Daisie D. Boettner

Proton Exchange Membrane Fuel Cell System Model for Automotive Vehicle Simulation and Control

This paper describes a proton exchange membrane (PEM) fuel cell system model for automotive applications that includes an air compressor, cooling system, and other auxiliaries. The fuel cell system model has been integrated into a vehicle performance simulator that determines fuel economy and allows consideration of control strategies. Significant fuel cell system efficiency improvements may be possible through control of the air compressor and other auxiliaries. Fuel cell system efficiency results are presented for two limiting air compressor cases: ideal control and no control. Extension of the present analysis to hybrid configurations consisting of a fuel cell system and battery is currently under study.

TEACHING THERMODYNAMICS VIA ANALYSIS OF THE WEST POINT POWER PLANT

Thermodynamic analyses can be performed based on energy-gross and exergy-net quantities. These topics are discussed in the context of the United States Military Academy at West Points power plant and the project that students work on as a part of their course requirements for three courses. A systematic, detailed, and comprehensive methodology is presented based on recent experiences that can be a standard for similar academic instruction of thermodynamic concepts and power plants. A well-defined case study for the classroom will yield more effective learning of and inspire a greater appreciation for critical power technologies.

On-board reforming effects on the performance of proton exchange membrane (PEM) fuel cell vehicles

This paper incorporates a methanol reformer model with a proton exchange membrane (PEM) fuel cell system model for automotive applications. The reformer model and fuel cell system model have been integrated into a vehicle performance simulator that determines fuel economy and other performance features. Fuel cell vehicle fuel economy using on-board methanol reforming is compared with fuel economy using direct-hydrogen fueling. The overall performance using reforming is significantly less than in a direct-hydrogen fuel cell vehicle.

On the Analysis of the Aerodynamic Heating Problem

A complete analytical solution to the problem of aerodynamic heating is lacking in heat transfer textbooks, which are used for undergraduate and graduate education. There are many issues that are very important from a convective heat transfer point of view. In practice, poor analyses lead to poor design, thus faulty manufacturing. Since, over the years analysis has given way to numerical studies, the instructors do not take the necessary time to go through analytical details. Thus the students just use the results without any awareness of how to get them and the inherent limitations of the analytical solution. The only intent of this paper, therefore, is to present the detailed analytical study of the aerodynamic heating problem.

On the Similarity Solution for Condensation Heat Transfer

Analytical solutions for laminar film condensation on a vertical plate are integral to many heat transfer applications, and have therefore been presented in numerous refereed articles and in most heat transfer textbooks. Commonly made assumptions achieve the well known similarity solution for the Nusselt number, heat transfer coefficient, and film thickness. Yet in all of these studies, several critical assumptions are made without justifying their use. Consequently, for a given problem one cannot determine whether these restrictive assumptions are actually satisfied, and thus, how these conditions can be checked for validity of the results. This study provides a detailed solution that clarifies these points.

On the Consistent Use of Sign Convention in Thermodynamics

In thermodynamics, various sign conventions are used for energy transfers in the form of heat and work. Regardless of the sign convention introduced, thermodynamics texts subsequently abandon their established conventions in favor of magnitudes or absolute values. This article illustrates the importance of consistent use of a sign convention throughout a text and applies it to power-producing and power-consuming engineering devices. Additionally, using a selected sign convention, a substantive proof is presented showing why the ratio of energy added/rejected in the form of heat equals the ratio of the absolute temperatures of the energy source/sink, respectively.

Teaching the Fundamentals of Thermodynamics and Fluid Mechanics Through an Integrated Systems Approach

The mechanical engineering faculty at the United States Military Academy recently implemented an integrated, two-course thermal-fluid systems sequence that presents fundamental thermodynamics and fluid mechanics topics. Instructors introduce students to these topics by exploring operational aspects of five complex systems: a helicopter, a power plant, a total air-conditioning system, an automotive system, and a high performance aircraft. Additionally, both courses incorporate laboratories, demonstrations and hands-on educational aids, design projects, and self-learning opportunities to reinforce understanding of fundamental concepts. Results from the first year the sequence was taught indicate students prefer learning topics from a global perspective and integrating thermodynamics and fluid mechanics topics reinforces student learning and retention of fundamental concepts. Challenges to teaching an integrated thermal-fluid systems sequence include lack of availability of textbooks that present thermodynamics and fluid mechanics topics in a truly integrated manner and establishing equivalency of courses within the integrated sequence with courses taught at other universities for those students on semester exchange programs.

Consistency Considerations for Integrated Thermodynamics and Fluid Mechanics Instruction

As a result of mechanical engineering curriculum revision at the United States Military Academy at West Point, separate courses in thermodynamics and fluid mechanics were integrated into a two-course sequence, Thermal-fluid Systems I and II, in academic year 2005–2006. After four years of instruction using available text books from publishers, the mechanical engineering faculty developed a text tailored specifically to the integrated two-course sequence. The experience in writing a text that integrates concepts in thermodynamics and fluid mechanics highlights the need for consistency between the two disciplines. Issues identified include logical organization of topics, selection of appropriate variables, consistent use of sign convention throughout all topics, recognition of various forms of the same fundamental principle, and definition of performance parameters. This paper explores these issues and how they were addressed for integrated instruction of thermodynamics and fluid mechanics.

Teaching Design in Context

As a result of recent curriculum revisions, the mechanical engineering faculty at the United States Military Academy teaches the formal design process “just in time” for students to apply the process to their capstone design projects. The design process consists of several phases and incorporates many engineering tools. During the initial offering of the course, Mechanical Engineering Design, instructors assigned students to capstone design teams early in the course. As the instructor taught the design process, team members applied the concepts to their capstone project. Based on instructors’ and students’ feedback, faculty revised the course structure to teach the design process in the context of a simple, in-class design project (design a portable illumination device) during the first half-semester. All in-class exercises were collaborative, hands-on experiences based on the project. To reinforce topics introduced in class and ensure all students develop a firm foundation in the design process, a separate common customer need (a device to store a West Point class ring) was the focus of all individual homework. Each student developed a design, built a prototype, and wrote an individual design report. Subsequent to formal design process instruction, students formed capstone teams and began their one and one-half semester capstone design projects. Results indicate that students more thoroughly understood the design process and its associated engineering tools allowing capstone teams to progress more efficiently through conceptual design; order parts, build prototypes, and test prototypes much earlier than the previous year; and enjoy a successful capstone experience.

On the Sign Convention in Thermodynamics: An Asset or an Evil?

In thermodynamics the sign convention normally used is energy added to a system in the form of heat is taken as positive and that added in the form of work is taken as negative – HIP to WIN (heat in positive – work in negative). This is a common sign convention although some texts specify that all forms of energy added to a system as heat or work are positive. However, regardless of the sign convention adopted for heat and work interactions, later in the same text the specified convention is abandoned in favor of magnitudes or absolute values. This occurs particularly in relation to cycle analyses in which the absolute value is used for energy transfers. Generally for reversible cycles there is no proof as to why the ratio of energy added/rejected via heat transfer equals the ratio of the absolute temperatures of the thermal reservoirs. To promote sign convention consistency, this paper develops the appropriate relationship between energy transfers and thermal reservoir temperatures for reversible cycles and applies the result to power producing and power consuming engineering devices.Copyright