Sudden Expansion Tube Research Articles

Python-based machine learning estimation ofthermo-hydraulic performance along varying nanoparticle shape, nanofluid and tube configuration

In this research article, a Python-based machine learning model prediction study was conducted based on the study results obtained from sudden expansion tubes containing different expansion angles, dimpled fin structures and nanofluids, whose thermo-hydraulic performance was previously examined. In the study, Artificial Neural Network and Ridge regression models were used to make predictions on the average Nusselt number (Nu), average Darcy friction factor (f) and performance evaluation criteria (PEC). Physical variations of the sudden expansion tube were taken into account and a detailed comparison of the results was made. A superior average Nu was acquired as 172.45 %, 22.05 %, 17.18 %, 13.65 %, and 7.76 % compared to Ag-MgO/H2O, Al2O3/H2O (blade), CoFe2O4/H2O, Al2O3/H2O (cylindrical), and Al2O3/H2O (platelet), respectively. The highest Performance Evaluation Criteria (PEC) for Re= 2000 based on Al2O3/H2O (platelet) shows an increase of 4.84 %, 12.08 %, 11.76 %, 66.05 %, and 148.94 % compared to Al2O3/H2O (cylindrical), Al2O3/H2O (blade), CoFe2O4/H2O, Fe3O4/H2O, and Ag-MgO/H2O, respectively. From the results obtained, it was determined that Python-based Machine Learning approach which facilitates custom optimizations showed a significant performance with small margins of error in predicting the heat transfer parameters. The lowest error rates of machine learning and polynomial ridge regression models ranged from 0.2 % to 5.4 % for the unseen test set and the application of Python-based algorithms provided considerable savings in calculation time compared to conventional methods. On the other hand, using machine learning models with feature engineering has been found to increase model performance by at least 30 %. In these years when studies on the predictions of thermo-hydraulic studies are very rare in the literature, this study is intended to facilitate scientists, engineers and academicians who will further study on this subject.

Experimental and numerical study on ferrohydrodynamic and magneto-convection of Fe3O4/water ferrofluid in a sudden expansion tube with dimpled fins

BackgroundThis study experimentally and numerically addresses magnetohydrodynamic forced convection including dimpled fins, Fe3O4/water ferrofluid, and DC magnetic field. In this research, focusing on the thermo-hydraulic performance improvement of a sudden expansion tube. It has been used different inlet diameters, dimple sizes, ferro nanoparticle concentrations, and magnetic field strengths to examine the heat transfer and fluid dynamics characteristics of the system. MethodsThe study consists of two parts, i) experimental and ii) numerical. Steady-state, incompressible, Newtonian flow were considered but chemical reaction, viscous dissipation, buoyancy, and radiative heat transfer were neglected in this study. On the other hand, numerical solutions were carried out for single-phase method. This study was first compared with the studies in the literature on the flow in a sudden expansion tube without dimpled fins and the error rate was found to be less than 10 %. In the analysis, dimpled fins with d=3, 5, and 7 mm at each P=15 mm (P/d=5.0, 3.0, and 2.14) have been used. As working fluid, Fe3O4/water ferrofluid with volume concentration of φ=1.0 % and 2.0 % have been analyzed. Additionally, DC magnetic fields, which strength of Ha=0.1, 0.3, 0.5, 1.1, 3.2, and 5.3 (B =0.01, 0.03, 0.05, 0.1, 0.3, and 0.5T), have been applied on the sudden expansion tube surface as external force. Significant findingsDimpled fins enhance the heat transfer by disrupting the boundary layer and forming secondary flows, while the ferrofluid increases the thermal conductivity and viscosity of the base fluid. Based on these explanations, dimpled fins increased the convective heat transfer rate at the rate of 96.0 % compared with smooth tube. In addition, Fe3O4/water ferrofluid with φ=2.0 % performed the highest performance and performance evaluation criteria increased by 8.5 %. The magnetic field also contributes to the heat transfer enhancement by inducing Lorentz force and mixing the flow. Excessive increasing of magnetic field strength adversely affected the system performance, and the highest performance evaluation criterion is acquired at Ha=3.2 by increasing 3.9 %. Compared with smooth tube, compound effect of dimpled fins, Fe3O4/water ferrofluid, and magnetic field improved the average Nusselt number and performance evaluation criterion at the rate of 279.8 % and 207.9 %, respectively.

