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See each listing for international shipping options and costs. Particle flow behavior in bends can be very problematic. Visual-An illustration of the roping phenomena; an actual pipe bend ruined by erosion. Particle storage in hoppers can also be problematic. Visual-Mass flow versus funnel flow-stagnation regions do not occur in fluid storage in a similar vessel; plugging of the outlet of a hopper. Particle flowrate out of hopper as the head decreases. Visual-Clear hopper and observation of outlet flowrate as a function of head-contrast with fluid flow out of a tank as head decreases.
Particle bulk density varies with "tapping. Large particle placed at the bottom of a container of a dry granular material will rise to the surface if the container is vibrated in a vertical plane. Visual-Shaking of a particulate material in a vial containing one larger particle and observation of the large particle movement. Fill volume of two types of particles can depend on the order of filling of the container. Visual-Filling ajar with two sizes of nuts and observa- tion of volume occupied-contrast with combining two fluids and the resulting volume. Stirring a mixture of two types of particles of different sizes may result in segregation rather than improved mixing quality.
Visual-Photographs of segregation patterns before and after a blending operation-contrast with mixing of two fluids. The first is a written report of at least ten pages prepared by the group that summarizes the background information on the topic and the novel aspects of the investigation. The second is an oral presentation of the topic, thirty to forty- five minutes in length.
All of the group members are required to participate in the oral presentation. Typically, one student outlines the discussion points in the beginning of the presenta- tion, and then the team members take turns speaking on each of the presentation bullets. Often the presentations are supplemented with visual aids or a short demonstration to introduce the topic and capture the attention of the audience.
The oral presentation is followed by a questioning period. During the questioning period, each of the project teams in the audience is required to ask at least two questions of the presenting team. This requirement is highly successful in keeping the class engaged in the presentations; the students also often generate outstanding questions. This peer question- ing is one aspect of peer review see task 3 below that is incorporated into the course project to help develop the communications skills of the students.
After the questioning period is over, the instructor gives the presenting team immediate feedback, both positive and negative, in front of the entire class. This helps to improve the quality of the subse- quent presentations since students get a better understanding of what is successful, what are some of the pitfalls, and what are the standards expected for the presentations.
Every team performs a peer evaluation of each of the other teams. The peer evaluation is on both the written and oral presentations of the course project. In the written report, each team serves as a reviewer of the other team reports, marking grammatical and typographical errors directly on the manu- script. They write a short summary of the manuscript that includes an overall evaluation, specific positive aspects, constructive criticisms, and suggestions.
For the oral presenta- tions, a structured evaluation form is used that is provided by the instructor. Therefore, at the end of the peer evaluation process, each team has a large amount of anonymous feed- back-a written and oral report from each of the other teams. Although these peer evaluations do not influence the grade of the team being evaluated, they are very instructive; the students tend to listen and readily accept the comments from their peers. The peer evaluations prepared by each team are graded for thoroughness and level of insight by the instructor.
The value of peer review has been documented in the litera- ture," 5] and its benefits are abundantly evident in the particle technology course. Perhaps this is due to the fact that the course is an elective course. Presumably, students already have some interest in the topic when they enroll in the course and the peer review merely enhances their involvement in it. Students take the reviewing task seriously.
They do an excellent job in identifying the strengths and weaknesses in the work of their fellow students. The peer review also aids the students in recognizing the strengths and weaknesses of their own oral and written reports. Finally, each team member submits to the instructor a summary report of the relative contributions of each of their own group members, including an assessment of their own contribution to the team effort. This helps the instructor assign appropriate individual grades to the group project.
Aside from the technical benefits a particle technology project brings to the course, there is the additional, more general benefit of improving team skills. Students, through the course project, gain more experience in how to capitalize on the unique skills of others, and, in turn, they often learn more about their own capabilities. In addition, they learn better how to motivate others, how to organize a group effort, and how to manage in difficult teams since team members are not reassigned even if a team is having problems working together.
In fact, student feedback indicates that while being a member of a "problem team" is certainly not a pleasant experience, those team members are the ones that make the strongest comments about their huge learning experiences in team skills. SUMMARY A survey course in particle technology is a highly effec- tive way to introduce the basics in this field to a diverse group of students.
