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When Things Go Wrong

William Josephson – A.U. Chem. Eng.Jaya Krishnagopalan – T.U. Chem. Eng.

Dave Mills – A.U. Chem. Eng.

2007 AIChE Annual MeetingSalt Lake City, Utah

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Outline & …

4 Experiments Conduction Reynolds Number Friction factor Viscosity

For Each Experiment What should occur What did occur Why it happened What was learned

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…Motivation

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Conduction Heat Transfer

Objectives To investigate Fourier’s Law for the linear

conduction of heat along a simple brass bar To determine the average thermal conductivity

of brass in the temperature range studied To observe the effect of temperature on the

thermal conductivity of brass in the range studied

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Conduction Heat Transfer Apparatus

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Conduction Heat Transfer

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Conduction Heat Transfer

Conduction Experiment - Ideal Case

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80

Position

Tem

per

atu

re

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Conduction Heat Transfer

Conduction Experiment - Thermocouple Error

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80

Position

Tem

per

atu

re

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Conduction Heat Transfer

Conduction Experiment - Thermocouple Errorplus T discrepancy across gaps

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80

Position

Tem

per

atu

re

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Conduction Heat Transfer

Told students of problem Let them devise workaround Most students made use of knowledge of

sample material – calculated 3 conductivities – eliminated bad thermocouple

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Reynolds Number

Objectives Compute Reynolds number Observe and quantify transitional flow

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Reynolds Number Apparatus

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Reynolds Number - “Ideal” Results

Re Observations

500 Parallel streamlines – laminar flow

1000 Laminar

1500 Laminar

2000 Laminar

2500 Parallel & interacting streamlines – transient flow

3000 Interacting streamlines - turbulent flow

3500 Turbulent

4000 Turbulent

4500 Turbulent

5000 Turbulent

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Reynolds Number

The Problem Mixing of streamlines at Re = 700 Occurred for all groups

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Reynolds Number Expected Reported Results

Re Observations

500 Parallel streamlines – laminar flow

600 Laminar

650 Parallel & interacting streamlines – transient flow

700 Turbulent flow

800 Turbulent

1000 Turbulent

2000 Turbulent

3000 Turbulent

4000 Turbulent

5000 Turbulent

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Reynolds Number Actual Reported Results

Re Observations

500 Parallel streamlines – laminar flow

600 Laminar

650 Parallel & interacting streamlines – laminar flow

700 Interacting streamlines - laminar flow

800 Interacting streamlines - laminar flow

1000 Interacting streamlines - laminar flow

2000 Interacting streamlines - laminar flow

3000 Interacting streamlines - transient flow

4000 Interacting streamlines - turbulent flow

5000 Turbulent

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Reynolds Number

Cause of the Problem (physical)Nozzle at end of dye introduction pipe

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Reynolds Number

Cause of the Problem (“mental”)Poor wording in handout: “If the Reynolds number

is less than 2100, the flow is considered laminar. If the Reynolds number is greater than 4000, the flow is considered turbulent.”

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Piping

Objectives To determine relationship between friction factor

and Reynolds Number & roughness Friction losses in fittings (globe valve, elbows) Orifice meter

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Piping Apparatus

Pipe A

Pipe CPipe D

Pipe E

Pipe B

Direction of Flow

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Piping What we want them to do

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Piping What we get (sometimes)

Important! – This is not the “problem”

Fanning Friction Factor versus Reynolds Number

0.0001

0.001

0.01

0.1

1000 10000 100000 1000000

Reynolds Number, NRe

Fan

nin

g F

rict

ion

Fac

tor,

f

Pipe A

Pipe B

Pipe C

Pipe D

Pipe E

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Piping What we get (other times)

0.001

0.01

10000 100000

Re

Fan

nin

g F

rict

ion

Fac

tor

D - 29.0 E-04

E - 3.7 E-04

C - 2.9 E-04

B - 2.1 E-04

A - 1.6 E-04

Important! – This is the “problem”

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Piping

The Problem – friction factors for SS Pipe below those of PVC

Consideration of the Problem Recheck the numbers A Lie in the handout?? (e.g., wrong info re pipe

size) Deeper Thoughts – is this an issue w/ the SS

pipe or the PVC pipes? Or both?

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Viscosity

Objectives To investigate rheology of several liquids

Confirm Newtonian fluids Determine if shear-thickening, shear-thinning or

something else Temperature effect on a Newtonian fluid

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Viscosity

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Viscosity Apparatus

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Viscosity – Ketchup Results

-50000

0

50000

100000

150000

200000

250000

0 10 20 30 40 50 60 70

Shear Rate (RPM)

Vis

cosi

ty (

cP)

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Viscosity – Corn Starch Results

Cornstarch

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 0.5 1 1.5 2 2.5 3 3.5

Speed (RPM)

Vis

cosi

ty (

cP)

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Corn Starch Viscosity

The Problem – data indicates shear thinning Consideration of the Problem

Recheck the numbers Try different concentrations Is corn starch really shear thickening?

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Corn Starch Viscosity

Is it really shear thickening??

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Corn Starch Viscosity

Consideration of the Problem (cont.) Observe operation of viscometer esp. spindle

interactions w/ fluid – closely read literature

The Answer (& the solution)

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Viscosity Corn Starch Results w/ Vane

150

155

160

165

170

175

180

185

190

195

200

0 10 20 30 40 50 60

RPM

Vis

cosi

ty (

cP)

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What Went Wrong & What Happened Conductivity

Bad Sensor, students were told a priori Students derived workaround

Reynolds Number Physical Setup Students re-examined their thinking (as did the instructor!)

Piping Arguably, nothing went wrong Students have to think

Viscosity Improper equipment Students had to think & observe

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A Sincere Thank You

To the students in

CENG 320 Unit Operations Laboratory I – T.U.

&

CHEN 3820 Chemical Engineering Laboratory I – A.U.