Experimental Design

Anthony E. ButterfieldCH EN 4903-1

“Research is what I'm doing when I don't know what I'm doing. ”

~ Wernher Von Braun (1912 – 1977)

Announcements

• Schedule preliminary exam before next lab period so you can get started Wednesday.

• Start writing now.• Introduction, theory, materials and

equipment table…• Draft of a new Projects Lab web page:

http://www.che.utah.edu/projectslab/• Has updated SOPs for some of your

experiments.

Experimental Design

• Terminology.

• Precautions.

• Factorial Design of Experiments.

• Put It to Use.

Terminology• Numeric Factors: Variable inputs to a process.

For example: pressure, temperature…

• Categorical Factors: Discrete inputs to a process.For example: equipment model, chemical substance…

• Responses: Effects of changes in factors.For example: Reaction rate increases with temperature and catalyst.

• Interactions: The influence of factors on each other.For example: (drinking, driving) vs (drunk driving)

Precautions• Controls.– Why spend the time and resources?– How would you decide if changing a factor gave results

significantly different from control experiments?• Randomizing.– Sampling.– When time is a possible factor.

• Blindness.– You can be easily fooled by your

expectations, wants, and pre-conscious processing of data.

• Repetition.– In your lab and others.

Experiments for Your Projects

• Group A – Immortal Yeast?

• Group B – Dirty Hydrogels?

• Group C – The Purple CSTR?

• Group D – CO2 Absorber?

• Group E – Stage Control?

Experimental Design

• In my lab, we want to know the effect of temperature, pressure, and time on microbubble volume.

• One option:

What Have We Actually Pinned Down?

• 3 factors.• 18 experiments.• So, what is the

problem?• Repeatability?• Effects?• Interactions?

Factorial Design

• 2-Level Factorial• 2 Levels, x• 3 Factors, y• 8 tests, (xy)

• Larger volume analyzed.

• Effect of factors at multiple surfaces.

• Some information on interactions.

• 2-Level Factorial with center points.

• Some information about repeatability.

• Some information about curvature.

• Box-Behnken• 3 Factors.• 3 Levels.• 12 Experiments

plus center points.

• Spherical and so extrapolation is less prone to error.

Why Ignore This Advice?

Competitive Experimental Design• What are the factors?• Numeric or categorical?• Are there interactions?

• Each team can perform10 experiments.

• Develop a model.• Take 15 shots at the opposing team’s target.