Combined effect of the magnetic field, orientation, and filling ratio on cylindrical pulsating heat pipe using distilled water and distilled water/Fe3O4 nanofluid

To investigate the effect of the magnetic field, a pulsating heat pipe was made in the shape of a cylinder and Fe3O4 nanoparticles (%0.1 wt) were used with the base fluid of distilled water as the working fluid. (Tetramethyl ammonium hydroxide) TMAH surfactant was used as a stabilizer. To investigate the effect of gravity on the performance of the pipe, the device was tested at different angles from zero to 90 degrees. In this research, the effect of different variables, including the type of working fluid (distilled water vs. nanofluid), filling ratio, slope, and amount of heat input to the evaporator (30–300 W), in two different states, once without the influence of the magnetic field and once again with the application of a magnetic field was investigated. The results of the tests showed that the performance of the device at 50 % filling ratio is better than 60 % filling ratio. The use of nanoparticles improved the performance of the device. Inclining the device increases the thermal resistance so that the device performs poorly in the horizontal mode in all modes except when it is under the influence of a magnetic field. The use of nanofluid, as well as the application of a magnetic field, makes the start-up time of the device decrease by 37 % and 30 %, respectively, compared to distilled water. The temperature of the start of fluctuations also decreases by 24 % and 32 %, respectively

Free convection heat transfer and entropy generation analysis of water-Fe 3 O 4 /CNT hybrid nanofluid in a concentric annulus

© 2018, Emerald Publishing Limited. Purpose: This paper aims to numerically investigate the heat transfer and entropy generation characteristics of water-based hybrid nanofluid in natural convection flow inside a concentric horizontal annulus. Design/methodology/approach: The hybrid nanofluid is prepared by suspending tetramethylammonium hydroxide-coated Fe 3 O 4 (magnetite) nanoparticles and gum arabic (GA)-coated carbon nanotubes (CNTs) in water. The effects of nanoparticle volume concentration and Rayleigh number on the streamlines, isotherms, average Nusselt number and the thermal, frictional and total entropy generation rates are investigated comprehensively. Findings: Results show the advantageous effect of hybrid nanofluid on the average Nusselt number. Furthermore, the study of entropy generation shows the increment of both frictional and thermal entropy generation rates by increasing Fe 3 O 4 and CNT concentrations at various Rayleigh numbers. Increasing Rayleigh number from 103 to 105, at Fe 3 O 4 concentration of 0.9 per cent and CNT concentration of 1.35 per cent, increases the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 224.95, 224.65 and 155.25 per cent, respectively. Moreover, increasing the Fe 3 O 4 concentration from 0.5 to 0.9 per cent, at Rayleigh number of 105 and CNT concentration of 1.35 per cent, intensifies the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 18.36, 22.78 and 72.7 per cent, respectively. Originality/value: To the best knowledge of the authors, there are not any archival publications considering the detailed behaviour of the natural convective heat transfer and entropy generation of hybrid nanofluid in a concentric annulus

Heat transfer and entropy generation analysis of water-Fe3O4/CNT hybrid magnetic nanofluid flow in a trapezoidal wavy enclosure containing porous media with the Galerkin finite element method

The present study addresses theoretically and computationally the performance of electrically conducting water-Fe3O4/CNT hybrid nanofluid in three-dimensional natural convective heat transfer and entropy generation within a wavy-walled trapezoidal enclosure. The enclosure has two layers - a hybrid nanofluid layer and a porous medium layer. A transverse magnetic field is applied in the upward direction. Newtonian flow is considered and the modified Navier-Stokes equations are employed with Lorentz hydromagnetic body force, Darcian and Forchheimer drag force terms. The wavy side planes are heated down while the top and vertical planes are thermally insulated. A rectangular heated fin is placed in the lower plane and several different locations of the fin are considered. The transformed, non-dimensional system of coupled non-linear partial differential equations with associated boundary conditions is solved numerically with the Galerkin finite element method (FEM) in the COMSOL Multiphysics software platform. The effects of Darcy number, Hartmann number, volume fraction, undulation number of the wavy wall and Rayleigh number (thermal buoyancy parameter) on the streamlines, isotherms and Bejan number contours are studied. Extensive visualization of the thermal flow characteristics is included. With increasing Hartmann number and Rayleigh number, the average Bejan number is reduced strongly whereas average Nusselt number is only depleted significantly at very high Rayleigh number and high Hartmann number. With increasing undulation number, there is a slight elevation in average Bejan number at intermediate Rayleigh numbers, whereas the average Nusselt number is substantially boosted, and the effect is maximized at very high Rayleigh number. Increment in Darcy number (i. e. reduction in permeability of the porous medium layer) is observed to considerably elevate average Nusselt number at high values of Rayleigh number, whereas the contrary response is computed in average Bejan number. The simulations are relevant to hybrid magnetic nanofluid fuel cells and electromagnetic nano-materials processing in cavities

Fabrication of 3D-printed hydroxyapatite using freeze-drying method for bone regeneration: RVE and finite element simulation analysis

Tissue engineering is an interdisciplinary approach that utilizes cells, scaffolds, and biofactors to develop biosynthetic bone scaffolds for bone regeneration applications. These scaffolds are three-dimensional porous structures with specific mechanical and biological properties that facilitate the attachment and proliferation of osteoinductive cells on their surfaces. In this study, bone scaffolds were 3D-printed using PLA material, and a variety of three-dimensional porous structures, including Kelvin, Octet truss, and Gibson Ashby, were employed. To improve the biological properties of the scaffolds, they were coated with alginate/hydroxyapatite using the Freeze-drying method. The Alginate/HA RVEs were analyzed under periodic boundary conditions, and the elastic modulus was found to improve from 100 MPa (pure alginate) to 149 MPa by adding 30 wt% HA particles. The mechanical properties of the scaffolds were investigated under compressive deformation using experiments and finite element simulations. The results show that the compressive strength of structures follows the order σOctettruss > σGibsonashby > σKelvin. The Freeze-drying process causes pore formation on the scaffold surface. According to the microstructural analysis, the pore size was observed for composite scaffolds approximately at 320–340 μm. After 21-day, most parts of the scaffold surface were coated by the apatite layer completely, and the surface of the pores was blocked by the apatite layer. To characterize cell viability, an MTT assay was used. The scaffolds expose high cell viability around 97% and did not show any significant toxicity