IRJET- Heat Exchanger Analysis and Method to Improve its Effectiveness

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 07 | July 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 1185
Heat Exchanger Analysis and Method to Improve its Effectiveness
Ujjwal Anand Jain
1
, Dr. Jeetendra K Tiwari
2
, Abhishek Singh
3
1M.Tech. Student (Thermal Engineering), Department of Mechanical Engineering, SSGI, Bhilai, Chhattisgarh, India
2,3Asst. Professor, Department of Mechanical Engineering, SSGI, Bhilai, Chhattisgarh, India
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Abstract - Heat exchanger has been a topic of interest
because of its various applications in power plant,
refrigeration, air conditioning etc. Heat exchanger is an
important unit contributes to efficiency and safety of many
processes. Heat exchanger analysis is quite complicated and
involves flow parameters and geometry quite heavily. Some
simpler methods of analysis are the Log-Mean Temperature
Difference (LMTD) method and the Number of Transfer Unit
(NTU) method. In this project I used this analysis method for
our calculation, in this project I varies the mass flow rate of
hot fluid and mass flow rate of cold fluid of counter flow heat
exchanger by keeping the same inlet temperature of hot
fluids and cold fluid and see its effect on various parameter
such as Log-Mean Temperature Difference (LMTD) , Number
of Transfer Unit (NTU) , Effectiveness of heat exchanger ,
Overall heat transfer coefficient , Capacity Ratio etc then we
Draw various curve of (a) Mass flow rate of fluids Vs
Number of Transfer Unit (NTU) , (b) Mass flow rate of fluids
Vs Log-Mean Temperature Difference (LMTD) (c) Mass flow
rate of fluids Vs Effectiveness. When I decreases the mass
flow rate of both hot and cold fluid I observe that the
effectiveness of counter flow heat exchanger increases.
Key Words: Effectiveness, NTU, Flow rate of mass
1. INTRODUCTION
Heat Exchanger is a steady flow, adiabatic open system in
which two flowing fluids exchange or transfer heat
between them without loosing or gaining any heat from
the ambient.
Heat exchangers are practical apparatus used to transfer
energy from one fluid to another to get fluid streams to the
right temperature for the next process reactions often
require feeds at high temperature.
1.1 Classification of Heat exchanger
Following are the classification of heat exchanger,
1.1.1 Direct Transfer type HEs. :-
In this both hot cold fluids, do not have any physical
contact between them but the transfer of heat occurs b/w
them through pipe wall of separation.
1.1.2 Direct Contact type HEs. :-
In this HE, both hot and cold fluids physically mix up with
each other and exchanger heat between them.
1.1.3 Regenerative or storage type of H.E
Hot and Cold fluids alternatively flow through HE, hot
fluids heating matrix and cold fluids picking up heat from it.
2. THEORY
2.1 Classification of Direct Transfer Type HEs
There are three types of direct transfer heat exchangers
mainly use in different application,
1. Parallel flow H.E - Hot & cold fluids
travel in the same direction.
2. Counter flow H.E- Hot & cold fluids flow
in opposite direction w. r. t. each other.
3. Cross flow H.E - Hot & cold fluids travel
in perpendicular direction w.r.t. each
other.
Configuration
Fig-1- Different flow arrangement

