Tube Of Circular Cross-section Research Articles

Influence of inhomogeneous magnetic field source location on the intensity of thermomagnetic convection in a closed loop

Purpose. Obtaining information on the influence of the location of the inhomogeneous magnetic field source relative to the heated section of a vertical hydrodynamic loop filled with magnetic fluid on the intensity of convective heat transfer along the loop.Methods. Experiments were carried out using a hydrodynamic loop made of a thin tube of circular cross-section and placed in a vertical plane. Heat source was carried out by a heater on a short vertical section of the loop, and heat removal was implement out by blowing the entire surface of the tube with thermostated air. The source of the magnetic field was the flat pole tips of the ferrite magnetic core, in the gap between which the heater was located. The position of the pole tips relative to the heater varied vertically in the experiments. In the control experiments, the source of the magnetic field was deleted. The circuit was filled with medium concentrated magnetic liquid of the type "magnetite - kerosene - oleic acid". The intensity of steady-state convective heat flow along the tube was calculated from the results of measuring the tube surface temperature by copper-constantane thermocouples. The measurement results were presented in dimensionless form - the relationship between the Nusselt number and Rayleigh number.Results. The unfluctuating mixed, thermomagnetic and gravitational, convection of the magnetic fluid in the loop was observed at any location of the pole tips of the magnetic core relative to the heater. At location of pole tips above the heater, competition of gravitational and thermomagnetic convection was observed, and the heat flux was weak. When the pole tips were placed below the heater, the Nusselt number was 2 - 4 times higher than in the control tests (only gravitational convection) with equal Rayleigh numbers. The highest Nusselt numbers were obtained when the field source was placed in center of the heater.Conclusion. Information on the influence of the relative location of the magnetic field source and the heater on convective heat transfer by magnetic fluid in a hydrodynamic loop is obtained experimentally. The optimal concerning of heat transfer intensity position of the field source was found.

Investigation of the Newtonian fluids flow in circular horizontal tubes at low inlet pressures

The issues of increasing hydrodynamic efficiency, improving the operational and technical characteristics of various apparatus and devices used in the fi eld of heat and mass transfer, as well as ensuring the required regime and flowow conditions of liquids of different viscosities do not lose their relevance. To solve these issues, in addition to studying the nature of the flowow of various liquids in round horizontal tubes (capillaries), it is necessary to determine the conditions when the flowow of liquid in capillaries and round tubes of small diameter is laminar and can be described by the Poiseuille equation. Experimental data on determining water flow ow through horizontal round tubes of various diameters are presented. Determining the patterns and features of such flow ows is mostly aimed at increasing hydrodynamic efficiency, improving the operational and technical characteristics of various apparatus and devices, as well as ensuring the required flow ow regime and conditions. Experimental data on determining the flow ow rate of water through horizontal tubes of circular cross-section with different diameters are presented in the article. The dependence of the volumetric flow ow rate on the pressure drop has been determined; it has been shown that the main parameters that determine the nature of the flow ow of liquids in horizontal tubes are the tube radius and the dynamic viscosity of the liquid. The flow ow of distilled water in tubes with diameters of 0.95, 1.6 and 2.0 mm at an overpressure of 0.266 kPa to 4 kPa is considered. It is shown that the dependence of the volumetric flow ow rate on the excess pressure remains linear at 0.95 mm in the entire considered pressure range. An increase in the tube radius increases the likelihood of velocity flow uctuations and the appearance of a radial velocity component, i.e. the occurrence of elements of a turbulent structure. In this regard, with tube diameters of 1.6 and 2.0 mm, a deviation of the water flow ow regime from the laminar character was established at pressures of more than 1.3 kPa and 1 kPa, respectively. The dependence of the volumetric flow ow rate on pressure for a 40 % aqueous solution of CaCl2, transformer, transmission and engine oils with dynamic viscosity coefficients from 0.002 Pa·s to 0.182 Pa·s remains linear up to pipe diameters of 5–6 mm. The experimental results are shown in the form of a nomogram of the dependence of the coefficient K* on the tube radius at different values of the viscosity coefficient. The results of studies of liquids of various viscosities are presented in the form of a nomogram of the dependence of the ratio of the radius of the tube to the fourth power to the viscosity of the liquid on the radius of the tube. The analysis of which makes it possible to predict the nature of the flow ow of the investigated liquid at the given values of the tube radius and the dynamic viscosity coefficient. Heat exchange devices for the design of which the presented results can be used include a variety of radiators that include tubes through which coolant circulates.

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.