A "gee-whiz"-type introductory lecture helps sell the importance of particle technology to different audiences. Visuals enhance presentation of the unique fea- tures of particulate systems. Incorporation of a team project into the course allows for students to focus on one particular topic in particle technology and adds depth to the breadth of material covered in this survey course. Also, the course project brings many positive factors to the learning experi- ence of the students. DOYLE, III University of Delaware Newark, DE A graduate-level class on process control tradition- ally employs a standard lecture-style course, possi- bly coupled with an independent course project car- ried out in a simulation environment.
If one steps back to critique this approach, it is important to first address the skills required by a practicing process-systems engineer. As a guide to the requisite abilities required of a process- systems engineer, one may consult the list of control design steps provided by Skogestad and Postlethwaite'" shown in Table 1. Is the typical engineering graduate well prepared to accomplish these tasks? There have been no comprehensive studies to answer this question, but Kheir, et al.
The highest rated aspects of the current methods of control education were control-system knowl- edge, job preparation, and curriculum. The analytical skills of the students were considered strong. Such responses seem to indicate some success for items 7 through 9 of Skogestad's list of control-design steps, areas that correspond to skills Ed Gatzke received his BSChE from the Georgia Institute of Technology in After two years of graduate study at Purdue University, he moved to the University of Delaware for completion of his PhD.
His interests include process control, optimization, and artificial intelligence. He moved to the University of Delaware in to complete his doctoral degree with Professor Francis J. His research focus includes modeling and analysis of control mechanisms in biological systems and distributed hierarchical methods for control of large-scale process systems. Meadows is a postdoctoral fellow at the University of Dela- ware, working in the areas of modeling and control of polymerization reactors as part of a broader research program in optimization and control of chemical processes.
He received his PhD degree from the University of Texas in He was an Assistant Professor at Purdue University before coming to the University of Delaware as an Associate Professor in the fall of , and his research interests are in the areas of process and biosystems analysis and control. Unfortunately, existing approaches to control engineering education are not necessarily producing engineers who are as knowledgeable in other areas. The Kheir survey respon- dents reported that control engineers received lower ratings in the areas of laboratories, hands-on experience, and inter- personal skills.
The course described in this paper uses both a standard lecture class and an experimental group project related to the course material. This provides an opportunity to address the deficiencies identified by Kheir and colleagues, while reinforcing the positive aspects of traditional control engineering education methods. Of the seven students taking the class for a grade, five were University of Delaware graduate students and two were industrial profes- sionals enrolled for continuing education credit. As a main reference, the course used the text by Skogestad and Postlethwaite,"1 and the major topics covered in the course included Classical multivariable control Analysis of performance limitations Uncertainty characterization Robust controller synthesis Control structure selection and plant-wide control One of the key strengths of the Skogestad and Postlethwaite text is the treatment of performance limitations, and this topic was covered in depth in the lecture and reinforced via the experimental project.
The course project was assigned in Copyright ChE Division of ASEE Chemical Engineering Education Graduate Education the middle of the semester, and the students were given the choice of a theoretical independent course project related to their thesis research or the opportunity to work on the experimental system as a group project. Of the five on-site students, four elected to carry out their project using the experimental four-tank system. The design is inspired by the benchtop appara- tus described in Johansson and Nunes. Two voltage-controlled pumps are used to pump water from a basin into four overhead tanks.
The two upper tanks drain freely into the two lower tanks, and the two bottom tanks drain freely into the reservoir basin. The liquid levels in the bottom two tanks are directly measured with pressure transducers, and the top tanks have high-level alarm signals generated by electro-optical sensors. As can be seen from the schematic, the piping system is configured such that each pump affects the liquid levels of both measured tanks.
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A portion of the flow from one pump flows directly into one of the lower-level tanks where the level is monitored. The rest of the flow from a single pump is diverted into an overhead tank, which drains into the other monitored tank. By adjusting the bypass valves on the system, the amount of interaction between the two pump flowrates inputs and the two lower tank level heights outputs can be varied. For this work, it is assumed that an external unmeasured disturbance flow may also be present that drains or fills the top tanks. The original work of Johansson and Nunes employed tanks with a volume of 0.
