Scaling of thermo-magnetic convection

The scaling to characterize unsteady boundary layer development for thermo-magnetic convection of paramagnetic fluids with the Prandtl number greater than one is developed. Under the consideration is a square cavity with initially quiescent isothermal fluid placed in microgravity condition (g = 0) and subject to a uniform, vertical gradient magnetic field. A distinct magnetic thermal-boundary layer is produced by sudden imposing of a higher temperature on the vertical sidewall and as an effect of magnetic body force generated on paramagnetic fluid. The transient flow behavior of the resulting boundary layer is shown to be described by three stages: the start-up stage, the transitional stage and the steady state. The scaling is verified by numerical simulations with the magnetic momentum parameter m variation and the parameter γRa variation.

Thermo-magnetic convection of paramagnetic fluids with non-instantaneous heating

The unsteady boundary-layer development for thermomagnetic convection of paramagnetic fluids inside a square cavity has been considered in this study. The cavity is placed in a microgravity condition (no gravitation acceleration) and under a uniform magnetic field which acts vertically. A ramp temperature boundary condition is applied on left vertical side wall of the cavity where the temperature initially increases with time up to some specific time and maintain constant thereafter. A distinct magnetic convection boundary layer is developed adjacent to the left vertical wall due to the effect of the magnetic body force generated on the paramagnetic fluid. An improved scaling analysis has been performed using triple-layer integral method and verified by numerical simulations. The Prandtl number has been chosen greater than unity varied over 5-100. Moreover, the effect of various values of the magnetic parameter and magnetic Rayleigh number on the fluid flow and heat transfer has been shown.

Effect of MHD and heat generation on natural convection flow in an open square cavity under microgravity condition

Purpose - Thermo-magnetic convection and heat transfer of paramagnetic fluid placed in a micro-gravity condition (g = 0) and under a uniform vertical gradient magnetic field in an open square cavity with three cold sidewalls have been studied numerically. Design/methodology/approach - This magnetic force is proportional to the magnetic susceptibility and the gradient of the square of the magnetic induction. The magnetic susceptibility is inversely proportional to the absolute temperature based on Curie’s law. Thermal convection of a paramagnetic fluid can therefore take place even in zero-gravity environment as a direct consequence of temperature differences occurring within the fluid due to a constant internal heat generation placed within a magnetic field gradient. Findings - Effects of magnetic Rayleigh number, Ra, Prandtl number, Pr, and paramagnetic fluid parameter, m, on the flow pattern and isotherms as well as on the heat absorption are presented graphically. It is found that the heat transfer rate is suppressed in increased of the magnetic Rayleigh number and the paramagnetic fluid parameter for the present investigation. Originality/value - It is possible to control the buoyancy force by using the super conducting magnet. To the best knowledge of the author no literature related to magnetic convection for this configuration is available.

Magnetic convection heat transfer in an open-ended enclosure filled with paramagnetic fluids

Numerical simulations of thermomagnetic convection of paramagnetic fluids placed in a micro-gravity condition (g ≈ 0) and under a uniform vertical gradient magnetic field in an open ended square enclosure with ramp heating temperature condition applied on a vertical wall is investigated in this study. In presence of the strong magnetic gradient field thermal convection of the paramagnetic fluid might take place even in a zero-gravity environment as a direct consequence of temperature differences occurring within the fluid. The thermal boundary layer develops adjacent to the hot wall as soon as the ramp temperature condition is applied on it. There are two scenarios can be observed based on the ramp heating time. The steady state of the thermal boundary layer can be reached before the ramp time is finished or vice versa. If the ramp time is larger than the quasi-steady time then the thermal boundary layer is in a quasi-steady mode with convection balancing conduction after the quasi-steady time. Further increase of the heat input simply accelerates the flow to maintain the proper thermal balance. Finally, the boundary layer becomes completely steady state when the ramp time is finished. Effects of magnetic Rayleigh number, Prandtl number and paramagnetic fluid parameter on the flow pattern and heat transfer are presented.

