Plant overview, working of compressors, pumps, cooling towers, gas turbines. Mini- Project on shell & tube type heat exchangers in ONGC, Uran plant. Hence, calculating the effectiveness of heat exchanger using the working data.

1. 1
INDUSTRIAL TRAINING & PROJECT REPORT
ON
HEAT EXCHANGERS
AT
OIL AND NATURAL GAS CORPORATION LIMITED
URAN PLANT, URAN
(AN ISO 9001, ISO 14001 & OHSAS 18001 CERTIFIED PLANT)
Submitted by :-
Akansha Jha
Mech. Engg. (III yr.)
AVCOE, Sangamner

2. 2
OIL AND NATURAL GAS CORPORATION LTD
URAN PLANT
CERTIFICATE
This is to certify that Miss. Akansha Jha, a student of VIth
semester, mechanical department, Amrutvahini College of
Engineering has undergone a one month Industrial
Training and completed the project report on ‘Heat
Exchanger’.
Mr. Bhupesh Kumar Mr. S.K.Gupta
Superintendent. Engg. (Mech.) Chief. Engg. (Chem.)
O.N.G.C. Plant, Uran O.N.G.C. Plant, Uran
(Mentor) (Head of Training Dept)

3. 3
ACKNOWLEDGEMENT
I take this opportunity to express my deepest regards towards
who have incorporated their invaluable guidance & help in the
hour of need.
I specially & most sincerely acknowledge with deep sense of
gratitude & indebtness my project guide Mr. Bhupesh Kumar,
AEE(M) for his continuous support, guidance & inspiration during
my training period. I would also wish to thank Mr. D.V. Koli, EE(M),
Mr. Anand Shankar, EE(M) & Mr. J.V.N Rao, CE.(M) for their
valuable guidance & support.
Finally, I wish to sincerely thank all the persons, who have directly
or indirectly helped me in the successful completion of my
training.

4. 4
INDEX
CHAPTERS TITLE PAGE NO
1 Introduction 1-8
1.1 Definition 2
1.2 Types Of Heat Exchangers 2
1.2.1 Transfer Process 3
1.2.2 Flow Arrangements 3
1.2.3 Geometry Of Construction 4
1.2.4 Heat Transfer Mechanism 8
2 Shell & Tube Heat Exchanger 8-16
2.1 Basic Equation In Design 10
2.2 Overall Heat Transfer Coefficient 10
2.3 Log Mean Temperature Difference, LMTD 12
2.4 NTU For Heat Exchanger Analysis 14
3 Fouling Factor 16-19
3.1 Causes Of Fouling 17
3.2 Effects Of Fouling 18
3.3 Cost Due To Fouling 19
4 Case Study 19-24
4.1 According To Design Data Sheet E-112 21
4.2 Presently Operating Condition 22
Conclusion
References
24

5. 5
ABSTRACT
Engineers are continually being asked to improve processes and increase efficiency.
These requests may arise as a result of the need to increase process throughput, increase
profitability, or accommodate capital limitations. Processes which use heat transfer
equipment must frequently be improved for these reasons. This paper involves the
method for calculation of effectiveness using LMTD and increasing shell-and-tube
exchanger E-112 performance.
1 INTRODUCTION
A device-which transfers heat from one fluid to another fluid, is called a heat exchanger.
In heat exchangers, there are usually no external heat and work interactions. Typical
applications involve heating or cooling of a fluid stream of concern and evaporation or
condensation of single or multi-component fluid streams. In other applications, the
objective may be to recover or reject heat, or sterilize, pasteurize, fractionate, distil,
concentrate, crystallize, or control a process fluid.[1] The simplest type of heat exchanger
is an open feed water heater used in thermal power plants. In an open-feed water heater, a
stream of steam is directly mixed with cold water and the mixture leaves the unit at a
uniform temperature. However, in most of the situations one is not interested in mixing
both the fluids but would like to transfer heat from a hot fluid to another cold fluid. There
are several types of devices or heat exchangers in which one fluid is separated from the
other by a wall or partition through which heat flows. The simplest type of heat–
exchanger is a double- pipe heat exchanger in which one fluid flows through the inner
pipe while the other fluid flows through the annular space between the inner and outer
pipes. In the design of a heat exchanger one should take into account the following
important factors:
 The thermal analysis : In this phase of design one is primarily concerned with the
estimation of heat transfer area for the transfer of heat at a specified rate for the
given flow rates and temperatures of the fluids.
 The mechanical Design : In this one takes into account the operating temperatures,
pressures, corrosive nature of the fluids, pressure drop, thermal stresses, etc.

