Browsing by Author "Said L.B."

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    Jet impingement cooling of a rotating hot circular cylinder with hybrid nanofluid under multiple magnetic field effects
    (MDPI, 2021) Ayadi B.; Selimefendigil F.; Alresheedi F.; Kolsi L.; Aich W.; Said L.B.
    The cooling performance of jet impinging hybrid nanofluid on a rotating hot circular cylinder was numerically assessed under the effects of multiple magnetic fields via finite element method. The numerical study was conducted for different values of Reynolds number (100 ≤ Re ≤ 300), rotational Reynolds number (0 ≤ Rew ≤ 800), lower and upper domain magnetic field strength (0 ≤ Ha ≤ 20), size of the rotating cylinder (2 w ≤ r ≤ 6 w) and distance between the jets (6 w ≤ H ≤ 16 w). In the presence of rotation at the highest speed, the Nu value was increased by about 5% when Re was increased from Re = 100 to Re = 300. This value was 48.5% for the configuration with the motionless cylinder. However, the rotations of the cylinder resulted in significant heat transfer enhancements in the absence or presence of magnetic field effects in the upper domain. At Ha1 = 0, the average Nu rose by about 175%, and the value was 249% at Ha1 = 20 when cases with the cylinder rotating at the highest speed were compared to the motionless cylinder case. When magnetic field strengths of the upper and lower domains are reduced, the average Nu decreases. The size of the cylinder is influential on the flow dynamics and heat transfer when the cylinder is rotating. An optimum value of the distance between the jets was obtained at H = 14 w, where the Nu value was highest for the rotating cylinder case. A modal analysis of the heat transfer dynamics was performed with the POD technique. As diverse applications of energy system technologies with impinging jets are available, considering the rotations of the cooled surface under the combined effects of using magnetic field and nanoparticle loading in heat transfer fluid is a novel contribution. The outcomes of the present work will be helpful in the initial design and optimization studies in applications from electronic cooling to convective drying, solar power and many other systems. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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    Forced convection of non–newtonian nanofluid flow over a backward facing step with simultaneous effects of using double rotating cylinders and inclined magnetic field
    (MDPI, 2021) Kolsi L.; Selimefendigil F.; Said L.B.; Mesloub A.; Alresheedi F.
    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. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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    Performance Optimization of a Thermoelectric Device by Using a Shear Thinning Nanofluid and Rotating Cylinder in a Cavity with Ventilation Ports
    (Multidisciplinary Digital Publishing Institute (MDPI), 2022) Ben Khedher N.; Selimefendigil F.; Kolsi L.; Aich W.; Said L.B.; Boukholda I.
    The combined effects of using a rotating cylinder and shear thinning nanofluid on the performance improvements of a thermoelectric generator (TEG)-installed cavity with multiple ventilation ports are numerically assessed. An optimization algorithm is used to find the best location, rotational speed and size of the cylinder to deliver the highest power generation of the TEG. The power generation features with varying Rew are different for the first nanofluid (NF1) when compared to the second one (NF2). The power rises with higher Rew when NF1 is used, and up to 49% enhancement is obtained. The output power variation between nanofluids NF1 and NF2 is the highest at Rew = 0, which is obtained as 68.5%. When the cylinder location is varied, the change in the output power becomes 61% when NF2 is used. The optimum case has 11.5%-and 161%-higher generated power when compared with the no-object case with NF1 and NF2. The computational effort of using the high-fidelity coupled system is reduced when optimization is considered. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.