scholarly journals Resistance force pulsations of annular flow in the Couette-Taylor system with counter-rotating cylinders

2019 ◽  
Vol 196 ◽  
pp. 00045
Author(s):  
Nikolay Miskiv ◽  
Anatoly Serov ◽  
Aleksandr Nazarov ◽  
Valery Mamonov
Keyword(s):  
Reynolds Numbers ◽  
Mean Value ◽  
Working Fluid ◽  
Resistance Force ◽  
Taylor Vortices ◽  
Slit Flow ◽  
Ring Channel ◽  
Resistance Moment ◽  
Tension Sensor ◽  
Rotation Resistance

The paper presents the results of an experimental study of the Couette-Taylor flow fluctuations in a ring channel with oppositely rotating multicylinder rotors. Experiments were carried out using water-glycerine solutions as a working fluid. The rotation resistance moment and its pulsations were investigated, using the system for measuring the torque resistance of rotation of rotors, made in the form of a digital dynamometer based on a tension sensor. The investigations made it possible to establish that the classic dependence of the appearance of Taylor vortices is observed in the slit flow of a multicylinder system rotating oppositely. It was shown that in the range of Reynolds numbers Re = (100 – 500), pulsations of dissipative processes with variable frequency and amplitude up to 10% of the mean value of rotation resistance are observed.

Simulation of Unsteady Flow Around a Cylinder

2015 ◽  
Vol 3 (2) ◽  
pp. 28-49
Author(s):  
Ridha Alwan Ahmed
Keyword(s):  
Stokes Equations ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Mean Value ◽  
Navier Stokes ◽  
Cylinder Surface ◽  
Navier Stokes Equations ◽  
Flow Around A Cylinder ◽  
Numerical Grid ◽  
Good Agreement

       In this paper, the phenomena of vortex shedding from the circular cylinder surface has been studied at several Reynolds Numbers (40≤Re≤ 300).The 2D, unsteady, incompressible, Laminar flow, continuity and Navier Stokes equations have been solved numerically by using CFD Package FLUENT. In this package PISO algorithm is used in the pressure-velocity coupling.        The numerical grid is generated by using Gambit program. The velocity and pressure fields are obtained upstream and downstream of the cylinder at each time and it is also calculated the mean value of drag coefficient and value of lift coefficient .The results showed that the flow is strongly unsteady and unsymmetrical at Re>60. The results have been compared with the available experiments and a good agreement has been found between them

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

Heat Transfer in Rotating Serpentine Coolant Passage With Ribbed Walls at Low Mach Numbers

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Shang-Feng Yang ◽  
Je-Chin Han ◽  
Salam Azad ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Mach Number ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Low Mach Number ◽  
Heat Transfer Coefficients ◽  
Rotation Numbers ◽  
Wide Range ◽  
Mach Numbers

This paper experimentally investigates the effect of rotation on heat transfer in typical turbine blade serpentine coolant passage with ribbed walls at low Mach numbers. To achieve the low Mach number (around 0.01) condition, pressurized Freon R-134a vapor is utilized as the working fluid. The flow in the first passage is radial outward, after the 180 deg tip turn the flow is radial inward to the second passage, and after the 180 deg hub turn the flow is radial outward to the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers up to 0.6 and Reynolds numbers from 30,000 to 70,000. Heat transfer coefficients were measured using the thermocouples-copper-plate-heater regional average method. Heat transfer results are obtained over a wide range of Reynolds numbers and rotation numbers. An increase in heat transfer rates due to rotation is observed in radially outward passes; a reduction in heat transfer rate is observed in the radially inward pass. Regional heat transfer coefficients are correlated with Reynolds numbers for nonrotation and with rotation numbers for rotating condition, respectively. The results can be useful for understanding real rotor blade coolant passage heat transfer under low Mach number, medium–high Reynolds number, and high rotation number conditions.

scholarly journals Radiation and Energetic Analysis of Nanofluid Based Volumetric Absorbers for Concentrated Solar Power

Nanomaterials ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 838 ◽  
Author(s):  
Jan Eggers ◽  
Eckart Lange ◽  
Stephan Kabelac
Keyword(s):  
Radiation Energy ◽  
Reynolds Numbers ◽  
Numerical Approach ◽  
Working Fluid ◽  
Concentrated Solar Power ◽  
Optical Efficiency ◽  
Solar Absorber ◽  
Energetic Analysis ◽  
High Reynolds ◽  
Very High

