Temperature-sensitive Magnetic Fluid Research Articles

Synthesis of Temperature-Sensitive Magnetic Microcapsules and Visualization of Cluster Formation

Temperature-sensitive magnetic fluids flow spontaneously in a magnetic field when there is a temperature difference and thus may be used in cooling devices operated without external power. However, magnetic fluids are difficult to mass-produce, and the dispersion ability of the working fluid cannot be controlled. We use magnetic material encapsulated in microcapsules of large diameter to function as a new type of refrigerant. By enclosing the magnetic material in capsules, they can be used with any working fluid. We made solid particles containing kerosene-based magnetic fluid in polymer. When a magnetic field was applied, the particles aggregated and formed clusters. A scanning electron microscope and focused ion beam system were used to determine the particle shapes. Particles 5–50 $\mu$ m in size could be created by varying the rotation speed of the homogenizer during the synthesis.

Tunable Curie temperature of Mn0.6Zn0.4Fe2O4 nanoparticles

Synthesis of stable temperature sensitive magnetic fluids that can be used in heat exchange devices having desired magnetic properties and tunable Curie temperature is quite challenging as their performance parameters are strongly correlated with preparation conditions of magnetic nanoparticles. In this article, we report size dependence of Curie temperature and saturation magnetization of Mn0.6Zn0.4Fe2O4 (MZ4) nanoparticles synthesized by co-precipitation method by controlling the pH, reaction temperature and reaction time. As-synthesized MZ4 nanoparticles have tunable Curie temperature that ranges between 392 K and 665 K. These magnetic nanoparticles are well suited for cooling applications in energy conversion electronic devices as their Curie temperatures are close to the working temperature of these devices. The observed tunability of Curie temperature and magnetization of MZ4 nanoparticles are analysed in terms of the corresponding changes in the magnetic particle size and distribution of Mn ions between tetrahedral (A-site) and octahedral (B-site) in an inverse spinel structure.

Long Distance Heat Transfer of Pump-Less Heat Transport Device Using Temperature-Sensitive Magnetic Fluids

Long Distance Heat Transfer of Pump-Less Heat Transport Device Using Temperature-Sensitive Magnetic Fluids

Synthesis and Flow Field Visualization of Temperature-sensitive Magnetic Fluid Microcapsules

Synthesis and Flow Field Visualization of Temperature-sensitive Magnetic Fluid Microcapsules

Effect of thermal aging on stability of transformer oil based temperature sensitive magnetic fluids

Synthesizing stable temperature sensitive magnetic fluids with tunable magnetic properties that can be used as coolant in transformers is of great interest, however not exploited commercially due to the lack of its stability at elevated temperatures in bulk quantities. The task is quite challenging as the performance parameters of magnetic fluids are strongly influenced by thermal aging. In this article, we report the effect of thermal aging on colloidal stability and magnetic properties of Mn1-xZnxFe2O4 magnetic fluids prepared in industrial grade transformer oil. As-synthesized magnetic fluids possess good dispersion stability and tunable magnetic properties. Effect of accelerated thermal aging on the dispersion stability and magnetic properties have been evaluated by photon correlation spectroscopy and vibration sample magnetometry, respectively. Magnetic fluids are stable under accelerated aging at elevated temperatures (from 50 °C to 125 °C), which is critical for their efficient performance in high power transformers.

Temperature dependent acoustic properties of temperature sensitive magnetic fluid subjected to magnetic field

The ultrasonic velocity of temperature sensitive magnetic fluid is investigated as a function of volume fraction, temperature and magnetic field. The ultrasonic velocity decreases with increasing volume fraction of magnetic nanoparticles. This is attributed to the particle-carrier interaction which leads to form shorter aggregates. The pre-aggregates in magnetic fluid break when temperature increases in the absence of a field. Magnetic field makes the system anisotropic to ultrasound wave propagation. The change in ultrasonic propagation velocity under the influence of magnetic field shows chain like alignment for low volume fraction of magnetic nanoparticles (1.6%) which changes to short dipolar chains at an intermediate volume fraction (6.8%). Above this volume fraction, short chains become thicker by aligning sidewise to the neighboring chains resulting in spherical drop like structures. The modified Tarapov's theory fit to change in ultrasonic propagation velocity confirms the transformation from chains to aggregates with increasing magnetic nanoparticles volume fraction. The optical microscopy study also confirms the results. Upon increasing the temperature the field dependent velocity variation shows breaking of thick chain like aggregates. The modified Tarapov's theory fit shows that this is attributed to decrease in magnetic moment with increasing temperature. The variation of magnetic moment with temperature obtained from the fitting gives the Curie temperature of fluid as 363K. This value agrees with those obtained from other techniques.

