rotating cylinders
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ACS Omega ◽  
2021 ◽  
Author(s):  
Walid Hassen ◽  
Fatih Selimefendigil ◽  
Nidhal Ben Khedher ◽  
Lioua Kolsi ◽  
Mohamed Naceur Borjini ◽  
...  

2021 ◽  
Author(s):  
Ehsanul Azim ◽  
Md. Jahid Hasan Sagor ◽  
Shadman Sakief Hridoy ◽  
Rafiqul Hasan ◽  
Ashrafur Rahman ◽  
...  

Abstract Conjugate pure mixed convection in a differentially heated square cavity with two vertically placed heat conductive revolving cylinders has been analyzed in computational approach applying the Finite Element Method. This analysis has been implemented considering the upper and lower wall as insulated simultaneously and the left vertical wall as heated maintaining constant temperature (i.e., isothermally heated) and the right vertical wall as isothermally cooled. The outcomes of this study have been examined concerning streamlines, isotherms, average Nusselt number (Nu) which unveils a noteworthy fact that both the rotating cylinders' inclination patterns and Reynolds number have a vital role upon the Nu, flow pattern, and isotherms. From that perspective, best heat transfer phenomena have been observed for counterclockwise circulation of both cylinders so that the condition for these cases has been assessed from a distance variation between the two cylinders maintaining a constant speed ratio (s). The best result has been specified for different speed ratios at different materials of the rotating cylinders.


Mathematics ◽  
2021 ◽  
Vol 9 (23) ◽  
pp. 3002
Author(s):  
Lioua Kolsi ◽  
Fatih Selimefendigil ◽  
Lotfi Ben Said ◽  
Abdelhakim Mesloub ◽  
Faisal Alresheedi

The forced convection of non-Newtonian nanofluid for a backward-facing flow system was analyzed under the combined use of magnetic field and double rotating cylinders by using finite element method. The power law nanofluid type was used with different solid volume fractions of alumina at 20 nm in diameter. The effects of the Re number (100≤Re≤300), rotational Re number (−2500≤Rew≤3000), Ha number (0≤Ha≤50), and magnetic field inclination (0≤γ≤90) on the convective heat transfer and flow features were numerically assessed. The non-Newtonian fluid power law index was taken between 0.8 and 1.2 while particle volume fractions up to 4% were considered. The presence of the rotating double cylinders made the flow field complicated where multiple recirculation regions were established near the step region. The impacts of the first (closer to the step) and second cylinders on the heat transfer behavior were different depending upon the direction of rotation. As the first cylinder rotated in the clockwise direction, the enhancement in the average heat transfer of 20% was achieved while it deteriorated by approximately 2% for counter-clockwise directional rotation. However, for the second cylinder, both the rotational direction resulted in heat transfer augmentation while the amounts were 14% and 18% at the highest speeds. Large vortices on the upper and lower channel walls behind the step were suppressed with magnetic field effects. The average Nu number generally increased with the higher strengths of the magnetic field and inclination. Up to 30% increment with strength was obtained while this amount was 44% with vertical orientation. Significant impacts of power law fluid index on the local and average Nu number were seen for an index of n = 1.2 as compared to the fluid with n = 0.8 and n = 1 while an average Nu number of 2.75 times was obtained for the flow system for fluid with n = 1.2 as compared to case for fluid with the n value of 0.8. Further improvements in the local and average heat transfer were achieved with using nanoparticles while at the highest particle amount, the enhancements of the average Nu number were 34%, 36% and 36.6% for the fluid with n values of 0.8, 1 and 1.2, respectively.


Author(s):  
A. T. Mackay ◽  
T. N. Phillips

AbstractA Taylor–Galerkin finite element time marching scheme is derived to numerically simulate the flow of a compressible and nonisothermal viscoelastic liquid between eccentrically rotating cylinders. Numerical approximations to the governing flow and constitutive equations are computed over a custom refined unstructured grid of piecewise linear Galerkin finite elements. An original extension to the DEVSS formulation for compressible fluids is introduced to stabilise solutions of the discrete problem. The predictions of two models: the extended White–Metzner and FENE-P-MP are presented. Comparisons between the torque and load bearing capacity predicted by both models are made over a range of viscoelastic parameters. The results highlight the significant and interacting effects of elasticity and compressibility on journal torque and resultant load, and the stability of the journal bearing system.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hamidreza Aghamiri ◽  
Mohammadreza Niknejadi ◽  
Davood Toghraie