6. 6
 The design of manufacture : In this phase of design, one concentrates on the
selection of material, seals, enclosures, cost of manufacturing and the
manufacturing procedures.[2]
1.1 DEFINITION OF HEAT EXCHANGERS [1]
A heat exchanger is a piece of equipment built for efficient heat transfer from one
medium to another (which may be between two or more fluids, between a solid surface
and a fluid, or between solid particulates and a fluid) at different temperatures and in
thermal contact while keeping them from mixing with each other. The media may be
separated by a solid wall, so that they never mix, or they may be in direct contact.
1.2 TYPES OF HEAT EXCHANGERS
The heat exchangers are classified based on :
Fig. 1.1 Classification of heat exchangers

7. 7
1.2.1 TRANSFER PROCESS [3]
According to the heat transfer process heat exchangers are classified as:
a) Indirect Contact Type Heat Exchangers
In this type of heat exchangers, the fluid streams remain separate, and the heat transfer
takes place continuously through a separating wall. There is no direct mixing of the fluids
because each fluid flows in separate fluid passages.
b) Direct Contact Type Heat Exchangers
In a direct-contact exchanger, two fluid streams come into direct contact, exchange heat,
and are then separated. Common applications of a direct-contact exchanger involve mass
transfer in addition to heat transfer, such as in evaporative cooling and rectification;
applications involving only sensible heat transfer are rare. The enthalpy of phase change
in such an exchanger generally represents a significant portion of the total energy transfer.
The phase change generally enhances the heat transfer rate.
1.2.2 FLOW ARRANGEMENTS [4]
There are three primary classifications of heat exchangers according to their flow arrangement.
 Parallel flow
 Counterflow
 Cross-flow
In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in
parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the
exchanger from opposite ends. The counter current design is most efficient, in that it can transfer
the most heat from the heat (transfer) medium. In a cross-flow heat exchanger, the fluids travel
roughly perpendicular to one another through the exchanger. Fig. 1.2 shows (a) Shell and tube
heat exchanger, single pass (1–1 parallel flow) (b)Shell and tube heat exchanger, 2-pass tube side
(1–2 crossflow) (c) Shell and tube heat exchanger, 2-pass shell side, 2-pass tube side (2-2
countercurrent).

8. 8
(a)parallel flow (b) Crossflow (c) countercurrent
Fig. 1.2 Classification of heat exchanger based on Flow Arrangements
1.2.3 GEOMETRY OF CONSTRUCTION [1]
Heat exchangers are frequently characterized by construction features. Four major
construction types are tubular, plate-type, extended surface, and regenerative exchangers.
1.2.3.1 Tubular Heat Exchangers
These exchangers are generally built of circular tubes, although elliptical, rectangular, or
round/flat twisted tubes have also been used in some applications. There is considerable
flexibility in the design because the core geometry can be varied easily by changing the
tube diameter, length, and arrangement. Tubular exchangers can be designed for high
pressures relative to the environment and high-pressure differences between the fluids.
Tubular exchangers are used primarily for liquid-to-liquid and liquid-to-phase change

9. 9
(condensing or evaporating) heat transfer applications. They are used for gas-to-liquid
and gas-to-gas heat transfer applications primarily when the operating temperature and/ or
pressure is very high or fouling is a severe problem on at least one fluid side and no other
types of exchangers would work. These exchangers may be classified as shell-and tube,
double-pipe, and spiral tube exchangers. They are all prime surface exchangers except for
exchangers having fins outside/inside tubes.
Shell & Tube Exchangers
It is generally built of a bundle of round tubes mounted in a cylindrical shell with the tube
axis parallel to that of the shell. One fluid flows inside the tubes, the other flows across
and along the tubes. The major components of this exchanger are tubes (or tube bundle),
shell, frontend head, rear-end head, baffles, and tubesheets. The complete detail is further
discussed
Double -Pipe Heat Exchangers.
This exchanger usually consists of two concentric pipes with the inner pipe plain or
finned. One fluid flows in the inner pipe and the other fluid flows in the annulus between
pipes in a counterflow direction for the ideal highest performance for the given surface
area. However, if the application requires an almost constant wall temperature, the fluids
may flow in a parallel flow direction. This is perhaps the simplest heat exchanger. Flow
distribution is no problem, and cleaning is done very easily by disassembly.
Spiral Tube Heat Exchangers.
These consist of one or more spirally wound coils fitted in a shell. Heat transfer rate
associated with a spiral tube is higher than that for a straight tube. In addition, a
considerable amount of surface can be accommodated in a given space by spiraling.
Thermal expansion is no problem, but cleaning is almost impossible.
1.2.3.2 Plate-Type Heat Exchangers
Plate-type heat exchangers are usually built of thin plates (all prime surface). The plates
are either smooth or have some form of corrugation, and they are either flat or wound in

