Heat Exchanger(Alat Penukar Kalor) MCF 41264 (4 SKS)

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Semester 1

Skripsi (6)

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Fisika 1*:Panas & Mekanik (4)

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Semester 2

Statistik & Probabilitas (2)

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Perpindahan Kalor dan Masa (4)

Fisika 2*:Listrik, Magnet, Gel & Optik (4)

Perancangan Mekanika (6)

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Pilihan 1 s/d 3(12 @ 4)

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Pilihan 4&5(8 @ 4)

Semester 3

Semester 4

Semester 5

Semester 6

Semester 7

Semester 8

Gambar 3.2.2 Diagram Alir Mata Kuliah Program Studi Teknik Mesin

Tujuan Pembelajaran

Mengenal jenis-jenis alat penukar kalor Mengetahui jenis APK yang paling baik untuk aplikasi industri yang adaMengerti parameter kunci dalam desain APKMampu mengestimasi ukuran dan harga APKMemiliki latarbelakang untuk menggunakan software komersial untuk mendesain APK

Pendahuluan Heat Exchangers

Untuk apakah Alat Penukar Kalor?Jenis-Jenis Alat Penukar KalorBagaimana Alat penukar kalor diklasifikasikan?Dasar-dasar perencanaan Alat Penukar Kalor?

ContentsMengapa kita membutuhkan APKKonstruksi APKMacam-macam APKProses Desain APK

Apakah fungsi APK itu ?Untuk memperoleh aliran fluida pada temperatur yang tepat untuk proses berikutnyaUntuk mengkondensasikan uapUntuk menguapkan fluidaUntuk memanfaatkan panas buang Untuk pembangkitan daya

Feed-effluent exchangerFeed-effluentexchangerExothermic reactionHeat recovery

DistillationBottom product

Typical crude oil distillationE2E1E3E4E5E6E2E5StorageKeroseneDesalterTop pumparoundTop pumparoundNaphthaand gasesKeroseneReduced crudeLightgas oilHeavygas oilReducedcrudeHeavy gas oilLight gas oilBottom pumparoundDistillation towerBottompumparound

Geothermal Power cycleFeedwaterheater

Nuclear Power Plant

Ocean Thermal Energy Conversion

Contoh sebuah APKBundle for shell-and-tube exchanger

Heat utilitiesHot utilitiesBoiler generating service steam (maybe a combined heat and power plant)Direct fired heaters (furnace)Electric heatersCold utilitiesCooling tower (wet or dry) providing service cooling waterDirect air-cooled heat exchanger

Jenis-Jenis Alat Penukar Kalor

KATEGORI UTAMA ALAT PENUKAR KALORKebanyakan Alat Penukar Kalor memeliki 2 aliran fluida, hot dan cold, tetapi beberapa memiliki lebih dari dua aliran fluidaHeat exchangersRecuperatorsRegeneratorsWall separating streamsDirect contact

Recuperators dan regeneratorsRecuperativeHas separate flow paths for each fluid which flow simultaneously through the exchanger transferring heat between the streamsRegenerativeHas a single flow path which the hot and cold fluids alternately pass through.Rotating wheel

CompactnessCan be measured by the heat-transfer area per unit volume or by channel sizeConventional exchangers (shell and tube) have channel size of 10 to 30 mm giving about 100m2/m3Plate-type exchangers have typically 5mm channel size with more than 200m2/m3More compact types available

Compactness

Double PipeSimplest type has one tube inside another - inner tube may have longitudinal fins on the outside

However, most have a number of tubes in the outer tube - can have very many tubes thus becoming a shell-and-tube

Shell and TubeAlat Penukar Kalor tipe shell and tube yang biasa digunakan pada industri proses

Shell-side flow

Baffle

Fin Tube

Complete shell-and-tube

Plate and framePlates hung vertically and clamped in a press or frame.Gaskets direct the streams between alternate plates and prevent external leakagePlates made of stainless steel or higher quality materialPlates corrugated to give points of support and increase heat transfer

Plate typesChevronWashboardCorrugations on plateimprove heart transfergive rigidity

Many points ofcontact and atortuous flow path

General view of plate exchangerPlate exchanger normally refers to a gasketted plate- and-frame exchanger

Flow Arrangement within a PHEAlternate plates (often same plate types inverted)Gasketsarranged foreach stream toflow betweenalternate plates

Air-cooled exchangerAir blown across finned tubes (forced draught type)Can suck air across (induced draught)Finned tubes

ACHE bundle

Plate-fin exchangerMade up of flat plates (parting sheets) and corrugated sheets which form finsBrazed by heating in vacuum furnace

Can have many streams7 or more streams are typical

Typical plate-fin

Spiral (plate)Good for streams with large solids

Cooling TowersLarge shell with packing at the bottom over which water is sprayedCooling by air flow and evaporationAir flow driven by forced or natural convectionNeed to continuously make up the cooling water lost by evaporation

Agitated VesselUsed for batch heating or cooling of fluidsAn agitator and baffles promote mixingA range of agitators are usedOften used for batch chemical reaction

Printed circuit heat exchangerPlates are etched to give flow channelsStacked to form exchanger blockBlock diffusion welded under high pressure and temperatureBond formed is as strong as the metal itself

Printed circuit exchangerNote that compact does notmean small but means largesurface area per unit volume

Distribution of typesin terms of market value in Europe

Preliminary points on selectionTubes and cylinders can withstand higher pressures than platesIf exchangers can be built with a variety of materials, then it is more likely that you can find a metal which will cope with extreme temperatures or corrosive fluidsMore specialist exchangers have fewer suppliers, longer delivery times and must be repaired by expertsS&Ts cannot normally give high thermal effectiveness, e

Design sequenceDesign the process flow flow-sheetSpecify the heat exchanger requirementsSelect the best exchanger type for the jobThermal design of exchangerMechanical design of exchangerLooping back may be necessary at any stage but can be difficult because of the project timetable

Who does what?Design the process flow flow-sheetSpecify the heat exchanger requirementsSelect the best exchanger type for the jobThermal design of exchangerMechanical design of exchangerProcessor/end userContractorManufacturer

The design of a process heat exchanger usually proceeds through the following steps:

Process conditions (stream compositions, flow rates, temperatures, pressures) must be specified.Required physical properties over the temperature and pressure ranges of interest must be obtained.The type of heat exchanger to be employed is chosen.A preliminary estimate of the size of the exchanger is made, using a heat-transfer coefficient appropriate to the fluids, the process,and the equipment.A first design is chosen, complete in all details necessary to carry out the design calculations.The design chosen in step 5 is evaluated, or rated, as to its ability to meet the process specifications with respect to both heat transfer and pressure drop.

