Circular Tube Research Articles

Heat Transfer Enhancement in Circular Cross Section Tube Using Inserts

Convective heat transfer was empirically examined in tubes with ballooned flat perforated steel inserts under turbulent flow conditions, encompassing Reynolds numbers ranging above 15000. The primary objective of this study is to expand the existing dataset concerning inserts. The external surface of the tube received a uniform heat flux, with air serving as the chosen fluid. Correlations were derived for the mass flow rate and heat absorption, utilizing the gathered measurements within the explored range of geometrical parameters and Reynolds numbers.

Elastic-plastic response for the foam-filled sandwich circular tube under internal blast loading

The dynamic response and the blast resistance of an aluminum foam-filled sandwich circular tube under internal blast loading was investigated theoretically. The deformation of the structure is decoupled into three phases corresponding to blast loading interacting with the internal tube, foam core crushing and external tube deformation. During the process, the theoretical model includes both the circumferential membrane forces and the axial moment components and considers an elastic-plastic strengthening model for internal/external tubes. The proposed model is tested against the experimental results for the mid-point deflection of the external/internal tubes. The influence of the physical and geometrical parameters of the structure on their deformation is investigated. It is shown that the dimensionless mid-point deflection of the external tube decreases as the tangent modulus of the internal/external tube increases, while the tangent modulus of the internal tube has a larger effect on the mid-point deflection of the external tube. The minimum mass of a sandwich circular tube can be found when the deformation of the external tube is specified. The research results can provide theoretical basis for lightweight structure design.

Prediction of optimal dimensions and arrangements of circular tubes of a fin and tube heat exchanger for an improved thermal-hydraulic performance

In the present work, the thermal-hydraulic performance of a fin and tube compact heat exchanger (FTHE) with different spatial arrangements of tubes and variations of tube diameter is investigated numerically. The three types of spatial arrangement of the tubes, namely inline, staggered row (SR), and staggered column (SC) arrangements, and five different tube diameters starting from Dc = 6.51 mm to Dc = 10.51 mm considered with a constant increment of 1 mm, are investigated for the augmentation of the heat transfer. The entire analysis is conducted under the low inlet velocity ranging from 0.7 m/s to 1.1 m/s. The results indicate that FTHEs (flow-through heat exchangers) have better thermal-hydraulic performance when arranged in staggered column configurations compared to inline and staggered row arrangements. However, it was observed that the pressure drop increased in staggered column arrangements compared to inline and staggered row arrangements. The performance ranking method MOORA is applied to optimize the spatial arrangements of tubes. The study’s findings suggest that the performance of FTHE is better in the case of staggered column arrangements, which offer a fair agreement with performance evaluation criteria (PEC3 = Q/(Pf +Pp )). After achieving the staggered column arrangement as an optimum spatial arrangement of the tubes, the influence of tube diameter on the performance of FTHEs is investigated for this arrangement only. The findings indicate that when the tube diameter is increased, there is a corresponding increase in both the characteristics like heat transfer coefficient and the pressure drop penalty. The performance ranking method MOORA is applied to get an optimum tube diameter, which is cross-checked by the TOPSIS method. Based on PEC3 and two optimization approaches, MOORA and TOPSIS, it is revealed that a larger tube diameter leads to better overall performance of the FTHEs.

Dynamic performance and wake flow characteristics of flow around a plate in a circular tube

The flow around a plate is a classic problem in fluid dynamics, with applications in fields such as aerospace, construction, energy, and chemical engineering. This paper studies the flow around a plate in a circular tube. The detached-eddy simulation method is used to calculate the unsteady flow near the plate, allowing the mechanical and wake flow characteristics of the plate to be analyzed at different open angles and the influence of the plate dome degree to be further investigated. The variation laws of the plate torque and pressure under the unsteady flow inside the circular tube are obtained. By comparing and analyzing the time-averaged velocity and instantaneous velocity fluctuations of the wake flow on the plate, the flow field distribution patterns under different structures and open angles are identified, and the unstable region of the wake flow is determined. The results presented in this paper provide a theoretical reference for applications involving the flow around a plate.