Magnetic convection heat transfer in an open ended enclosure filled with paramagnetic fluids

Numerical simulations of thermomagnetic convection of paramagnetic fluids placed in a micro-gravity condition (g nearly 0) and under a uniform vertical gradient magnetic field in an open ended square enclosure with ramp heating temperature condition applied on a vertical wall is investigated in this study. In presence of the strong magnetic gradient field thermal convection of the paramagnetic fluid might take place even in a zero-gravity environment as a direct consequence of temperature differences occurring within the fluid. The thermal boundary layer develops adjacent to the hot wall as soon as the ramp temperature condition is applied on it. There are two scenario that can be observed based on the ramp heating time. The steady state of the thermal boundary layer can be reached before the ramp time is finished or vice versa. If the ramp time is larger than the quasi-steady time then the thermal boundary layer is in a quasi-steady mode with convection balancing conduction after the quasi-steady time. Further increase of the heat input simply accelerates the flow to maintain the proper thermal balance. Finally, the boundary layer becomes completely steady state when the ramp time is finished. Effects of magnetic Rayleigh number, Prandtl number and paramagnetic fluid parameter on the flow pattern and heat transfer are presented.

两层流体热毛细对流空间实验研究=Space Experiments of Thermo Capillary Convection in Two-liquid Layers

1999年,在我国实践5号卫星上完成了两层流体空间实验,实验研究两层不相混合流体的纯Marangoni对流（温度梯度与界面垂直）与热毛细对流（温度梯度方向与流体界面平行）.前者存在发生Marangoni对流的最小临界温差值△Tc,低于该值流体系统处于静止状态;后者中只要存在沿界面的温度梯度便会产生热毛细对流.空间实验采用石蜡和氟化液两层流体新体系,实现了平整的液-液交界面,并从卫星上传回上万幅数字图像.通过多幅图像叠加处理得到了定量的流速场.数值模拟计算分析了相应工况时对流流动的速度场,两者的流场结构和速度大小基本一致,实验验证了理论模型.

Magnetic damping of levitated liquid droplets in AC and DC field

The intense AC magnetic field required to produce levitation in terrestrial conditions, along with the buoyancy and thermo-capillary forces, results in turbulent convective flow within the droplet. The use of a homogenous DC magnetic field allows the convective flow to be damped. However the turbulence properties are affected at the same time, leading to a possibility that the effective turbulent damping is considerably reduced. The MHD modified K-Omega turbulence model allows the investigation of the effect of magnetic field on the turbulence. The model incorporates free surface deformation, the temperature dependent surface tension, turbulent momentum transport, electromagnetic and gravity forces. The model is adapted to incorporate a periodic laser heating at the top of the droplet, which have been used to measure the thermal conductivity of the material by calculating the phase lag between the frequency of the laser heating and the temperature response at the bottom. The numerical simulations show that with the gradual increase of the DC field the fluid flow within the droplet is initially increasing in intensity. Only after a certain threshold magnitude of the field the flow intensity starts to decrease. In order to achieve the flow conditions close to the ‘laminar’ a D.C. magnetic field >4 Tesla is required to measure the thermal conductivity accurately. The reduction in the AC field driven flow in the main body of the drop leads to a noticeable thermo-capillary convection at the edge of the droplet. The uniform vertical DC magnetic field does not stop a translational oscillation of the droplet along the field, which is caused by the variation in total levitation force due to the time-dependent surface deformation.

Structural and Magnetic Properties of Amorphous Tb-Dy-Fe-Co Thin Films

This paper reports the effect of film thickness (50, 200, 400 and 800 nm) on the structural and magnetic properties of amorphous Tb-Dy-Fe-Co alloy thin films. All the films are found to exhibit perpendicular magnetic anisotropy (PMA) irrespective of the film thickness. The PMA is found to decrease with increase in film thickness due to the decrease in the magnetic texture and anisotropy energy. While the coercivity deduced from the out-of-plane magnetization curve increases with increasing film thickness, the in-plane coercivity exhibits weak thickness dependence. The irreversibility point in the thermo-magnetic curves obtained from field-cooled and zero-field-cooled measurements along the out-of-plane direction is found to shift towards higher temperature compared to the measurements in in-plane directions, indicating the presence of strong PMA.

Levitated droplet oscillations: effect of internal flow

The numerical model for electrically conducting liquid droplets levitated in AC magnetic field is extended to demonstrate various factors affecting the accuracy of material property value measurements. The effects included are the electromagnetic force induced stirring and the resulting turbulence, thermo-capillary convection, and the droplet rotation. The results are validated against available analytical solutions.