10. 10
an exchanger. Generally, these exchangers cannot accommodate very high pressures,
temperatures, or pressure and temperature differences. Plate heat exchangers (PHEs){ can
be classified as gasketed, welded (one or both fluid passages), or brazed, depending on
the leak tightness required. Other plate-type exchangers are spiral plate, lamella, and
platecoil exchangers.
Gasketed Plate Heat Exchangers
The plate-and-frame or gasketed plate heat exchanger (PHE) consists of a number of thin
rectangular metal plates sealed around the edges by gaskets and held together in a frame.
The frame usually has a fixed end cover (headpiece) fitted with connecting ports and a
movable end cover (pressure plate, follower, or tailpiece). In the frame, the plates are
suspended from an upper carrying bar and guided by a bottom carrying bar to ensure
proper alignment.
Spiral Plate Heat Exchangers
A spiral plate heat exchanger consists of two relatively long strips of sheet metal,
normally provided with welded studs for plate spacing, wrapped helically around a split
mandrel to form a pair of spiral channels for two fluids. Alternate passage edges are
closed. Thus, each fluid has a long single passage arranged in a compact package. To
complete the exchanger, covers are fitted at each end. The basic spiral element is sealed
either by welding at each side of the channel or by providing a gasket (non–asbestos
based) at each end cover to obtain the following alternative arrangements of the two
fluids: (1) both fluids in spiral counterflow; (2) one fluid in spiral flow, the other in
crossflow across the spiral; or (3) one fluid in spiral flow, the other in a combination of
crossflow and spiral flow. The entire assembly is housed in a cylindrical shell enclosed by
two (or only one or no) circular end covers (depending on the flow arrangements above),
either flat or conical.
Lamella Heat Exchangers
A lamella heat exchanger consists of an outer tubular shell surrounding an inside bundle
of heat transfer elements. These elements, referred to as lamellas, are flat tubes (pairs of

11. 11
thin dimpled plates, edge welded, resulting in high-aspect-ratio rectangular channels),.
Lamellas are stacked close to each other to form narrow channels on the shell side.
Lamellas are inserted in the end fittings with gaskets to prevent the leakage from shell to
tube side, or vice versa.
1.2.3.3 Extended Surface Heat Exchangers
The tubular and plate-type exchangers described previously are all prime surface heat
exchangers, except for a shell-and-tube exchanger with low finned tubing. Their heat
exchanger effectiveness is usually 60% or below, and the heat transfer surface area
density is usually less than 700m2/m3 (213 ft2/ft3). In some applications, much higher
(up to about 98%) exchanger effectiveness is essential, and the box volume and mass are
limited so that a much more compact surface is mandated. Also, in a heat exchanger with
gases or some liquids, the heat transfer coefficient is quite low on one or both fluid sides.
This results in a large heat transfer surface area requirement. One of the most common
methods to increase the surface area and exchanger effectiveness is to add fins.
Plate-Fin Heat Exchangers
This type of exchanger has corrugated fins (most commonly having triangular and
rectangular cross sections) or spacers sandwiched between parallel plates (referred to as
plates or parting sheets. Sometimes fins are incorporated in a flat tube with rounded
corners (referred to as a formed tube), thus eliminating the need for side bars. If liquid or
phase-change fluid flows on the other side, the parting sheet is usually replaced by a flat
tube with or without inserts or webs.
Tube-Fin Heat Exchangers
These exchangers may be classified as conventional and specialized tube-fin exchangers.
In a conventional tube-fin exchanger, heat transfer between the two fluids takes place by
conduction through the tube wall. However, in a heat pipe exchanger (a specialized type
of tube-fin exchanger), tubes with both ends closed act as a separating wall, and heat
transfer between the two fluids takes place through this ‘‘separating wall’’ (heat pipe) by
conduction, and evaporation and condensation of the heat pipe fluid.

12. 12
1.2.4 HEAT TRANSFER MECHANISMS [5]
The basic heat transfer mechanisms employed for transfer of thermal energy from the
fluid on one side of the exchanger to the wall (separating the fluid on the other side) are
single-phase convection (forced or free), two-phase convection (condensation or
evaporation, by forced or free convection), and combined convection and radiation heat
transfer. Any of these mechanisms individually or in combination could be active on each
fluid side of the exchanger. Single-phase convection occurs on both sides of the following
two-fluid exchangers: automotive radiators and passenger space heaters, regenerators,
intercoolers, economizers, and so on. Single-phase convection on one side and two-phase
convection on the other side (with or without desuperheating or superheating, and sub
cooling, and with or without non-condensables) occur in the following two-fluid
exchangers: steam power plant condensers, automotive and process/power plant air-
cooled condensers, gas or liquid heated evaporators, steam generators, humidifiers,
dehumidifiers, and so on. Two-phase convection could occur on each side of a two-fluid
heat exchanger, such as condensation on one side and evaporation on the other side, as in
an air-conditioning evaporator. Multi-component two-phase convection occurs in
condensation of mixed vapours in distillation of hydrocarbons. Radiant heat transfer
combined with convective heat transfer plays a role in liquid metal heat exchangers and
high-temperature waste heat recovery exchangers. Radiation heat transfer is a primary
mode in fossil-fuel power plant boilers, steam generators, coal gasification plant
exchangers, incinerators, and other fired heat exchangers.
2 SHELL AND TUBE TYPE HEAT EXCHANGER [6]
Shell And Tube Heat Exchanger is a class of heat exchanger designs. It is the most
common type of heat exchanger in oil refineries and other large chemical processes, and
is suited for higher-pressure applications. As its name implies, this type of heat exchanger
consists of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid runs
through the tubes, and another fluid flows over the tubes (through the shell) to transfer
heat between the two fluids. The set of tubes is called a tube bundle, and may be
composed by several types of tubes: plain, longitudinally finned, etc. Shell-and-tube heat
exchangers contain a large number of tubes (sometimes several hundred) packed in a
shell with their axes parallel to that of the shell. Heat transfer takes place as one fluid
flows inside the tubes while the other fluid flows outside the tubes through the shell.

