Concentric Annular Tubes Research Articles

Flow enhancement produced by a pulsatile flow of shear-thinning fluids in circular and concentric annular tubes

Although the analysis of the flow enhancement of non-Newtonian fluids produced by pulsatile flows through tubes is common in the literature, the case of Carreau fluid has not been analyzed, which is the aim of this work. This study determines the flow enhancement caused by the pulsatile fluid flow through (a) a circular tube and (b) a concentric annular tube. We show that the flow rate enhancement of the shear-thinning fluid is controlled by the Carreau number Cu, the Womersley number Wo, the fluid power-law index n, the ratio between the outer and inner radii κ, a parameter β that represents the ratio between the infinite and zero-shear viscosities, and the amplitude of the oscillatory signal ɛ. In both cases (a) and (b), a numerical solution of the start-up of the hydrodynamic is evaluated. With the aid of the velocity solution, the volumetric flow rate is determined under periodic conditions after the initial transient has vanished. Then, the fractional increase in the mean flow rate I due to the pulsatile pressure gradient is calculated. Furthermore, an asymptotic solution for small, intermediate, and very large values of the Carreau number is performed to provide physical insight into flow enhancement.

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.

Performance analysis of a novel direct absorption parabolic trough solar collector with combined absorption using MCRT and FVM coupled method

Direct absorption parabolic trough solar collector (DAPTSC) using nanofluid absorber has been demonstrated as an efficient technology for exploiting solar energy at high temperature. However, most mono nanofluids are unable to achieve broadband absorption and hybrid nanofluids are unstable at high temperature. In this work, the mono nanofluid and optical glass combined absorption is proposed for the DAPTSC. In which the absorption glass (HB850) and an outer glass tubes form an annular space for indium-tin-oxide (ITO)/Therminol VP-1 nanofluid flowing. Monte Carlo Ray-Tracing and Finite Volume Method (MCRT-FVM) coupled model is developed and validated for system investigation. The results show that the novel collector with the combined absorber exhibits obvious enhancement in thermal performance compared to Therminol VP-1 or ITO/Therminol VP-1 nanofluid. The DAPTSC with concentric annular tube (CAT) has a significantly superior thermal performance to that of the single tube collector, with 45.91 % higher achievable temperature gain and 1.15 % more achievable exergy efficiency. Finally, an eccentric annular tube (EAT) is proposed for further improvement. To quantify the performance improvement of the DAPTSC with EAT, a comparison has been made to that of a DAPTSC with CAT. The results indicate that EAT configuration shows 1.96 % enhancement in the exergy efficiency.

Computational study of heat transfer from the inner surface of a circular tube to force high temperature liquid metal flow in laminar and transition regions

Heat transfer through forced convection from the inner surface of a circular tube to force the flow of liquid sodium in the laminar and transition regions were numerically analysed for two types of tube geometries (concentric annular and circular tubes) and two types of equivalent diameters (hydraulic and thermal equivalent diameters). The unsteady laminar three-dimensional basic equations for forced convection heat transfer caused by a step heat flux were numerically solved until a steady state is attained. The code of the parabolic hyperbolic or elliptic numerical integration code series (PHOENICS) was used for calculations by considering relevant temperature dependent thermo-physical properties. The concentric annular tube has a test tube with inner and outer diameters of 7.6 and 14.3 mm, respectively, has a heated length of 52 mm, and an L/d of 6.84. The two circular tubes have inner diameters of 6.7 and 19.3 mm with L/d of 7.76 and 2.69, respectively, and a heated length of 52 mm. The inlet liquid temperature, inlet liquid velocity, and surface heat flux were equally set for each test tube as Tin≅573 to 585 K, uin = 0.0852 to 1 m/s, and q = 2×105 to 2.5×106 W/m2, respectively. The increase in temperature from the leading edge of the heated section to the outlet of the circular tubes (with a hydraulic diameter of dH = 6.7 mm and a thermal equivalent diameter dte = 19.3 mm) was approximately 2.70 and 1.21 times as large as the corresponding values of the concentric annular tube with an inner diameter of 7.6 mm and an outer diameter of 14.3 mm, respectively. A quantity in the laminar and transition regions was suggested as the dominant variable involved in the forced convection heat transfer in the circular tube. The values of the local and average Nusselt numbers, Nuz and Nuav, respectively, for a concentric annular tube with dH = 6.7 mm and for a circular tube with dH = 6.7 mm were calculated to examine the effects of q, Tin, and Pe on heat transfer. The general correlation in the laminar and turbulent regions for a high temperature liquid metal was identified for the circular tube with a hydraulic diameter.

