This document summarizes different types of heat exchangers and heat transfer concepts. It discusses four main types of heat exchangers: double pipe, shell and tube, plate, and cross flow. It also covers key heat transfer equations like log mean temperature difference (LMTD) and heat exchanger effectiveness. Important heat exchanger design parameters like number of transfer units (NTU), heat capacity ratio, and fouling factors are defined. Tables of typical fouling coefficients and overall heat transfer coefficients are also included.

1. BIRLA VISHVAKARMA
MAHAVIDYALAYA
VALLABH VIDYANAGAR
Dept.-Production engineering
Subject:-Engineering thermodynamics &
heat transfer
Faculty name:-Dr. Manish mehta
Prepared by….
140080125021- Brijesh patel
140080125022- Dhruv patel
140080125023- Hardik patel
140080125024- Harshil patel
Group no.14

2. HEAT EXCHANGERS
• Types of heat exchangers:
1. Double pipe heat exchanger
2. Shell and tube exchanger
3. Plate-type exchanger
4. Cross flow exchanger
• The function of a heat exchanger is to increase
the temperature of a cooler fluid and decrease
that of a hotter fluid.

3. 1. Double pipe heat exchanger
• The simplest configuration in fig.
• One fluid flow through the inside pipe, and the second fluid
flows through the annular space between the outside and the
inside pipe.
• The fluid can be in co-current or countercurrent flow.
• Useful for small flow rates and when not more than 100 – 150
ft2
of surface is required.

4. 2. Shell and Tube Exchanger
• The most important type of exchanger in use in oil refineries
and larger chemical processes and is suited for higher-pressure
applications.
• Useful for larger flow rates as compared to double pipe heat
exchanger.
• The simplest configuration: 1-1 counterflow exchanger (one
shell pass and one tube pass) – refer to Figure 1.2.
• 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.

5. • The cold fluid enters and flow inside through all the tubes in
parallel in one pass
• The hot fluid enters at the other end and flow counterflow across
the outside the tubes in the shell side.
• Cross-baffles – increase the shell side heat transfer coefficient
Fig 1.2 Shell and tube heat exchanger
(1 shell pass and 1 tube passes (1-1 exchanger))

6. Fig 1.3 Shell and tube heat exchanger
(1 shell pass and 2 tube passes (1-2 exchanger))
• The liquid on the tube side flows in two passes
• The shell-side liquid flows in one pass
• In the first pass of the tube side, the cold fluid is flowing
counterflow to the hot shell-side fluid
• In the second pass of the tube side, the cold fluid flows in parallel
(co-current)

7. 3. Plate heat exchanger
• Use metal plates to transfer heat between two fluids
• Consist of many corrugated stainless steel sheets separated
by polymer gaskets and clamped in a steel frame.
• The corrugation induce turbulence for improve heat transfer
• The space between plates is equal to the depth of the
corrugations (2 - 5 mm)
• The plates are compressed in a rigid frame to create an
arrangement of parallel flow channels with alternating hot
and cold fluids.

8. • A common device used to heat or cool a gas such as air
• One of the fluids, which is a liquid, flows inside through the tubes,
and the exterior gas flows across the tube bundle by forced or
sometimes natural convection.
4. Cross-flow exchanger
Fig. 1.4 Cross-flow heat exchangers: (a) one fluid mixed (gas)
and one fluid unmixed; (b) both fluids unmixed.

9. • The fluid inside the tubes is considered to be unmixed, since it is
confined and cannot mix with any other stream.
• The gas flow outside the tubes is mixed, since it can move about
freely between the tubes, and there will be a tendency for the gas
temperature to equalize in the direction normal to the flow.
• For the unmixed fluid inside the tubes, there will be a
temperature gradient both parallel and normal to the direction of
flow.
• A second type of cross-flow heat exchanger shown in Fig. 1.4(b)
is typically used in air- conditioning and space-heating
applications.
•In this type the gas flows across a finned-tube bundle and is
unmixed, since it is confined in separate flow channels between
the fins as it passes over the tubes. The fluid in the tubes is
unmixed.

