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 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

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

14. Reynolds Number The Problem • Mixing of streamlines at Re = 700 • Occurred for all groups

15. Reynolds Number Expected Reported Results

16. Reynolds Number Actual Reported Results

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.