UC Berkeley

This dissertation presents the design, development, and experimental results of the Scaled Heat Exchange Frequency Response Analysis (SHEFRA) experiment, which aimed to investigate the use of frequency response methods for measuring quasi-steady Nusselt number values in forced convection of a surrogate fluid for molten fluoride salt in circular ducts. The dynamic response in the flow channel was initiated by a periodically-varying fluid temperature at the inlet. Initial experimental results obtained from the SHEFRA experiment suggest that quasi-steady conditions are achievable for laminar flow conditions, showing good agreement with steady-state analytical predictions. The theoretical modeling and frequency scaling analysis provided insights into the relevant dimensionless parameters and their impact on the system’s behavior, allowing for optimal experimental parameters and conditions to be determined. Quasi-steady state heat transfer conditions are best approximated at high or low values of a dimensionless parameter, b*, defined as the dimensionless frequency multiplied by the ratio of wall thermal capacitance and fluid thermal conductivity. At the limit of high frequency, the quasi-steady regime approximates the analytically-predicted steady state heat transfer with an isothermal wall temperature boundary condition. Meanwhile, at the limit of low frequency, the quasi-steady state conditions approximate steady state pre- dictions for a constant flux boundary condition. In comparison, high frequency tests resulted in a better approximation of quasi-steady state near the inlet of the test section. The most deviation in the instantaneous Nusselt number exists in the middle frequency range. The results suggest that additional experimental data, covering a range of Prandtl and Reynolds numbers of interest for molten fluoride salt reactor operation, can be used to create Nusselt number correlations that can be compared with prototypical molten salt experiment data and hence qualify the use of surrogate fluids in scaled experiments. Additionally, frequency response parameter estimation techniques presented in this dissertation offer promising av- enues for future research in improving the accuracy of Nusselt number measurements with the potential of estimating other system parameters such as thermophysical properties. The SHEFRA experiment demonstrates the potential of using surrogate fluids and frequency response methods to obtain high-fidelity heat transfer data measurements relevant for molten salt reactor development.