Magneto-convection of nanofluid flow over multiple rotating cylinders in a confined space with elastic walls and ventilated ports.

In this study, convective heat transfer for nanofluid flow over multiple rotating cylinder in a confined space is analyzed under magnetic field while enclosure has one inlet and one outlet port. Three identical circular cylinder are used and the two walls of the cavity are considered to be elastic. The coupled fluid-structure interaction and magneto-convection problem is solved by finite element method. Impacts of rotational Reynolds number (Rew between -100 and 100), Hartmann number (Ha between 0 and 50), cylinder size (R between 0.001H and 0.11H) and Cauchy number (Ca between 10-8 and 10-3) on the flow and thermal performance features are explored. The flow field and recirculation inside the cavity are significantly affected by the activation of rotation and magnetic field. The vortices are suppressed by increasing the strength of magnetic field and thermal performance is improved. Thermal performance of 56.6% is achieved by activation of magnetic field at the highest strength with rotations of the circular cylinders. When rotations are active, heat transfer rate is reduced while up to 40% reduction is obtained without magnetic field. Cylinder size has the highest impact on the overall thermal performance improvement while up to 132% enhancements are achieved. The contribution of elastic walls on the thermal performance is slight while less than 5% improvements in the average heat transfer is obtained. An optimization study leads to 12.7% higher thermal performance improvements as compared to best case of parametric computational fluid dynamics simulation results while the optimum values of (Rew, Ha, R) is obtained as (-80.66, 50, 0.11H).

Assessment of Low-Density Force Myography Armband for Classification of Upper Limb Gestures.

Using force myography (FMG) to monitor volumetric changes in limb muscles is a promising and effective alternative for controlling bio-robotic prosthetic devices. In recent years, there has been a focus on developing new methods to improve the performance of FMG technology in the control of bio-robotic devices. This study aimed to design and evaluate a novel low-density FMG (LD-FMG) armband for controlling upper limb prostheses. The study investigated the number of sensors and sampling rate for the newly developed LD-FMG band. The performance of the band was evaluated by detecting nine gestures of the hand, wrist, and forearm at varying elbow and shoulder positions. Six subjects, including both fit and amputated individuals, participated in this study and completed two experimental protocols: static and dynamic. The static protocol measured volumetric changes in forearm muscles at the fixed elbow and shoulder positions. In contrast, the dynamic protocol included continuous motion of the elbow and shoulder joints. The results showed that the number of sensors significantly impacts gesture prediction accuracy, with the best accuracy achieved on the 7-sensor FMG band arrangement. Compared to the number of sensors, the sampling rate had a lower influence on prediction accuracy. Additionally, variations in limb position greatly affect the classification accuracy of gestures. The static protocol shows an accuracy above 90% when considering nine gestures. Among dynamic results, shoulder movement shows the least classification error compared to elbow and elbow-shoulder (ES) movements.

Conjugate Heat Transfer Analysis for Cooling of a Conductive Panel by Combined Utilization of Nanoimpinging Jets and Double Rotating Cylinders.

In this work, double rotating active cylinders and slot nanojet impingement are considered for the cooling system of a conductive panel. Colder surface temperatures of the cylinders are used, while different rotational speeds are assigned for each of the cylinders. The impacts of cylinder rotational speeds, size and distance between them on the cooling performance are evaluated. The rotational effects and size of the cylinders are found to be very effective on the overall thermal performance. At the highest rotational speeds of the cylinders, the average Nusselt number (Nu) rises by about 30.8%, while the panel temperature drops by about 5.84 °C. When increasing the cylinder sizes, temperature drops become 7 °C, while they are only 1.75 °C when varying the distance between the cylinders. Subcooling and nanofluid utilization contributes positively to the cooling performance, while 1.25 °C and 10 °C temperature drops are found by varying the subcooled temperature and solid volume fraction. An artificial neural network is used for the estimation of maximum and average panel temperatures when double cylinder parameters are used as the input.

Coupled Effects of Using Magnetic Field, Rotation and Wavy Porous Layer on the Forced Convection of Hybrid Nanoliquid Flow over 3D-Backward Facing Step.

