Horizontal Concentric Annulus Research Articles

Experimental investigation into thermal characteristics of subcooled flow boiling in horizontal concentric annuli for cooling ultra-fast electric vehicle charging cables

In an effort to reduce the charging time of electric vehicles (EVs), the thermal management of the charging system has emerged as one of the most urgent issues. The charging rate has been restricted to avoid thermal failure especially in charging cable. Recently, a direct contact cooling technique that utilizes subcooled flow boiling for charging cables has been proposed and has shown promising thermal management performance. However, there has been a lack of clear explanation regarding its thermal characteristics due to its intrinsically complicated flow features. This study investigates the thermal characteristics of subcooled flow boiling in a horizontally aligned concentric annular tube intended to simulate the direct contact cooling technique employed for charging cables. For the experimental investigation, the wall temperature measurements and high-speed flow visualization images acquired from the transparent test module annulus, with inner and outer diameters of 6.35 mm and 22.0 mm, were utilized. Three key axial thermal characteristics of subcooled flow boiling in annulus have been analyzed, and they are flow regime transition, variation of heat transfer mechanisms, and occurrence of critical heat flux (CHF). The transition of flow regimes and the variation of dominant heat transfer mechanisms in the axial direction are mutually influencing due to the coupled effects between the hydrodynamic and thermal characteristics of simultaneously developing flows. The flow regime changes from partially developed boiling (PDB) to fully developed boiling (FDB) as the intensities of nucleate boiling and bubble recondensation vary in the axial direction, while the dominant heat transfer mechanism shifts from single-phase convection to nucleate boiling, corresponding to the flow regime transition from PDB to FDB. The departure from nucleate boiling (DNB) type CHF is observed, manifested by the wavy interface propagating from the far downstream to the upstream region, and the intensities of nucleate boiling and bubble recondensation are also identified as the dominant parameters in determining the occurrence of CHF. Charging time estimation reveals that the proposed method can achieve an 80 % charge for 100-kWh EV batteries in 98 s, while maintaining the cable wire temperature below the safety limit of 80 °C. This strongly supports its potential as a promising thermal management technique for future ultra-fast charging systems.

Numerical simulation of two-phase gas-liquid flowthrough horizontal annulus pipe

Chemical, petroleum and nuclear systems are only a few of the industrial processes that utilize gas-liquid flow in annular closed channels. However, concentric horizontal annuli flow patterns have received little attention. The ability to precisely characterize two-phase flow patterns using computational techniques is crucial for the production, transportation, and optimization of designs. This current research aims to establish the accuracy of the computational fluid dynamics (CFD) model in predicting the gas-liquid flow pattern in the concentric annulus pipe and validating the flow pattern of liquid holdup with experimental results from the literature. The simulations were done on a test section of a 12.8 m length pipe with a hydraulic diameter of 0.0168 m using air and water as the working fluids. The volume of fluid (VOF) model in Ansys Fluent based on the Eulerian- Eulerian approach in conjunction with the realizable k-ε turbulence model was used to model the gas-liquid flow pattern, i.e. dispersed bubble, elongated bubble, and slug in a horizontal annulus. A comparison of the model with the experimental high-speed video images shows a reasonable agreement for the flow pattern and liquid holdup data.

FLT-HPM for Two-dimensional Transient Natural Convection in a Horizontal Cylindrical Concentric Annulus

FLT-HPM for Two-dimensional Transient Natural Convection in a Horizontal Cylindrical Concentric Annulus

FLT-HPM for Two-dimensional Transient Natural Convection in a Horizontal Cylindrical Concentric Annulus

FLT-HPM for Two-dimensional Transient Natural Convection in a Horizontal Cylindrical Concentric Annulus

Magnetohydrodynamic natural convection of In-Ga-Sn alloy in a horizontal concentric annulus with tree-shaped internal fins

The use of low melting point liquid metals for convective cooling has seen a recent increase in interest in the literature. Few studies have explored the use of such metals in concentric annuli with fins to enhance heat transfer. In this study, numerical simulations are conducted using COMSOL Multiphysics® to investigate the magnetohydrodynamic (MHD) natural convection heat transfer inside a concentric annulus with tree-shaped fins. The fluid in the enclosure is eutectic In20.5Ga67Sn12.5. The tree-shaped fins feature three geometric parameters: (i) length of branches a, (ii) fin spacing angle θ, and (iii) branch angle α. Constant temperature boundary conditions are used. The average Nu at the outer walls is used to gauge the heat transfer. Transient simulations are performed to observe stability of the flow profile over time due to the low Pr of the In-Ga-Sn. Steady-state simulations are performed to sweep the fin parameters. A uniform magnetic field is added to investigate the effects on the heat transfer. This is the first study to use the tree-shaped fins in the annulus with liquid metal and in the presence of an external magnetic field. The fins are generated using Constructal theory, in that each pair of branches (or construction) is sequentially built from the previous pair of branches. The optimum case with the tree-shaped fins and no magnetic field is found to increase Nu by 789.7%. With the magnetic field, the “intermediate” tree-shaped fins produced the highest Nu (8.66) of the fin geometries explored at Ha = 20.