Numerical investigation on flow and heat transfer of supercritical CO2 in variable cross-section tubes under precooler working conditions

The performance of the precooler in the supercritical CO2 (S-CO2) Brayton cycle may be greatly affected by the interactions between the structure and the thermophysical properties. Variable cross-section tubes, which can effectively enhance heat transfer and reduce pressure drop, can be adopted in the precooler. In this paper, the flow and heat transfer performance of S-CO2 in a circular tube and variable cross-section tubes with different unit length divergent ratio (DR) and convergent ratio (CR) is firstly investigated when the heat transfer area is kept constant. The results show that the converging tubes can effectively enhance the heat transfer compared with the circular tube, and a greater CR is more beneficial for heat transfer. The heat transfer coefficient (htotal) is increased by 84.77% at the maximum. The diverging tubes are found to have a strong advantage in reducing the pressure drop, and a larger DR is more helpful to reduce pressure drop, with a maximum decrease of 84.4%. The heat transfer mechanism is analyzed from the aspects of flow field distribution, thermophysical property changes and buoyancy effect. Furthermore, combined with the performance of different variable cross-section tubes, two new hybrid tubes are proposed based on the idea of partitioned heat transfer enhancement matching the thermophysical property changes under the constant heat transfer area condition. The comprehensive thermal–hydraulic performance of the two hybrid tubes is significantly improved compared with that of the converging tube. A 34.81% higher htotal and a 6.25% lower pressure drop can be obtained when using the hybrid tube A under high heat flux conditions. The hybrid tube B is found to enhance heat transfer by 54.98% and reduced pressure drop by 55.14% under low heat flux conditions. Finally, the flow and heat transfer characteristics of different types of tubes are also further studied under the constant inlet Reynolds number condition. This study can provide some guidance for the design and optimization of precoolers where the thermophysical properties of the working fluid are highly variable.

Evaporation in a single channel in the presence of particles

Liquid corner films in channels or pores of polygonal cross-section are known to have a strong impact on evaporation with a much faster evaporation compared to a tube of circular cross section. The aim of this work is to study the interplay between colloidal particles, development of the corner films and evaporation in a micro channel from a combination of visualization experiments with fluorescent particles and numerical simulations. It is shown that the triple line pinning along the corner films due to particle accumulation in the films leads to the thinning of the corner films. As a result of the film thinning, evaporation is slower in the presence of particles compared to pure water. The identification of such an evaporation reduction mechanism at pore scale shed new light on the phenomenon of reduced evaporation in porous media due to the presence of colloidal particles reported in previous works.

Circular tube-in-tube dampers for seismic resilience of structures

A new brace-type slit damper, called ‘Circular Tube-in-Tube Damper (C-TTD), comprises two solid steel cylinders and one circular cross-section tube equipped with slotted holes, is proposed for seismic resilience of structures. In the proposed damper, a system of bolts was used to connect up various components of the damper, allowing inspection and replacement of the damaged components without any requirement for the replacement of the entire damper. Nonlinear finite element analyses using ABAQUS were carried out to verify the experimental results and to investigate the effect of damper geometric properties on the yield load capacity of the C-TTD dampers. The seismic performance characteristics of 4-storey, 8-storey, and 15-storey steel structures equipped with C-TTD dampers were determined by nonlinear time history analyses using three different earthquake excitations. The results indicated that when the structures were equipped with C-TTD dampers, the inter storey drift decreased in the range of 8%–55%, the base shear load decreased in the range of 27%–35%, and the input energy decreased in the range of 70%–80%, depending on the number of storeys and the earthquake type, compared to the counterpart structures without the damper.

Tubes of non-circular cross-section to destabilize liquid plugs in heat transfer devices

The stability of a liquid plug inside a vertical tube depends on the balance between the weight of the liquid and the capillary forces. Contact angle hysteresis is required for a liquid plug to be at equilibrium; it has a stabilizing effect. On the other hand, capillary drainage into corners or grooves destabilizes liquid plugs and may lead to their dislocation. Following a detailed literature review about the influence of the tube cross-section on plug stability, this paper provides original numerical and experimental results obtained in tubes of circular, regular polygonal and fluted cross-sections. The cross-section may affect stability either through direct modification of the menisci curvature, or through that of apparent contact angle hysteresis. The latter was characterized experimentally for the first time to our knowledge in tubes of non-circular cross-section. Among the studied shapes, the fluted and triangular ones are the most promising for destabilizing liquid plugs. They both promote capillary drainage. Besides, fluted tubes reduce stability by a direct effect on curvature, while triangular tubes decrease apparent contact angle hysteresis. These findings could help improve the performance of two-phase closed thermosyphons of small dimensions by mitigating liquid hold-up in the condenser section. Indeed, recent advances in additive manufacturing processes enable the fabrication of thermosyphons with very complex shapes. Other devices such as fuel cells could also benefit from the optimization of their geometry to prevent channel occlusion.

