Concentric Tube Research Articles

Experimental determination of the convection heat transfer coefficient in an eccentric annular duct

The use of bayonet tube heat exchangers and heaters is widespread in many industrial applications and an improvement in the heat transfer coefficient may provide benefits over other technologies. This work presents novel experimental results about the turbulent convection heat transfer coefficient of air in the annular section of a bayonet tube for two different configurations: concentric and eccentric tubes. For both configurations, the convection heat transfer coefficient was obtained at different air flow rates, therefore, at different Reynolds numbers. In the case of the eccentric configuration, the angular position of the inner tube was varied to determine the circumferential distribution of the local convective heat transfer coefficient. An increase of the convection coefficient was observed for both configurations at higher Reynolds numbers. Concerning the angular position with regard the inner tube, the largest local convective heat transfer coefficient was obtained at the angular position where the distance between the inner and outer tubes was maximum, yielding a value 22.3% higher than in the case of a concentric annular section. All these experimental results were used to propose a new correlation for the local convective heat transfer coefficient as a function of the Prandtl and Reynolds numbers, the eccentricity, and the angular position of the inner tube, with a maximum discrepancy between correlation and experimental data below 10%.

Performance Examination of Concentric Tube Spiral Coil Heat Exchanger for Heat Transfer Analysis

Hot fluid passes through the inner tube and cold fluid flows through the outer tube in an experimental study of a Concentric Tube Spiral Coil Heat Exchanger conducted in a Counter Current method. The temperature data was recorded while the flow rates in the inner tube and Annulus were altered five times each. To get total heat transfer coefficients as well as heat transfer coefficients for the inner tube and annulus, the Wilson Plot method is utilised. The Nusselt Number gained from the experiment was compared to the Nusselt Number obtained through the development of a mathematical model using Regression Analysis. The inner Nusselt Number was linked to Dean Number, while the Annulus Nusselt Number was linked to Modified Dean Number and a new Dimensionless Number called "M Number." The experimental data was well-fitting with the Theoretical one. The hydrodynamics (pressure drop) and heat transfer properties of the concentric tube spiral coil heat exchanger were also examined.

Comparison of heat transfer performance of water-based graphene nanoplatelet- and multi-walled carbon nanotube-nanofluids in a concentric tube heat exchanger

Carbon nanomaterials are of great interest for next generation nanofluids. Carbon nanotubes and graphene are, in particular, highly thermally conductive and their use as thermal fluid is gaining momentum among the research community. This work investigates the thermal performance of graphene nanoplatelet (GnP)-nanofluid and multi-walled carbon nanotube (MWCNT)-nanofluid by using a concentric pipe heat exchanger. The prepared nanofluid flowed in the inner pipe as hot fluid, which was in the opposite direction of a colder water flow in the annulus pipe. The investigation was conducted by varying the volumetric flow (from 1.5 to 2.5 L/min) and nanofluid concentration (from 0.01 to 0.35 vol%). The heat transfer coefficient (HTC) of GnP-nanofluid was observed to be superior to that of MWCNT-nanofluid. The maximum increase in HTC relative to the pure base fluid is approximately 16.8, 24.2 and 26.1% for GnP-nanofluid; and 8.8, 13.8 and 14.4% for MWCNT-nanofluid flowing at 1.5, 2.0 and 2.5 L/min, respectively. This positive impact on heat transfer performance enhancement reached the maximum when an optimum concentration is reached in both nanofluids. Compared to the maximum HTC ratio brought by MWCNT-nanofluid at 0.15 vol% and 2.5 L/min, GnP-nanofluid produced a greater HTC ratio, even at relatively low concentration (0.05 vol%) and volumetric flow (1.5 L/min) which is rather desirable for practical applications.

