Thermomagnetic Convective Cooling of Hall Effect Thruster

This work proposes and shows that thermomagnetic convection could be used in zero gravity to cool components of a Hall-effect thruster. A ferrofluid cavity was develop in the thermal and geometric model of a Hall-effect thruster. Simulations show that with an Ionic Liquid Ferrofluid after two minutes of thruster operations thermomagnetic convection occurs and in zero gravity will produce a larger velocity then natural convection that occurs in earth gravity. However, experiments did not result in heat transfer enhancement due to the limitation of the ferrofluid. Replacement of the Ferrotec EFH1 dispersant with dodecylbenzene did not result in Ionic Liquid Ferrofluid equivalent ferrofluid and did not lower of vapor pressure as intended and limited test to 60 °C. This limitation did not allow for the fluid to experience the largest difference in magnetic susceptibility that occurs near the Curie temperature

Heat transfer through thermomagnetic convection in magnetic fluids induced by varying magnetic fields

Magnetic fluid flow by thermomagnetic convection with and without buoyancy was studied in experiments and computational simulations. A mineral oil based ferro magnetic fluid was subjected to varying magnetic fields to induce thermomagnetic convection. As such fluids are mainly developed to increase heat transfer for cooling the fundamental effects on magnetic fluid flow was investigated using various magnetic field distributions. Computational simulations of natural and thermomagnetic convection are based on a Finite-Element technique and considered a constant magnetic field gradient, a realistic magnetic field generated by a permanent magnet and alternating magnetic fields. The magnetic field within the fluid domain was calculated by the magneto-static Maxwell equations and considered in an additional magnetic body force known as the Kelvin body force by numerical simulations. The computational model coupled the solutions of the magnetic field equations with the heat and fluid flow equations. Experiments to investigate thermomagnetic convection in the presence of terrestrial gravity used infrared thermography to record temperature fields that are validated by a corresponding numerical analysis. All configurations were chosen to investigate the response of the magnetic fluid to the applied body forces and their competition by varying the magnetic field intensity and its spatial distribution. As both body forces are temperature dependent, situations were analysed numerically and experimentally to give an indication of the degree by which heat transfer may be enhanced or reduced. Results demonstrate that the Kelvin body force can be much stronger than buoyancy and can induce convection where buoyancy is not able to. This was evident in a transition area if parts of a fluid domain are not fully magnetically saturated. Results for the transition from natural convection to thermomagnetic convection suggest that the domain of influence of the Kelvin body force is aligned with the dominance of the respective body force. To characterise the transition a body force ratio of the Kelvin body force to buoyancy was developed that identified the respective driving forces of the convection cells. The effects on heat transfer was quantified by the Nusselt number and a suitable Rayleigh number. A modified Rayleigh number was used when both body forces were active to define an effective body force by taking the relative orientation of both forces into account. Results for the alternating magnetic field presented flow fields that altered with the frequency of the applied magnetic field but with varying amplitude. This affected the heat transfer that alternated with the frequency but failed to respond instantaneously and a phase lag was observed which was characterised by three different time scales

Thermomagnetic convection in two- and three-dimensional channels using the lattice Boltzmann method

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The influence of a magnetic field on heat transfer is studied by using the lattice Boltzmann method for a magnetic fluid (ferrofluid) flowing through a two-dimensional micro channel; to analyse the effect of the sidewalls upon the flow and heat transfer, the three-dimensional version of the micro channel is also studied. This problem is of considerable interest when dealing with cooling of micro-electronic devices. The magnitude of the magnetic force is controlled by changing the electrical current through a dipole. The results indicate that the flow is relatively uninfluenced by the magnetic field until its strength is large enough for the Kelvin body force to overcome the viscous force. It was observed that the magnetic force was able to change the flow field and increase the heat transfer in the channel.dc201

Magneto-convective flow through a porous enclosure with Hall current and Thermal radiation effects : numerical study

This paper reports the numerical study of magnetohydrodynamic radiative-convective flow in a square cavity containing a porous medium with Hall currents. This study is relevant to hydromagnetic fuel cell design and thermofluidic dynamics of complex magnetic liquid fabrication in enclosures. The governing equations of this fluid system are solved by a finitedifference vorticity stream function approach executed in MATLAB software. A detailed parametric investigation of the impact of Rayleigh number (thermal buoyancy parameter), Hartman number (magnetic body force parameter), Darcy number (permeability parameter), Hall parameter and radiation parameter on the streamline, temperature contours, local Nusselt number along the hot wall and mid-section velocity profiles is computed. Validation with previous special cases in the literature is included. Hall current and radiative effects are found to significantly modify thermofluidic characteristics. From the numerical results, it is found that the magnetic field suppresses the natural convection only for small buoyancy ratios. But, for larger buoyancy ratio, the magnetic field is effective in suppressing the thermal convective flow

Impact of Magnetic Fields and Fins on Entropy Generation, Thermal, and Hydrodynamic Performance in the Ferrofluids Flow within a Mini Channel

