Coaxial Tube Research Articles

Multi-objective optimization of printed circuit heat exchanger used for hydrogen cooler by exergoeconomic method

Hydrogen cooler is a key equipment of the precooling unit in hydrogen refueling stations with the requirement of high heat transfer efficiency, high compactness and high pressure resistance. Printed circuit heat exchanger is a promising candidate for the hydrogen cooler due to its great performance on extremely high pressure and high temperature working environment. In this paper, a hydrogen cooler with a thermal load of 72 kW is firstly designed by using the segmented thermal design method and logarithmic mean temperature difference method. Then, the capital model of the hydrogen cooler is established to evaluate the performance using the exergoeconomic method. The results show that the operating cost, which is related to exergy destruction, accounts for 94.5% of the total cost of the hydrogen cooler. The thermal exergy destruction accounts for 92.4% of the total exergy destruction. Finally, the geometrical parameters of the channel are optimized by using the multi-objective optimization. The channel radius shows the most significant impact on the construction cost and operating cost among the three geometrical parameters. Compared with the coaxial tube evaporators, the printed circuit heat exchanger has better performance on the volume and total cost, which are reduced by 88.0% and 4.0% respectively.

Electrothermal blood streaming conveying hybridized nanoparticles in a non-uniform endoscopic conduit.

The novelty of nanoparticles in transferrals of medications and biological fluids via electrokinetic mechanism has been competently recognized. Due to the impressive role of nanoparticles suspended in blood or physiological fluids in medical fields, the current research article is planned to formulate an effective mathematical model to analyze the dynamism of bloodstream infused with hybridized nanoparticles in a non-uniform endoscopic conduit (space between two coaxial tubes) under the interactivities of electroosmosis, peristalsis, and buoyancy forces. The dual impact of heat source, Joule heating, and convectively cooling wall condition is examined. The geometrical shapes (sphere, brick, cylinder, and platelet) of nanoparticles injected into blood are accounted for in the formulation of modelled equations. The blood doped with hybridized nanoparticles is regarded as an electrolyte solution. The lubrication and Debye-Hückel linearization estimations are invoked in order to linearize the flow equations. Analytical solutions for the resulting leading equations are computed by implementing an analytical approach. The amendments in the physiognomies under variations in sundry parameters are explained through the line, bar graphs, and numerical tables. Outcomes admit that the flow of ionized blood is significantly amended across the endoscopic conduit due to the electrostatic body force. Blood is warmed or cooled with positive or negative values of Joule heating parameter. Blood is cooled with augmenting volumetric concentration of hybridized nanoparticles. The trapping phenomenon is also described by designing streamline plots. The size of confined blood boluses expands due to the thin electric double layer (EDL). The novel findings of this hemodynamic simulation furnish significant applicabilities in modelling of transportation of medications and drugs, physiological fluid mixers, testing and assessment of human diseases, detection of bacteria and viruses, etc.

Experimental investigation on the stability of turbulent swirling methane/air-O2 flames

This work investigates the combustion characteristics of CH4-air/O2 turbulent swirling flames in a co-axial burner with radial fuel injection. The burner configuration consists of two coaxial tubes with a swirler positioned within the annular space for the oxidizer flow. The central tube delivers the fuel through eight holes placed that are uniformly distributed along the circumference of the inner tube nearby the burner exit. The experiments were carried out in a 25-kW combustion chamber of dimensions 50x50x120 cm3. Stereo Particle Image Velocimetry (SPIV) was used to characterize the different velocity fields, whereas the OH* Chemiluminescence is employed to examine the flame structure and stability. The exhaust gas compositions were measured using multi-gas analyzers. The structure and stability of flames, temperature evolutions, CO2, and pollutant emissions (NOx, CO) were examined under different parameters, such as: oxygen enrichment (21–50 %), global equivalence ratio (0.4–1), swirl number (0.5 and 1.4), injection type of fuel (axial or radial). Experiments were conducted at a constant power of 9.41 kW and variable powers in the range from 9.41 to 22.42 kW. The present results show that the oxygen enrichment decreases the lift-off height and enhances the flame stability using constant flame power. Increasing the swirl number improves the flame stability and produces a better attached flame. At constant flame power and variable oxidizer flow rate, a high oxygen concentration yields lower NOx emissions. For lean combustion with excessive oxygen enrichment over 35 %, retaining the same flame power leads to a significant decrease in NOx emissions. The radial injection of CH4 does not affects the NOx emissions, however, the axial injection is shown to be advantageous in terms of CO emissions in the present studied configurations.

