InnoVenton and The Downstream Chemicals Technology Station
In an experiment, we deliberately change one or more process variables (or factors) in order to observe the effect the changes have on one or more response variables. The (statistical) design of experiments (DOE) is an efficient procedure for planning experiments so that the data obtained can be analyzed to yield valid and objective conclusions.
DOE begins with determining the objectives of an experiment and selecting the process factors for the study. An Experimental Design is the laying out of a detailed experimental plan in advance of doing the experiment. Well-chosen experimental designs maximize the amount of "information" that can be obtained for a given amount of experimental effort.
Below are four examples illustrating situations in which experimental design can be used effectively:
During the development of a new detergent, experimenters varied three components: X1-water, X2-alcohol and X3-urea.
These three components add to 9% of the total volume when measured in their original units, other ingredients were kept constant.
Objective: To find the proportion of water, alcohol and urea which will minimize the viscosity of the detergent.
Mixture problems are in many ways similar to other experimental optimization experiments, except for one important aspect: the properties of the final product do not depend on the quantities of its components but on the relative proportions of these components.
The fitted regression model shows that the blend alcohol-urea has the strongest synergistic effect on the viscosity of the detergent. The effect is highly significant (p<0.0001). The proportion of water in the blend has relatively little effect on the viscosity.
The effectiveness of all components is clearly shown in a trace plot:
A 3-D plot visualizes the relationships between the blends components and the viscosity:
By using an iterative optimization procedure we can obtain a blend which gives a minimum viscosity at 74% water, 2% alcohol and 24% urea. This blend will give a viscosity of 33.2 units (95% confidence interval from 19.6 to 46.8 units).
Tel: +27 (0) 41 504 1111
Fax: +27 (0) 41 504 2574 / 2731
PO Box 77000, Nelson Mandela Metropolitan University
Port Elizabeth, 6031, South Africa
Privacy statement Mail & Portals BEE & Tax Certificate PAIA ISPA FAQ NMMU Sitemap A - Z Index WCMS