Microsoft Word - Cengel and Boles TOC _2-03-05_.doc

There are two other cycles that involve an isothermal heat-addition process

at THand an isothermal heat-rejection process at TL: the Stirling cycleand

the Ericsson cycle.They differ from the Carnot cycle in that the two isen-

tropic processes are replaced by two constant-volume regeneration processes

in the Stirling cycle and by two constant-pressure regeneration processes in

the Ericsson cycle. Both cycles utilize regeneration,a process during which

heat is transferred to a thermal energy storage device (called a regenerator)

during one part of the cycle and is transferred back to the working fluid dur-

ing another part of the cycle (Fig. 9–25).

Figure 9–26(b) shows the T-sand P-vdiagrams of the Stirling cycle,

which is made up of four totally reversible processes:

1-2 T
constantexpansion (heat addition from the external source)

2-3 v
constantregeneration (internal heat transfer from the working

fluid to the regenerator)

3-4 T
constantcompression (heat rejection to the external sink)

4-1 v
constantregeneration (internal heat transfer from the

regenerator back to the working fluid)

The execution of the Stirling cycle requires rather innovative hardware.

The actual Stirling engines, including the original one patented by Robert

Stirling, are heavy and complicated. To spare the reader the complexities,

the execution of the Stirling cycle in a closed system is explained with the

help of the hypothetical engine shown in Fig. 9–27.

This system consists of a cylinder with two pistons on each side and a

regenerator in the middle. The regenerator can be a wire or a ceramic mesh

504 | Thermodynamics

Energy

Energy

REGENERATOR

Working fluid

FIGURE 9–25

A regenerator is a device that borrows
energy from the working fluid during
one part of the cycle and pays it back
(without interest) during another part.

s

12

4 3

T

s = const. s = const.

TH

TL

1

2

3

4

P

TH

= const.

TH

= const.

TH

= const.

TL = const. TL = const.

TL

= const.

1

2

3

4

P

Regeneration Regeneration

1

3 2

4

P

s

1 2

4 3

T

v = const.

v = const.

Regeneration

s

1 2

4 3

P = const.

P = const.

Regeneration

(a) Carnot cycle (b) Stirling cycle (c) Ericsson cycle

qin

qout

TH

TL

T

TH

TL

qin

qout

qin

qout

qin

qout

qin

qin

qout

qout

vv v

FIGURE 9–26

T-sand P-vdiagrams of Carnot,
Stirling, and Ericsson cycles.