13. 13
Baffles are commonly placed in the shell to force the shell-side fluid to flow across the
shell to enhance heat transfer and to maintain uniform spacing between the tubes. Despite
their widespread use, shell and tube heat exchangers are not suitable for use in automotive
and aircraft applications because of their relatively large size and weight. Note that the
tubes in a shell-and-tube heat exchanger open to some large flow areas called headers at
both ends of the shell, where the tube-side fluid accumulates before entering the tubes and
after leaving them. Shell-and-tube heat exchangers are further classified according to the
number of shell and tube passes involved. Heat exchangers in which all the tubes make
one U-turn in the shell, for example, are called one-shell-pass and twotube- passes heat
exchangers. Likewise, a heat exchanger that involves two passes in the shell and four
passes in the tubes is called a two-shell-passes an four-tube-passes heat exchanger.
Fig. 2.1 Shell & Tube Heat Exchanger
Fig. 2.2 Main Components of Shell-and-Tube Heat Exchangers

14. 14
2.1 BASIC EQUATIONS IN DESIGN [7]
The rate of heat transfer between the two fluid streams in the heat exchanger, Q, is,
Q = (mcp)h (Tho – Thi) = (mcp)c (Tco – Tci)
Where mcp is the heat capacity rate of one of the fluid streams.
Fig. 2.3 Heat Transfer in heat exchanger
2.2 OVERALL HEAT TRANSFER COEFFICIENT[6]
A heat exchanger typically involves two flowing fluids separated by a solid wall. Heat is
first transferred from the hot fluid to the wall by convection, through the wall by
conduction, and from the wall to the cold fluid again by convection. Any radiation effects
are usually included in the convection heat transfer coefficients.
The thermal resistance network associated with this heat transfer process involves two
convection and one conduction resistances, as shown in Fig. 2.4 . Here the subscripts i
and o represent the inner and outer surfaces of the inner tube. For a double-pipe heat
exchanger, we have Ai =πDiL and Ao =πDoL, and the thermal resistance of the tube wall
in this case is
Rwall =
ln (𝐷𝑜 /𝐷𝑖 )
2π𝑘𝐿
where k is the thermal conductivity of the wall material and L is the length of the tube.
Then the total thermal resistance becomes

15. 15
𝑅 = Rtotal = Ri + Rwall + Ro =
1
ℎ𝑖𝐴𝑖
+
ln (𝐷𝑜 /𝐷𝑖 )
2π𝑘𝐿
+
1
ℎ𝑜𝐴𝑜
Fig. 2.4 Thermal Resistance network associated with Heat Exchanger
The Ai is the area of the inner surface of the wall that separates the two fluids, and Ao is
the area of the outer surface of the wall. In other words, Ai and Ao are surface areas of the
separating wall wetted by the inner and the outer fluids, respectively. When one fluid
flows inside a circular tube and the other outside of it, we have Ai =πDiL and Ao =πDoL,
In the analysis of heat exchangers, it is convenient to combine all the thermal resistances
in the path of heat flow from the hot fluid to the cold one into a single resistance R, and to
express the rate of heat transfer between the two fluids as
Q · =
∆𝑇
𝑅
= UA∆𝑇LMTD =UoAo∆𝑇LMTD
Or
1
𝑈𝐴
=
𝑄
∆𝑇LMTD
where U is the overall heat transfer coefficient, whose unit is W/m2 · °C, which is
identical to the unit of the ordinary convection coefficient h.

16. 16
1
𝑈𝐴𝑠
=
1
𝑈𝐴𝑖
=
1
𝑈𝐴𝑜
= R =
1
ℎ𝑖 𝐴𝑖
+ Rwall +
1
ℎ𝑜 𝐴𝑜
Heat transfer coefficient can be increased on :
 Tube Side by Increasing number of tube and decreasing tube outside diameter
 Shell Side by decreasing the baffle spacing and the baffle cut
However these are the basic factors which must be taken into account for increasing the
value of ‘U’ :-
a) Increase surface area
b) Increase tube length
c) Increase shell diameter
d) increased number of tubes
e) Employ multiple shells in series or parallel
f) Increase LMTD correction factor and heat exchanger effectiveness
g) Use counterflow configuration
h) Use multiple shell configuration
2.3 LOG-MEAN TEMPERATURE DIFFERENCE, LMTD [6]
The temperature difference between the hot and cold fluids varies along the heat
exchanger, and it is convenient to have a mean temperature difference ∆Tlm for use in the
relation
Q=UA∆Tlm (1)
U = Overall heat transfer coefficient
A = surface area of tube
∆Tlm = mean temperature difference
In order to develop a relation for the equivalent average temperature difference between
the two fluids, consider the parallel-flow double-pipe heat exchanger shown in Fig. 2.5 .
Note that the temperature difference ∆Tbetween the hot and cold fluids is large at the inlet
of the heat exchanger but decreases exponentially toward the outlet.