The present work reports a CFD study of the magneto-convection of a ferrofluid (Fe3O4/water) circulating in a mini-channel under the influence of different vortex generators (fins and permanent magnets). The lower surface of the mini-channel is maintained at a constant temperature, while the upper surface is thermally insulated. The influence of fins, magnetic field intensity, and Reynolds number on the thermal and dynamic characteristics of the flow was numerically investigated using the finite volume method. The obtained results show that the coexistence of these two types of vortex generators considerably affects the flow structure; Entropy generation and heat transfer rate. Finally, the analysis of the different results shows that the concurrent presence of both the magnetic field and the fins results in a notably more efficient system. Using magnetic sources and fins simultaneously in a system with an intense magnetic field and a low Reynolds number can lead to a large gain in heat transfer

Workshops Proceedings

The idea behind the Workshops Proceedings document is to collect in an eBook the information of all the Nanouptake Working Group (WG) Workshops before April 2019 where the participants have been presenting their last research work in nanofluids

Proceedings of the 10th Australasian Heat and Mass Transfer Conference (AHMT2016)

Proceedings of The 10th Australasian Heat and Mass Transfer Conference (AHMT2016). The proceedings contain the selected full-length papers from the 10th Australasian Conference of Heat and Mass Transfer held in Brisbane, Australia on 14-15 July 2016. The conference was organised by Queensland University of Technology under the auspices of the Australasian Fluid and Thermal Engineering Society (AFTES) of Engineers Australia. Scientifically, these collected articles reflect recent progress made in heat and mass transfer in the Australasian community, including both fundamental and applied topics in the broad areas of convection, conduction, radiation, turbulence, multi-phase flow, combustion, drying, heat exchangers, phase change, computational methods, experimental methods, and other significant thermal processes in environmental, industrial, and process engineering. All the papers published in this volume were reviewed under a rigorous review process, where at least two reviews were received for each paper, according to the HERDC standard. The Organizing Committee is grateful to all of the contributors who made this volume possible. We would like to express our sincere appreciation to all authors and reviewers for their excellent contributions as well as the AHMT2016 scientific committee and financial support provided by Queensland University of Technology and Engineers Australi

Steady and unsteady aligned magnetohydrodynamics free convection flows of magnetic and non magnetic nanofluids along a wedge, vertical and inclined plates

Nanofluids are a new type of heat transfer fluid engineered by uniform and stable suspension of nanometer sized particles into liquids. The heat transfer in nanofluids is important especially in the context of chemical engineering, aerospace engineering and industrial manufacturing processes. The reason is that, nanofluids were found to transfer heat more efficiently than the conventional fluids. Therefore, nanofluids research could lead to a major breakthrough in developing next generation coolants for numerous engineering applications. Due to this reason, several flow problems related to heat transfer over vertical flat plate, inclined plate and wedge were studied in this thesis. The main purpose of this study was to investigate the characteristics of two dimensional flow and surface heat transfer for two cases which are steady and unsteady convection flows. Nanofluids with two different base fluids (water and kerosene) containing magnetic and non magnetic nanoparticles were considered. The effect of magnetohydrodynamics (MHD) on the flow and heat transfer was also studied. The study starts with the formulation of the mathematical models that governed the fluid flow and heat transfer. Next, the governing nonlinear equations in the form of partial differential equations were reduced into ordinary differential equations using appropriate similarity transformation. The resulting systems of ordinary differential equations were then solved numerically using Keller box method. The numerical values of the skin friction coefficient, the local Nusselt number which represents the heat transfer rate at the surface as well as the velocity and temperature profiles were obtained for various values of the magnetic field inclination angle, magnetic interaction, plate inclination angle, nanoparticles volume fraction, wedge angle, moving wedge, unsteadiness, Grashof number and thermal buoyancy. All results obtained, were displayed graphically in addition to tabular form. The comparisons of results with previous studies were made to validate the results. For both steady and unsteady problems, it is found that magnetic field inclination angle can be used as controlling factor for certain situation because it enhances the skin friction and heat transfer rate. The plate inclination angle parameter and nanoparticles volume fraction parameter have tendency to increase momentum and thermal boundary layers thickness. For unsteady problems, it is observed that the unsteadiness parameter has significant effect on the nanofluids motion and heat transfer characteristic

Transformation Thermotics and Extended Theories

This open access book describes the theory of transformation thermotics and its extended theories for the active control of macroscopic thermal phenomena of artificial systems, which is in sharp contrast to classical thermodynamics comprising the four thermodynamic laws for the passive description of macroscopic thermal phenomena of natural systems. This monograph consists of two parts, i.e., inside and outside metamaterials, and covers the basic concepts and mathematical methods, which are necessary to understand the thermal problems extensively investigated in physics, but also in other disciplines of engineering and materials. The analyses rely on models solved by analytical techniques accompanied by computer simulations and laboratory experiments. This monograph can not only be a bridge linking three first-class disciplines, i.e., physics, thermophysics, and materials science, but also contribute to interdisciplinary development