Round Tube Research Articles

FEM simulation optimization and slab method on rotating extrusion of thin-walled round tube under constant shear friction

This research considering constant shear friction is to explore the rotating extrusion of thin-walled round tube based on FEM simulation and slab method, and compares the results of both models to realize the variations and acceptance. The effective stress, the effective strain, the velocity field, the average thickness, the extrusion force, and the extrusion torque can be obtained from this study. It reveals the average thickness obtained from rotating extrusion is more uniform than that obtained from no rotating extrusion. The FEM optimization for extrusion force can be combined with Taguchi method, the L934 orthogonal table considers the four control factors which are outer diameter to thickness ratio, frictional factor, rotating angular velocity, half die angle, and three levels. The ranking of influence factors and the optimization combination can be obtained from FEM simulation optimization. Eventually the extrusion force between FEM simulation and slab method is compared under rotating angular velocity, 0.2 rad/s, the maximum error is 10.49 % and the minimum error is -0.29%; the average error is 4.16%, so the trend is in good agreement each other. Therefore, the both models can be verified.

Development of map-based models for the performance characterization in a new prototype of Dual Source Heat Pump

This paper presents the development of accurate map-based models for characterizing a new Dual Source Heat Pump prototype. This unit includes three braze plate heat exchangers and a round tube fin heat exchanger, allowing the unit to select different operating modes such as heat pump, chiller, and domestic hot water production using as source the ground or air. Therefore, due to the hybrid typology of this unit and the possibility of reversing the cycle, this work covers the main heat pump and refrigeration equipment technologies currently available on the market (air source and ground source units). The modeling strategy selected has been to provide several polynomial expressions to predict the performance of these units, i.e., compressor energy consumption and condenser and evaporator capacities. This approach allows obtaining accurate, compact, and easy-to-implement models for developing dynamic models of more complex systems where this type of unit – the heat pump – is an integrated part of the system. Currently, a clear example of this modeling strategy can be found in characterizing one of the main components installed in these machines, the compressor. The AHRI-540 standard specifies a polynomial model as a function of evaporating and condensing temperatures. In this sense, for the characterization of heat pumps, the polynomials developed depend only on the unit’s external variables, so they can be useful in many scenarios, obtaining direct feedback on the heat pump performance when developing a dynamic model to optimize system control strategies or to develop techno-economic studies. In this case, the hybrid typology of this unit makes it particularly relevant to optimize the control to manage the type of source to be used (air or ground), allowing the development of a more efficient and sustainable technology by selecting the most adequate source in terms of performance. This study focuses on obtaining the polynomial expressions that minimize the number of terms while simultaneously minimizing prediction error. By carefully selecting the most significant terms and suitable transformations in the characterized variables, the goal is to prevent overfitting, minimize potential extrapolation or interpolation errors and obtain polynomial expressions that can be fitted with small experimental samples. For this purpose, a detailed model implemented in a commercial software for heat pump characterization has been used, with which a large number of simulation results were generated. These simulation results include a fine meshing working map of the unit that allowed us to analyze the relationships between the characterized and external variables.

Numerical Investigation of the Effect of the Wall Properties on Downward Mercury Flow and Temperature Fluctuations in a Vertical Heated Pipe under a Transverse Magnetic Field

The work is motivated by the need to study the effect of abnormal quasi-periodic high-amplitude temperature fluctuations in a liquid metal flow in pipes and channels, which arise under conditions close to those specific for liquid metal (PbLi alloy, etc.) hydrodynamics and heat transfer in blankets of tokamak fusion reactors. Such temperature fluctuations in the cooling channels of the fusion reactor blanket pose a threat to the strength of the channel walls. The influence of the physical properties of the channel walls and potential fouling of their inner surface on the generation of these fluctuations has not been studied as yet. Therefore, this problem has been numerically investigated for a MHD mixed convection of a liquid metal in a round tube for a downward flow of mercury with the one-side heating condition under a strong transverse magnetic field using conjugate problem statement by the LES (Large Eddy Simulation) method. Numerical simulation was performed for four cases: (i) the effect of thermophysical and electrophysical properties of the steel pipe wall is neglected, (ii) the effect of wall material properties is included, (iii) the effect of the moderate contact electrical resistance caused by a layer of fouling deposits or oxides on the inner surface of the pipe is accounted for, and (iv) the resistance of the thin fouling layer is assumed to be very high. The predictions for the cases (i) and (iv) are in good agreement with the experimental data and the results of the direct numerical simulation. They demonstrate the existence of quasi-periodic abnormal high-amplitude temperature fluctuations in the fluid with a frequency of approximately 0.14 Hz. With a relatively low electrical resistance of the fouling film (case iii), the frequency of high-amplitude temperature fluctuations was considerably lower (0.07 Hz). In the absence of electrical contact resistance on the inner surface of the steel pipe (case ii), high-amplitude velocity and temperature fluctuations were not revealed in the fluid. Thus, it was shown for the first time that the physical properties of a wall and the electrical resistance between the fluid and the electrically conducting wall were responsible for the development of abnormal temperature fluctuations in the liquid and the wall and control of their amplitude and frequency. The causes of the revealed effects are discussed.