17. 17
Fig. 2.5 Variation of temperature in parallel flow
Assuming the outer surface of the heat exchanger to be well insulated so that any heat
transfer occurs between the two fluids, and disregarding any changes in kinetic and
potential energy, an energy balance on each fluid in a differential section of the heat
exchanger can be expressed as
∆Q = -mh*ch*∆Th = mh*ch(Tho- Thi) (2)
mh = mass flow rate of hot fluid
ch = specific heat capacity of hot fluid
and
∆Q = mc*cc*∆Tc= mc*cc(Tco- Tci) (3)
mc = mass flow rate of cold fluid
ch = specific heat capacity of hot fluid
That is, the rate of heat loss from the hot fluid at any section of a heat exchanger is equal
to the rate of heat gain by the cold fluid in that section. The temperature change of the hot
fluid is a negative quantity, and so a negative sign is added to Eq. (2) to make the heat
transfer rate Q a positive quantity.
Solving the equations above for ∆Th and ∆Tc gives
∆Th= -∆Q /mh*ch (4)

18. 18
and
∆Tc= ∆Q /mc*cc (5)
Taking their difference, we get
∆Th- ∆Tc=∆(Th-Tc) = -∆Q*(1/ mh*ch+1/mc*cc) (6)
The rate of heat transfer in the differential section of the heat exchanger can also be
expressed as:
∆Q =U*(Th-Tc)*∆A (7)
Substituting this equation into Eq. 6 and rearranging gives
∆(Th-Tc)/(Th-Tc) = -U*∆A*(1/ mh*ch+1/mc*cc) (8)
Integrating from the inlet of the heat exchanger to its outlet, we obtain
ln{(Tho– Tco)/(Thi– Tci)} = -U*A*(1/ mh*ch+1/mc*cc) (9)
Finally, solving Eqs. 2 and 3 for mc*ccand mh*chand substituting into
Eq. (9) gives, after some rearrangement
Q =UA∆Tlm (10)
where
∆𝑇LMTD =
∆𝑇2− ∆𝑇1
𝑙𝑛
∆𝑇2
∆𝑇1
(11)
is the log mean temperature difference, which is the suitable form of the average
temperature difference for use in the analysis of heat exchangers. Here ∆T1 and ∆T2
represent the temperature difference between the two fluids at the two ends (inlet and
outlet) of the heat exchanger.
2.4 €-NTU FOR HEAT EXCHANGER ANALYSIS[6]
This method is based on a dimensionless parameter called the heat transfer
Effectiveness €, defined as
€=Q /Qmax
€ =Actual heat transfer rate/Maximum possible heat transfer rate (12)
Q = Actual heat transfer rate
Qmax = Maximum possible heat transfer rate
The actual heat transfer rate in a heat exchanger can be determined from an energy
balance on the hot or cold fluids and can be expressed as
Q = Cc(Tco-Tci) = Ch(Thi-Tho) (13)

19. 19
whereCc = mcccand Ch= mhchCc = mccc are the heat capacity rates of the cold and the hot
fluids, respectively.
Tco = Outlet temperature of cold fluid
Tci = Inlet temperature of cold fluid
Tho = Outlet temperature of hot fluid
Thi = Inlet temperature of hot fluid
∆Tmax= Thi - Tci (14)
The heat transfer in a heat exchanger will reach its maximum value when (1) the cold
fluid is heated to the inlet temperature of the hot fluid or (2) the hot fluid is cooled to the
inlet temperature of the cold fluid. Therefore, the maximum possible heat transfer rate in
a heat exchanger is
Qmax =Cmin*(Thi -Tci) (15)
whereCmin is the smaller of Cc =mcccand Ch=mhch.
The effectiveness of a heat exchanger depends on the geometry of the heat exchanger as
well as the flow arrangement. Therefore, different types of heat exchangers have different
effectiveness relations. Below we illustrate the development of the effectiveness €
relation for the double-pipe parallel-flow heat exchanger.
Equation 9 for a parallel-flow heat exchanger can be rearranged as
ln{(Tho– Tco)/(Thi– Tci)} = -
𝑈∗𝐴
𝐶𝑐
(1 +
𝐶𝑐
𝐶ℎ
) (16)
Also, solving Eq. 13 for Tho gives
Tho= Thi – Cc*(Tco–Tci)/Ch (17)
Substituting this relation into Eq. 16 after adding and subtracting Tci gives
ln[{Thi – Tci+Tci -Tco - Cc*(Tco– Tci)/Ch}/(Thi - Tci) = -
𝑈∗𝐴
𝐶𝑐
(1 +
𝐶𝑐
𝐶ℎ
)
which simplifies to
ln[1-(1+Cc/Ch){(Tco– Tci)/(Thi - Tci)}] = -
𝑈∗𝐴
𝐶𝑐
(1 +
𝐶𝑐
𝐶ℎ
) (18)
We now manipulate the definition of effectiveness to obtain
€ = Q/Qmax= [Cc(Tco -Tci)/Cmin(Thi - Tci)]
Or (Tco -Tci)/Cmin(Thi - Tci) = €*Cmin/Cc
Substituting this result into Eq. 18 and solving for € gives the following relation for the
effectiveness of a parallel-flow heat exchanger:

