Thermodynamic Cycles

Computer-Aided Design and Optimization

Chih Wu

• Publisher: CRC Press
• Year: 2003
• ISBN:
  9781135525019
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

This reference illustrates the efficacy of CyclePad software for enhanced simulation of thermodynamic devices and cycles. It improves thermodynamic studies by reducing calculation time, ensuring design accuracy, and allowing for case-specific analyses. Offering a wide-range of pedagogical aids, chapter summaries, review problems, and worked example

1

Thermodynamic Concepts

1.1 Introduction

Research in cognitive science potentially offers tremendous benefits in education, industry, and training. Psychological studies of human learning can yield insights as to what forms of instruction might be most beneficial for particular purposes, and what mental models and misconceptions students might have. Artificial intelligence research can provide formal representations and reasoning techniques that can be used in new kinds of educational software that itself contains a deep understanding of the domain being taught. These scientific advances, coupled with dramatic changes in computing technology (i.e., increased computing power at decreasing costs), provide new opportunities for exploring how intelligent software can be used in thermodynamic education and industry.

Thermodynamic design, for example, can be relieved of repetitive hand calculation, iterative solution techniques, and two-way interpolations. Beyond this is a pervasive cultural preference of this generation towards interacting with computers.

Throughout, the book is software oriented. The text is tightly integrated with “CyclePad,” an intelligent, user-friendly software which performs first and second law analyses for user-defined inputs and processes, solves simultaneous equations, looks up state data, and attractively graphs processes in phase spaces. In reducing computational effort more than 10-fold, this software enables and requires engineers to work many more cycle problems, and just as importantly, to do so in a timely way. Such efficient learning strategy boosts engineer confidence.

1.2 Intelligent Computer-Aided Software

An intelligent computer software called CyclePad is used throughout the book. CyclePad has been codeveloped by Oxford University and Northwestern University since 1995, and evaluated by Professor C. Wu in the Mechanical Engineering Department at the U.S. Naval Academy.

Normally, calculation in a cycle analysis is lengthy, complex, and tedious for an engineer. The analysis would be more meaningful, time saving, and fun for engineers using CyclePad as a tool to help in the cycle analysis, design, and optimization. Engineers would be able to change any parameter in the cycle and see the effect of the parameter on the performance of the cycle.

The value that CyclePad brings to its users is a reduction in time while moving from concept to finished design. This time saving allows the user to move to his physical prototyping stage faster, thereby eliminating certain prototyping costs and improving cycle design more rapidly. Virtual prototyping with CyclePad follows the same basic steps used in traditional or physical design process. The user builds his cycle design, runs it through analyses, validates results, refines the design, and iterates this process until the cycle’s performance is optimized. The difference is that the user manages this process virtually through a computer, much more quickly, easily, and cost-efficiently.

Design is a trying and learning process. Engineers would be able to choose various components in their design of power plants or choose different working fluids in the plants for a specific mission by using CyclePad as a tool. They would be able to gain a tremendous design experience and knowing what they are doing in a relative short time.

CyclePad is made from a design and coaching perspective view. CyclePad is designed to help with the learning and conceptual design of thermodynamic cycles. It works in two phases, build and analysis. There are three modes (build, analysis, and contradiction) in the software.

1.2.1 Build Mode

In the build mode, a user takes components out from either a thermodynamic open-system inventory shop or a thermodynamic closed-system inventory shop and connects them to form a state or several states, a process or several processes, or a cycle or several cycles.

1.2.2 Analysis Mode

In the analysis mode, a user chooses working fluid, process assumption for each component, and input numerical property values. All the calculations are then quickly done by the software. There is a sensitivity tool that makes cycle performance parameter effects easy and quick, and generates the effect in graph form.

1.2.3 Contradiction Mode

There is a coach (senior engineer) in the software. If there is a mistake or a contradiction made by the user, the coach will show up and tell the contradiction and suggest ways to solve the contradiction.

CyclePad can be downloaded (free from Northwestern University’s web page at http://www.qrg.ils.northwestern.edu) by the following steps:

Internet Explorer

http://www.qrg.ils.northwestern.edu

Software

Download CyclePad v2.0

Fill in form—submit form

License agreement—download software

Save this program to disk—OK

Choose a location—save

Close Internet Explorer

Open my computer

Go to the location you save the file to

Double click on webcpad—#######.exe

Double click on Setup.exe

Install

Yes

OK

OK—CyclePad is downloaded

1.2.4 Installation Into Your Own PC

CyclePad can be installed into your own PC by the following steps:

Make new folder

Temp-CyclePad

Copy files from Zip to new folder Temp-CyclePad

Go to Temp-CyclePad

Double click–webcpad–20000504 20000504 (date)

Double click–cpadinst

Double click–setup

Install

Yes

Yes

C:\CyclePad

OK

OK

1.3 Review of Thermodynamic Concepts

Thermodynamics is a science in which the storage, transformation, and transfer of energy E and entropy S are studied. Thermodynamics is governed by four basic laws called (1) the zeroth law of thermodynamics, (2) the first law of thermodynamics, (3) the second law of thermodynamics, and (4) the third law of thermodynamics.

The zeroth law states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.

The first law is an expression of the conservation of energy.

The second law states that actual isolated processes occur in the direction of decreasing quality of energy.

The third law states that the entropy of a pure substance at absolute zero temperature is zero.

A thermodynamic system is either a quantity of matter called a control mass or closed system, or a region in space called a control volume or open system chosen for study. The mass or region outside the system is called the surroundings. The real or imaginary surface that separates the system from its surroundings is called the boundary. A closed system or a control mass consists of a fixed amount of mass, and no mass can cross its boundary. It usually encloses a device that involves no mass flow such as gas contained in a cylinder-piston setup. An open system or a control volume is a selected region in space. It usually encloses a device that involves mass flow such as a pump, compressor, turbine, mixing chamber, separator, heat exchanger, boiler, condenser, or evaporator. Flow through these devices is best studied by selecting the region within the device as the open system.

Any characteristic of a system is called a property. The essential feature of a property is that it has a unique value when a system is in a particular state. Properties are considered to be either intensive or extensive. Intensive properties are those that are independent of the size of a system, such as temperat...