Size and Shape Matter: Cell Viability of Preloaded Descemet Stripping Automated Endothelial Keratoplasty Grafts in Three Different Carriers.

The aim of this study was to examine endothelial cell loss (ECL) associated with preloaded Descemet stripping automated endothelial keratoplasty (DSAEK) grafts loaded into 3 carriers of different size and shape. Thirty-six donor corneas were prepared for DSAEK and loaded into an EndoGlide Ultrathin (control) (2.0 mm × 3.5 mm lumen, 4.5 mm/4.9 mm incision for scleral tunnel/clear corneal insertion), Descemet membrane endothelial keratoplasty EndoGlide (experimental) (1.1 mm × 1.7 mm lumen, 2.65 mm incision), or round glass Jones tube (experimental) (1.8 mm lumen, 3.0 mm incision). Control grafts were stored for 6 days in Optisol-GS and experimental grafts stored for 24 hours in Life4C before analysis using Calcein AM staining. Grafts were imaged and ECL was analyzed by FIJI segmentation. The statistical significance of ECL was determined using 1-way ANOVA and Tukey post hoc analysis. There were no significant differences in donor characteristics for grafts in each cohort. ECL for grafts loaded into the EndoGlide Ultrathin was 10.3% ± 2.3% (graft thickness: 60-189 μm, n = 9). ECL for grafts loaded into the Descemet membrane endothelial keratoplasty EndoGlide was 22.2% ± 7.1% (graft thickness: 38-63 μm, n = 9). ECL for thin grafts (34-60 μm, n = 9) loaded into the Jones tube was 24.0% ± 5.0%. ECL for thick grafts (92-119 μm, n = 9) loaded into the Jones tube was 34.2% ± 6.1% ECL ( P < 0.001). Combined regression analysis revealed that graft thickness is directly correlated to ECL ( P < 0.01). The size and shape of the carrier can influence the cell viability of preloaded DSAEK grafts. Compared with a larger carrier, smaller lumen carriers are associated with greater ECL. In smaller lumen carriers, ECL increases with increasing DSAEK graft thickness.

Simulation Study on Thermal Performance of an Indirect Boiling Cooling Cylindrical Battery System with Two‐Phase Coolant R141b

In this study, a novel indirect boiling cooling battery thermal management system with two‐phase coolant R141b is proposed for the commercial cylindrical lithium‐ion battery pack. The heat conduction blocks are used to enlarge the heat transfer area between batteries and straight round tubes, and the R141b coolant flows and boils inside tubes to remove heat generated from batteries. Three‐dimensional simulation models are built and used to study the influence of partial structural parameters (height of heat conduction blocks, number and diameter of round tubes), the flow pattern layout, the coolant flow rate, and the battery discharge rate on the cooling performance of battery thermal management system (BTMS). The results show that the cross‐flow layout significantly improves the temperature uniformity of the batteries, with the maximum temperature difference reduced by 30% compared to the concurrent flow. Meanwhile, the appropriate geometrical parameters can further improve both cooling capacity of the BTMS and the temperature uniformity of the batteries. When the optimized structure with a coolant flow rate of 0.1 under the cross‐flow layout, the maximum temperature and maximum temperature difference of batteries discharged at 2 C reduced to 38.6 and 3.81 which are 97% and 64% of those in the concurrent flow, respectively.