Numerical simulation of sudden expansion tubes with Ag-MgO nanofluid and innovative fin structure: A thermo-fluidic analysis

This study introduces an innovative approach to employing mono/hybrid nanofluids in tubes with sudden expansion, structured at various expansion angles and equipped with novel capsule-type dimpled fins. Pumping of hybrid nanofluids into sudden expansion tube combined with capsule-type dimpled fins and different expansion angles (ranging from 30° to 90°) has not been investigated so far in terms of energy, exergy, and entropy analyses. Recognizing the attention currently devoted to the climate effect of a system exposed to high thermal loads, this study sheds light on the literature how a system preferred by engineers and professionals can be cooled down efficiently to increase the performance of the system. The objective is to analyze a detailed 3E-study (energy, exergy, and entropy production) on water-based mono and hybrid nanofluids, exploring various volume fractions and combinations (including 2.0% Ag, 2.0% MgO, and blends of Ag-MgO). The study finds that a 45° expansion angle, combined with capsule-type dimpled fins and 0.5% Ag-1.5% MgO nanofluid, offers the most efficient tube design, enhancing the average Nusselt number by 20.0%. This configuration, also, reduces total entropy generation by approximately 23.0 % and shows exergy output by 26.0%, though it does lead to a 26.0% decrease in second law efficiency due to increased pumping power. Interestingly, the first law efficiency remains unchanged mainly across different nanofluid types. These findings provide valuable insights into optimizing heat transfer and fluid dynamics in engineering applications.

On the rising dynamics of a Taylor bubble in sudden/gradual expansion tubes filled with viscoelastic liquids

In this paper, the rise behaviors of Taylor bubbles are investigated in sudden/gradual tubes filled with viscoelastic media via grid adaptive direct numerical simulations (DNS). The exponential Phan–Thien–Tanner (PTT) constitutive model is used to describe the viscoelastic rheological characteristics, and the phase interface is captured via the volume of fluid (VOF) method. The effects of tube structure (diameter ratio and structural angle) and fluid elasticity (expressed by the Weissenberg number Wi) on bubble dynamics have been studied. Our results indicate that bubbles are prone to rupture in the expansion tubes, mainly due to the dual effects of the wall and the elastic relaxation. The fluid elasticity suppresses the jet effect in a sudden expansion tube. Meantime, as the structural angle or the diameter ratio increases, the wall effect is weakened on axial or radial scales, inhibiting the bubble rupture. A large structure angle attenuates the wall effect, while changes in the diameter ratio slow down the radial momentum transfer near the wall region, both of which favor bubble integrity. We also obtain an exponential relationship between the critical rupture time and the structure angle. The dynamical Taylor bubbles can be operated by the structure of the tube and surrounding fluid viscoelasticity, which is of great significance in chemical engineering applications involving complex non-Newtonian fluids.

Investigation of magneto-convection characteristics in a sudden expanding channel with convex surface geometry under thermally developing flow conditions

PurposeThe purpose of this study is to analyse the magnetic field effect on Fe3O4/H2O Ferrofluid flowing in a sudden expansion tube, which has specific behaviour in terms of rheology, with convex dimple fins. Because the investigation of flow separation is a prominent application in performance, the effect of magnetic field and convex dimple on the thermo-hydraulic performance of sudden expansion tube are examined, in detail.Design/methodology/approachDuring the solution of the boundary conditions of the sudden expansion tube, finite volume method was used. Analyses have been conducted considering the single-phase solution, steady-state, incompressible fluid and no-slip condition of the wall under forced convection conditions. In the analyses, it has been assumed that the flow was developing thermally and has been fully developed hydrodynamically.FindingsThe present study focuses on exploring the influence of the magnetic field, nanofluid concentration and convex dimple fins on the thermo-hydraulic performance of sudden expansion tube. The results indicate that the strength of the magnetic field, nanofluid concentration and convex dimple fins have a positive effect on the convective heat transfer in the system.Originality/valueThe authors conducted numerical studies, determining through a literature search that no one had yet investigated enhancing heat transfer on a sudden expansion tube using combinations of magnetic fields, nanofluids and convex dimple fins. The results of the numerical analyses provide valuable information about the improvement of heat transfer and system performance in electronic device cooling and heat exchangers.