On the basis of the result of step 6, a new configuration is chosen if necessary and step 6 is repeated. If the first design was inadequate to meet the required heat load, it is usually necessary to increase the size of the exchanger while still remaining within specified or feasible limits of pressure drop, tube length, shell diameter, etc. This will sometimes mean going to multiple-exchanger configurations. If the first design more than meets heat-load requirements or does not use all the allowable pressure drop, a less expensive exchanger can usually be designed to fulfill process requirements.

8. The final design should meet process requirements (within reasonable expectations of error) at lowest cost. The lowest cost should include operation and maintenance costs and credit for ability to meet long-term process changes, as well as installed (capital) cost. Exchangers should not be selected entirely on a lowest-first-cost basis, which frequently results in future penalties.

Exchanger specificationHeat load (duty) along with the terminal temperatures of the streamsMaximum pressure drop each streamsliquids - 0.5 bargases/vapours below 2bar - 10% of inlet pressureDesign pressures and temperaturesSize/weight constraintsStandards to applyGeneral standards like ISO, TEMA, ASME, API etcCompanies own standardsOther requirements

The designer must supply an exchanger whichMeets the stated specificationHas reasonable initial costs and operating costs (most exchangers are bought on the basis of the cheapest tender)Has a reasonable lifetimeno damaging vibrationno thermal fatigueno unexpected fouling or corrosion

1. Corrosion fouling. The heat transfer surface reacts chemically with elements of the fluid stream producing a less conductive,corrosion layer on all or part of the surface.2. Biofouling. Organisms present in the fluid stream are attracted to the warm heat-transfer surface where they attach, grow, and reproduce. The two subgroups are microbiofoulants such as slime and algae and macrobiofoulants such as snails and barnacles.3. Particulate fouling. Particles held in suspension in the flow stream will deposit out on the heat-transfer surface in areas of sufficiently lower velocity.4. Chemical reaction fouling (ex.Coking). Chemical reaction of the fluid takes place on the heat-transfer surface producing an adhering solid product of reaction.5. Precipitation fouling (ex.Scaling). A fluid containing some dissolved material becomes supersaturated with respect to this material at the temperatures seen at the heat-transfer surface. This results in a crystallization of the material which plates out on the warmer surface.6. Freezing fouling. Overcooling of a fluid below the fluids freezing point at the heat-transfer surface causes solidification and coating of the heat-transfer surface.Fouling may be classified by mechanism into six basic categories:

Pemilihan Heat ExchangerChoosing the best exchanger for a given process application

Langkah-langkahCoarse filterBuang Jenis Alat Penukar Kalor yang tidak memenuhi ketentuan tekanan dan temperatur operasi, fluid-material compatibilitas, kondisi termal yang extremFine filterEstimasi Harga

Coarse filterUse information on next few slides to reject those exchangers which are clearly out of range or are otherwise unsuitableThe information is summarised in the tableAt this stage, if in doubt, include the exchanger (poor choices are likely to turn out expensive at the fine filter stage)

Point-point utamaTube /pipa dan cylinders dapat menahan tekanan yang lebih besar dibanding dengan platesJika APK dapat dibangun dengan material yang bervariasi, berarti anda dapat menentukan metal yang dapat tahan terhadap temperatur yang extrem dan fluida-fluida yang korosifAPK yang khusus hanya memiliki supplier yang sangat sedikit, waktu pengiriman barang yang lebih lama dan harus diperbaiki oleh orang yang sangat ahli.

Thermal effectivenessStream temperature rise divided by the theoretically maximum possible temperature rise T1,inT1,outT2,outT2,in

Double PipeTipe APK ini adalah yang paling simpel, memiliki satu tube di dalam dan satu tube pada bagian luar, Tube paling dalam bisa memiliki sirip secara longitudinal pada bagian luarnya

Walaupun demikian terdapat pula jenis APK ini yang memeiliki beberpa tube didalam tube luarnya.

Double pipeUkuran Normal 0.25 to 200m2 (2.5 to 2000 ft2) per unitNote multiple units are often usedBuilt of carbon steel where possible

Advantages/disadvantages of double-pipeAdvantagesEasy to obtain counter-current flowCan handle high pressureModular constructionEasy to maintain and repairMany suppliersDisadvantageBecome expensive for large duties (above 1MW)

Maximum pressure 300 bar(abs) (4500 psia) on shell side1400 bar(abs) (21000 psia) on tubesideTemperature range-100 to 600oC (-150 to 1100oF)possibly wider with special materials Fluid limitationsFew since can be built of many metalsMaximum e = 0.9Minimum DT = 5 KScope of double pipe

Shell and tubeSize per unit 100 - 10000 ft2 (10 - 1000 m2)Easy to build multiple unitsMade of carbon steel where possible

Advantages/disadvantages of S&TAdvantagesExtremely flexible and robust designEasy to maintain and repairCan be designed to be dismantled for cleaningVery many suppliers world-wideDisadvantagesRequire large plot (footprint) area - often need extra space to remove the bundlePlate may be cheaper for pressure below 16 bar (240 psia) and temps. below 200oC (400oF)