Further Study and Development of Correlations for Heat Transfer during Subcooled Boiling in Plain Channels

The author’s published correlations for subcooled boiling in channels are further studied and developed in this work. The areas explored include choice of equivalent diameters for annuli and partially heated channels, effects of flow direction, micro-gravity, and orientation of heated surface. A new correlation is developed, which is a modification of the author’s earlier correlation. The author’s previous correlations and the new correlation are compared with a very wide range of test data for round tubes, rectangular channels, and annuli. Several other correlations are also compared with the same data. The authors’ correlations provide good agreement with data, the new correlation giving the least deviation. The data included hydraulic diameters from 0.176 to 22.8 mm, reduced pressure from 0.0046 to 0.922, subcooling from 0 to 165 K, mass flux from 59 to 31,500 kgm−2s−1, all flow directions, and terrestial to micro gravity. The new correlation has mean absolute deviation (MAD) of 13.3% with 2270 data points from 49 sources. Correlations by others had MAD of 18% to 116%. The results are presented and discussed.

Modeling local interfacial area concentration for adiabatic and boiling bubbly flows

Bubbly flows appear in various heat and mass transfer systems, and interfacial area concentration (IAC) is a critical geometrical parameter for the flows. The fidelity of accurately computed IACs is essential for reliable three-dimensional computational fluid dynamics analyses of bubbly flows because the IACs directly affect the interfacial force and interfacial heat and mass transfer rates. This study targeted development of a simple and robust model for predicting the local IAC under steady-state bubbly flows with and without phase change. The dependent two-phase flow parameters of the IAC were derived by considering bubble coalescence and breakup rates. The IAC transport equation simplified under steady-state conditions was used for this purpose. A simplified turbulence model was introduced to formulate the energy dissipation rate per unit mass necessary for computing the bubble coalescence and breakup rates. The prediction accuracy of the local IAC model for bubbly flow conditions with area-average void fraction values less than 10 % was estimated to be 20 % based on 803 local data collected for adiabatic air–water bubbly flows in round tubes with diameters ranging from 9.0 to 200 mm. The model was also applied to predict the local IAC data of subcooled boiling flows in heated channels with hydraulic diameters ranging from 18.5 to 22.2 mm. The test conditions covered pressures from 0.1 to 1.46 MPa. The model prediction accuracy for bubbly flow conditions with area-average void fraction values less than 10 % was estimated to be 40 % based on 155 subcooled boiling flow data.

Numerical and Experimental Design of the Former for TORT Cables

TORT (Tapes on Round Tube) cables, which implement high-temperature superconducting (HTS) tapes, offer additional benefit over other HTS cables, which is the internal cooling in the former itself. Up to now, the superconducting tapes of existing TORT cables have been wound on a copper tube of various diameters. However, in the alternating current (AC) mode, the high conductivity of the former causes undesirable eddy currents. Therefore, it is necessary to replace the copper with a less electrically conductive material. We designed a former from polyethylene terephthalate glycol-modified and reinforced with carbon fibers (PETG CF), polycarbonate (PC) and polycarbonate reinforced with carbon fibers (PC CF) materials in order to reduce the AC losses in TORT cables, using 3D printing technology. Because of the low thermal conductivity of polymers, the former must be specially designed to improve the cooling of the HTS tapes inside the former. Moreover, thermal deformation of the former during cooling from room temperature to liquid nitrogen temperature and resilience against low-diameter bending is another important issue that was taken into account. Detailed structural finite-element (FE) analysis was carried out using the FE modeling software ANSYS, in prototyping of the former. Based on the numerical models, formers differing in the materials used were fabricated, and subsequently a short TORT cable with wound HTS tape was electromagnetically characterized.

Distinctive Features of Plume Formation on Collision of Two Laminar Gas Jets

The results of an investigation of the interaction between two colliding axisymmetric laminar microjets of propane-butane mixture with and without diffusion combustion are presented. The gas mixture components flow out through round tubes at the same velocities. In the course of the experiments the lateral position of the tubes with respect to each other was varied with conservation of the angle between them. The distinctive features of the resulting jet formation are established as functions of the transverse position of the tubes. If the tubes lie in the same plane, then the resulting jet is formed in the plane orthogonal to them. This process can be observable in the case of the interaction between the jets both with and without flame. With increase in the jet outflow velocity a region of local discontinuity of the flame front is found to exist.

