Concentric Tube Research Articles

Multi-Objective Optimization of a Concentric Tube Heat Exchanger for Waste Heat Recovery in a Natural Gas Turbocharged Engine

Climate change and the growing demand for fossil fuels have encouraged researchers to provide more efficient engineering solutions for waste heat recovery in the industrial sector. The heat transfer between the exhaust gas and the thermal oil fluid in the concentric tube heat exchanger implies heat transfer irreversibility and high investment costs, which have been considered as objective functions to be minimized in this study. Therefore, the main objective of this article is to present the multi-objective optimization results applied to a concentric tube heat exchanger integrated to a GE Jenbacher turbocharged engine type 6, in which genetic algorithms are used to generate multiple solutions to the problem, choosing the best option through the Multiple-criteria decision technique known as TOPSIS. The CAD of the device has been recreated using the SolidWorks software, and the computational fluid dynamics (CFD) model has been made with the open-source tool OpenFOAM. The geometric configuration selected allows energy recovery, with a purchase equipment cost, and its entropy generation number (NGE), using Therminol-75 as thermal oil to exchange heat with the engine exhaust gases. This type of result provides the insertion of this equipment to the industrial sector because of the increase in the overall thermal efficiency of the natural gas engine.

Optical Performance Analysis of Single Flow Through and Concentric Tube Receiver Coupled with a Modified CPC Collector Under Different Configurations

Compound parabolic concentrating (CPC) collectors have great potential to provide sustainable solar thermal energy for many applications operating in the medium temperature range. This paper presents the design, development and performance evaluation of a modified CPC collector integrated with an evacuated tube receiver. The optical performance of the designed CPC paired with concentric tube receiver is compared with that of a CPC coupled with single flow through evacuated tube receiver for stationary installation in the East-West and North-South directions. Ray tracing simulations of different configurations demonstrate that CPC coupled with single flow through receivers suffer high gap losses, especially at smaller incidence angles which are considerably alleviated by a concentric tube receiver arrangement. East-West installation of CPC paired with concentric tube receiver exhibited superior optical performance than all other configurations. The yearly average optical efficiency of CPC with concentric tube receiver was 5% higher than that of a single flow through receiver within the acceptance angle. A 60% truncated CPC coupled with concentric tube receiver emerged as the most effective design, which was fabricated for experimental testing. The tests conducted under actual outdoor tropical environmental conditions demonstrated that the experimental optical efficiency reached to about 69% in the case of N-S installation and 66.5% in an E-W arrangement. The experimental results closely match the simulation outcomes, which indicate the proposed performance prediction technique as instrumental for selecting the most effective configuration of CPC collectors for medium temperature heat supply.

Multiple-Criteria Decision Analysis and characterisation of phase change materials for waste heat recovery at high temperature for sustainable energy-intensive industry

A latent heat storage system based on Phase Change Materials (PCMs) is proposed to increase the energy and environmental efficiency by recovering and storing waste heat from combustion gases or other surplus sources at in the energy-intensive industries (EII), currently unused. The final configuration design is specifically adapted to the plant operational requirements, by means of a methodology combining the search of the best conceptual design and a proper selection of core PCMs. To that end, a selection of suitable PCM is carried out by using characterisation techniques and thermal stability testing. Furthermore, relevant key factors are weighted by an in-house Multiple-Criteria Decision Analysis (MCDA) to define the most promising design options to be implemented in two plants belonging to the EII sector. For the ceramic sector, the design resulted in a shell-and-tube system with 1188 kg of a PCM melting at 885 °C and encapsulated in double concentric tubes, involving a storage capacity of 227 MJ. Similarly, 1606 kg of PCM, whose phase-change temperature is 509 °C, is selected for the steel sector providing a PCM-TES system capable to store 420 MJ.

Calibration of Concentric Tube Continuum Robots: Automatic Alignment of Precurved Elastic Tubes

Joint level calibration is an integral part of robotics as it directly influences the achievable accuracy. As opposed to serial robotic arms, continuum robots are not composed of any rigid links or joints, but of elastic materials that undergo bending and torsion. The jointless composition requires dedicated calibration procedures. In this letter, we introduce an automatic method for aligning precurved elastic tubes for joint level calibration of concentric tube continuum robots. The robot tip is equipped with a sensor in order to track its position during calibration such that subsequent data processing can extract the rotational zero position automatically. While we present a general framework independent of the utilized sensor technology, we evaluate our approach using three different sensing methodologies, i.e. magnetic, inductive, and electromagnetic. Furthermore, we advise on properties for appropriate sensors. Our experimental results show, that the rotational home position can be found reproducibly with a minimal dispersion of 0.011 $^\circ$ .