Experimental study of sensible heat storage/retrieval in/from a nanofluid enclosed between concentric annular tubes

In this work, an experimental study has been carried out to quantify an amount of sensible heat storage/recovery in a specific nanofluid (distilled water +Titanium dioxide). The experimental results show, especially, the influence of nanoparticles mass concentration on the heat storage/recovery performance for a fixed mass flow rate (Γ= 300 kg/ℎ) of heat transfer fluid (HTF). This parameter contributes to the improvement of the heat transfer and therefore the enhancement of the sensible heat storage/retrieval.

Numerical Simulation of the Laminar Forced Convective Heat Transfer between Two Concentric Cylinders

The dual reciprocity method (DRM) is a highly efficient numerical method of transforming domain integrals arising from the non-homogeneous term of the Poisson equation into equivalent boundary integrals. In this paper, the velocity and temperature fields of laminar forced heat convection in a concentric annular tube, with constant heat flux boundary conditions, have been studied using numerical simulations. The DRM has been used to solve the governing equation, which is expressed in the form of a Poisson equation. A test problem is employed to verify the DRM solutions with different boundary element discretizations and numbers of internal points. The results of the numerical simulations are discussed and compared with exact analytical solutions. Good agreement between the numerical results and exact solutions is evident, as the maximum relative errors are less than 5% to 6%, and the R2-values are greater than 0.999 in all cases. These results confirm the effectiveness and accuracy of the proposed numerical model, which is based on the DRM.

An empirical investigation on Cu/Ethylene Glycol nanofluid through a concentric annular tube and proposing a correlation for predicting Nusselt number

The investigation indicates an experimental study on the convective heat transfer of Cu/Ethylene Glycol nanofluid flow inside a concentric annular tube with constant heat flux boundary condition and proposes a novel correlation for the prediction of Nusselt number. For extending the previous study by Jafarimoghaddam et al., we selected the nanoparticles with the average size of 20nm and also other conditions of the experiment are based on Jafarimoghaddam et al. (2016) [1]. The applied nanofluid was prepared by Electrical Explosion of Wire technique with no accumulation during the experiment. The tube was heated using an electrical heating coil covered it. The effects of different parameters such as flow Reynolds number and nanofluid particle concentration on heat transfer coefficient are studied. The acquired experimental data were used to establish a correlation for predicting Nusselt number of nanofluid flow inside the annular tube. This correlation has been presented by using the exponential regression analysis and least square method. Correlation is valid for Cu/Base Ethylene Glycol nanofluid flow with the volume concentrations between 0.011 and 0.171 in the hydrodynamically fully developed laminar flow regime with Re<160 which is most applicable in micro heat sinks.

Experimental Study on Cu/Oil Nanofluids through Concentric Annular Tube: A Correlation

This study deals with an empirical investigation on the convective heat transfer of Cu/oil nanofluid flow inside a concentric annular tube with constant heat flux boundary condition and suggests a correlation to predict the Nusselt number. The average size of particles was 20 nm and the applied nanofluid was prepared by Electrical Explosion of Wire technique with no nanoparticle agglomeration during nanofluid preparation process and experiments. The nanofluid flowing between the tubes is heated by an electrical heating coil wrapped around it. The effects of different parameters such as the flow Reynolds number, tube diameter ratio, and nanofluid particle concentration on heat transfer coefficient are studied. Using the acquired experimental data, a correlation is developed for the estimation of the Nusselt number of nanofluid flow inside the annular tube. This correlation has been presented by using the exponential regression analysis and least‐squares method. The correlation is valid for Cu/base oil nanofluid flow with weight concentrations of 0.12, 0.36, and 0.72 in the hydrodynamically full‐developed laminar flow regime with Re &lt;140, which is applicable in mini‐ and microchannel heat exchangers, and it is in good agreement with the experimental data.

An empirical investigation on thermal characteristics and pressure drop of Ag-oil nanofluid in concentric annular tube

In this work an experimental study on Silver-oil nanofluid was carried out in order to present the laminar convective heat transfer coefficient and friction factor in a concentric annulus with constant heat flux boundary condition. Silver-oil nanofluid prepared by Electrical Explosion of Wire technique with no nanoparticles agglomeration during nanofluid preparation process and experiments. The average sizes of particles were 20 nm. Nanofluids with various particle Volume fractions of 0.011, 0.044 and 0.171 vol% were employed. The nanofluid flowing between the tubes is heated by an electrical heating coil wrapped around it. The effects of different parameters such as flow Reynolds number, tube diameter ratio and nanofluid particle concentration on heat transfer coefficient are studied. Results show that, heat transfer coefficient increased by using nanofluid instead of pure oil. Maximum enhancement of heat transfer coefficient occurs in 0.171 vol%. In addition the results showed that, there are slight increases in pressure drop of nanofluid by increasing the nanoparticle concentration of nanofluid in compared to pure oil.

