When Things Go Wrong

1
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

2
Outline

• 4 Experiments
• Conduction
• Reynolds Number
• Friction factor
• Viscosity
• For Each Experiment
• What should occur
• What did occur
• Why it happened
• What was learned

3
Motivation
4
Conduction Heat Transfer

• Objectives
• To investigate Fouriers 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

5
Conduction Heat Transfer Apparatus
6
Conduction Heat Transfer
7
Conduction Heat Transfer
8
Conduction Heat Transfer
9
Conduction Heat Transfer
10
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

11
Reynolds Number

• Objectives
• Compute Reynolds number
• Observe and quantify transitional flow

12
Reynolds Number Apparatus
13
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
14
Reynolds Number

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

15
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
16
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
17
Reynolds Number

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

18
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.

19
Piping

• Objectives
• To determine relationship between friction factor
  and Reynolds Number roughness
• Friction losses in fittings (globe valve, elbows)
• Orifice meter

20
Piping Apparatus
Direction of Flow
Pipe A
Pipe B
Pipe C
Pipe D
Pipe E
21
Piping What we want them to do
22
Piping What we get (sometimes)

• Important! This is not the problem

23
Piping What we get (other times)
Important! This is the problem
24
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?

25
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

26
Viscosity
27
Viscosity Apparatus
28
Viscosity Ketchup Results
29
Viscosity Corn Starch Results
30
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?

31
Corn Starch Viscosity

• Is it really shear thickening??

32
Corn Starch Viscosity

• Consideration of the Problem (cont.)
• Observe operation of viscometer esp. spindle
  interactions w/ fluid closely read literature
• The Answer ( the solution)

33
Viscosity Corn Starch Results w/ Vane
34
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

35
A Sincere Thank You
To the students in CENG 320 Unit Operations
Laboratory I T.U. CHEN 3820 Chemical
Engineering Laboratory I A.U.