Elliptical Tube Research Articles

Design and error analysis of simple terahertz high birefringence microstructured fiber

Abstract High birefringence fibers are significant in the terahertz technology field, serving as waveguides for terahertz transmission. They are applicable in various fields such as communication, imaging. Integrating metal microstructures into polymer microstructured optical fibers can effectively modulate the transmission characteristics of the fiber, enhancing birefringence and reducing loss, thereby achieving better performance compared to traditional single-material fibers. This paper presents a structurally simple terahertz high birefringence microstructured fiber, where the introduction of gold microstructures enhances the birefringence of fiber, with a maximum birefringence of up to 1.089 × 10-2. We also discuss several manufacturing errors that may occur during the fiber fabrication process. The results indicate that the designed fiber exhibits significant manufacturing tolerance. Variations in the thickness and angle of the gold microstructures, as well as the angular offset of the elliptical cladding wall, peak-to-valley errors, and changes in the aspect ratio of the elliptical tube, have relatively minor effects on the overall transmission performance. The research findings provide insights for designing subsequent high birefringence terahertz fibers, thereby propelling advancements in this field. They offer a theoretical basis for the preparation of related microstructured fiber structures and provide valuable understanding for optimizing fiber manufacturing processes.

Experimental and numerical investigation of the thermal - hydraulic performance of flow inside helical coil elliptic tubes

Helical coil tubes are essential in a variety of engineering applications due to their improved heat transfer and compact shape. The current study presents an experimental and numerical investigation of geometrical optimization for helical coil elliptic tubes. Four distinct coil pitch values are examined with a constant perimeter for all geometries and three aspect ratio values (1, 0.75, 0.5) utilizing water as the working fluid across varying the volume flow rates. The helical coil has the same surface area as the tube for each coil. The numerical simulation is conducted using the ANSYS FLUENT CFD software (Version 19.2). The experimental and numerical results indicate that the increase in heat transfer due to an increase in mass flow rate is significantly greater than the improvement gained by changing the aspect ratios. Increasing the volume flow rate to 3 L/min significantly improves the average heat transfer coefficient, with a 66.6 % increase found at a maximum coil pitch of 0.08 m and an aspect ratio of 0.5. Furthermore, a helical coil with an aspect ratio of one (circular cross-section) exhibits the best compromise between pressure drop penalty and heat transfer enhancement, resulting in the greatest hydraulic thermal performance parameter.

Numerical simulation study of boiling heat transfer of R290 flow in horizontal microtubes

Abstract R290 is considered to be an excellent alternative refrigerant for domestic air conditioners in the future. In this paper, CFD numerical simulation was used to obtain the flow field distribution of R290 in a micro-fine circular tube with an inner diameter of 2mm under a specific range of working conditions, and the effects of saturation temperature, mass flow density, heat flow density and tube type on the boiling heat transfer characteristics of R290 tube were investigated. The results show that the boiling heat transfer coefficient increases with the increase of saturation temperature, and the maximum value of the heat transfer coefficient increases by 8.1% when the saturation temperature increases from 284K to 286K. The boiling heat transfer coefficient increases with the increase of mass flow density, and the maximum value appears in the medium dryness range. The boiling heat transfer coefficient in the tube increases and then decreases when the heat flow density increases from 10 kW/m2 to 20 kW/m2 and increases faster at high heat flow density conditions. In addition, compared with the circular tube, the boiling heat transfer coefficient in the elliptical tube with an aspect ratio of 1.56 increases by 2.78% for R290 under the same flow area.

