Temperature-sensitive Magnetic Fluid Research Articles

Lattice Boltzmann simulation for temperature-sensitive magnetic fluids in a porous square cavity

A lattice Boltzmann method is developed to simulate temperature-sensitive magnetic fluids in a porous cavity. In the simulation, the magnetic force, efficient gravity, viscous loss term and geometric loss term in porous medium are imported to the momentum equation. To test the reliability of the method, a validation with water in porous cavity is carried out. Good agreements with the previous results verify that the present lattice Boltzmann method is promising for simulation of magnetic fluids in porous medium. In this study, we investigate the change of magnetization with external magnetic field, and we present numerical results for the streamlines, isotherms, and magnetization at vertical or horizontal mid-profiles for different values of Ram. In addition, Nusselt numbers changing with magnetic Rayleigh numbers are also investigated.

Natural Convection of Temperature-Sensitive Magnetic Fluids in Porous Media

AbstractIn 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.

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.

Magnetically-driven heat transport device using a binary temperature-sensitive magnetic fluid

The magnetic body force in boiling two-phase temperature-sensitive magnetic fluid (TSMF) flow is known to effectively increase the driving force of magnetic fluid in a non-uniform magnetic field. Based on this mechanism, in the present study, a binary TSMF, which is a mixture of the TSMF and a low-boiling-saturation-temperature organic solution, is proposed to be used in a heat transport device to enhance its circulation. In order to see its performance in the heat transport device, the pressure difference at different heated temperatures, magnetic fields and inclination angles of the heating section are investigated experimentally and theoretically. Results showed that the driving force increases remarkably due to more gas phase appearing in the test fluid and the magnetization of it decreasing. At low magnetic field the driving force is enhanced greatly when the inclination angle is close to 60°, while at high magnetic field the driving force is remarkably enhanced due to the effect of the magnetic force in the inclination angle range from 0° to 30° and 60° to 90°.

S0501-4-4 2流体混合磁性流体を用いた熱輸送装置([S0501-4]複雑流体の流動現象(4))

Temperature sensitive magnetic fluid (TSMF) has a property of magnetization dependent on temperature subjected to an applied magnetic field. In the present study, a binary magnetic fluid, which is a mixture of the TSMF and an organic secondary fluid, is utilized in a heat transport device to enhance its circulation. In order to verify the performance of the TSMF mixture in the heat transport device, the driving characteristics of this heat transport device are studied both experimentally and numerically. From the results it is found the driving force is enhanced greatly when the magnetic field intensity increases.

Design method of automatic energy transport devices based on the thermomagnetic effect of magnetic fluids

The present work is aimed at developing a design method for automatic energy transport devices based on the thermomagnetic effect of magnetic fluids. A model for describing thermomagnetic convection of a temperature-sensitive magnetic fluid in a loop is established, which includes the coupling of the three fundamental phenomena, i.e. magnetic, thermal, and fluid dynamic features. The thermomagnetic convection of the temperature-sensitive magnetic fluid in a loop-shape energy transport device is simulated in the presence of an external magnetic field. Comparison between experimental data and numerical results is carried out to validate the model. The effects of different factors such as input heat load, heat sink temperature and magnetic field distribution along the loop on the performance of the energy transport device are analyzed and discussed according to the numerical simulation results.

A new miniaturized engine based on thermomagnetic effect of magnetic fluids

A new engine system, essentially consisting of a permanent NdFeB magnet, a kerosene-based magnetic fluid and a rotor, is proposed based on the thermomagnetic effect of a temperature-sensitive magnetic fluid. The rotor was driven by the thermal convection of the magnetic fluid in the presence of a homogeneous external magnetic field. A digital camera was used to record the rotation speed of the rotor to investigate the performance of the engine system under varying conditions such as heat load, heat sink temperature, and magnetic field distribution. The peak angle velocity obtained for the rotor was about 2.1 rad/min. The results illustrate that the rotation speed of the rotor increases as the input heat load increases, or as the heat sink temperature decreases. The performance of the motor is considerably influenced by the magnetic field imposed. Therefore, the performance of such an engine can be controlled conveniently by changing the external magnetic field and/or the temperature distribution in the fluid.

Characterization of miniature automatic energy transport devices based on the thermomagnetic effect

The synergetic effect of an external magnetic field and the temperature gradient in the fluid constitutes a magnetocaloric pump. The miniature automatic energy transport device (AETD) is developed by using a temperature sensitive magnetic fluid as a coolant, in which the magnetic force resulting from the integrated effect of the external magnetic field and the fluid temperature variation drives the fluid in a loop. The flow and heat transport features of the AETD are experimentally examined in order to get insight into the mechanism and controlling approaches for such an automatic operation device. The micro-scale particle image velocimetry (μPIV) technique is used to visualize the flow field of the magnetic fluid in the loop. Three types of AETD systems are established to study the effect of the loop structure and components on the AETD performance. By means of experimental data about the magnetic field, flow velocity and fluid temperature along the loop, the constitutive thermal, magnetic and fluid dynamic relationships of the AETD are discussed.