Numerical analysis of the heat transfer and pressure drop of a wavy fin and Kammtail tube condenser: An investigative study

The aim of this study was to numerically investigate the factors affecting the air-side performance of an innovative condenser for a domestic refrigerator. Novel condenser with a smooth Kammtail tube form was investigated due to delaying flow separation. For the first time in the literature, the kammtail form was used instead of round or ellipse geometry in a finned tube heat exchanger, and the advantages of this form was demonstrated both experimentally and numerically. This study incorporated design parameters such as air velocity (0.5, 0.7, 1 m/s), number of tube rows (4 or 5), tube arrangement (inline, staggered), fin pitches (5, 7, 10, 5–7, 5–10, 7–10 mm), and fin arrangement (homogeneous or hybrid). The findings indicated that, for identical fin types and fin surface areas, the proposed Kammtail shape of 3 × 6 mm exhibited 19% lower pressure drop and 9% higher heat-transfer coefficient compared to the original circular tube profile. Furthermore, decreasing the fin pitches resulted in a 32.9–97% increase in static pressure drop, while the heat-transfer coefficient decreased by about 4.7–11.7%. The examination of two new designs revealed a marked reduction of 7–20.4% in the static pressure drop, a decline in air flow rate of 30%, an increase in heat transfer of 5.6–12.2%, and a corresponding decrease in the volume of the condenser of 20%. The numerical results of this study are in good agreement with experimental results, with deviations of less than 10%.

Design optimization of the bamboo-inspired foam-filled tube for high-speed train collision energy absorption

This study first developed a novel bamboo-inspired foam-filled tube (BFFT) for potential application in high-speed trains, considering the practical use conditions. The BFFT was initially designed by mimicking the macro and micro characteristics of bamboo culms and understanding their axial crushing mechanical behavior. The key bionic parameters are drawn based on the crashworthiness indices of natural bamboos with various geometric sizes and growth ages. The numerical simulation model of the BFFT under axial impact load was established and verified using simplified super folding element (SSFE) theory and drop-weight experiments. A multi-objective optimization on the BFFT was conducted to find the optimal parameter alternative, integrating experimental design method of the optimal Latin hypercube, the response surface agent model and the non-dominated sorting genetic algorithm (NSGA-II). The crashworthiness performance of the optimized BFFT was compared with the initial design scheme, a conventional circular tube and other existing energy absorbers of rail vehicles. The results indicated that the EA, SEA and IPCF values of the optimized BFFT can be improved by 150.2 %, 63.3 %, and 48.5 %, respectively, when considering the single target requirement. In comparison to the initial design scheme and conventional circular tube, the SEA value of the final optimized BFFT increased by 44.7 % and 53.0 %, respectively. The proposed novel BFFT demonstrated a superior crashworthiness, providing inspiration for enhancing and optimizing passive safety performance of high-speed trains.

Numerical study of the melting rate enhancement of nano phase change material in a modified shell and tube heat exchanger

The current investigation employs numerical analysis using ANSYS Fluent software to explore the melting behaviour of phase change material (PCM) and nano-PCM in a semi-circular shell and tube heat exchanger, utilizing dual side heating for enhanced conduction and convection rates of heat transfer. The study incorporates aluminium oxide nanoparticles at volume concentrations of 2 %, 4 % and 6 % within paraffin wax and assessing their impact on melting and thermal energy storage rates. Notably, the 2 % nanoparticle volume concentration exhibits an enhanced storage rate as compared to higher concentrations. The increase in nanoparticle concentration from 0 % to 2 %, 2 % to 4 % and 4 % to 6 % results in percentage reduction in melting time of 21 %, 3.51 % and 2.8 % respectively. Semi-circular configuration shows significant improvement in the energy storage rate as compared to the circular triplex tube configuration. The maximum energy storage rate of PCM for the semi-circular and circular configurations is 1.15 kW and 1.04 kW respectively, marking a 9.56 % increase over the circular configuration. Moreover, the semi-circular and circular configurations using nano-PCM achieve a maximum energy storage rate of 1.19 kW and 1.14 kW, representing a 4.20 % increase over the circular configuration.