In the present study, the effects of using a corrugated porous layer on the forced convection of a hybrid nanofluid flow over a 3D backward facing step are analyzed under the coupled effects of magnetic field and surface rotation. The thermal analysis is conducted for different values of the Reynolds number (Re between 100 and 500), the rotational Reynolds number (Rew between 0 and 2000), the Hartmann number (Ha between 0 and 15), the permeability of the porous layer (the Darcy number, Da between 10-5 and 10-2) and the amplitude (ax between 0.01 ap and 0.7 ap) and wave number (N between 1 and 16) of the porous layer corrugation. When rotations are activated, the average Nusselt number (Nu) and pressure coefficient values rise, while the increment of the latter is less. The increment in the average Nu is higher for the case with a higher permeability of the layer. When the corrugation amplitude and wave number are increased, favorable impacts of the average Nu are observed, but at the same time pressure coefficients are increased. Successful thermal performance estimations are made by using a neural-based modeling approach with a four input-two output system.

Entropy Analysis of the Thermal Convection of Nanosuspension within a Chamber with a Heat-Conducting Solid Fin.

Heat transport augmentation in closed chambers can be achieved using nanofluids and extended heat transfer surfaces. This research is devoted to the computational analysis of natural convection energy transport and entropy emission within a closed region, with isothermal vertical borders and a heat-conducting solid fin placed on the hot border. Horizontal walls were assumed to be adiabatic. Control relations written using non-primitive variables with experimentally based correlations for nanofluid properties were computed by the finite difference technique. The impacts of the fin size, fin position, and nanoadditive concentration on energy transfer performance and entropy production were studied. It was found that location of the long fin near the bottom wall allowed for the intensification of convective heat transfer within the chamber. Moreover, this position was characterized by high entropy generation. Therefore, the minimization of the entropy generation can define the optimal location of the heat-conducting fin using the obtained results. An addition of nanoparticles reduced the heat transfer strength and minimized the entropy generation.

Thermal Management and Modeling of Forced Convection and Entropy Generation in a Vented Cavity by Simultaneous Use of a Curved Porous Layer and Magnetic Field.

The effects of using a partly curved porous layer on the thermal management and entropy generation features are studied in a ventilated cavity filled with hybrid nanofluid under the effects of inclined magnetic field by using finite volume method. This study is performed for the range of pertinent parameters of Reynolds number (100≤Re≤1000), magnetic field strength (0≤Ha≤80), permeability of porous region (10-4≤Da≤5×10-2), porous layer height (0.15H≤tp≤0.45H), porous layer position (0.25H≤yp≤0.45H), and curvature size (0≤b≤0.3H). The magnetic field reduces the vortex size, while the average Nusselt number of hot walls increases for Ha number above 20 and highest enhancement is 47% for left vertical wall. The variation in the average Nu with permeability of the layer is about 12.5% and 21% for left and right vertical walls, respectively, while these amounts are 12.5% and 32.5% when the location of the porous layer changes. The entropy generation increases with Hartmann number above 20, while there is 22% increase in the entropy generation for the case at the highest magnetic field. The porous layer height reduced the entropy generation for domain above it and it give the highest contribution to the overall entropy generation. When location of the curved porous layer is varied, the highest variation of entropy generation is attained for the domain below it while the lowest value is obtained at yp=0.3H. When the size of elliptic curvature is varied, the overall entropy generation decreases from b=0 to b=0.2H by about 10% and then increases by 5% from b=0.2H to b=0.3H.

Control of Magnetohydrodynamic Mixed Convection and Entropy Generation in a Porous Cavity by Using Double Rotating Cylinders and Curved Partition.

In this work, mixed convection and entropy generation analyses in a partitioned porous cavity with double inner rotating cylinders are explored under magnetic field effects. A curved partition shape is considered with identical rotating cylinders and an inclined magnetic field, while the right vertical wall moves with a constant speed in the y-direction. Numerical simulations are performed by considering various values of Rayleigh number, Hartman number, Darcy number, inclination of the magnetic field, size of the curved partitions, and rotational speeds of the inner cylinders and their vertical locations with the cavity. Complicated flow field with multicellular structures are observed due to the complex interaction between the natural convection, moving wall, and rotational effects of inner cylinders. Improved heat-transfer performance is obtained with higher values of magnetic field inclination, higher values of permeability/porosity of the medium, and higher rotational speeds of the cylinders. Almost doubling of the average Nu number is obtained by decreasing the value of the Hartmann number from 25 to 0 or varying the magnetic field inclination from 90 to 0. When rotational effects of the cylinders are considered, average heat-transfer improvements by a factor of 5 and 5.9 are obtained for nondimensional rotational speeds of 5 and -5 in comparison with the case of motionless cylinders. An optimum length of the porous layer is achieved for which the best heat-transfer performance is achieved. As the curvature size of the partition is increased, better heat transfer of the hot wall is obtained and up to 138% enhancement is achieved. Significant increments of entropy generation are observed for left and right domains including the rotating cylinders. The magnetic field parameter also affects the entropy generation and contributions of different domains including the curved porous partition.