The present work uses 19L 5 gallon tanks, attempting to create a visual impression of practical reality for the students. The scale of the apparatus is indicated in Figure 2. Study the system plant to be controlled and obtain initial information about the control objectives. Model the system and simplify the model, if necessary. Analyze the resulting model; determine its properties. Decide which variables are to be controlled controlled outputs. Select the control configuration. Decide on the type of controller to be used. Decide on performance specifications, based on the overall control objectives.
Analyze the resulting controlled system to see if the specifications are satisfied; and if they are not satisfied, modify the specifications or the type of controller. Simulate the resulting controlled system, either on a computer or pilot plant. Repeat from step 2, if necessary. Choose hardware and software, and implement the controller. Test and validate the control system, and tune the controller on-line, if necessary. Furthermore, the PC-based architec- ture made the system cost-effective for a univer- sity application and facilitates hardware and soft- ware upgrade paths.
The experimental package consists of three sepa- Pumpl T Pump 2 Figure 1. Schematic of the four-tank system. Fall Graduate Education rate components, as shown in Figure 3: The Freelance applica- tion package DigiTool was used to create a process database that is loaded onto the Process Station. The DigiVis applica- tion allows operator interaction with the Process Station and process database. Operator displays were created that al- lowed the students to operate the four-tank system see Fig- ure 4 as well as to track the trends of key operating variables see Figure 5.
For the graduate control class, it is necessary to use more complex control algorithms than can be easily implemented using the Freelance packages. The Simulink dis- play Figure 6 emulates a standard simulation flowsheet. Once the student has toggledd" control to Matlab from Bailey , however, the Simulink "simulation" drives the inputs to the Bailey system as the simulation proceeds. This creates a very flexible environment for imple- menting complex control algorithms on a moderately com- plex experimental system. The models used for this work include the disturbance effects of flows in or out of tanks 3 and 4.
The nonlinear differential equations governing the heights in this four-tank system are given in Table 2, and the linearized version is seen in Table 3. The liquid levels in tanks one and two, h, and h2, are considered measured variables. The speed of the pumps, v, and v2, are considered as manipulated inputs.
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The pump speeds are manipulated as a percentage of the maximum pump speed. The disturbances dl and d2 model the unmeasured disturbance effects of flows in or out of tanks three and four. This model is a simple mass balance, assuming Bernoulli's law for flow out of the orifice. The gamma values, yi, correspond to the portion of the flow going into an upper tank from pump i.
In Johansson and Nunes,l31 it is shown that inverse response in the modeled outputs will occur when Matlab DigiTool Schematic of the control system.
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Screenshot of Freelance four-tank schematic. Screenshot of Freelance tank-level trends. These disturbances' effects are modeled as a constant leak into or out of the upper tanks. It should be noted that each of the four elements modeling, analysis, synthesis, and imple- mentation was performed by each student group. A more detailed theo- retical treatment of the results can be found in Vadigepalli, et al. The tank areas A, can be mea- sured directly from the apparatus.
Using tank drainage data, the cross-sectional out- let areas ai can also be determined. The students designed a suit- able test input sequence to gen- erate data for the estimation of the remaining parameters. In this case, they elected to identify the parameters of the original non- linear model, requiring the solu- tion of a nonlinear optimization problem. The problem was for- mulated to minimize the 2-norm of the difference between the nonlinear model and actual mea- surements, searching over four parameters.
Using dynamic data from the experiments, the optimi- zation routine found the optimal pump gains k, and gamma values yi as depicted in Table 4. A simi- lar routine was employed to model the characteristics of the distur- bance introduced by the submers- ible pumps, kd, and kd2. Fall Figure 6. Screenshot of the Matlab interface.
The stu- dents were successful in validating the model that resulted from the pre- vious optimization problem. They were able to capture the known in- verse response in the system, and they also were able to compare the nonlinear model response to a lin- ear approximation, which was sub- sequently used for analysis. Once the students had obtained the physical mod- els of the system, they computed a linearized approximation at a steady-state operating point and analyzed the controlla- bility properties of the resulting linear system. The inputs and outputs of the system were appropriately scaled before the controllability analysis was carried out.