Scope of shell and tubeEssentially the same as a double pipeMaximum pressure 300 bar(abs) (4500 psia) on shell side1400 bar(abs) (21000 psia) on tubesideTemperature range-100 to 600oC (-150 to 1100oF)possibly wider with special materials Fluid limitationsFew since can be built of many metalsMaximum e = 0.9 (less with multipass)Minimum DT = 5 K

Plate and framePlates pressed from stainless steel or higher grade materialtitaniumincoloyhastalloyGaskets are the weak point. Made ofnitrile rubberhypalonvitonneoprene

Advantages of plate and frameHigh heat transfer - turbulence on both sidesHigh thermal effectiveness - 0.9 - 0.95 possibleLow T - down to 1KCompact - compared with a S&TCost - low because plates are thin Accessibility - can easily be opened up for inspection and cleaningFlexibility - Extra plates can be addedShort retention time with low liquid inventory hence good for heat sensitive or expensive liquidsLess fouling - low r values often possible

Disadvantages of plate & framePressure - maximum value limited by the sealing of the gaskets and the construction of the frame.Temperature - limited by the gasket material.Capacity - limited by the size of the ports Block easily when solids in suspension unless special wide gap plates are usedCorrosion - Plates good but the gaskets may not be suitable for organic solventsLeakage - Gaskets always increase the riskFire resistance - Cannot withstand prolonged fire (usually not considered for refinery duties)

Scope of plate-frameMaximum pressure25 bar (abs) normal (375 psia)40 bar (abs) with special designs (600 psia)Temperature range-25 to +1750C normal (-13 to +3500F)-40 t0 +2000C special (-40 to +3900F)Fluid limitationsMainly limited by gasketMaximum e = 0.95Minimum DT = 1 K

Welded platesWide variety of proprietary types each with one or two manufacturesOvercomes the gasket problem but then cannot be opened upPairs of plates can be welded and stacked in conventional frameConventional plate and frame types with all-welded (using lasers) construction have been developed Many other proprietary types have been developedTend to be used in niche markets as replacement to shell-and-tube

Air-cooled exchangers

Advantages of ACHEsAir is always availableMaintenance costs normally less than for water cooled systemsIn the event of power failure they can still transfer some heat due to natural convectionThe mechanical design is normally simpler due to the pressure on the air side always being closer to atmospheric.The fouling of the air side of can normally be ignored

Disadvantages of ACHEsNoise - low noise fans are reducing this problem but at the cost of fan efficiency and hence higher energy costsMay need special features for cold weather protectionCannot cool to the same low temperature as cooling tower

Scope of Air Cooled ExchangersMaximum pressure- tube(process) side:500 bar (7500psia)Maximum temperature: 600oC (1100o F)Fluids: subject to tube materials Size per unit: 5 - 350m2 (50 - 3500ft2 ) per bundle (based on bare tube)

Plate Fin ExchangersFormed by vacuum brazing aluminium plates separated by sheets of finningNoted for small size and weight. Typically, 500 m2/m3 of volume but can be 1800 m2/m3Main use in cryogenic applications (air liquifaction)Also in stainless steel

Scope of plate-fin exchangerMax. Pressure90 bar (size dependent)Temperatures-200 to 150oC in AlUp to 600 with stainlessFluidsLimited by material DutiesSingle and two phaseFlow configurationCross flow, Counter flowMultistreamUp to 12 streams (7 normal)Low DTDown to 0.1oCMaximum DT50oC typicalHigh eUp to 0.98Important to use only with clean fluids

Printed Circuit ExchangerVery compactVery strong construction from diffusion weldingSmall channels (typically 1 - 2 mm mean hydraulic diameter)Can be made in stainless steel, nickel (and alloys), copper (and alloys) and titanium

Scope of PCHEMaximum Pressure1000bar (difference 200bar)Temperature -200 to +800oC for stainless steel but depends on metalFluidsWide rangebut must be low foulingNormal Size1 to 1000m2Flow configurationCrossflow or counterflowEffectiveness up to 0.98Low TYesThermal cyclingHas caused problems

ExampleWhich exchanger types can be used for condensing organic vapour at -60oC and 60 bar by boiling organic at -100oC and 70 bar?Would you modify your choice if the boiling stream were subject to fouling requiring mechanical cleaning?

Heat exchanger costing - fine filterFull cost made up ofCapital costInstallation costOperating costThe cost estimation method given here is based only on capital cost - which is the way it is often doneNote: installation costs can be as high as capital cost except for compact exchangersInstallation cost considerations can predominate on offshore plant

ScopingThe cost estimate method given here is for the preliminary plant design stage - scopingNote that we are trying to estimate the cost of an exchanger before we have designed itFull design and cost would be done later

Quick sizing of heat exchangersWe estimate the area fromTaTbWhere

FT correction factorThis correction accounts for the two streams not following pure counter-current flowAt the estimation stage, we do not know the detailed flow/pass arrangement so we useFT = 1.0 for counter flow which includes most compact and double-pipeFT = 0.7 for pure cross flow which includes air-cooled and other types when operated in pure cross flow (e.g. shell-and-tube)FT = 0.9 for multi-passFT = 1.0 if one stream is isothermal (typically boiling and condensation)

Estimating UThis may be estimated for a given exchanger type using the tables from ESDU (given below)These tables give U values as a function of Q/T (the significance of this group will become clear later)Example: high pressure gas cooled by treated cooling water in a shell-and-tube, whereQ/T = 30 000 W/Kgives U = 600 W/m2KThis includes typical fouling resistances

Estimating costThis has often been done by multiplying the calculated area, A, by a cost per unit areaBut, when comparing exchangers, U and A vary widely from type to type. It is also difficult to define A if there is a complicated extended surface. Hence, ESDU give tables of C values where C is the cost per UA - using 1992 pricesNote, from our basic heat transfer equationUA = Q / DT

ESDUESDU gives tables for a range of heat exchanger types but we can only include here those for shell-and-tube and plate-and-frame Full data Item 92013 is available fromESDU International plc27 Corsham StreetLondon N1 6UATel 0171 490 5151 Fax 0171 490 2701esdu@esdu.com