Numerical study of phase change heat accumulator with distribution of Hanoi tower-shaped fin

Hanoi tower-shaped fin distribution was proposed to improve the shell-and-tube phase change accumulator's ability for heat storage. Unlike the common annular fin group, the fin spacing of the Hanoi tower-shaped fin distribution is distributed in an arithmetic sequence, the fin length increases in a fixed proportion, and the fin group's overall position changes with the bottommost spacing. In this paper, the effects of no fin, uniform fin distribution, and Hanoi tower-shaped fin distribution on the melting process were compared and analyzed. The single-factor effects of bottommost spacing, spacing tolerance, and length ratio were analyzed for the Hanoi tower-shaped fin distribution. The solid–liquid phase change frontier, melting time, temperature distribution, and streamline distribution were simulated and studied for different fin structures. Fins' combined effects on heat conduction and natural convection were examined. The Hanoi tower-shaped fins' structural parameters were optimized by applying response surface methodology (RSM). The results indicated that the Hanoi tower-shaped fin distribution considerably enhanced the phase change material's (PCM) melting rate and uniformity in the vertical circular tube heat accumulator. The significance levels of factors affecting the whole melting time were spacing tolerance (d) < length ratio (k) < bottommost spacing (P1). Within a certain range, the larger the bottommost spacing was, the synergistic heat transfer effect of natural convection and heat conduction was better. According to the RSM optimization results, when the length ratio was 1.2, the fin's bottommost spacing was 17.82 mm, and the spacing tolerance was 3.38 mm, the model had the shortest melting time. Compared with the uniform fin distribution, the total heat storage time was reduced by 18.04 %.

Thermal performance enhancement of multiple tubes latent heat thermal energy storage system using sinusoidal wavy fins and tubes geometry modification

In this paper, performance enhancement of a shell and multiple tube latent heat thermal energy storage system (LHTESS) is numerically investigated by implementing sinusoidal wavy fins and different geometrical designs of heat transfer tubes. The annular space of the shell is filled with the paraffin wax RT35 as phase change material (PCM) and absorbs heat from hot water through the multiple tubes. With the constant total cross-section area of all tubes and fins as the constraint condition, the effect of tube number and tube shape incorporated with the proposed fins on the heat transfer properties of PCM during the melting process is evaluated. The computational results demonstrate that the sinusoidal wavy fins can improve the phase change efficiency compared to the conventional straight fins. The double-pitch sinusoidal wavy fins decrease the total melting time by 9.5% compared to the straight fins for the single-tube case. As the number of HTF tubes increased from one to four, the complete PCM melting time decreased by 38.3%. Geometrical design alterations of heat transfer tubes from circular to petal-shaped are proposed to further improve the thermal performance of multiple tubes LHTESS. The melting rate of PCM is accelerated with an increase in the number of petals. The petal tubes with nine petals can save the charging time up to 24 % in comparison with the circular tubes in a four-tube case with double-pitch sinusoidal wavy fins, and up to 57% compared to the base case with a single circular HTF tube and straight fins.

Experimental study of the influence of buoyancy on turbulent mixed convection in lead–bismuth eutectic flow under inclination conditions

The effects of inclination conditions on the heat transfer characteristics of lead–bismuth eutectic in a vertical circular tube are investigated experimentally. The results show that, compared to the vertical flow, inclination conditions result in lower wall temperature, increased fluid temperature and higher local heat transfer intensity of LBE. The effects of inclination conditions on the heat transfer characteristics of LBE flow decrease with increasing Reynolds number. Mixed convection determination criterion Y divides the heat transfer region into mixed convection and forced convection zones. The threshold value is around 2.0 × 10-3. The inclination conditions enhance the heat transfer characteristics only under mixed convection when the natural convection due to buoyancy force is more significant compared to the forced convection. The effects of inclination conditions increase with Y and inclination angle and decrease with Peclet number. The heat transfer correlation for LBE vertical flow cannot predict the Nusselt number under inclination conditions well. Therefore, a relevant empirical correlation for inclination conditions is developed. The research would be helpful for the mechanism analysis and engineering design when liquid metals are applied for motion conditions.

