Title:

Control of Flow and Mixing in Stirred Tanks

Speaker:

Prof. Sumanta Acharya

Affiliation:

National Science Foundation

When:

Friday, April 8, 2011 at 11:00:00 AM   Add to Calendar

Where:

MRDC Building, Room 4211

Host:

Dr. Satish Kumar
satish.kumar@me.gatech.edu
404-385-6640

Abstract

Stirred Tank Reactors (STRs) represent over $350 billion of product yield in the U. S chemical industry with nearly $1-20 billion per year lost due to inefficient operation of the mixing devices (Tatterson et al., 1991). Therefore, improvements in existing technologies can potentially translate to several billion dollars in annual cost savings. At low and moderate Reynolds numbers, stirred tank flows show poor mixing behavior due to formation of segregated zones inside which both magnitude and fluctuation level of velocity components show lower values compared to the active fluid regime (i.e., impeller jet stream, circulation loops). Active perturbation of the STR flow using a time-dependent impeller rotational speed can potentially enhance mixing by breaking up these segregated unmixed zones and enhancing the turbulence level throughout the tank volume. In the present study, the effect of different perturbation cycles on an unbaffled turbulent stirred tank flow at a moderate Reynolds number (rotational speed N=3 rps) is studied using a large-eddy simulation (LES) technique coupled with immersed boundary method (IBM). The perturbation frequency (f) is chosen to correspond to a dominant macroinstability in the flow (f/N=0.022). Measurements in a STR are also undertaken and reported for validation of the CFD. Different perturbation amplitudes and shapes are investigated, and changes in the mean flow field, turbulence level and impeller jet spreading are examined. Large-scale periodic velocity fluctuations due to perturbations are noticed to produce higher turbulence levels inside the tank. Fluctuations in power consumption due to perturbation are also calculated, and shown to correlate with the perturbation amplitude. A BRIEF DESCRIPTION OF NSF THERMAL TRANSPORT PROGRAM AND ITS PRIORITIES WILL ALSO BE PRESENTED

Biography

Dr. Sumanta Acharya has been on the faculty of mechanical engineering at Louisiana State University since 1982 where he is the L. R. Daniel Professor and the Director of Turbine Innovation & Energy Research (TIER) Center. His interests are in computational fluids, gas turbine heat transfer and combustion, and he has published or presented nearly 375 technical articles on these and related fields. He has supervised the work of nearly 60 graduate students and has been a principal investigator (PI) or co-PI of nearly $25 million of funded research. He is currently at the National Science Foundation as the Program Director of the Thermal Transport Process in the Chemical, Bio-Engineering, Environmental and Transport (CBET) Division.