LESSONS LEARNED FROM THE DEVELOPMENT OF A FOLLOW ...

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Çengel and Turner's Fundamentals of Thermal-Fluid Sciences. While this textbook was more complete than others the faculty considered, it lacked many of the ...
LESSONS LEARNED FROM THE DEVELOPMENT OF A FOLLOW-ON COURSE IN THERMAL-FLUIDS ENGINEERING Justin Highley [email protected] United States Military Academy West Point, NY 10996 Abstract: In the fall of 2005 the Mechanical Engineering program at the Unites States Military Academy taught the first semester of an integrated two-course thermal-fluid systems engineering sequence. The first course, ME311: Thermal Fluid Systems I, addressed the fundamental conservation principles: mass, energy, and momentum. These concepts are common to both thermodynamics and fluid mechanics and are readily integrated into a single course. The remaining topics, including external flow, gas power cycles, and modeling, were introduced in the follow-on course, ME312: Thermal Fluid Systems II, but are not as easily integrated. This paper describes the development process for a second course in thermal-fluids engineering and the challenges encountered with integrating disparate subjects in thermodynamics and fluid mechanics. Methods of incorporating these various topics are discussed and the challenges and benefits of the integration process are presented. Key words: Thermal Fluids Integration, Thermodynamics, Fluid Mechanics

Background Prior to Fall 2005, the Civil and Mechanical Engineering (CME) Department at the United States Military Academy (USMA) used the traditional approach of teaching thermodynamics and fluid mechanics as two separate subjects. These courses, ME301: Thermodynamics, and ME362: Fluid Mechanics were required classes for all majors, including Chemical, Civil, Environmental, Mechanical, and Nuclear Engineering, as well as Engineering Management. This traditional approach had two significant disadvantages. First, students often failed to see the commonality between these courses and believed the two subjects to be unrelated. This is because thermodynamics is often taught from an energy perspective, with focus on the first and second laws of thermodynamics, while fluid mechanics focuses on mechanical energy and internal/external flow. However, the same conservation principles (mass, energy, momentum) apply to both subjects - only the application is different. Second, some of the engineering disciplines (Civil, Environmental, Engineering Management) were required to take both courses to gain enough background knowledge to perform well on the Fundamentals of Engineering Exam (FE). This in turn detracted from their ability to take electives in their chosen field of study. In light of these issues and as part of a proposal to combine several engineering courses, the CME faculty decided to integrate the two topics into a two course sequence: ME311: Thermal Fluid Systems I and ME312: Thermal

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Fluid Systems II [1]. The decision to use two courses was based on presenting the same amount of material from the original Thermodynamics (ME301) and Fluid Mechanics (ME362) courses. Additionally, the new courses would be designed such that the Civil, Environmental, and Engineering Management majors would take only ME311 in order to create room for another elective in their academic plan. Based on this requirement and the desire to ensure their success on the FE exam, the ME311 curriculum focused on the topics that not only lent themselves to integration, but also other topics on the FE exam (hydrostatics, internal flow). With these topics identified, the remaining subjects from Thermodynamics and Fluid Mechanics were placed into ME312. The breakdown of subjects into the two courses can be seen in Figure 1. ME301: Thermodynamics • 1st Law (Energy/Heat/Work) • 2nd Law (Entropy) • Conservation of Mass • Ideal Gas / Steam / Refrigerant Properties • Cycles (Carnot, Rankine, Brayton, Otto, Diesel, VCRC) • Psychrometrics

ME311: Thermal Fluid Systems I • 1st Law (Energy/Heat/Work) • 2nd Law (Entropy) • Conservation of Mass • Steam / Refrigerant Properties • Cycles (Carnot, Rankine, VCRC) • Psychrometrics • Hydrostatics / Fluid Properties • Conservation of Momentum • Internal Flow • Mechanical Energy

ME362: Fluid Mechanics • Hydrostatics • Fluid Properties • Conservation of Mass • Consvervation of Momentum • Modeling and Similitude • External Flow • Boundary Layers • Drag • Internal Flow • Mechanical Energy • Compressible Flow • Differential Approach

ME312: Thermal Fluid Systems II • Ideal Gas Properties / Relationships • Cycles (Brayton, Otto, Diesel) • Modeling and Similitude • External Flow • Boundary Layers • Lift / Drag • Compressible Flow • Differential Approach