Parametric analysis of different Al2O3 nanoparticle shapes and expansion angles for sudden expanded tube regarding the first law of thermodynamics

The thermo-hydraulic performance of Al2O3/H2O nanofluid with different nanoparticle shapes flowing in a sudden expansion tube with variable sudden expansion inclination angles and elliptical dimpled fins with different diameters were numerically investigated. Investigation of variable sudden expansion inclination angles, elliptic dimpled fins, and different nanoparticle shapes together reveals the novelty of this study. The main purpose of this study is to analyse the effect of nanofluid particle shapes, sudden expansion inclination angles, and elliptical dimpled fin on thermo-hydraulic performance for sudden expansion tube. The platelet, cylindrical, and blade nanoparticle shapes of Al2O3 nanoparticle (φ = 1.0 %) were separately mixed into base fluid to obtain working fluid. Numerical studies were carried out under laminar flow regime (500 ≤ Re ≤ 2000). Furthermore, the sudden expansion tube was assumed to have inclination angles with α = 30°, 45°, 60°, and 90°. The results presented that the highest Performance Evaluation Criterion is obtained for the case of DT6 using Al2O3/H2O with platelet nanoparticle shape at Re = 2000. Besides, the highest Nusselt number and Performance Evaluation Criterion were realized at the inclination angle of 45°. The increment rate of Nusselt number and Performance Evaluation Criterion at α = 45° were determined as 8.75 % and 10.52 % compared to α = 30°, respectively. Moreover, elliptical dimpled fins with sized as a = 6 mm and b = 12 mm presented the highest thermo-hydraulic performance, and this condition showed an increment of 153.9 % compared to case of a = 2 mm and b = 4 mm.

The first and second law analyses of thermodynamics for CoFe2O4/H2O flow in a sudden expansion tube inserted elliptical dimpled fins

In this paper, thermo-hydraulic performance and entropy generation of the sudden expansion tube with elliptical dimpled fins (DFs) at different directions was computationally performed at different Reynolds (Re) numbers ranging between 100≤Re≤2000 using cobalt ferrite/H2O (CoFe2O4/H2O) nanofluid (NF) (0.0≤φ≤ 2.0). The novelty of this study is to investigate the effect of the elliptical DF and its arrays in the sudden expansion tube in terms of thermodynamics laws (energy and entropy generations). While the sudden expansion ratio (D2/D1) is 2.5, elliptical dimple width (a) and height (b) show variations between 4 and 8 mm. In addition, the distances among elliptical DFs (P) are taken as P = 10, 15, and 20 mm while the diameter (D1) and length (L1) of the inlet tube are D1=8 mm and L1=375 mm. The diameter (D2) and length (L2) of the tube with the sudden expanding and elliptical DFs are D2=20 mm and L2=1125 mm, respectively. The study comprehensively exhibits results of the thermo-hydraulic performance and entropy generation based on numerical data. The results demonstrated that the highest heat transfer rate is recorded by the case of DT3, and DT3 enhances the convective heat transfer rate by 221%, and increases the pressure drop by 17.38% at Re=2000 compared to smooth tube (ST). It was observed that as the Re increases, the performance evaluation criteria (PEC) gradually increases too, and the highest PEC has been obtained for DT3 as 2.11 at Re=2000. The entropy generation (EnG) was also evaluated in terms of both geometric designs and volumetric concentrations. Moreover, the best total EnG was found around 17% for DT3 at the Re=1000 and φ=2.0% compared to ST using H2O. Consequence of the applied analyses, the use of elliptic DFs in a sudden expansion tube enhances the convective heat transfer rate and decreases total EnG.