A two-dimensional finite element approach to evaluate the sound transmission loss in perforated silencers

In this work, the two-dimensional finite element method approach is presented to evaluate sound transmission loss (TL) of perforated reactive silencers with holes uniformly distributed. In the hole domain, the sound pressure was described using a periodic positive square wave function to simplify the evaluation of sound waves in the azimuthal direction. Eight different models with perforated inner concentric tube are evaluated in terms of their TL. The proposed formulation results were verified using the traditional three-dimensional finite element method (FEM), showing good agreement. An additional verification was also performed using the three-dimensional FEM and the specific acoustic impedance of perforated inner concentric tube to couple the inner concentric duct with an expansion chamber. The periodic formulation and three-dimensional finite element analysis (FEA) used 4-node quadrilateral and 4-node tetrahedral elements, respectively. A final check was carried out with experimental analysis of 8 models and there was good agreement with results of the three numerical methods.

A technique to establish liquid ethanol tubular combustion by dual swirl

This study proposes a compact dual swirl combustor to establish a steady liquid ethanol tubular flame, in which tangential air is injected through two stages. The outer intense swirl induces reversed flame on the surface wall of a concentric copper tube, and the central liquid fuel is heated to vaporize through the inner swirling air inside the copper tube. By enhancing the heat transfer process and promoting the mixing of the reactant, the overall heat output approaches 10 kW, much higher than the original combustor. With temperature measurement and heat transfer analysis, the flame stabilization mechanism has been elucidated. Two kinds of typical flame structures, a tubular flame and an anchored conical flame, have been obtained under various operating conditions. As the flow rate of inner air gradually increases, plenty of the heat aiming to vaporize the liquid fuel is taken off by the air flow, and small droplets occasionally appear downstream the nozzle; furthermore, the global equivalence ratio (Φgl) at the nozzle exit gradually decreases, and an anchored flame appears, which interrupts the fuel mixing with outer swirling air, resulting in soot formation in some cases. Plenty of tests illustrates that as Φgl is below 11, the flame anchoring will appear.

Nanofluids as heat transfer fluids: Hurdles to industrial application and economic considerations

AbstractNanofluids have gained substantial interest over the past years due to their enhanced thermal properties. However, these nanoparticle dispersions remain scarcely used in industrial applications. In this work, we demonstrate how the stability of nanofluids and economic factors are the major hurdles preventing their industrial large‐scale use through an economic analysis. The cost‐effectiveness of multiwalled carbon nanotubes (MWCNT)–water and copper oxide–water nanofluids used in a concentric tube heat exchanger as substitutes for freshwater was assessed in four different scenarios. It was determined that three of the four cases were not economically viable, as a deficit was generated due to a recurring annual investment for the renewal of the nanofluids because they destabilized with time. The fourth case, however, was sustainable because of the nanofluid's high stability (5 years) and showed a payback period on investment of less than a year. Finally, a tool illustrating the operating window for nanofluid economics in our selected heat exchanger geometry was developed.

Metal foam and fin implementation into a triple concentric tube heat exchanger over melting evolution

It is believed that it is going to be a sizeable mismatch between supply and demand when it comes to renewable resources. Lately, researchers are on course to compensate for the unpredictabilityof such resources by the employment of phase change materials (PCMs). Having multiple advantages, PCMs generally suffer from inadequate thermal conductivity which causes prolonged transition procedures. To tackle this issue, this study is fixated on two parameterswhich are linked to fins addition and porous media incorporation in a melting process within a triple concentric tube heat exchanger (TCTHX). The results provided by multiple cases underlined the significance of natural convection in the bare system, although finned and copper-metal-foam cases outshine buoyancy forces by roughly 45% and 97%, respectively. Material is a major determent when it comes to the selection of porous media as Al2O3 registered the weakest performance among SiC, Ni and Cu, however, it managed to speed up the process by 75% which still is much higher than the finned system, implying that porous media is of higher priority over fins. The best scenario transpiredwhile fins and copper metal foam were integrated as 26% and 97% soars in efficacy have been obtained compared to individual incorporation of porous media and fins, respectively.

