ExperimentalMethods for CFD Evaluation

							Experimental Methods
 for CFD Evaluation

       Lynn Melton
       University of Texas at Dallas

       Chemical Reaction Engineering VII
       August 6-11, 2000
I do diagnostics, and I work
with others on applications.
       s   Fuel Sprays - United Technologies
           Research Center
           Eckbreth, Winter, Stufflebeam
       s   Mixing - Dow Chemical Company
           Lipp, Larkins, Spradling, Sen, Tsai
My Propositions:
s   We have asked “What diagnostics
    are readily available?
s   Let’s move to the question “What
    combination of diagnostics, flows,
    and CFD will provide incisive
    answers?’
s   Fluorescence imaging can give
    more than concentration images.
    What about rate images? Or
    byproduct images? Imagine...
A short tour of diagnostics
“made for the problem”
s   Problem: How to image the vapor in an
    evaporating fuel spray?
    Response: exciplex-based vapor/liquid
    visualization
s   Problem: Does aerodynamic shear
    induce internal circulation in small
    droplets?
    Response: oxygen quenching of
    naphthalene fluorescence coupled with
    “droplet slicing imaging”
Vapor/Liquid Visualization in
Hydrocarbon Fuel Sprays
s   Vapor fluoresces blue; liquid
    fluoresces green; “exciplex” method
s   Experiments carried out while Melton
    was on leave at United Technologies
    Research Center
s   “Exciplex” is the standard method for
    real time imaging of vapor in
    evaporating fuel spray (automotive
    engine and gas turbine applications)
Concept: Exciplex Fluorescence
Spray Apparatus
Application: Diesel Engine
Bracco and Felton, Princeton
Internal Circulation in
Droplets?
 s   Does a moving droplet acquire
     internal circulation?
 s   Does a droplet heat by diffusion
     (only) of heat (hot surface) or by
     convection of mass and heat
     (homogenous temperature) ?
 s   Experiment performed by Michael
     Winter (United Technologies
     Research Center)
Concept: Internal Circulation
Droplets on Demand
Droplet Slicing Imaging
Internal Circulation
Rotating Droplet
Fluorescent Diagnostics
Coupled to Reactions
s   Beyond “dilution diagnostics” -DPLIF

s   Mixing Time
s   PIV/RPLIF
s   Mixing Fraction - Ratiometric
s   Reaction Rate
s   Ratio of Byproduct to Desired Product
s   Streamline diagnostics
                   DISMT
Dual Indicator System for Mixing Time
         (colorimetric for now,
    but fluorescent version coming)
   •Mix red liquid with blue liquid
   •Obtain yellow liquid only when mixture is within ±5%
   of ideal mixing
   •Acid-base reaction with two indicators (methyl red and
   thymol blue)
   •Must adjust initial pH’s carefully
Jet mixing

(1) Jet of base (blue)
from lower right into
acid (red)

Base accumulates at
lower left
Jet mixing
(2) Acid core (red);
base circulates
clockwise

Yellow (full
mixing) first
appears at top
right.
Jet mixing
(3) Acid core
(orange) mixes
slowly with zone of
base (blue) at left
Jet mixing

(4) After external
mixing, solution is
uniformly yellow.
               Simultaneous PIV/PLIF
                           (dilution PLIF)
                   532 nm Pulsed Laser (Nd:YAG)


                                                    PLIF
  Particle Image
   Velocimetry
                                                    Camera
                                           Filter
   Seed: Hollow
glass spheres coated                      Planar Laser Induced
     with silver                              Fluorescence

                       Filter              Dye- Rhodamine WT

            PIV Camera
Reacting PLIF
s   Fe(II) + H2O2 ==> Fe(III) + OH- + OHi
s   OHi+ Rh-WT ==> non-fluorescent Rh
s   OHi+ H2O2 ==> H2O + HO2i
s   Rh-WT* +Fe(III) ==> quenching of
                         fluorescence
s   Plus more reactions (very complex)
s   Currently working on better systems
Simultaneous PIV/Reacting PLIF
         532 nm; Rhodamine WT
Reactive PLIF
measurements
in shear flow
Pulsed PLIF images of Fe(II)/H2O2
reaction zone. Lightest contour
corresponds to 10% reaction;
darkest to 80%.
Mixing Fraction -ratiometric
     s   Carries mixing fraction information
         in shape of fluorescence spectrum
     s   Robust in complex geometries,
         since fluctuations in laser power
         and laser sheet ratio out
     s   Acid-base chemistry
     s   System under development
Reaction rate
s   Make fluorescence intensity at
    particular wavelength proportional
    to overall reaction rate
s   Multi-component fluorescent
    system
s   Currently in the concept stage
Formation of Byproduct
s   Capture images of byproduct
    formation (and also primary
    product ?)
s   Would like to have tunable ratio of
    byproduct rate to primary rate
s   Preliminary experimental work has
    been done
Streamline RPLIF

s   Suppose PIV seed contained an
    RPLIF system ?
s   Correlation of velocity and
    reactions?
s   Just a dream for now
What diagnostics do you want?
     s   Low viscosity liquids?
     s   High viscosity liquids?
     s   High viscosity liquids into low
         viscosity or vice versa?
     s   Temperature? Strain rate?
     s   Gases?
Real Life

s   Your mother told you that you can’t
    have everything you wish for.

s   If you don’t ask, you know the
    answer.
The menu - a la carte
flows
s   Stirred tanks
s   Jet mixed tanks
s   T mixers
s   Idealized 2-D flows
s   Other?

s   Laminar/transition/turbulent
The menu - a la carte
calculations
s   2-D CFD
s   3-D CFD
s   Other methods?

s   Include reaction kinetics?

s   Laminar/transition/turbulent
The menu - a la carte
diagnostics
s   colorimetric
s   PIV/DPLIF
s   PIV/RPLIF (mixing fraction)
s   PIV/RPLIF (formation of byproduct)
s   PIV/PLIF (reaction rate)
s   PIV/RPLIF-streamlines
s   Imagine ….
The BIG Question
How will we judge the
results of an integrated
evaluation which has
diagnostic, flow, and CFD
components?
      Acknowledgements

s   Dow Chemical Company
s   United Technologies Research Center
s   U.S. Army Research Office
s   Air Force Office of Scientific Research
s   Texas Higher Education Coordinating
    Board -Advanced Technology Program