Experimental study on the influence factors of falling film heat transfer characteristics outside different types of horizontal tubes

An experimental setup was established to analyze the performance of a spiral wound heat exchanger applied to natural gas liquefaction. The boiling behavior of subcooled flow over a small diameter, non-round, horizontal tube was investigated using n-pentane as the working fluid. The effects of flow rate, heat flux, fluid inlet temperature and tube spacing on heat transfer performance were investigated. Based on the experimental conditions of this study, the results indicate that: (1) raising the Reynolds number can effectively enhance the heat transfer coefficient; (2) the increasing in heat flux also has a positive impact on heat transfer performance, but the extent of which is related to the Reynolds number; (3) increasing the tube spacing resulted in higher heat transfer coefficients; (4) under the same working conditions, the heat transfer performance of non-round tubes is higher than that of round tubes; (5) correlation equations were developed to calculate the Nu for smooth, round, elliptical, and egg-shaped tubes. The predictions made by these correlation equations deviated by less than 10 % from the experimental results for the entirety of the experimental conditions.

Free energy and extension of stiff polymer chains confined in nanotubes with diverse cross-sectional shapes

The statistical mechanics of stiff polymer chains confined within narrow tubes is a foundational topic in polymer physics, extensively analyzed in prior research. For cylindrical, rectangular, and slit-like confinements, the chains’ free energy and extension adhere to a scaling law consistent with the Odijk theory. While this scaling law may not apply to tubes with different cross-sectional geometries, there is a lack of research examining the behavior of stiff chains in tubes with intricate cross-sectional shapes. In this study, we investigate the partition function of a stiff chain confined within an elliptic tube using the path integral approach, deriving a deflection length in a concise closed form through dimensional analysis. This length scale facilitates straightforward expressions for the chain's free energy and extension. Notably, we discover a shape-independent property of these expressions applicable to tubes with a wide variety of cross-sectional geometries. Extensive numerical simulations are conducted using a biased chain-growth Monte Carlo method, incorporating the Pruned and Enriched Rosenbluth algorithm, to validate the theoretical predictions on the confinement free energy and extension of chains in tubes with differing shapes.

Numerical investigation on a novel milli-sized heat sink equipped by twisted elliptical tubes

Thermal management in some small chemical reactors is essential to achieve a final high-quality product and heat sinks can play a remarkable role in dissipating heat from such systems. In this regard, this study attends to evaluate the conjugate heat transfer problem in a heat sink equipped by twisted elliptical tubes (TETs). The effects of significant parameters such as Reynolds number (Re = 250, 350, 500, 700 and 950) and twist ratio (TR = 2.5, 5 and 10) on hydrothermal and thermodynamics performance of the novel heat sink are investigated. The swirling flow is the main reason of fluid particles migration from hot surface to cold one and vice versa, leading a better heat transfer occurs at the expense of not significant pressure loss augmentation. The results revealed that the TETs are responsible of more wall temperature uniformity and avoids generating hot spots. Compared with plain elliptical tubes, the presence of TETs inside heat sink improves the heat transfer rate and enlarges the pressure drop by 1.08–2.03 times and by 1.02–1.92 times, respectively. In addition, the TETs decrease the entropy generation rate inside heat sink and the best value of second law efficiency is about 35 %, detected at TR = 2.5 and Re = 250.

Experimental Analysis and Design of 3D-Printed Polymer Elliptical Tubes in Compression

Experimental Analysis and Design of 3D-Printed Polymer Elliptical Tubes in Compression

Falling film hydrodynamics of horizontal elliptical tube under column flow

Flow characteristics of falling film around a horizontal elliptical tube under column flow were numerically investigated with the volume of fluid method. The three-dimensional film thickness distributions for elliptical tubes with three ellipticities and two arrangements (the major axis oriented vertically and the major axis oriented horizontally) were captured. This investigation also considered the effects of spray Reynolds number and contact angle on film thickness distribution. A comparison between elliptical tube and circular tube was also performed under typical spray Reynolds number of 258 and tube spacing of 20 mm. The results show that the tube shape has a great influence on the film thickness and flow behaviors: The liquid film formed outside the elliptical tube with the major axis oriented vertically is thinner and more uniform than that of the circular tube. Conversely, the film on the elliptical tube with the major axis oriented horizontally is thicker and more non-uniform than that of the circular tube. The increasing of Reynolds number generally increases film thickness, particularly in the crest region. Under incompletely wetted condition, the increasing of ellipticity decreases the liquid film coverage rate around the tube. In addition, a correlation for predicting the film thickness around elliptical tubes was proposed.