Effects of geometry in the operation of coaxial electrosprays

Coaxial electrospray is a well established procedure to generate coaxial micro- and nano-structures (microcapsules and coaxial fibers). In this work we show the capabilities of a high-precision numerical code using dynamic mapping, analytic Jacobian formulation and the Taylor–Melcher leaky dielectric model (LDM) to deal with real coaxial electrospray configurations. Since the number of parameters involved in the problem is large, we focus on an experimentally tested liquid pair configuration where the thickness, relative position, and end sharpness of the coaxial feeding tubes are geometrical parameters of interest. The effects of those parameters and the voltage applied at the tubes on the coaxial liquid menisci, liquid streamlines, size of jet and core, and electric current are discussed.

Reactions

Reactions

Coaxial Drainage versus Standard Chest Tube after Pulmonary Lobectomy: A Randomized Controlled Study.

Chest tubes are routinely inserted after thoracic surgery procedures in different sizes and numbers. The aim of this study is to assess the efficacy of Smart Drain Coaxial drainage compared with two standard chest tubes in patients undergoing thoracotomy for pulmonary lobectomy. Ninety-eight patients (57 males and 41 females, mean age 68.3 ± 7.4 years) with lung cancer undergoing open pulmonary lobectomy were randomized in two groups: 50 received one upper 28-Fr and one lower 32-Fr standard chest tube (ST group) and 48 received one 28-Fr Smart Drain Coaxial tube (SDC group). Hospitalization, quantity of fluid output, air leaks, radiograph findings, pain control and costs were assessed. SDC group showed shorter hospitalization (7.3 vs. 6.1 days, p = 0.02), lower pain in postoperative day-1 (p = 0.02) and a lower use of analgesic drugs (p = 0.04). Pleural effusion drainage was lower in SDC group in the first postoperative day (median 400.0 ± 200.0 mL vs. 450.0 ± 193.8 mL, p = 0.04) and as a mean of first three PODs (median 325.0 ± 137.5 mL vs. 362.5 ± 96.7 mL, p = 0.01). No difference in terms of fluid retention, residual pleural space, subcutaneous emphysema and complications after chest tubes removal was found. In conclusion, Smart Drain Coaxial chest tube seems a feasible option after thoracotomy for pulmonary lobectomy. The SDC group showed a shorter hospitalization and decreased analgesic drugs use and, thus, a reduction of costs.

Bioconvection peristaltic transport of Williamson hybrid nanofluid with motile microorganism, Ohmic heating, and entropy generation through an endoscope

On account of the significance of entropy generation and bioconvection in biomedical and bioengineering, valuable contributions have been made by scientists in the present decade. The current study explores the impact of entropy generation, bioconvection of microorganisms, and Ohmic heating on the peristaltic transport of Williamson fluid containing molybdenum disulfide and silver nanoparticles through an endoscope with a long wavelength and low Reynolds number assumptions. The second law of thermodynamics is used to examine the entropy generation, and also Ohmic heating effect is used in the system. Between two coaxial tubes, a non-Newtonian Williamson fluid with molybdenum disulfide and silver nanoparticles is considered. The Homotopy perturbation method (HPM) is applied to describe the nonlinear partial differential equations. We were able to arrive at analytical solutions for velocity, nanoparticle concentration, microbes’ density, and temperature. In the end, the impact of distinct physical parameters on temperature, nanoparticle concentration, velocity, microorganism density, entropy generation, Bejan number, and the heat transfer rate was graphically depicted. The significant outcome of the present study is that the impact of the Peclet number enhances the velocity profile. But Peclet number and bioconvection constantly decline the density of motile microorganisms. One more significant outcome is that the Brinkman number declines the entropy generation near the inner tube and in the rest of the part, enhances the entropy generation. Brinkman number enhances the heat transfer rate. These findings have applications in biological sciences, engineering, geothermal energy, and industry, including the construction of microbial fuel cells and bio-convection nanotechnology devices. Microorganisms are beneficial in the degradation of biomaterials, resulting in the production of oxygen and the preservation of human health.