Steps in calculationCalculate Tln and hence estimate TDetermine Q/TLook up C value from tableTo determine C at intermediate Q/T, use logarithmic interpolation - see next slideCalculate exchanger cost from - Cost = C(Q/T)Taking the last shell-and-tube example, C = 0.4. Hence, Cost = 0.4 X 30 000 = 12 000Make sure that you take account of footnotes in tables

Logarithmic interpolationln(C1) ln(C2)ln(C)ln(V1)ln(V)ln(V2)Where the Vs are the values of Q/T. V1 and V2 are the values either side of the required value V

Desain Termal Alat Penukar Kalor

Harga Lokal dan harga rata-rataOverall artinya dari the hot side ke the cold side termasuk semua termal resistanTitik khusus pada alat penukar kalor adalah localJadi kita memiliki lokal, overall coefficientLOKAL

KESELURUHAN ALAT PENUKA KALOR

Q = U A DTkThotTcoldyw

Integral terhadap area alat penukar kalorPersamaan Lokal

Rearranging

IntegraldQdATotal area AT

Definisi dari harga rata-rata (mean values )Dari slide sebelumnya

Bandingkan dua sides

Kasus Khusus dimana Ts linear terhadap QEqn. integrates to give log. mean temperature difference - LMTDTa

Pararel Flow

Counter Flow

Cross Flow

Multipass exchangersUntuk single-phase duties, Faktor correction teoritis, FT, sudah diturunkan (lihar referensi)Harga FT Kurang dari 1Jangan Merancang untuk FT kurang dari 0.8QTemp.T1T2t1t2

Typical FT correction factor curvesFor shell and tube with 2 or more tube-side passes T, t = Shell / tube side 1, 2 = inlet / outletCurves are for different values of R

Thermal effectivenessStream temperature rise divided by the theoretically maximum possible temperature rise T1,inT1,outT2,outT2,in

ALAT PENUKAR KALOR Shell-and-Tube Memilih tipe TEMA yang tepat dan menentukan fluida kerja yang mengalir di dalam tube

Daftar isiMengapa shell-and-tube?Scope dari shell-and-tubeKonstruksiTEMA standardsMemilih tipe TEMA Alokasi Fluid Design problemsEnhancementImproved designs

Why shell-and-tube?Can be designed for almost any duty with a very wide range of temperatures and pressuresCan be built in many materialsMany suppliersRepair can be by non-specialistsDesign methods and mechanical codes have been established from many years of experience

Scope of shell-and-tubeMaximum pressure Shell 300 bar (4500 psia) Tube 1400 bar (20000 psia)Temperature range Maximum 600oC (1100oF) or even 650oC Minimum -100oC (-150oF)Fluids Subject to materials Available in a wide range of materialsSize per unit 100 - 10000 ft2 (10 - 1000 m2)Can be extended with special designs/materials

ConstructionBundle of tubes in large cylindrical shellBaffles used both to support the tubes and to direct into multiple cross flowGaps or clearances must be left between the baffle and the shell and between the tubes and the baffle to enable assemblyShellTubesBaffle

Shell-side flow

Tube layoutsTypically, 1 in tubes on a 1.25 in pitch or 0.75 in tubes on a 1 in pitchTriangular layouts give more tubes in a given shellSquare layouts give cleaning lanes with close pitchpitchTriangular30oRotatedtriangular60oSquare90oRotatedsquare45o

TEMA standardsThe design and construction is usually based on TEMA 8th Edition 1998Supplements pressure vessel codes like ASME and BS 5500Sets out constructional details, recommended tube sizes, allowable clearances, terminology etc.Provides basis for contractsTends to be followed rigidly even when not strictly necessaryMany users have their own additions to the standard which suppliers must follow

TEMA terminologyLetters given for the front end, shell and rear end typesExchanger given three letter designationAbove is AELShellFront endstationary head typeRear endhead type

Front head typeA-type is standard for dirty tube sideB-type for clean tube side duties. Use if possible since cheap and simple.

BChannel and removable coverBonnet (integral cover)A

More front-end head typesC-type with removable shell for hazardous tube-side fluids, heavy bundles or services that need frequent shell-side cleaningN-type for fixed for hazardous fluids on shell sideD-type or welded to tube sheet bonnet for high pressure (over 150 bar)BND

Shell typeE-type shell should be used if possible butF shell gives pure counter-current flow with two tube passes (avoids very long exchangers)EFOne-pass shellTwo-pass shellLongitudinal baffleNote, longitudinal baffles are difficult to seal withthe shell especially when reinserting the shell aftermaintenance

More shell typesG and H shells normally only used for horizontal thermosyphon reboilersJ and X shells if allowable pressure drop can not be achieved in an E shellJHGXSplit flowDouble split flowDivided flowCross flowLongitudinalbaffles

Rear head typeThese fall into three general typesfixed tube sheet (L, M, N)U-tubefloating head (P, S, T, W)Use fixed tube sheet if T below 50oC, otherwise use other types to allow for differential thermal expansionYou can use bellows in shell to allow for expansion but these are special items which have pressure limitations (max. 35 bar)

Fixed rear head typesL is a mirror of the A front end headM is a mirror of the bonnet (B) front endN is the mirror of the N front end LFixed tube sheet

Floating heads and U tubeAllow bundle removal and mechanical cleaning on the shell sideU tube is simple design but it is difficult to clean the tube side round the bend

Floating headsTSPull through floating headNote large shell/bundle gapSimilar to T but with smaller shell/bundle gap Split backing ring

Other floating headsNot used often and then with small exchangersPWOutside packing to give smaller shell/bundle gapExternally sealed floating tube sheetmaximum of 2 tube passes

Shell-to-bundle clearance (on diameter)0.51.01.52.02.50Shell diameter, mClearance, mm015010050Fixed and U-tubeP and ST

ExampleBESBonnet front end, single shell pass and split backing ring floating head

Apakah ini ?