Energy analysis of magnetite nanofluid flowing in newly designed sudden expansion tube retrofitted with dimpled fin

Sudden expansion geometry plays an important role in the design of many engineering applications such as heat exchangers to avoid thermal stress on welded joints. While the heat transfer in these geometries is maximized at the reattachment points, it decreases to a minimum in the recirculation regions created by the fluid. To prevent this situation and improve the performance of the expansion tubes, nanofluid, and expanded surfaces can be used. For this purpose, forced convection of magnetite nanofluid flow in various expansion ratios has been investigated numerically in this study. Analyses have been performed on Reynolds (Re) numbers ranging from 100 to 2000, constant and uniform heat flux at 600 W/m2, and volume concentrations (1.0≤φ≤2.0 vol.%). The result showed that while the Nu number increases with increasing Re number, the most efficient case is Dimpled Tube (DT) 9, and the highest value of performance evaluation criteria (PEC) has been obtained at φ=2.0 vol.%. Compared with the water, the highest Nu number value has been obtained as 3.34% increased at Re=2000 and φ=2.0 vol.%. When compared to the DT9 and Smooth Tube (ST) 1 where water was used as the working fluid at Re=2000 and φ=2.0 vol.%, the PEC value increased by 8.66% and 110.31%, respectively. In addition, the bottom wall of the DT9 case performs higher convective heat transfer rate than the top wall.

Experimental investigation on the void fraction characteristics of a sudden expansion tube using wire-mesh sensors

Void fraction is an essential parameter of gas-liquid two-phase flow and experiments were executed to investigate the void fraction fluctuation characteristics of gas-liquid two phase flow through a sudden expansion tube. Two 16 × 16 wires mesh sensors were applied to measure the phase distribution of upstream pipe(pipe-32) and downstream pipe(pipe-50). The superficial gas velocity is in the range of 3.46 m/s - 22.46 m/s and the superficial liquid velocity ranges from 0.034 m/s to 0.414 m/s. Flow pattern evolution of upstream and downstream pipes was reconstructed and compared. The experiment results show that, in contrast to pipe-32, the void fraction of pipe-50 shows different trends with the increase of liquid and gas velocity. Liquid-carrying capacity is essential in the relationship between the void fraction of pipe-32 and pipe-50. The critical superficial liquid and gas velocities are proposed to characterize the liquid-carrying capacity. The maximum critical superficial gas and liquid velocity is 15.56 m/s and 0.207 m/s, respectively. Besides, a model is proposed to describe the relationship of void fraction between pipe-32 and pipe-50. It is found that the prediction error is less than ±10% in the case of annular flow.

Investigation of effect of process parameters on suddenly Expanded flows through an axi-symmetric nozzle for different Mach Numbers using Design of Experiments

Experiments are conducted to determine base pressure variation through micro-jets from a suddenly expanded axisymmetric passage. Four micro-jets having an orifice diameter of 1mm are situated at 90° interims along the base at 6.5 mm from the geometrical axis of the main jet. The Mach number and L/D ratios were the process parameters employed in the study. The flow stream was extended all of a sudden into an axi-symmetric duct of 4.84 cross-sectional area for all the Mach numbers and L/D ratios respectively. The test Mach numbers used in the study was 2, 2.5 and 3; length-to-diameter ratios selected for the sudden expansion tube were 4, 6 and 8. The jets were operated at an overexpansion level of (Pe/Pa = 0.277). The experiments are conducted as per Taguchi design of experiments. From this investigation, one will be able to identify the enlargement length to diameter ratio resulting in maximum increasing or decreasing base pressure. Mathematical models are also developed for base pressure based on Mach number and L/D ratio with a maximum error of ± 10%.

