chee 470 heat exchangers - chemeng.queensu.ca...chee 470 heat exchangers ... • double pipe heat...

CHEE 470CHEE 470HEAT EXCHANGERSHEAT EXCHANGERSHEAT EXCHANGERSHEAT EXCHANGERS

BOB HEASLIPBOB HEASLIP

AGENDAAGENDA

Types of Heat ExchangersTypes of Heat Exchangers

TEMA Type Shell & Tube Heat ExchangersTEMA Type Shell & Tube Heat Exchangers TEMA Type Shell & Tube Heat ExchangersTEMA Type Shell & Tube Heat Exchangers

Shell & Tube Exchanger ArrangementsShell & Tube Exchanger Arrangements

Selection of Exchanger Type & OrientationSelection of Exchanger Type & Orientation

Shell & Tube Exchanger Thermal DesignShell & Tube Exchanger Thermal Design

Estimation of Film CoefficientsEstimation of Film Coefficients

Pressure Drop CalculationsPressure Drop Calculations

Thermal DesignThermal Design –– Other Exchanger TypesOther Exchanger Types

TYPES OF HEAT EXCHANGERS

• DOUBLE PIPE HEAT EXCHANGERS

SIMPLEST TYPE

A PIPE INSIDE A PIPEA PIPE INSIDE A PIPE

SMALL HEAT TRANSFER AREAS

TYPES OF HEAT EXCHANGERS

• HAIRPIN HEAT EXCHANGERS

TUBES INSIDE A U SHAPED SHELL

GOOD FOR HIGH TEMPERATURES ANDPRESSURES

LIMITED SIZE

TYPES OF HEAT EXCHANGERS

• PLATE & FRAME HEAT EXCHANGERS

FLUIDS FLOW BETWEEN THINFLUIDS FLOW BETWEEN THINPLATES

COMPACT DESIGN

HIGH HEAT TRANSFERCOEFFICIENTS

GASKETS LIMIT PRESSURE &TEMPERATURETEMPERATURE

NOT USED WITH HAZARDOUSCHEMICALS

TYPES OF HEAT EXCHANGERS

• SPIRAL PLATE HEAT EXCHANGERS

FLUIDS FLOW BETWEEN TWOPLATES WOUND AROUND EACHOTHER

GOOD FOR SLURRIES

LOW PRESSURE DROP

OFTEN USED IN VACUUMOFTEN USED IN VACUUMSERVICE

TYPES OF HEAT EXCHANGERS

• SPIRAL TUBE HEAT EXCHANGERS

FABRICATED FROM BENT TUBINGFABRICATED FROM BENT TUBING

AVAILABLE “OFF THE SHELF”

