Thermal Damping in Industrial Applications. Rheology of Coconut Oil-Silica Gels

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Abstract
Phase change materials (PCM) as liquid phase have the advantage of using the latent thermal heat as energy storage. Coconut oil (CO) has attracted much attention as PCM due to its high stability against oxidation. The addition of fumed silica has exhibited superior performance in thickening, thixotropy, sag resistance, reinforcement, and caking resistance. Although viscosity of CO-based dispersions has extensively been studied, few research has been done on time-dependent flow be-haviors. In this work, the rheological properties of fumed silica dispersed in CO at fractions of 1, 2, 3, and 4 vol.% were investigated. All suspensions showed shear-thinning behavior, which became more Newtonian at temperatures above the phase change. The 3 and 4 vol. % suspensions showed gel-like microstructures. The thixotropic properties of the 3 vol.% suspension at 30 °C and 35 °C were mainly studied through stepwise changes in shear rate. The results were consistent with thixotropic behavior with a complete recovery of the microstructure. The sweep frequency of this sample demonstrated the dominance of the elastic modulus at both temperatures. Therefore, a thixoelastic nature of this gel could be inferred.
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