Date on Master's Thesis/Doctoral Dissertation

12-2017

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Chemical Engineering

Committee Chair

Berson, Eric

Committee Co-Chair (if applicable)

Lian, Yongsheng

Committee Member

Lian, Yongsheng

Committee Member

Willing, Gerold

Author's Keywords

Mean age theory; CFD; Mixing; Residence time distributions

Abstract

A comparison between mean age theory and conventional residence time distributions over a range of quantified mixing levels was conducted using computational fluid dynamics (CFD). The system was a stirred tubular reactor. The model was validated by comparing computationally derived RTD curves with experimentally obtained RTD curves, with quantified differences less than 3%. Mixing was quantified using the Tanks-in-Series model. Mixing levels were set by varying flow rate and impeller rpm. Mean age distributions at the outlet, where experimental RTD’s were measured, were very narrow for all levels of mixing studied. RTD’s showed expected characteristics; a wider distribution and long decay for high mixing cases and a narrow distribution centered around the mean time for cases approaching plug flow. Mean age distributions remained substantially narrower than RTD’s. RTD’s and mean age distributions were measured at several locations along the length of the reactor to determine changes in characteristics of each along the reactor. RTD’s and mean age distributions exhibited a narrowing along the length of the reactor, indicating a transition from well-mixed characteristics near the entrance to plug flow behavior near the exit. Differences in the mean age and mean residence time at the outlet increased from 7% at low mixing to 30% at high mixing. Ultimately, this study showed mean age distributions are not comparable to RTD curves over a range of mixing levels. Mean age theory can provide age of material throughout an entire system volume, while RTD’s provide a distribution only at a single measurable location.

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