Low-Viscosity Measurement by Capillary Electromagnetically Spinning Technique

We study sphere rotation against viscous torque confined in a small space. Our new invention, the electromagnetically spinning sphere (EMS) viscometer measures liquid viscosity through the observation of sphere rotation driven by electromagnetic interaction in a noncontact manner. The lower limit of the measurable viscosity is determined from the ratio between the viscous torque and the mechanical friction, and the apparent increase in the contribution of the viscous term leads to the improvement of the accuracy of low-viscosity measurement. We propose a theoretical expression of the torque applied to a sphere rotating in a cylinder and obtained the power law with respect to the gap in between. The results of the numerical simulation and experiment provide evidence of the validity of the theory. # 2011 The Japan Society of Applied Physics