Levitated droplet oscillations: effect of internal flow

The numerical model for electrically conducting liquid droplets levitated in AC magnetic field is applied to demonstrate various factors affecting the accuracy of material property value measurements in microgravity conditions. The included effects are the electromagnetic force induced stirring and the resulting turbulence, the thermo-capillary convection, and the droplet rotation. The results are validated against available analytical solutions.

Structural, electronic structure and magnetic studies of SmFe1-xNixO3 (x <= 0.5)

We present the structural, electronic structure and magnetic studies of Ni doped SmFeO3. The X-ray diffraction (XRD) studies confirm the single phase nature of the samples having orthorhombic Pbnm structure and the unit-cell volume is decreasing with the increase of Ni concentration. X-ray absorption spectroscopy (XAS) studies on O K. Fe L-3.2, Ni L-3.2 and Sm M-5.4 edges of SmFe1-xNixO3 (x <= 0.5) samples along with the reference compounds revealed the homo-valence state of Fe and Ni in these materials. From magnetization studies it has been observed the materials exhibit ferromagnetic and anti-ferromagnetic sub-lattices, which are strongly dependent on the thermo-magnetic state of the system. (C) 2010 Elsevier B.V. All rights reserved.

Rheological flow from a die and painting on a moving solid wall

Die swell is an important, phenomenon. in polymer processing, and is explained usually by rheological properties of the fluid. Because of the nonuniform of temperature distribution on the free surface of the liquid jet, the thermo capillary convection driven by surface tension gradient exists. The rheological fluid flowing out of a die and painting on a moving solid wall is studied by the numerical finite element method of a two-dimensional and unsteady model in the present paper, and both the rheological effect of a non-Newtonian fluid and the thermocapillary effect are considered. The results show that both,effects; will enlarge the cross-section of the fluid jet, and the rheological effect of non-Newtonian fluid dominates the process in general.

AE指数的可靠性研究

Auroral electrojet index (AE) are usually used to quantitatively describe the activity of the geomagnetic field in the polar region. AE is a means to identify the level of a substorm as well. The auroral electrojet indices (AU, AL, and AE) have served well for more than four decades as measures of magnetospheric substorm activity. However, as substorm studies have progressed considerably during the past several years, the accuracy of the present electrojet indices have become an important issue. Thus it is fortunate for us to reexamine and evaluate the accuracy of the present electrojet indices and improve them if necessary. For a better use of the present indices and for future improvement we examine the limitations of the auroral electrojet indices as an accurate quantitative measure of the auroral electrojets and magnetospheric substorms. Some of the limitations arise from the data availability and also from the present simplified scheme in deriving them, but some of them originate in the definition themselves. In the present paper, we analyze the characteristics of aurora, ionospheric current system and the AE index. It is noted that for the pseudo-breakup events the variations of AE ( > 500 nT) clearly show the sudden increase and slow decrease phases. However, aurora does not expand to poleward or equatorward, and the ionospheric currents presents the features of the magnetic convection. We mainly focus on investigating what time the AE could be used to identify the subtorm.

