api - heat exchanger

HEAT TRANSFER THROUGH TUBES If the temperature of a fluid flowing inside a tube is differ- ent from the temperature of the atmosphere outside the tube, ____ flows through the tube wall.

HEAT EXCHANGERS

EXHIBIT BOOKLET

EXHIBIT 1

TUBING CHARACTERISTICS

Sq Ft Sq Ft Weight External Internal Per Ft

Thick- Internal Surface Surface Length I.D

O.D of B.W.G ness Area Per Foot Per Foot Steel Tubing Tubing Gauge Inches Sq Inch Length Length Lbs Inches 1/4 22 028 0295 0655 0508 066 194 1⁄4 24 022 0333 0655 0539 054 206 1/4 26 018 0360 0655 0560 045 214 3/8 18 049 0603 0982 0725 171 277 3/8 20 035 0731 0982 0798 127 305 3/8 22 028 0799 0982 0835 104 319 3/8 24 022 0860 0982 0867 083 j1 _L

2 11 120 2.433 5236 4608 2.410 1.760

2 13 095 2573 5236 4739 1.934 1.810 2-1/2 9 148 3.815 6540 5770 3.719 2.204

§PLIT FLOW

A

DOUBLE SPLIT FLOW

INTEGRAL WITH TUBESHEET

EXHIBIT 4

CLEARANCE

LIQUID ISOBUTANE

195°F 123 ISOBUTANE 200°F RECYCLED

OIL ENTERING AT 665°F

LIQUID ISOBUTANE LEAVING AT 200°F

WARM WATER OUT

WARM KEROSENE IN

EXHIBIT 8

FRACTIONATING

BOILER

OIL OUT

EXHIBIT 10

4209F

0

convenser || 400F _ REACTOR

OCTANE GASOLINE KHUUÊN FURNACE

HEAT EXCHANGERS

HEAT EXCHANGERS introduces the learner to the phenomenon of heat transfer as it is applied in modern refining techniques In Section 1: Heat Transfer, conduction and convection as methods of heat transfer are explained before the more practical matter of heat transfer in tubes is discussed

Section 2: Heat Exchange Equipment first details the various parts of heat exchangers as well as their functions It then describes the various types of

shell and tube heat exchangers

Section 3: Exchanger Operation and Maintenance goes into startup and

shutdown procedures and deals with various problems of exchanger main-

tenance It then describes the flow and mechanisms of various heat exchange

systems.

INSTRUCTIONS

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RATCHET CAP

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the and the _contact the object

to be measured

small

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HEAT EXCHANGERS

Section 1: Heat Transfer

HEAT TRANSFER BY CONDUCTION

Exhibits 1 through 10 are printed in a special pull-out section in

the center of this book Please pull them out now so that you can

| refer to them as they are mentioned in the text

1 Heat is a form of energy

Like other forms of energy, heat can be

2 The process by which heat travels through a substance is

called conduction

Thus, the material through which heat passes is called the

3 Suppose a container of hot water is placed next to a con-

tainer holding an equal amount of cold water

If the containers are touching, eventually the temperature

| of the cold water ( increases / decreases )

4 And, the temperature of the hot water

5 Heat has been conducted from the container of hot water

to the container of cold water

When the water in the two containers reaches the same

temperature, heat transfer ( stops / still continues )

6 Inother words, conduction of heat continues until the heat

is evenly distributed throughout the substance

The final temperature is ( greater than / less than / an

average of ) the two beginning temperatures

7 One thing that the rate at which heat is conducted through

a conducting material depends on is the nature of the

8 Copper, for example, is a better conductor of heat than

cast iron

Astove made of solid copper conducts heat ( more rapidly

/ more slowly ) than one made of cast iron

9 Suppose equal amounts of heat are applied to a one-inch

thick piece of steel and to a two-inch thick piece of steel

11 Look at this drawing of two sets of containers

40° 140” 185°

đa

Fig 1 Fig 2

In Figure 1, the difference in temperature between con-

12 In Figure 2, the difference in temperature is — 150°

13 Conduction takes place at a faster rate in Figure 2

Therefore, the rate of conduction varies with the size of

14 Astandard measure of the rate at which conduction takes

place is called thermal conductivity

Thermal conductivity takes into account whether the mate-

and of the conductor, and the amount length

HEAT TRANSFER BY CONVECTION

15 This drawing represents a room containing a heat source

in one corner

The air which touches the heat source is heated by XS So | `

conduction

As the air touching the heat source is heated, it expands

the room

Because it is lighter, the warm air ( rises / falls )

Cooler air from the floor level moves up and contacts the

source

It too becomes lighter from expansion and ( rises / falls )

