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Convection
Published in Greg F. Naterer, Advanced Heat Transfer, 2018
Gravitational convection is similar to natural convection but arises from buoyancy forces due to property variations other than temperature, such as concentration (also called solutal convection). For example, variable salinity is a significant factor of convection in the oceans. Thermomagnetic convection may occur when an external magnetic field in the presence of a temperature gradient leads to a nonuniform magnetic body force and fluid movement. Another less common mode of convection, called granular convection, occurs in powders and granulated materials in containers as a result of surface vibrations. When an axis of vibration in a container is parallel to the gravitational force, a slow relative movement of particles may occur along the sides when the container accelerates in the vertical direction.
Magnetic-Particle-Based Microfluidics
Published in Sushanta K. Mitra, Suman Chakraborty, Fabrication, Implementation, and Applications, 2016
Ranjan Ganguly, Ashok Sinha, Ishwar K. Puri
Magnetic body forces on ferrofluids can be harnessed in a forced flow configuration to augur cross-stream advection. Ganguly et al. (2004) showed the possibility of generating thermomagnetic convection in miniaturized channels to enhance the wall heat transfer in a forced flow. A combined influence of spatially nonuniform magnetic susceptibility (generated in this case due to temperature nonuniformity) of the ferrofluid and an imposed magnetic field gradient (created by a line dipole) is found to produce strong advective rolls in the flow. The same principle can be extended to auger mixing.
Applications of nano-and microdispersed media
Published in V.M. Polunin, A.M. Storozhenko, P.A. Ryaplolv, Mechanics of Liquid Nano-and Microdispersed Magnetic Media, 2017
V.M. Polunin, A.M. Storozhenko, P.A. Ryaplolv
If the magnetic fluid with different susceptibility (for example, as a result of a temperature gradient) is subjected to the effect of the magnetic field, this results in the formation of a heterogeneous magnetic volume force leading to a mechanism of heat transfer referred to as thermomagnetic convection. This form of heat transfer may be used in applications where it is not possible to use commercial convection, for example, in microdevices or in conditions with reduced gravitation.
Assessment of thermal performance of hybrid nanofluid flow in a tilted porous enclosure by imposing partial magnetic fields
Published in Waves in Random and Complex Media, 2022
Milan K. Mondal, Nirmalendu Biswas, Dipak Kumar Mandal, Nirmal K. Manna, Ali J. Chamkha
From the generic widespread literature survey, the importance of magnetohydrodynamic convection is well recognized in various types of geometries. However, there partial magnetic field has been addressed in some of the studies without emphasizing the local transport phenomena, which plays a key role in modulating the undergoing processes. Thus, the purpose of this work is to explore the thermomagnetic convection coupled to multiphysical conditions adopting a partially active magnetic field instead of the completely acted magnetic field towards improving the controllability of the transport process. To illustrate this, a spatially active partial field is applied perpendicularly to a differentially hot oblique porous enclosure packed with Cu-Al2O3/water hybrid nanoliquid. To assess the influence of the partial magnetic field, the length of the active zone of magnetic fields is varied and compared with the full-domain magnetic field and without any magnetic field cases. The local heat transport mechanisms are visualized through Kimura and Bejan’s heatlines [52,53]. The study is conducted for a wide range of involved parameters like Hartmann number (Ha), the width of the active magnetic field (Wb), Darcy number (Da), Darcy-Rayleigh number (Ram), hybrid nanofluid concentration (ζ), and cavity inclination angle (γ). The concept of the study will help the researchers to improve their knowledge of a magneto-thermo-fluidic system involving various multiphysical conditions for many sophisticated applications.
A segregated spectral element method for thermomagnetic convection of paramagnetic fluid in rectangular enclosures with sinusoidal temperature distribution on one side wall
Published in Numerical Heat Transfer, Part A: Applications, 2019
Wenqiang He, Guoliang Qin, Yazhou Wang, Zhenzhong Bao
With the advent of high-temperature superconducting magnet, strong magnetic field in the order of several tesla or more has been available in the laboratory. The study of thermomagnetic convection of nonferrous materials such as air, water, and others has become attractive, in which the magnetic force is employed to control the fluid flow and heat transfer. Braithwaite et al. [1] investigated both the enhancement and suppression of thermal-convection of paramagnetic fluids due to an inhomogeneous magnetic field in the Rayleigh-Bénard system. Wakayama and coworkers [2,3] theoretically and numerically examined the mechanism of thermomagnetic convection in two-dimensional enclosures with an electrically non-conducting or low-conducting fluid. Tagawa et al. [4,5] reported the thermomagnetic convection of nonferrous materials in a cubic enclosure and derived a model equation using a method similar to the Boussinesq approximation. Akamatsu et al. [6] studied the control of aerial flow in a cylindrical enclosure heated by the vertical wall and cooled by the horizontal walls with an external magnetic field. Jiang et al. [7] numerically simulated the thermomagnetic convection of air in a porous rectangular enclosure and investigated the heat transfer characteristics with and without gravitational field.
Resonant enhancement of thermomagnetic convection of paramagnetic fluid in an enclosure due to time-periodic magnetizing force
Published in Numerical Heat Transfer, Part A: Applications, 2020
Wenqiang He, Guoliang Qin, Xiaoping Wen, Jingxiang Lin, Cheng Jia
Under the strong magnetic field produced by the superconducting magnets, the magnetizing force becomes remarkable not only in the ferrous materials but also in the nonferrous materials. The study of heat transfer enhancement in thermomagnetic convection of electrically non-conducting fluids having paramagnetic or diamagnetic properties is becoming attractive. Braithwaite et al. [4] reported the effect of a magnetic field on thermomagnetic convection of paramagnetic fluids in the Rayleigh-Bénard configuration. Wakayama and coworkers [5, 6] studied the magnetic control of thermal convection in two-dimensional enclosures with electrically non-conducting or low-conducting fluids. Tagawa et al. [7, 8] investigated the thermomagnetic convection in cubic enclosures under thermal and magnetic field gradients and derived a model equation using a method similar to the Boussinesq approximation. Bednarz et al. [9–12] demonstrated numerically and experimentally the heat transfer enhancement by the application of a magnetic field and analyzed the influence of magnet positions relative to the enclosure. Kaneda et al. [13] examined the flow and heat transfer characteristics of a paramagnetic fluid under external magnetic field in a horizontal pipe heated at a constant heat flux. Jiang et al. [14] numerically simulated the thermomagnetic convection of air in a two-dimensional porous square enclosure under a magnetic quadrupole field in the presence or absence of gravity. In the above mentioned study of thermomagnetic convection, the augment of magnetic field intensity is the main approach for heat transfer enhancement. Resonance is not involved, and unnecessary loss in the system will lead to a decrease in energy utilization.