A novel all-glass evacuated tubular solar steam generator with simplified CPC

A low-cost all-glass evacuated tubular solar steam generator with simplified CPC (Compound Parabolic Concentrator) is presented in the paper. It can produce steam exceeding 200°C with pressure ranging from 0.10 to 0.55MPa. The solar steam generator primarily consists of 60 collecting units with a total aperture area of 32m2 and each unit is comprised of an all-glass evacuated tube, a simplified CPC and a metal concentric annular tube which is inserted into the all-glass evacuated tube. The high viscosity mixture made of high temperature oil and graphite powder is filled in the annular space between the inner glass tube and the copper concentric tube in order to enhance heat transfer from the selective absorbing layer to working fluid flowing in the concentric tube. Outdoor experimental studies have been carried out to investigate the actual performance of the designed solar steam generator in summer time under different operating conditions. Experimental results show that the maximum steam outlet temperature can exceed 200°C with pressure of 0.55MPa. The present solar steam generator can steadily produce saturated steam over 150°C at the pressure range of 0.1–0.55MPa with a collecting efficiency over 0.30, which can be used as an industrial steam supplier with great potentials for various applications.

Numerical Study of Laminar Mixed Convection Heat Transfer of a Nanofluid in a Concentric Annular Tube Using Two-Phase Mixture Model

Numerical Study of Laminar Mixed Convection Heat Transfer of a Nanofluid in a Concentric Annular Tube Using Two-Phase Mixture Model

Friction Factor Correlations for Compressible Gaseous Flow in a Concentric Micro Annular Tube

Compressible momentum and energy equations were solved numerically for concentric micro annular tubes with slip velocity and temperature jump wall boundary conditions. The results were expressed in the form of the product of friction factor and Reynolds number (f · Re) for a quasi-fully developed condition and for the ranges of Re < 1000 and Ma < 1. The numerical methodology was based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The outer tube radius ranged from 5 to 40 µm with radius ratios of 0.2, 0.5, and 0.8. The length to hydraulic diameter ratio was more than 100. The stagnation pressure was chosen in such a way that the exit Mach number ranged from 0.1 to 1.0, and the outlet pressure was fixed at the atmospheric pressure. For the case of incompressible slip flow, f · Re is calculated as a function of radius ratio and Knudsen number. For high speed flows, the values of f · Re for compressible slip flow were higher than those for incompressible slip flow due to compressibility effects. Also, f · Re correlation for compressible slip flow was obtained from compressible no-slip flow and incompressible slip flow as a function of Mach and Knudsen numbers and radius ratio. In addition, a correlation for microchannel, microtube, and micro annular tube was obtained from the authors' previous work.

0316 粘性子午面解析による軸流タービン内部流れの評価(OS3 流体機械の研究開発とそれに関連した複雑流動現象,オーガナイズドセッション)

In the blade design process, flow pattern prediction tools have an essential role to create a highly efficient blade shape. A viscous throughflow code, which can take into account the effects of boundary layer and blade thickness, was developed to evaluate axial turbine flows. In the present paper, the throughflow code is validated by applying it to a concentric annular tube flow. In addition* axial turbine internal flows were evaluated by the throughflow code. The simulation results showed that the throughflow code can predict the flow patterns very well if the effects of secondary flow are marginal.

HYDRAULIC STUDY OF DRILLING FLUID FLOW IN CIRCULAR AND ANNULAR TUBES

This study investigates the drilling fluid flow behavior of two water-based drilling fluids in circular and annular tubes. The study has four main objectives: 1) to evaluate correlations between the Power Law and the Casson rheological models, 2) to characterize the flow behavior, 3) to evaluate five hydraulic-diameter equations, and 4) to evaluate the correlations of five turbulent flow-friction factors. The experimental fluid flow loop consisted of one positive displacement pump of 25 HP connected to a 500-liter tank agitated by a 3-HP mixer. The fluids passed through six meters long tubes, arranged in three horizontal rows with independent inlets and outlets. The circular tubes had a 1 inch diameter and were configured as two concentric annular tubes. Annular Tube I had an outer diameter of 1 ¼ inch and an inner diameter of ½ inch. Annular Tube II had an outer diameter of 2 inches and an inner diameter of ¾ inch. The results show that, for the fluids in exam, correlations proposed in the literature were inaccurate as far as predicting hydraulic diameter, estimating pressure drop, and defining the flow regime. In general, the performance of those correlations depended on the fluid properties and on the system’s geometry. Finally, literature parameters for some of the correlations were estimated for the two drilling fluids studied. These estimations improved the predictive capacity of calculating the friction factor for real drilling fluids applications for both circular and annular tubes.