Nested hollow-core anti-resonant fiber with elliptical cladding for 2 µm laser transmission

In this work, a nested hollow-core anti-resonant fiber (HC-ARF) with an elliptical cladding for high-power lasers for 2 µm laser transmission was proposed and theoretically investigated. The dual-layer elliptical tubes nested within the fiber enable the low-loss single-mode transmission. The finite element method (FEM) was employed to analyze and optimize the structure of fiber, with a total loss of less than 5 × 10−4 dB/m across the wavelength range of 1920nm to 2040nm. An extremely low loss of 1.22 × 10−5 dB/m at 1948nm was realized. A high-order mode extinction ratio (HOMER) exceeding 3 × 104 was maintained across a significant bandwidth and a size tolerance ratio under 15%. Furthermore, a low loss of 5 × 10−5 dB/m at 1948nm with a bending radius over 15 cm was obtained, indicating high bending resistance. It was demonstrated that the proposed fiber has exceptional transmission performance for 2 µm laser transmission.

Numerical investigation of twisting technique on thermal and hydraulic performance of elliptical tube exposed to concentrated nonuniform heat flux

Numerical investigation of twisting technique on thermal and hydraulic performance of elliptical tube exposed to concentrated nonuniform heat flux

A parametric optimization framework for fin-and-tube heat exchangers based on response surface methodology and artificial intelligence

This study presents a numerical investigation and provides a novel framework for the rapid parametric optimization of attack angles (α) and aspect ratios (e) in plate fin-and-tube heat exchangers (PFTHEs) featuring elliptical tubes. The methodology incorporates three-dimensional numerical simulations, response surface methodology (RSM), backpropagation neural network (BPNN), and Entropy-VIKOR. The study focuses on a PFTHE with a single elliptical tube, varying the attack angles (α) from −30° to 0° in 5° increments and the aspect ratios (e) from 0.4 to 1.0 in a step of 0.1. Air velocities (u) range from 0.4 to 3.2 m/s with an interval of 0.2 m/s, corresponding Reynolds number from 200 to 2200. The results indicate that using elliptical tubes reduces Δp and enhances heat transfer capacity, with the most significant improvements at an e of 0.4. Exponential relationships between dimensionless parameters Nu or f and Re are established for different range of α at specific e values. The synergistic effect of e, α, and Re or u on PFTHE performance is confirmed through RSM and BPNN analysis. Their R2 values are no less than 0.896 and reach a maximum of 0.998, indicating excellent predictive accuracy. Utilizing Entropy-VIKOR method, the framework identifies a suitable design solution with e = 0.6, α = -20°, and u = 3.2 m/s. This solution exhibits a 5 % increase in h and a 58 % reduction in Δp relative to the corresponding circular tube. The study provides specific expressions relating design variables to thermal–hydraulic behavior and indicates carefully selecting the α and e can improve the overall performance. In summary, these findings have significant implications for reducing optimization design period for PFTHEs with small tube diameters.

An Experimental Study of Porous Coated Hybrid Elliptical Tubes in Phase Change Heat Transfer

