HEAT EXCHANGER

Hanim ZA

2012

Types of Heat Exchanger

Types of Heat Exchanger

Heat Exchanger Analysis

The Log Mean Temperature Difference Method

1.Parallel Flow

hhhhph dTCdTCmdq ,

hphh Cm

dqdT

,

1.Parallel Flow

Hot Fluid

Parallel Flow

ccccpc dTCdTCmdq ,

cpcc Cm

dqdT

,

Cold Fluid

Parallel Flow

Temperature Difference (1)

p,ccp,hhchch CmCm

dq)Td(TdTdT11

Parallel Flow

Heat Transfer in Differential section (2)

)( ch TTdAUdq

Parallel Flow

Substituting equation (2) to (1)

cpchphch

ch

cpchphchch

CmCmdAU

TT

TTd

CmCmTTdAUTTd

,,

,,

11

)(

)(

11)()(

Parallel Flow

integrating equation

cpchphicih

ocoh

CmCmAU

TT

TT

,,,,

,, 11

)(

)(ln

Parallel Flow

q

TT

q

TTAU

TT

TT

q

TT

q

TTAU

TT

TT

q

TT

q

TTAU

TT

TT

icihocoh

icih

ocoh

ocohicih

icih

ocoh

ocicohih

icih

ocoh

)()(

)(

)(ln

)()(

)(

)(ln

)()(

)(

)(ln

,,,,

,,

,,

,,,,

,,

,,

,,,,

,,

,,

cpc

outcinc

hph

outhinh

Cmq

TTand

Cmq

TT

,

,,

,

,, 1)(1)(

Parallel Flow

1

2

12

lnTTTT

AUq

TAUq lm

Counter Flow

Variation of fluid temperature

Counter Flow

Heat Rate

)(

)(ln

)()(

)()(

)(

)(ln

,,

,,

,,,,

,,,,

,,

,,

ocih

icoh

ocihicoh

ocihicoh

ocih

icoh

TT

TTTTTT

AUq

q

TT

q

TTAU

TT

TT

lmTAUq

TTTT

AUq

1

2

12

ln

Cross Flow

Heat Rate

Asumsi : ΔTlm sama dengan aliran counter flowUntuk menghitung nilai q ada faktor koreksi terhadap ΔTlm yang nilainya dipengaruhi oleh tipe Heat Exchager dan temperatur

1

2

12

lnTTTT

AUFqTFAUq lm

Contoh soal

A counter flow double pipe heat exchanger is used to heat water from 20oC to 80oC at a rate of 1,2 kg/s. The heating is to be accomplished with geothermal available at 160oC at a mass flow rate 2 kg/s. the inner tube is thin-walled and has a diameter of 1,5 cm. If the overall heat transfer coefficient of heat exchanger is 640 W/m2 oC, determine the lenght of heat exchanger required to achieve the desired heating (Cp,c= 4,1 8 kJ/kgoC ; Cp,h= 4,31 kJ/kgoC )