Figure 1: Division of Thermodynamics and Fluid Mechanics Subjects

From this breakdown, one would think that most of the original material from ME301: Thermodynamics and ME362: Fluid Mechanics was placed in ME311. While this is true to a degree, many of the subjects from the two courses are redundant and easily combined into fewer lessons. An example is the mechanical energy equation from fluid mechanics. This equation is simply another expression of the 1st Law from thermodynamics and therefore does not require an additional lesson dedicated to its application. Likewise, the successful integration of topics in ME311 increases student efficiency, requiring less time be spent reviewing common topics. For instance, both ME301 and ME362 spend one lesson in the development of the Conservation of Mass equations, and dedicate significant class time to reinforcing this concept throughout the semester. In ME311, this topic was taught only once and then continuously used throughout the course. This eliminated redundant lesson periods which allowed more material to be covered in the semester [1]. The resulting increase in efficiency allowed the introduction of three new topics to ME312 that were not in either ME301 or ME362: exergy, combustion reactions, and aircraft propulsion systems.

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ME311 integration Once the subjects were allocated between the two courses, the integration process began. One common method of integration is to simply teach both subjects sequentially– first in a thermodynamics block and then in a fluids block. Indeed, all Thermal Fluids texts found by the author are written this way and support this format. However, the intent of integration is to highlight the similarities of topics, and this approach simply reinforces the traditional division of thermodynamics and fluid mechanics. Therefore, a case-study approach was used in the development of ME311, which allowed students to analyze real world systems through the application of various thermal-fluid principles [2]. The case studies included the AH-64 Apache helicopter, the West Point power plant, and a complete air conditioning system. Each case study allowed the instructor to introduce new concepts as they were applied to these complex systems. This approach was effective in presenting new concepts in an integrated manner. ME312 integration As seen in Figure 2, ME312 addresses a wide range of topics in Thermal-Fluids engineering, including three new topics not previously taught in either Thermodynamics or Fluid Mechanics at USMA.

Thermodynamics • Internal Combustion Engines (Otto/Diesel Cycle) • Gas Turbine Engines • Aircraft Propulsion (turbojets, turbofans)* • Combustion* • Exergy*

Fluid Mechanics • External Flow / Boundary Layers • Lift / Drag • Dimensional Analysis • Modeling and Similitude • Compressible Flow • Differential Approach (Navier-Stokes) • Experimental Methods / Design of Experiments

* - New topic

Figure 2: ME312 Subjects by Discipline

Unfortunately, these topics were much more disparate in nature than those taught in ME311 and could not be integrated easily. Upon inspecting the subjects, however, the CME faculty realized that the thermodynamic topics (excluding aircraft propulsion and turbines) could be addressed through the analysis of an automotive system, specifically an internal combustion engine. Similarly, the topics listed under fluid mechanics are all disciplines used in the analysis of aeronautical systems. Based on this observation, a modified case study approach similar to that used in ME311 was employed. However, unlike ME311, the intent of this approach was not to integrate the subjects themselves, but to demonstrate to the students that multiple disciplines are required to analyze complex mechanical systems. Indeed, many of the subjects in ME312 would be extremely difficult, if not impossible to integrate at the undergraduate level (exergy and compressible flow being a prime example). By applying different Thermal-Fluid topics to the individual case studies students could see how the different disciplines can be used to analyze 3

a system even if the subjects themselves are not necessarily related. This served to emphasize the continuity between subjects, and reinforce previously taught concepts as they were applied throughout the semester. The two case studies used in ME312 were a Chevrolet Corvette and an F-22 Raptor high performance aircraft. These systems were chosen based on the wide range of technical data available from open sources, as well as their appeal to undergraduate engineering students.

Figure 3: ME312 Case Studies

In each case study, the students were introduced to the system which precipitated a discussion of what types of engineering disciplines were required for its analysis. In this manner students were able to understand that while the different topics in ME312 were not necessarily related to each other in theory, they were very much integrated in application. These case studies divided the course into roughly two sections: automotive (Corvette case study) and aircraft performance (F-22 case study). As shown in Figure 4, the Corvette case study deals primarily with thermodynamic topics, whereas the F-22 case study addresses the fluid mechanics subjects.

