Experimental Research On The Formation And Transport Of Magnetic Liquid Droplets Under A Non-uniform Magnetic Field

Due to its advantages of dispersion,small size and high flux,droplet has been widely used in biomedicine,which has aroused the research interest in various research fields.Manipulation of droplets is an important concern in various studies.Because of its fluidity and paramagnetism,the magnetic droplet can be controlled by non-contact,which provides convenience for the control of the droplet.As a non-contact control mode,magnetic field is not affected by PH value,ionic strength,surface charge and temperature,and it is easy to realize and control a wide range.It's a very advantageous form of manipulation.Under the magnetic field,the flow characteristics of magnetic droplets will become extremely complex,especially under the action of non-uniform magnetic field,which will have a great impact on the deformation,velocity and motion trajectory of droplets.In order to better achieve the control of magnetic droplets,such as controlling their directional drug delivery,it is necessary to conduct experimental research on the generation and movement of magnetic droplets under non-uniform magnetic field.Aiming at the two-phase flow of magnetic droplets,this paper carried out an experimental study on the formation,drop and lateral movement of magnetic droplets under non-uniform magnetic field,providing experimental reference for the control and application of magnetic droplets.Based on the theory of magnetization intensity and the hypothesis of molecular circulation,this paper deduces the magnetic volume force of magnetic droplets,and uses Matlab software to calculate the magnetic field of rectangular permanent magnet and the magnetic volume force of magnetic droplets in this magnetic field.We give the governing equation of magnetic droplet two-phase flow,which includes Maxwell equation,momentum equation coupling surface tension and magnetic force,and deduce the expression of magnetic force term.In the case of uniform magnetic field,the theoretical solution of Maxwell equation is derived and calculated.It can be seen from the calculation results that the magnetic field will change due to the presence of magnetic droplet interface.In view of the droplet formation process of oil-based magnetic liquid in deionized water,we carried out an experimental study and discussed the influence of vertical gradient magnetic field(the direction of magnetic field gradient is the same as the direction of gravity)on the quality,shape and stability of droplet formation.Under the action of the magnetic field,the mass of the magnetic droplets will become smaller,their shape will be elongated,and their stability will become worse.With the increase of magnetic field intensity,the mass of magnetic droplets gradually decreases,the aspect ratio gradually increases,and the generation time becomes shorter.This is mainly because in the gradient magnetic field,the magnetic droplet will be subject to the magnetic volume force,and the magnetic volume force will increase with the increase of the magnetic field strength,and the influence on the magnetic droplet will become more obvious.After the magnetic droplet breaks to form a complete droplet,we continue to study its falling process.In the process of droplet falling after formation,it firstly becomes shorter due to the sudden fracture of the long axis,and then gradually elongates to form teardrop shape.Finally,due to the rapid increase of the transverse magnetic field gradient,the droplet is lengthened and deformed into a hemispherical or even a meniscus.The degree of deformation at each stage becomes obvious with the increase of magnetic field.The application of magnetic field makes the drop drop velocity increase obviously,and increases with the increase of magnetic field intensity.Based on the application prospect of magnetic droplet drug delivery,we experimentally studied the movement process of water-based magnetic droplet in lateral flow of silicone oil.In this experiment,the movement process of magnetic droplets in the magnetic field arranged by single block,phase attracting and repulsion magnets was compared,and the deformation and velocity change of magnetic droplets in each magnetic field was summarized,which provided an experimental basis for controlling the transport process of magnetic droplets.The two-phase flow of magnetic droplets is studied experimentally.In the experiment,the gradient magnetic field can be set to influence the generation and movement of droplets,which deepens the understanding of the influence of magnetic field on magnetic droplets and provides a good experimental reference for the control and application of magnetic droplets.