FACULTY OF ENGINEERING
Department of Mechanical Engineering
THE HASHIMITE UNIVERSITY
Exp. # (3)
Double pipe concentric tube heat exchanger
Objective:To study the performance and the characteristics of double pipe, water to water,
concentric tube heat exchanger in both parallel and counter flow.
Theory:One of the most common, conductive-convective, heat exchanger types is the concentric tube
heat exchanger.
These exchangers are built of coaxial tubes placed the ones inside the others. When both the
fluids enter from the same side and flow through the same direction we have the parallel flow
(concurrent flow), otherwise, if the fluids enter from opposite sides and flow through the
contrary direction we have the countercurrent flow.
Usually the countercurrent flow is more efficient from the heat transfer point of view.
This type of heat exchangers can also be built with the internal tube made with longitudinal fins
which could be placed either in its internal surface or in its external one or both.
This configuration is useful mainly if one of the fluids is a gas or a liquid with a very high
viscosity and it's very difficult to have a good thermal convection coefficient.
The heat transfer from the hot fluid to the cold fluid is given by the following equation:
q = U × A × LMTD
Where: U is the overall heat transfer coefficient.
A is the internal exchange surface area between the two fluids.
∆T1 − ∆T 2
LMTD is a log mean temperature difference, and it's given by
ln(∆T1 / ∆T 2 )
∆T1=T hot in- T cold in
∆T2=T hot out- T cold out for the parallel flow exchanger.
∆T1=T hot in- T cold out
∆T2=T hot out- T cold in for the counter flow exchanger.
Counter flow
Figure(1): Temperature distribution for counter flow heat exchangers
Heat transfer lab Lab. - Exp # (3): Double pipe concentric tube heat exchanger
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FACULTY OF ENGINEERING
Department of Mechanical Engineering
THE HASHIMITE UNIVERSITY
Parallel flow
Figure(2): Temperature distribution for parallel flow heat exchangers.
Apparatus:The apparatus is a double – pipe, water to water heat exchanger test unit with 4m concentric
pipes.
The built in heater includes a series of resistors with fixed and variable heating capacity.
Figure (3): double – pipe heat exchanger (Photo)
Heat transfer lab Lab. - Exp # (3): Double pipe concentric tube heat exchanger
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FACULTY OF ENGINEERING
Department of Mechanical Engineering
THE HASHIMITE UNIVERSITY
Figure (): double – pipe heat exchanger (layout)
Procedure:1. Adjust V5 and V6 valves to get the parallel flow circuit.
2. Adjust the hot circuit valve V3 so as to obtain the required flow rate m hot with turbulent
rate.
3. Adjust the cold circuit valve V4 so as to obtain the required flow rate m cold with
turbulent rate.
4. Wait until the stationary heat flow between the two fluids is obtained and measure the
values of inlet, intermediate and outlet temperature of the two circuits
5. Keep the hot flow rate m hot at a constant level; increase the cold flow rate, wait for
steady state then repeat the temperature reading.
6. Repeat same procedure for the counter flow circuit.
Heat transfer lab Lab. - Exp # (3): Double pipe concentric tube heat exchanger
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FACULTY OF ENGINEERING
Department of Mechanical Engineering
THE HASHIMITE UNIVERSITY
Results:Temperatures (οC)
Flow meters
Hot water
Hot
water
(L/hr)
Cold
water
(L/hr)
Inlet
T1
320
100
50
320
150
50
320
200
50
320
250
50
Middle
T2
Cold water
Outlet
T3
Outlet
T4
Middle
T5
Inlet
T6
LMTD
(οC)
U
(W/m2K)
LMTD
(οC)
U
(W/m2K)
Table(1): Parallel flow results
Temperatures (οC)
Flow meters
Hot water
Hot
water
(L/hr)
Cold
water
(L/hr)
Inlet
T1
320
100
50
320
150
50
320
200
50
320
250
50
Middle
T2
Cold water
Outlet
T3
Inlet
T4
Middle
T5
Outlet
T6
Table (2): Counter flow results
Heat transfer lab Lab. - Exp # (3): Double pipe concentric tube heat exchanger
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FACULTY OF ENGINEERING
Department of Mechanical Engineering
THE HASHIMITE UNIVERSITY
Analysis:NOTE: The following analysis should be performed for both parallel and counter flow heat
exchangers.
1. Characteristic curve:
• Plot ∆Thot versus cold water flow rate.
2. Temperature distribution in heat exchanger.
• Plot the average inlet, intermediate and outlet temperatures of the two fluids as a
function of the length of the heat exchanger.
3. Overall heat transfer coefficient U
• Q = U × A × LMTD
Qhot
• U=
A × LMTD
• Qhot = m hot × C pw × ∆Thot
•
Qcold = mcold × C pw × ∆Tcold
• Qloss = Qhot − Qcold
• Plot U versus cold water flow rate.
• Plot Qloss versus cold water flow rate
Where:
∆Thot = Thot water inlet – Thot water outlet
∆Tcold = Tcold water outlet – Tcold water inlet
Cpw = 4.18 kj/kgK.
A = Internal exchange surface area between the two fluids = 0.226 m2
Heat transfer lab Lab. - Exp # (3): Double pipe concentric tube heat exchanger
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