Particle heating systems are promising candidates for Concentrator Solar Power, but particle to fluid heat exchangers, especially for the needed high temperatures, are an underdeveloped technology. To advance this technology, this thesis was conducted to develop an equivalent CFD model to represent the flow and heat transfer processes in a moving packed bed heat exchanger. This model has been developed and refined to simulate experimental results and applied to proposed practical geometries.
In a moving packed bed of particles, the velocity in the bed should be nearly uniform with little mixing, and the velocity gradient is expected to be small except very near solid surfaces. Therefore, two CFD modeling approaches were examined for particulate fluid: (1) laminar flow with negligible fluid viscosity and (2) Euler-Euler laminar flow with zero viscosity.
The CFD model was first verified by comparison with classic simple cases of a fluid between parallel plates. The parallel-plates geometry was initially tested with a simple fluid (air) with constant material properties, for both laminar flow and Euler-Euler laminar flow. The simulated heat transfer coefficient and Nusselt number were almost equal to the theoretical values for both approaches. Then the moving packed bed represented by the hypothetical particulate fluid (HPF) was simulated with constant density equal to the measured bulk density of the particulate and the measured heat capacity. Simulation results suggested that the Euler-Euler laminar flow approach was better in preserving the uniform velocity field.
Then, the particulate heat exchanger is modeled with Euler-Euler laminar flow module. Other details such as geometry offset and near-wall thermal resistance is added to the model. The simulation results highly agree with the results from other sources, indicating the model has successfully represent the particle flow in both fluid dynamic and heat transfer performance.