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 Meeting
Salt Lake City, Utah
1
Outline & …
4 Experiments




Conduction
Reynolds Number
Friction factor
Viscosity
For Each Experiment




What should occur
What did occur
Why it happened
What was learned
2
…Motivation
3
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
4
Conduction Heat Transfer Apparatus
5
Conduction Heat Transfer
6
Conduction Heat Transfer
Conduction Experiment - Ideal Case
120
Temperature
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
Position
7
Conduction Heat Transfer
Conduction Experiment - Thermocouple Error
120
Temperature
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
Position
8
Conduction Heat Transfer
Conduction Experiment - Thermocouple Error
plus T discrepancy across gaps
120
Temperature
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
Position
9
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
10
Reynolds Number

Objectives


Compute Reynolds number
Observe and quantify transitional flow
11
Reynolds Number Apparatus
12
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
13
Reynolds Number
The Problem


Mixing of streamlines at Re = 700
Occurred for all groups
14
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
15
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
16
Reynolds Number
Cause of the Problem (physical)
Nozzle at end of dye introduction pipe
17
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.”
18
Piping

Objectives



To determine relationship between friction factor
and Reynolds Number & roughness
Friction losses in fittings (globe valve, elbows)
Orifice meter
19
Piping Apparatus
Direction of Flow
Pipe A
Pipe B
Pipe C
Pipe D
Pipe E
20
Piping
What we want them to do
21
Piping
What we get (sometimes)
Fanning Friction Factor versus Reynolds Number
Fanning Friction Factor, f
0.1
1000
10000
100000
1000000
0.01
Pipe A
Pipe B
Pipe C
Pipe D
Pipe E
0.001
0.0001
Reynolds Number, NRe
Important! – This is not the “problem”
22
Piping
What we get (other times)
Fanning Friction Factor
0.01
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
0.001
10000
100000
Re
Important! – This is the “problem”
23
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?
24
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

25
Viscosity
26
Viscosity Apparatus
27
Viscosity – Ketchup Results
250000
Viscosity (cP)
200000
150000
100000
50000
0
0
10
20
30
40
50
60
70
-50000
Shear Rate (RPM)
28
Viscosity – Corn Starch Results
Cornstarch
2000
1800
Viscosity (cP)
1600
1400
1200
1000
800
600
400
200
0
0
0.5
1
1.5
2
2.5
3
3.5
Speed (RPM)
29
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?
30
Corn Starch Viscosity

Is it really shear thickening??
31
Corn Starch Viscosity
Consideration of the Problem (cont.)

Observe operation of viscometer esp. spindle
interactions w/ fluid – closely read literature
The Answer (& the solution)
32
Viscosity
Corn Starch Results w/ Vane
200
195
190
Viscosity (cP)
185
180
175
170
165
160
155
150
0
10
20
30
40
50
60
RPM
33
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
34
A Sincere Thank You
To the students in
CENG 320 Unit Operations Laboratory I – T.U.
&
CHEN 3820 Chemical Engineering Laboratory I – A.U.
35