A Novel Robotic Endoscopic Device used for Operative Hysteroscopy

Video Objective To trial the use of a novel robotic endoscopic surgery platform for operative hysteroscopy. Setting A uterine tissue model with simulated polyps in various locations (Gynesim). Interventions The robotic endoscope is a surgical platform that simultaneously delivers two instruments that are 2-3mm in size using concentric tube technology. These instruments extend from the tip of a standard rigid endoscope outer sheath and are controlled robotically by an operator distant from the surgical field. In this pilot, a probe and monopolar needle were used to resect simulated endometrial polyps. Surgical principles of adequate exposure and traction and counter-traction are demonstrated. Conclusion The robotic endoscope platform may offer advantages over conventional hysteroscopy that could be useful for some applications. These advantages include: improved exposure, finer dissection capability, and use of two handed technique to allow traction and counter-traction. Further study regarding the safe, efficient, and cost-effective use of the robotic endoscope in gynecology is needed. To trial the use of a novel robotic endoscopic surgery platform for operative hysteroscopy. A uterine tissue model with simulated polyps in various locations (Gynesim). The robotic endoscope is a surgical platform that simultaneously delivers two instruments that are 2-3mm in size using concentric tube technology. These instruments extend from the tip of a standard rigid endoscope outer sheath and are controlled robotically by an operator distant from the surgical field. In this pilot, a probe and monopolar needle were used to resect simulated endometrial polyps. Surgical principles of adequate exposure and traction and counter-traction are demonstrated. The robotic endoscope platform may offer advantages over conventional hysteroscopy that could be useful for some applications. These advantages include: improved exposure, finer dissection capability, and use of two handed technique to allow traction and counter-traction. Further study regarding the safe, efficient, and cost-effective use of the robotic endoscope in gynecology is needed.

Consequence of nanoparticle physiognomies on heat transfer characteristics of heat exchanger

ABSTRACT In this paper, the heat transfer coefficient and the heat transfer rate of a heat exchanger is evaluated by using nanofluids. The silicon carbide nanoparticles, milled and sonificated as nanofluids with volume fractions of 0.01499(%) and 0.01399(%) are used. The heat transfer characteristics of SiC(P)/water, SiC(M)/water, SiC(P)/EG, and SiC(M)/EG are measured in a concentric tube heat exchanger under laminar flow condition. The consequence of nanoparticle physiognomies and Reynolds number, on the heat transfer characteristics are evaluated. It has been found that the addition of milled nanoparticle in the base fluids enhances the heat transfer characteristics rather than the normal nanoparticle. The experimental results shows that the heat transfer coefficient rate of SiC(M) is higher than that of SiC(P) in both the case of water and EG. Further the Reynolds number and Nusselt number for SiC (M) was found higher than SiC (P), which is essential for heat transfer flow.

The design of noise attenuation for gas turbine GTS 22 engine

Nowadays, awareness of global society to the green concept where life should be in harmony with nature has been increasing. One of the ideas in the green concept is to reduce excessive sound exposures or noise. Within this context, gas turbine GTS 22 engine is one of mechanical system that generates a very high sound pressure level. Hence, it is instructive to develop noise controls for the gas turbine in order to have acceptable sound pressure level. This research is focused on the design of muffler as noise control treatment after carefully analyzing the dominant noise spectrum of the gas turbine. In this paper, numerical approach is employed to design the muffler. The results are then validated by experimental ones. Moreover, noise reduction (NR) is used to assess the muffler performances. The design of muffler in this research contains all of combination treatment: area cross section expansion chamber, perforated system (micro perforated panel), porous material, partition chamber and concentric tube. The chosen final design of muffler is combination treatment design where NR 38.77 dB is present. This NR leads to sound pressure level of 80.82 dB or 68.95 dBA exist after the muffler applied on the exhaust of gas turbine. The deviation of experimental results compared to numerical ones is 7.14% in average. Moreover, the pressure drop (ΔP) of the muffler is only 0.4042% which is acceptable to keep the mechanical performance.

