Analysis of Heat Exchange Efficiency in a Double
Pipe Heat Exchanger
James G. Dominguez, ChE-3A
Bicol University, Legazpi City Philippines; jamesgutlay.dominguez@bicol-u.edu.ph
MATERIALS & METHODS
INTRODUCTION
Heat exchangers are used in various industrial processes,
facilitating the transfer of heat between fluids. The efficiency
of a heat exchanger is crucial for optimizing energy usage and
process performance.
A double-pipe heat transfer exchanger consists of one or more
pipes placed concentrically inside another pipe of a larger
diameter with appropriate fittings to direct the flow from one
section to the next. One fluid flows through the inner pipe
(tube side), and the other flows through the annular space
(annulus). The inner pipe is connected by U-shaped return
bends enclosed in a return-bend housing. Double-pipe heat
exchangers can be arranged in various series and parallel
arrangements to meet pressure drop. The major use of the
double-pipe heat exchanger is the sensible heating or cooling
process of fluids where small heat transfer areas (up to 50 m2)
are required. This configuration is also very suitable for one
or both of the fluids at high pressure because of the smaller
diameter of the pipes. The major disadvantage is that they are
bulky and expensive per unit of heat transfer surface area.
Heat exchangers works by exchanging the heat between two
fluids of different temperatures that are separated by a solid
wall. The temperature gradient or differences in temperature
is the driving force for heat transfer. Conduction occurs as the
heat from the higher temperature fluid passes through the
solid pipe wall. Meanwhile convection occurs as heat is
transferred through the pipe wall then the flow of the cooler
stream removes the transferred heat. This maintains a
temperature gradient between the two fluids. Flow in a
double-pipe heat exchanger can be co-current or
countercurrent. There are two flow configurations: co-current
is when the flow of the two streams is in the same direction.
Countercurrent is when the flow of the streams is in opposite
directions.
In this experiment, we investigate the heat exchange
efficiency of a double pipe heat exchanger, a common and
compact design used in many applications. By analyzing
temperature changes and flow rates of hot and cold fluids, we
aim to quantify the effectiveness of heat transfer within the
equipment. The experiment will consists of sets of
experiments using cold, tap and hot water.
I. Materials
•
Double pipe heat exchanger apparatus
•
Hot water
•
Cold water
•
Tap water
•
Thermometer
•
Stopwatch
II. Methodology
1.
The double pipe heat exchanger apparatus was
repaired.
2.
The necessary materials were gathered. Hot water
is obtained through heating tap water and cold
water is obtained through pouring ice to tap water.
3.
The temperatures were measured and then set-up.
4.
For cold water and tap water countercurrent flow:
•
The hotter liquid was circulated through the inner
pipe of the heat exchanger.
•
The colder liquid was circulated through the
outer pipe in the other side of the equipment.
•
Initial temperatures of both liquid streams were
recorded.
•
Flow rates of hot and cold water were adjusted to
be equal.
5.
Repeat step four for countercurrent flow and coldhot water co-current and countercurrent flow
6.
Data Collection:
•
Thermometers were placed in the outlet of both
hot and cold-water streams to measure the
temperature change.
•
The temperature reading was recorded after 15
minutes.
7.