AbstractIn the present work, the forced convection of nanofluid flow in a microchannel containing rotating cylinders is investigated in different geometries. The heat flux applied to the microchannel wall is 10,000 W m−2. The effects of Reynolds number, the volume fraction of nanoparticles, and the porosity percentage of the porous medium are investigated on the flow fields, temperature, and heat transfer rate. Reynolds number values vary from Re = 250–1000, non-dimensional rotational velocities 1 and 2, respectively, and volume fraction of nanoparticles 0–2%. The results show that increasing the velocity of rotating cylinders increases the heat transfer; also, increasing the Reynolds number and volume fraction of nanoparticles increases the heat transfer, pressure drop, and Cf,ave. By comparing the porosity percentages with each other, it is concluded that due to the greater contact of the nanofluid with the porous medium and the creation of higher velocity gradients, the porosity percentage is 45% and the values of are 90% higher than the porosity percentage. Comparing porosity percentages with each other, at porosity percentage 90% is greater than at porosity percentage 45%. On the other hand, increasing the Reynolds number reduces the entropy generation due to heat transfer and increases the entropy generation due to friction. Increasing the volume fraction of nanoparticles increases the entropy generations due to heat transfer and friction.


2021 ◽  
Vol 97 ◽  
pp. 329-343
Author(s):  
Ammar I. Alsabery ◽  
Muneer A. Ismael ◽  
Engin Gedik ◽  
Ali J. Chamkha ◽  
Ishak Hashim

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nima Shirani ◽  
Davood Toghraie

AbstractMixed convection of nanofluid in a 2D square enclosure with a porous block in its center and four rotating cylinders, which are forced by a simple harmonic function, was studied numerically. The porous zone was studied by considering the Forchheimer–Brinkman-extended Darcy model. Effects of various parameters including Darcy number (10–5 ≤ Da ≤ 10–2), porosity (0.2 ≤ ɛ ≤ 0.7), Richardson number (0.1 ≤ Ri ≤ 10), and volume fraction of nanoparticles (0 ≤ ϕ ≤ 0.03), on heat transfer, entropy generation, PEC, velocity, streamline and isotherm contours were demonstrated. The results show that decreasing the Darcy number as well as reducing the Richardson number leads to an increase in the average Nusselt number. However, porosity changes had no decisive effect on heat transfer. Maximize the volume fraction of copper nanoparticles in the base fluid enhanced heat transfer. In the case of the high permeability of the porous medium, the impact of the harmonic rotation of the cylinders on the flow patterns became more pronounced.


2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sameh E. Ahmed ◽  
Muflih Alhazmi

Purpose This paper aims to study the mixed convective process due to various dynamics, namely, inner rotating cylinders and upper-wavy wall movement for the first time. Design/methodology/approach The Galerkin finite element method together with the characteristic-based split scheme is applied to solve the governing system. Findings The main outcomes revealed that the direction of the rotation of the cylinders, radius and locations of the rotating shapes are beneficial controlling elements for the enhancement of heat transfer. Also, for all the considered cases, values of the Bejan number indicate that the fluid friction irreversibility is dominance compared to the heat transfer irreversibility. Further, average values of the heat transfer entropy, fluid friction entropy and total entropy are minimized in the case of fixed cylinders regardless of the cylinder radius. Originality/value The authors are interested in the mixed convection case due to regular boundaries and hence this simulation purposes a first attempt to examine the mixed convective flow due to irregular wavy boundaries. This study considered various dynamics, namely, inner rotating cylinders and wavy-lid driven wall which makes it more attractive to the readers. Various cases based on radius of the cylinder and direction of the rotations together with several locations of the rotating shapes are taken into account which makes the current simulation is comprehensive. Various studies presented in this field are made by commercial software and these treatments need special conditions (having limitation) but the current solution methodology is based on a finite element method home-code. Various important impacts, are, also, examined, namely, inclined geometry, inclined magnetic field, thermal radiation and heat generation/absorption. The entropy of the current complex system is analyzed based on the second law of thermodynamics.


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