Multi-Output Regression Algorithm-Based Non-Dominated Sorting Genetic Algorithm II Optimization for L-Shaped Twisted Tape Insertions in Circular Heat Exchange Tubes

In this study, an optimization method using various multi-output regression models as model proxies within the NSGA-II framework was applied to determine the geometric parameters (P, W, D) of L-shaped twisted tape inserts for achieving the optimal overall heat transfer performance in a circular heat exchange tube. Herein, 4 multi-output regression models, namely, MOLR, MOSVR, MOGPR, and BPNN, were selected as proxy models and trained on a dataset containing 74 groups of data. The training results indicated that the MOGPR model, balancing high accuracy and low error conditions, exhibited moderate training times among the four algorithms. BPNN showed a comparatively lower comprehensive training effect, obtaining training accuracy close to that of the MOGPR algorithm but with approximately twice the training time. The worst fitting performance was gained with the MOSVR algorithm. Due to its fitting performance, the MOSVR algorithm was excluded from the subsequent NSGA-II model proxy. Through multi-objective optimization with NSGA-II, the optimal structural dimensions for three sets of L-shaped twisted tape inserts were obtained to achieve the best overall heat transfer efficiency within the tube.

Experimental Investigation of Heat Transfer and Pressure Drop Performance of a Circular Tube with Coiled Wire Inserts

This paper evaluates the thermo-hydraulic performance of a coiled wire passive insert for internal turbulent flow through a circular copper tube test section in an in-tube exchanger. Experiments were carried out using water as the working fluid with Reynolds number ranging from 8000 to 32000. The experimental setup was validated for Nusselt number and friction factor with well-established equations for plain tubes. The average Nusselt number ratios (Nua/Nup) and the friction factor ratios (fa/fp) for the augmented tube case over the plain tube case are reported to range from 1.55 to 1.38 and from 1.513 to 1.583, respectively. The average performance ratios considering equal pumping power criteria are also reported and found in the range of 0.846 to 0.921. The study concludes that coiled wire inserts are suitable for heat transfer augmentation applications where pumping power is of minor concern.

Streamwise dispersion of soluble matter in solvent flowing through a tube

For the dispersion of soluble matter in solvent flowing through a tube as investigated originally by G.I. Taylor, a streamwise dispersion theory is developed from a Lagrangian perspective for the whole process with multi-scale effects. By means of a convected coordinate system to decouple convection from diffusion, a diffusion-type governing equation is presented to reflect superposable diffusion processes with a multi-scale time-dependent anisotropic diffusivity tensor. A short-time benchmark, complementing the existing Taylor–Aris solution, is obtained to reveal novel statistical and physical features of mean concentration for an initial phase with isotropic molecular diffusion. For long times, effective streamwise diffusion prevails asymptotically corresponding to the overall enhanced diffusion in Taylor's classical theory. By inverse integral expansions of local concentration moments, a general streamwise dispersion model is devised to match the short- and long-time asymptotic solutions. Analytical solutions are provided for most typical cases of point and area sources in a Poiseuille tube flow, predicting persistent long tails and skewed platforms. The theoretical findings are substantiated through Monte Carlo simulations, from the initial release to the Taylor dispersion regime. Asymmetries of concentration distribution in a circular tube are certified as originated from (a) initial non-uniformity, (b) unidirectional flow convection, and (c) non-penetration boundary effect. Peculiar peaks in the concentration cloud, enhanced streamwise dispersivity and asymmetric collective phenomena of concentration distributions are illustrated heuristically and characterised to depict the non-equilibrium dispersion. The streamwise perspective could advance our understanding of macro-transport processes of both passive solutes and active suspensions.

Effects of horizontal self-rotation on flow and heat transfer of supercritical n-decane in regenerative circular/rectangular cooling channels