Long Bubble Penetration through Viscoelastic Fluids in a Suddenly Contracting and Expanding Tube

This study investigated the properties of long bubbles penetrating viscoelastic fluids in a suddenly contracting and expanding tube. Injection gas flow is controlled by a mass flow controller (MFC). Some of dimensionless parameters, such as the capillary number (Ca), the Reynolds number (Re), the fractional ratio (m), and the Weissenberg number (Wi), are discussed herein. The experimental results showed that bubble velocity, Ca, and Wi increase as shear viscosity increases under a constant gas flow by MFC. However, as shear viscosity increases, bubble diameter decreases, andmincreases. When gas flow is 200 mL/min and shear viscosity increases, the bubble front is sharper in the contraction tube, and the bubble front shape is blunter in the sudden expansion tube. When gas flow is 600 mL/min and shear viscosity increases, the bubble front is blunter in the contraction tube and exhibits a torch shape in the sudden expansion tube.

Experimental Determination of Local Resistance Coefficient of Sudden Expansion Tube

Theoretical derivation of local resistance coefficient of sudden expansion tube is presented. Several assumptions are analyzed in the theoretical derivation. That the head loss shall be neglected is affirmed. Experimental data proves that the pressure before and after sudden expansion section is basically the same. That the friction force on the side face of control body is neglected is denied and it is pointed out that such neglect is the main cause for error between theoretical calculation and actual measurement. Experimental device for measuring local resistance coefficient is designed in combination with theoretical derivation process. Optimal gradually varied flow section is selected after sudden expansion pipe in Bernoulli equation based on variation of piezometer tube head. It is pointed out in accordance with experimental data analysis that the value of local resistance coefficient of sudden expansion tube determined through experimental data is closer to the actual situation during pipeline design.

C02 急拡大空間を有するパルス管エンジンの基本特性(パルス管冷凍機,熱音響機器及び関連要素と応用システム(1))

The pulse tube engine consists of one piston in one cylinder, cooler with orifice, pulse tube, heater and gas damper with stacked wire gauzes. The pulse tube has the work source in this engine. The gas damper has the function breaking the thermodynamic symmetry. For this research, the engine replaced a gas damper with a sudden expansion tube is proposed. A simple prototype engine, using air at normal atmospheric pressure as the working gas, was fabricated. Effects of expansion tube shape on the engine performance were examined experimentally. The effect of sudden expansion tube was confirmed.

3D PIV 기법을 이용한 선회유동의 급팽창에 관한 실험적 연구

The effect of swirl on the flow characteristics in a sudden expansion tube was examined experimentally by using 3D PIV(particle image velocimetry) to capture the velocity profiles. The swirling flow of water through a sudden 1:2 axisymmetric expansion has previously been studied experimentally within a horizontal round tube. A kind of tangential slot is used as a swirl generator for swirling flow and a honey comb is used for without swirl flow. The work with the swirl and without swirl results are compared to each other at the same Reynolds number. Liquid crystal was employed to measure temperature profiles and heating coil used for heat transfer with and without swirl flow. And then the Nusselt number ratoes(Nu/Nudb) are calculated along the test section.

Control of base pressure with micro‐jets : part I

PurposeThis paper aims to present the results of an experimental investigation carried out to control the base pressure in a suddenly expanded axi‐symmetric passage.Design/methodology/approachFour micro‐jets of 1 mm orifice diameter located at 90° interval along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region was employed as active controls. The test Mach numbers were 1.25, 1.3, 1.48, 1.6, 1.8, 2.0, 2.5 and 3.0. The jets were expanded suddenly into an axi‐symmetric tube with cross‐sectional area 4.84 times that of nozzle exit area. The length‐to‐diameter ratio of the sudden expansion tube was varied from 10 to 1. Nozzles generating the above jet Mach numbers were operated with nozzle pressure ratio in the range 3‐11. As high as 40 per cent increase in base pressure was achieved. In addition to base pressure, the wall pressure in the duct was also measured.FindingsIt is found that the wall pressure is not adversely influenced by the micro jets.Originality/valueThe paper provides information on internal supersonic flow.