Exergy modeling and simulation of a horizontal concentric tube heat exchanger

The present study deals with the exergy modeling and simulation of a horizontal concentric tube heat exchanger. In this context, a fundamental thermodynamics-based exergy model is developed here to predict the irreversibility and entropy generation numberfor various fluid flow arrangements of a concentric tube heat exchanger. To develop the same, a second law of thermodynamics-based approach is utilized. Additionally, a finite volume method-based simulation of the same heat exchanger is also performed using a computer-aided engineering software named ANSYS R15.0. At last, the analytical and simulation results are compared and validated with experimental results, and a good agreement is achieved.

Enhancement of Heat Transfer in a Concentric Tube Counter Flow Heat Exchanger using CuO Nanofluids

Engineers and Scientists have always tried to increase the rate of heat transfer. The most commonly used base fluids do not provide a very high rate of heat transfer. This research work aims to investigate the enhancement of heat transfer rate in a concentric type (double pipe) counter flow heat exchanger using CuO nanofluids at different volume concentrations (0.01%, 0.05% and 0.1%). The experiments conducted on nanofluids showed that, at 0.1% volume concentration of nanofluid at 2.5 LPM, the heat transfer rate, Reynolds’s number and effectiveness were increased by 16.25%, 15.52% and 2.88% respectively compared to base fluid without nano-particles. Hence it was concluded that, CuO nanofluid is having a great potential to be used as a better heat transfer fluid in heat exchangers.

A simulation study to investigate the use of concentric tube robots for epilepsy surgery.

Patients with pharmacoresistant refractory epilepsy may require epilepsy surgery to prevent future seizure occurrences. Conventional surgery consists of a large craniotomy with straight rigid tools with associated outcomes of morbidity, large tissue resections, and long post-operative recovery times. Concentric tube robots have recently been developed as a promising application to neurosurgery due to their nonlinear form and small diameter. The authors present a concept study to explore the feasibility of performing minimally invasive hemispherotomy with concentric tube robots. A model simulation was used to achieve the optimal design and surgical path planning parameters of the concentric tube robot for corpus callosotomy and temporal lobectomy. A single medial burr hole was chosen to access the lateral ventricles for both white matter disconnections. The concentric tube robot was able to accurately reach the designated surgical paths on the corpus callosum and the temporal lobe. In a model simulation, the authors demonstrated the feasibility of performing corpus callosotomy and temporal lobectomy using concentric tube robots. Further advancements in the technology may increase the applicability of this technique for epilepsy surgery to better patient outcomes.

Experimental investigation and annual performance mathematical-prediction on a novel LT-PV/T system using spiral-descent concentric copper tube heat exchanger as the condenser for large-scale application

The condensers of loop thermosyphon PV/T systems (LT-PV/T) are usually integrated inside water tanks, which may bring some challenges during combination use. This research innovatively proposed a concentric copper tube heat exchanger as the condenser, which is combined with a copper tube evaporator beneath the absorber. The gaseous working fluid flows in the inner tube and the cooling water flows in the outer tube. Since ordinary water pipes are used for water circulating between the outer tube and water tank, this LT-PV/T collector can be used individually or combined with other collectors flexibly. To access its' performance, researches have been conducted: (1) Designing and fabricating the system prototypes; (2) Investigating system performance with different volume-filling ratios (26.5%, 34.8%, 43.2%); (3) Investigating the influences of working fluid (water, ethanol and R134A). (4) Evaluating the systems’ performance with energy efficiency, exergy efficiency, and semi-empirical system efficiency models; (5) Conducting two case studies in South China (an individual collector & a 4 parallelly/serially-combined LT-PV/T collectors system). The system is first-of-its-kind and has obvious advantages in reliability, flexibility, space-saving and large-scale applications. The typical primary energy-saving efficiency of the LT-PV/T with R134a of 40% filling ratio can reach 78.0%, higher than the published LT-PV/T systems.

