Stirling-Engine.pdf

Texas Space Grant Consortium Advanced Design Project - Spring 1997 -

Solar Power From Space

Stirling Engine

Texas Christian University

By: Tanya Hardy

David Meek

Nathan Moser

Majin Sierra

Winyu Vongstapanalert

Greg White

Aaron Williams

28 April 1997

Written by undergraduate students at:

Distributed by:

Texas Christian University

Texas Space Grant Consortium

http://www.tcu.edu/

http://www.tsgc.utexas.edu/

0.0 Abstract

The seven-member team at Texas Christian University has been working on the Stirling engine

contribution to the Texas Space Grant Consortium’s Advanced Design Project. We hope to

demonstrate how a Stirling engine in conjunction with a parabolic mirror can be an efficient way of

obtaining solar power from space. We are approaching this project as a one-hour, one-semester junior

research class. This semester’s activities consist of studying the feasibility of using Stirling engines for

space power generation.

We have begun to study how a Stirling engine and reflective dish will work together in order to

utilize the sun's heat to produce energy. In order to better understand how this type of system will

perform, we have purchased a model engine with a solar concentrator. Along with the purchased

motor, we have fabricated our own engine. We also purchased an alternator and used it in conjunction

with our purchased model engine in order to convert the mechanical power into electrical power. We

then ran tests on our system to see how much energy we could get out of the system.

Our objective this semester was to see if a Stirling engine/dish system can be used instead of

photovoltaic cells. The Stirling engine/dish system is both more efficient and less expensive. We gave a

good starting point for those who will continue this project and many of the aspects that need to be

considered are discussed in this paper.

Written by undergraduate students at:

Distributed by:

Texas Christian University

Texas Space Grant Consortium

http://www.tcu.edu/

http://www.tsgc.utexas.edu/

Table of Contents

0.0 Abstract...............................................................................................................................pg. 1

1.0 Mission Overview..............................................................................................................pg. 3

2.0 The Stirling Engine.......................................................................................................pgs. 3-5

2.1 The Stirling Cycle

2.2 Model Stirling Engine

2.3 Fabricated Stirling Engine

2.4 Working Stirling Engines

3.0 Gathering the Sun’s Rays: Parabolic Mirrors.................................................................pgs.5-6

3.1 Temperature Effects

3.2 Collar Design

3.3 Alternative Solutions

4.0 Rocket Choice....................................................................................................................pg. 6

4.1 Titan IV

5.0 Space Effects.................................................................................................................pgs. 6-9

5.1 Elements of Space Flight

5.2 Vacuum Environment

5.3 States of Matter and Orbital Debris

5.4 Radiation and Space Welding

5.5 Other Space Effect Considerations

6.0 Energy Conversion........................................................................................................pgs. 8-9

6.1 Shaft Rotational Torques

6.2 Converting Into an Oscillating Form

6.3 Specifications and Considerations

7.0 Benefits Over Solar Cells...................................................................................................pg. 9

8.0 Conclusion.........................................................................................................................pg. 9

9.0 Appendix...................................................................................................................pgs. 10-16

Written by undergraduate students at:

Distributed by:

Texas Christian University

Texas Space Grant Consortium

http://www.tcu.edu/

http://www.tsgc.utexas.edu/

9.1 Appendix A

9.2 Appendix B - Engine Drawings (see jpeg image files)

9.3 Appendix C (biographies)

Written by undergraduate students at:

Distributed by:

Texas Christian University

Texas Space Grant Consortium

http://www.tcu.edu/

http://www.tsgc.utexas.edu/

1.0 Mission Overview

During the 1970's there was an increased awareness of the limited energy resources available on

earth. Oil, natural gas, coal, and nuclear energy are currently the fuels of choice; however, society is

becoming increasingly aware of the damage to the environment caused by fossil fuels, yet no one wants

a nuclear reactor in the backyard. A possible solution to this dilemma is an almost infinite energy source

waiting to exercise its full potential: THE SUN!

An alternative means of solar power collection, besides photovoltaic cells, is the use of a Stirling

motor-solar concentrator system. The solar concentrator consists of a parabolic mirror focusing the

sun’s energy on a receiver which then powers the Stirling motor. The motor produces mechanical

power. This power is converted to electrical power which in turn is transmitted through microwaves to

earth. It will be a clean and effective way to get energy without depleting the earth of any of its natural

resources and without the pollution.

2.0 Stirling Engines

The Stirling engine is one of the most efficient devices for converting heat into mechanical work;

however, it requires relatively high temperatures. With a solar collector, the high temperatures

necessary for efficient power production can be achieved, thus making the Stirling engine an ideal

candidate for harnessing the power from the sun. The high temperatures we are dealing with will not

affect any of the electrical or other materials because they will be behind the mirror and thus protected.

As the temperature that drives the Stirling motor increases, the efficiency of the system increases.

The temperature at the receiver is dependent upon the size and curvature of the concentrator. The

melting point temperature of the receiver is a limiting factor. Stirling engines generally operate at the

thermal limits of the material used for their construction. Typical temperatures range from 650 to 800

o C (1200 to 1470 o F), resulting in an engine efficiency of around 30% to 40%.

Hydrogen and helium are commonly used as the working gas for the engine because of their high

heat-transfer capabilities. Hydrogen, thermodynamically, is a better choice. This gas generally results in

more efficient engines than those with helium. However, helium has fewer material compatibility

problems and is safer to work with, being a Noble gas.

Engines typically operate at high pressures for maximized power, ranging from 5 to 20 MPa (725 to

2900 psi). Operations at these high pressures make sealing between components difficult.

To make space environment systems economical, a system lifetime of at least 20 years with

minimum maintenance is generally required. However, a major overhaul of engines, including

replacement of seals and bearings, may be necessary within the 40,000 to 60,000-hour (4.56 to 6.84-

yrs.) lifetime, which adds to the operating cost. A major challenge, therefore, in the design of Stirling

engines is to reduce the potential for wear in critical components or create novel ways for them to

perform their tasks.

2.1 The Stirling Cycle

For our purposes, the Stirling cycle can be described as a heat engine cycle in which heat is

accepted at a high temperature and rejected at a lower temperature, an action which will produce net

Written by undergraduate students at:

Distributed by:

Texas Christian University

Texas Space Grant Consortium

http://www.tcu.edu/

http://www.tsgc.utexas.edu/

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: