heat exchangers for food processing heat exchangers for food

ITP 330/Heat Exchanger 8/24/2011

Purwiyatno Hariyadi/ITP/Fateta/IPB --Heat Exchanger 1

Heat ExchangersHeat Exchangersfor Food Processingfor Food ProcessingHeat ExchangersHeat Exchangersfor Food Processingfor Food ProcessingL t N tL t N tLecture Note Lecture Note Principles of Food Principles of Food EngineeringEngineering (ITP 330)(ITP 330)

Prof. Prof. DrDr. . PurwiyatnoPurwiyatno SSHariyadiHariyadi, , MScMSc

Dept of FoodDept of Food Science &Science & TechnologyTechnologyDept of Food Dept of Food Science & Science & TechnologyTechnologyFaculty of Agricultural TechnologyFaculty of Agricultural TechnologyBogor Agricultural UniversityBogor Agricultural UniversityBOGORBOGOR

Heat ExchangersHeat ExchangersLearning ObjectivesLearning Objectives

•• Understand basic principles of the designUnderstand basic principles of the design•• Understand basic principles of the design Understand basic principles of the design and operation of heat exchangersand operation of heat exchangers

•• Be able to list and discuss various Be able to list and discuss various applications of heat exchangersapplications of heat exchangers

•• Be able to describe applications of various Be able to describe applications of various types of heat exchangestypes of heat exchangestypes of heat exchangestypes of heat exchanges

PurwiyatnoPurwiyatno HariyadiHariyadi/ITP//ITP/FatetaFateta/IPB /IPB



•• Heating and cooling systemsHeating and cooling systemso use a flowing fluid to provide the heating or o use a flowing fluid to provide the heating or cooling effectcooling effect

HEAT EXCHANGERSHEAT EXCHANGERS

o Examples: o Examples: > refrigeration systems> refrigeration systems> steam jacketed kettles> steam jacketed kettles> plate heat exchangers> plate heat exchangers

•• Need to know how much heat can be transferred Need to know how much heat can be transferred to (or from) a fluid flowing in a systemto (or from) a fluid flowing in a system

•• Other important factors include:Other important factors include:o fluid flow rateo fluid flow rateo fluid propertieso fluid propertieso fluid thickness (or pipe diameter)o fluid thickness (or pipe diameter)


•• Heat exchangers are used extensively in many food Heat exchangers are used extensively in many food operationsoperations


•• Used where many heating and cooling operations are Used where many heating and cooling operations are involvedinvolved

•• Basis function is to transfer heat from one fluid to Basis function is to transfer heat from one fluid to anotheranother

•• Some cases fluids are mixed Some cases fluids are mixed -- when steam is added to when steam is added to waterwaterwaterwater

•• In most cases, the fluids must be physically separated In most cases, the fluids must be physically separated by a plate, pipe wall, or other good conductorby a plate, pipe wall, or other good conductor




•• Simple heat exchanger Simple heat exchanger --one pipe mounted inside anotherone pipe mounted inside another



•• DoubleDouble--type heat exchanger is excellent for analyzing type heat exchanger is excellent for analyzing heat exchanger characteristicsheat exchanger characteristics

HEAT EXCHANGERS : HEAT EXCHANGERS : Multi Tube Tubular HXMulti Tube Tubular HX





ShellShell--andand--tube heat exchangertube heat exchanger

o has tubes mounted inside an outer shell o has tubes mounted inside an outer shell


o One fluid flows through the tube while the o One fluid flows through the tube while the other is in the shell surrounding the tubesother is in the shell surrounding the tubes

•• bundle of parallel tubes contained within a shellbundle of parallel tubes contained within a shell


ShellShell--andand--tube HXtube HX

•• bundle of parallel tubes contained within a shellbundle of parallel tubes contained within a shell•• tubetube--side: food productside: food product•• shellshell--side: heating or cooling medium side: heating or cooling medium •• shell side not sanitaryshell side not sanitary•• NONO regenerationregeneration•• very inexpensivevery inexpensive




Example :Example :Tube HXTube HXExample :Example :Tube HXTube HX

PurwiyatnoPurwiyatno HariyadiHariyadi/ITP//ITP/FatetaFateta/IPB /IPB PurwiyatnoPurwiyatno HariyadiHariyadi/ITP//ITP/FatetaFateta/IPB /IPB

plate heat exchanger. plate heat exchanger.




SweptSwept--surfacesurfaceHXHX


SweptSwept--surfacesurfaceHXHX

•• viscous fluidsviscous fluids––cheese saucecheese sauce

––puddingpudding

•• NONO regenerationregeneration

expensiveexpensive


•• expensiveexpensive

Vertical typeof scraped-surfaceheat exchanger

Purwiyatno Hariyadi/ITP/Fateta/IPB




•• Heat exchangers also identified by the flow pattern Heat exchangers also identified by the flow pattern of the fluids in the exchangerof the fluids in the exchanger

•• DoubleDouble--pipe heat exchanger pipe heat exchanger -- a parallel flow unit a parallel flow unit since the fluids flow in parallel.since the fluids flow in parallel.