Oxygen enrichment effects on CH4-air turbulent flow characteristics in a coaxial swirl burner

ABSTRACT This paper reports results on the effect of oxygen enrichment on flow and turbulent flames in a coaxial swirl burner. The investigation was performed by S-PIV in CH4-air-O2 non-reacting and reacting flows. This work is the continuation of studies carried out previously by the authors on the same burner, with different new operating conditions. The burner consists of 2 concentric tubes, with a swirler located in the annular part through which the oxidant (air-O2) is supplied. The CH4 gas is delivered into the central tube and injected radially into the combustion chamber through small holes. The burner is placed in a parallelepiped combustion chamber with a volume of 120×50×50 cm3. The paper reports detailed results on mean velocity fields, profiles of the three velocity components (U,V,W) and velocity fluctuations (U’,V’,W’) in the case of a 150 Nl/min oxidant flow rate, a swirl number Sn = 1.4 and an equivalence ratio Φ = 1. Three cases of O2 addition were investigated, 21%, 25%, and 30% (in vol.) corresponding to 9.4 kW, 11.7 kW, and 14.5 kW of combustion power, respectively. In-depth analysis of the field velocity differences between reactive and non-reactive cases was carried out and showed a significant difference in flow velocities between reacting and non-reacting flows. The profiles of the mean velocities, fluctuations and velocity decays differed, and higher values were observed in the reacting case. The enrichment of air with oxygen affected the velocity fields and their fluctuations in both distribution and values. The addition of O2 increased the flame temperature, leading to a greater radial expansion and a reduction in the size of the recirculation zone. The maximum axial velocity increased significantly as a function of the O2 rate, whereas the swirling velocity varied only slightly. The velocity fluctuation results also revealed a difference in profiles and values depending on O2 enrichments and locations along the flow.

TMS is Superior to Residual CHCl3 for Use as the Internal Reference for Routine 1H NMR Spectra Recorded in CDCl3.

Tetramethylsilane was recommended for use as an internal reference compound in proton NMR spectroscopy over 60 years ago. However, it is a common practice that researchers reference the analyte chemical shifts to the residual proton resonance in the deuterated solvent in which the spectrum is recorded. Because CDCl3 is the most commonly used NMR solvent for routine analysis of organic compounds, the effect of various functional groups on the CHCl3 resonance is important. Described here are results that show why referencing spectra to TMS rather than CHCl3 in CDCl3 results in more accurate chemical shifts and should be the recommended practice. Simultaneous measurement of separate compartments of unperturbed CDCl3/TMS vis-à-vis CDCl3/TMS/solute solutions using a concentric tube arrangement was key. This study is reported in this venue because the audience/readership is quite appropriate and is, hopefully, both receptive to and appreciative of the guidance provided.

Heat transfer characteristics of molten salt flowing in steam generator

The paper respectively investigated the heat transfer characteristics of molten salt flowed in shell-and-tube and double-pipe steam generator. The shell-and-tube steam generator had seven tubes and molten salt flowed outside the tubes, while the double-pipe steam generator had two concentric tubes and molten salt flowed in the annular duct formed by two tubes. Inlet temperature of molten salt ranged from 270? to 420?. The experimental results showed the effect of temperature on heat transfer coefficient was more significant in the double-pipe steam generator compared to the shell-and-tube steam generator. The heat transfer coefficient firstly increased and then decreased as the increase of temperature. Further numerical study was conducted and the results showed, in the shell-and-tube steam generator, the flow is disturbed by the tube bundle and the boundary-layer near the inner wall is deformed, so the temperature of molten salt cannot obviously affect the heat transfer. In the double-pipe steam generator, an opposite flow was generated in the near cooled wall region by the buoyancy force. When the inlet temperature was below 315?, the velocity of the opposite flow was quite low. In this stage, the heat transfer coefficient increased with the increase of temperature. When the inlet temperature continues to rise to 390?, the opposite flow was enhanced and a stable layer with low velocity formed between the mainstream and the inner cooled wall, resulting increase of heat transfer resistance and impairment of heat transfer coefficient.