Performance of Mn-Zn ferrite magnetic fluid in a prototype distribution transformer under varying loading conditions

The temperature distribution performance of prototype transformer has been evaluated for varying loads. A 3 KVA single phase transformer is prototyped for this purpose and thermocouples were inserted at various places for the study. A novel temperature sensitive magnetic fluid (TSMF - Mn-Zn ferrite magnetic fluid) is proposed to improve the cooling performance. Winding temperature reduces when prototype transformer is submerged in TSMF compared to the same experiment performed with transformer oil, for all loading (normal load, under load, overload). The reduction in temperature with TSMF attributes to the thermo-magnetic convection, and it is the maximum when the Curie temperature of the magnetic fluid is comparable to the hot spot temperature of the transformer. The experimental results match with numerical calculation and the existing simulation. The maximum cooling is observed with TSMF for overload condition and increases normal life expectancy nine times. In case of planned overload condition normal life expectancy doubles for all situations. Study leads to the conclusion that TSMF works as a better transformer coolant under all conditions, delivers more power than its nameplate rating without using any external accessories, and improves normal life of transformer. This will reduce the basic investment cost and maintenance of transformer.

Energy transport in cooling device by magnetic fluid

Temperature sensitive magnetic fluid has a great potential with high performance heat transport ability as well as long distance energy (heat) transporting. In the present study experimental set-up was newly designed and constructed in order to measure basic heat transport characteristics under various magnetic field conditions. Angular dependence for the device (heat transfer section) was also taken into consideration for a sake of practical applications. The energy transfer characteristic (heat transport capability) in the magnetically-driven heat transport (cooling) device using the binary TSMF was fully investigated with the set-up. The obtained results indicate that boiling of the organic mixture (before the magnetic fluid itself reaching boiling point) effectively enhances the heat transfer as well as boosting the flow to circulate in the closed loop by itself. A long-distance heat transport of 5m is experimentally confirmed, transferring the thermal energy of 35.8W, even when the device (circulation loop) is horizontally placed. The highlighted results reveal that the proposed cooling device is innovative in a sense of transporting substantial amount of thermal energy (heat) as well as a long distance heat transport. The development of the magnetically-driven heat transport device has a great potential to be replaced for the conventional heat pipe in application of thermal engineering.

感温性磁性流体を用いた MHD 方式熱エナジーハーベスタ

This paper proposes a thermal energy harvester of MHD system using a temperature sensitive magnetic fluid (TSMF) which is magnetized by the temperature changes. Heat transport systems using TSMF have already been proposed by several studies, but both heat transport system and thermal energy harvester of MHD system have not been yet developed. The device is a 244 mm length rectangular closed channel of 4 × 5 mm. The operation of this device is carried out by two permanent magnets between the cooling and heating sections. The maximum voltage was about 0.055 mV in this experiment. It was about 80 % of the voltage obtained theoretically. Furthermore, parameters of the thermal characteristics were calculated.

感温性磁性流体を用いた磁気熱輸送に関する研究

感温性磁性流体を用いた磁気熱輸送に関する研究

A Nondimensional Analysis to Characterize Thermomagnetic Convection of a Temperature Sensitive Magnetic Fluid in a Flow Loop

This paper presents results from theoretical and numerical studies of a single-phase, temperature sensitive magnetic fluid operating under steady-state laminar flow conditions in a partially heated thermomagnetic circulation loop under the influence of an external magnetic field (created by a solenoid). A one-dimensional theoretical model has been developed using scaling arguments to characterize thermomagnetic circulation in this loop in terms of the geometric length scales, magnetic fluid properties, and the strength of the imposed magnetic field. In parallel to this theoretical analysis, supporting numerical simulations using Comsol Multiphysics simulation software have been undertaken to obtain data for use in this 1D model. Comparison between experimental data and numerical simulation results and also a grid sensitivity analysis was carried out to validate the numerical simulation. A correlation for the nondimensional heat transfer (Nusselt number) as a function of the appropriate magnetic Rayleigh number and a correlation for the mass flow rate based on the system's properties are developed.

Application of a Binary Temperature-Sensitive Magnetic Fluid for a Mini Magnetically-Driven Heat Transport Device

Application of a Binary Temperature-Sensitive Magnetic Fluid for a Mini Magnetically-Driven Heat Transport Device

Slip Flow and Heat Transfer of Magnetic Fluids in Micro Porous Media Using a Lattice Boltzmann Method

In this paper, a Lattice Boltzmann method was used to simulate the flow of temperature-sensitive magnetic fluids in a micro porous cavity. According to Navier’s linear slip length model, slip boundary conditions were used on all the walls of the micro porous cavity. The effects of the horizontal slip length and the vertical slip length on the flow and heat transfer characteristics were investigated. The results showed that with the increase of the slip length, the velocities and their gradients became smaller, so the convection was harder to occur, and the temperature was more stable. On the walls, the effects of the slip lengths on the Nusselt numbers at the edges and at the centers were different, so the local heat transfer efficiencies were changed accordingly. It was also found that when the horizontal slip length was set to be zero, the flow developed from one vertex to two vortexes along the vertical direction with the increase of vertical slip length. The corresponding critical vertical slip length first increased and then decreased with the Rayleigh number and the magnetic Rayleigh number.