Allocation of fluidsPut dirty stream on the tube side - easier to clean inside the tubesPut high pressure stream in the tubes to avoid thick, expensive shellWhen special materials required for one stream, put that one in the tubes to avoid expensive shellCross flow gives higher coefficients than in plane tubes, hence put fluid with lowest coefficient on the shell sideIf no obvious benefit, try streams both ways and see which gives best design

Example 1Debutaniser overhead condenser

Hot sideCold side

FluidLight hydrocarbonCooling waterCorrosiveNoNoPressure(bar)4.95.0Temp. In/Out (oC)46 / 4220 / 30Vap. fract. In/Out1 / 00 / 0Fouling res. (m2K/W)0.000090.00018

Example 2Crude tank outlet heater

Cold sideHot side

FluidCrude oilSteamCorrosiveNoNoPressure(bar)2.010Temp. In/Out (oC)10 / 75180 / 180Vap. fract. In/Out0 / 01 / 0Fouling res. (m2K/W)0.00050.0001

Rule of thumb on costingPrice increases strongly with shell diameter/number of tubes because of shell thickness and tube/tube-sheet fixing Price increases little with tube lengthHence, long thin exchangers are usually bestConsider two exchangers with the same area: fixed tubesheet, 30 bar both side, carbon steel, area 6060 ft2 (564 m2), 3/4 in (19 mm) tubesLengthDiameterTubesCost10ft60 in3139$112k (70k)60ft25 in523$54k (34k)

Shell thicknessp is the guage pressure in the shellt is the shell wall thickness is the stress in the shellFrom a force balancepDstpthence

Typical maximum exchanger sizes Floating HeadFixed head & U tube

Diameter60 in (1524 mm)80 in (2000 mm)Length30 ft (9 m) 40 ft (12 m)Area13 650 ft2 (1270 m2)46 400 ft2 (4310 m2)

Note that, to remove bundle, you need to allow at least as much length as the length of the bundle

FoulingShell and tubes can handle fouling but it can be reduced bykeeping velocities sufficiently high to avoid depositsavoiding stagnant regions where dirt will collectavoiding hot spots where coking or scaling might occuravoiding cold spots where liquids might freeze or where corrosive products may condense for gases

High fouling resistances are a self-fulfilling prophecy

Flow-induced vibrationTwo types - RESONANCE and INSTABILITY Resonance occurs when the natural frequency coincides with a resonant frequencyFluid elastic instabilityBoth depend on span length and velocity-VelocityVelocityResonanceInstabilityTube displacement

Avoiding vibrationInlet support baffles - partial baffles in first few tube rows under the nozzlesDouble segmental baffles - approximately halve cross flow velocity but also reduce heat transfer coefficientsPatent tube-support devicesNo tubes in the window (with intermediate support baffles)J-Shell - velocity is halved for same baffle spacing as an E shell but decreased heat transfer coefficients

Avoiding vibration (cont.) Inlet support bafflesDouble-segmental bafflesNo tubes in the window - with intermediate support bafflesTubesWindows with no tubesIntermediate baffles

Shell-side enhancementUsually done with integral, low-fin tubes11 to 40 fpi (fins per inch). High end for condensationfin heights 0.8 to 1.5 mmDesigned with o.d. (over the fin) to fit into the a standard shell-and-tubeThe enhancement for single phase arises from the extra surface area (50 to 250% extra area)Special surfaces have been developed for boiling and condensation

Low-finned TubesFlat end to go into tube sheet and intermediate flat portions for baffle locations

Available in variety of metals including stainless steel, titanium and inconels

Tube-side enhancement using insertsSpiral wound wire and twisted tapeIncrease tube side heat transfer coefficient but at the cost of larger pressure drop (although exchanger can be reconfigured to allow for higher pressure drop)In some circumstances, they can significantly reduce fouling. In others they may make things worseCan be retrofittedTwisted tape

Wire-wound inserts (HiTRAN)Both mixes the core (radial mixing) and breaks up the boundary layerAvailable in range of wire densities for different duties

Problems of Conventional S & TZigzag path on shell side leads toPoor use of shell-side pressure dropPossible vibration from cross flowDead spotsPoor heat transferAllows foulingRecirculation zonesPoor thermal effectiveness,

Conventional Shell-side Flow

Shell-side axial flowSome problems can be overcome by having axial flowGood heat transfer per unit pressure drop but for a given duty may get very long thin unitsproblems in supporting the tubeRODbaffles (Phillips petroleum)introduced to avoid vibrations by providing additional support for the tubesalso found other advantageslow pressure droplow fouling and easy to cleanhigh thermal effectiveness

RODbafflesTend to be about 10% more expensive for the same shell diameter

Twisted tube (Brown Fintube)Tubes support each otherUsed for single phase and condensing duties in the power, chemical and pulp and paper industries

Shell-side helical flow (ABB Lummus)Independently developed by two groups in Norway and Czech Republic

Comparison of shell side geometries

Twisted

tube

Segmental baffles

Helical

baffles

ROD

baffles

Good a/Dp

Y

N

Y

Y

High a shell

N

Y

Y

N

Low fouling

Y

N

Y

Y

Easy cleaning

Y

With square pitch

With square pitch

Y

Tube-side enhance.

Included

With inserts

With inserts

With inserts

Can give high e

Y

N

N

Y

Low vibration

Y

With special designs

With double helix

Y

Designing Shell-and-Tube ExchangersWill this exchanger do the duty? Developing a design envelope. Choosing the best design.