Abstract Porous coating over hybrid elliptical tubes are presented as the state-of-the-art in heat transmission during phase change maintaining its wide-ranging applicability. The saturated nucleate boiling heat transfer performance of porous coated hybrid elliptical tubes exposed to varying orientation angles is compared to that of conventional circular tubes in an accompanying experimental study conducted at atmospheric pressure. Four different copper porous coating thicknesses are varied from 34 µm to 128 µm with a heat flux range of 14.87-94.82 kW/m2. A greater coefficient of heat transfer is claimed for the coated hybrid elliptical tube compared to the uncoated circular tube, regardless of the orientation angle or coating thickness. The uncoated and porous coated hybrid elliptical tube provided a greater coefficient of heat transmission at 0° than at 90°. At 0° orientation angle, the coating with a thickness of 66 µm improve heat transmission by 1.27 - 1.5 times than that of uncoated surface while minimum enhancement about 1.16 - 1.24 times is found in 34 µm. Furthermore, a dimensionless semi-empirical correlation is established to predict own heat transmission coefficient findings within ±12%, independent of coating thicknesses and orientation angles.

Development of a Prototype Non-volatile Heating Circuit with Pulsating Mode

The emergence of global energy crisis makes energy saving technology become the key technology of sustainable development. Enhanced heat transfer technology can improve the efficiency of various heat transfer equipment and reduce the weight and volume, which plays a vital role in energy saving and sustainable economic development. In recent years, based on theoretical and experimental research, Chinese researchers and technicians have developed many new technologies to strengthen heat transfer, such as cross-scaled elliptic tube, discontinuous double-inclined inner rib tube, spiral groove tube, spiral groove tube, inner fin tube, twisted elliptic tube and so on. Among them, the pulsating heat transfer technology is an efficient and energy-saving means that can significantly strengthen the convective transport operation and improve the heat transfer effect. Through fluid pulsation or the vibration of the heat transfer pipe, the technology can remove the dirt deposited on the heat exchange surface, reduce the thermal resistance of the dirt, and improve the performance and life of the heat exchanger. It is widely used in the cooling of electronic components, automobile turbines, and the utilization of atomic energy in Marine environment. Firstly, the construction scheme of the experimental device is proposed, and the working principle of the experimental device is described in detail. The complex impedance, frequency function, amplitude-frequency characteristic and phase-frequency characteristic are obtained by mathematical transformation of power supply circuit. Finally, the frequency response of the circuit is constructed.

Negative curvature fiber (NCF) polarization filter with large polarization loss ratio and ultralow loss in the terahertz range

A high-performance polarization filter based on the negative curvature fiber (NCF) with an asymmetric cladding structure is proposed and analyzed. The resonant effects of the x-polarization fundamental mode (XPFM) of the NCF are enhanced by the single-layer semi-elliptical tubes with a gradient wall thickness in the x-axis direction, while the anti-resonant effects of the y-polarization fundamental mode (YPFM) are strengthened by the nested double-layer elliptical tubes in the y-axis direction. The optimized structure shows a polarization loss ratio of greater than 100 in the range of 0.98–1.02 THz in addition to propagation losses of 0.94 dB/m and 7.43 × 10−4 dB/m at 1 THz for XPFM and YPFM, respectively. A polarization loss ratio of 1,276 is achieved and the polarization loss ratio is 6,321 at 0.98 THz. Our results show that the NCF polarization filter delivers better performance than recently reported filters in the terahertz band and the results reveal a new strategy to design high-performance polarization filters.

Damped kink motions in a system of two solar coronal tubes with elliptic cross sections