Numerical Study of Vortex Flow in a Classifier with Coaxial Tubes

Centrifugal air classifiers are one of the most used separation devices in particle technology. The study aims to obtain a detailed description of the bulk material classification mechanism in the developed centrifugal classifier. The classifier design and the mechanism of the stable vortex structure formation in the inter-tube space of the device are described. Velocities within and between the vortices are studied to identify regions with inverse flows, which serve as transport channels for particles. The computational fluid dynamics modeling results indicate three channels with negative or near-zero axial velocities: between the vortices, near the outer wall of the internal tube, and the inner wall of the external tube. The selectivity of the device decreases when transport channels are disrupted due to flow mixing, which is caused by the height shifting of the vortex centers.

Steady state diffusion in tubular structures: Assessment of one-dimensional models

Steady-state diffusion in long axisymmetric structures is considered. The goal is to assess one-dimensional approximations by comparing them with axisymmetric eigenfunction expansions. Two problems are considered in detail: a finite tube with one end that is partly absorbing and partly reflecting; and two finite coaxial tubes with different cross-sectional radii joined together abruptly. Both problems may be modelled using effective boundary conditions, containing a parameter known as the trapping rate. We show that trapping rates depend on the lengths of the finite tubes (and that they decay slowly as these lengths increase) and we show how trapping rates are related to blockage coefficients, which are well known in the context of potential flow along tubes of infinite length.

Experimental study of the evolution of H line profile in a pulse hydrogen discharge

This study reports on experimental technique for investigation of the dynamics of neutrals in direct current hydrogen discharges at low pressures. It is based on analysis of anomalous broadening of the H emission line profile in a pulsed regime of operation of the source. The application of the technique is relatively simple and it is illustrated in a coaxial discharge tube, but can be readily extended to various discharge sources. The emission line is analyzed by a Fabry-Pérot interferometer and therefore high spectral resolution and fast temporal response can be combined. By observing the evolution of the profile with the pulse duration the experimental technique, extended with numerical modelling, gives opportunity for obtaining useful information about the temporal dependence of the processes responsible for formation of the components of the profile.

Numerical investigation on the influence of radial thermal conduction in a co-axial pulse tube cooler

A co-axial pulse tube cooler, whose regenerator normally surrounds the pulse tube, has the most compact structure. Internal radial thermal conduction may occur between the regenerator and pulse tube due to the temperature mismatch at the same axial location. Theoretical analysis indicates that radial transferred heat flow from pulse tube to regenerator can increase the cooling power, while the opposite radial heat flow which flows from regenerator to pulse tube would decrease the cooling power. Then CFD models with and without radial thermal conduction based on a practical single-stage pulse tube cooler have been conducted to further analyze the mechanism and effect. Simulation results show that after introducing radial thermal conduction, the maximum temperature difference between the gas in regenerator and pulse tube is reduced from 25 K to below 10 K, and cooling power is reduced by 5.8% as a result of the time-averaged radial heat flow from regenerator to pulse tube. The influence of thermal conductivity of the coupled wall between regenerator and pulse tube is also discussed. This study provides a better understanding on the radial heat thermal conduction in a single stage co-axial pulse tube cooler, which sets the basis for optimizing the geometrical arrangement of co-axial pulse tube coolers.

CO2 decomposition using the coaxial dielectric barrier discharge: effect of additive gas and double outer electrodes

This work has studied CO2 decomposition through the dielectric barrier discharge (DBD). The configuration of the DBD reactor was performed as a coaxial DBD tube. The dielectric barrier was made of a quartz tube with 1 mm thickness, while an outer electrode was made of a copper flat sheet wrapping around a quartz tube. The coaxial axis was made of stainless steel rod to be an inner electrode. The power source was applied by the alternative current (AC) high voltage with 7.8 kHz of frequency to both electrodes of the plasma reactor. The experiment was conducted on various conditions such as a mixed gas ratio, discharge gap, applied voltage, outer electrode length, two outer electrodes, and gas flow rate. The results showed that CO2 conversion was decreased when CO2 concentration increased. Similarly, the increase of gas flow rate also caused the decrease of CO2 conversion. Whilst the increase of an applied voltage causes the CO2 conversion clearly increased. Similarly, the CO2:Ar ratio of 60%:40% achieved 30% of CO2 conversion. Furthermore, the high percentage of CO2 conversion of 47.2% has been obtained from a 1.3 mm discharge gap with 40 ml/min of gas flow rate.

