A method for altering one or more properties of a dielectric fluid for use in an electrohydrodynamic, EHD, thermal management system (100), as well as the system, are provided. The system comprises at least one EHD pump unit (110) comprising at least two electrodes for pumping the dielectric fluid and at least one enclosure (120) for accommodating the fluid within the system. The method comprises exposing the dielectric fluid to an ionizing process (122) configured to ionize the dielectric fluid, and operating the pump unit to circulate the exposed fluid in the enclosure.