optimized protocol.

Application of CT Image Scanning Technology Based on Iris Algorithm in Clinical Diagnosis of Patients with Hepatobiliary Stones

Objective: To investigate the value of multi-slice spiral CT in the diagnosis of extrahepatic bile duct stones using Iris algorithm. Methods: 66 cases of extrahepatic bile duct stones underwent plain and enhanced multiline spiral CT. Observe the density, size, location and number of stones during the plain scan. According to the venous phase enhanced scan, the extrahepatic bile duct wall ≥2 mm was used as the thickening criterion to evaluate the stone density, size, number, and composition ratio of the site and its relationship with tube wall thickening. Results: A total of 57 cases of stones of different densities were found on CT. Nine cases of stones of equal density were not identified. Among the 56 cases with thickened wall, 87.50% (49/56) were concentric and 12.50% (7/56) were eccentric. The wall thickening occurred 62.50% (35/56) below the stone; 17.86% (10/56) was located on the level or above the stone, and 8.93% (5/56) was above the stone. 6 cases (6/56) (10.71%) showed extensive tube wall thickening, all caused by multiple stones. Conclusion: In the study of extrahepatic bile duct stones using the Iris algorithm, it was found that most concentric circular tube wall thickening occurred on or below the stone level. When plain CT scan does not show clear bile duct stones, and this phenomenon appears in the portal vein phase of enhanced scan, the possibility of stones should be considered.

Concentric chiral nematic polymeric fibers from cellulose nanocrystals.

Hierarchical biological materials, such as osteons and plant cell walls, are complex structures that are difficult to mimic. Here, we combine liquid crystal systems and polymerization techniques within confined systems to develop complex structures. A single-domain concentric chiral nematic polymeric fiber was obtained by confining cellulose nanocrystals (CNCs) and hydroxyethyl acrylate inside a capillary tube followed by UV-initiated polymerization. The concentric chiral nematic structure continues uniformly throughout the length of the fiber. The pitch of the chiral nematic structure could be controlled by changing the CNC concentration. We tracked the formation of the concentric structure over time and under different conditions with variation of the tube orientation, CNC concentration, CNC type, and capillary tube size. We show that the inner radius of the capillary tube is important and a single-domain structure was only obtained inside small-diameter tubes. At low CNC concentration, the concentric chiral nematic structure did not completely cover the cross-section of the fiber. The highly ordered structure was studied using imaging techniques and X-ray diffraction, and the mechanical properties and structure of the chiral nematic fiber were compared to a pseudo-nematic fiber. CNC polymeric fibers could become a platform for many applications from photonics to complex hierarchical materials.

Concrete filled double skin square tubular stub columns subjected to compression load

Concrete filled double skin tubular members (CFDST) consist of double concentric circular or square steel tubes with concrete filled between the two steel tubes. The CFDST members, having a hollow section inside the internal tube, are generally lighter than ordinary concrete filled steel tubular members (CFT) which have a solid cross-section. Therefore, when the CFDST members are applied to bridge piers, reduction of seismic action can be expected. The present study aims to investigate, experimentally, the behavior of CFDST stub columns with double concentric square steel tubes filled with concrete (SS-CFDST) when working under centric compression. Two test parameters, namely, inner-to-outer width ratio and outer square steel tube's width-to-thickness were selected and outer steel tube's width-to-thickness ratio ranging from 70 to 160 were considered. In the results, shear failure of the concrete fill and local buckling of the double skin tubes having largest inner-toouter width ratio were observed. A method to predict axial loading capacity of SS-CFDST is also proposed. In addition, the load capacity in the axial direction of stub column test on SS-CFDST is compared with that of double circular CFDST. Finally, the biaxial stress behavior of both steel tubes under plane stress is discussed.