Heat transfer rate predictions in dilute and dense gas-solid flow

The addition of particles to a clear gas has a significant impact on heat transfer rates. Experimental measurements of heat transfer rates in gas-solid flow have conclusively shown the dependence of these rates on the details of the flow behavior such as the local solids density. The prediction of heat transfer rates is especially crucial and valuable for the design, scale-up, and optimization of reactive gas-solid processes. However, the flow behavior of these suspensions is very complex, rendering heat transfer prediction an extremely difficult task.; Existing empirical correlations and mechanistic heat transfer models are not valid over a wide range of system parameters and operating conditions since they are based on limited experimental data. However, the heat transfer model presented in this work is based on first principles and involves fundamental descriptions for fluid and particle interactions. The overall goal is to employ this heat transfer model to gain a more thorough understanding of the role of flow variables on the heat transfer rates in gas-solid flow.; Coupled thermal energy balances for the gas and particle phases, which incorporate detailed flow information, are used to predict fully-developed temperature profiles and heat transfer coefficients for a range of operating conditions and system parameters. The model predictions reproduce much of the observed heat transfer behavior in these two-phase systems and this behavior can in large part be related to the hydrodynamics. For example, in dilute-phase flow, it is known that the heat transfer coefficient can either increase or decrease with increased solids loading depending on the particle size and magnitude of the solids loading. The model is able to reproduce the trends observed experimentally by considering the modulation of gas-phase turbulence and gas thermal conductivity due to the presence of the particles, as well as the increase in conduction in the solid phase due to individual particle-particle interactions. Also, in dense-phase flow, for example, the significant increase in the observed heat transfer rates with increased solids loading is explained by incorporating two mechanisms which augment conduction in the solid phase--namely, individual particle velocity fluctuations and fluctuations associated with loose clusters of particles or "particle-phase turbulence".