MIXED CONVECTIVE AND RADIATIVE HEAT TRANSFER IN A HORIZONTAL CONCENTRIC AND ECCENTRIC CYLINDRICAL ANNULI

A numerical investigation has been performed to study the effect of eccentricity on unsteady state, laminar aiding mixed convection in a horizontal concentric and eccentric cylindrical annulus. The outer cylinder was kept at a constant temperaturewhile the inner cylinder was heated with constant heat flux. The study involved numerical solution of transient momentum (Navier-Stokes) and energy equation using finite difference method (FDM), where the body fitted coordinate system (BFC) wasused to generate the grid mesh for computational plane. The governing equations were transformed to the vorticity-stream function formula as for momentum equations and to the temperature and stream function for energy equation.A computer program (Fortran 90) was built to calculate the bulk Nusselt number (Nub) after reaching steady state condition for fluid Prandtl number fixed at 0.7 (air) with radius ratio ( =2.6), Rayleigh number (Ra=200), Reynolds number (Re=50) for both concentric and eccentric cylindrical annulus with different eccentricity ratios (ε=0, 0.25, 0.50, 0.75) and angular positions (φo=0o, 45o , 90o , 135o , 180o ).The results show a reasonable representation to the relation between Nusselt number and (ε, φo). Generally, Nub decreased with the increase in (ε and φo). Also, results show that the best thermal performance for the inner cylinder was at the angularposition (φo=0o ) for eccentricity ratio (ε=0.25), while the maximum reduction in the rate of heat transfer for the inner cylinder was at the angular position (φo=180o) for eccentricity ratio (ε=0.75).Comparison of the result with the previous work shows a good agreement.

Analysis of Influence of Vertical Vibration on Natural Heat Convection Coefficients from Horizontal Concentric and Eccentric Annulus

Renewable energy is crucial for reducing emissions and meeting future energy demands. However, due to concerns regarding intermittent supply, integrating RE into a multi-microgrid system might pose various power system problems, for instance, unstable electrical power output. As a result, increased load reactive power demands result in voltage losses during peak load demand. Therefore, it can be minimized by utilizing Flexible Alternating Current Transmission System (FACTS) devices in electrical networks, which are designed to strengthen the stability and control of power transfer and act as a controller for the AC transmission specification, which also provides speed and flexibility for certain applications. By identifying the need to implement solutions that can sustain the electric power quality of a microgrid, this paper presents a review of various method approaches which could be used to evaluate the impact of integrating the multi-microgrid systems with FACTS devices for voltage profile improvement and real power loss reduction in power system. In this paper, a comprehensive study is carried out for optimum multi-microgrid placement, considering the minimization of power losses, enhancement of voltage stability, and improvement of the voltage profile. An attempt has been made to summarize the existing approaches and present a detailed discussion that can help the energy planners decide which objective and planning factors need more attention for optimum locations and capacity for multi-microgrid and FACTS devices.

A regularized diffuse domain-lattice Boltzmann model for heat transfer in complex geometries with temperature Dirichlet boundary condition

In this paper, a regularized diffuse domain-lattice Boltzmann model for heat transfer with the Dirichlet boundary condition in complex geometries is proposed. In this model the complex computational domain is embedded into a larger and regular domain. The level set function is used to capture the complex interface. A diffuse domain formulation for the temperature field is established on the larger domain. To remove the ill-conditioned property of the original diffuse domain equation, we develop a new regularization technique to tackle this issue. We also give a multiple-relaxation-time lattice Boltzmann model to solve the regularized diffuse domain equation. The convergence rate of present model is investigated by the steady state and time-decay heat conduction problems. Then the natural convection problems in a square enclosure with a heated circular cylinder and in a horizontal concentric annulus are simulated. Both the uniform and non-uniform wall temperature cases are considered. Moreover, an alternative method to calculate the average Nusselt number on the complex boundary is employed. The numerical results show a good agreement with the previous solutions in previous literatures. The effect of non-uniform wall temperature on the heat transfer rate is also investigated. At last, the forced convection across the staggered tube banks is also simulated to verify the potential capability of the present model in solving practical heat transfer problem with the complex geometries.