Impact of electroosmosis and joule heating effects on peristaltic transport with thermal radiation of hyperbolic tangent fluid through a porous media in an endoscope

The current study explores the impact of electro-osmotic flow, radiation, Joule heating through porous medium on the peristaltic motion of tangent hyperbolic fluid in an endoscope with the assumptions of low Reynolds number and long wavelength. Between two coaxial tubes, a non-Newtonian hyperbolic tangent fluid is considered in cylindrical form. The Helmholtz–Smoluchowski model is used to describe the electroosmosis processes. The Homotopy Perturbation technique (HPM) is imposed to deal the equations of nonlinear partial differential equations. The impact of various physical parameters on velocity, temperature, heat generation coefficient, and coefficient of skin friction were graphically depicted. The significant outcome of the present study is that the impact of the electro-osmotic parameter in the first half diminishes and then enhances the velocity profile for the positive value of electroosmosis parameter. Joule heating enhances the temperature profile whereas Hartmann number and thermal radiation diminish the rate of heat transfer. And also, Darcy number enhances the skin friction coefficient. The present study can be applicable in the bio microfluidics to regulate fluid flow through microchannels and also examining the cancer tumour elimination and artery blockage treatment in biomedical.

Numerical study of discharge characteristics of an atmospheric pressure plasma jet with a coaxial dual-channel inlet

A two-dimensional axisymmetric fluid model was applied to investigate the influence of N2 flow velocity on the discharge characteristics of a He plasma jet with a coaxial dual-channel inlet. Helium working gas flowed in the annular space of a coaxial tube and N2 flowed in a central stainless steel tube powered by a DC voltage. When N2 flow velocity increases from 0 m/s, the jet appears to be stratified, forming the outer side and inner side of the jet, and the electron density on the outside of the jet is much higher than that on the inside. For different N2 flow velocities, the peak densities of He+ and N2(c3π) appear in the jet head, while the peak densities of He* and N2+ both appear at the dielectric nozzle and the jet head. When N2 flow velocity is low, the Penning ionization rate is lower than the electron impact ionization rate, but when N2 flow velocity is high, it is just the opposite, which can increase the concentration of reactive species and contribute to the practical application of the jet. N2 flow velocity not only changes the length and structure of the jet but also controls the uniformity of the distribution of reactive species in the jet, which indicates that there is an optimal N2 flow velocity to make the jet longer and more uniform in space, which will greatly promote the practicality and flexibility of the plasma jet and also provide meaningful insights for optimizing and controlling the characteristics of the plasma jet.

Thermal performance of cylindrical battery module with both axial and radial thermal paths: Numerical simulation and thermal resistance network analysis

In this paper, the thermal performance of a cylindrical battery module with axial-radial thermal paths is investigated by both numerical simulation and analytical thermal resistance network analysis. The 7×7 cylindrical lithium-ion batteries are arranged orthogonally in the module, with their base surface dissipating heat to the cold plate through bottom electrical insulation layer. The upper part of the battery is connected to the cold plate by the surrounding coaxial tube, thermal diffusion plate and thermal column, thus forming the cooperative cooling thermal structure in both axial and radial directions. The temperature distribution in the battery module is first analyzed by numerical modeling, and then the structural parameters are investigated including the spacing between the adjacent battery centers, the cross-sectional shape and area of thermal column, the thickness of thermal diffusion plate, the height of thermal diffusion plate and the length of coaxial tube. It is found that the effect of the cross-sectional area of the thermal column surpasses the other affecting parameters. For the thermal resistance analysis, the representative unit cell (RUC) with the corresponding thermal structure is examined and the analytical model of the battery module with internal heat source is established based on the criteria of minimized battery temperature gradient. The comparison between analytical solution and numerical simulation shows that the maximum relative deviations of battery temperature and temperature difference are 4.6% and 6.5%, respectively, validating the effectiveness of the analytical results. The present analytical method can be a useful tool in the fast analysis of the battery thermal designs with acceptable accuracy validated by real and mock-up battery experimental tests.

Analysis of the transient performance of coaxial and u-tube borehole heat exchangers

While coaxial borehole heat exchangers often have lower borehole thermal resistances than u-tubes, studies in the literature have mixed results as to whether the coaxial design always outperforms the u-tube. This study contributes a systematic comparison between the two designs, accomplished using a custom numerical model in OpenFOAM that provides detailed predictions of the heat transfer within the ground heat exchangers. The modelling and subsequent analysis of system thermal resistances demonstrated that the u-tube and coaxial heat exchanger performances differed the most during the early, transient phase of operation. Furthermore, modelling showed that the coaxial design does not necessarily exceed the u-tube performance long term; testing of coaxial heat exchangers with polyethylene piping showed small differences in outlet temperature compared to the u-tube after 72 h. Additional testing showed that using a steel coaxial outer tube could provide a 22% improvement to performance over the u-tube design. These findings are used to compare predictions of thermal resistance with available analytical models. The impact of the results on the potential for length reductions is also discussed.

