Numerical Analysis Of Heat Transfer Parameters Using Ferrofluid

Experimental investigation on heat transfer characteristics of magnetic fluid flow around a fine wire under the influence of an external magnetic field

In the present work we report the investigation of heat exchange processes at stationary boiling regime of magnetic fluid on a horizontal surface under magnetic field H ≤ 4.2 kA/m. In the presence of uniform magnetic field the specific thermal flow arriving to boiling magnetic fluid increases by 1.5 - 2 times. We offer the mechanism of magnetic field influence on heat exchange intensity in boiling magnetic fluid. The volume, shape and contact area of steam bubbles in horizontal heating surface in magnetic field is studied. The equation, connecting a specific thermal flow, magnetic field gradient and magnetic fluid magnetization in bubble boiling regime of magnetic fluid is written.

The article presents the results of an experimental study of the heat transfer process in magnetic fluid under the influence of electric and magnetic fields of various configurations. It is shown that a constant electric field leads to an increase in the heat transfer coefficient when a certain threshold value of tension in a thin layer of magnetic fluid is reached. The possibilities of controlling the heat transfer process using the additional effects of homogeneous and inhomogeneous magnetic fields are found.

자성유체는 고액혼상유체로 뉴턴유체와 달리 자기력에 반응하는 유체이다. 본 연구에서는 금속과 유체의 특성을 겸비한 자성유체의 열전달 특성을 밀도 있게 연구함을 목적으로, 그 대상을 이중원관으로 하여 열대류현상을 고찰하기 위해 내부원관을 가열하고, 외부원관을 냉각하면서, 또한 외부에서 인가자장의 세기와 방향에 따라 자연대류 현상의 변화 및 열전달 특성을 수치해석적으로 연구하여, 실험결과와 비교 검토하였다. 자성유체의 자연대류현상은 인가자장에 따라 제어할 수 있었고, 평균 뉴셀트수를 구한 결과로서 자장을 가하지 않았을 경우와 비교해 보면 열전달은 자장을 중력방향으로 가하거나 중력과 반대방향으로 그세기를 -14 mT이상 가했을 때 증가하였고, 중력과 반대방향으로 감했을 때 감소하였다. 특히 자장의 세기가 -14 mT가 되면 열전달은 최소가 되었다. Compared with Newtonial fluids, magnetic fluids have effects on magnetic force. In this study, the purpose is to research the heat transfer characteristic of magnetic fluids which have metalic and fluid characteristics as the external pipe is being cooled and internal pipe is heated. This study found the experimental results from the study of the variety of natural convection for magnetic fluids and the characteristics of the heat transfer by using numerical analysis according to the strength and direction of the magnetic fields from being imposed from the outside. Natural convection of magnetic fluids was controlled by the impressed magnetic fields, and the result of mean nusselt number was calculated. If the impressed magnetic field is in the direction of gravity or the strength of impressed magnetic field is more than -14 mT in the opposite direction, the heat transfer is more than that without the impressed magnetic field. If the strength of impressed magnetic field is less than -14 mT in the opposite direction, it is smaller than that without the impressed magnetic field. Especially, when the strength of the magnetic field is -14 mT, the heat transfer was at the minimum.

Stability properties of a cylindrical flow in magnetic fluids: Effect of mass and heat transfer and periodic radial field

The object of research is the process of obtaining silicon nanomaterials for lithium-ion batteries of energy storage devices, and the subject of research is the technology of gas-phase plasma-chemical synthesis for the production of Si-nanoparticles. In the course of the study, numerical simulation methods were used, which made it possible to determine the parameters of temperature fields, velocities and concentrations. To study the processes of synthesis of nanopowders, a plasma reactor with an electric arc plasma torch of a linear scheme and using an argon-hydrogen mixture as a plasma-forming gas was developed. To analyze the influence of an external magnetic field on the control of the plasma jet parameters, a series of experiments was carried out using an electric arc plasma torch on plasma laboratory facilities with a power of 30 and 150 kW. The influence of a magnetic field on the process of formation and evaporation of a gas-powder flow in a plasma jet was studied by determining the configuration, geometric dimensions, and structure of the initial section of the jet. In this case, the dispersed material – silicon powder was fed to the plasma torch nozzle section according to the radial scheme. Experimental confirmation of the phenomenon of elongation of the high-temperature initial section of the plasma jet in a longitudinal magnetic field has been obtained. The experimental results indicate that the creation of a peripheral gas curtain significantly changes the characteristics of heat and mass transfer in the reactor. It should be expected that for optimization it is possible to exclude the deposition of nanosilicon particles on the walls of the reactor and provide conditions for continuous operation. The effect of two-phase flow, heat transfer, and mass flow of nanoparticles, including the surface of a plasma reactor with limited jet flow, in the processes of obtaining silicon nanopowders has been studied. This made it possible to correct a number of technological characteristics of the process of constructive design of the actions of plasma synthesis of nanopowders. The patterns obtained can be used for constructive and technological design in the creation and development of a pilot plant for high-performance production of nanosilicon powders.