Design of UVA-LED concentric glass tube microreactor and evaluation of photocatalysis with simultaneous adsorption and hydrodynamic cavitation for fluorescent dye degradation

Design of UVA-LED concentric glass tube microreactor and evaluation of photocatalysis with simultaneous adsorption and hydrodynamic cavitation for fluorescent dye degradation

Comparative study on concentric cylindrical glass tube microreactor, UV-LED strip photocatalytic reactor and classical annular reactor on Acid Red 87 removal

Comparative study on concentric cylindrical glass tube microreactor, UV-LED strip photocatalytic reactor and classical annular reactor on Acid Red 87 removal

A study on self-curing self-compacting concrete filled steel columns subjected to axial compression

For vehicle parking areas, in multi-storey buildings and bridge piers, composite tubular columns have been considered as a better solution. The cold-formed steel and concrete combination is notable, because of the benefits of inherent material properties of both the materials. Concrete filled tubular (CFT) columns is in-filled with concrete having single tubes or concentric double tubes leaving the core as hollow. Moreover, for the design of such composite columns a specific design code is yet to be released in India. Henceforth, this experimental research intends to study the structural behaviour of CFT columns, consisting steel tube in terms of load- deflection graph, ultimate load carrying capacity, confinement of concrete and ductility. The structural use of a unique Self-Curing and Self-Compacting Concrete (SCSCC) using 10% granite saw dust waste and 25% fly ash as partial replacement to cement was confirmed. The experimental results are compared with computer modelling analysis done using ABAQUS for a better understanding of the column specimen's behaviour. Based on experimental studies percentage of super plasticizer and Super Absorbent Polymer (SAP) is determined as 1.3% & 0.3% respectively. The variation between experimental and analytical results is minimum and is due to minor material defects in steel sections. In this present experimental study three different cross sections namely: (i) cylindrical (ii) rectangular and (iii) square cross sections with 500 mm length and 2 mm thickness was used. Secondly a parametric study was conducted for 3 different lengths and 3 thickness which also showed that the performance of square cross sections was effective irrespective of the lengths. The load carrying capability of columns with increased steel section thickness is seen to be greater for the same length of column. When compared to cylindrical sections, rectangular and square sections show a significant reduction in load carrying capability as the thickness of the steel section is reduced. These changes in load carrying capacity are mainly due to the shape factor. The main advantage of the CFST column is that it has a better ultimate strength than a regular column due to the concrete confinement. This increased strength due to confinement is higher in cylindrical specimens.

Experimental set up for the investigation of partial phase changes of phase change materials

Thermal energy storage with phase change materials (PCMs) has attracted a lot of attention in the last several decades. Most PCMs do not change phase at a constant temperature but rather in a certain temperature range. It means that the PCM need to transit through its phase change temperature range to fully change phase from the solid state to the liquid state and vice-versa. The situation, in which the phase transition begins and/or ends within the phase change temperature range (in the mushy zone), is usually called a partial phase transition (or a partial phase change). The partial phase transitions occur quite often in real-life thermal energy storage systems with PCMs; especially when a PCM has a wide phase change temperature range. The behavior of PCMs during the partial phase transitions is poorly understood at the moment, because the experimental techniques used for the characterization of PCMs (such as the differential scanning calorimetry – DSC) are difficult to apply for the study of partial phase transitions. The lack of knowledge in this area influences the accuracy of phase change simulation models. The main goal of the experimental investigations, described in the paper, was to obtain data for the development of a simulation model for partial phase changes. The experimental set up for the investigation of partial phase changes of PCMs has been proposed, assembled, and the pilot measurements have been conducted. The experimental set up consists of two water storage tanks (that can be maintained at different water temperatures), a water-PCM concentric tube type heat exchanger and a data acquisition system. The water flows through the central tube of the heat exchanger while the PCM is located in the annular space of the exchanger. The water storage tanks, maintained at the temperatures within the phase change temperature range of a PCM, allow for the investigations of the heat storage cycles consisting of partial phase changes.

Magnetic concentric tube robots: introduction and analysis

Magnetic concentric tube robots: introduction and analysis

UPGRADING THE HEAT TRANSFER IN THE CONCENTRIC TUBE HEAT EXCHANGERS BY USING GRAPHENE/WATER NANOFLUID

UPGRADING THE HEAT TRANSFER IN THE CONCENTRIC TUBE HEAT EXCHANGERS BY USING GRAPHENE/WATER NANOFLUID