Enhanced Thermo-Fluidic Performance of Aqueous SiO2 Nanofluid Flow Through a Horizontal Tube—An Experimental Investigation

The thermo-fluidic performance of SiO2-water nanofluid (NF) flow inside a horizontal tube of circular cross section were examined applying constant heat flux. An aqua based dispersion of SiO2 nanopowders with 16.58 nm average particle diameter were used as the working fluid with 0.15–0.35 vol.%. Experiments are conducted in the Reynolds number (Re) range of 2798.96–27989.62 maintaining the bulk temperature of the flow at 45 °C. Thermo-physical properties namely conductivity (k) and viscosity (μ) of NF were determined at various temperatures range of 25–65 °C. Maximum 13% enhancement in k and a maximum of 20% enhancement in μ were obtained at 0.35 vol.% as compared to basefluid. Heat transfer and friction factor (f) were increased with enhancing concentration and Re. The Nusselt number (Nu) increased upto 40% along with a maximum increase of 28.57% in f as compared to their basefluid. New empirical correlations for Nu and f of nanofluids were developed. Finally, a figure of merit (FOM) was determined, which reveals the potency of nanofluids as working fluid for rapid cooling applications.

Numerical study on thermal-hydraulic characteristics of flattened microfin tubes

Abstract The thermal-hydraulic characteristics and performance of the circular and flattened straight tubes with longitudinal inward microfins are studied with isothermal wall condition and Reynold numbers (Re) between 10,000 and 30,000. The geometric models with fins (8, 12, and 16 fins) and three flattening ratios (1.4, 2, and 3.4) are considered for the simulation. The results indicate that the longitudinal microfins have a limited effect on the improvement of heat transfer, but the application of microfins increases the pressure drop significantly. Furthermore, an increase in Reynolds number increases the heat transfer characteristics. Therefore, a discriminative use of longitudinal microfins for circular tubes to improve thermal performance is advised. Flattening the microfin tubes has shown a significant increase in heat transfer coefficient and friction factor compared to circular cross-section tubes with microfins. The percentage gain in heat transfer with the flattening ratio of 3.4 is about 52% compared to the circular fin tube at Re = 30,000. A 61% increase in centreline velocity is observed at Re = 10,000. Area-based Enhancement Factor (AEF) and performance evolution factor (PEF) are more than 1 for flattened tubes with microfins. It shows an improvement in the overall thermal-hydraulic characteristics of tubes.

Theoretical and experimental results of stepped tubes with circular cross-sections

The present work focuses on investigating the axial crushing process of circular cross-section tubes with variable diameters using theoretical and experimental methods. In case of an impact, the energy should be consumed by the controlled deformation of the sacrificial structures. The specimens are designed as structures with the same height and have sectors with different diameters and thicknesses. Following the experimental tests, finite element analysis was performed, and the dataset was processed using Matlab. The solution generates a theoretical mean crushing force curve, including the height sectors with different diameters and the mean crushing force curves for experimental and simulation results. The methodology provides the background for a future investigation.

Non-conventional tube shapes for lifetime extend of solar external receivers

In this work, several novel tube shapes of solar tubular receivers that differ from the classical circular shape are analysed aiming to reduce the stresses of the receiver tubes, without penalizing its thermal efficiency. The analysis is performed using analytical thermal and mechanical models of the literature adapted for their use with non-circular tube shapes, verifying the assumptions made with FEM simulations due to the lack of experimental data available.Among the geometries studied, the results show that oval cross-section tubes improve the thermal efficiency of the receiver at the expense of increasing the stresses considerably. Ovoidal tubes show worse thermal and mechanical behaviour when the frontal part becomes peakier. Semicircle tubes reduce the stress by 10.9%, while keeping constant or even slightly improving the thermal performance. The last ones, increase the lifetime of the receiver and reduces the receiver costs if the manufacturing of the new geometries does no overpass 3.5 times the present price of production of the circular tubes. Therefore, the use of asymmetric cross-section tubes with low rear-front surface ratios, and smooth front surfaces can be considered a good alternative for substituting traditional circular cross-section tubes in central receivers.