地球化学新方法在隐状矿床找矿预测中的应用研究

With the progress of prospecting, the need for the discovery of blind ore deposits become more and more urgent. To study and find out the method and technology for the discovery of blind and buried ores is now a priority task. New geochemical methods are key technology to discover blind ores. Information of mobile components related to blind ores were extracted using this new methods. These methods were tested and applied based on element' s mobile components migrating and enriched in geophysical-geochemical process. Several kinds of partial extraction techniques have tested based on element' s occurrence in hypergenic zone. Middle-large scale geochemical methods for exploration in forest and swamp have been tested. A serious of methods were tested and applied effetely about evaluation of regional geochemical anomaly, 1:25000 bedrock or soil geochemical methods sampling based on the net in dendritic water system instead of the normal net. 1. Element related with ores can be mobiled to migrate upwards and be absorpted by surface soil. These abnomal components can be concentrated by natural or artificial methods. These trace metalic ions partially exist in dissovlvable ion forms of active state, and partially have been absorbed by Fe-Mn oxide, soil and organic matter in the soil so that a series of reaction such as complex reaction have take place. Employing various partial extraction techniques, metallic ions related with the phase of the blind ores can be extracted, such as the technique of organic complex extraction, Fe-Mn oxide extraction and the extraction technique of metallic ions of various absorption phases. 2.1:200000 regional geochemical evaluation anomaly methods: Advantageous ore-forming areas were selected firstly. Center, concentration, morphological feature, belt of anomaly were choosed then. Geological and geochemical anomalies were combined. And geological and geochemical background information were restrained. Xilekuduke area in Fuyun sheet , Zhaheba area in Qiakuerte sheet, the west-north part in Ertai sheet and Hongshanzui anomaly in Daqiao sheet were selected as target areas, in Alertai, in the north of Xinjiang. in Xilekuduke area, 1:25000 soil geochemical methods sampling based on the net in dendritic water system was carried out. Cu anomaly and copper mineralization were determined in the center area. Au , Cu anomalies and high polarization anomaly were determined in the south part. Prospecting by primary halo and organic complex extraction were used to prognosis blind ore in widely rang outcrop of bedrock. 1:25000 bedrock or soil geochemical methods sampling based on the net in dendritic water system were used in transported overburden outside of mining area. Shallow seismic method and primary halo found a new blind orebody in mining area. A mineralization site was fou and outside of Puziwan gold mine, in the north of Shanxi province. Developing middle-large scale geochemical exploration method is a key technique based 1:200000 regional geochemical exploration. Some conditions were tested as Sampling density , distribution sites of sample, grain size of sample and occurrence of element for exploration. 1:50000 exploration method was advanced to sample clast sediment supplement clast sediment in valley. 1:25000 bedrock or soil geochemical methods sampling based on the net in dendritic water system was applied to sample residual material in A or C horizon. 1:2000 primary or soil halo methods used to check anomalies and determine mineralization. Daliang gold mineralization in the northern Moerdaoga was found appling these methods. Thermomagnetic method was tested in miniqi copper-polymetallic ore. Process methods such as grain size of sample, heated temperature, magnetic separating technique were tested. A suite of Thermomagnetic geochemical method was formed. This method was applied in Xiangshan Cu~Ni deposit which is cover by clast or Gobi in the eastern Xinjiang. Element's content and contrast of anomaly with Thermomagnetic geochemical method were higher than soil anomaly. Susceptibility after samples were heated could be as a assessment conference for anomaly. In some sectors thermo-magnetic Cu, Ni, Ti anomalious were found outside deposits area. There were strong anomal ies response up ore tested by several kind of partial extraction methods include Thermomagnetic, enzyme leach and other partial extractions in Kalatongke Cu-Ni deposit in hungriness area in the northern of Xinjiang. Element's anomalies of meobile were mainly in Fe-Mn oxide and salt. A Copper mineralization site in Xilekuduke anomaly area had been determined. A blind ore was foung by shallow seismic and geochemical method and a mineralization site was found outside this mining area in Puziwan gold deposit in shanxi province. A Gold mineralization site was found by 1:50000 geochemical exploration in Daliang, Inner Mongolia.

Component NRM directions for sediment core HLY0503-06JPC

The Arctic oceans have been fertile ground for the recording of apparent excursions of the geomagnetic field, implying that the high latitude field had unusual characteristics at least over the last 1-2 Myrs. Alternating field demagnetization of the natural remanent magnetization (NRM) of Core HLY0503-6JPC from the Mendeleev Ridge (Arctic Ocean) implies the presence of primary magnetizations with negative inclination apparently recording excursions in sediments deposited during the Brunhes Chron. Thermal demagnetization, on the other hand, indicates the presence of multiple (often anti-parallel) magnetization components with negative inclination components having blocking temperatures predominantly, but not entirely, below ~ 350 °C. Thermo-magnetic tests, X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the negative inclination components are carried by titanomaghemite, presumably formed by seafloor oxidation of titanomagnetite. The titanomaghemite apparently carries a chemical remanent magnetization (CRM) that is partially self-reversed relative to the detrital remanent magnetization (DRM) carried by the host titanomagnetite. The partial self-reversal could have been accomplished by ionic ordering during oxidation, thereby changing the balance of the magnetic moments in the ferrimagnetic sublattices.