The first metric considered was the relative gain array RGA as a function of frequency. For the system configura- tion employed in this study, the students found that the diagonal RGA elements were very near to 1 at low fre- quency, suggesting an easily decoupled system.
But as the frequency increased to the bandwidth region, the students discovered that the diagonal RGA values de- creased significantly, indicating the importance of multi- variable interactions in the bandwidth of interest. Such an insight is particularly valuable at the graduate control level to highlight the limited interpretation of the steady- state RGA value. Additional insight is derived from an analysis of the singu- lar values of the system. More specifically, their ratio the condition number gives an indication of the sensitivity of the plant to uncertainty. The condition number at low fre- quencies was small, between 1 and 3.
But it decreases with frequency, implying that the plant is more sensitive to uncer- tainty at steady state than at higher frequencies. In addition, the low frequency minimum singular value is above 1. This means that adequate control action should be possible; the input moves will be able to move the outputs a sufficient amount to track setpoints.
This indicates a poten- tial constraint on the controller bandwidth because of high frequency input saturation. Another quantity of interest in control systems in general, and the four-tank system in particular, is the location and direction of multi- variable process zeros. For the operat- ing conditions in this study, the multi- variable zeros are found to be at The input zero di- rection corresponding to the right-half- plane RHP zero is [ From these directions, one can see that forcing one pump up while the other is forced down causes the sys- tem to display inverse response.
The lesson that the stu- dents will take away from this analysis is that the RHP-zero also limits the controller bandwidth. The technical details can be found in Vadigepalli, et al. A multiplicative input uncertainty structure was de- termined by the students to adequately represent the actual non-ideal behavior of the system.
This uncer- tainty characterization is central to the robust controller de- sign task that is described below. J5 Using a D-K iteration procedure, a robust 12l-order controller with a structured singular value, g, less than 1 was obtained. The controller was implemented in the real system. As one might expect with a physical system, the simulations did not precisely match reality.
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The nonidealities of the pumps, level sensors, and head losses in the piping all contributed to these discrepancies. Other unmodeled phe- nomena witnessed by the students include the formation of vortices in the upper water tanks above the drainage holes and spontaneous triggering of the level alarms due to con- densation.
Representative results demonstrating the disturbance rejection capa- bility and setpoint tracking performance of one controller design are shown in Figures 7 and 8, respectively. This controller was designed for disturbance rejection, which results in excessive input moves for setpoint moves. A robustly performing setpoint tracking controller was also implemented. This design requires an additional setpoint filter in order to satisfy the constraints on the input moves.
The students clearly mastered a moderately complex control problem. Time seconds Figure 7.
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Disturbance rejection using robust controller. Although the over- all physics of the process are not very sophisti- cated, we have shown that the system exhibits rich behavior that can be used to exercise principles in modeling, analysis, and advanced control design. The PC-based system was more flexible than traditional DCS systems, and the DDE interface facilitated a range of complex control designs that are appropriate for the graduate level. Our ongoing efforts with this experiment in- clude the use of the four-tank system in a multidisciplinary control engineering laboratory. The course was first offered in the spring of as a senior-level elective and drew students from chemical, electrical, and mechanical engineering.
We plan to report our experiences with this imple- mentation in a future publication. None of this work would have been possible without the expert craftsmanship of George Whitmyre, who constructed the four-tank system. We would also like to acknowledge the additional graduate students who worked on the four-tank sys- tem-Luis J.
Puig and Radhakrishnan Mahadevan. Reference tracking using robust controller. II Active Learning vs. Early in our workshops-usually within the first 15 min- utes-we suggest that instructors include brief active exer- cises in their lectures. Some participants invariably express concern that they have to present a lot of material in their courses, and one of them poses Question 2: How can I take the time for those exercises and still cover the syllabus? Another follows up by observing that he or she teaches a lecture class to students and raises Question 3: Can you use these methods in large classes?