Magnetohydrodynamic Natural Convection in a Horizontal Concentric Annulus with In-Ga-Sn Alloy and Internal Fins

Magnetohydrodynamic Natural Convection in a Horizontal Concentric Annulus with In-Ga-Sn Alloy and Internal Fins

Magnetohydrodynamic Natural Convection of In-Ga-Sn Alloy in a Horizontal Concentric Annulus with Tree-Shaped Internal Fins

Magnetohydrodynamic Natural Convection of In-Ga-Sn Alloy in a Horizontal Concentric Annulus with Tree-Shaped Internal Fins

Heat Transfer and Hydrodynamic Properties Using Different Metal-Oxide Nanostructures in Horizontal Concentric Annular Tube: An Optimization Study.

Numerical studies were performed to estimate the heat transfer and hydrodynamic properties of a forced convection turbulent flow using three-dimensional horizontal concentric annuli. This paper applied the standard k–ε turbulence model for the flow range 1 × 104 ≤ Re ≥ 24 × 103. A wide range of parameters like different nanomaterials (Al2O3, CuO, SiO2 and ZnO), different particle nanoshapes (spherical, cylindrical, blades, platelets and bricks), different heat flux ratio (HFR) (0, 0.5, 1 and 2) and different aspect ratios (AR) (1.5, 2, 2.5 and 3) were examined. Also, the effect of inner cylinder rotation was discussed. An experiment was conducted out using a field-emission scanning electron microscope (FE-SEM) to characterize metallic oxides in spherical morphologies. Nano-platelet particles showed the best enhancements in heat transfer properties, followed by nano-cylinders, nano-bricks, nano-blades, and nano-spheres. The maximum heat transfer enhancement was found in SiO2, followed by ZnO, CuO, and Al2O3, in that order. Meanwhile, the effect of the HFR parameter was insignificant. At Re = 24,000, the inner wall rotation enhanced the heat transfer about 47.94%, 43.03%, 42.06% and 39.79% for SiO2, ZnO, CuO and Al2O3, respectively. Moreover, the AR of 2.5 presented the higher heat transfer improvement followed by 3, 2, and 1.5.

Analytical Simulation for Transient Natural Convection in a Horizontal Cylindrical Concentric Annulus

In this study, a new scheme is suggested to find the analytical approximating solutions for a two-dimensional transient natural convection in a horizontal cylindrical concentric annulus bounded by two isothermal surfaces. The new methodology depends on combining the algorithms of Yang transform and the homotopy perturbation methods. Analytical solutions for the core, the outer layer and the inner layer at small times are found by a new method. Also, the effect of Grashof number, Prandtl number and radius proportion on the heat transfer and the flow of fluid (air) at different values was studied. Moreover, the study calculates the mean of the Nusselt number along with the effect of the Grashof number and radius proportion on it as parameters which acts as clues for heat transfer calculations of the natural convection for the annulus. The results, obtained by using the new method, prove that it is efficient and has high exactness compared to the other methods, used to find the analytical approximate solution for the transient natural convection in a horizontal cylindrical concentric annulus. The convergence of the new method was also discussed theoretically by referring to some theorems, and experientially by a verification of the solutions resulting from the simulations of the convergent condition. Furthermore, the graphs of the new solutions show the veracity, utility and exigency of the new method, and come in line with solutions offered by previous studies.

Lattice Boltzmann analysis for electro–thermo-convection with a melting boundary in horizontal concentric annuli

In this paper, we perform a two-dimensional numerical investigation into the electro–thermoconvection with a melting boundary in horizontal concentric annuli filled with a dielectric phase change material. The whole set of coupled equations is solved by lattice Boltzmann method: Navier–Stokes equations, electrohydrodynamics (EHD) equations, and the energy equation. It is found that there exist three regimes during melting with EHD, namely, diffusive regime, thermal convection regime, and electroconvection regime, and the augmentation of melting heat transfer is due to the radial electroconvective flow induced by Coulomb force in the third regime. Moreover, the continuous melting of solid leads to the dynamical transition between the different flow patterns of electro–thermo-convection, as well as the interesting evolutions of temperature and charge density distribution. In different regimes of melting, the liquid fraction fl and Nusselt number Nu follow different power laws. In detail, before the onset of radial flow motion, fl scales as Fo1/2 whereas Nu scales as fl−4/5 (Fo represents the Fourier number), and in the electroconvection dominated regime, we have fl ∼ Fo and Nu ∼ fl0.