ContentsOverview of designSingle phase rating methods used in DEVIZETube sideShell sideDesign envelope concept in DEVIZEDemonstration of DEVIZE

Overall design processDecide fluid allocation (last lecture)Decide TEMA type (last lecture)Make some guesses about the designGenerate design envelope using DEVIZEDo a rating using DEVIZEReview the envelope and the rating in order to improve your initial guessFinally select the best designRepeat until satisfiedwith design

Starting point of ratingWe knowThe duty which we need to achieve (i.e. flow rates and temperature changes of the two streams)The full exchanger geometryThe allowable pressure drops for the two streamsWe are checking whether that exchanger can do that duty within the imposed constraints

The thermal ratingThe actual heat transfer area (based on the tube o.d.), Ao is knownWe calculate the required area, Areq from One output of the thermal rating is the ratio

Overall coefficientWe have thermal resistances in seriesThotTcoldywDiDoywWhere

Thermal conductivityTypical values of thermal conductivity

Material

W/m k

Stainless Steel

15

Copper

390

Aluminium

208

Carbon Steel

50

Gases

0.02 - 0.3

Liquids

0.03 - 0.7

Polystyrene foam

0.003

Pipe Lagging

0.092

Typical values of stream coefficientsFluidStatehtc W/m2.kWaterSingle Phase5000 - 7500WaterBoiling

Typical fouling resistanceFluidStater (m2.k/W)WaterSingle Phase0.0001 - 0.00025WaterBoiling

Single phase exchangersWe will now concentrate on a single phase in both streamsThis is a limitation of DEVIZEBut the principles of the design process are similar for boiling and condensing streamsIn single phasecoefficients do not vary much and can be treated as constantand DTm = FT DTLM

Tube side heat transfer coefficientIn the transition region, Nu is calculated from a linear interpolation with Re of the values at Re = 2000 and 8000Note: wall-to-bulk property variations and natural convection effects are neglected

Tube side pressure dropGeneral equation

Laminar flow (transition taken as crossover with turbulent equation)

Turbulent flow in a commercial rough tube

Nozzle, tube entry and return lossesK is taken as 1.8 per tube-side pass to allow for tube entry, tube exit and header losses 10% of the total pressure drop is assumed to occur in the nozzles

Shell side - the Bell MethodDEVIZE uses the Bell-Delaware method as set out by Taborek in HEDHThis method starts with the coefficients and pressure drops for ideal cross flow and then corrects these for the non-idealities which occur in real shell-side flowsThe method gives reasonable accuracy while remaining simpleMore accurate proprietary methods have been developed based on network models

Shell-side non-idealtiesWindoweffectsBypassTube-to-baffleleakageShell-to-baffle leakage

Bell method for heat transferWhereJw corrects for some tubes being in the windowJL corrects for leakage through and around the baffleJB corrects for flow around the bundleJLam corrects for special effects which occur at very low Reynolds numbers (not applied in DEVIZE)

What do the factors depend upon?Jw - ratio of tubes in cross flow to tubes in windowsJL - ratio of leakage areas to cross-flow areaJB - ratio of bypass flow area to cross flow area and the number of pairs of sealing stripsSealing strips to reduce bypass

Example correction factor - bypass

Ideal crossflow coefficientThe j-factor is given as a function of Reynolds number, defined by

Re = umin di /

Where umin is the velocity calculated at the minimum flow area near the equator of the bundle (assuming no leakage and bypass)

Shell-side pressure drop and vibrationPressure dropThe Bell method for pressure drop is similar to that for heat transfer but with some extra complications in the end zonesAn additional 10% is assumed for the nozzles

VibrationDEVIZE uses the methods in ESDU Data Item 87019 for fluid-elastic instability

Outputs of ratingArea ratio (already discussed): RA = Ao / AreqPressure drop ratios for the shell side and the tube side: Rp= Dpcalc/ DpspecVelocity ratio for vibration ratio: Rv = u / ucritFor an acceptable design,RA > 1, RpT < 1, RpS < 1, Rv < 1The closer these ratios are to 1, the tighter the design (i.e. the lower the safety margins)

Thermal resistance diagramGood way of viewing where the main resistances lie and therefore where it is best to make changes to improve the designShell SideTube SideStreamFoulingWall

Envelope design conceptDescription of the envelope design concept and the demonstration of DEVIZEStarting point is to make guesses about key geometrical featuresnumber of passesbaffle pitch (say as factor on the shell diameter)baffle cut (say to equalise the cross-flow and window-flow areas)

Tube side pressure dropShell diameterTube lengthFor given shell diameterDEVIZE can calc.The tube length whichjust uses up the Dp

Tube-side pressure drop limitTube lengthShell diameterDesigns valid in this regionNot valid in this regionRepeating for range of shell diameters gives curve

Shell-side pressure drop limitTube lengthShell diameterWe can do similar thing for the shell sideTube-side Dp limitShell-side Dp limit

Heat transfer limitTube lengthShell diameterAnd then for the heat transferPressure drop limitsHeat transfer area limit

Add limits on tube-side velocity

Danger areas for vibration may also be shownTube lengthShell diameterMin.Max.Vibration

Highlight valid design regionTube lengthShell diameterMin.Max.Design envelope

Rating at optimum pointTube lengthShell diameterMin.Max.Smallest diameter and shortest tubesso likely to be the cheapest

Preferred shell diameters and tube lengthsTube lengthShell diameterMin.Max.AB

Design processStart with a set of assumptions about number of passes, baffle configuration, etc.Generate envelopeChange initial assumptions to obtain better envelopesThen Rate good geometries within the best envelopesConsider advantages of ratings outside the envelope assuming constraint may be relaxedSelect the best Rating

Hambatan Termal pada Radiator

This first lecture is mainly qualitative as a lead in to the later lectures.

It is very helpful to obtain samples from exchanger manufacturers to show the students. Possibilities areA small, chevron-type plate for a plate and frame exchangerVarious fin types for a plate-fin exchangerEtched plates and a sample block for a plate of a printed-circuit exchangerHigh-finned tube of the type used in air-cooled heat exchangersSamples of fins used in plate-fin exchangers

CopyrightHyprotech UK Ltd holds the copyright to these lectures. Lecturers have permission to use the slides and other documents in their lectures and in handouts to students provided that they give full acknowledgement to Hyprotech. The information must not be incorporated into any publication without the written permission of Hyprotech.

