STIRLING ENGINE

The Analysis of a…

WHY A STIRLING ENGINE?Here is what we wanted to learn: How do stirling engines work? Which design aspects have the greatest effect on their

performance? How do they compare to more common engines? Where would a stirling engine be used?

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DEMONSTRATION

WHAT IS A STIRLING ENGINE?

Gamma type stirling engine A stirling engine uses heat flux

from a temperature differential to create a cycle of expanding and contracting air

The expansion and contraction causes a pressure change which moves the green piston

The green piston rotates the shaft and the flywheel which moves the displacer

Why are they 90° out of phase?

Invented in 1816 by Robert Stirling

First used in Dundee Foundry in Scotland for power generation

Applications include mechanical and electrical power generation, cryogenic cooling and HVAC.

Typical efficiency is 30-50% of Carnot cycle (15-30% overall)

BACKGROUND

SOLAR POWER

approximately 31% efficient

We measured… System dimensions Temperature difference RPM

EXPERIMENT

We assumed… Steady state heat reaction

for engine Laminar flow Insulated cylinder No loss through bottom of

coffee cup or sides of plate Frictionless

Significant calculations: Work output per cycle Heat loss from mug

CALCULATIONS

V1 = minimum volume V2 = maximum volume

POWER

qin = 12.50 Watts

Work = 0.14 Wattsqout = 12.36 Watts

Material Thot °C Tcold °C T(delta) RPMTime to

Stop(sec)

Power output (Watts)

Power Water

(Watts)qconv qin Efficiency

Aluminum 67 2 65 87   0.14 20 6.8 13.4 1.0%Aluminum 60 3 57 108   0.17 18 5.7 12.1 1.4%Aluminum 44 4 40 46 70 0.07 12 3.1 9.3 0.8%Aluminum 25 -3 28 39   0.06 9 0.0 8.6 0.7%Aluminum 93 -3 96 127   0.20 30 10.9 18.9 1.1%Aluminum 85 -4 89 132   0.21 28 9.7 18.0 1.2%Aluminum 59 22 37 58   0.09 12 5.5 6.1 1.5%

Steel 50 -3 53 84   0.13 16 4.1 12.4 1.1%Steel 64 0 64 100 380 0.16 20 6.3 13.6 1.2%

Average     59 87   0.14 18 5.8 12.5 1.1%

RESULTS

20 30 40 50 60 70 80 90 1000.00

0.05

0.10

0.15

0.20

0.25

f(x) = 0.00252506106685977 xf(x) = 0.002313346706129 x

Power vs Temperature Difference

Aluminum Linear (Aluminum)Steel Linear (Steel)

Temperature Difference (C)

Pow

er

(Watt

s)

qin Work qout0

2

4

6

8

10

12

14

Power

Watt

s

RESULTS

OVERVIEW Plate properties and dimensions have no effect on power output

for steady-state A larger diameter cylinder can operate on a smaller temperature

difference Gases with large (m*R) J/kg, such as helium, are the best working

fluids Temperature difference is directly proportional to power output

Efficiency comparison:- Stirling engine: 12% - 20%- Steam engine: 8%- Internal combustion: 35%

Stirling engines are increasingly being used in solar power applications. They are useful because they are extremely low maintenance and do not require fuel to run. Renewable energy!

Questions?