Recently, better quality protein crystals have been obtained by using a superconducting magnet. One of important factors that determine crystal quality is natural convection in the fluid where the crystals are grown. This paper presents a comprehensive, comparative numerical study of natural convection around a growing protein crystal when a vertical magnetization force caused by a gradient magnetic field acts on protein aqueous solution and the viscosity of the solution increases. The study shows that natural convection around a crystal can be damped most effectively and the crystal growth rate is reduced when an upward magnetization acts on a protein solution and the viscosity increases. The decrease of crystal growth is thought to contribute to the improvement of crystal quality. The technique of obtaining low gravity environments and damping natural convection in electric low-and non-conducting fluid will be useful for the preparation of many materials.

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