10. Log Mean Temperature Difference (LMTD)
•For counter-current flow, LMTD for 1-1 exchanger with one shell
pass and one tube pass is given by:
Where:
ΔTlm = log mean temperature difference
ΔT1 = T1- t1
ΔT2=T2–t2
T1= inlet shell-side fluid temperature
T2= outlet shell-side fluid temperature
t1= outlet tube-side temperature
T1
t1
T2
t2
Temperature cross
----------------- Eq. (1)
ΔT1 ΔT2






∆
∆
∆−∆
=∆
2
1
21
ln
T
T
TT
Tlm

11. •For co-current flow, LMTD for 1-1 exchanger with one shell pass
and one tube pass is given by:
Where:
ΔTlm = log mean temperature difference
ΔT1 = T1 - t1
ΔT2=T2-t2
T1= inlet shell-side fluid temperature
T2= outlet shell-side fluid temperature
t1= inlet tube-side temperature
t2= outlet tube-side temperature
T1
t1
T2
t2
Temperature cross
----------------- Eq. (2)






∆
∆
∆−∆
=∆
2
1
21
ln
T
T
TT
Tlm
ΔT1 ΔT2

12. LMTD in Multi pass Exchanger
• Multipass exchangers have more tube passes than shell passes.
• The LMTD as given in Eq (1 & 2) does not apply in this case
and it is customary to define a correction factor, FT.
• The relationship between LMTD and FT is define as below:
Where is define as the correct mean temperature drop.
• The general equation for heat transfer across surface of an
exchanger is:
lmTm TFT ∆=∆
mT∆
moomii TAUTAUq ∆=∆=
---------------- Eq. (3)
----------------- Eq. (4)

13. • Figure 4.9-4 (Geankoplis, 4th
ed.) shows the correction factor to
LMTD for:
a) 1-2 and 1-4 exchangers
b) 2-4 exchangers
• Two dimensionless ratios are used as follows:
• Using the nomenclature of Eqs. (5 & 6), the of Eq. (1) can be
written as:
cico
hohi
TT
TT
Z
−
−
=
cihi
cico
TT
TT
Y
−
−
=
( ) ( )






−
−
−−−
=∆
ciho
cohi
cihocohi
lm
TT
TT
TTTT
T
ln
----------------- Eq. (5 & 6)
---------------- Eq. (7)

14. Figure 4.9-4(a) Correction factor to LMTD for 1-2 and 1-4
exchangers

15. Figure 4.9-4(b) Correction factor to LMTD for 2-4
exchangers

16. Heat Exchanger Effectiveness – NTU Method
•The LMTD is used in equation if the inlet and outlet
temperatures of the two fluids are known and can be determined
by a heat balance.
•The surface area can be determined if U is known.
•However, when the temperature of the fluids leaving the
exchanger are not known, the tedious trial-and-error procedure is
necessary.
•To solve these cases, a method called the heat exchanger
effectiveness is used which does not involve any of the outlet
temperatures.
•The Effectiveness – NTU (Number of Transfer Unit) method is a
procedure for evaluating the performance of heat exchangers if
heat transfer area, A and construction details are known .
lmTUAq ∆=

17. •Heat balance for the cold (C ) and hot (H ) fluids is:
•Calling
, then CH > CC
•Designate CC as Cmin or minimum heat capacity.
•If there is an infinite area available for heat transfer, TCo = THi, the
effectiveness ε is
•If the hot fluid is the minimum fluid, THo = TCi, and
)(
)(
)(
)(
min
max
CiHi
HoHi
CiHiC
HoHiH
TTC
TTC
TTC
TTC
−
−
=
−
−
=ε
)(
)(
)(
)(
min
max
CiHi
CiCo
CiHiH
CiCoC
TTC
TTC
TTC
TTC
−
−
=
−
−
=ε
)()()()( CoCiCpHoHiHp TTmCTTmCq −=−= ----------- Eq. (8)
CCp
HHp
CmC
CmC
=
=
)(
)(
----------- Eq. (10)
----------- Eq. (9)