Calculation:
•
Heat transfer rate (Q) was calculated using the
energy balance equation:
𝑄𝑄 = 𝑚𝑚𝑐𝑐 ⋅ 𝑐𝑐𝑐𝑐 ⋅ (𝑇𝑇𝑐𝑐,𝑖𝑖𝑖𝑖 − 𝑇𝑇𝑐𝑐,𝑜𝑜𝑜𝑜𝑜𝑜 )
Where:
𝑚𝑚c = mass flow rate of cold water
Cc = specific heat capacity of cold water
𝑇𝑇𝑐𝑐,𝑖𝑖𝑖𝑖 = inlet temperature of cold water
•
𝑄𝑄 = 𝑚𝑚𝑐𝑐 ⋅ 𝑐𝑐𝑐𝑐 ⋅ �𝑇𝑇𝑐𝑐,𝑖𝑖𝑖𝑖 − 𝑇𝑇𝑐𝑐,𝑜𝑜𝑜𝑜𝑜𝑜 �
0.07𝑘𝑘𝑘𝑘 4182𝐽𝐽
(20.5 − 27.5)
=
×
𝑠𝑠
𝑘𝑘𝑘𝑘 · °𝐶𝐶
𝐽𝐽
= 1,463
𝑠𝑠
𝜂𝜂 =
𝑇𝑇𝑐𝑐,𝑜𝑜𝑜𝑜𝑡𝑡 = outlet temperature of cold water
Heat exchange efficiency (𝜂𝜂) of the heat exchanger
was calculated using:
Where:
𝜂𝜂 =
𝑄𝑄
𝑚𝑚ℎ ⋅ 𝑐𝑐ℎ ⋅ (𝑇𝑇ℎ,𝑖𝑖𝑖𝑖 − 𝑇𝑇ℎ,𝑜𝑜𝑜𝑜𝑜𝑜 )
𝑚𝑚h = mass flow rate of hot water
Ch = specific heat capacity of hot water
𝑇𝑇ℎ,𝑖𝑖𝑖𝑖 = inlet temperature of hot water
𝑇𝑇ℎ,𝑜𝑜𝑜𝑜𝑜𝑜 = outlet temperature of hot water
RESULTS AND DISCUSSION
The table below summarizes the temperature readings for cocurrent and countercurrent flow in tap-cold and hot-cold
experimental set-up.
TABLE I
TEMPERATURE READINGS
Set-up
Inlet Temperature
COLD-TAP
Tc = 20.5 °C
COUNTERCURRENT
Th = 31 °C
Outlet Temperature
Tc = 27.5 °C
Th = 25 °C
COLD-TAP COCURRENT
Tc = 15 °C
Th = 31 °C
Tc = 21.5 °C
Th = 21.5 °C
COLD-HOT
COUNTERCURRENT
Tc = 9 °C
Th = 66 °C
Tc = 29 °C
Th = 38 °C
COLD-HOT COCURRENT
Tc = 9 °C
Th = 72 °C
Tc = 24 °C
Th = 41 °C
Using the above data, the heat transfer rate (Q) and heat
exchange efficiency (𝜂𝜂) were calculated from each set-up.
The flow rate is estimated to be around 0.07 kg/s. The specific
heat capacity of water is 4182 J/kg·°C.
For Cold-Tap Countercurrent:
𝑄𝑄
𝑚𝑚ℎ ⋅ 𝑐𝑐ℎ ⋅ �𝑇𝑇ℎ,𝑖𝑖𝑖𝑖 − 𝑇𝑇ℎ,𝑜𝑜𝑜𝑜𝑜𝑜 �
For Cold-Tap Co-current:
𝐽𝐽
𝑠𝑠
=
𝑘𝑘𝑘𝑘 4182𝐽𝐽
(31 − 25)
0.07
×
𝑠𝑠
𝑘𝑘𝑘𝑘 ∙ °𝐶𝐶
= 0.8333 𝑜𝑜𝑜𝑜 83.33%
1463
𝑄𝑄 = 𝑚𝑚𝑐𝑐 ⋅ 𝑐𝑐𝑐𝑐 ⋅ �𝑇𝑇𝑐𝑐,𝑖𝑖𝑖𝑖 − 𝑇𝑇𝑐𝑐,𝑜𝑜𝑜𝑜𝑜𝑜 �
0.07𝑘𝑘𝑘𝑘 4182𝐽𝐽
(15 − 21.5)
=
×
𝑠𝑠
𝑘𝑘𝑘𝑘 · °𝐶𝐶
𝐽𝐽
= 1,902.81
𝑠𝑠
𝜂𝜂 =
𝑄𝑄
𝑚𝑚ℎ ⋅ 𝑐𝑐ℎ ⋅ �𝑇𝑇ℎ,𝑖𝑖𝑖𝑖 − 𝑇𝑇ℎ,𝑜𝑜𝑜𝑜𝑜𝑜 �
=
1,902.81
𝐽𝐽
𝑠𝑠
𝑘𝑘𝑘𝑘 4182𝐽𝐽
(31 − 21.5)
×
𝑠𝑠
𝑘𝑘𝑘𝑘 ∙ °𝐶𝐶
= 0.6842 𝑜𝑜𝑜𝑜 68.42%
0.07
For Cold-Hot Countercurrent:
𝑄𝑄 = 𝑚𝑚𝑐𝑐 ⋅ 𝑐𝑐𝑐𝑐 ⋅ �𝑇𝑇𝑐𝑐,𝑖𝑖𝑖𝑖 − 𝑇𝑇𝑐𝑐,𝑜𝑜𝑜𝑜𝑜𝑜 �
0.07𝑘𝑘𝑘𝑘 4182𝐽𝐽
(9 − 29)
=
×
𝑠𝑠
𝑘𝑘𝑘𝑘 · °𝐶𝐶
𝐽𝐽
= 5,854.8
𝑠𝑠
𝜂𝜂 =
𝑄𝑄
𝑚𝑚ℎ ⋅ 𝑐𝑐ℎ ⋅ �𝑇𝑇ℎ,𝑖𝑖𝑖𝑖 − 𝑇𝑇ℎ,𝑜𝑜𝑜𝑜𝑜𝑜 �
=