This process is repeated again and again and produces a

circular flow pattern

As the air flows around the room it carries

with it

As warm and cold air meet near the center of the room,

the circular flow pattern is interrupted and turbulence

occurs

Warm air and cold air are mixed together, and heat is

transferred from the _ to the

air

Convection is heat transfer from one point to another

within a liquid or gas by the mixing of one portion with

another

Heat is transferred from the heat source to the air by

( conduction / convection ) and from the warm air to the

cold air by ( conduction / convection )

HEAT TRANSFER THROUGH TUBES

If the temperature of a fluid flowing inside a tube is differ-

ent from the temperature of the atmosphere outside the

tube, flows through the tube wall heat

The amount of heat that flows depends on the tempera-

The type of flow in which the fluid flows in smooth stream-

As the fluid flows, the molecules of the fluid rub against

one another

The friction of the molecules against each other causes

a resistance to flow, which tends to ( speed up / slow

28

29

30

31

This drawing shows fluid flowing near the wall of a tube

TUBE WALL The fluid that is flowing closest to the tube wall ( is / is not )

turbulent

The friction of the fluid closest to the tube wall causes this

fluid to flow ( quickly / slowly )

This slow-flowing fluid acts as a static film covering the

tube wall

Heat travels through the tube wall by conduction, and, in

order for the heat to reach the main stream, it must pass

through the static film by — also

In a turbulent stream, the fluid molecules mix to a great

extent

As the mixing process continues, ( many / few ) fluid mole-

cules come in contact with the static film

aaeWhen these fluid molecules come in contact with the

static film, they ( absorb / give off ) heat

The molecules which have absorbed heat from the static

film —_—. _ some of the heat to other molecules

in the mainstream

Heat is transferred to the molecules that come in contact

with the static film by ( conduction / convection )

These molecules carry the heat to another part of the

mainstream and transfer some of the heat to other mole-

cules

This is heat transfer by

In turbulent flow, the transfer of heat from the static film

Fluid farther from the tube wall flows ( faster / slower )

The fluid that is flowing fastest is ( in the center / at the

edges ) of the mainstream

in the center

89 Fluid in laminar flow acts much as if it consisted of many,

thin-walled tubes of the fluid, one inside the other

TUBE

In order for the mainstream to absorb heat, the heat must

41 In comparison to metals, fluids are poor conductors

In comparison to the tube wall, the time it takes for heat

= to transfer through the static film is ( greater / less ) less

z, )

†

transfer time

44 The thickness of the static film depends on the amount of

turbulence When turbulence is slight, the static film is

As turbulence becomes greater, the static film becomes

thinner, or less

45 Heattransfer time through the static film can be decreased

by increasing the of the fluid turbulence

i

The friction of the outside fluid on the tube wall causes the

fluid closest to the wall to flow ( quickly / slowly )

Thé fluid closest to the tube wall becomes a —

film

Assume that the fluid outside the tube is hotter than the

fluid inside the tube

Heat flows from ( inside to outside / outside to inside ) of

the tube

In order for the heat to reach the tube wall, it must pass

from the mainstream through the static

The greater the turbulence outside the tube, the ( thicker /

thinner ) the static film

The greater the turbulence outside the tube, the ( more /

fewer ) molecules come in contact with the static film

The factors affecting heat flow inside and outside tubes

are ( similar / different )

53 This drawing illustrates flow inside and outside a tube

FLUID INSIDE TUBE

INSIDE FOULING MATERIAL FLUID OUTSIDE TUBE OUTSIDE FOULING MATERIAL

OUTSIDE FLUID FILM

Ti, the temperature inside the tube is ( higher than / higher than lower than ) Ts, the temperature outside the tube

erature drop across the inside — = 5, fluid film

55 T3 to Ta is the temperature drop across the inside scale

or fouling material

Compared to the drop from Tz to Ts, the drop from Ta to Ta

-

56 T,toTs represents the temperature drop through the tube

wall and Ts to Ts represents the drop through the outside

fouling material

The temperature drop through the tube wall is close to

Sĩ

58

The temperature drop is greater ( through the tube wall /

through the inside and outside static films )

The shape of the outside temperature curve is ( similar to /

different from ) the shape of the inside temperature curve

Heat flows from one fluid to another if there isa

in temperature between the two fluids

Assume that fluid is flowing along both the inside and the

outside of a tube and that both streams of fluid are flowing

in the same direction and that the fluid inside is hotter

than the fluid outside

Heat is transferred from the _ fluid to the

fluid

The temperature of the hotter fluid ( increases / decreases )

