Christen thesis defense – March 12

Solid particles are being considered in several high temperature thermal energy storage systems and as heat transfer media in concentrated solar power (CSP) plants. The downside of such an approach is the low overall heat transfer coefficients in shell-and-plate moving packed bed heat exchangers caused from inherently low packed bed thermal conductivity values of the low-cost solid media. Choosing the right particle size distribution of currently available solid media can make a substantial difference in packed bed thermal conductivity, and thus, a substantial difference in the overall heat transfer coefficient of shell-and-plate moving packed bed heat exchangers. Current research exclusively focuses on continuous unimodal distributions of particles such as CARBOBEAD HSP 16/30. This method becomes disadvantageous for larger particle sizes, which has higher thermal conductivity than smaller particles at elevated temperatures, because larger channel thicknesses that have been shown to result in lower overall heat transfer coefficients are needed to meet particle flowability requirements. As a result, only small particle sizes with low packed bed thermal conductivities have been considered for the use in the falling-particle Gen3 CSP concepts. Here, binary particle mixtures, which are defined in this paper as a mixture of two continuous unimodal particle distributions leading to a continuous bimodal particle distribution, are considered as a way to increase thermal conductivity, decrease packed bed porosity, and improve moving packed bed heat exchanger performance. This is the first study related to CSP solid particle heat transfer that has considered the thermal conductivity and moving packed bed heat exchanger performance of bimodal particle size distributions at room and elevated temperatures. Considering binary particle mixtures that meet particle sifting segregation criteria, the overall heat transfer coefficient of shell-and-plate moving packed bed heat exchangers can be increased by 22% when compared to a monodisperse particle system. This work demonstrates that binary particle mixtures should be seriously considered as a way to improve shell-and-plate moving packed bed heat exchangers.

Chase is a member of the Thermal Transport and Solar Energy Laboratory. Outside of research, he enjoys being active outdoors and cooking.