Heat transfer based flowmeter for high temperature flow rate measurements: Design, implementation and testing

The present work deals with the design, implementation and testing of a new heat transfer-based flowmeter. The suggested flowmeter allows the measurement of flow rates in applications involving hot fluid flows, mainly gas flows. The suggested flowmeter operates by circulating a cold fluid (water) of a known flow rate and temperature in a concentric tube heat exchanger in an opposite direction to the main flow of hot fluid of unknown flow rate. The flowmeter enables, from temperature measurements and the energy balance of the exchanger, the determination of the unknown flow rate. It was shown that the suggested flowmeter can reach accuracies greater than 90% depending on different parameters. The flowmeter's precision was shown to be increased with the increase of both cold and hot flow rates. The suggested flowmeter can be enhanced when the fluid temperatures are within the optimal range of operation which are achieved and specified by the design parameters.

The thermophysical properties and the stability of nanofluids containing carboxyl-functionalized graphene nano-platelets and multi-walled carbon nanotubes

Two structures of carbon-based materials with sp2-hybridized are carbon nanotubes and graphene arrayed in the concentric tube and two-dimensional sheet, respectively. The most important problems of graphene and carbon nanotube for use in various applications are insufficient dispersibility and their inadequate stability in different organic and aqueous solvents. The low interaction with other materials is second category problems of carbon nanostructures. Functionalization, a common method suggested by numerous researchers, can be employed to enhance this property. In this regard, the nanofluids containing graphene nanoplatelets and carboxylated multi-walled carbon nanotube were synthesized and dispersed in deionized water to prepare homogeneous samples of 0.1 and 0.2 wt%. The stability dependency of samples was investigated, for the first time, on ultrasonic time and microwave irradiation. Thermophysical properties including shear stress, viscosity, surface tension, density and stability were also measured and reported.

Heat Transfer Enhancement of a Concentric Tube Heat Exchanger with Circumferential Circular Staggered Fins

Heat Transfer Enhancement of a Concentric Tube Heat Exchanger with Circumferential Circular Staggered Fins

Thermal Analysis and Performance Evaluation of Triple Concentric Tube Heat Exchanger

Triple concentric-tube exchanger (TCTHE) is an improved version of double concentric tube heat exchanger (DCTHE). Introducing an intermediate tube to a DCTHE provides TCTHE and enhances the heat transfer performance. Recognizing the need of experimental results, extremely scarce in the literature and essential to validate theoretical analyses, the aim of this work is to investigate thermal behavior of TCTHE. The present study includes design, development and experimental analysis of TCTHE for oil (ISO VG 22) cooling application required for industrial purposes. It comprises of water (cooling fluid) flowing through innermost tube as well as outer annulus and oil (hot fluid) flows through inner annulus. The experimental studies of the temperature distribution for three fluids along the length and heat transfer characteristics for TCTHE under insulated condition for counter current flow mode are carried out and discussed. The effect of change in oil (hot fluid) temperatures is analyzed keeping water inlet temperatures same at various operating conditions. The experiments have been conducted by varying flow rate of one of the fluids at a time and keeping other two fluid flow rates constant. The results are expressed in terms of temperature variation for all three fluids along the length. The effect of change in hot fluid inlet temperature is expressed in terms of heat transfer rate variation with respect to Reynolds number. The variation of non-dimensional parameters as temperature effectiveness and thermal conductance with respect to Reynolds number is also presented in this paper. Theoretical studies are carried out for evaluation of heat transfer rate using empirical correlations. Experimental validation is carried out for degree of cooling at different Reynolds numbers with theoretical analysis.

An Automated Extracorporeal Knot-tying System Using Two Concentric Tube Robotic Arms for Deployment through a 3-mm Port

Ligation is a process of closing or blocking a blood vessel or duct intracorporeally to obstruct the flow of fluid before cutting it. Ligation through knot tying using a suture is a quite complex procedure and needs the use of dexterous tools to properly secure the knot. In case of natural orifice transluminal endoscopic surgery (NOTES) and single-incision laparoscopic surgery (SILS), ligation through suture knot tying is even more difficult because of the small diameters of the accessible ports. In this study, a robotic solution for suture ligation has been proposed for possible use in SILS and NOTES. The developed device can operate through a 3-mm laparoscopic port and has a workspace of 35 × 10x5 mm (length × width x height) around the duct. The device uses a pre-tied Roeder’s knot, which is pushed down onto the duct by the operation of two concentric tube-based manipulator arms. Preliminary evaluation validates that the device can work around a phantom duct with 7 mm outer diameter without any collisions. The operation takes an average of 128.10 s with a standard deviation of 15.72 s. The knot tied is secure enough to abduct the fluid flow inside the duct, which is validated by testing on a water-filled rubber tube. The proposed device assists surgeons for suture ligation in SILS and NOTES without the requirement for any other tools and with a possibility of decreasing the operating time.

