Analysis and experimental study of radiative heat transfer through electrorheological fluids

Radiation heat transfer control utilizing the unique properties of electrorheological (ER) fluids has recently been the subject of considerable interest as an innovative new area of research. While some work has been done to demonstrate the concept and to show the potential for radiation transmittance control, little has been done to specifically characterize the fundamental radiation transport mechanisms involved. This work seeks to identify the dominant modes for attenuation of radiant energy incident upon a typical ER fluid. Models are developed to predict radiation heat transfer through a composite window featuring a central layer of ER fluid while the particles are in a randomly dispersed state. A model for prediction of the enhanced levels of energy transport in the electric field-induced chained particle state was then developed by taking into account particle chain geometries. Additionally, the effect of radiation wavelength was studied for incident light beams ranging from 500 nm to 800 nm. Furthermore, the effect of the angle of incidence of the striking beam onto the composite window was studied, and a model is proposed to predict the change in transmittance associated with the angle of incidence. The levels of transmittance predicted by these models were compared to data obtained by experimental measurement, and excellent agreement was shown. The result of this work is a set of models for radiative heat transfer in ER fluid-based composite windows, both in the particle-dispersed and particle-chained states for cases when the plane of the window is held normal to the path of the incident light beam and when it is off normal by some angle, for wavelengths of incident light ranging from 500 nm to 800 nm. Clearly, an understanding of the physical mechanisms involved will provide insight into understanding heat transfer augmentation in the other primary modes. The models developed can be used to develop sensors used for optimal control strategies to manage the response of ER fluids for reliable use in commercial and industrial applications. Furthermore, with reliable control of the heat transfer properties of ER fluids will come the opportunity to develop thermally "smart" materials that will provide solutions to advanced heat transfer problems encountered in next generation technologies and applications.