Oscillatory flow of Koo–Kleinstreuer and aggregate nanofluids in cylindrical annuli: Toward an innovative solution to deal with nanofluids instability

This paper exhibits the oscillatory characteristics of a free convective flow of nanofluids in horizontal concentric annuli of pilot dimensions to provide a mechanical solution against their particles settling which occurs by aggregation. These nanofluids are generated according to each class of particles that may exist with four types of industrial base liquids. Koo–Kleinstreuer semi-empirical models are used to generate databases of ideal suspended particles with Brownian motion. Meanwhile, Maxwell–Bruggeman and Kreiger–Dougherty semi-empirical models are used to incorporate the aggregation mechanism. A hybrid lattice Boltzmann/finite-difference approach is adopted to provide the space-time solutions. The accuracy of this numerical tool is inspected by providing over nine validations based on literature data. Hence, an improved flow pattern chart is accomplished to expand the open literature, depending on the flow nature of the base liquids in the annuli. Next, the oscillatory nature is fully revealed for each nanofluid processed. Following the frontiers toward the non-settling of aggregates, three main regimes are identified depending on the annulus size and the combination between ideal and aggregate mechanisms. Owing to this, a new settling chart is established to emerge the sheer limit of the annulus size for a non-settling process.

A Numerical Investigation on Natural Convection Heat Transfer in Annular-Finned Concentric Horizontal Annulus Using Nanofluids: A Parametric Study

Natural convection heat transfer in a concentric horizontal annulus with annular fins is numerically studied. Due to the low thermal conductivity of water, CuO-water and Al2O3-water nanofluids were used as heat transfer fluids. The effect of three different parameters, including fin spacing, fin eccentricity, and fin thickness at different fin diameters and Rayleigh number range of 104 to 9 105, were studied. The obtained results revealed that Al2O3-water nanofluid has the highest heat transfer rate. The calculated heat transfer rates for Al2O3-water nanofluid for Rayleigh numbers of 9 105, 105, and 104 were respectively up to 12.1%, 26.2%, and 31.6% higher than the heat transfer rate obtained for water. The best heat transfer rate occurred at the fin spacing range of 2 to 3 mm at Rayleigh number of 9 105. Moreover, it was observed that by decreasing the Rayleigh number, the maximum heat transfer rate took place at higher fin spacing. It was concluded that fin eccentricity improves the heat transfer rate, especially for low fin spacing. Furthermore, it was demonstrated that fin eccentricity could improve the heat transfer rate by up to 50.2%. Simulation results indicated that fins with low thickness have higher heat transfer rates than those with higher thickness at lower fin spacing. However, fins with high thickness have higher heat transfer rates than those with lower thickness at higher fin spacing.

A centrifugal buoyancy formulation for Boussinesq‐type natural convection flows applied to the annulus cavity problem

SummaryTraditionally, the Boussinesq approximation is adopted for numerical simulation of natural convection phenomena where density variations are supposed negligible except through the gravity term of the momentum equation. In this study, a recently developed formulation based on a Boussinesq approximation is presented in which the density variations are also considered in the advection terms. Extending density‐variations to the advection terms captures centrifugal effects arising from both bulk enclosure rotation and within individual vortices, and thus more accurate results are expected. In this respect, the results of the proposed formulation are compared against the conventional Boussinesq simulations and weakly compressible approximation in the concentric horizontal annulus cavity. A new relation is established which maps the magnitude of the non‐Boussinesq parameter of incompressible flow to the corresponding relative temperature difference of a compressible flow simulation which is in agreement with the maximum allowed Gay‐Lussac number to avoid unphysical density values. For comparison purposes, variations of different thermo‐fluid parameters including average and local Nusselt number, entropy generation, and skin friction up to Ra = 105 are computed. Results obtained under the proposed approximation agree with the classical Boussinesq approximation up to Ra = 103 for large non‐Boussinesq parameter corresponding to the large relative temperature difference, but at Ra = 105, computed thermo‐fluid parameters via the two approaches are not identical which justifies the inclusion of large Gay‐Lussac number for convection dominated regime in natural convection problems.

Numerical study of conjugate natural convection heat transfer of a blood filled horizontal concentric annulus

Abstract A numerical investigation is accomplished on the natural convection flow and heat transfer in a horizontal concentric annulus in the presence of cylindrical solid wall and Carreau non-Newtonian blood model. The inner circular surface of the cavity is heated to a constant temperature and the outer circular surface is cooled. The boundaries of the annulus are assumed to be impermeable, the fluid within the cavity is assumed to be non-Newtonian blood when the Boussinesq approximation is applicable. The Galerkin weighted residual method is applied numerically to solve the dimensionless governing equations subject to the boundary conditions. The numerical results explained in the form of streamlines, isotherms, local and average heat transfer with variation of the Rayleigh number, Prandtl number, power-law index and the thermal conductivity of the cylindrical solid wall within the range of (103 ≤ Ra ≤ 106), (5 ≤ Pr ≤ 50), (0.2 ≤ n ≤ 0.8) and (0.25 ≤ kw ≤ 1.45), respectively. Validations with experimental/numerical data are accomplished which provide a clear conviction to the numerical data of the existing code. It has been found that a low power-law index improves the fluid flow and increases the rate of heat transfer.