Shell-side heat transfer characteristics of floating liquefied natural gas spiral wound heat exchanger under sloshing conditions

To study the influence of offshore sloshing motion on the performance of a spiral wound heat exchanger (SWHE) installed on a floating liquefied natural gas (FLNG) platform and to explore potential methods to improve heat transfer efficiency, a sloshing experimental platform was established. This platform facilitated the experimental study of the boiling heat transfer process of a subcooled falling film on the outer surface of the heat exchanger tube. A quantitative analysis of the change in the heat transfer coefficient with respect to the amplitude and period of the rolling and swaying motion was performed. The experimental results indicated that both rolling and swaying changed the liquid film morphology, leading to a decrease in the heat transfer coefficient of the heat exchanger tube. The fluctuation in the heat transfer coefficient became more drastic with an increase in amplitude, but the effect of the swaying motion was less than that of the rolling motion. When the rolling angle was 12° and the Re number was 569, the average heat transfer coefficient of the round tube decreased by 55% compared with that at the static condition. Furthermore, the research encompassed the design, processing, and rigorous testing of elliptical and egg-shaped tubes to improve their heat transfer performance, and the results were compared with those of round tubes. Under the same rolling or swaying conditions, the heat transfer coefficients of the egg-shaped and elliptical tubes were 5.1–21.5% higher than that of the round tubes. The results of this study can be used as a reference for the operational and structural design of SWHEs under sloshing conditions.

Broadband sound focusing with tunable focus based on reconfigurable acoustic coding metagrating

In this paper, we propose a reconfigurable acoustic coding metagrating composed of rotatable open-ended round tubes for realizing broadband sound focusing with tunable focus. Integrating reconfigurable idea into coding metagrating, we can implement the conversion of the logical units 0 and 1 simply by mechanically adjusting the rotational angle of the open-ended round tubes. The theoretical analysis, the numerical simulations, and experimental results demonstrate that the proposed coding metagrating can precisely manipulate the focus by alternating the coding arrangements. The proposed metagrating has the advantages of broadband property, precise focusing, and tunable focus. Our work provides promising applications in acoustic imaging, medical ultrasound treatment, and nondestructive testing.

DDT run-up distance in an obstructed tube

Self-luminous high-speed photography was used to study flame acceleration and deflagration-to-detonation transition (DDT) in a clear polycarbonate round tube equipped with orifice plates. The 288 cm long, 7.6 cm inner-diameter tube was equipped with equally spaced 50% and 75% area-blockage orifice plates. The primary test mixture was stoichiometric ethylene–oxygen diluted with varying amounts of nitrogen, and the initial pressure was varied between 5 and 90 kPa. Tests were also performed with stoichiometric hydrogen–oxygen with large argon dilution to study the effect of detonation cell structure regularity. High-speed video showed that the initial DDT always occurred following shock reflection off an obstacle, allowing an accurate determination of the DDT run-up distance. Soot foils were used to measure cell size at the end of the obstacle-free tube. A correlation for flame acceleration to one-half the Chapman–Jouguet detonation velocity (VCJ) predicted the measured DDT run-up distance successfully for the most reactive mixture conditions. However, the measured DDT run-up distance increasingly deviated from the correlation with decreasing initial pressure, significantly under predicting the run-up distance at the DDT limit. A correlation for the DDT run-up distance was proposed based on the concept of flame acceleration to one-half VCJ followed by an induction phase that ends with the transition to detonation. For a given tube and obstacle configuration, the flame acceleration distance depends on the flame properties, and the DDT induction distance depends on the properties that quantify the detonation length-scale and stability.