Dependence of the Piezoelectric Micropump Operating Mode on Its Geometry

A mathematical and computer axisymmetric models in which periodic oscillations of ring piezoelectric actuators placed on an elastic tube of circular cross-section leads to radial deformations of the tube is constructed. The result of these displacements is a local compression of the microchannel, which leads to changes in its volume and the corresponding pushing of the fluid. If a non-symmetrical oscillation scheme is used, the average fluid flow over the period will be non-zero and the device can be used as a micropump. The aim of the work is a computer study of the geometric features of an axisymmetric piezoelectric micropump, taking into account the processes of heat transfer by a fluid in the channel. The dependence of the average fluid flow rate on the channel parameters and the frequency of oscillations of the piezoelectric actuators is determined by the method of factorial experiment. The parameters preventing heat backflow have been determinate, which makes it possible to use a device for supplying coolant to a microgripper cooling system.

Experimental Investigation of Heat Transfer of Nanofluid in Elliptical and Circular Tubes

The paper presents experimental comparison of forced convection for steady state turbulent flow of nanofluid (Al2O3-distilled water) inside circular and elliptical (aspect ratio of 0.75) cross section tubes of identical circumference and tube surface area. Convection coefficient, pressure change, and fiction factor were compared at different Reynolds number (3,000-9,230) with different nanoparticles volume concentration (0.5%, 1.0%, and 1.5%). The results showed that Nusselt number increases with increasing Reynolds number and nanoparticle volume concentration. The pressure drops and friction factor of nanofluid are higher than the distilled water and are increasing as the volume concentration increases. Furthermore, the elliptical tube provided small increase in Nusselt number compared to that of circular cross sectional tube. However, the friction factor in the elliptical tube was slightly higher.

“DURYSTA” the first biodegradable sustained release implant for the treatment of open-angle glaucoma

A study for “DURYSTA” in the treatment of open angle glaucoma has been done in this work. A angle between the cornea and iris is open whereas the trabecular meshwork is partially blocked, that obstructs the outflow of aqeous humor and lead to vision loss and damage the optic nurve that is known as open angle glucoma. This model presented the study for outflow of watery clear liquid called aqueous humor from the eye through the trabacular meshwork into the Schlemm's Canal in the human eye. This circular lymphatic-like vessel which is called Canal of Schlemm is modeled as a permeable flexible canal with a trabecular meshwork that keeps it open. Aqueous humor seeps through trabacular meshwork and reaches to Schlemm's canal. The inner wall of the canal is porous and it is considered that between two collecting channels the segment of canal is assumed as a circular cross-section tube. In this model, the flow and pressure characteristics of the aqueous fluid are drawn, and the effect of the main limitations and parameters on these profiles is extracted and explained. The effects of “DURYSTA” on these parameter have also been extracted and shown.

A Heat Recovery Device using Oscillating Heat Pipe with Circular and Elliptical Tubes

In this study, an oscillating heat pipe heat exchanger has been used as a heat recovery device in air ductwork, and the characteristics of the thermal performance of the energy-saving were investigated by using a circular and elliptical cross-sectional tubes. An experimental study was conducted by oscillating heat pipe made from copper with an inner diameter of 3.5 mm for the conventional tube, and the major and minor axis of 4.2 and 2.2 mm for the elliptical tube. The working fluid was water with filling ratio of 50% of the total volume. The experimental data implied that the thermal effectiveness and the energy-saving highly affected by the inlet air temperature and velocity. The proposed model of the oscillating heat pipe heat exchanger possessed the effectiveness of 19.5% at 50 ºC and 0.5 m/s, and the potential energy-saving of 1117 W at 50 ºC and 2 m/s. The comparison results between the elliptical and conventional cross-sectional area of oscillating heat pipe heat exchanger indicated that the energy-saving and effectiveness enhanced by the ratio of 18%, and 14%.

A regressive model for dynamic impulsive instabilities during the condensation of R134a, R1234ze(E) and R1234yf refrigerants

This article presents a proposal for a regressive model describing dynamic pressure vp and temperature vT impulsive instabilities during condensation of R134a refrigerant and isomers R1234yf and R1234ze(E) in minichannels. The model was verified in relation to the obtained experimental results. In the development of the model, a dimensionless analysis using Buckingham's Π theorem was applied to obtain the dependence on dimensionless values of the propagation velocities of the pressure instability vp+ related to the acoustic speed vp and of the temperature instability vT+ related to the condensation front vFC. Experimental studies were carried out with the use of miniature tubes of circular cross-section with hydraulic internal diameter dh = 3.30, 2.30, 1.92, 1.44, and 1.40. The comparison of the computational results obtained from the model with experimental results showed a satisfactory compliance of ±25%.