3. Specification of Various Parts of Heat
Exchanger-
The flow rate of mass of both hot and cold streams, their
terminal temperatures and fluid properties are the
primary inputs of thermal design of heat exchangers.
3.1 Shell
Shell is the pot for the fluid and the tubes are placed
inside the shell. Shell diameter must be elected in such a
way to give a seal fit of the tubes.
3.2 Tube
Tube OD of 0.75 inc and 1 inc are very common to design
a compact heat exchanger. The most pleasant condition
for heat transfer is to have the utmost number of tubes in
the shell to increase turbulence.
3.3 Tube pitch, tube-layout and tube-count
Tube pitch is the smallest centre to centre distance
between the adjacent tubes. The tubes are generally
placed in square or triangular patterns (pitch).
3.4 Tube passes
The number of passes is chosen to get the required tube
side fluid velocity to obtain greater heat transfer co-
efficient and also to reduce scale formation.
Fig 2- Dimensions and pitch type
3.5 Tube sheet
The tubes are set with tube sheet that creates the
blockade between the tube and shell fluids. The tubes can
be joined with the tube sheet using ferrule and a
malleable metal packing ring.
3.6 Baffles
Baffles are used to raise the fluid speed by diverting the
flow across the tubes to obtain higher transfer co-
efficient. The distance between neighboring baffles is
called baffle-spacing.
Fig 3- Different types of baffles
3.7 Fouling Considerations
The majority of the process fluids in the exchanger foul the
heat transfer surface. The material deposited decreases the
effective heat transfer rate due to relatively low thermal
conductivity. Therefore, net heat transfer rate with clean
surface should be higher to compensate the reduction in
performance during operation.
Fig 4 – Fouling Factors of different fluids
3.8 Selection of fluids for tube and the shell side
The routing of the shell side and tube side fluids has
significant effects on the heat exchanger design
Fig5- General guidelines for positioning the fluids

4. METHODOLOGY
Here all the value is calculated using counter flow heat
exchangers of our college.
T1=46
t2= 38oC
T2
t1=10oC
Given data,
T1 = 46oC
t1 = 10oC
t2 = 38oC
T2 = ?
ρwater = 1000 kg/m3
mc = 0.19 kg/s
mh = 0.25kg/s
Cc = Ch = 4200 J/kg-K
From energy balance,
mc Cc (t2-t1 ) = mh Ch (T1 – T2)
0.19 (38-10) = 0.25 (46 – T2)
T2 = 24.72oC
1 = T1 – t2 = 46 – 38 = 8oC
2 = T2 – t1 = 24.72 – 10 = 14.72 oC
LMTD =
 


=
=11.02 oC
Q = UA m
Q = mc Cc (t2 – t1 )
Q = 0.19 x 4200 (38 - 10)
Q = 22344.0 W
22344.0 = UA x 11.02
UA = 2027.586 W/K
NTU = UA/Cmin
Cmin = mc x Cc = 0.19 x 4200 = 798 W/K
Cmax = mh x Ch = 0.25 x 4200 = 1050 W/K
Effectiveness = Qact / Qmax
Qmax = Cmin (T1 – t1 )
Qmax = 798 (46 – 10)
Qmax = 28728 W
Effectiveness = 22344/28728
Effectiveness = 0.778
Specification of heat exchanger pipe
Outer diameter of pipe (do) = 15 mm
Length of pipe (L) = 4.5 m
Number of pipe (n) = 3
Number of pass (p) = 3
Area of surface of heat exchanger (A) = d L n p
= x .015 x 4.5 x 3 x 3
= 1.908 m2
Their for,
UA = 2027.5 W/K
U = 1062.3428 W /m2K
After above calculation,
T2 = 24.72oC
LMTD = 11.02oC
Qact = 22344 W
Qmax = 28278 W
NTU = 2.54
C = 0.76
UA = 2027.58 W/K
Area (A) = 1.908 m2
Over all heat transfer coefficient (U) = 1062.3428 W /m2K
Now I am changing the flow rate of mass with the help of
valve, we are decreasing the flow rate of mass of hot and
cold fluid and study its effect on various parameters.
Following values are obtained,
Case 1
Now I am decreasing the flow rate of mass of both hot as
well as cold fluid by keeping the inlet condition similar to
previous.
mc = 0.17 kg/s
mh = 0.23 kg/s
After calculation we get following value,
Qact = 20434.76 W
NTU = 2.679

