Convective heat transfer in particle-laden flows
While thermally evolving and wall-bounded, single-phase flows are of great importance (e.g., cooling systems for nuclear reactors, tube heat exchangers, etc.), many applications of interest also contain a disperse phase that exchanges heat with the fluid. Of particular interest in this work are turbulent and thermally evolving gas-solid flows. This class of flows is pervasive in nature and industry, spanning applications from volcanic eruptions to the storage of thermal energy and the upgrading of feedstock to usable fuels in circulating fluidized bed (CFB) reactors.
In both experimental and computational studies, it has been observed that particles spontaneously organize into coherent structures (clusters), thereby reducing contact between the phases, impeding mixing and delaying heat transfer.
In both experimental and computational studies, it has been observed that particles spontaneously organize into coherent structures (clusters), thereby reducing contact between the phases, impeding mixing and delaying heat transfer.
In this work, the thermal entrance length is examined via Eulerian-Lagrangian simulations by employing a two-step approach. First a
moderately dense isothermal, gas-particle flow is simulated to generate realistic clustering. Next, the cold flow simulations are fed into a statistically one-dimensional domain with a prescribed temperature difference between the phases at the inlet boundary:
moderately dense isothermal, gas-particle flow is simulated to generate realistic clustering. Next, the cold flow simulations are fed into a statistically one-dimensional domain with a prescribed temperature difference between the phases at the inlet boundary:
For the moderately dense systems considered here, clustering leads to a factor of 2-3 increase in the thermal entrance length, as compared to an uncorrelated (perfectly mixed) distribution of particles. The observed increase is found to be primarily due to the
covariance between volume fraction and temperature fluctuations, referred to as the fluid drift temperature. Using scaling arguments and Gene Expression Programming, closure is obtained for this term in a one-dimensional averaged two-fluid equation and is shown to be accurate under a wide range of flow conditions.
covariance between volume fraction and temperature fluctuations, referred to as the fluid drift temperature. Using scaling arguments and Gene Expression Programming, closure is obtained for this term in a one-dimensional averaged two-fluid equation and is shown to be accurate under a wide range of flow conditions.
- Beetham S., Lattanzi A.M. & Capecelatro J. 2021 On the thermal entrance length of moderately dense gas-particle
flows. arXiv preprint arXiv:2106.10395.