Condensation heat transfer and pressure drop characteristics inside smooth and enhanced tubes with R410A and R32

An experimental investigation was performed to evaluate the condensation heat transfer characteristics for R32 and R410A inside four horizontal round tubes with 12.7 mm outer diameter. The saturation temperatures were 35 °C and 45 °C, the vapor qualities ranged from 0.2 to 0.8, and the mass flux ranged from 50 kg m−2 s−1 to 200 kg m−2 s−1. Different inside surface structures of the four tubes were smooth (ST), hydrophobic (HYD), herringbone (HB) and hydrophobic/herringbone (HYD/HB), respectively. Effects of mass flux, vapor quality, refrigerant and saturation temperature on condensation heat transfer in different tubes were discussed with the aid of flow pattern visualizations. Experimental results show that the heat transfer coefficient of R32 was higher than that of R410A due to different physical properties of the refrigerant. HB tube had the highest heat transfer coefficient at low vapor quality and HYD tube was the best at high vapor quality. The performance enhancement factors (PEF) of HB tube and HYD tube were better, ranging from 1.07 to 1.4 and from 1.02 to 1.31, respectively. However, as the composite of HB and HYD, the HYD/HB tube had the lowest overall performance, with the PEF ranged from 0.94 to 1.12. Additionally, the specific sensitivity factor (SSF) was used to evaluate the influence of various parameters on heat transfer and pressure drop.

THE STUDY OF HEAT TRANSFER INTENSITY AND AERODYNAMIC DRAG INSIDE A FLAT PIPE

It is know that a heat exchange tube with a flat-oval profile has excellent thermal and aerodynamic characteristics in contrast to a round tube. Thus, with the same planes, a flat tube has a significant increase in thermal and aerodynamic efficiency compared to a round tube, which is widely used in industry. However, at present, there are a limited number of publications on the study of heat transfer and aerodynamics inside a flat pipe.&#x0D; In this paper, we present the methodology and results of the study of heat transfer and aerodynamic drag in a pipe, and describe the experimental stand for such studies.&#x0D; The experiments performed in a flowing wind tunnel with an internal diameter of 36 mm, operating in an open-loop circuit. The working medium is air drawn from the laboratory room. The prototype was a steel pipe with a flat-oval profile, 320 mm long, 30x15 mm cross section, and 2 mm wall thickness.&#x0D; The created experimental stand allows us to study the heat transfer and aerodynamic drag of a flat pipe under the boundary condition q=const. An electric heater ensured this condition, which is a nichrome wire with a diameter of 0.6 mm wound along the entire length of the pipe and insulated from the external environment.&#x0D; The experiments were carried out in the range of Reynolds numbers (10.5 - 55.0) 103 and dissipated powers (50 - 150) W. The average air temperature in the pipe was set in the range (20 - 55) 0C, and the average temperature of the pipe wall was set in the range (24 - 140) 0C in accordance with the electric power supplied to the heater.&#x0D; Empirical correlations proposed for determining the intensity of heat transfer and aerodynamic drag inside a flat pipe. The data had compared with a round tube. The results had analyzed, and it had shown for the first time that the intensity of heat transfer and aerodynamic drag in a flat-oval pipe is 1.1 to 1.2 times and 1.4 to 1.7 times higher, respectively.

Numerical calculation of the boundaries of vortex zones at the entrance to round suction tubes with three shelves

The article proposes to reduce the size of the vortex zones (VZ) formed when the flow is separated from the sharp edges, due to the formation of three fractures of the round suction socket. The lengths of the first and third bell shelves in the range of 0,1‒0,5 caliber (the radius of the suction pipe) correspond to the angles of their inclination, at which the lengths of the vortex zones are equal to the lengths of these shelves. Calculations were performed for the angles of inclination of the second shelf of the bell 30, 60 and 90 with lengths from 1, 2 and 5 calibers. The boundaries of vortex zones for the specified sizes are found, analytical dependences for their determination are proposed. Profiling according to these boundaries will eliminate the formation of vortices and reduce the coefficient of local resistance at the entrance to the bell.

Experimental study on flow and heat-transfer characteristics of Ga-In-Sn alloy in a round tube applied for high heat flux device cooling

Experimental study on flow and heat-transfer characteristics of Ga-In-Sn alloy in a round tube applied for high heat flux device cooling

Experimental Investigations of Forced Convection of Nanofluids in Smooth, Horizontal, Round Tubes: A Review

A comprehensive review of published works dealing with experimental studies of forced convection heat transfer of nanofluids is presented. The survey is limited to straight, smooth, and round tubes. Moreover, only mono nanofluids exhibiting Newtonian behaviour are considered. Works on experimental research of forced convection in tubes are presented in a chronological order in the first part of the article. In this part, attention was paid to the influence of nanoparticles on the intensification of heat transfer. Information on the tested nanofluids, the measurement technique used, and the measurement range are presented in tabular form. Correlation equations proposed by individual researchers are also presented. In order to explain the controversy regarding the different influences of nanoparticles on the intensity of heat transfer during forced convection of nanofluids, the second part of the paper presents a comparison of the test results obtained by different researchers for the same nanofluid, possibly under the same thermal and flow conditions. Finally, the main conclusions are discussed.

