1. Chem Eng 3A04
Heat Exchanger Design Problem
Submitted by:
Patrick Fondevilla 1213786
Jesse Carreau 1219430
Eryk Taylor 1220016
2. Part 1
The material chosen for the tubes of the heat exchanger was pure aluminum. This is because
aluminum is relatively cheap in comparison to other metals and alloys with the same desired
properties. Aluminum has a high thermal conductivity, and therefore is a viable choice of metal
for the construction of the heat exchanger. The material chosen for the shells of the heat
exchanger was a mild carbon steel due to its low cost and it is an easily accessible metal. The
outside of the shell was then perfectly insulated.
Properties of the Antigen:
Temperature upon entering: 70°C
Temperature upon leaving: 1.07°C
Flow rate: 0.05 L/s
The antigen shares the same properties as water at 37.5°C, which is the calculated mean
temperature. The temperature upon leaving was calculated using temperatures and methods that
will be described later. The reason that properties were not adjusted to achieve a temperature of
5˚C was because the specification was 5˚C or less, and the temperature of 1.07˚C adds room for
variability should the machine slightly malfunction. The flow rate was decided to be 0.05 L/s
because that is the flow rate at which the antigen exits the gamma ray sterilizer. Therefore, it was
easiest to keep a consistent flow rate throughout the entire process.
Properties of Refrigerant-22:
Temperature upon entering: -43°C
Temperature upon leaving: -27°C
Flow rate: 0.8 L/s
Refrigerant-22 was chosen because out of the refrigerants that were researched, it had the
highest thermal conductivity. The entering temperature of -43°C was chosen because this is the
coldest temperature that refrigerant-22 can reach. The exiting temperature of the refrigerant was
originally estimated to be 22˚C to show the same temperature difference as the antigen, but when
it was recalculated to check the viability of the estimation, an outlet temperature of -30.6˚C was
found and thus the estimation was not valid. The calculation was reiterated and evaluated at a
temperature of -36.8˚C, which is the mean temperature between the entering temperature and the
newly calculated exiting temperature. The fluid properties were evaluated at this mean
temperature of -36.8°C and then an exiting temperature for the antigen was calculated to be
1.07˚C. Finally, the exiting temperature of the refrigerant was then recalculated at the end again
to check its viability and was found to be -27˚C, which is only a temperature difference of 9˚C
from the mean temperature and therefore viable. A flow rate of 0.8 L/s of seconds was not the
3. original choice for flow rate, but the flow rate was the variable that could be varied to obtain an
exiting antigen temperature that met the criteria of the demand.
The type of heat exchanger that was chosen for this problem was a shell and tube heat
exchanger. The machine contains three shells with a diameter of 0.1m and a length of 3.5 meters.
Each shell contains one tube with three passes per tube. The volume of this machine is
0.10996m3 and can definitely fit in any industrial site as well as a confined laboratory.
The refrigerant used, Refrigerent-22, is quite expensive at $400/13.6kg (from Amazon),
but is near the price of other leading refrigerants but with the added heat exchanger desired
properties. However, because the refrigerant only heats to a final output temperature of -27˚C,
the refrigerant could be recycled in a second heat exchanger that has a slower flow rate of
antigen flowing through it. By doing this, EbolaOff will not only save money, but be able to
produce more antigen at one time. However, the materials that make up the heat exchanger are
very cheap and easily accessible. Also, because of the small size of the heat exchanger, multiple
heat exchangers could be made and put in close proximity to other machines during production.
The sensitivity test shown in the attached spread sheet raises an interesting question for the
employees of EbolaOff: what is the freezing temperature of the antigen and what is the minimum
temperature they would allow the antigen to be cooled until? This is a beneficial question
because the heat exchanger can be adjusted to increase or decrease the output temperature of the
antigen. The focus of the sensitivity tests was to identify what a change in flow rate of the
refrigerant would do to the temperature of the antigen.
EbolaOff should purchase this heat exchanger because it is small, effective, affordable, and
easily meets the criteria of cooling the antigen from 70˚C to 5˚C w or less ithin 20 seconds. The
small size means that EbolaOff could utilize the heat exchanger within a laboratory setting,
rather than just in an industrial setting. Since the outlet temperature of the antigen is
approximately 1.07˚C, an error margin is provided should something malfunction in the heat
exchanger. This further ensures that the outlet temperature is 5˚C or less. Additionally, the small
size means that multiple heat exchangers can be placed within a small setting to increase the
output of the antigen.
This heat exchanger made by the test group meets and surpasses the request of Ebolaoff.
By consulting with EbolaOff, a truly great machine can be forged for the pharmaceutical
company to cure such a dreadful disease.
Part 2
The heat exchanger contained 3 shells and 3 tubes. The diameter of the tubes were 0.1m,
and the length of the entire heat exchanger was 3.5m. The heat exchanger is a reasonable size; it
would be able to fit into a lab environment. Due to its length, the heat exchanger would be
installed on a table to allow the client to easily monitor the system and make any repairs. If it
4. were installed vertically, gravity would have to be taken into account with the flow rate and that
would change the heat transfer calculations.
There is potential for chemical pollution in the system because of the refrigerant-22. This
fluid contains chlorodifluoromethane, which destroys ozone in the atmosphere [1]. To ensure
that the heat exchanger does not cause any pollution, the refrigerant will not be vented out but
will be recycled, reused, and recooled. This will reduce the cost of buying more refrigerant and
also eliminate pollution.
To minimize the energy needed to run the heat exchanger, the refrigerant will be recycled
and reused. Energy is also saved by insulating the entire system, which ensures that heat would
not be lost during any process. The shell and tube heat exchanger further reduces the energy due
to the fact that the lower number of tubes increases the flow rate, which as a result increases the
convective heat transfer coefficient. Since this design contains a reasonable number of tubes,
more heat will be transferred and less energy will be needed.
In order to minimize the costs of the heat exchanger, materials were used that were cheap
but still effective in transferring heat. From MetalsDepot, aluminum ¾ SCH40 costs
approximately $11/m with a diameter of 0.0301m and carbon steel 4” SCH40 costs
approximately $66/m. Therefore, considering only the metal cost, the heat exchanger would cost
around $808.50. If metals such as titanium or stainless steel were considered, the heat exchanger
would be more effective, but it would be very expensive to produce. The cost of Refrigerant-22
is also considered, which costs about $400/13.6kg through Amazon. Although this seems
expensive, in the grand scheme of the project, the cost of the refrigerant-22 and the heat
exchanger is inexpensive when compared to the life of a human being.