Can you use active learning and still cover the syllabus? A huge volume of material can be "covered" in a short period of time. If you put all of your lecture notes in PowerPoint or on transparencies and flash through them in class, you can get through several hundred pages of text in a month. The question is, what is your objective? If it is simply to present all of the prescribed course material, re- gardless of how much or little of it the students actually absorb, then you should not use active learning exercises- they do indeed slow things down.
On the other hand, if the objective relates to what the students learn as opposed to what you present, then the goal should not be to cover the syllabus but to uncover the most important parts of it.
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People acquire knowledge and develop skills only through repeated practice and feedback, not by watching and listen- ing to someone else showing and telling them what to do. They are just sitting there- sometimes watching and listening to the lecture, sometimes thinking of other things, sometimes daydreaming or sleep- ing. Most of them would learn just as much if the classes were cancelled and they were simply given the lecture notes and homework assignments and perhaps review sessions before the tests.
It's a much different story if lectures are punctuated with brief active exercises that call on students-working indi- vidually or in small teams-to answer questions, begin prob- lem solutions, fill in missing steps in derivations, brain- storm, formulate questions about material just presented, summarize, or do anything else that they may subsequently be asked to do in homework and on tests.
The exercises energize the students sometimes literally waking them up , direct their focus to the most important points in the lecture, and increase their subsequent concentration when the lecture continues. They give the students practice in the methods and skills the course is intended to teach them and immedi- ate feedback on their efforts, thus meeting the criteria for learning to occur.
Even if some material were dropped from the course syllabus to make way for the exercises, the in- creased learning would more than compensate for the loss. But there is no need to shorten the syllabus. Suppose that instead of saying every word and writing every statement and drawing every diagram and deriving every equation in class, you were to put a lot of the material in class handouts that include gaps-skipped steps in derivations, axes with no curves showing-and exercises with spaces left for re- sponses.
Most of the students will then actually read the handouts-at least after the first test, when they discover that you meant it. This strategy accomplishes several things. By eliminating the need to say and write and draw everything in class, you buy yourself many classroom hours that can be devoted to the things that make learning happen-spending more time on conceptually difficult material, giving more examples, asking and answering questions, and implementing active learning.
You can fill in some of the gaps in the handouts in class; get the students to fill in others in active learning exercises; and leave some for them to work out for them- selves before the test. The students learn more we learn by doing, not by watching and listening , the classes are more lively, daily attendance increases, and the syllabus is safe. Do active learning methods work in large classes? The larger a class, the more essential it is to use active learning.
In a class with 40 students it is extremely difficult to do so, and in a class of 75 or more it is virtually impossible. Few students have the self-confidence to risk looking foolish by asking or answering questions in front of a large number of classmates, and the traditional pep talks proclaiming that there are no dumb questions and that wrong answers are also valuable generally have little effect. On the other hand, when a class is periodically given some- thing to do in groups of two or three, the risk of embarrassment is minimal-the only real difference between a class of 20 and a class of is that the latter class is noisier during activities.
A key to making active learning work in large classes is to stop the activity after the prescribed time interval and call on individual students or teams to state their results. If they know that any of them could be called on, the same fear of embarrassment that keeps them from volunteering responses in the whole class will prompt most of them to work with the small group so they will be ready with something if they are picked. Instructors who have never used active learning in a large When we do this, we tend to overload on the back of the class- room, where many students go to avoid the instructor's attention.
In our classes the students quickly learn that they can run but they can't hide. They worry that some students will refuse to participate under any circumstances and that the noise level during the activity will make it difficult to regain control of the class. Nevertheless, it disturbs instructors to see even one student sitting with arms crossed, pointedly refusing to par- ticipate, and the instructors often take such observations as evidence that the method is failing.
That's the wrong way to look at it. In a typical traditional lecture, the percentage of the class actively engaged in think- ing about the lecture content at any given time, let alone trying to apply it, is generally very low. No instructional method-lecturing, active learning, multimedia tutorials, or anything else-is guaranteed to reach every stu- dent.
As an instructor, the best you can do is go with the odds. It is true that in a large class the noise level can make it more difficult to bring the students' attention back to you, which makes it important to establish a signal e. After the first few exercises, we have never had to wait for more than 10 seconds for the room to quiet down, even with people there.