Aims. This study is motivated by observations of coordinated transverse displacements in neighboring solar active region loops, addressing specifically how the behavior of kink motions in straight two-tube equilibria is impacted by tube interactions and tube cross-sectional shapes. Methods. We worked with linear, ideal, pressureless magnetohydrodynamics. Axially standing kink motions were examined as an initial value problem for transversely structured equilibria involving two identical, field-aligned, density-enhanced tubes with elliptic cross sections (elliptic tubes). Continuously nonuniform layers were implemented around both tube boundaries. We numerically followed the system response to external velocity drivers, largely focusing on the quasi-mode stage of internal flows to derive the pertinent periods and damping times. Results. The periods and damping times that we derive for two-circular-tube setups justify the available modal results found with the T-matrix approach. Regardless of cross-sectional shapes, our nonuniform layers feature the development of small-scale shears and energy accumulation around Alfvén resonances, indicative of resonant absorption and phase mixing. As with two-circular-tube systems, our configurational symmetries still make it possible to classify lower-order kink motions by the polarization and symmetric properties of the internal flows; hence, such motions are labeled as S​x and Ax. However, the periods and damping times for two-elliptic-tube setups further depend on cross-sectional aspect ratios, with Ax motions occasionally damped less rapidly than S​x motions. We find uncertainties up to ∼20% (∼50%) for the axial Alfvén time (the inhomogeneity lengthscale) if the periods (damping times) computed for two-elliptic-tube setups are seismologically inverted with canonical theories for isolated circular tubes. Conclusions. The effects of loop interactions and cross-sectional shapes need to be considered when the periods, and in particular the damping times, are seismologically exploited for coordinated transverse displacements in adjacent coronal loops.

Investigation of thermo-hydraulics performance and vapour bubble behaviour over 5×3 smooth hybrid elliptical tube bundle under saturated cross flow boiling condition - An experimental study

In the current experimental study, the thermal-hydraulic behaviour of a novel smooth hybrid elliptical tube bundle (TB) is compared with the performance of the corresponding conventional smooth circular TB. The smooth hybrid elliptical tube, made up of AISI-304, is in the form of a conventional elliptical shape from the outside but a circular shape from the inside. The operating parameters encountered in the current investigation are Heat Flux (10–75 kW/m2), Mass Flux (19–100 kg/m2s), and pitch-to-diameter ratio (P/D) (1.25 - 1.95). The outcomes show that the thermal-hydraulics performance in the case of a smooth hybrid elliptical TB is higher than a conventional smooth circular TB. The augmentation in the heat transfer coefficient obtained with a smooth hybrid elliptical TB is limited to 12 % in the entire range. The pressure drop improvement is found to be 48 % to 120 % equated to the conventional smooth circular TB. However, the effective performance of the smooth hybrid elliptical TB measured in terms of H/P ratio (H/P = heat transfer coefficient/total pressure drop) is found to be in the range of 0.3–2.5 compared to the conventional smooth circular TB which is in the range of 0.2–1.1. This is evident from the present experimental study that the employment of the elliptical TB will lead to lower pumping power than a conventional smooth circular TB owing to its lower pressure because of the streamlined surface. The obtained two-phase heat transfer enhancement efficiency based on enhancement factor and pressure drop penalty factor showed a higher gap TB (P/D = 1.95) has higher performance. Moreover, for the first time, an effort has been made to analyze the physics associated with vapor bubble dynamics and interaction along the height of the smooth hybrid elliptical TB.

Thermal storage performance of a novel shell-and-tube latent heat storage system: Active role of inner tube improvement and fin distribution optimization

This study presents a numerical analysis of the melting process in a shell-and-tube latent heat thermal energy storage (LHTES) system, featuring a twisted elliptical inner tube with annular fins. Utilizing paraffin as the phase change material (PCM) and water as the heat transfer fluid (HTF), this research examines the impact of varying twist degrees, fin quantity and fin distribution on the system's thermal performance during melting process. The analysis of the melting process includes complete melting time, temperature, and the contour of the solid-liquid interface. Notably, the study identifies that both fin quantity and distribution play a significant role in the melting process. The findings indicate that an optimal configuration, comprising a 720° twisted degree, 11 fins, and a base number a of 0.80, enhances the melting efficiency of the LHTES system by 156.44 % and reduces ineffective heat loss by 41.36 %. These results highlight the potential advantages of the twisted elliptical inner tube structure and propose an innovative approach with an exponentially non-uniform fin distribution, marking an advancement in the field of thermal energy storage.