For Cold-Tap Co-current:
5,854.8
𝐽𝐽
𝑠𝑠
𝑘𝑘𝑘𝑘 4182𝐽𝐽
(66 − 38)
×
𝑠𝑠
𝑘𝑘𝑘𝑘 ∙ °𝐶𝐶
= 0.7143 𝑜𝑜𝑜𝑜 71.43%
0.07
𝑄𝑄 = 𝑚𝑚𝑐𝑐 ⋅ 𝑐𝑐𝑐𝑐 ⋅ �𝑇𝑇𝑐𝑐,𝑖𝑖𝑖𝑖 − 𝑇𝑇𝑐𝑐,𝑜𝑜𝑜𝑜𝑜𝑜 �
0.07𝑘𝑘𝑘𝑘 4182𝐽𝐽
(9 − 24)
=
×
𝑠𝑠
𝑘𝑘𝑘𝑘 · °𝐶𝐶
𝐽𝐽
= 4,391.1
𝑠𝑠
𝜂𝜂 =
𝑄𝑄
𝑚𝑚ℎ ⋅ 𝑐𝑐ℎ ⋅ �𝑇𝑇ℎ,𝑖𝑖𝑖𝑖 − 𝑇𝑇ℎ,𝑜𝑜𝑜𝑜𝑜𝑜 �
=
4,391.1
𝐽𝐽
𝑠𝑠
𝑘𝑘𝑘𝑘 4182𝐽𝐽
(72 − 41)
×
𝑠𝑠
𝑘𝑘𝑘𝑘 ∙ °𝐶𝐶
= 0.4838 𝑜𝑜𝑜𝑜 48.38%
0.07
By calculating for the average efficiency of the heat
exchanger across the different set-ups, the overall efficiency
for countercurrent flow is,
𝜂𝜂 =
83.33 + 71.43
= 77.38%
2
FIGURE I
HEAT EXCHANGER APPARATUS
Meanwhile, the overall efficiency for co-current flow is,
𝜂𝜂 =
68.42 + 48.38
= 58.4%
2
The calculated heat transfer efficiency represents the
effectiveness of the double pipe heat exchanger in
transferring heat between the hot and cold water streams.
Factors influencing the efficiency include flow rates,
temperature differences, and the design characteristics of the
heat exchanger.
CONCLUSION
In conclusion, the experiment measured the heat exchange
efficiency of the double pipe heat exchanger to be 77.38% for
a countercurrent flow and 58.4% for a co-current flow. We
can conclude that the efficiency of a countercurrent flow is
greater than that of a co-current flow. This observation
matches with theory wherein a countercurrent flow will
induce a greater temperature gradient that will allow better
heat transfer rate. In addition, we can conclude that a greater
temperature difference will result in a higher heat transfer
rate. This is because temperature difference drives the flow
of heat. As described by Fourier's Law of Heat Conduction,
which states that the rate of heat transfer through a material
is proportional to the temperature across the material and
inversely proportional to the material's thermal resistance.
Overall, this experiment contributes to a deeper
understanding of heat exchanger calculations and the
importance of such calculations for an accurate operating
system.
FIGURE II
HEAT EXCHANGER APPARATUS
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