Effects Of Extremely Low Frequency Electromagnetic Field On Freezing Process Of Two Liquid Systems

Freezing process assisted by electromagnetic field is one of the emerging novel food freezing technology,related researches are concentrated on middle and high frequency bands such as microwave and radiofrequency with less literatures in low frequency.This study suggested that extremely low frequency electromagnetic field（ELF-EMF）has effects on freezing process of aqueous solutions,which were different with changes in components,and concluded that the strong feedback appeared when the aqueous solution contained some charged groups and large amounts of hydrogen bond.The experimental platform was designed and set up,and then pure water,0.9%sodium chloride and FeSO₄ solutions,10mmol/l PDADMAC and PSS solutions were chosen as samples,the indexes during freezing process were collected in different frequency bands such as supercooling degree and some parameters of thawed samples are also tested.The main results are as follows:1.The supercooling degree of pure water increased slightly under ELF-EMF,and other parameters were not changed.2.The supercooling degree of sodium chloride and FeSO₄ solutions significantly decreased 13.57%and 8.52%at 200 Hz and 250 Hz,respectively.The trends of change in surface tension and contact angle were similar as supercooling degree.3.The impacts of ELF-EMF on polyelectrolyte solutions were complex,the supercooling degree of them were increased 17.06%and 10.03%at 100 Hz,and then decreased 10.31%and 19.56%at 250 Hz,and the parameters of thawed samples were changed significantly as well.4.The ice crystals for most samples were also impacted by ELF-EMF,especially for polyelectrolyte solutions,the cracks of their ice crystals were increased and become deeper,while some gas were also infiltrated.