SMALL SERVICES FOR EXAMPLE SAMPLE COOLERSAND PILOT PLANTS

TYPES OF HEAT EXCHANGERS

• AIR COOLED EXCHANGERS

USED WHEN WATER EXPENSIVE OR NOT AVAILABLE

MUST BE DESIGNED TO HANDLE SEASONAL AND DIURNALTEMPERATURE CHANGES

EXPENSIVE AND TAKE UP A LOT OF ROOM

SMALLER PACKAGED “RADIATOR” TYPE UNITS AVAILABLE

SHELL & TUBE HEATSHELL & TUBE HEATEXCHANGERSEXCHANGERS

• THE MOST COMMON HEAT EXCHANGER TYPE – BY FAR• THE MOST COMMON HEAT EXCHANGER TYPE – BY FAR

• A LOT OF HEAT TRANSFER AREA IN A SMALL VOLUME

• BEEN IN USE FOR OVER 150 YEARS

• CAN BE DESIGNED FOR ALMOST ANY SERVICE

• DESIGN PRINCIPLES WELL KNOWN

• MANY DESIGN & FABRICATION SHOPS AROUND THE WORLD• MANY DESIGN & FABRICATION SHOPS AROUND THE WORLD

• AVAILABLE IN MANY DIFFERENT MATERIALS

• CAN BE DESIGNED FOR ALL PRESSURES & TEMPERATURES

TEMA

TUBULAR

EXCHANGEREXCHANGER

MANUFACTURERS

ASSOCIATION

SHELL & TUBE HEATEXCHANGER COMPONENTS

TUBES

SIZE IS OUTSIDE DIAMETER

¾” IS MOST COMMON SIZE

BIRMINGHAM WIRE GAUGEIS THICKNESS

AVAILABLE IN MANY ALLOYS

LENGTHS IN 2’ INCREMENTSUP TO 24 FEET LONG

TUBE LAYOUTS

TUBES ARE ARRANGED INSPECIFIC PATTERNSSPECIFIC PATTERNS

TRIANGULAR LAYOUT ISTHE MOST COMMON

DISTANCE BETWEEN TUBESCENTERS IS THE PITCH

LAYOUT & PITCH AFFECTSHEAT TRANSFER AND

TRIANGULAR SQUARE

HEAT TRANSFER ANDPRESSURE DROP

TUBESHEETS

TUBESHEETS HOLD THE ENDS OF THETUBES AND PROVIDE A BARRIERBETWEEN TUBE & SHELLSIDE FLUIDS

TUBES ARE CONNECTED TO THETUBES ARE CONNECTED TO THETUBESHEETS BY “GROOVING &ROLLING” OR BY WELDING

TUBESHEET MATERIALS MUST BESUITABLE FOR BOTH FLUIDS

SHELL

THE SHELL IS THE CONTAINER FOR THESHELL SIDE FLUID

FABRICATED FROM PIPE OR ROLLED SHEETFABRICATED FROM PIPE OR ROLLED SHEET

THE LEAST CORROSIVE & LOWESTPRESSURE FLUIDS ARE PLACED ON THESHELL SIDE TO REDUCE COSTS

SEVERAL DIFFERENT STYLES ARE USEDFOR DIFFERENT SERVICES

BAFFLESHORIZONTALSEGMENTAL

VERTICALSEGMENTAL

BAFFLES SUPPORT TUBES ANDDIRECT SHELL FLUID FLOW ACROSSTUBES

BAFFLE CUT IS % OF SHELLDIAMETER REMOVED

BAFFLE SPACING IS THE DISTANCEBAFFLE SPACING IS THE DISTANCEBETWEEN BAFFLES

SINGLE SEGMENTAL SINGLE SEGMENTAL

SHELL SIDENOZZLES

IMPINGEMENTPLATE

TUBESIDENOZZLES

BONNET TYPECHANNELCHANNEL

CHANNEL WITHGASKETED

PASS DIVIDER

COVER

S&T HEAT EXCHANGERS&T HEAT EXCHANGERARRANGEMENTSARRANGEMENTS

3 BASIC ARRANGEMENTS3 BASIC ARRANGEMENTS

FIXED TUBESHEETFIXED TUBESHEET

FLOATING HEADFLOATING HEAD

UU--TUBETUBE

3 BASIC ARRANGEMENTS3 BASIC ARRANGEMENTS

UU--TUBETUBE

FLOATING HEAD

TEMA W TEMA T TEMA SExternally Sealed Pull Through Floating Head

Floating Tubesheet Floating Head with Backing Device

FIXED TUBESHEET

EXPANSION JOINT

U-TUBE BUNDLE

REBOILER TYPES

REBOILER TYPE SELECTION CHART

FILM THEORY OF HEAT TRANSFER

There are five layers through which the heatmust flow:

1. The inside boundary layer2. The inside fouling layer3. The tube wall

DEVELOPMENT OF BASIC HEAT TRANSFER EQUATIONS

3. The tube wall4. The outside fouling layer5. The outside boundary layer

The quantity of heat flow is the same througheach layer.

Therefore (assuming that the outside area is equal to the inside area):

q = Q/A = h (T -T ) = h (T -T ) = h (T -T ) = h (T -T ) = h (T -T )q = Q/A = hi(TH-T1) = hfi(T1-T2) = hw(T2-T3) = hfo(T3-T4) = ho(T4-TC)

Where : q = heat flux, BTU/hr/ft2 or W/mQ = Total Heat Transfer, BTU/hr or WA = Heat Transfer Area, ft2 or m2

h = Heat Transfer Coefficient, BTU/hr-ft2-oF or W/m-oKT = Temperature, oF or oK

DEVELOPMENT OF BASIC HEAT TRANSFER EQUATIONS

The thermal resistance to heat flow, r is the reciprocal of the heat transfer coefficient.i.e. r = 1/h