Reducing the systematic error of the average fluid flow rate in axisymmetric computer model of piezoelectric micropump

Mathematical and computer models of an axisymmetric coupled problem of interaction of a fluid and an elastic body for the solving partial differential equations by the finite element method FreeFem ++ software are proposed. In these models, periodic vibrations of annular piezoelectric actuators placed on an elastic tube of circular cross-section lead to radial deformations of the tube. With a synchronous oscillation of the system of piezoelectric actuators, the average fluid flow rate is zero. An asymmetric oscillation pattern (micropump mode) results in a nonzero average flow rate. Two types of boundary conditions are considered in the region of contact between the piezoelectric drive and the tube — Dirichlet and Neumann. The computer model was tested for unsteady fluid flow induced by a pressure gradient applied along the pipe with a circular cross section. With synchronous oscillation of piezoelectric actuators, a nonzero average fluid flow is a systematic error. This value was compared with the asymmetric oscillation pattern of piezoelectric actuators to determine the contribution of the systematic error to the pump-generated fluid flow rate. Based on the fluid flow velocity profile and the results of profiling the program code, the optimal parameters of the computational meshes for the channel (dense uniform) and tube walls (nonuniform, consistent with the velocity profile and reconstructing at each time step) were determined, which reduce the magnitude of the systematic error. The main way to reduce the error is to increase the density of the computational mesh, which leads to an increase in the required computing resources. An alternative method is proposed for reducing the systematic error due to an additional pressure drop applied to the channel. Depending on the type of boundary conditions and the number of piezoelectric actuators, this method can reduce the systematic error by 1 − 2 orders of magnitude without increasing the simulation time.

Two-bay pultruded GFRP safety Barrier/Guardrail – Testing, analysis and compliance with standards

The paper describes a series of material/structural property tests on pultruded GFRP (glass fibre reinforced polymer) circular cross-section tubes used in guardrails. The tests enabled the elastic flexural and shear moduli of the tubes and the rotational stiffness of the post-base connections to be quantified. This information was then used to set up ANSYS FE (finite element) models of the guardrails using cubic beam elements and revolute joints to simulate the out-of-plane deflections of a two-bay plane guardrail loaded at the top of the centre-post and the mid-bays of the handrail. Load tests were carried on a full-scale guardrail in order to demonstrate that it complied with the load and deflection requirements given in the most recent design standard for guardrails. Thereafter, the ANSYS FE model deflection predictions were compared with those recorded during the load tests on the guardrail. It was shown, that including revolute joints in the model gave deflections that were, in the worst instances, within 15% of the values recorded in the physical tests.

МОДЕЛИРОВАНИЕ ПРОЦЕССА ХИМИКО-ТЕРМИЧЕСКОЙ ПЕРЕРАБОТКИ ЦЕЛЛЮЛОЗОСОДЕРЖАЩИХ МАТЕРИАЛОВ

The issues of numerical modeling of chemical-thermal processing of cellulose-containing waste are considered. The simulation results are presented in comparison with the data of experiments carried out in a horizontal pyrolysis reactor with a turner at various process temperatures. The process and the resulting products are influenced by the factors of the mixing rate of the products in the reactor core and the temperature distribution in this zone. To describe the thermal processes and chemical kinetics of cellulose pyrolysis, a model proposed by Yu. Dean was chosen, in which the process is represented by a heterogeneous n-order reaction and the Arrhenius equation. It is assumed that the process of heat transfer during pyrolysis takes place inside a horizontal tube of circular cross-section under conditions of free convection in a limited volume, which has an excess temperature in relation to the surrounding space. It is shown that the results obtained with the help of numerical modeling make it possible to choose the most optimal value of the linear movement of the material in the reactor vessel, depending on the required mode of chemical-thermal processing of cellulose-containing waste.

Дослідження періодичної вісесиметричної течії в’язкопружної рідини по циліндричній трубці

A generalized Womersley model of a nonstationary axisymmetric flow of a viscous incompressible fluid through a tube of circular cross-section to periodic pressure fluctuations at the inlet of the tube is obtained due for the case of a fluid with complicated rheology. The rheological parameters of the fluid are viscosity and four relaxation coefficients for strains and stresses of the first and second order. Such rheology is proper to the non-Newtonian viscoelastic fluids with mesostructure, namely technical and biological micro/ nanofluids. It was shown that with the increase of the relaxation coefficients of the first/second order the flow rate, the average and maximum velocities decrease/increase, accordingly. Simultaneous changes in these parameters can lead to complex changes in the velocity profile, especially for higher harmonics. The studied regularities can explain the deviations of the flow parameters of different micro/nanofluids from the values predicted by the classical Womersley solution for a homogeneous Newtonian fluid, which does not take into account viscous dissipation during the rearrangement of the fluid mesostructure.