Concerning the rotation flight of a hypersonic vehicle centered on its geometric axis, the rotational flow and heat transfer characteristics of supercritical n-decane in horizontal circular and rectangular tubes were comprehensively analyzed based on numerical simulation. The computational domain was established and the corresponding governing equations of mass conservation, momentum conservation, and energy conservation were mathematically formulated as well were the thermophysical properties and boundary conditions. A procedure for setting up the numerical simulation was finally implemented. A mesh independence study in the case of a rotating speed of 300 rpm and a turbulence model study based on a stationary/swinging tube were comprehensively conducted and the RANS model was well validated. For the circular tube, the wall temperature distribution trend along the flow direction is similar but the magnitude is not uniform. Also, the fluid temperature near the upper wall is larger than that in the vicinity of the lower wall, i.e., the relaminarization plays an essential role in this phenomenon. The velocity difference near the wall can be weakened by the centrifugal force. For the rectangular tube, the velocity magnitude and temperature distribution are found to be greatly affected by the rotation (i.e., centrifugal force). The relative temperature magnitude near the upper and lower walls will be reversed at a rotation speed of n = 100–500 rpm. Subsequently, a symmetrical temperature distribution can be observed once the speed increases to a certain value (e.g., n = 700–900 rpm). In summary, the centrifugal force plays a more important role in a rectangular tube than in a circular tube.

Experimental study on axial compressive behavior of steel tube‐reinforced recycled aggregate concrete composite columns with steel bars

AbstractIn this paper, five specimens were designed to test under monotonic static loading to study the axial compression performance of steel tube‐reinforced high‐strength recycled aggregate concrete composite columns with steel bars. The design parameters for these specimens include the type of concrete, the sectional shape of the steel tube (circular or square), and the internal structure of the core column, specifically the presence or absence of cross‐shaped tie bars in the square steel tube. The effects of different parameters on the axial load–displacement curve, bearing capacity, and ductility were analyzed. The test results show that the failure of all specimens was caused by the concrete cover spalling of outer reinforced concrete, which occurred after the longitudinal strain of the steel tube exceeded the yield strain. The ultimate bearing capacity of the recycled aggregate concrete (RAC) specimen is higher than that of the natural aggregate concrete (NAC) specimen, but the latter has a more robust deformation performance. Furthermore, under the condition of the same steel tube cross‐sectional area and similar material strength, the bearing capacity and deformation capacity of specimens with circular steel tubes are higher than those of specimens with square steel tubes. A similar conclusion was also obtained for square steel tube specimens with cross‐shaped tie bars. Finally, four international design methods were applied to estimate the axial compression capacity of 40 composite columns, as detailed in this paper and other sources.

Strength and Deformation of Concrete-Encased Grouting-Filled Steel Tubes Columns Exposed to Monotonic Quasi-Static Loading Conditions

This study aimed to evaluate the effectiveness of a novel concrete-encased column (CE) using small circular steel tubes filled with cementitious grouting material (GFST) as the primary reinforcement instead of traditional steel bars. The research involved three different types of reinforcement: conventional steel bars, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars, and concrete-filled steel tubes with the same reinforcement ratio as steel bars. Twenty-four circular concrete columns were tested and categorized into six groups based on the type of reinforcement employed. Each group comprised four columns, with one subjected to concentric axial load, two subjected to eccentric axial load (with eccentricities of 25 mm and 50 mm, respectively), and one tested under lateral flexural loads. To validate the experimental results, finite element (FE) analysis was conducted using ABAQUS software version 6.14. The experimental findings for concentric load reveal that columns with the second type of reinforcement, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars exhibited a failure load 19% lower than those with steel bars, while columns with the third type of reinforcement, concrete-filled steel tubes with the same reinforcement ratio as steel bars achieved a failure load 17% greater than the traditional steel bars. The FE analysis demonstrates good agreement with the experimental outcomes in terms of ultimate strength, deformation, and failure modes.

Collapsing behavior of spark-induced cavitation bubble in rigid tube

The phenomenon of cavitation within tubes is a common scenario in the fields of medicine and industry. This paper focuses on the effects of rigid circular tube length, diameter and the distance of bubble - tube port on the behavior of bubble in tube. The low-voltage discharge technique was utilized to induce a cavitation bubble in deionized water. The effects of rigid tube lengths, diameters, and bubble-tube port distances on the morphology of bubbles are observed using high-speed camera. It has been found that as the length of the rigid tube increases, so does the period, and this effect is more pronounced in tubes with smaller diameters. Conversely, the cavitation bubble period decreased and then stabilized as the tube diameter increased, the ratio of tube radius and the bubble radius exceeds 4.8, the period of bubble in tube is similar to that of bubble in free field. Further analysis of the influence of tube characteristics on microjets reveals that a pair of oppositely microjets were formed along the tube axis by the bubble near the midpoint of the tube axis. Moreover, when the non-dimensional tube length η < 3.5, the increase tube diameter results in a decrease microjet velocity. It has also been observed that as the bubble gradually approaches the interior of the tube, the velocity of microjets directed inward decreases. Additionally, the smaller the diameter of the tube, the greater the bubble-tube port distance required for the microjets to reach the same level of velocity as bubble near the center of the tube axis. These findings hold theoretical implications for improvement of targeted drug delivery efficiency in medicine and enhance the operational efficiency of inertial micropumps in industries.