As heat is transferred to the colder fluid, its temperature

All the fluid represented here is flowing in the same direc-

tion

POINT POINT c

66 The temperature of the outside fluid is highest at point

(A/B/C)

67 This graph shows the temperature of the two fluids in

relation to the length of the tube

PARALLEL FLOW

| | INSIDE FLUID |

The difference in temperature is greatest at point ( A /

B/C)

68 The heat transfer rate ( depends / does not depend ) on

the temperature difference

69 The heat transfer rate is greatest at point(A/B/C)

70 At point C, there (is / is no ) temperature difference

71 At point C, heat (is / is not ) transferred

72 In parallel flow, when both fluids flow in the same direc-

tion, the hot fluid ( can / cannot ) be cooled below the

highest temperature of the cooler fluid

73 The fluids are flowing countercurrently

POINT

In this kind of flow the fluids are flowing in ( the same

direction / opposite directions )

Suppose that two fluids are in counterflow inside and out-

side a tube, and the hotter fluid is inside

The temperature of the hotter inside fluid is greatest at

(A/B/C)

The temperature of the inside fluid decreases in the direc-

tion(AtoC/CtoA)

The outside colder fluid is coolest at (A/B/C)

The outside fluid is hottest at( A/B/C)

This graph shows the temperature in relation to the length

POINT A POINT B POINT C

In counterflow, the temperature difference along the tube

is (more constant / less constant ) than the temperature

difference in parallel flow

The heat transfer rate in counterflow varies ( consider-

Notice the area on the graph that is represented with a

double arrow

Counterflow ( permits / prevents ) cooling a fluid to a

temperature lower than the highest temperature of the

Section 2: Heat Exchanger Equipment

OIL OUTLET

The tank represents the shell of the exchanger and, in

this case, is filled with

Heat is transferred from the hot oil flowing through the

tubes to the cool water around the tubes

The shell-side of an exchanger is the area inside the shell

and outside the tubes

The tube-side of an exchanger is the area

the tubes

In the example shown, the shell-side fluid is

and the tube-side fluid is

water

tube

inside

water oil

85 This drawing shows the construction of a typical shell and

TUBESHEET

The tubes are anchored between two _— _ tubesheets

86 The combination of tubes and tubesheets is called the

87 This drawing shows the fluid flow path through a shell and

tube exchanger

TUBESIDE INLET SHELL SIDE INLET

Hot oil flows into the tube-side inlet, through the tubes,

and out through the — —— outlet tube-side

88 Cool water flows into the shell-side inlet, around the

, and out through the shell-side outlet tubes

shell-side )fluidtothe_ —— fluid tube-side; shell-side

an

less ) quickly heat is conducted

A bundle of small tubes has ( more / less ) surface area

than a single large tube

Shell and tube exchangers use a bundle of small tubes,

rather than a single large tube

This ( increases / decreases ) the area for heat transfer

Exchanger tubes can be either plain or finned

As these drawings show, fins are either

or ————— — the tubes

Fins ( add to / subtract from ) the tube surface area

Thus, they _ the rate of heat transfer

lfacorrosive fluid passes through either side of an exchanger,

something usually must be done to prevent

Sometimes the tubes can be made of a metal which is not

In practice, the most common tube O D.'s are the 1/2-inch,

the 3/4-inch, and the one-inch

As the chart shows, tubes with O.D.'s at the extremes of

the range, either high or low, are usually produced in

( greater / fewer ) varieties of gauges than the more com-

100 So, tubing with a 2-1/2 inch O.D is usually produced in

only one

101 Exchangers are usually produced in standard lengths of

8, 10, 12, 16, and 20 feet Sixteen and 20 feet are the most

103 As the length of an exchanger increases, its cost gener-

ally ( increases / decreases )

104 One of the basic considerations in exchanger design is to

meet operating requirements while minimizing —

TUBESHEETS

105 The tube bundle is made by fastening the tube ends into

openings in the tubesheet

TUBE SHEET

Because the tubes cannot move in the tubesheets, the

tubesheets and tubes form a( solid / flexible ) unit

106

107

108

109

In some exchangers, the tube and tubesheets are fixed

†o the shell

Therefore, they ( are free to move / are prevented from

moving )

Heat causes metal to ( expand / contract )

When the tubes expand because of heat, stress is placed

on the tubes and tubesheet

TUBESHEET

A tube can come loose, allowing fluid to leak between the

tube wall and the opening inthe —

This results in the contamination of one fluid by another

To guard against this, a double tubesheet can be used in

cases wheea = absolutely cannot be

110 Here is a design which can help reduce the possibility of

leaks at the tubesheet

111 Ifaleak occurs, fluid passes into this space

Since the space between the tubesheets is open, fluid is

allowed to ( drain from / collect in ) the exchanger drain from

TUBE JOINTS

112 The tube joint is the connection between the tube and the

tubesheet

the possibility that there is leakage

113 Tube joints are usually either rolled press fit or welded

PRESS FIT (EXAGGERATED)