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• Exergy • Internal Combustion Engines • Otto Cycle • Diesel Cycle • Engine Cooling Systems • Combustion

• Gas Turbine Engines (Brayton Cycle / Regeneration) • Aircraft Propulsion • Dimensional Analysis • Modeling and Similitude • Experimental Methods / Design of Experiments • External Flow / Boundary Layers • Lift / Drag • Compressible Flow • Differential Approach (Navier-Stokes)

Figure 4: Breakdown of Topics by Case Study

By observation, one can see that the breakdown of subjects leans heavily towards topics traditionally taught in fluid mechanics. Indeed, the course syllabus lists the F-22 as the case study for 23 of the course’s 40 lessons. However, this block also contains several thermodynamic based topics, including gas turbine engines and aircraft propulsion systems. Additionally, dimensional analysis and modeling are addressed within this case study, which is the logical place to put them based on their relevance to the wind tunnel testing of models. In contrast to the F-22’s command of 23 lessons in ME312, the Corvette case study is used for only 13 lessons. However, many of these topics are discussed in depth during the course of 2-3 lessons, and rely heavily upon the Conservation of Energy principles taught in ME311. In a traditional thermodynamics course, these subjects would be taught later in the semester, after the student had learned the 1st Law. In the case of ME312, these lessons can be placed without regard to those requirements since they are simply applications of concepts taught in the previous course. An abbreviated course syllabus appears in Figure 5.

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Figure 5: Course Syllabus

During the 13 lessons of the Corvette case study only three topics are addressed: exergy, Otto/Diesel cycles, and combustion. Therefore, the students are given the opportunity to expand their learning base through individual briefings. Labeled the Advanced Automotive Topic Briefs, students are tasked to research an automotive topic of their choice with the intent of giving a 4-5 minute presentation to the class. The students are told to research a subject that deals with automotive engineering but otherwise given no constraints on the material. To ensure uniformity and succinctness, a standard briefing format is provided to the students, which includes the purpose of the system, its basic operation, common applications, and areas for improvement. In this manner, a multitude of case study specific materials are presented, enhancing the student’s learning beyond the three topics formally covered during this block. Additionally, these briefings serve to reinforce the multi-disciplinary approach to engineering

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being presented through the case study methodology. Some examples of student presentations include superchargers / turbochargers, anti-lock braking systems, hybrid vehicles, and high flow exhaust systems. As seen in the syllabus, the course also incorporates three laboratory exercises in order to reinforce the theoretical concepts taught in the classroom. The first lab, the internal combustion CFR lab, employs four spark ignition engines that enable the user to vary the compression ratio and spark timing angle for various types of fuels (87 and 110 octane). Prior to the lab, each engine is set to a different compression ratio and connected to an oscilloscope that displays the pressure and volume trace of the engine cycle. The students (in groups) then rotate through each engine, manually varying the spark timing angle and recording the torque output. At the higher compression ratios, students experience first hand the onset of engine knock and its affect on engine performance (via decreased torque output). Once each group has rotated through all the engines, the experiment is repeated using the higher octane fuel. During this iteration students see the effectiveness of the higher octane fuel at resisting engine knock. Finally, one of the engines is connected to an exhaust gas analyzer, which enables the students to analyze the affect that varying the air-fuel ratio has on emissions.

Figure 6: CFR Engine Lab

During the next block of instruction, students complete the gas turbine lab, which utilizes the auxiliary power unit engine from a UH-60 Blackhawk helicopter. In this lab, students are able to predict engine performance parameters and then compare them to the actual parameters as measured on the turbine. Finally, in the last lab of the course, students use wind tunnels to validate boundary layer theory, finding the variation of pressure within the boundary layer as a function of distance from the leading edge of a flat plate. 7

Textbook In addition to the challenges in making a cohesive course of the disparate subject matter, the CME faculty was unable to find a textbook suitable for the course. In ME311, students used Çengel and Turner’s Fundamentals of Thermal-Fluid Sciences. While this textbook was more complete than others the faculty considered, it lacked many of the topics required for ME312. As with most Thermal-Fluids texts, Çengel and Turner was simply a compendium of the common materials used from thermodynamics and fluid mechanics texts rebound into a new product. Specifically, Fundamentals of Thermal-Fluid Sciences was a combination of Thermodynamics: An Engineering Approach by Çengel and Boles and Fluid Mechanics: Fundamentals and Applications by Çengel and Cimbala. While this text worked well for the “mainstream” thermal-fluids subjects of ME311, it failed to adequately address the materials in ME312. In fact, several of the topics, including combustion, exergy, and compressible flow were not addressed at all. However, the texts from which the Fundamentals of Thermal-Fluid Sciences was compiled did contain the subjects required for ME312 - they simply were not included in the combined product. Fortunately, the publisher of Fundamentals of Thermal Fluid Sciences, McGraw-Hill, has the ability to create custom textbooks using materials from any of the texts they publish. This is accomplished through the use a functionality known as PRIMUS which is readily accessible through their website. This ability enables one to select specific chapters from different textbooks and combine them into a single, soft cover text. The result is a custom made textbook complete with a unique ISBN that can be ordered through any university book store. The process is extremely simple, and instructors can receive a courtesy copy of the custom text in 2-3 business days. With the password supplied by USMA’s McGraw-Hill representative, a custom text was created using the materials from Çengel and Boles’ Thermodynamics, and Çengel and Cimbala’s Fluid Mechanics. Extracting subjects from these texts proved extremely useful since all the material in the current ME311 text came directly from them to begin with. This yielded two very important benefits. First, the students were familiar with Çengel’s nomenclature from ME311, which would reduce any confusion that normally arises with the addition of a new textbook. Second, students were not required to purchase a completely new book, and simply bought a small supplement to their existing text. A picture of the text appears below in Figure 7.