Experimental investigation of heat transfer characteristics of an inverse diffusion flame in a coaxial tube burner for with and without swirl

Heat transfer by flame jet impingement is widely used in many of the industrial and domestic applications like heating metal bars, scrap melting, shaping the glass, metal slab cutting, domestic cooking and others. Aim of the present experimental work is to study an effect of swirl on a local heat flux distribution of an inverse diffusion flame (IDF) jet impinging on a flat target surface in a coaxial tube burner. The twisted tape of twist ratio 3 (corresponding to the swirl number, S = 0.52) is used to create a swirl in the central air jet of the burner. The flame shapes and heat flux distributions are compared for the with and without swirling IDF under the different air jet Reynolds number (Rea) of 1000 to 2500, equivalence ratio (ϕ) of 0.4 to 1.3 and a burner-to-impingement plate distance (H) of 10 to 100mm. The distributions of heat fluxes are studied within a radius of 75 mm from the point of stagnation on an impingement plate. Results show that the swirling IDF helps in clean combustion of the fuel with much shorter flame height. Swirling in the flame jet enhances the peak heat flux for the higher air jet Reynolds number for slightly fuel rich conditions of ϕ = 1.1 at the optimal burner-to-target plate distance of 40 mm.

Endoscopy applications for the second law analysis in hydromagnetic peristaltic nanomaterial rheology

In current study, analysis is presented for peristaltic motion of applied magnetic field and entropy generation within couple stress (Cu/H2O) nanofluid through an endoscope. An endoscope contains two coaxial cylindrical tubes in which the internal tube is nonflexible while the external tube has sinusoidal wave passing through the boundary. Influences of mixed convection along with applied magnetic field are encountered as well. Formulated governing model is fabricated introducing long wavelength and creeping Stokesian flow approximation which are then analyzed numerically by utilizing Adams Bashforth method. For a physical insight, results are demonstrated to examine the behaviors of flow profiles and entropy generation number for emerging flow parameters with the help of graphs, bar-charts and tables.

Double-diffusive convective peristaltic motion of Casson nanofluid with variable-viscosity in an endoscope

ABSTRACT Endoscope effect on Casson nanofluid with variable viscosity, double-diffusive convection, and shape factors are examined in the current research. We also investigated using a non-Newtonian Casson fluid containing Titanium dioxide nanoparticles in the space between two coaxial tubes as a potential solution. The Homotopy Perturbation Technique (HPM) combines the standard perturbation strategy with topological homotopy. Using the (HPM), coupled equations were solved with the temperature, concentration profiles, and nanoparticle phenomena. The analytical solutions of velocity, pressure gradient, and pressure rise were achieved. The influence of different physical parameters on temperature, the concentration of nanoparticles, velocity, pressure rise, and frictional force of inner and outer tubes were graphically represented at the end. The results reveal that the platelets will attain a greater temperature than the cylinders as well as bricks, temperature increases with volume fraction and also Casson fluid with TiO2 nanoparticles will attain higher velocity as compared to Casson fluid.

Cattaneo–Christov heat flux effect on MHD peristaltic transport of Bingham Al2O3 nanofluid through a non-Darcy porous medium

The present investigation analyzes the influence of Cattaneo–Christov heat and mass fluxes on peristaltic transport of an incompressible flow. The fluid is obeying Bingham alumina nanofluid. The fluid flows between two co-axial vertical tubes. The system is expressed by a varying radially magnetic field with respect to the space. Soret effect and non-Darcy porous medium are taken into account. The governing system of equations is tackled by utilizing the approximations of long wave length with low Reynolds number and with the help of homotopy perturbation method (HPM). It is noticed that the axial velocity magnifies with an increase in the value of Bingham parameter. Meanwhile, the value of the axial velocity reduces with the elevation in the value of the magnetic field parameter. On the other hand, the elevation in the value of thermal relaxation time leads to a reduction in the value of fluid temperature. Furthermore, increasing in the value of mass relaxation time parameter makes an enhancement in the value of nanoparticles concentration. It is noticed also that the size of the trapped bolus enhances with the increment in the value of Bingham parameter. The current study has many accomplishments in several scientific areas like medical industry, medicine, and others. Therefore, it represents the depiction of the gastric juice motion in the small intestine when an endoscope is inserted through it.