Reversing either fluid would produce a counter flow systemReversing either fluid would produce a counter flow system





•• Heat exchangers vary greatly in the design to obtain Heat exchangers vary greatly in the design to obtain desired heat transfer characteristicsdesired heat transfer characteristics


desired heat transfer characteristicsdesired heat transfer characteristics

•• CrossCross--flow system flow system -- fluids flow perpendicular to fluids flow perpendicular to each othereach other

•• Combinations of several designs are sometimes Combinations of several designs are sometimes used in special situationsused in special situations


SPIRALSPIRAL--TUBE HXTUBE HX•• helical tube within shellhelical tube within shell•• used on some aseptic systemsused on some aseptic systems

STEAMSTEAM--INFUSION HXINFUSION HX•• thin layer of food cascades through steam thin layer of food cascades through steam

chamberchamber•• direct contact with steam=dilutiondirect contact with steam=dilution

i f di f d•• viscous foodsviscous foods•• possibly foods with particulatespossibly foods with particulates




The concentric tubes

Consentric tubes wound cylindricallyt f il

The concentric tubesin a triple tube heat exchanger

to form coils. The unit is placed ina stainless steel jacket


(Cold fluid)

HEAT EXCHANGERS : HEAT EXCHANGERS : AnalysisAnalysis•• Assume the following: Assume the following:

o doubleo double--pipe heat exchanger pipe heat exchanger

(Hot fluid)


o hot fluid flowing in the inner pipeo hot fluid flowing in the inner pipeo cooler fluid flows in outer pipeo cooler fluid flows in outer pipeo flow is parallelo flow is parallel



Temperature distribution along length of heat exchanger

HEAT EXCHANGERS : HEAT EXCHANGERS : AnalysisAnalysis

Hot Fluid Out

ΔT1

Cold FluidIn Cold

FluidOut

1 12 2

ΔT2


Hot Fluid In1 12 2

Temperature distribution along length of heat exchanger

ΔT


ΔT

1 2

ΔT1ΔT2


1 2




ΔT1ΔT2dΔT −=

UiΔTdAidq =

qΔT1ΔT2

dqdΔT −=Temperature distribution along

length of heat exchanger

ΔT

dAiqΔT1ΔT2

ΔTdΔT

Ui

1 −=⎟⎠⎞⎜

⎝⎛

qUiΔTdAi

dAiqΔT1ΔT2

ΔTdΔT

Ui

1 Ai

0

DT2

DT1

−=⎟⎠⎞⎜

⎝⎛ ∫∫

ΔT

1 2

ΔT1ΔT2


ΔT1

ΔT2lnΔT1ΔT2LMTD

dimana−=

ΔT1

ΔT2lnΔT1ΔT2UiAiq −=

1 2

Energy balance :


Total energy lost (by hot fluid) :


Total energy lost (by cold fluid) :






60

80Contoh Soal

Diketahui :

0

20

40

0 1 2 3 4

P j Pi

Suhu


• Laju aliran air pendingin = 0.028 kg/s• Luas area HX = 0.1226 m2

• Kapasitas panas air = 4.1868 kJ/kg.oK Ditanya :• Berapa nilai U (overall Heat Transfer Coef)?

Panjang Pipa




Dari data yang ada :q = m c ΔT;

60

80Contoh Soal

q = m cp ΔT; Diketahui : mc = 0.028 kg/s

Cp = 4.1868 kJ/kg.oC

0

20

40

0 1 2 3 4

P j PiSu

hu


Jadi,q = (0.028 kg/s)(4.1868 kJ/kg.oC)(51.8-28.1)oC= 2.778 kW

Panjang Pipa


60

80Menggunakan data yang ada (lihat grafik), cari LMTD

0

20

40

0 1 2 3 4

P j Pi

Suhu

Diketahui A = 0.1226 m2


Panjang Pipa

Maka, sesuai dengan teori Pindah panasq = U A ΔTm = U A (LMTD)U = q/[A(LMTD)]U = (2.778 kW)/(0.1226*16.72)m2.oc = 1.355 kW/m2.oc



•• regenerative heat/coolregenerative heat/cool•• regenerative heat/coolregenerative heat/cool


Plate HXPlate HX


Plate HXPlate HX

regenerative heat/coolregenerative heat/cool•• compactcompact•• THE THE standard for milk pasteurizationstandard for milk pasteurization•• lowlow--viscosity fluidsviscosity fluids

–– juicejuice–– UHT milkUHT milk

regenerative heat/coolregenerative heat/cool•• compactcompact•• THE THE standard for milk pasteurizationstandard for milk pasteurization•• lowlow--viscosity fluidsviscosity fluids

–– juicejuice–– UHT milkUHT milk


Selesai ….……….Selesai ….……….Sekarang ke…….Sekarang ke…….Proses TermalProses Termal

heat exchangers for food processing heat exchangers for food

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