Where: r = thermal resistance, hr-ft2-oF/Btu or m2-oK/W

Therefore the above equation can be modified as follows:Therefore the above equation can be modified as follows:

q = Q/A = hi(TH-T1) = (T1-T2)/rfi = (T2-T3)/ rw = (T3-T4)/rfo = ho(T4-TC)

In terms of temperature differences one can write:

TH-T1 = q/hi & T1-T2 = q rfi & T2-T3 = q rw & T3-T4 = q rfo &T4-TC = q/ho

Substituting one gets: T -T = DT = q(1/h + r + r + r + 1/h )Substituting one gets: TH-TC = DT = q(1/hi + rfi + rw + rfo + 1/ho)

Since q = Q/A, the above equation can be rearranged to give the following:

Q = A (TH-TC)(1/hi + rfi + rw + rfo + 1/ho)

The term 1/(1/hi + rfi + rw + rfo + 1/ho) is referred to as the overall Heat TransferCoefficient, U which has the units BTU/hr-ft2-oF or W/m2-oK.

Substituting U into the previous equation gives:

DEVELOPMENT OF BASIC HEAT TRANSFER EQUATIONS

Q = U A (TH – TC) also written as Q = U A DT

Previously it had been assumed that the outside area is equal to the inside area.However, this is not the case when tubes are being used.Modifying the above equations to take into account differences in areas gives:

U = 11/ho + Ao/Aihi + rw + rfo + Ao rfi/Ai

Often when carrying out heat transfer calculations, the goal is to determinethe heat transfer area, A.

A = Q / U DT

TYPICAL OVERALL HEATTYPICAL OVERALL HEATTRANSFER COEFFICIENTSTRANSFER COEFFICIENTS

AREA = QAREA = QAREA = QAREA = Q

U xU x DDTT

PROCESS SIMULATION GIVES Q &PROCESS SIMULATION GIVES Q & DDT.T.

WE WANT TO KNOW THE AREA.WE WANT TO KNOW THE AREA.

BY USING TYPICAL U’s WE CAN ESTIMATE THE AREA.BY USING TYPICAL U’s WE CAN ESTIMATE THE AREA.

TYPICAL U’s ARE THOSE EXPERIENCED IN SIMILARTYPICAL U’s ARE THOSE EXPERIENCED IN SIMILAREQUIPMENT UNDER SIMILAR CONDITIONS.EQUIPMENT UNDER SIMILAR CONDITIONS.

COCURRENT & COUNTERCURRENT FLOW

T2

t1

t2

T1

T2 t2

t2

t1

COUNTERCURRENT FLOW

t2T2

T1

COCURRENT FLOW

LOG MEAN TEMPERATURE DIFFERENCE (LMTD)LOG MEAN TEMPERATURE DIFFERENCE (LMTD)

T1

T2t2 LTTD

GTTD

THE TEMPERATURE DIFFERENCE BETWEEN THE FLUIDSTHE TEMPERATURE DIFFERENCE BETWEEN THE FLUIDSUSUALLY VARIES IN DIFFERENT PARTS OF THE EXCHANGER.USUALLY VARIES IN DIFFERENT PARTS OF THE EXCHANGER.THE APPROPRIATE AVERAGE TEMPERATURE DIFFERENCE FORTHE APPROPRIATE AVERAGE TEMPERATURE DIFFERENCE FORCOUNTERCURRENT OR COCURRENT FLOW IS THE LOG MEANCOUNTERCURRENT OR COCURRENT FLOW IS THE LOG MEANTEMPERATURE DIFFERENCE CALCULATED AS :TEMPERATURE DIFFERENCE CALCULATED AS :

t1t2 LTTD

TEMPERATURE DIFFERENCE CALCULATED AS :TEMPERATURE DIFFERENCE CALCULATED AS :

GTTD - LTTDLMTD =

ln(GTTD/LTTD)

LMTD CORRECTION FACTORS

IN THIS REGION FLUID JUST ENTERING THESHELLSIDE IS EXCHANGING HEAT WITH FLUIDJUST ENTERING THE TUBESIDE. THEREFOREFLOW IS CO-CURRENT.

