Material Selection and Manufacturing of Heat Exchanger Components

This report provides a comprehensive analysis of the material selection and manufacturing processes for a heat exchanger. It begins by outlining the function and operating environment of the heat exchanger component, emphasizing the need for high thermal performance, corrosion resistance, and durability. The report then examines various materials, including Aluminum 2008, T4, Aluminum Bronze, Brass, and Stainless Steel, evaluating their properties such as thermal conductivity, thermal distortion resistance, and maximum service temperature. Based on these criteria, Aluminum 2008, T4 is selected as the optimal material. The report further details the manufacturing route, including shaping through press forming and joining via brazing, justifying these choices based on cost, efficiency, and suitability for mass production. Alternative materials and manufacturing routes are also considered, highlighting the key differences between the initial and alternative choices. This report offers a detailed case study for mechanical engineering students to understand the process of material selection and manufacturing route planning.

MANUFACTURING TECHNOLOGY
AND MATERIALS
1. COMPONENT FUNCTION AND OPERATING
ENVIRONMENT
1.1. FUNCTION OF THE COMPONENT
A heat exchanger is an appliance which allows heat from a hot fluid such as water or gas to pass to a
second fluid (also may be a gas or a liquid) without the two fluid coming into contact or mixing. The
basic principle of heat exchangers is to transfer heat energy from a hot fluid to another fluid without
transferring the liquid or gas which is carrying the heat energy.
Heat exchangers plays major roles in cooling and heating of buildings. They expel heat from a
compartment or room where it's not needed and siphon it away in a liquid to some other spot where it
tends to be dumped off the beaten path. The heat exchanger shown above is part of an air conditioner
device placed in buildings to expel cold from the building.
1.2. SERVICE CONDITIONS
The heat exchangers are exposed to high temperature. When properly heated, they transport water in
form of steam which is at high temperatures (above 100 0C). Thermal stresses are also occur on the heat
exchanger parts. A component in the heat exchanger may experience hot temperatures at one end and
low temperatures on the opposite end. As a result, thermal stresses occur. Corrosion also act on the
heat exchangers since water is used. There are
2. MATERIAL PROPERTIES AND SELECTION
2.1. MATERIAL PROPERTY REQUIREMENTS
A good material for heat exchanger should have the following properties;
a) Thermal performance and size reduction
The material should offer a very good deal of cooling or heating with high heat transfer efficiency in a
small and compact size. In most applications, materials used should have a big heat transfer coefficient
in order to do away with pre-coolers.
b) Excellent corrosion resistance
The material should be corrosion resistant. Water at high temperatures is usually high corrosive and the
material should be able to withstand this corrosiveness. The material used should also be resistant to
pitting corrosion and other coolant used.
c) Durability
The assembly should have stronger joints. The joints should also withstand very high temperatures of
steam while maintaining the thermal-fatigue and mechanical strength. Stronger materials allows use of
thinner parts and encourages on space saving designs.
d) Maintainability.

The material should be easily repaired using common methods such as silver brazing and soft soldering.
The material should thus bond perfectly with this brazing and soldering material.
2.2. MATERIALS USED TO MAKE THE HEAT EXCHANGER
The following materials are can be used to make the heat exchanger.
a) Aluminum 2008, T4
b) Aluminum Bronze CuAl10 as extruded
c) Brass, CuZn40Pb3, hot worked
d) Stainless steel, AISI 309, Annealed
PROPERTY Thermal
conductivity
(W/m. 0C)
Thermal distortion
resistance
(MW/m)
Maximum
service
temperature (0C)
Durability with
water (fresh,
salt).
Aluminum 2008, T4 168 7.49 190 Excellent
Aluminum Bronze
CuAl10 as extruded
70 4.57 310 Excellent
Brass, CuZn40Pb3,
hot worked
121 6.29 180 Excellent
Stainless steel, AISI
309, Annealed
19 1.28 1100 Excellent
All the materials were very excellent in durability with fresh and salty water. Stainless steel AISI 309,
Annealed was ruled out due to its small thermal conductivity. The remaining three materials were
checked for their thermal distortions. Aluminum Bronze CuAl10 as extruded was then ruled out since it
had the least thermal conductivity. This left Aluminum 2008, T4 and Brass, CuZn40Pb3, hot worked.
These materials were checked for their maximum service temperature. Brass, CuZn40Pb3, hot worked
was ruled out due to its small maximum service temperature of 180. Aluminum 2008, T4 survived. Thus
the material used in the heat exchanger is Aluminum 2008, T4.

3. COMPONENT MANUFACTURING ROUTE
3.1. MANUFACTURING ROUTE SEELCTION
Shaping. This includes cutting the interlocking tubes using hacksaw or shearing machine.
Joining. The interlocking sheet metal can be joined by welding together. The pipes into the
Surface treatment. The heat exchanger may be treated using aluminizing processes.
For the shaping process, the following can be chosen.
Capital cost Batch size Relative cost
index (EUR)
Mass range
(Kg)
Press forming 807000 250000 29 -351 50 Kg
Cold die forging 32000 - 807000 100000 15 – 30.5 12 kg
Stamping 807000 250000 11.2 – 26.6 1 kg
Deep drawing 80700- 807000 100000 18.6 – 38.3 5 kg
All the above process are used to shape sheet metal. From the table above, considering the maximum
mass that can be processed by the processes, press forming is more appropriate for shaping process
since it can be used to shape sheet metal of up to 50 kg. In therms of cost, Cold die forging is
appropriate since it has the lowest capital cost.
3.2. SELECTED ROUTE
The selected route is
Shaping: Press forming
Joining:

3.3. JOINING PROCESS FOR SHEETS
The joining method has to thermally conductive and watertight
a) Plasma arc
b) Brazing
c) Soldering
d) Laser beam welding
e) Projection welding
f) Seam welding
The above processes are compared in order to select the best joining method.
Relative
equipment costing
Set up time Labour intensity Capital cost
Plasma arc 4 - 20 0.2 – 0.5 low
Brazing 0.5 - 2 0.2 - 1 low 80.7 - 80700
Soldering 0.1 - 10 0.2 - 1 Low 80.7 - 80700
Laser beam
welding
15 - 200 1 – 2 Low 32300 - 161000
Seam welding 10 - 30 0.2 - 4 Low
Projection welding 2 - 10 1 -4 Low
All the five welding processes had low labour intensity. However, comparing the other properties and
set up time, the processes can be selected. The laser beam, seam, plasma arc and projection welding
were ruled out due to their high relative equipment costing.
This leaves us with brazing and soldering. The two have the same capital cost and set up time. Of the
two, brazing is easily adopted to mass production and produces more strong joints than soldering. Thus,
Brazing was used.
4. ALTERNATIVE MATERIALS AND MANUFACTURING
ROUTES
4.1. ALTERNATIVE MATERIALS
a) Aluminum Bronze CuAl10 as extruded
b) Brass, CuZn40Pb3, hot worked
c) Stainless steel, AISI 309, Annealed
4.2. MAIN DIFFERENCE BETWEEN FIST CHOICE AND SECOND CHOICE