Experimental study on the slosh-induced force generated by a partially filled spherical capsule

When a capsule is partially filled with liquid, the internal inconsistent movement will result in its flow dynamics deviating a lot from a fully filled capsule. In this study, an equivalent slosh-induced force that originates from the internal moving liquid is proposed and experimentally tested. A designated linear acceleration of more than twice the gravity is exerted on the spherical capsule by a servo motor driven synchronous belt. The instantaneous force from spheres of different sizes and filling ratios is obtained based on the measured external forces. Water and tetradecane are used to test the effect of liquid properties. Slosh-induced force of magnitude from less to larger than the inertial force of the capsule can be generated, and it persists with an attenuating fluctuating feature even if the acceleration stops. Fast Fourier transformation confirms the existence of a dominant frequency, which decreases with the sphere diameter, increases with the filling ratio, and decreases with the viscosity of the liquid. All the obtained peak values of slosh-induced force in this study have been fitted into a correlation, which can be used to make predictions based on known factors. These findings shed light on the dynamic behavior of liquid in moving small or micro spherical capsules, which are important to the design and operation of related equipment.