20. 20
€parallel flow= [1-exp{-
𝑈∗𝐴
𝐶𝑐
(1 +
𝐶𝑐
𝐶ℎ
)}]/{(1 +
𝐶𝑐
𝐶ℎ
)Cmin/Cc} (19)
Taking either Ccor Chto be Cmin (both approaches give the same result), the relation above
can be expressed more conveniently as
€parallel flow = [1-exp[- U*A*(1+Cmin/Cmax)/Cmin]/{1+Cmin/Cmax} (20)
Again Cmin is the smaller heat capacity ratio and Cmax is the larger one, and it
makes no difference whether Cmin belongs to the hot or cold fluid.
N = NTU = U*A/Cmin = U*A/(mcp)min
This quantity is called the number of transfer units NTU.
C = Cmin/Cmax
C = capacity ratio
Where both C and NTU are the dimensionless quantities.
Therefore effectiveness for a double pipe parallel flow is
€ = [1-exp{-N(1+C)}]/(1+C)
Similiarly, for shell and tube having one-shell pass and 2,4,….. tube passes
€ = 2/[1+C+(1+C2)0.5{1+Y}/{1-Y}]
Where A = exp[-N(1+C2)0.5
3 FOULING FACTOR
The performance of heat exchangers usually deteriorates with time as a result of
accumulation of deposits on heat transfer surfaces. The layer of deposits represents
additional resistance to heat transfer and causes the rate of heat transfer in a heat
exchanger to decrease. The net effect of these accumulations on heat transfer is
represented by a fouling factor Rf , which is a measure of the thermal resistance
introduced by fouling. A heat exchanger in a steam power station contaminated with
macrofouling. In applications where it is likely to occur, fouling should be considered in
the design and selection of heat exchangers. In such applications, it may be necessary to
select a larger and thus more expensive heat exchanger to ensure that it meets the design
heat transfer requirements even after fouling occurs. The periodic cleaning of heat

21. 21
exchangers and the resulting down time are additional penalties associated with fouling.
The fouling factor is obviously zero for a new heat exchanger and increases with time as
the solid deposits build up on the heat exchanger surface. The fouling factor depends on
the operating temperature and the velocity of the fluids, as well as the length of service.
Fouling increases with increasing temperature and decreasing velocity. The overall heat
transfer coefficient relation given above is valid for clean surfaces and needs to be
modified to account for the effects of fouling on both the inner and the outer surfaces of
the tube. For an unfinned shell-and-tube heat exchanger, it can be expressed as
1
𝑈𝐴𝑠
=
1
𝑈𝐴𝑖
=
1
𝑈𝐴𝑜
= R =
1
ℎ𝑖 𝐴𝑖
+
𝑅f,i
𝐴𝑖
+
ln (𝐷𝑜 /𝐷𝑖 )
2π𝑘𝐿
+
𝑅f,o
𝐴𝑖
+
1
ℎ𝑜𝐴𝑜
where Ai =πDiL and Ao =πDoL are the areas of inner and outer surfaces, and Rf, i and Rf,
o are the fouling factors at those surfaces.
3.1 Fouling of heat exchangers
3.1 CAUSES OF FOULING[4]
Fouling occurs when impurities deposit on the heat exchange surface. Deposition of these
impurities can be caused by:
 Low wall shear stress
 Low fluid velocities
 High fluid velocities
 Reaction product solid precipitation

22. 22
 Precipitation of dissolved impurities due to elevated wall temperatures
The rate of heat exchanger fouling is determined by the rate of particle deposition less re-
entrainment/suppression. This model was originally proposed in 1959 by Kern and
Seaton.
Crude Oil Exchanger Fouling. In commercial crude oil refining, crude oil is heated from
21 °C to 343 °C prior to entering the distillation column. A series of shell and tube heat
exchangers is typically used to exchange heat between the crude oil and other oil streams,
in order to get the crude to 260 °C prior to heating in a furnace. Fouling occurs on the
crude side of these exchangers due to asphaltene insolubility. The nature of asphaltene
solubility in crude oil was successfully modeled by Wiehe and Kennedy.[15] The
precipitation of insoluble asphaltenes in crude preheat trains has been successfully
modeled as a first order reaction by Ebert and Panchal[16] who expanded on the work of
Kern and Seaton.
Cooling Water Fouling. Cooling water systems are susceptible to fouling. Cooling water
typically has a high total dissolved solids content and suspended colloidal solids.
Localized precipitation of dissolved solids occurs at the heat exchange surface due to wall
temperatures higher than bulk fluid temperature. Low fluid velocities allow suspended
solids to settle on the heat exchange surface. Cooling water is typically on the tube side of
a shell and tube exchanger because it's easy to clean. To prevent fouling, designers
typically ensure that cooling water velocity is greater than 0.9 m/s and bulk fluid
temperature is maintained less than 60 °C. Other approaches to control fouling control
combine the “blind” application of biocides and anti-scale chemicals with periodic lab
testing
3.2 EFFECTS OF FOULING[8]
Fouling has been recognized as a nearly universal problem in design and operation and
affects the operation of equipment in two ways:
 The fouling layer has a low thermal conductivity. This increases the resistance to
heat transfer and reduces the effectiveness of heat exchangers – increasing
temperature

