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

Advancing Micromixing Techniques: the Role of Surface Acoustic Waves and Fluid–structure Interaction in Non-Newtonian Fluids

This study numerically investigated the enhancement of micromixing efficiency through integrating surface acoustic waves (SAWs) and hyper-elastic channel walls, modeled using a power-law fluid representative of human blood flow. The governing equations are systematically divided into zeroth, first, and second orders based on perturbation theory. This facilitates the development of a fully coupled two-way fluid–structure interaction (FSI) framework implemented via the Arbitrary Lagrangian–Eulerian (ALE) method. The combination of SAWs and hyper-elastic materials demonstrated a marked improvement in mixing efficiency, increasing from 0 to 0.99, alongside a significant reduction in pressure drop within the microchannel. The interaction between SAWs and the deformable walls induces localized instabilities and shear stresses that effectively disrupt the laminar flow, promoting enhanced mixing. The study highlights the critical role of hyper-elastic walls in modulating normal forces on the fluid and reducing pressure drop, offering insights into the interaction between fluid viscosity, acoustic pressure fields, and flow dynamics. These findings provide a framework for designing micromixers with optimized efficiency and reduced channel length, offering practical advancements in microfluidic systems. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.Science Citation Index Expande