Recently, several publications gave attention to nanofluid based solar absorber systems in which the solar radiation energy is directly absorbed in the volume of the fluid. This idea could provide advantages over conventionally used surface absorbers regarding the optical and thermal efficiency. For the evaluation of this concept, a numerical approach is introduced and validated in this contribution. The results show that the optical efficiency of a volumetric absorber strongly depends on the scattering behavior of the nanofluid and can reach competitive values only if the particle size distribution is narrow and small. If this is achieved, the surface temperature and therefore the heat loss can be lowered significantly. Furthermore, the surface absorber requires very high Reynolds numbers to transfer the absorbed energy into the working fluid and avoid overheating of the absorber tube. This demand of pumping power can be reduced significantly using the concept of volumetric absorption.

scholarly journals Numerical study of flow patterns and heat transfer in mini twisted oval tubes

2015 ◽  
Vol 26 (12) ◽  
pp. 1550140 ◽  
Author(s):  
Amin Ebrahimi ◽  
Ehsan Roohi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Critical Role ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Working Fluid ◽  
Transfer Performance ◽  
Temperature Dependent ◽  
Overall Performance

Flow patterns and heat transfer inside mini twisted oval tubes (TOTs) heated by constant-temperature walls are numerically investigated. Different configurations of tubes are simulated using water as the working fluid with temperature-dependent thermo-physical properties at Reynolds numbers ranging between 500 and 1100. After validating the numerical method with the published correlations and available experimental results, the performance of TOTs is compared to a smooth circular tube. The overall performance of TOTs is evaluated by investigating the thermal-hydraulic performance and the results are analyzed in terms of the field synergy principle and entropy generation. Enhanced heat transfer performance for TOTs is observed at the expense of a higher pressure drop. Additionally, the secondary flow generated by the tube-wall twist is concluded to play a critical role in the augmentation of convective heat transfer, and consequently, better heat transfer performance. It is also observed that the improvement of synergy between velocity and temperature gradient and lower irreversibility cause heat transfer enhancement for TOTs.

scholarly journals Experimental Study of Forced Convective Heat Transfer in a Coiled Flow Inverter Using TiO2–Water Nanofluids

2020 ◽  
Vol 10 (15) ◽  
pp. 5225
Author(s):  
Barbara Arevalo-Torres ◽  
Jose L. Lopez-Salinas ◽  
Alejandro J. García-Cuéllar
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Thermal ◽  
Convective Heat Transfer Coefficients

The curved geometry of a coiled flow inverter (CFI) promotes chaotic mixing through a combination of coils and bends. Besides the heat exchanger geometry, the heat transfer can be enhanced by improving the thermophysical properties of the working fluid. In this work, aqueous solutions of dispersed TiO2 nanometer-sized particles (i.e., nanofluids) were prepared and characterized, and their effects on heat transfer were experimentally investigated in a CFI heat exchanger inserted in a forced convective thermal loop. The physical and transport properties of the nanofluids were measured within the temperature and volume concentration domains. The convective heat transfer coefficients were obtained at Reynolds numbers (NRe) and TiO2 nanoparticle volume concentrations ranging from 1400 to 9500 and 0–1.5 v/v%, respectively. The Nusselt number (NNu) in the CFI containing 1.0 v/v% nanofluid was 41–52% higher than in the CFI containing pure base fluid (i.e., water), while the 1.5 v/v% nanofluid increased the NNu by 4–8% compared to water. Two new correlations to predict the NNu of TiO2–water nanofluids in the CFI at Reynolds numbers of 1400 ≤ NRe ≤ 9500 and nanoparticle volume concentrations ranges of 0.2–1.0 v/v% and 0.2–1.5 v/v% are proposed.

scholarly journals Interface-resolved simulations of particle suspensions in Newtonian, shear thinning and shear thickening carrier fluids

2018 ◽  
Vol 852 ◽  
pp. 329-357 ◽  
Author(s):  
Dhiya Alghalibi ◽  
Iman Lashgari ◽  
Luca Brandt ◽  
Sarah Hormozi
Keyword(s):  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Shear Thickening ◽  
Fluid Phase ◽  
Local Strain ◽  
Reynolds Numbers ◽  
Mean Value ◽  
Strain Rates ◽  
Local Shear ◽  
The Mean