Case 2
previous.
mc = 0.15 kg/s
mh = 0.21 kg/s
Qact = 18370 W
NTU = 2.856
Over all heat transfer coefficient (U) = 943 W /m2K
Case 3
previous.
mc = 0.13 kg/s
mh = 0.19 kg/s
Qact = 16117.92 W
NTU = 2.92
5. RESULT AND DISCUSSIONS
5.1 EFFECT ON EFFECTIVENESS
1. When I decrease flow rate of mass of hot fluid from
0.25 to 0.23 and decrease the flow rate of mass of cold
from 0.19 to 0.17 by keeping the inlet temperature of hot
and cold fluids same then the effectiveness of counter
flow heat exchanger increases from 0.77 to 0.795.
2. When I decrease the flow rate of mass of hot fluid from
Chart 1 - Effectiveness Vs Mass flow rate of cold fluid
Chart 2 - Effectiveness Vs Mass flow rate of hot fluid
5.2 EFFECT ON ACTUAL HEAT TRANSFER RATE
0.25 to 0.23 and decrease the flow rate of mass of cold from
0.19 to 0.17 by keeping the inlet temperature of hot and
cold fluids same then the heat transfer rate of counter flow
heat exchanger decreases from 22344 W to 20434.76 W.
heat exchanger decreases from 20434.76 W to 18370 W.
heat exchanger decreases from 18370 W to 16117 W.

Chart 3-Heat transfer rate Vs Mass flow rate of cold fluid
Chart 4- Heat transfer rate Vs Mass flow rate of hot fluid
5.3 EFFECT ON NTU
1. When I decrease flow rate of mass of hot fluid from
and cold fluids same then the NTU of counter flow heat
exchanger increases from 2.541 to 2.679
exchanger increases from 2.679 to 2.856.
0.21 to 0.19 and decrease flow rate of mass of cold from
cold fluids same then the NTU of counter flow heat
exchanger increases from 2.856 to 2.92.
Chart 5- NTU Vs Mass flow rate of cold fluid
Chart 6- NTU Vs Mass flow rate of hot fluid
6. CONCLUSIONS
6.1 EFFECTIVENESS
a. When I decrease the flow rate of mass of hot fluid from
cold fluids same then the effectiveness of counter flow heat
exchanger increases by 3.24%.
b. When I decrease the flow rate of mass of hot fluid from
exchanger increases by 1.88 %.
c. When I decrease the flow rate of mass of hot fluid from
6.2 NTU (Number of transfer unit)
cold fluids same then the NTU of counter flow heat

exchanger increases 6.61%
6.3 ACTUAL HEAT TRANSFER RATE
and cold fluids same then the heat transfer rate of
counter flow heat exchanger decreases by 8.54%.
counter flow heat exchanger decreases by 11.5%.
c. When I decrease the flow rate of mass of hot fluid from
counter flow heat exchanger decreases from by 12.26%.
7. REFERENCES
1. R. Hosseini, A. Hosseini-Ghaffar, M. Soltani,
“Experimental determination of shell side heat transfer
coefficient and pressure drop for an oil cooler shell and
tube heat exchanger with three different tube bundles”,
Applied Thermal Engineering 27 (2007) 1001–1008.
2. Andre L.H. Costa, Eduardo M. Queiroz, “Design
optimization of shell-and-tube heat exchangers”, Applied
Thermal Engineering 28 (2008) 1798–1805.
3. Jiangfeng Guo, Lin Cheng, Mingtian Xu, “Optimization
design of shell and tube heat exchanger by entropy
generation minimization and genetic algorithm”, Applied
Thermal Engineering 29 (2009) 2954–2960.
4. Professor Sunilkumar Shinde, Mustansir Hatim Pancha
/ International Journal of Engineering Research and
Applications (IJERA) ,”Comparative Thermal performance
of shell and tube heat Exchanger with continuous helical
baffle using “, Vol. 2, Issue4,July-August 2012.
5. Thirumarimurugan, M., Kannadasan, T., Ramasamy, E.,
Performance Analysis of Shell and Tube Heat Exchanger
Using Miscible System, American Journal of Applied
Sciences 5 (2008), pp. 548-552.
6.”Heat Transfer Coefficient”. Wikipedia. Wikimedia
Foundation, 11 May 2014. Web. 13 Nov. 2014.
7.”Overall Heat Transfer Coefficients.” Overall Heat
Transfer Coefficients, Blackmonk En-
gineering. N.p., n.d. Web. 12 Nov. 2014. http:
//blackmonk.co.uk/2009/10/22/overall heat transfer
coefficients/.
8. Douglas, John F.”Chapter 11 (Section 11 - 11.7).” Fluid
Mechanics. Harlow, England :Pearson /p rentice Hall, 2005.
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IRJET- Heat Exchanger Analysis and Method to Improve its Effectiveness