Heat transfer augmentation of internal flow using twisted tape insert in turbulent flow

Heat transfer augmentation of turbulent single-phase flow in a concentric tube heat exchanger with short-length twisted tape inserts was numerically examined herein. The twisted tape length ratios were 0.25, 0.5, 0.75, and 1.0. The twisted tape was comprised of an aluminum strip with a constant thickness, a pitch, and a width of 0.7, 35, and 12.6 mm, respectively. This study was conducted for heat exchangers with/without twisted tape inserts. The Reynolds numbers ranging from 4,500 to 18,500 were applied. The analyses showed an improvement in heat transfer and friction factor in each of the tube systems, and the results were used to determine the system that delivered the best performance. The correlations of Gnielinski and Petukhov were also used for validating the predicted Nusselt number and friction factor for the plain tube. The results indicated that heat transfer augmentation was elevated as the tape-length ratio increased. The respective highest average Nusselt number and friction factor obtained in this study were 0.51 and 2.84 times greater than that of the plain tube.

Experimental study on Al2O3 /H2O nanofluid with conical sectional insert in concentric tube heat exchanger

ABSTRACT A parallel flow heat exchanger containing conical sectional inserts with three different pitch ratio (i.e., 1, 2, and 3) in a different orientation to the flow direction of the working fluid had been fabricated. Al2O3 with different volume concentration, i.e., 0%, 2%, and 4% nanoparticles (90 nm size) were added to De-ionized water as the working fluid. The combined effect of the Nanofluid and the inserts in different orientations was studied. It was concluded that the insert, flow direction, and Nanofluid volume concentration provided most augmented heat transfer and enhanced the thermal properties.

Evaluation of Concentric Tube Model for Pressure Tube to Calandria Tube Gap Measurement

The CANDU® nuclear reactor fuel channels consist of a pressure tube (PT) contained within a calandria tube (CT). The gap between the hot (~300° C) PT and cooler (~50° C) CT is required since the contact could lead to hydride blister formation with subsequent cracking. This gap is measured using a drive-receive eddy current technology, providing assurance that the contact is not imminent. The analytical models of probe response to gap use flat plates to approximate the PT and CT geometry. In this paper, a semi-analytical model that approximates the PT within the CT geometry as two concentric tubes with correct PT curvature, but a CT diameter, which is adjusted to change gap, is compared with a flat-plate model of probe response to changing gap against experimental measurements using standard CT and PT samples, with varying wall thickness and resistivity that simulates in-reactor variation of these parameters. The concentric and flat plate models both predict gap values with an average error of 0.1 mm between contact and 5 mm gap at 4.2 kHz and 8.0 kHz. The concentric model has an average relative gap error at the maximum gap of 2% at 4.2 kHz and 8.0 kHz, whereas that of the flat-plate model is 10% and 12%, respectively. The improved accuracy of the concentric model at larger gaps is attributed to the incorporation of tube curvature, which limits the probe’s magnetic field spread when compared to the flat-plate model.

Operating cost analysis of a concentric aluminum tubes electrodes electrocoagulation reactor

Energy consumed by the electrochemical treatment of wastewater has more responsibility in designing such a process. The objective of the present study was to investigate the effect of electrodes geometry used in the electrocoagulation cell on the operating cost that required to remove lead from the industrial wastewater. The studied operating variables in the present study were the initial concentration of lead (10–300)ppm, electrolysis time (5–60)minutes, applied electric current (0.5–2.5)Amps., pH (2–12), and stirring speed (0–300)rpm. It has shown that cost was affected by the configuration of aluminum electrodes as well as other studied parameters. Statistical methods and programs were used to estimate an empirical correlation of the operating cost as well as the consumption of aluminum electrodes and energy.

Control no competitivo en L2/D aplicado a intercambiadores de calor de tubos concéntricos contínuos

L2/D proportional integral (PI) control was applied to continuous concentric tubes heat exchangers as example of space distributed parameter systems, both in SISO and MIMO structures. Dynamic model was expressed in continuous space state and leaded to demonstrate that L2/D control is a class of parametric geometric control. Results show that proposed control applied in heat exchangers, gives similar performance and robustness with less parameters than previous geometric controls reported in literature in SISO structures. The proposed L2/D PI control was easily extended to MIMO structure.

