1

Alternative Cooling Processes 2

Hans Jonsson

Agenda• Expansion Cycles

- Joule Cycle with applications- Stirling Cycle- Hilsch Tube (Ranque Vortex Tube)

• Thermoelectric Processes- Peltier Process

2

Expansion Cycles• Cycles utilizing a gaseous working media.• No phase change!• Usually used when large temperature lifts

are needed (i.e. for achieving low temperatures).

Expansion Cycles

3

Joule Cycle 1

Joule Cycle 2

4

Joule Cycle 3Coefficient of performance, COP

( )( ) ( )[ ] =−−−⋅⋅

−⋅⋅=

−==

adbcp

abp

ExK

222 TTTTcm

TTcmEE

QE

QCOP&

&

&&

&

&

&

( )( ) ( ) =

η⋅−−η−−

=Exis,adKbis,c

abTTTT

TT

( )( ) ( )

( )( )( )

=

⎪⎪

⎭

⎪⎪

⎬

⎫

⎪⎪

⎩

⎪⎪

⎨

⎧

η⋅−−=

η⋅−=−

η−=−=

−−−−

=

Exis,adda

Exis,adad

Kbis,cbc

adbc

ab

TTTT

TTTT

TTTTesefficienci Isentropic

TTTTTT

Joule Cycle 4( )( )

( ) ( ) =η⋅−−η−

η⋅−−−=

Exis,adKbis,c

Exis,addb

TTTTTTTT

( )

( )

=

⎪⎪

⎭

⎪⎪

⎬

⎫

⎪⎪

⎩

⎪⎪

⎨

⎧

τ==→

τ==→=

κ−κ

κ−κ

121is,ad

121bis,c

ppTT:ad

ppTT:cb

processes Isentropic

( )( )( ) ( ) =

η⋅−⋅−η−⋅η⋅−−⋅−

=Exdis,adKbis,cb

Exdis,adb

TT1T1TTTTT11TT

5

Joule Cycle 5( )( )

( ) ( ) =η⋅τ−⋅−η−τ⋅

η⋅τ−−⋅−=

ExdKb

Exdb11T1T

111TT

( )11COP2 −τ

=

( )( )( )

τη⋅−ηη⋅τ−−⋅−

⋅−τ

=ExdKb

Exdb

TT111TT

11

If ηEx = ηK = 1, then

Joule Cycle 6

ηEx = ηK=

6

Joule Cycle 7If air is used as the working media, heat exchangers can be omitted which gives better performance.

System A System B

Joule Cycle 8

7

Joule Cycle 9Systems without heat exchangers.

Joule Cycle 10Systems with multiple stages.

8

Joule Cycle 11

Joule Cycle 12

9

Joule Cycle - Applications• Cold stores• Cooling of aircraft

Cooling of aircraft• Cockpit + Cabin pressurization,

heating/cooling• Avionics cooling (electronics cooling)• Radar cooling• Windshield defrosting/defogging• Pressurization of fuel tanks• Military: G-protection, Canopy seal etc.

10

Cockpit+Cabin pressurization

Joule Cycle - Applications

11

Joule Cycle - Applications

Compressed air. High pressure and temperature

Compressor

Turbine

Heat exchangers

Condenser

Modern Fighter Aircraft

12

Stirling cycle• Can achieve very

low temperatures• Has best

performance at large temperature lifts

• Ideal Stirling cycle has the same COP as the Carnot cycle

Hilsch Tube/Ranque Vortex Tube

13

Vortex tubes

Dimension –length (mm)

Max. Refrigeration

(W)

Price(USD)

Small size 100 40 130

Medium size

150 190 170

Large size 300 1900 680

Hilsch Tube / Ranque Vortex Tube

Peltier process• Thermoelectric process• Give a very even temperature distribution

that can be controlled very accurately.• Utilize the Seebeck effect

14

Seebeck effectIf temperatures T1and T2 are not the same, there will be a (small) voltage between the two solder points (Seebeck effect).Wires of two

different materials are soldered together.

Solder points

Peltier process

Peltier discovered that if you put a voltage across the two wires, the two solder points will be at different temperatures.

15

Peltier process

Peltier process

16

Peltier process

Peltier process• The Seebeck effect is very dependent on the

material properties. In order to have a good performance, the materials should have:

• Low electric resistance• Low thermal conductivity

17

Peltier process

To achieve a high Joffe number, R and K should tend to zero!

In order to describe the materials, a figure of merit has been defined:

e: Seebeck constant for the material combination

R: Electric resistance

K: Thermal conductivity

KReZ

2

⋅=

Joffe number, Z

Peltier process

1ZT1TTZT1

TTTCOP

m

21m

21

2opt,2 +⋅+

−⋅+⋅

−=

Tm: Mean temperature between T1 and T2

A corresponding Carnot efficiency can be defined as:

C,2

opt,2C COP

COP=η

Theoretically, an optimum COP could be found as:

18

Peltier process

New ”materials” bring new hope

19

New ”materials” bring new hope

Next (last) lecture• Bring SEU book• Please fill out the questionnaire regarding

the computer lab 4 (System Analysis)