Bluesil FLD 550 HT Silicone Oil as Heat Transfer Fluid for Power Plant Applications: Thermal Stability Properties

Thermal oils have been utilized as heat transfer fluids for several decades in many applications, including industrial facilities, power plants and solar receiver systems. Despite their large employment, very few data are available about oils behavior under thermal stress and related degradation processes. For these reasons, the thermal stability of a silicone-based diathermic oil, Bluesil FLD 550 HT, was investigated in the present work. A laboratory-scale set-up was assessed to perform controlled heating tests, and fresh and thermally aged oils samples were analyzed to determine changes in chemical composition and thermo-physical features. Degradation products in the gaseous and vapor phase were also detected and analyzed by online and offline measurements. The obtained results are compared with the ones present for aromatic oils, largely employed as heat transfer media. Bluesil showed a higher thermal resistance compared to aromatic materials, and, thanks to its low volatility together with a high chemical stability, it was successfully tested up to 500 °C. According to its polymeric structure, thermal degradation processes occur mainly through Si-O bond scission, leading to both the segmentation of silicone chains and the formation of cross-linked species as byproducts.