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## PowerPoint Slideshow about 'Reactors' - lynton

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Reactors

- Reactor: a “container” where a reaction occurs
- Examples:
- Clear well at water treatment plant (chlorine contact)
- Activated sludge tank at wastewater treatment plant
- Treated wastewater discharge into a stream: stream = reactor
- Treated wastewater discharge into Cayuga lake:lake = reactor
- Gas tank leaking into soil:soil = reactor

C

t

Completely Mixed reactor

t

Pipe flow reactor

t

Reactor typesWhat are your expectations?

Feed Solution (glucose solution for pipe flow)

Injection port

Peristaltic pump

or

C

C

or

reactors

x

Dispersion: velocity fluctuationsFick's first law

Fick's second law

What does it look like a short time later?

C

x

Reactors: Closed vs. Open

- Closed: have little dispersion across the inlet and outlet boundaries
- Well defined reactor volume
- Examples
- __________________________________
- ______

- Open: have significant dispersion across the inlet and outlet boundaries
- Backmixing
- Example
- _______

tank with a small inlet and a small outlet

lake

river

Reactor Characterization

volume

- Time scales
- hydraulic residence time
- average time for tracer to get from inlet to outlet

- Closed systems
- “dead volume”

- Open systems
- dispersion upstream
- “dead volume”

=

flow rate

?

Peclet Number

- Ratio of advection to dispersion
- how far does advection carry the fluid/width of tracer plume

- High Peclet means primarily advection (_______________)
- Low Peclet means lots of mixing
- Approximation for low dispersion (Pe>10)

plug flow

Completely Mixed Flow Reactor

- Closed reactor with no dead volume so theoretically t = .
- What is C0? How might you check this?

Flow With Dispersion Equation

- Solution for pulse mass input with advection and dispersion in only one direction
- Beware of units!!!! Adopt a consistent set!
- How can we get the dispersion coefficient?

Estimating the Dispersion Coefficient

Approximation for Pe>10

Definition of Pe

Solve for Dd

Substitute approximation

Mass conservation

- How much tracer comes out in 10 seconds?
- What are the potential errors?
- What level of accuracy do you expect?

Ideal Tracer

- same properties as fluid
- viscosity
- temperature
- density
- non reactive

- additional properties
- low background concentrations
- easily measured
- cheap
- non toxic

Real Tracers

Tracer type

distinguishing

analytical

examples

property

instrument

salt

conductivity

Conductivity

NaCl

meter

Dyes

color

Spectrophoto-

methylene blue

meter

fluorescent

fluorescence

Fluorometer

rhodamine WT

dye

radioactive

radioactive

Liquid

C14

ions

decay

scintillation

counter

Dissolved gas

Gas

Gas

Sulfur

chromatograph

hexafluoride

Reactor Lab Tracer

- Sodium chloride measured with conductivity probe
- Red dye # 40 so we can see it
- Density problem: 1.012 g/cm3
- Which reactors would be affected by density difference?
- How can we solve it?

Monitoring

- Conductivity Probe location
- pipe flow
- porous media column
- completely mixed flow reactor

- Data acquisition
- conductivity probe monitored by meter that sends data to computer
- computer will display a graph of conductivity vs. time
- output is a tab delimited text file containing
- sample times
- conductivity

Porous Media Reactor

- What are x, A, and U for the porous media reactor?
- How could we get the dispersion coefficient?
- What part of our laboratory model doesn’t this equation describe?

Data Manipulation

- What would happen if you collected data for a week?
- No clear approach, perhaps eliminate data after 99% of the mass is accounted for?
- No need to collect data after the effluent concentration is stable.

Conductivity as f(NaCl)

- Use the slope of the four point calibration curve and the baseline conductivity of each of the reactors to convert the conductivity data to NaCl concentration

600

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