SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS DH Jeggels and RT Dobson Department of

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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013

iThemba LABS

DH Jeggels and RT Dobson

Department of Mechanical Engineering,University of Stellenbosch,

Stellenbosch, Western Cape Province, South AfricaDawood Jeggels and RT Dobson presentation for EPC2013 as at 8 August 2013

Theoretical and Experimental Simulation

of a

Li-Br Water Dual Function Absorption system

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Preamble

The world, in general, has become very aware of the fact that we are polluting the planet irreversibly; “you don’t get nothing for free” so if “If it isn’t green, paint it green”.

Environmental impact studies, global warming, ozone depletion, pollution, renewable energy such as solar, “CSP”, wind, tidal, hydroelectric and waste minimization have all become important words in both business and academic circles.

Power utilities and big-business must be seen to be saving energy, generating power more efficiently, reducing their carbon footprint, and reducing their production of polluting and global warming effluent/waste/toxic materials.

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Power stations using a Rankine cycle or a Brayton cycle reject some 33% of the energy supplied, “irreversibly”, back into the environment.

The higher the source temperature the higher the thermal efficiency

The lower the waste temperature the higher the thermal efficiency BUT the rate of improvement decreases and the power generating equipment becomes exponentially more expensive

The idea is then to combine a Rankine cycle which is more efficient at higher temperature with another cycle which is more efficient at a lower temperature and thereby increase the overall efficiency

Pre-amble (cont.)

=1− 𝑇 sink +273𝑇 source +273

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Pre-amble (cont.)

Thermal efficiency as a function of heat source temperature

14% of 100°C waste heat can be recovered using a DFAC

Stirling cycle engine (SC)

Rankine cycle (RC)

Dual function absorption cycle (DFAC)

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Contents

Preamble

Why a dual function absorption cycle

Objectives: To build and test an absorption system that can be used to get a better understanding of its functioning and control

strategies and to assist in validating the theoretical simulation model of the cycle

Experimental Apparatus

Transient theoretical modelling

Discussion, Conclusions and Recommendations

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+ - ~

turbineW

Electrical generator

Turbine

Super heater

ionrefrigeratQ

Evaporator

Absorber

Pump

coolingQ

Waste heat supply

Control Valve

Rectifier

Vapour generator

hwm

12°C

hwT

refrigm refrigT

-8°C

58°C 58°C

82°C

Recouperator

58°C

58°C

280kPa

22°C, 44kPa

Figure 1 Dual function (power and refrigeration ammonia-water absorption system

74°C

27°C

Dual function (power and refrigeration) ammonia-water (or Li-Br water) absorption

system

Power

Refrigeration

Cooling water

Waste heat

supply

How does it work

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�ሶେ�

�ሶେ� �ሶେେେ�� ሶେେେ��

PGC TGC

Generator-Condenser vapour space

�ሶେ�୪୭ୱୱ �ሶେ��୪୭ୱୱ

�ሶେେେ�� ሶେେେ�� ሶେେ��୪୭ୱୱ

Tamb

�ሶେ�

�ሶେ�� TGhw

TCcw

�ሶ୮ �ሶ

�ሶ

PEA TEA mEA

�ሶେ�� ൌߩ�� ሶ୮

�ሶେ��

�ሶ ൌߩ��ி� �ሶ୮ �ሶ

�ሶ୪୭ୱୱ �ሶ୪୭ୱୱ

�ሶୡୟ୮

�ሶୡୟ୮

TE mE TEhw

�ሶ

�ሶ �ሶ

Tamb

TA

THEAG

Tamb

�ሶ୪୭ୱୱ

mALF TALF

�ሶୋୋୋୋୋୋୋୋୋୋୋୋୋୋ ൌߩ��ி� �ሶ୮

THEGA

TAcw �ሶ

Figure 1 Schematic layout of the absorption cycle system

TCLP mCLP mG TG

�ሶ

CG

CALF

CA mA

mGC

Evaporator-Absorber vapour space

TcapE

Capillary tube dcap and Lcap

Generator

Absorber Evaporator

Pump

Condenser liquid pool

Heat Exchanger

Control valve

�ሶୡୟ୮

Control valve

TCLF

Experimental apparatus

Stand, generator

and condenser

Heat exchangers

Evaporator and

absorber

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Theoretical Simulation Process

Figure Error! No text of specified style in document..1: Conservation equations control volumes, (a) Mass, (b) Momentum, (c) Energy

g

ሺŵሶŚሻŽƵƚ WŽƵƚ

WŝŶ

ŵŐƐŝŶɽ

ሺŵሶǀ ሻŽƵƚ

ሺŵሶǀ ሻŝŶ

ѐǌ ѐǌ ѐǌ

ሺŵሶŚሻŝŶ ߠ

Yሶ ѐWĨƌŝĐƚ ůŽƐƐ

ŵሶŝŶ

ŵሶŽƵƚ

z

(a) (b) (c)

Conservation of mass

Conservation of energy (Ignoring KE and PE )

and noting that h = u + PdV

Conservation of energy where Conservation of mass

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Results

For example, for the Generator-Condenser, and similarly for the rest

2 164 326 488 650 812 974 1136129814601622178419462108227024320

10

20

30

40

50

60

70

80

90

Time, t (s)

Tem

pera

ture

, T (°

C) TG

TCl

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Discussion, Conclusions and Recommendations

• We have shown what an absorption cycle works and how it can generate both power and cooling using a low-grade (low temperature) source of (waste) heat

• We have shown how we mathematically simulate such a system

• We have so far completed the generator-condenser/turbine part, the absorber-evaporator, the pump.

• We have manufactured the parts but still need to complete the assembly of the system parts

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AcknowledgementsSouth African Heat Pipe Association

University of Stellenbosch

Thanks

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Condenser

Stand

Generator

Back

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Heat exchangers

Back

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Evaporator and absorber

Evaporator Absorber

Back

Documents

SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS DH Jeggels and RT Dobson Department of