Interferometric study of the heat and mass transfer during the mixing and evaporation of liquid oxygen and nitrogen under non-uniform magnetic field

Improving the separation efficiency and reducing the energy consumption in air separation units is of great importance to the development of petrochemical, iron and steel industries. A new method was proposed to improve the efficiency of cryogenic distillation by comprehensive utilizing of the boiling point and magnetic differences of oxygen and nitrogen. Laser interferometry system was designed and constructed to validate the effect of non-uniform magnetic field on the mass and heat transfer process between liquid oxygen and nitrogen. One-dimensional continuous wavelet transform was used to extract the two-dimensional concentration distribution from the interference patterns. Results have revealed 4 stages during the mass transfer process, including liquid oxygen filling stage, stratified diffusion stage, stable evaporation stage and unstable bubbling stage. The time for the stratified diffusion under magnetic field was maintained longer than that without magnetic field. The high gradient magnetic medium, which filled between the magnet poles, can further enhance the effect of magnetic field. With 0.5 g steel wools, the mole fraction of oxygen decreased by 30% at 120 min from the beginning of mass transfer compared to that without medium and decreased by 38% compared with that without magnetic field. The stratified diffusion and the bubbling phenomenon revealed in the experiments will provide a basis for the further development of the magnetically enhanced air separation units.