Rarefied gas flow in concentric annular tube: Estimation of the Poiseuille number and the exact hydraulic diameter

The fully developed flow of rarefied gases through circular ducts of concentric annular cross sections is solved via kinetic theory. The flow is due to an externally imposed pressure gradient in the longitudinal direction and it is simulated by the BGK kinetic equation, subject to Maxwell diffuse-specular boundary conditions. The approximate principal of the hydraulic diameter is investigated for first time in the field of rarefied gas dynamics. For the specific flow pattern, in addition to the flow rates, results are reported for the Poiseuille number and the exact hydraulic diameter. The corresponding parameters include the whole range of the Knudsen number and various values of the accommodation coefficient and the ratio of the inner over the outer radius. The accuracy of the results is validated in several ways, including the recovery of the analytical solutions at the hydrodynamic and free molecular limits.

擬塑性流体の粗面同心二重円管内流れの管摩擦係数とレイノルズ数との関係

The aim of this paper is to derive the relation between friction factor and the Reynolds number for the pseudo-plastic fluid flow in concentric annular tubes with roughness, which is assumed the model of drilling mud flow in a well, because the estimation methods of the friction factor in the fluid flow are needed.Based on the estimation methods of the friction factor of Newtonian fluid flow in a circular tube with roughness given by Colebrook and the relation between friction factor and the Reynolds number for the pseudo-plastic fluid flow in a circular tube with smooth wall given by Dodge and Metzner, the relation between friction factor and the Reynolds number for the pseudo-plastic fluid flow in concentric annular tubes with roughness, is obtained as Eq.(21) that is capable of calculating the friction factor in the turbulent flow region of pseudo-plastic fluids in concentric annular tubes with roughness at any values of rheology parameter, relative roughness and Reynolds number by using the subroutine subprogram shown in the appendix.The relation presented here includes the cases of Newtonian fluid and pseudo-plastic fluid flow in the circular tubes.

Quantitative void fraction measurement method by neutron radiography and applications to two-phase flow researches

Quantitative void fraction measurement method by neutron radiography was developed using a neutron absorber grid based on an umbra method. The cross-sectionally averaged void fraction for various flow patterns in air–water two-phase flow in a tube was measured quantitatively. Uncertainty analyses were carried out for the measured values and the accuracy of the measurement was discussed for each flow pattern. Experimental results agree well with the prediction by drift flux model. The quantitative measurement method was applied to two-phase flow in a concentric annular tube, a tube with a spiral wire, a rod bundle, a capillary tube and a plate fin heat exchanger. The CT reconstruction method was applied to measure the quantitative void fraction distributions in the cross section.

同心二重円管内擬塑性流体流れのレイノルズ数の簡便表示と下限臨界レイノルズ数

The aim of this paper is to derive a simple expression of the Reynolds number and an estimation method of the lower critical Reynolds number for the pseudo-plastic fluid flow in concentric annular tubes assumed the model of drilling mud flow in a well, because interpolation methods are used in the calculation of the Reynolds number and the theoretical estimation methods of the lower critical Reynolds number are needed.Based on the theoretical function for the pseudo-plastic fluid flow given by Fredrickson and Bird(1977), the simple expression for the Reynolds number is obtained as Eq.(20) that is capable of estimating the theoretical value of one within 2% error at any rheology constant values where the values of the pipe diameter ratio are more than 0.2, and zero.The estimation method of the lower critical Reynolds number by applying the flow stability parameter given by Masuyama and Kawashima(1977) is shown as Eq.(32) and Eq.(33). When the reciprocal number of the rheology constant is positive integer, the analytical solution of Eq.(32) is derived and shown as Eqs.(A-4) to (A-12) in the appendix. It appears from the comparison of experimental and predicted lower critical Reynolds numbers for pseudo-plastic fluid flow in concentric annular tubes that the estimated values show agreement with the experimental ones within 20% error.

수직 동심 환형관 내부유동에서 과냉 유체의 비등 시작 열유속에 관한 표면 볼록 곡률의 영향

Effect of Convex Surface Curvature on the Onset of Nucleate Boiling of Subcooled Fluid Flow in Vertical Concentric Annuli An experimental study has been carried out to investigate the effect of the transverse convex surface curvature of core tubes on heat transfer in concentric annular tubes. Water is used as the working fluid. Three annuli having a different radius of the inner cores, Ri