Besides, if you are teaching a class in which the students are so involved in answering your questions or working out your problems that you have trouble getting them to stop, there are far worse problems you could have. McCormick, Cognition, Teaching and Assess- ment. Problems of the type that can be used to motivate the student by presenting a particular principle in class, or in a new light, or that can be assigned as a novel home problem, are requested, as well as those that are more traditional in nature and that elucidate difficult concepts.
Manuscripts should not exceed ten double-spaced pages if possible and should be accompanied by the originals of any figures or photographs. Please submit them to Professor James O. PRATT National University of Malaysia Bangi, Selangor, Malaysia he Peng-Robinson equation of state and its close kin, the Soave-Redlich-Kwong equation, are simple yet very effective tools for solving phase equilibria prob- lems involving hydrocarbons and other nonpolar and slightly polar species.
Being cubic equations, when solved for the compressibility factor, Z, they will either yield three real roots or a single real root and a complex pair. It would be most convenient and is sometimes believed that one single root implies a single phase while three real roots imply liquid and vapor phases are in equilibrium. Sadly, such is not the case. Care must always be taken to extract the correct root.
Major blunders can be made, as we will show in the following problem. What is the tem- Ronald M. Pratt is a lecturer in the engineering department at the National University of Malaysia. Research interests involve molecular dynamics and fractal modeling, and his teaching responsibilities have included undergraduate, gradu- ate, and statistical thermodynamics courses and molecular simulation. Throttling of n-butane to known final pressure. This requires that we be able to calculate the enthalpy change across the valve, AH. A temperature for the stream leaving the valve may be guessed and AH calculated as indicated above.
Proceeding by trial and error the secant method]41 could be used to impose self-consistency and avoid a trial-and-error solu- tion , we obtain Table 2. The "solution" is that the exit stream is n-butane vapor at This is shown in Figure 2. The actual state of n-butane at 10 bar 0 kJ Ikg Figure 2. Pressure-enthalpy diagram for n-butane. Fall and The calculation has been deceiving us with bogus quasi- vapor roots.
Vapor roots can only be used for temperatures above the boiling point. Below this temperature, liquid roots must be used. Therefore, to proceed with the solution to this problem, we should first determine the boiling point, Tsat, for n-butane at 10 bar. Since at the boiling point, liquid and vapor phases must be in equilibrium, we must find the tem- perature at which the chemical potentials of both phases are equal.
For a pure component, this is equivalent to saying that the Gibbs free energies must be equal for the two phases. Since the ideal gas contribution to the Gibbs free energy is the same for each phase, we only need concern ourselves with the residual contribution. Similarly, the liquid GR should be calculated using the smallest root. Different tem- perature values may be selected on a trial-and-error basis until the equivalence of Eq. Again the secant method can be used to facilitate coding of this algorithm. Proceeding in this manner, we find that at For this problem, one will find that AH is positive when using the vapor roots at T'"", and AH is large and negative when using the liquid root at Tsat.
When the calculation is made using Eq. Therefore, the correct solution to the problem is that the exit stream is at its saturation temperature of Obviously, at 10 bar, n- butane exists as a superheated vapor above Ta"" and as a subcooled liquid below T"s'. Which roots are valid? Certainly we can rule out all of the intermediate or middle values. These in- termediate roots that lie within the saturation en- velope are of use in sta- bility analysis, some- thing we are not con- cerned with here.
Also, any liquid roots above the boiling point must be ruled out, and any vapor roots below the boiling point must be eliminated. Only the values in bold print hold any physical significance for us. The Peng-Robinson equation is not recommended for calculating subcooled liq- uid values, but values are 0. This area is marked "Danger!
The polynomial crosses the zero horizontal axis three times within the danger region K fore, in our example above, at A similar situation exists at temperatures above the boiling point. Between the boiling point and temperatures as high as K a 43K spread , bogus liquid roots are calculated.
This dangerous region is also marked on Figure 4. At tempera- tures over K, only a single vapor root is calculated, and there is no danger of bogus roots. The key point is that before we can decide which roots are valid and which are bo- gus, we must already know the boiling point. Figure 3 is a magnified PV diagram in the region of 10 bar and shows the bogus liquid root at K 0.