23. 23
 As deposition occurs, the cross-sectional area is reduced, which causes an increase
in pressure drop across the apparatus
3.3 COST DUE TO FOULING[8]
Despite the enormous costs associated with fouling, only very limited research has been
done on this subject. Reliable knowledge of fouling economics is important when
evaluating the cost efficiency of various mitigation strategies. The total fouling-related
cost can be broken down into three main areas:
 Capital expenditure, which includes excess surface area (10-50%, with an average
around 35%), costs for stronger foundations, provisions for extra space, increased
transport and installation costs.
 Extra fuel costs, which arise if fouling leads to extra fuel burning in furnaces or
boilers or if more secondary energy such as electricity or process steam is needed
to overcome the effects of fouling.
 Production losses during planned and unplanned plant shutdowns due to fouling.
These are often considered to be the main costs of fouling and are very difficult to
estimate.
According to Pritchard and Thackery (Harwell Laboratories), about 15% of the
maintenance costs of a process plant can be attributed to heat exchangers and boilers, and
of this, half is probably caused by fouling. Fouling can be very costly in refinery and
petrochemical plants since it increases fuel usage, results in interrupted operation and
production losses, and increases maintenance costs.
4 CASE STUDY
The shell and tube Heat Exchanger in LPG- I Recovery is used for the purpose of cooling
the propane gas obtained from the compressor. This propane gas is chilled to produce
refrigerant in the so called Propane Refrigerant Condenser. Our study is based on th
Parallel flow, Indirect- contact type Tubular Heat exchanger E-112.
Here, Water at atmospheric temperature is used as a cooling fluid whereas Propane gas is
the hot fluid which is passing through the shell side. The tube containing water is 4-pass.

24. 24
We are calculating the effectiveness of E-112 by two methods:
1) Based on Design data sheet (as shown in Fig. 4.1)
2) Based on present operating condition
Fig. 4.1 Design Data Sheet of E-112

25. 25
4.1 ACCORDING TO DESIGN DATA SHEET E-112[9]
Given Data:
Thi = 70 ℃ Tci =33℃
Tho = 40 ℃ Tco =37 ℃
∆Th =30 ℃ ∆Tc =4 ℃
mh = 101985*1.1 Kg/hr =101985*1.1 /3600 Kg/s
mh =31.16 Kg/s
mc = 2266400*1.1 Kg/hr = 2266400*1.1/3600 Kg/s
mc = 692.5 Kg/s
Calculation:
we know that,
Q = mh*ch*∆Th = mc*cc*∆Tc
Ch =mhch Cc =mccc = 4186*692.5 KW/℃
Ch = 2898.851 *4/30 KW/℃ Cc = 2898.851 KW/℃
Ch = 386.513 KW/℃
Q = Cc*∆Tc =11595.40 KW
C = Cmin / Cmax = Ch/Cc = 386.513 KW/℃/2898.851 KW/℃
C = 0.133
The correction factor F for multipass tubes can be calculated or find from the graph.
P = (Tco- Tci)/( Thi- Tci) = (37-33)/(70-33)
P = 0.108
Z = Cc/Ch = 2898.851 KW/℃/386.513 KW/℃ Z = 7.5

26. 26
Accoding Z and p value F = 0.93
Q = UAF∆Tlm
∆Tlm = (∆T1-∆T2)/ln(∆T1/∆T2)
∆T1 = Thi – Tci = 70 ℃ - 33℃ =37 ℃
∆T2 = Tho – Tco = 40 ℃ - 37℃ = 3℃
∆Tlm = (37 ℃ - 3℃)/ln(37/3) = 13.53℃
NTU = N = UA/ Cmin = Q/(F*∆Tlm* Cmin) = 11595.40/(386.513*13.53*.93)
N = 2.38
€ = Effectiveness of heat exchanger
€ =
2
1+C+(√(1+C 2)∗{(1+ e^[−N](√(1+C 2) )/ (1− e^[−N](√(1+C 2) )}
€ =
2
1+0.133+(√(1+0.133 2)∗{(1+ 𝑒^[−2.38](√(1+0.133 2) )/(1− 𝑒^[−2.38](√(1+0.133 2) )}
€ = 0.853
€ = Qact/Qmax
Qmax = Qact/€ = 11595.40 KW/0.853
Qmax = 9780.37 KW
Hence, the maximum effectiveness is 0.853 under specified conditions of Design data
Sheet.
4.2 PRESENTLY OPERATING CONDITION [9]
As per the data’s collected from RPS unit from Mr. JVN Rao. The present operating
scenario for E-112 is given as follows:
Given Data:
Thi = 65 ℃ Tci =28 ℃
Tho = 46.5 ℃ Tco =37 ℃

