ChE253MSp08 Expt04 ExampleRpt-1

ChE253MSp08 Expt04 ExampleRpt-1 - Experiment 4 Statistical...

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Experiment 4: Statistical Process Control by Joseph Chen Submitted to Dr. C. Grant Willson and Ian Mullet CHE 253M: Fundamentals Lab The University of Texas at Austin Fall 2007
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2 Experiment 4: Statistical Process Control Abstract This experiment explored a dye mixing process to illuminate the concepts of process control and control charts. The mixing process used an inline mixer to dilute a 0.20 wt% green dye solution with water to a 0.10 wt% product. Two spectrophotometer cells sampled light intensity, which was converted into concentration using Beer’s Law. First, the concentration of the bulk dye solution was measured by pumping just the dye solution through the mixer. Analysis of this data yielded the path length of the pre-mixer cell (0.547 cm). Control charts for this data indicated dye stratification and incomplete mixing, and the bulk dye tank probably required more mixing time. Increasing the water flow rate produced a 0.10 wt% product. Control charts for the concentration data, constructed via the estimation and standard deviation methods, revealed several issues. The mixer reduced the concentration variability 24 times; however, nonrandom data reduced the ranges and tightened the control limits, forcing the mixer out of control for the estimation method. The standard deviation method produced control limits 3.5 times wider making it the mixer in control, but more data points are needed to use this method. Laminar flow in the pipes (Re = 1099) probably lent to the nonrandom data, as the tortuous path of the mixer would have trapped the dye, causing back mixing and autocorrelation. The mixer also increased the process capability index from 0.21 to 5.05 using the estimation method and 0.09 to 1.31 using the standard deviation method. Though the Cp for the mixer using the estimation method was greater than the desired value of 1.3, it was likely skewed by the narrow control limits. Indeed, the standard deviation method produced a Cp lower than 1.3 due to its wider control limits. Nevertheless, the mixer greatly reduces the variability of dye concentration and should be used. Recommendations include increasing the flow rate to promote turbulent flow and mixing.
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3 Contents Introduction 5 Methods 5 R e s u l t s 9 Conclusions and Recommendations 17 Appendices Appendix A 18 Appendix B 26 R e f e r e n c e s 3 1 List of Tables Table A1. Pump calibration and rotameter setting 18 List of Figures Figure 1 . Process diagram 5 Figure 2 . Spectrophotometer diagram 8 Figure 3 . X-bar chart of pre-mixer pure dye concentration 9 Figure 4 . R-bar chart of pre-mixer pure dye concentration 10 Figure 5 . X-bar chart of post-mixer pure dye concentration 10 Figure 6 . R-bar chart of post-mixer pure dye concentration 11 Figure 7 . X-bar chart of pre-mixer mixed dye concentration 12 Figure 8 . R-bar chart of pre-mixer mixed dye concentration 12 Figure 9 . X-bar chart of post-mixer mixed dye concentration 13 Figure 10 . R-bar chart of post-mixer mixed dye concentration 13 Figure 11 . X-bar chart for pre-mixer; std dev method 15 Figure 12 . X-bar chart for post-mixer; std dev method
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ChE253MSp08 Expt04 ExampleRpt-1 - Experiment 4 Statistical...

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