Test plan
1. Research problem and goal
Electric vehicles need powerful batteries. A problem is, that powerful batteries tend to overheat,
which is why they need cooling. One cooling method is using liquid cooling plates. In this
research we examine cooling plates manufactured with different methods. Different plates are
friction stir channeling, extruded plate and sinked pipe. Plates are compared by their ability to
cool a heated plate. We also want to find out how the cooling channel shape, size and route
affects the cooling.
Friction stir channeling is a relatively new manufacturing method to create channels, but it isn’t
yet used in many applications. We want to find out if friction stir channeling is an appropriate
method to manufacture effective cooling plates. We are especially interested in finding out if
friction stir channeling plates are more effective than other plates.
2. Theoretical background
2.1 The geometry of the cooling plates
The geometry of the cooling plate has a big impact on its effectiveness. Plates can have
different surface areas and thicknesses. In addition the shape of the cooling channel can differ
by route, width, length and cross-section (Jarrett et al. 2011).
Possible shapes of the channels are for example square, rectangular, triangle, round or ellipse.
Sinked pipe and extruded plate have round channels and FSC trapezoid-shape channels. The
shape of the channel effects for example the type of the flow. It also defines how large area of
the cooling liquid touches the cooled plate side. Usually channels with high aspect ratio
(channel height-to-width ratio) have an excellent cooling efficiency (Pizzarelli et al. 2013). The
route of the channel defines in which parts of the plate the cooling liquid is cooled and where it
has already warmed, in other words, where the cooling plate is most cooled.
Different manufacturing methods make different kind of surface roughnesses, which also affects
the flow and pressure drop in the cooling channel. For example FSC makes a quite flat bottom
surface and a rough surface (Ferraz 2012).
Figure 1. Channel shape of FSC. (Ferraz 2012)
2.2 Cooling power
We are going to compare different plate’s cooling abilities by calculating their cooling powers
with different flow rates. First we need to calculate the amount of heat that the cooling plate
transfers from the aluminium plate located on top of the system. The amount of heat can be
calculated with:
,
where m is the mass of the aluminium plate, c is the specific heat capacity, T1 is the
temperature of the aluminium plate in the beginning and T2 is the temperature at the end.
(Lampinen 2010).
The transferred amount of heat should be the same in all tests, since we have the same
aluminium plates in all tests and we assume that the aluminium plates will reach same end
temperature in all tests. What should differ, however, is the time it takes a specific cooling plate
to cool the aluminium plate. Hence, we will calculate the cooling power by dividing the amount
of heat by time:
,
where t is time it takes the aluminium plate to cool from temperature T1 to temperature T2.
We know mass m and specific cooling capacity c. We can determine temperature T1 ourselves
and measure T2 during the test. Hence, we only need to measure time.
3. Research methods
In this research we are going to test different cooling plates and compare their ability to cool a
hot aluminium plate. The cooling ability is going to be measured with thermal cameras and
thermocouples. From the results we are going to calculate the plates’ cooling power.
3.1 Different plates used in measurements
There are three different plates that are going to be tested: FSC, extruded plate and sinked
pipe. All three plates are going to be tested similarly and their ability to cool is going to be
compared. The three plates differ from each other a bit, because their different manufacturing
techniques have their own limitations. All plates are made mainly out of aluminium.
The plate’s sizes were supposed to be approximately A5, because it’s quite practical for testing.
Many manufacturers offered a few standard widths and of those 140 mm was closest to wanted
size. The length was optional, so it was chosen to be 190 mm.
3.1.1 FSC
The first plate is manufactured by friction stir channeling. The plate will be manufactured at
school, so we don’t know its specific measurements yet. A difficulty is that for now at least, FSC
channels aren’t as large by cross section as the channels in two other plates. This can make it a
bit more difficult to get comparable data. However, this can maybe be compensated with a
longer cooling channel. In addition, FSC channel won’t probably be in the middle of the plate,
contrary to other plates. It will also have a rougher surface, which can cause pressure drop in
the channel.
