(358h) Experimental Temperature and Fluid Flow Measurements in Packed Beds with Magnetic Resonance Imaging

Packed bed units are of industrial importance in the development of thermal energy storage systems such as those associated with concentrated solar-power operations. Such units experience a temperature front that propagates through the bed and control of this front is key to improved efficiency of operations. A challenge in this field is measuring high-accuracy temperature profiles inside these systems. Also, assessing local heat-transfer processes are hampered by limited information on local flow conditions. To determine the spatial and temporal temperature and velocity profiles, magnetic resonance imaging (MRI) is used with encapsulated phase change materials as particles and a fluorinated fluid as heat transfer fluid. The encapsulated phase change materials generate signal as they change phase so that the melt front at a fixed melting temperature is detected in the images. Thus, the propagation of the melt front can serve as a proxy to the local temperature conditions. Additionally, MRI measurements using ¹⁹F NMR provide local fluid-phase velocity profiles that can identify flow maldistribution and help assess local heat-transfer environments by providing one or more components of the local velocity vector. Results are presented for a range of flow rates (10-600 mL/hr) using encapsulated eicosane particles for the solid phase (T_melt = 37^oC , d_p = 5 mm) and Flourinert FC-43 for the fluid phase. Preliminary results show qualitative agreement with discrete element method based computational fluid dynamics studies.