Worth emphasising on this case that the feed-effluent exchanger needs a temperature difference to drive it, so there is a limit to what can be removed by the heat recovery exchanger exchanger. Typically. Feed-effluent exchangers involve a number of exchangers in series so that the picture is a simple case.This illustrates that real flow-sheets are much more complicated than the idealised cases shown previously. The many exchangers are to heat up streams to the required temperature for distillation. The main heat input is from the furnace or fired heater shown. Also, as much heat as possible is recovered when the refined streams are cooled down. As if this were not complicated enough, many of the exchangers shown would actually be groups of exchangers.There, in practice, many more heat exchangers in a real plant.Exchanger from Motherwell Bridge Thermal, Scotland

Picture just to introduce a real exchanger early on.The refinery example shown previously, the hot utility is the furnace.The case of recuperators with the wall separating the streams is highlighted. It is the most important and the main subject of these lectures.As has been noted, the human lung acts as a regenerator because the cold stream (the incoming air) passes through the same passages as the hot stream (the outgoing stale air).

The regenerator shown above is a heat wheel.Photograph from APVForced draught most common because it is easier then to service the fan motor and also the fan motor runs coolerPicture from Motherwell Bridge ThermalFigure shows a number of interesting pointsThe way headers are arrangedThe way gaps are left at appropriate places to allow flow between the layer and the headerThe use of low frequency finning to distribute the flow across the channelPhotograph from Chart Heat Exchangers LtdPhotograph from Heatric LtdPhotograph from Heatric LtdThis is for a wide range of industrial heat exchangers. If we look at chemical and refinery applications, the shell and tube type predominates (see lecture 3).CopyrightHyprotech UK Ltd holds the copyright to these lectures. Lecturers have permission to use the slides and other documents in their lectures and in handouts to students provided that they give full acknowledgement to Hyprotech. The information must not be incorporated into any publication without the written permission of Hyprotech.

The table in the accompanying Lecturer Pack should be copied for students use in the examples.The last point means that specialist exchangers are not favoured in less developed parts of the worldThe effectiveness can be calculated for each stream. The higher of the two is the one that is important. Typically, exchangers are designed with an effectiveness of 60 - 80 per cent. All exchanger types can handle this. However, more specialist exchangers are required for an effectiveness above about 90 per cent, as will be seen.It should be noted that the ranges and limits quoted above are a guide as to what is normal today. This limits are being extended. Also, with care in design and with specialist manufacture, it is possible to extend the limits, although this may be at additional cost.Inset figure is of an induced draught ACHE whereas a forced draught type was shown in the last lecture. Induced draught tends to give better air-flow distribution. However, the fan is working in hotter air and is less efficient. Furthermore, access and maintenance are more difficult with induced draught.The evaporative cooling in a cooling tower produces cooler waterAs a rough guide, a plate fin would be a fifth the size of a shell and tube for the same duty. Of course, a shell and tube exchanger is often not suitable for many plate-fin applications involving many streams and small temperature differences.The standards of ALPEMA (Brazed Aluminium Plate-fin Exchanger Manufacturers Association) may be downloaded free of charge from the ALPEMA web site - www.alpema.orgThe exchangers which can handle the pressure and temperature are

Double pipeShell-and-tube (with special material)Plate-finSome welded plate designs could be investigated

Fouling would rule out plate-fin and some welded plate designs.Using an FT of 0.9 for multipass exchangers assumes that the designer is going to avoid having a value less than 0.8. It cannot be higher than 1.0 so 0.9 seems a reasonable average within the accuracy of these estimates.The tables are included in the Lecturer Pack with the required table entry circled.

It is worth also noting the the C value of 0.4 at this stage - the significance will become clear later.The costs were obtained from manufacturers who looked a the typical costs of exchangers built for the different applicationsIn the example given previously, the Q / DT value happens to be in the table. Usually, however, you must interpolate between entries in the table. This is done effectively by plotting on log-log paper and doing a linear interpolation. The slide gives the formula for this.It is worth mentioning that the log mean becomes the arithmetic mean when the two end temperature differences become the same.

Students could try the derivation. The starting point is a simple change of variables. Given that DT varies as a straight line with Q, the equation from the last slide may be rewritten as

It should be stressed that modern design software does not use these correction factors because their derivation involves too many assumptions that are not realised in practice. In stead, modern software carries out numerical intigrateions to obtain the results.There are two values of e depending on which stream is taken as stream 1. We are concerned with the higher of the two in this lecture series.TEMA is the Tubular Exchanger Manufacturers Association. Their Standards are almost universally accepted.

CopyrightHyprotech UK Ltd holds the copyright to these lectures. Lecturers have permission to use the slides and other documents in their lectures and in handouts to students provided that they give full acknowledgement to Hyprotech. The information must not be incorporated into any publication without the written permission of Hyprotech.

Fluid allocation means which stream goes on the shell side and which in the tubes85 per cent is a higher figure than in the pie chart in lecture 1. The difference is that the above figure is for the limited range of industries shown while the pie chart is for all industrial applications.Message, use 30 or 600 layouts unless you need to clean the shell side mechanically.Standards are a good thing because they give the designers confidence (they have covered themselves if they have used the standards and then something goes wrong).

They are bad because they can stifle innovation.

The TEMA standards contain recommendations along with the mandatory statements. Some engineers interpret using TEMA Standards as meaning following the recommendations as well even though they might not be appropriate to that particular design.

Users of exchangers supplement the TEMA standards with extra rules based on their own experience. This is now thought to be overdone since it may lead to over-expensive designs. The user is, therefore, tending now to give the supplier more freedom but also to emphasise that it is his responsibility.Message: use B unless you want to clean inside the tubes frequently.Some users ban the use of F shells because of the problem of sealing the longitudinal baffle against the shell. Some manufacturers have their own systems which can maintain a god seal.When G and H shells are used in reboilers (with boiling on the shell side) the longitudinal baffle may be perforated. Its purpose is to help distribute the boiling stream along the length of the exchanger. The seal problem which was noted for F shells is therefore not important.