Optimization study on acid condensation and anti-corrosion performance of 3-D finned tube heat exchangers

Low-temperature acid corrosion on flue gas heat exchanger surfaces seriously reduces the stability, safety, and economy of equipment operation. Efficient strategies are urgently required to improve the anti-corrosion performance of heat exchangers. In present paper, a three-dimensional heat and mass transfer model integrating the acid dew point, acid condensation rate, and solution concentration was developed to predict the corrosion characteristics on the surfaces of 3-D finned tube heat exchangers. Firstly, a comparative analysis of acid condensate characteristics for 3-D finned tubes with different configurations was performed. The results showed that the elliptical tube effectively improves the distribution uniformity of acid condensate rate and promotes anti-corrosion performance. Then, the effects of five operating parameters (gas temperature, gas velocity, water vapor concentration, acid vapor concentration and wall temperature) on overall corrosion characteristics were systematically examined in terms of acid dew point, condensation rate and solution concentration using single-factor and orthogonal analysis, and the effect order of each factor was determined. Furthermore, optimization analysis of anti-corrosion performance was conducted based on the orthogonal results, and the optimum working conditions (water vapor concentration below 11.8% and wall temperature of 347 K to 355 K) are recommended. This research can provide theoretical guidance for the anti-corrosion designation and optimization of 3-D finned tube exchangers.

Investigation of Thermal Performance of Heat Exchangers of Inclined-Elliptic-Tube Bundle

Passive performance improvement of heat exchangers is cost-effective and crucial for energy efficiency as well as sustainability of thermal systems. In this paper, an investigation is presented on a compact configuration of heat exchanger composed of a bundle of inclined elliptical tubes. The effect of geometrical parameters on the thermal performance of the heat exchanger is investigated for two tube arrangements i.e. inline and staggered configurations. These parameters include longitudinal (SL/a = 3 to 6) and transversal (ST/a = 2.5 to 5.5) pitch ratios. A CFD commercial code is used for simulation of heat transfer and fluid flow. Computations are performed for the Reynolds number range Re = 300-1500. The outcomes indicate higher performance of the staggered arrangement when compared with the inline inclined tubes. The best thermal performance is observed for a staggered configuration with SL/a = 6, ST/a = 5.5 at Re = 1500. Furthermore, correlations are provided for Nusselt number for heat exchangers of inclined elliptic tubes.

Employing uniform and non-uniform inner twisted elliptical tubes in a double-pipe heat exchanger

Turbulent hydrothermal characteristics in a double-pipe heat exchanger with an internal twisted elliptical tube (TET) are investigated. The impacts of aspect ratio (AR = 1.4–2), uniform twist pitch (p = 100 mm-400 mm), and non-uniform twist pitch (five cases) on flow stream characteristics and heat transfer of parallel and counter-flows are investigated numerically. Utilizing a TET with a non-uniform twist pitch as an innovative approach yields noteworthy results, particularly in contrast to the traditional use of TETs with uniform twist pitch, owing to the longitudinal asymmetry. The outcomes depict that the pressure drop and heat transfer augment as the uniform twist pitch declines and the AR rises. The counter-flow has a more significant average Nusselt number than the parallel-flow by about 2–4 % without increasing the friction factor. Still, in some cases of non-uniform twist pitch, the average Nusselt number of the parallel flow is even 4 % higher than the counter-flow. The case with p = 100–200–400 mm (three parts with various twist pitches) and parallel-flow exhibits the most significant performance evaluation criterion (PEC) among the non-uniform twist pitch. As the aspect ratio increases from AR = 1.4 to AR = 2, the PEC factor in the counter-flow mode increases; however, there is an out-of-trend point at AR = 2 for the parallel-flow mode. The PEC factor augments about 8.47 % and 6.16 % for the counter-flow and the parallel-flow modes, respectively. The growth of TET twist pitch by 300 % reduces PEC by about 13.3 % in the counter-flow. The most significant PEC value is 1.166, which belongs to the case with the counter-flow condition and p = 100 mm.