The capillary tube viscometer is used to measure the viscosity of aqueous magnetic fluids under the influence of parallel and perpendicular magnetic fields. The effects of the volume fraction of the suspended magnetic particles, the concentration of surfactants, and the external magnetic field strength, as well as the orientation, on the viscosity of the magnetic fluid are analyzed. The experimental results show that the viscosity of the sample magnetic fluids increases with increases in the concentrations of suspended magnetic particles and surfactants. The external magnetic field is also an important factor that affects the viscosity of the magnetic fluid. The viscosity first increases with the magnetic field and finally approaches a constant as the magnetization attains a saturation state. For the same magnetic fluid, the viscosity in a perpendicular magnetic field is larger than that in a parallel magnetic field for the same magnetic field.

The potential of colloidal subdomain ferrite particle suspensions (SDP) (‘magnetic fluids’), exposed to an alternating magnetic field, is evaluated for hyperthermia. Power absorption measurements of different magnetic fluids are presented in comparison to multidomain ferrite particles (MDP). Variations with frequency as well as magnetic field strength have been investigated. The experimental results clearly indicate a definite superiority of even non-optimized magnetic fluids over MDP ferrites regarding their specific absorption rate (SAR). Based on the work of [Shliomis, Pshenichnikov, Morozov, Shurubor. Magnetic properties of ferrocolloids. J Magn Magn Mater 1990;85:40–46 and [Hanson The frequency dependence of the complex susceptibility of magnetic fluids. J Magn Magn Mater, 1991;96 (In press).], a solid-state physical model is applied to explain the specific properties of magnetic fluids with respect to a possible use in hyperthermia. The experimentally determined SAR data on magnetic fluids are used to estimate the heating capabilities of a magnetic induction heating technique assuming typical human dimensions and tissue parameters. It is considered that for a moderate concentration of 5 mg ferrite per gram tumour (i.e. 0.5% w/w) and clinically acceptable magnetic fields, intratumoral power absorption is comparable to RF heating with local applicators and superior to regional RF heating (by comparison with clinical SAR measurements from regional and local hyperthermia treatments). Owing to the high particle density per volume, inductive heating by magnetic fluids can improve temperature distributions in critical regions. Furthermore, localized application of magnetic fluids in a tumour might be easier and less traumatic than interstitial implantation techniques.

Purpose. Study of the dependence of the thermal modulus of elasticity of a two-component magnetic fluid on the magnitude of the magnetic field strength, the frequency of external disturbance and the volumetric concentration of magnetic particles.Method. The research method is based on the kinetic theory of liquid systems. Based on previously constructed kinetic equations for one-particle and two-particle distribution functions and a microscopic expression for the heat flux vector, an explicit dynamic expression for the thermal modulus of elasticity of magnetic fluids is obtained. In fast processes in liquids, heat transfer occurs in waves and their propagation is similar to the propagation of second sound in helium II. The thermal modulus of elasticity in liquids appears at high frequencies and ensures the propagation of second sound. The expression for the thermal modulus of elasticity consists of potential and kinetic parts, taking into account structural and translational relaxation processes, respectively. To study the thermoelastic properties of magnetic fluids, appropriate expressions of potential interaction energies were selected for each subsystem, allowing for numerical calculations.Results. Numerical calculations of the frequency and concentration dependence of the dynamic thermal modulus of elasticity in the presence of an external magnetic field in a kerosene-based magnetic fluid were carried out. The calculation results show that an increase in the influence of external disturbances leads to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid. An increase in the volume concentration of magnetic particles and an increase in the magnetic field strength also led to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid.Conclusion. It has been established that, due to taking into account translational and structural relaxation processes, the region of frequency dispersion of the thermal elastic modulus is wide. Numerical calculations carried out at different values of the external magnetic field and the volume concentration of magnetic particles showed that although an increase in the magnetic field and concentration of magnetic particles leads to an increase in the thermal modulus of elasticity, their increase does not affect the change in the frequency dispersion region.