27. 27
∆Th =18.5 ℃ ∆Tc =9 ℃
mh = 11250 Nm3/hr =11250*28.2/3600 Kg/s
mh =88.125 Kg/s
mc =500 m3/hr = 500*1000/3600 Kg/s
mc = 138.89 Kg/s
Calculation:
we know that
Q = mh*ch*∆Th = mc*cc*∆Tc
Ch =mhch Cc =mccc = 4186*138.89 KW/℃
Ch = 581.393*9/18.5 KW/℃ Cc = 581.393 KW/℃
Ch = 282.84 KW/℃
Q = Cc*∆Tc =5232.5KW
C = Cmin / Cmax = Ch/Cc = 282.84/581.393
C = 0.486
The correction factor F for multipass tubes can be calculated or find from the graph.
P = (Tco- Tci)/( Thi- Tci) = (37-28)/(65-28)
P = 0.243
Z = Cc/Ch = 581.393/282.84
Z = 2.05
Accoding Z and p value F = 0.94
Q = UAF∆Tlm
∆Tlm = (∆T1-∆T2)/ln(∆T1/∆T2)

28. 28
∆T1 = Thi – Tci = 65.C – 28.C = 37.C
∆T2 = Tho – Tco = 46.5.C – 37.C = 9.5℃
∆Tlm = (37.C - 9.5.C)/ln(37/9.5) = 20.23℃
NTU = N = UA/ Cmin = Q/(F*∆Tlm* Cmin) = 5232.5/(282.84*20.23*.94)
N = 0.973
€ = Effectiveness of heat exchanger
€ =
2
1+C+(√(1+C 2)∗{(1+ e^[−N](√(1+C 2) )/ (1− e^[−N](√(1+C 2) )}
€ =
2
1+0.486+(√(1+0.486 2)∗{(1+ 𝑒^[−0.973](√(1+0.486 2) )/ (1− 𝑒^[−0.973](√(1+0.486 2) )}
€ = 0.535
€ = Qact/Qmax
Qmax = Qact/€ = 5232.5 KW/0.535
Qmax = 9780.37 KW
The effectiveness obtained under working condition is 0.535 which is 62.7 % of the
effectiveness obtained from the Design Data Sheet.
CONCLUSION
For efficiency, heat exchangers are designed to maximize the surface area of the wall
between the two fluids, while minimizing resistance to fluid flow through the exchanger.
The exchanger's performance can also be affected by the addition of fins or corrugations
in one or both directions, which increase surface area and may channel fluid flow or
induce turbulence.The following observations can be made by the theoretical calculations
and observations:
1. The heat exchanger thermal effectiveness increases with increase in value of NTU
for a specified C.
2. The heat exchanger thermal effectiveness increases with decrease in value of C for
a specified NTU.[10]

29. 29
In second case effectiveness is more since amount of cold fluid (water) is much more
than hot fluid (propane).
1. Here we can increase the effectiveness of heat exchanger by increasing mass flow
rate of water.
2. Scale formation should be least as these are bad conductor of heat transfer. So we
can minimize this by using pure water.
3. Effectiveness may also increase by using counter flow. As counter follow gives
the highest effectiveness for given NTU and C. parallel flow has least
effectiveness.

30. 30
REFERENCES
[1] Shah, R. K., and Sekulic, D. P. (2003) "Fundamentals of Heat Exchanger Design"
(John Wiley and Sons)
[2] http://www.scribd.com/doc/41150335/Heat-Exchanger
[3] http://www.brazetek.com/articles/69-classification-of-heat-exchangers-according-to-
transfer-process
[4] http://en.wikipedia.org/wiki/Heat_exchanger
[5] http://www.scribd.com/doc/67126715/18/CLASSIFICATION-ACCORDING-TO-
HEAT-TRANSFER-MECHANISMS
[6] Cengel, Yunus A. and Ghajar, Afshin J. "Heat and Mass Transfer: Fundamentals and
Applications." , McGraw-Hill, 4th Edition, 2010.
[7] http://www.scribd.com/doc/17508927/Heat-Exchanger-Notes
[8] http://www.biodescale.com/water_scale.htm
[9] Pitts, Donald. Schaum's outline of theory and problems of heat transfer. New York:
McGraw-Hill, 1998.
[10] Sadik Kakaç and Hongtan Liu (2002). Heat Exchangers: Selection, Rating and
Thermal Design (2nd Edition ed.). CRC Press. ISBN 0849309026.