Experimental Investigation On Mass Transfer Process Of Cryogenic Oxygen And Nitrogen Under Gradient Magnetic Field Using Laser Interference

Industrial gases are the "blood" of modern industry, and oxygen, nitrogen and argon have the greatest demand, which mainly come from air separation. Under the tendency of developing large-size and energy-efficient air separation equipment, researchers try to combine different air separation principles and methods together, to explore novel air separation methods with the advantages of strong adaptability, low energy consumption and high efficiency. Among these researches, cryogenic distillation with magnetic field is a novel and promising solution.The fundamental of magnetic air separation is the magnetic susceptibility difference of oxygen and nitrogen gas. There are some preliminary theoretical and experimental exploration related to this novel method for now, but mostly at room temperature. Oxygen is a kind of paramagnetic substance and obeys Curie law, which means the magnetic separation can be significantly enhanced under low temperatures. However, there is no detailed study at these operating conditions. To visually observe the different behaviors of liquid oxygen and nitrogen under magnetic field, this paper designed and built a visualization experimental device based on laser interferometry, which overcame the vacuum sealing, cryogenic insulation and light intensity problems of cryogenic visualization system. Subtle changes of the concentration of oxygen and nitrogen in test area can be visually reflected by the real-time change of interference fringes within the optical measurement system, and optical phenomena of pure oxygen, pure nitrogen and compound of oxygen and nitrogen under gradient magnetic field were observed. Dynamic mass transfer experiments of liquid oxygen and nitrogen under gradient magnetic field were also conducted and a "drawing" phenomenon of liquid oxygen induced by gradient magnetic field was observed. According to the processing results of the interferograms, the different concentration distribution and its variation process during the mass transfer process of liquid oxygen and nitrogen with/without magnetic field was obtained. All of these results provide the experimental basis for the practical application of gradient magnetic field in the cryogenic distillation units.The experimental study is still in the initial stage, and there is a lot of work to do before practical application. In the next stage, there are many improved methods which can be added such as subcooling device, precise flow control and electromagnet (especially superconducting magnet), so the relationship between flow rate, magnet field and concentration can be explored. A small-scale cryogenic distillation device with magnetic field also need to be constructed if possible.