Magnetic fields can be used to control the process of magnetic fluid dispersion in microfluidics. Here we demonstrate a method for generating magnetic fluid droplets of a given size and shape in a microfluidic chip with a flow-focusing configuration under the influence of a transverse magnetic field. The results of the study show that a magnetic field can have a significant impact on ferrofluid dispersion. At low volumetric flow rates of the continuous phase, magnetic force plays a primary role in ferrofluid dispersion due to disturbances on the magnetic fluid surface. Furthermore, the droplet diameter decreases with increasing magnetic field Dd ∼ H-1/3. At high volumetric flow rates of the continuous phase, shear stress plays a primary role in ferrofluid dispersion. In this case, the droplet diameter depends on the continuous phase velocity according to the law Dd ∼ u-1. The magnetic field and the volumetric flow rate of the continuous phase affect not only the liquid dispersion process but also the coalescence and deformation of droplets. The pressure gradient in the channel and the magnetic field contribute to droplet deformation. The thickness of the deformed droplet decreases with increasing volumetric flow rate according to the law l ∼ Q-1. The non-uniformity of the velocity field distribution over the channel thickness is responsible for droplet coalescence. The magnetic field, on the contrary, prevents droplet coalescence. These findings open up new possibilities for generating soft magnetic robots of a given size and shape.

Solar water heater are manufactured throughout the world and considered an appropriate technology at present for it is a simple, economic and environmental friendly technology. The heat transfer coefficient of the heat pipe plays an interval role on the efficient of making use of solar energy. This experimental research focuses on the heat transfer performance of heat pipes by introduce the magnetic fields and Nanofluid. The experimental results show that: without magnetic field, the heat transfer rate of the heat pipe with magnetic fluid is 13.9% higher than that of traditional heat pipe; under DC magnetic field, the heat transfer rate of magnetic fluid heat pipe is improved an average of 10.6%, and that of water heat pipe is improve 6% The outcomes have proved that the heat transfer performance can be enhanced by the magnetic field and magnetic fluid. The improvement of efficiency of solar energy usage would contribute to decreasing the environment limit on application of the solar heater in a wide range.

The magnetic fluid (MF) viscosity in MF targeting drug delivery system isn’t constant. With the change of magnetic field strength, MF viscosity will change due to MF magnetoviscous effect. The magnetoviscous effect mechanisms in low and high concentration MF are different and qualitatively analyzed respectively. Drop needle movement method under controlled temperature was adopted to measure magnetoviscous effect. Experiment results show the viscosity linearly increases by magnetic filed strength under low magnetic field. The viscosity reaches max value when MF is magnetic saturation. Through curve fitting, the magnetoviscous effect formula is got. Based on this formula, the MF viscosity in changed magnetic field can be obtained. The MF drug movement behave will be controlled by magnetic field and can be transferred accurately to target. This result also can be generalized to other MF viscosity research field.

Magnetic characteristics of magnetic compound fluid (MCF) under DC and AC magnetic fields

A novel method of controlling gas flow rate using magnetic fluid is proposed. Magnetic fluids under non-uniform magnetic field have strong dynamic pressure distribution along the magnetic field gradient at the gas-liquid interface with bulk magnetic body force. The principle of proposed gas flow rate control technique is based on controlling the pressure distribution, which can be controlled by magnetic field. In this report, controlling technique is introduced and the accuracy of the flow rate control with resolution of the control technique is reported. From measured data (giving a reference for measuring the small gas flow rate), it was found that the flow rate decreases with increasing magnetic flux intensity, and is largely dependent on the magnetic pressure which acts on magnetic fluid, particularly to the interface of gas-liquid phase. The flow rate and the magnetic pressure have a definite relation with the flow coefficient, so that, the flow rate can be controlled only by the magnetic pressure. It was satisfactory verified from the proposed controlling technique that the proposed gas flow controlling method is useful to control the low gas flow rate as low as 0.3×10-5m3/s with the excellent resolution.

Ferrofluid aggregation in chains under the influence of a magnetic field