Experimental Research On Effects Of Magnetic Field On Supercooling Degree And Crystallization Process Of Low-Temperature Cool Storage Materials

Under the macro environment of energy shortage, phase change materials for cool storage are attracting extensive attention for their energy-saving performance, which might play an important role in future energy strategy. As a form of cool storage phase change material with good application prospect, inorganic salt solution usually has a moderately high supercooling degree, bringing down the efficiency of the cool storage system. In order to reduce the supercooling degree and increase the efficiency of the cool storage system, people have been seeking for various external conditions to promote crystal nucleus formation and crystal growth, including adding nucleating agents, cold fingering method and exerting physical fields (ultrasonic field, electramagnetic field, magnetic field, etc.). There has been relatively few research on the effect of magnetic field on inorganic salt solution so far, and as a result there exists no uniform conclusions on its influence performance and mechanism. Carrying on research on this aspect is helpful for providing experimental data for basic research in this field, and reference for engineering design.This paper systematically studies the supercooling and crystallization process of low temperature cool storage materials under the effect of constant magnetic field, static magnetic field and alternating magnetic field with different intensities. Considering that the phase change process should proceed in a stable and visible environment, the experiment table in this paper is designed and built accordingly, which operates well during the experiment, with detailed and accurate experimental data accquired. The cooling phase change and crystallization process of five working fulids, natural water, deionized water,5% NaCl solution,7% KCl solution and 5% NH4Cl solution under the effects of different magnetic fields is performed on the experiment table.The experiment results show that the effects of magnetic field on water and inorganic salt solutions are different, while magnetic field effects little on their crystallization temperature and time; magnetic field increases the supercooling degree of water and shortens its supercooling time, while for inorganic salt solutions magnetic field reduces the supercooling degree and shortens the supercooling time, and the effect is more evident with higher magnetic field intensity; the effects of magnetic field on crystallization process of water and inorganic salt solutions are different as well, for the former magnetic field increases the diameter of crystal particles, making the ice crystals fluffier and easier to melt, and for the latter magnetic field advances crystal growth, increases crystal amount and the diameter of crystal particles; besides, magnetic field exerts some restraint on the annular icing of metal cation solutions. These differences are caused by the diversity in the mechanism of effects of magnetic field on water and inorganic salt solutions. The effects of different types of magnetic field are differences as well:the effects of magnet constant magnetic field and direct current static magnetic field are only in relation to the intensity; while at the same intensity, the effect of alternating magnetic field is the most obvious of all. This is because the value and direction of magnetic force exerted by alternating magnetic field is periodically changing, which does repeated cutting on the hydrogen bonds and ionic interaction inside the solution and exerts continued magnetic effects on the solution.