Particle image velocimetry for an automatic cooling device using temperature-sensitive magnetic fluid

An automatic cooling device has been developed by using a temperature-sensitive magnetic fluid as the coolant. A particle image velocimetry (PIV) system was used to measure the flow velocity of the fluid inside the loop. The efficiency of the device under varying conditions such as the heat load and the power of cooling were experimentally investigated. The effect of cooperation between external magnetic field and thermal field on the performance of the device was studied. As expected, a continuous flow induced by the thermal and magnetic field was observed in the loop, where heat was transferred by the circulating magnetic fluid. The synergic effect between the magnetic field and the temperature gradient has impact on the performance of the device.

Investigation on operational characteristics of a miniature automatic cooling device

The magnetocaloric effect is a well-known phenomenon, which can be applied to develop a system for the magnetic conversion of heat to work or automatic cooling of a working fluid without any mechanical pump. A prototype of a miniature automatic cooling device is established, which is mainly composed of a temperature-sensitive magnetic fluid, a permanent NdFeB magnet, heat sources and heat sink. A series of experiments are conducted to investigate the feasibility, the performance capacity of the cooling device. A model for simulating the operation process is provided and the principle of parameter estimation is applied to determine the flow velocity of the fluid in the loop. The effects of several factors such as the external magnetic field and the temperature distribution of the magnetic fluid on the cooling performance of the device are discussed.

Magneto-optical techniques to determine Curie temperature of magnetic fluids

Magnetic field induced extinction of light and birefringence as a function of temperature is used to study the temperature dependence of magnetic moment as well as the domain magnetization of the temperature sensitive magnetic fluids. Subsequently, the Curie temperature and pyromagnetic coefficient of the same are determined. The results obtained from this technique are compared with the results obtained from other techniques. This technique is remarkably simple and low cost.

Heat Transport and Driving Force Characteristics of Heat Transport Device Using Magnetic Fluid in Various Magnetic Fields

In order to evaluate the heat transport capability in the thermomagnetic cycle using temperature sensitive magnetic fluids, a fundamental design work is conducted for practical applications. In the present study, the heat transport characteristics together with pressure characteristics are examined for various magnetic field configurations by means of a numerical analysis and experiments. It is found that the distribution of magnetic field in the radial direction of an electromagnet largely affects the force and the heat transport characteristics. From results, it is shown that the aspect ratio of an electromagnet is the key factor.

Preparation and properties of temperature-sensitive magnetic fluid having Co0.5Zn0.5Fe2O4 and Mn0.5Zn0.5Fe2O4 nanoparticles

Magnetic properties of Co0.5Zn0.5Fe2O4 and Mn0.5Zn0.5Fe2O4 nanoparticles and preparation of temperature-sensitive magnetic fluid are discussed in this paper. Ferrofluids having Co0.5Zn0.5Fe2O4 and Mn0.5Zn0.5Fe2O4 fine particles were prepared by co-precipitation and by ball milling the precipitated fine particles. Ball milling technique was used for coating of the surfactant rather than size reduction. The final cation contents estimated from the prepared powder samples agree with the initial degree of substitution. The powder samples were characterized by XRD, VSM and Mossbauer studies. The precipitated particles were less than 10nm size and showed FCC spinel structure. Mossbauer studies confirm the single domain nature of the fine particles. Temperature-sensitive ferrofluid having transformer oil as the carrier liquid was prepared by carrier exchange technique. Co0.5Zn0.5Fe2O4 particles can be used for the preparation of temperature-sensitive magnetic fluid with relatively large magnetic volume force.

Characteristics of thermo-magnetic driven motor using magnetic fluid

A basic study of a newly designed direct-heat-to-power energy conversion device, using temperature-sensitive magnetic fluid, was conducted. Results of numerical analysis demonstrated that the magnetic fluid does circulate around the rotaion disc as thought by the theory, indicating that vortices generated in the flow field reduce the overall flow circulation when magnetic field was highly strengthened. Although the device did not give the shaft output yet in experiment, the measured temperature field showed qualitatively good agreement with the numerical results particularly at the strong magnetic field.

