Some experiences using a ferrofluid seal against a liquid

A diester-based ferrofluid was tested in several small seals at very low rotation rates against air, water, and fluorocarbon liquid coolant. Essentially identical results were obtained with both gas and liquid. A finite-element computer program was used to calculate the magnetic fields in one specially designed miniature seal, and the supplied nonlinear magnetization curve for the ferrofluid was integrated in the calculation of maximum pressure drop across the seal. The experimental results were in good agreement with theory.