Some metals cannot be welded, so tubes of these metals

114 Rolled joints usually make a very good seal, and they can

be used in reasonably high pressure service, up to about

2,000 psi

However, in special cases or severe service, — == welded

tube joints are usually used

115 An exchanger is likely to be more expensive if the tube

TUBESHEET LAYOUT

116 Exchanger tubes can be installed in a variety of patterns

TRIANGULAR IN-LINE TRIANGULAR

When the tubes are arranged in parallel rows, vertically

and horizontally, the pitch is called — gi -—————= in-line pitch

In-line square pitch offers the ( most / least.) resistance to

shell-side flow through an exchanger

The greater the resistance to flow, the greater the result-

ing pressure drop

For this reason, in-line square pitch is particularly efficient

when conditions require a ( high / low ) pressure drop

Staggering the tubes, as in the three other main types of

pitch, allows ( more / fewer ) tubes in a given area than the

even spacing in square pitch does

A disadvantage of square pitch is the relatively

number of tubes in a given area

Compare the number of tubes in a given area in square

pitch and triangular pitch

Ina 42-inch, double-pass exchanger, there are

tubes in a square pitch arrangement and _ tubes

in a triangular pitch arrangement

The more tubes there are in a given area, the

the heat transfer rate

Since the square pitch arrangement results in the lowest

number of tubes in a given area, it also results in the

heat transfer rate

When the pitch is triangular, the pressure drop is ( higher /

lower ) than when the pitch is square

But, the heat transfer rate is greater when pitch is

lowest

higher

triangular

126 Foragiven set of operating conditions the choice of pitch

arrangements depends upon what pressure drop is needed

in relation to the transfer rate desired heat

BAFFLES AND TYPES OF BAFFLES

127 The longer the tubes in an exchanger are, the ( heavier /

128 The heavier they are, the _ the chance greater

that they will sag

Since they support the weight, baffles help to _— decrease, or relieve the stress on the tubing and tubesheet

130 In both laminar and turbulent flow, a layer of fluid sur-

rounds each tube, acting as an insulator

This layer of fluid acts to ( increase / decrease ) the rate decrease

of heat transfer

21

131

132

133

The thicker the insulating layer, the _—_—————— it

decreases heat transfer

The insulating layer is likely to be thicker when flow is

(laminar / turbulent )

In addition to supporting the tubes, baffles break up

_ flow, decreasing the layer of insulating

A segmental baffle is a circle from which either a vertical

or horizontal portion has been cut

VAPOR INLET

CONDENSATE OUTLET

In this case, the baffles are ( vertically cut / horizontally

cut ) segmental baffles

Segmental baffles are positioned so that the cut-out areas

(all face in the same direction / face in alternate directions )

Alternating the baffles causes flow to — the

tubes a number of times

It also provides better for the tubes

138 In addition to the portion cut from the side or top of a seg-

mental baffle, a portion is often removed from the bottom

HORIZONTAL

uous fluid flow along the bottom of the exchanger

139 Whether the baffle is cut vertically or horizontally depends

on the type of fluid and on the operation

HORIZONTAL

The baffle most likely to catch suspended materials is the

140 But, suppose horizontal baffles were used in a condenser

GAS INLET

BAFFLES

CONDENSED FLUID OUTLET

Condensed fluid builds up behind baffles A and C, thus

——— flow

ciency of the exchanger is ===

Disc and Doughnut Baffles

142 The pattern of flow through disc and doughnut baffles is

relatively uniform

SEDIMENT

But, if the fluids are not clean, sediment builds up behind

the ( disc / doughnut )

restricting

decreased

doughnut

143

144

Since the cutout area of the baffle is in the center, the

flow of condensed fluids along the bottom of the exchanger

can also be :

For these reasons, disc and doughnut baffles are used

( more / less ) often than segmental baffles

At high inlet-fluid velocities, the fluid can seriously erode

the tubes as it strikes them

If the inlet fluid contains suspended solid particles, the

problem is ( more / less ) severe

Impingement baffles are sometimes placed at inlet flow

areas to the shell-side

NO PLATE BAFFLE

PLATE BAFFLE VERTICAL CUTS

PLATE BAFFLE HORIZONTAL CUTS

As this comparative illustration shows, the impingement

An impingement baffle directs the flow ( toward the sides

of the exchanger / toward the tubes )

The baffle effectively reduces the 7 of the