We present a numerical study of non-colloidal spherical and rigid particles suspended in Newtonian, shear thinning and shear thickening fluids employing an immersed boundary method. We consider a linear Couette configuration to explore a wide range of solid volume fractions ($0.1\leqslant \unicode[STIX]{x1D6F7}\leqslant 0.4$) and particle Reynolds numbers ($0.1\leqslant Re_{p}\leqslant 10$). We report the distribution of solid and fluid phase velocity and solid volume fraction and show that close to the boundaries inertial effects result in a significant slip velocity between the solid and fluid phase. The local solid volume fraction profiles indicate particle layering close to the walls, which increases with the nominal $\unicode[STIX]{x1D6F7}$. This feature is associated with the confinement effects. We calculate the probability density function of local strain rates and compare the latter’s mean value with the values estimated from the homogenisation theory of Chateau et al. (J. Rheol., vol. 52, 2008, pp. 489–506), indicating a reasonable agreement in the Stokesian regime. Both the mean value and standard deviation of the local strain rates increase primarily with the solid volume fraction and secondarily with the $Re_{p}$. The wide spectrum of the local shear rate and its dependency on $\unicode[STIX]{x1D6F7}$ and $Re_{p}$ point to the deficiencies of the mean value of the local shear rates in estimating the rheology of these non-colloidal complex suspensions. Finally, we show that in the presence of inertia, the effective viscosity of these non-colloidal suspensions deviates from that of Stokesian suspensions. We discuss how inertia affects the microstructure and provide a scaling argument to give a closure for the suspension shear stress for both Newtonian and power-law suspending fluids. The stress closure is valid for moderate particle Reynolds numbers, $O(Re_{p})\sim 10$.

Turbulent Flow Characteristics Over Offset Wall Confined Columns in a Channel at Low Reynolds Numbers

2018 ◽  
Author(s):  
Kira Toxopeus ◽  
Kamran Siddiqui
Keyword(s):  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Turbulent Energy ◽  
Narrow Channel ◽  
Thermal Regulation ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Mean Flow ◽  
Bulk Fluid ◽  
Flow Characterization

The current study is focused on the flow through offset, wall confined vertical inserts in a channel. The columns are intended to act as the thermal storage media, which continuously exchange heat with the channel fluid to regulate it thermally. These columns could, for example, be filled with a phase change material (PCM) for passive thermal regulation, or have hot or cold fluid pumped through them for active thermal regulation. The current study has two parts: (1) the flow characterization without heat transfer, and (2) flow characterization during thermal exchange with a PCM used for regulation of bulk fluid temperature. The work presented here is focused only on the first part of the study. The experiments were conducted in a narrow channel, with water as the working fluid. Two geometries of the vertical columns (circular and square) and two offset lengths were considered. For each configuration, experiments were conducted at Reynolds numbers of 20, 50 and 90 (based of the column’s characteristic length). Particle image velocimetry was used to measure the two-dimensional velocity field in a horizontal plane at multiple regions of interest along the length of the channel to characterize the flow passing over columns. The results indicate vortex shedding at the two higher Reynolds numbers. The generation, magnitude and decay rate of turbulent energy is shown to have an offset dependency at Re = 90, but a column shape dependency at Re = 50. The mean flow has a shape dependency due to the difference in separation point over the square and circular columns.

Enhancement of Single-Phase Refrigerant Mixture (R-407C) Flow in Meso-Scale Heat Exchangers Using Micro-Coils

2007 ◽  
Author(s):  
Yasir M. Shariff ◽  
T. S. Ravigururajan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Single Phase ◽  
Heat Transfer Performance ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Mixture Flow ◽  
Refrigerant Mixture ◽  
R 134A ◽  
The Heat Transfer Coefficient

Experimental results from single-phase refrigerant mixture flow in smooth and micro-coil enhanced meso-channels are presented. R-407C — a mixture of R-32 (23%)/R-125 (25%)/R-134a (52%) — is used as the working fluid and different micro-coils are used in conjunction with two meso-channels (2.78mm and 3.97 mm) to obtain distinct roughness parameters. The flow was varied over a range of Reynolds numbers and experiments were conducted over a heat flux range of 2 to 11 kW/m2. The heat transfer coefficient was found to be dependent on both the heat flux as well as mass flux levels. Results show that heat transfer characteristics are comparable to R-113, and that micro-coil inserts enhanced the heat transfer performance compared to the performance in smooth meso-channels.

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