Gas-liquid two-phase flow pressure drop in flattened tubes: an experimental and numerical study

Experimental, numerical and empirical research is carried out on pressure drop features of air-water two-phase flow in horizontal flattened tubes. Circular tubes of 10.5 mm I.D. made of copper were successively flattened into inner heights of 9, 8, and 6 mm (AR=1.27, 1.5, and 2.2, respectively). The experiment operation conditions were 200, 500, and 1000 kg/m2s for mass velocity, 6, 8, 10 LPM for flow rate, and 0 to 0.005 for gas quality. Also, the pressure drop for R134a and R410A was estimated numerically using ANSYS Fluent. The simulation test condi-tions were for vapor quality of 0.1 to 0.9 and saturation temperature of 40°C, while the condi-tions for mass velocity and flowrate are taken as that of the experiment test. The experimental data were examined to see how different factors affect on the pressure gradient. According to the outcomes and as compared to the circular tube, the pressure gradient was raised up to 27%, 95%, and 218% for tubes flattened with aspect ratio of 1.27, 1.5, and 2.2, respectively. More-over, the pressure drop for either air-water or refrigerant fluids is increased dramatically with increasing flow rate, but it decreases with increasing vapor quality. When compared to known circular tube correlations, a good agreement was achieved. Finally, the minimum difference between the experimental, numerical, and correlated results was less than 3% for gas quality of 0.0048 and aspect ratio of 2.2.

Flexural Performance of a Continuous Circular Tube Girder Bridge

This study introduces a continuous pedestrian-bridge design utilizing a circular tube girder and brackets for extended spans. The flexural performance evaluation in the negative moment region focuses on the support section of the continuous pedestrian bridge. In this regard, a full-scale test unit of the negative moment region was fabricated for a loading test. The test unit consists of a circular steel-tube girder, loading plates, vertical steel plates, and support. Subsequently, a finite element analysis (FEA) was employed to compare with the loading test results. The experimental and FEA results showed that the stresses in the members of the proposed pedestrian bridge are within the allowable stresses under service load. However, local buckling was observed in the circular steel-tube girder adjacent to the vertical steel plate under ultimate loading. To prevent the local buckling in the girder and improve the flexural performance of the negative moment region, a parametric study was performed by increasing the filling ratio of concrete inside the girder. The load–deflection relationship of the parametric study indicates that filling the negative moment region of a circular steel tube with concrete has a structural effect. Consequently, based on these results, an optimal filling ratio for the proposed bridge is suggested.

Effects of flow direction and thermal short-circuiting on the performance of coaxial ground heat exchangers

The effects of flow direction and thermal short-circuiting on the performance of coaxial ground heat exchangers are studied by finite-element simulations, performed through COMSOL Multiphysics 3.4 (©Comsol, Inc.). The real 2-D axisymmetric unsteady heat conduction and convection problem is considered. The distribution of the fluid bulk temperature in the inner circular tube is determined by means of the “weak boundary form” boundary condition available in COMSOL Multiphysics; the laminar convective heat transfer in the outer annular passage is simulated directly. Two Coaxial Ground Heat Exchangers (CGHEs) with the same length but different cross sections are examined; moreover, two values of the ground thermal conductivity, as well as two materials for the inner tube wall are considered. The results point out that the annulus-in flow direction (fluid inlet in the outer annular passage) is more efficient than the center-in flow direction (fluid inlet in the inner circular tube) and that the effect of short circuiting is not very important, if the annulus-in flow direction is employed. Indeed, with this inlet configuration the energy loss for thermal short-circuiting is less than 1% for time intervals longer than 1 hour.