A novel structure tube for supercritical CO2 turbulent flow with high non-uniform heat flux

Supercritical CO2 has been a promising alternative working medium in coal-fired power plants, high-temperature solar power systems, and fuel cells. In these cases, supercritical carbon dioxide is in a round tube under high temperature and pressure with high non-uniform heat flux. In this study, a novel structure tube is proposed by optimizing the coupling between circumferential heat flux and tube thickness on the heat-absorbing side to improve its comprehensive performance. A thermal-fluid-mechanical coupling model was developed. The novel structure can reduce maximum temperature and temperature difference effectively for the half-cycle uniform and non-uniform heat flux. The maximum thermal stress decreased by 23 and 29% and the maximum temperature decreased by 29.6 and 24.8 K for half-cycle uniform and non-uniform heat flux when the Eccentricity increased from 0 to 0.4. A comparison was made between the proposed structure, thin-walled tube, and traditional tube. Results showed that the performance of the proposed tube is the best. The maximum temperature decreases by approximately 55 K compared with the traditional and thin-walled tubes. The maximum equivalent stress of proposed tube is the smallest. Furthermore, the structure will improve the safety and economics of the tube.

Experimental research on heat transfer characteristic of HITEC molten salt in evacuated tube solar collector

HITEC molten salt (7% NaNO3, 53% KNO3, 40% NaNO2) has been identified as a suitable heat transfer fluid for concentrated solar power (CSP) systems, such as parabolic trough collectors (PTC) and evacuated tube solar collectors (ETSC). In order to optimize the flow and heat transfer performance of HITEC in ETSC, a molten salt heat transfer test rig was built to conduct an experimental study, varying inlet and outlet temperatures and mass flow rates of HITEC. Results show that the heat loss of HITEC in ETSC is lower than the other tubes. The convective heat transfer coefficient of HITEC is much lower than that of HITEC in round tube. Because the experimental data of HITEC in ETSC largely differed from the classical correlation equations, a new empirical heat transfer correlation equation was set for HITEC in ETSC, and the deviation between the experiment data and new correlation was within ±19.2%. Finally, by comparing the inlet and outlet temperatures of ETSC under different irradiation intensities, it is concluded that the ETSC can work stably when the temperature exceeds 700 W/m2.

Thermal performance and exergy analysis in a round tube with louvered trapezoidal winglets

An experiment was performed to investigate the influence of inserting a louver-punched trapezoidal-winglet (LPTW) into a uniform heat-fluxed tube in order to create a longitudinal vortex generator. This research aims to maximize both the thermal performance to increase energy savings, and the relative Nusselt number (NuR) at the optimal performance to reduce heat exchanger sizes. Therefore, the experimental result was emphasized on the thermal and pressure loss characteristics including entropy, and exergy analysis of the turbulent tube flow for Reynolds numbers (Re) that extended from 4760 to 29,280. The LPTWs were arranged by letting V-tip direct downstream with three attack angles (α = 30°, 45° and 60°) and five louver angles (θ1 = 0°, 25°, 30°, 45° and 90°), all at a single relative winglet pitch (PR = 1.0) and height (BR = 0.25). According to the findings, it revealed that the friction factor (f) and Nusselt number (Nu) of the LPTW at α= 60° and θ1 = 0° are, respectively, up to 29.1 and 5.5 times above those of the plain tube. With decreasing Re and θ1, the entropy generation (S˙′gen) was reduced to a lower value and the maximum exergy efficiency (ηEx) was obtained for the LPTW at α = 60° and θ1 = 0° The peak thermal performance around 2.5 together with NuR = 4.68 was found at a= 60°, θ1 = 45° and the lowest Re. However, the optimal condition at α= 60°, θ1 = 30° was preferable because it provides the greatest NuR = 5.04 at TEF = 2.47. Additionally, correlations for f and Nu were derived and presented for the range of parameters that were taken into consideration.