IN THIS REGION FLUID ENTERING THESHELLSIDE OF THE EXCHANGER ISEXCHANGING HEAT WITH FLUIDEXITING THE TUBESIDE. THEREFOREMOSTLY COUNTERFLOW FLOW ISBEING ACHIEVED.

MOST EXCHANGERS HAVE ACOMBINATION OF COCURRENTCOMBINATION OF COCURRENTAND COUNTERCURRENTFLOW. CORRECTION FACTORSARE APPLIED TO THE LMTDUSING A DIFFERENT CHARTFOR EACH EXCHANGERCONFIGURATION

NON-LINEAR TEMPERATURE PROFILES

WATCH OUT FOR THISSITUATION

CALCULATION OF THE OVERALL HEATTRANSFER COEFFICIENT

U = Overall Heat Transfer Coefficient

ho = Outside Film Coefficient

hi = Inside Film Coefficient

rw = Tube Metal Resistance

r = Outside Fouling Resistancerfo = Outside Fouling Resistance

rfi = Inside Fouling Resistance

Ao = Outside Area

Ai = Inside Area

METAL RESISTANCE IN TUBES

rw normally has little affect on the heat transfer coefficient

FOULING FACTORS

ESTIMATION OF FILM COEFFICIENTS

• SENSIBLE HEAT TRANSFER

• CONDENSING

THREE MECHANISMS

• BOILING

EACH CAN OCCUR INSIDE OR OUTSIDE THE TUBE.

EACH CAN OCCUR IN COMBINATION WITH ANY OTHER.

SENSIBLE HEAT TRANSFERINSIDE THE TUBE

1. Calculate Reynolds Number.

2. Read Nusselt Number, jH off Sieder and Tate chart.2. Read Nusselt Number, jH off Sieder and Tate chart.

3. Calculate the film coefficient, hi.

HEAT TRANSFER COEFFICIENTSFOR SENSIBLE HEAT TRANSFER

INSIDE THE TUBE - WATER

KERN METHODKERN METHOD

1. Calculate velocity in tubes.

2. Determine average watertemperature.

3. Read film coefficient off thechart.

4. Correct for tube inside4. Correct for tube insidediameter.

HEAT TRANSFER COEFFICIENTSFOR SENSIBLE HEAT TRANSFER

OUTSIDE THE TUBE

1. Calculate Reynolds Number.

2. Read Nusselt Number, jH off the Kern chart.

3. Calculate the film coefficient, hi.

USE OF FINNED TUBES FORENHANCED HEAT TRANSFER

IN CASES WHERE A LOW COEFFICIENTON THE OUTSIDE OF THE TUBES LIMITSON THE OUTSIDE OF THE TUBES LIMITSTHE HEAT TRANSFER, FINNED TUBESCAN BE USED TO INCREASE THEOUTSIDE AREA.

CONDENSING COEFFICIENTSOUTSIDE TUBES & INSIDE HORIZONTAL TUBES

1. Calculate Condensing Load

2. Read Condensing Coefficient of f Chart

CONDENSING COEFFICIENTSINSIDE VERTICAL TUBES

1. Calculate Reynolds Number.

2. Read Nusselt Number off chart.

3. Calculate the film coefficient, hi.

VAPORIZATION

HEAT TRANSFER IN VAPORIZING OPERATIONS ISLIMITED BY MAXIMUM FLUX

ABOVE THE MAXIMUM FLUX HEAT TRANFER IS HINDERED BY ALAYER OF VAPOUR INSULATING THE SURFACE.

VAPORIZATION

Btu/hr-ft2MAXIMUM FLUX

ORGANIC FLUIDS – NATURAL CIRCULATION 12,000

ORGANIC FLUIDS – FORCED CIRCULATION 20,000

WATER & AQUEOUS SOLUTIONS 30,000

MAXIMUM FILMCOEFFICIENT

ORGANIC FLUIDS 300

WATER & AQUEOUS SOLUTIONS 1000

Btu/hr-ft2-oFCOEFFICIENT

PRESSURE DROPTUBESIDE – THROUGH TUBES

PRESSURE DROPTUBESIDE – THROUGH HEADS

PRESSURE DROPSHELLSIDE

CHEE 470HEAT EXCHANGERSHEAT EXCHANGERS

ASSIGNMENT