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Figure 7: Custom Made Supplemental Text

In addition to the relevant materials from the thermodynamics and fluids texts, a section of the Fundamentals of Thermal-Fluid Sciences that was issued via CD was also included in the supplemental text. The table of contents of the supplemental text appears in Figure 8.

Figure 8: Supplemental Text Table of Contents

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Another advantage of creating a custom textbook is the ability to order the subjects so they mirror the syllabus. In other words, the material can be addressed progressively through the semester so the students do not need to move back and forth in the text. This eases confusion and helps facilitate a smooth transition between subjects. The only limitation in the creation of the supplemental text occurred with the addition of tables from Çengel and Boles’ Thermodynamics. Several tables were needed for ME312 that were not present in the primary text, including compressible flow tables, enthalpy of formation data, and the ideal gas properties of common gases. Unfortunately, these tables could not be added individually, and the entire appendix of the thermodynamics textbook needed to be inserted. The result was 90 additional pages of tabulated data, most of which was already present in the primary text and therefore redundant. Since the custom made texts are priced according to the number of pages, this carried a slight economic penalty. Additionally, the steam table data varied slightly between the primary text and the supplemental text, which led to confusion when working in class problems using these tables. Future Work As with the development of any new course, adjustments are inevitable since the first iteration almost always brings with it valuable lessons learned. Prior to each exam, the instructors and course director hold a lesson conference to assess the previous block of instruction. In this manner the course is continually evaluated. Additionally, at the end of the semester each student is required to complete a course assessment, which will be used to adjust the course as necessary to ensure the students receive the best instruction possible. The development of ME311 and ME312 is making an impact beyond the integration of ME301: Thermodynamics and ME362: Fluid Mechanics, and the final result is still being uncovered. The increase in efficiency and the corresponding ability to include more topics in the curriculum has impacted other courses in CME. For example, exergy and combustion reactions, topics not seen in either ME301 or ME362, are normally taught in ME472: Energy Conversion Systems, an advanced elective. The addition of these topics to ME312 gives the ME472 course director additional leeway to adjust his/her curriculum. Likewise, students focusing in Aerospace Engineering take ME481: Aircraft Performance and Static Stability, where they analyze aircraft propulsion systems in depth. New students will now have a better understanding of these systems having already seen them in ME312. These are two prime examples of how the integration process has enabled advanced electives to adjust their curriculum based on the student’s increased level of prerequisite knowledge. Conclusion The recent integration of thermodynamics and fluid mechanics at the United States Military Academy follows a common trend among leading universities. This integration enables students to see the commonality between these two fundamentally related topics and increases efficiency by eliminating redundancy. However, when retaining all the individual subjects from a semester each of thermodynamics and fluid mechanics, not all of the topics can be readily integrated. In the case of ME312: Thermal Fluid Systems II, the CME faculty at the USMA employed a modified case study approach to demonstrate how each topic could be used in the

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analysis of a complex mechanical system. This enabled students to see that while the subjects themselves may not be related, their application is. An additional challenge in developing a follow on course in thermal fluids is the selection of a suitable textbook. This was resolved with the creation of a custom text that contained specific sections of related texts. The result was a supplemental textbook that maintained the same nomenclature and symbology as the student’s primary text, thereby mitigating any continuity issues that normally accompany the introduction of a new resource. References [1] Bret Van Poppel, Blace Albert, and Daisie Boettner, “A Proposal for an Integrated Mechanical Engineering Program at the United States Military Academy,” Proceedings, ASEE National Conference, 2003. [2] Richard Melnyk, Philip Root, Michael Rounds, Daisie Boettner, “Lessons Learned from an Integrated Thermal Fluids Course,” To be Published, Proceedings, ASEE National Conference, 2006.

Biography Major Justin Highley is an instructor at the United States Military Academy where he has served for two years. Major Highley graduated from USMA in 1995 where he received a M.S. in Mechanical Engineering (Auto). He received an M.S. in Aeronautical Engineering from the Georgia Institute of Technology in 2004.

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