(126c) Turbulence Measurement and Simultation in a Microscale Confined Impinging Jets Reactor

Authors: 
Olsen, M. G., Iowa State University
Somashekar, V., Iowa State University
Liu, Y., Iowa State University
Fox, R. O., Iowa State University


Microscale chemical reactors capable of operating in the turbulent flow regime, such as confined impinging jets reactors (CIJR), offer many advantages for rapid chemical processing at the microscale. One application where these reactors is used is flash nanoprecipitation, a method for producing functional nanoparticles. Because these reactors often operate in a flow regime just beyond transition to turbulence, modeling flows in these reactors can be problematic. With high-performance computational power becoming more affordable, large eddy simulation (LES) has become a viable option. However, validation of computational fluid dynamics models (CFD) like LES requires detailed and accurate experimental data, the availability of which has been very limited for turbulent microscale flows. In the present work, microscopic particle image velocimetry (microPIV) was employed on a planar CIJR to obtain instantaneous velocity fields for jet Reynolds numbers of 200, 600 and 1000, corresponding to the completely laminar, the transition from laminar to turbulent, and the fully turbulent regimes, respectively, in the reaction zone. For each Reynolds number, approximately 1500 instantaneous velocity fields realizations were collected to analyze the flow fields and calculate pointwise and spatial turbulence statistics. LES was then performed for the same Reynolds numbers on a grid having approximately 4.3 million hexahedral cells. The subgrid scales were modeled using the Smagorinsky-lilly model. The simulations were performed using OpenFOAM (OF) on a high performance computing cluster. The time resolved simulated velocity fields were then used to compare the simulation with experimental results. When the mean velocity fields, Reynolds normal and shear stresses, and two dimensional turbulent kinetic energy were compared, good agreement was observed between the experimental results and the LES results. These results demonstrate the viability of using large eddy simulation as a tool for designing microscale reactors.

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