0804 高熱伝導率を有する非磁性粒子混入系における感温性磁性流体の伝熱特性調査(OS8-1 機能性流体工学の融合化新展開,OS8 機能性流体工学の融合化新展開)

In the present work, heat transfer characteristics in cubic cavity are investigated experimentally in thermoma gnetic natural convection of temperature sensitive magnetic fluid(TSMF) with Copper particles(non-magnetic particles) under magnetic field. Also we studied on cooling capacity of TSMF with non-magnetic particles in cubic cavity under magnetic field. The experimental results show that the heat transfer characteristic is enhanced when the magnetic field is applied to the TSMF and Copper particles are immersed in the TSMF.

Magnetic ejection effect under uniform magnetic field

In the present work, a study of the ejection of a non-magnetic particle due to the magnetic buoyancy force under a uniform magnetic field was carried out. The simulation is based on a hybrid Lattice Boltzmann Method (LBM). The non-magnetic particle’s trajectory was calculated using resultant numerical flow field solutions. Generally, no magnetic body force acts on the fluid under a uniform magnetic field if the magnetization of the magnetic fluid has no temperature dependence. However, when Temperature-Sensitive Magnetic Fluid (TSMF) is combined with a gradient of temperature, the phenomenon of magnetic ejection happens for a particle. In the present work, it is revealed that the particle is ejected from its initial position and moves towards the low pressure regions regardless of the liquid flow direction.

Heat transport with temperature-sensitive magnetic fluid for application to micro-cooling device

Heat transport with temperature-sensitive magnetic fluid for application to micro-cooling device

Effect of temperature on rotational viscosity in magnetic nano fluids

Flow behavior of magnetic nano fluids with simultaneous effect of magnetic field and temperature is important for its application for cooling devices such as transformer, loud speakers, electronic cooling and for its efficiency in targeted drug delivery and hyperthermia treatment. Using a specially designed horizontal capillary viscometer, temperature-sensitive and non-temperature-sensitive magnetic nano fluids are studied. In both these case the temperature-dependent rotational viscosity decreases, but follows a quite different mechanism. For temperature-sensitive magnetic nano fluids, the reduction in rotational viscosity is due to the temperature dependence of magnetization. Curie temperature ((T)(c)) and pyromagnetic coefficient are extracted from the study. A fluid with low T(c) and high pyromagnetic coefficient is useful for thermo-sensitive cooling devices and magnetic hyperthermia. For non-temperature-sensitive magnetic nano fluids, reduction in rotational viscosity is due to removal of physisorbed secondary surfactant on the particle because of thermal and frictional effects. This can be a good analogy for removal of drug from the magnetic particles in the case of targeted drug delivery.

Heat transport characteristics of a magnetically-driven heat transport device using a binary temperature-sensitive magnetic fluid

Heat transport characteristics of a magnetically-driven heat transport device using a binary temperature-sensitive magnetic fluid

Analysis of temperature-sensitive magnetic fluids in a porous square cavity depending on different porosity and Darcy number

Magnetic fluids are thermo-sensitive and whose flow and energy transport processes can be controlled by temperature and external magnetic field. In the natural convection of porous cavity, magnetic force is not only the driving force, the effective gravity is also a force related to the natural convection, and the effective gravity is closely depending on the porosity and permeability of porous medium. As is known, the porous medium is in solid state with high heat capacity but low heat transfer coefficient, while the magnetic fluid is a kind of fluid with high heat transfer coefficient and easy to be controlled. Combining the complementary characteristic of magnetic fluids and porous medium, we present a study for temperature-sensitive magnetic fluids in a porous square cavity. In the study, a Lattice Boltzmann method is developed to simulate the laminar convection of temperature-sensitive magnetic fluids in a porous square cavity. We present numerical results for the streamlines, isotherms, magnetization for different values of porosity and Darcy number. In addition, Nusselt numbers on heated and cooled wall and the average Nusselt numbers are also investigated.

NATURAL CONVECTION OF TEMPERATURE-SENSITIVE MAGNETIC FLUIDS IN POROUS MEDIA

In this article, natural convection of a temperature-sensitive magnetic fluid in a porous media is studied numerically by using lattice Boltzmann method. Results show that the heat transfer decreases when the ball numbers increase. When the magnetic field is increased, the heat transfer is enhanced; however the average wall Nusselt number increases at small ball numbers but decreases at large ball numbers due to the induced flow being more likely confined near the bottom walls with a high number of obstacles.