J shells will have normal segmental baffles as in E shells.

X shells may often have a few inlet and outlet nozzles to help distribute the flow over the length.U-tubes are a simple way of achieving a floating head.

While it is difficult to clean round the bends, some companies offer cleaning devices which can cope with tight bends.Note that the T type requires a large shell and therefore a large shell-to-bundle clearance in order to slide the bundle in and out of the shell. The S type introduces the split backing ring which enables the return header to be dismantled and the bundle withdrawn through a smaller diameter shell.

The S type is very common in refinery applications because it enables access to the shell side for maintenance and cleaning without giving a large shell-to-bundle clearance. The students should be able to identify this as a BJM (we are guessing at the M because we cannot see the back end).Ask the students first which stream to put on the shell side and why

Answer: light hydrocarbon because of low fouling and slightly lower pressure. Also condensation works well on the shell side.

Ask what front end type

Answer: A in order to clean easily in the tubes.

Ask what rear head

Answer: fixed head since DT small. M could be used or L if access to back end required.This one is not so straight forward.

One option is to put the crude oil in the tubes and use an AES. This puts the fouling oil in the tubes and makes cleaning easy.

The use of an S rear head is to allow for differential thermal expansion arising from the large DT. However, one can also argue that the shell-side coefficient is so high compared to the tube side, that the tubes is close to the steam condensing temperature (as, of course, is the shell). Hence, a fix head could be used. Provided that access to the shell were never required.

However, because of the high steam pressure you may decide to put this in the tubes. Then you would go for a BEU, and have the tubes on a 90 or 450 layout. This makes it easy to remove the the bundle and clean outside the tubes. Putting the crude outside the tubes would also be likely to give a higher overall coefficient.

It would be worth designing both fully to see which option was the cheapest.This is just illustrative since, normally, the overall coefficient will change as the shell diameter is changed, hence the area required to achieve the heat duty will also change. However, this does not negate the point made in the slide.Hence the shell thickness increases as the diameter increases thus compounding the higher cost of larger shells.

Referring back to the crude oil tank heater example, putting the oil on the shell side will increase the shell thickness because of the higher pressure. However, the shell diameter may decrease with the higher overall coefficient. Against that, the square pitch gives a lower packing density thus tending to increase the shell diameter. Only detailed design and costing will resolve this.If you specify a very high fouling resistance, the clean exchanger will over perform when fist installed. The operators will then throttle back on the flow of the service stream thus helping to promote fouling. Then the designer can say, I told you it has a high fouling.A resonance would occur if the tube natural frequency corresponded with the vortex-shedding frequency.

Usually, instabilities are worse because and can lead to failures in a short time. Pictures illustrating some of these arrangements are show on the next slide.This picture shows colour dyes clinging to the wall without mixing with the main stream until they hit the wire matrix and become mixed.These are illustrated on the next slideRODbaffles are really grids to support the tubes. Picture on next slide.The grids are offset so that it takes a set of 4 grids to support a given tube on the top, bottom left and right.Despite the fact that the tubes touch in places, there are lines of sight through the bundle in many places which allows for cleaning.Note that the shell-side flow near the shell will have different heat transfer characteristics than flow near the centre of the bundle. This make this exchanger unsatisfactory for high e duties.CopyrightHyprotech UK Ltd holds the copyright to these lectures. Lecturers have permission to use the slides and other documents in their lectures and in handouts to students provided that they give full acknowledgement to Hyprotech. The information must not be incorporated into any publication without the written permission of Hyprotech.

HEDH is the Heat Exchanger Design Handbook available fromRay JohnsonHEDU office3 St. Peters Street, Wallingford, OX10 0BQ, UKTel: +44 (0)1491 834930ESDU27 Corsham StreetLondon, N1 6UAesdu@esdu.comHeat transfer engineers talk in terms of heat transfer coefficients for streams but thermal resistances for fouling. It is helpful to put this all on the same bases and the best way to do this is in terms of resistances as in the little diagram which is output in a DEVIZE rating. During the design, it is usually best to find ways of lowering the highest resistance.

In addition to showing where the main resistances are, this illustrate the proportion of the heat exchanger surface area required to cope with each resistance. Often, this diagram shows dramatically that a large proportion of the surface area is required to overcome the fouling. In such cases, the choice of fouling resistance should be questioned.

Another useful way of looking at this diagram is that each part is proportional to the temperature difference resulting from the thermal resistance. Hence, the diagram can be used a s quick guide to what the wall temperature is. This may be important if high wall temperatures must be avoided (to prevent scale formation, say). Take the case of a single pass, as an example, for a known shell diameter we can calculate the number of tubes that fit in the shell. Hence, we can calculate the velocity in the tubes and the pressure gradient along the tubes. From the gradient, we can calculate the exact tube length to just use up the allowably pressure drop.Repeating the calculation for different shell diameters gives the locus shown by the blue curve.

Remember, blue equals tube from now on in this lecture.

The region for valid designs is shown yellow here. This convention is used again later in the lecture but is dropped for the next few slides.A similar set of calculations may be done for the shell side pressure drop thus giving the green curve.

Immediately we see that the tube side pressure drop is no longer having an effect on the design in this case. Hence we might be able to improve the design by introducing tube side enhancement of increasing the number of tube side passes. We might not for other reasons but these curves are already giving us useful clues for improving the design.We can do the same thing for the heat transfer area thus giving the red curve.Often we set limits on the maximum and minimum velocities in the tubes. The minimum may be to avoid fouling while the maximum would be to avoid erosion.Doing a rating at this point will generate a resistance diagram which will give more clues on how to improve the design.If you are working with fixed tube lengths and shell diameters, you can introduce the grid of these as shown and select the point closest to the optimum. This is point A but a good designer might think of ways of modifying the design so that point B falls within the yellow area.