Hydro-thermal behaviour determination and optimization of fully developed turbulent flow in horizontal concentric annulus with ethylene glycol and water mixture based Al2O3 nanofluids

In this study, a comprehensive analysis of forced convection heat transfer and pressure drop through a concentric annulus heated from the inner wall and utilizing ethylene glycol (EG)-water based nanofluids for fully developed turbulent flow are conducted. In this context, effects of Reynolds number (10000–100,000), annulus radius ratio (0.1–0.9), EG concentration (0%–60%), nanoparticle volume fraction (0%- 1.5%) and nanofluid inlet temperature (0 °C - 50 °C) on Nusselt Number and pumping power have been analysed. To obtain nanofluids thermophysical properties, experimental data is implemented. To calculate the Nusselt number and friction factor, generalized formulations obtained from the direct numerical simulation are used. It is concluded that the Nusselt number increases with increasing Reynolds number and EG concentration while decreases with increasing radius ratio and inlet temperature in all conditions. In most cases, as nanoparticle volume fraction increases, Nusselt number increases while there are some opposite conditions. Besides, it is determined that the pumping power increases with increasing Reynolds number, EG concentration, nanoparticle volume fraction and radius ratio and decreases with increasing nanofluid inlet temperature. In addition, Response Surface Methodology and desirability function approach is implemented to determine the optimum operating conditions by maximizing Nusselt Number and minimizing pumping power for different scenarios.

Two- and three-dimensional simulation of natural convection flow of CuO-water in a horizontal concentric annulus considering nanoparticles’ Brownian motion

A numerical study of two- and three-dimensional natural convection flows of copper oxide water-based nanofluid in a horizontal concentric annulus has been conducted to investigate the influence of Rayleigh number () and nanoparticles volume fraction () on both hydrodynamic and thermal behaviors, and further to examine the difference between two- and three-dimensional simulations. The Brownian motion of nanoparticles is considered in evaluating the effective thermal conductivity and dynamic viscosity of nanofluid. The mass, momentum and energy conservation equations are solved numerically by the finite volume method together with the artificial compressibility algorithm for pressure-velocity coupling. The obtained results indicate that the addition of nanoparticles in water leads to an existence of the general flow structure, but causes more complicated changes in flow intensity. The thermal performance of the nanofluid increases with increment of nanoparticles volume fraction up to a critical particle loading at which the maximum heat transfer occurs. The corresponding maximum heat transfer enhancement, at three different Rayleigh numbers (), is approximately 17.2% (19.0%), 11.2% (11.1%), and 13.6% (12.8%) for 2-D (3-D) configuration.

Gas–liquid slug flow in a horizontal concentric annulus, a comparison of numerical simulations and experimental data

Multiphase flow simulations were run in OpenFOAM utilizing InterFoam, a volume of fluid type solver. A concentric annulus geometry was constructed and periodic boundary conditions were applied to alleviate the requirement for a longer domain. The simulations were run in 3, 5 and 7 m long domains with the annulus dimensioned such that the outer and inner cylinder diameter were 0.1 and 0.05 m respectively. The 4 individual mesh designs were constructed such that the coarsest mesh consists of 102k cells/m while the finest mesh was generated with 400k cells/m. Each mesh was significantly refined within 0.005 m of both the inner and outer cylinder wall. The simulation data was compared with experimental pressure and holdup data collected at Institute for Energy Technology in Norway. The 3 and 7 m domains reproduced slug frequencies to within 9% of the experiment results of 1.43 Hz for all mesh densities. Comparatively, the 5 m domain has larger errors with respect to slugging frequency (22–27%). The 5 m case performs poorly, probably due to an artificial restraint introduced by the limitation of available liquid which is set as αoil=0.53 for all cases. The αoil restriction combined with the domain length determines the amount of liquid in the system. This interaction of factors means that the domain length is an important parameter when preparing the simulation. The pressure data display a stronger dependence on the mesh quality in comparison to the slug frequency analysis. The 3 m domain with a 400k cells/m mesh resulted in a maximum and minimum pressure gradient of 1783.5 and 803.9 Pa/m, compared to the experiment values of 1785 and 822 Pa/m, which are within 3% of the expected results.