Research on Driving Force Characteristics of Low Boiling Point Solution Mixture of Temperature Sensitive Magnetic Fluid

In the present study, we propose a method for realizing the thermo-magnetic cycle with a gas-liquid two-phase flow by boiling a binary mixture of temperature sensitive magnetic fluid (TSMF) with an organic liquid of n-hexane, which has a lower boiling point. The boiling point of the fluid was adjusted below the boiling point of TSMF. From results of experiment, it was found that with the two-phase flow, the driving force was highly enhanced by applying magnetic field, showing substantial decrease in spatial averaging magnetization by n-hexane gas bubbles. Owing to sufficient magnetic driving force, it was observed that a self-circulation state of the device is possible, yielding that the proposed binary mixture of TSMF enables to design the self-circulation heat transport system by utilization of two-phase flow, which can operate only with its own magnetic driving force provided from temperature difference.

Flow Boiling Heat Transfer Characteristics of a Binary Mixed Magnetic Fluid

Boiling heat transfer characteristics were verified for a temperature sensitive magnetic fluid, to which the organic fluid was mixed, yielding a binary-carrier-fluids magnetic fluid. Substantial increase of heat transport capability was achieved in comparison with an ordinary magnetic fluid. In the present study, n-hexane, which has lower boiling point than that of kerosene (mother carrier fluid), was mixed. It was found that the heat transport capability is surely improved with applying magnetic field to the binary mixed magnetic fluid flow. And the effect of vortices predicted by predicted by previous numerical studies is confirmed in the present study, thus the heat transfer characteristics from the heated wall is strongly affected by the vortices.

Mn–Zn ferrite with higher magnetization for temperature sensitive magnetic fluid

A growth-assisted coprecipitation process is proposed to achieve highly magnetic Mn–Zn ferrite particles. In this method, first, the particles were synthesized by coprecipitation under optimum condition. Then, further enhancement in particle size was obtained by using the already prepared particles as seed. The average crystallite size of the particles prepared by the proposed method was 12 nm. Furthermore, the magnetization at 1 T applied field was 50 emu/g compared to 37 emu/g of coprecipitated particles. It should be noted that the Curie temperature of the particles remained similar to the coprecipitated particles suggesting that the composition of the Mn–Zn ferrite particles has not been affected by the modified synthesis technique. The gradient of the magnetization-temperature curve was enhanced as a consequence of the rise in magnetization. These particles could be used for the synthesis of temperature sensitive magnetic fluid with higher magnetization and magnetization-temperature gradient.

Study of a Simple Power Generating Device Using Temperature-Sensitive Magnetic Fluid.

A study of direct-heat-to-power energy conversion device, using temperature-sensitive magnetic fluid, was conducted. Numerial simulation was carried out in order to obtain fundamental characteristics of the device. The working principle of the device is based on the thermo-magnetic effect of magnetic fluid, in which the driving force (the driving pressure) needed to circulate magnetic fluid in the thermodynamical power cycle can be derived from the magnetization difference in a temperature field. When a magnetic field is imposed on the rectangle box in which a magnetic fluid is enclosed, a magnetic fluid is made to circulate so that a rotation disc inside the rectangle box is rotated by the friction of the fluid flow. Magnetic fluid is modeled by Rosensweig equation and its magnetization is calculated with Langivin type equation. results of numerical analysis showed various aspects of the device, indicating that the device is feasible as thought by the theory (power generating thermo dynamical system). Optimization of the device is also considered to gain sufficient shaft output and the efficiecy. It is concluded that further development of the device is possible with different structure of the device as well as the direction of imposing magnetic field.

Study for Magnetically Controlled Heat Transport Device with Axial Rotation.

A basic study was conducted for a heat transport device utilizing a temperature-sensitive magnetic fluid whose magnetization largely depends on temperature. The device is rotated with its own axis in a magnetic field, and it is functioned by driving forces derived from the centrifugal force and the thermo-magnetic body force. In the present study, heat transport characteristics for the device were investigated numerically and experimentally. The flow and temperature states of the device was obtained by numerical analysis in order to examine the basic heat transport performance. It has been clearfied that heat transport characteristics largely depends on the flow states of the device when the magnetic field and rotation are effected.

Electron spin resonance study of a temperature sensitive magnetic fluid

Electron spin resonance spectra of a temperature sensitive magnetic fluid involving polydispersed Mn0.5Zn0.5Fe2O4 ferrite particles are scanned from 200 to 400 K. For such a polydispersed system, the deconvolutions of the spectra suggest coexistence of two different resonance modes: (i) a broad line due to ferrimagnetic resonance and (ii) a sharp line at g=2 due to intrinsic superparamagnetic phase. From the intensity variation of the line at g=2, it is found that the contribution due to the superparamagnetic phase increases with temperature. A study of peak-to-peak linewidth variation with temperature indicates that the weakening of the magnetic moment is responsible for the observed reduction in the linewidth.