Effects of a Rotating Cone on the Mixed Convection in a Double Lid-Driven 3D Porous Trapezoidal Nanofluid Filled Cavity under the Impact of Magnetic Field.

Effects of a rotating cone in 3D mixed convection of CNT-water nanofluid in a double lid-driven porous trapezoidal cavity is numerically studied considering magnetic field effects. The numerical simulations are performed by using the finite element method. Impacts of Richardson number (between 0.05 and 50), angular rotational velocity of the cone (between -300 and 300), Hartmann number (between 0 and 50), Darcy number (between 10 - 4 and 5 × 10 - 2 ), aspect ratio of the cone (between 0.25 and 2.5), horizontal location of the cone (between 0.35 H and 0.65 H) and solid particle volume fraction (between 0 and 0.004) on the convective heat transfer performance was studied. It was observed that the average Nusselt number rises with higher Richardson numbers for stationary cone while the effect is reverse for when the cone is rotating in clockwise direction at the highest supped. Higher discrepancies between the average Nusselt number is obtained for 2D cylinder and 3D cylinder configuration which is 28.5% at the highest rotational speed. Even though there are very slight variations between the average Nu values for 3D cylinder and 3D cone case, there are significant variations in the local variation of the average Nusselt number. Higher enhancements in the average Nusselt number are achieved with CNT particles even though the magnetic field reduced the convection and the value is 84.3% at the highest strength of magnetic field. Increasing the permeability resulted in higher local and average heat transfer rates for the 3D porous cavity. In this study, the aspect ratio of the cone was found to be an excellent tool for heat transfer enhancement while 95% enhancements in the average Nusselt number were obtained. The horizontal location of the cone was found to have slight effects on the Nusselt number variations.

MHD Free Convection and Entropy Generation in a Corrugated Cavity Filled with a Porous Medium Saturated with Nanofluids.

MHD free convection inside a triangular-wave-shaped corrugated porous cavity with Cu-water nanofluid is numerically studied with the finite element method. The influences of the Grashof number ( 10 4 ≤ Gr ≤ 10 6 ), Hartmann number ( 0 ≤ Ha ≤ 50 ), Darcy number ( 10 - 4 ≤ Da ≤ 10 - 1 ) and solid volume fraction of the nanoparticle ( 0 ≤ ϕ ≤ 0.05 ) on the convective flow features are examined. It is observed that increasing the Grashof number and Darcy number enhances the heat transfer, while the effect is opposite for the Hartmann number. As the corrugation frequency of the triangular wave increases, the local and averaged heat transfer rates decrease, which is more effective for higher values of Grashof and Darcy numbers. Normalized total entropy generation increases as the Darcy number and solid volume fraction of the nanoparticles increase and decreases as the Hartmann number increases both for flat and corrugated wall configurations.

MHD Mixed Convection and Entropy Generation in a Lid-Driven Triangular Cavity for Various Electrical Conductivity Models.

In this study, effects of different electrical conductivity models for magneto- hydrodynamic mixed convection of nanofluids in a lid-driven triangular cavity was numerically investigated with a finite element method. Effects of Richardson number and Hartmann number on the convective heat transfer characteristics were analyzed for various electrical conductivity models of nanofluids. Average Nusselt number decreases for higher Hartmann and Richardson numbers. Discrepancies in the local and average heat transfer exist between different electrical conductivity models, which is higher for higher values of Richardson number and Hartmann number. The total entropy generation rate was found reduced with higher values of Richardson number and Hartmann number while discrepancies exist between various electrical conductivity models. When the magnetic field is imposed, different behaviors of entropy generation rate versus solid particle volume fraction curve is obtained and it is dependent upon the range of solid particle volume fraction.