Control of suddenly expanded flow

PurposeThis paper presents an experimental investigation to study the effectiveness of micro jets under the influence of Over, Under, and Correct expansion to control the base pressure in suddenly expanded axi‐symmetric ducts.Design/methodology/approachFour micro jets of 1 mm orifice diameter located at 90° intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region was employed as active controls. The tests were conducted for Mach numbers 1.5, 1.3, 1.6, 1.8, 2.0, 2.5, and 3.0. The jets were expanded suddenly into an axi‐symmetric tube with cross‐sectional area 2.56 times that of nozzle exit area. The L/D ratio of the sudden expansion tube was varied from 10 to 1.FindingsFrom the present studies, it was found that the maximum increase in base pressure is 152 percent for Mach number 2.58. It is found that the micro jets do not adversely influence the wall pressure distribution.Research limitations/implicationsAs a result of developments in space flights and missile technology, the base flows at high Reynolds numbers continues to be an important area of research. Our understanding of many features of base flows remains poor, due to inadequate knowledge of turbulence, particularly in the presence of strong pressure gradient.Originality/valueThe paper shows that micro jets can serve as an effective controller raising the base suction to almost zero level for some combination for parameters. The nozzle pressure ratio has a definite role to play in fixing the base pressure with and without control. There is no adverse effect of the micro jets on the flow field in the duct.

Active Control of Suddenly Expanded Flows from Underexpanded Nozzles

An experimental investigation was carried out to study the effectiveness of micro-jets to control base pressure in suddenly expanded axi-symmetric ducts. Four micro-jets of 1 mm orifice diameter located at 90$^\circ$ interval along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region was employed as active controls. The Mach numbers of the suddenly expanded flows were studies 2.0, 2.5 and 3.0. The jets were expanded suddenly into an axi-symmetric tube with cross-sectional area 2.56, 3.24, 4.84, and 6.25 times that of nozzle exit diameter. The length-to-diameter ratio of the sudden expansion tube was varied from 10 to 1. The jets were operated at an over expansion level of Pe/Pa = 0.277. The wall pressure distribution in the suddenly enlarged duct was also measured. It is found that the micro-jets can serve as active controllers for base pressure. Also, the wall pressure distribution is not adversely influenced by the micro-jets. From the present investigation it is evident that for a given Mach number and nozzle pressure ratio one can identify the enlargement length to diameter ratio which will result in maximum increase/decrease of base pressure.

Control of Suddenly Expanded Flows from Correctly Expanded Nozzles

The effectiveness of micro jets to control base pressure in suddenly expanded axi-symmetric ducts has been presented in this paper. Four micro jets of 1 mm orifice diameter located at 90° intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region were employed as active controls. The Mach numbers of the suddenly expanded flows were 1.25, 1.30, 1.48, 1.6, 1.8 and 2.0. The jets were expanded suddenly into an axi-symmetric tube with cross-sectional area 2.56, 3.24, 4.84, and 6.25 times that of nozzle exit area. The length-to-diameter ratio of the sudden expansion tube was varied from 10 to 1. The jets at all Mach numbers were correctly expanded. It is found that the micro jets can serve as active controllers for base pressure. Also, the wall pressure distribution is not adversely influenced by the micro jets.

Active Control of Suddenly Expanded Flows from Overexpanded Nozzles

An experimental investigation was carried out to study the effectiveness of micro-jets to control base pressure in suddenly expanded axi-symmetric ducts. Four micro-jets of 1 mm orifice diameter located at 90$^\circ$ interval along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region was employed as active controls. The Mach numbers of the suddenly expanded flows were studies 2.0, 2.5 and 3.0. The jets were expanded suddenly into an axi-symmetric tube with cross-sectional area 2.56, 3.24, 4.84, and 6.25 times that of nozzle exit diameter. The length-to-diameter ratio of the sudden expansion tube was varied from 10 to 1. The jets were operated at an over expansion level of Pe/Pa = 0.277. The wall pressure distribution in the suddenly enlarged duct was also measured. It is found that the micro-jets can serve as active controllers for base pressure. Also, the wall pressure distribution is not adversely influenced by the micro-jets. From the present investigation it is evident that for a given Mach number and nozzle pressure ratio one can identify the enlargement length to diameter ratio which will result in maximum increase/decrease of base pressure.

96/04165 An observation of near-planar spinning premixed flames in a sudden expansion tube

96/04165 An observation of near-planar spinning premixed flames in a sudden expansion tube