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Session 2793

LASER DIAGNOSTIC ANALYSIS OF COMPLEX FLOW PATTERNS

A New Chemical Engineering Experiment Using Applied Optics Rocco Ciccolini and Robert Barat Chemical Engineering Department New Jersey Institute of Technology University Heights Newark, NJ 07102

ABSTRACT

A simple, yet effective, undergraduate experiment has been developed in collaboration between the Chemical Engineering Department and the Optical Sciences and Engineering Program at NJIT. During step change tracer experiments, absorption of red laser light serves as the diagnostic to reveal complex flow patterns in short and long lengths of square cross section clear pipe. The transient absorbance curves constructed from the optical data reveal significant back-mixing in the short flow cell. The long flow cell shows behavior consistent with laminar flow with dispersion in a conduit. This analysis is performed without invoking the complications of the residence time distribution.

INTRODUCTION

The National Science Foundation has declared that applied optics is an "enabling technology," and has stressed that engineering and science curricula should include optics research and education (NSF, 1994). In addition to bulk optics (e.g. lens, mirrors, mounts), modern applied optics experiments provide students with exposure to computers and electronics for data acquisition and manipulation as they explore phenomena in the sciences and engineering (Barat et al., 1998). Fluid mechanics, of interest to many engineering students, is an important phenomenon that can be investigated optically. For example, the recognition by chemical engineering (ChE) students that real reaction vessels might not be "ideal" due to fluid mechanical issues can be a rude awakening. In some universities, undergraduate ChE programs include in their senior laboratory courses a tubular flow reactor experiment that students expect to be an exercise in ideal "plug flow reactors." The students actually face non-ideal behavior, and are challenged to understand that plug flow behavior is usually limited to turbulent flow in reactor tubes with higher length/diameter ratios. In this paper, a new undergraduate engineering student experiment is introduced. Laser absorption is used as an optical diagnostic to illustrate the complex and non-ideal flow patterns that arise in short and long conduits with laminar flow. Data are explained in terms of the limiting cases of plug flow and mixed flow without the complexities of the residence time distribution. The

“Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition, Copyright 2003, American Society for Engineering Education”

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Ciccolini, R., & Barat, R. (2003, June), Laser Diagnostic Analysis Of Complex Flow Patterns: A Chemical Engineering Experiment Using Applied Optics Paper presented at 2003 Annual Conference, Nashville, Tennessee. 10.18260/1-2--12581