Tube-in-tube membrane microreactor for photochemical UVC/H2O2 processes: A proof of concept

This work proposes a disruptive tube-in-tube membrane microreactor for the intensification of photochemical UVC/H2O2 processes, towards contaminants of emerging concern (CECs) removal from urban wastewaters. The main novelty of this system relies on the radial addition of H2O2 through the porous membrane into the annular reaction zone, providing a more homogeneous distribution of the injected chemical across the whole reactor length. The proposed novel reactor consists of a ceramic ultrafiltration membrane inner tubing and a concentric quartz outer tubing that compose the annulus of the reactor (path length of 3.85 mm). The ultrafiltration membrane is used as a dosing system to deliver small amounts of H2O2 into the annulus of the reactor. In the annulus, where a 2 mg/L of oxytetracycline (OTC) solution flows, UVC light is provided via four mercury lamps located externally to the outer tube. The helical motion of OTC solution around the membrane shell-side enhances H2O2 radial mixing. The efficiency of the photochemical UVC/H2O2 process was evaluated as a function of the OTC flowrate, H2O2 dose, H2O2 dosage method and water matrix. OTC removal efficiencies of ~36% and ~7% were obtained for a synthetic OTC solution and an urban wastewater fortified with the same OTC concentration, using a H2O2 dose of 15.8 mg/L. Besides providing a good performance using low UVC fluence (34 mJ/cm2) and reactor residence time (4.6 s), the reactor has the advantage of an easy upscaling into a real plant by integrating multiple parallel membranes into a single shell.

Effect of carbon nanomaterial on latent heat storage performance of carbonate salts in horizontal concentric tube

During the preparation of nanocomposite phase change material (nanoCPCM), more attentions are focused on thermal conductivity. In fact, adding nanomaterial not only affects thermal conductivity, but also changes the other thermophysical properties of PCM and causes complicated effects on latent heat storage performance. In present study, melting behavior of pure phase change material and its four kinds of nanocomposites in a horizontal concentric tube were investigated and a new evaluation index was developed to examine the effects of nanomaterial on heat storage performance of nanoCPCM. The results show that both thermal conductivity and melting temperature have significant effects on nanoCPCM melting behavior and heat storage rate. Sometimes, although the thermal conductivity is enhanced, the heat storage rate is decreased due to its melting temperature increasing caused by nanomaterial. Especially, when the heat source temperature and PCM melting temperature is close, the variation of melting temperature is more significant. For example, nanoCPCM with SWCNT has the higher thermal conductivity, but its heat storage rate is slower than nanoCPCM with MWCNT, because of its higher melting temperature. Therefore, more attention must be paid to the variation of melting temperature caused by nanomaterial during the preparation and application of nanoCPCMs.

Effects of shear inhomogeneities on the structure of turbulent premixed flames

This paper studies the effects of shear inhomogeneities on the structure and stability characteristics of turbulent piloted premixed flames. The shear is introduced by splitting the fuel-air mixture in two stream and feeding each stream at different velocities through two annular concentric tubes residing within the pilot annulus. The shear is varied by varying the proportion of fluid injected through the streams and also by changing the recess distance of the inner tube with respect to the jet exit plane. It is noted that with increasing rates of shear, the Bunsen-like flames become shorter with the flame tip opening downstream of the pilot stream. Measurements of flow fields reveal useful information about the level and location of the shear layers. Joint imaging of Laser-Induced Fluorescence (LIF) of OH and CH show that, with increasing rates of shear, the degree of flame front fragmentation increases implying the occurrence of local extinction even in regions extremely close to the pilot. The flame surface area, marked by LIF-CH is taken as an indicator of consumption rates of reactants. For all flames examined here, the peak flame surface area increases with increasing shear and subsequently decreases as the flame shortens and approaches blow-off. The peak flame surface density decreases with increasing shear. Regime diagrams show that the flames investigated here bridge the regions of broadened preheat thin reactions as well as the distributed reaction zone. While the thickness of the CH layer remain somewhat uniform, the number of flame fragments, as indicated by breaks in the CH profiles, increases with increasing shear before stabilizing at some peak value. The observed mechanism of local extinction in highly sheared Bunsen-like, turbulent piloted premixed flames complements existing results for bluff-body stabilised flames.