Radiative Heat Transfer Properties of Electro-Controllable Fluids

Active control of radiation heat transfer in liquids can be accomplished with the use of a class of fluids referred to here as electro-controllable (EC) fluids. EC fluids in general consist of a colloidal suspension of polarizable, micron-size particles dispersed in a carrier fluid with an appropriate dielectric constant. When an electric field is applied, the particles redistribute in the fluid, changing from a uniformly dispersed configuration to a tightly organized chain formation that follows the lines of the electric field, thus causing a change in the thermal radiation transport. In an example application, experiments are conducted and models are developed for thermal radiation transmittance through a composite window featuring a central layer of EC fluid. The specific EC fluids of this study are made of micron-sized Zeolite particles suspended in a light Silicone oil carrier fluid of appropriate dielectric strength. The incident thermal radiation ranged in wavelength between 500 nm and 800 nm, and the strength of the applied electric field ranged from 100 V/mm to 500 V/mm. The models are applicable for both the dispersed organizational state and the field induced chained state. Absorption was demonstrated to be the fundamental radiation transport property enabling the control process. The EC fluid transmittance predicted by these models are compared to the data obtained by experimental measurement demonstrate very good agreement.