18. • In both equations the denominators are the same and the
numerator gives the actual heat transfer:
• Note that Eq. (11) uses only inlet temperatures.
• For the case of a single-pass, counterflow exchanger, combining
Eqs (9 & 10):
• We consider first the case when the cold fluid is the minimum
fluid. Using the present nomenclature,
)(min CiHi TTCq −= ε
----------- Eq. (13)
----------- Eq. (12)
----------- Eq. (11)
)(
)(
)(
)(
minmin CiHi
CiCoC
CiHi
HoHiH
TTC
TTC
TTC
TTC
−
−
=
−
−
=ε
( ) ( ) ( )
( )
( )





−
−
−−−
=−=
CoHi
CiHo
CoHiCiHo
CiCoC
TT
TT
TTTT
UATTCq
ln

19. •Combining Eq. (8) with the left side of Eq. (12) and solving for
THi.
•Subtracting TCo from both sides,
•From Eq. (8) for Cmin = CC and Cmax = CH ,
•This can be rearranged to give the following:
)(1
1
)(
1
CiCoCiCoCoCiCoHi TTTTTTTT −





−=−+−=−
εε
)(
1
CiCoCiHi TTTT −+=
ε
----------- Eq. (14)
----------- Eq. (16)
----------- Eq. (15)
----------- Eq. (17)
)(
max
min
CiCoHiHo TT
C
C
TT −−=
)(
max
min
CiCoCiHiCiHo TT
C
C
TTTT −−−=−

20. •Substituting Eq. (14) into Eq. (17),
•Finally, substituting Eq. (15) and Eq. (18) into Eq. (13),
rearranging, taking the antilog of both sides, and solving for ε,
•We define NTU as the number of transfer unit as follows:
•The same results would have been obtained if CH= Cmin
( ) )(
1
max
min
CiCoCiCoCiHo TT
C
C
TTTT −−−=−
ε
----------- Eq. (19)
----------- Eq. (18)
----------- Eq. (20)












−−−












−−−
=
max
min
minmax
min
max
min
min
1exp1
1exp1
C
C
C
UA
C
C
C
C
C
UA
ε
UA
NTU
minC
=

21. •For parallel flow we obtain:
•Figure 4.9-7 shows the heat exchanger effectiveness, ε for
a)counterflow exchanger – using Eq. (19)
b)parallel flow exchanger – using Eq. (21)
max
min
max
min
min
1
1exp1
C
C
C
C
C
UA
+












+−−
=ε ----------- Eq. (21)

22. Figure 4.9-7 Heat exchanger effectiveness, ε:
a)counter flow exchanger; b)parallel flow exchanger

23. Fouling Factors and Typical Overall heat
transfer coefficient
• After a period of operation, the heat transfer surface for a heat
exchanger may become coated with various deposits present in the
flow system, dirt, soot or the surface may become corroded as a
result of the interaction between the fluids and the material used
for construction of the heat exchanger.
• Biological growth such as algae can occur with cooling water in
the biological industries.
• These deposits offer additional resistance to the flow of heat and
reduce the overall heat transfer coefficient U.
• To avoid or lessen these fouling problems, chemical inhibitors are
often added to minimize corrosion, salt deposition and algae
growth.
• It is necessary to oversize an exchanger to allow for the reduction
in performance during operation.

24. •The effect of fouling is allowed for in design by including the
resistance of the fouling on the inside and outside of the tube in Eq.
(22).
Where:
hdi = fouling coefficient for inside of the tube (W/m2
.K)
hdo = fouling coefficient for outside of the tube (W/m2
.K)
•Fouling coefficients or fouling factors must be obtained
experimentally by determining the value of U for both clean and
dirty conditions in the heat exchanger. The fouling factor, Rf is
define as:
( )
doo
i
oo
i
AA
iio
dii
i
hA
A
hA
A
Ak
Arr
hh
U
++
−
++
=
lm
11
1
----------- Eq. (22)
cleandirty
f
UU
R
11
−= ----------- Eq. (23)

25. •Typical Fouling Coefficients is shown in Table 1 and the typical
values of overall heat transfer coefficients are given in Table 2.
Table 1 Typical Fouling Coefficients
hd
(W/m2
.K)
hd
(btu/h.ft2
.0
F)
Distilled and seawater
City water
Muddy water
Gases
Vaporizing liquids
Vegetable and gas oils
11350
5680
1990-2840
2840
2840
1990
2000
1000
350-500
500
500
350

26. THANK YOU……….