One possible FSC plate to manufacture is shown in picture 2 below.
Figure 2. FSC cooling plate with a massplate on top.
3.1.2 Extruded plate
The second plate is an extruded plate ordered from DAU GmbH. It is a standard plate KW140
from Easy System model, and it is 23 mm thick. The diameter of the cooling channel is 10 mm.
Ends’ connections can be seen from picture 3a and completed model from picture 3b.
Figure 3a. Ends’ connections.
Figure 3b. Extruded cooling plate with massplate on top.
3.1.3 Sinked pipe
The third plate is also ordered from DAU GmbH and it is a plate with a sinked pipe. It has the
same dimensions as FSC and extruded plate, but the channel route is different. The plate is
mainly aluminium but the tube is stainless steel with 10 mm diameter.
Figure 4. Sinked pipe.
3.2 Measuring devices
3.2.1 Thermal camera FLIR SC660 and i5
We have two different cameras to be used in tests, FLIR i5 and FLIR SC660. i5 is a cheaper
thermal camera, which can be used for practicing and quick measurements. SC660 is more
expensive thermal camera and is used for final measurements. We can take images with both
cameras, and also video with SC660. Images and videos can be transferred to a computer for
future analysis, which can be done with a program that comes with SC660 camera.
3.2.2 Thermocouples
In this study we will measure the temperature of the cooling liquid with thermocouples. There
are different types of thermocouples, for example T and K. The measurement data is recorded
by a computer program called TKK Cold Chamber Recorder. The program draws a graph, and
the information can be saved as a chart. Thermocouples can also be connected to a
thermometer (for example Fluke 52 K/J Thermometer), which can be used as a quick way to
see the measured temperature. However, it doesn’t record any data.
3.3 Measuring system
Measuring will be performed the same way for all three plates. In the test set-up the cooling
plate is going to be set in a hole of a quite thick urethane plate. The urethane plate is going to
have small holes for cooling plates that are attached to the cooling plate. Because the three
plates differ from each other, we might need to have three different urethane plates. On top of
the cooling plate we are going to place an aluminium plate that is a few centimeters longer and
wider than the cooling plate (210x160x6). In this way the cooling plate is completely covered. A
thermal camera will be targeted towards the surface of the aluminium plate. Thermocouples will
be placed inside the output and input of the cooling plate and they will measure the temperature
of the cooling liquid. However, it seems that the temperature of the cooling liquid won’t be
needed in calculations.
The aluminium plate is going to be heated to 40 degrees before it is placed on top of the cooling
plate. The plate will be heated in temperature cabinet. Glycol will cycle through the cooling plate
and cool the aluminium plate. The glycol will be 10 degrees. During the test, the thermal camera
will monitor the temperature of the aluminium plate as it cools down. With a thermal camera, we
are able to determine the average surface temperature, maximum surface temperature and heat
distribution in the plate. Thermocouples will also measure the surface temperature of the
aluminium plate on top from three points.
Figure 5. Picture of the test system from two different view angles.
3.4 Chosen test parameters
We tried to choose such test parameters, that our tests would give as reliable results as
possible. Test time will depend on how long it takes for the aluminium plate to reach
approximately the temperature of the cooling liquid. The tests will continue a bit longer, so that
we can be sure the temperature doesn’t change anymore.
We decided to test each plate with six different flow rates and each flow rate three times, so that
we have enough comparable data. We can also notice possible test errors more easily. Flow
rates were decided by researching cooling plate manufacturer’s websites and choosing some
commonly used flow rates.
The aluminium plate on top was chosen to be 6 mm thick. This is because battery plates are
usually 10 mm thick, and they are cooled from both sides. We have a cooling plate only in one
side, so best thickness for the aluminium plate would be 5 mm. Aluminium plates are usually
available in thicknesses 4 mm and 6 mm, so we decided on 6 mm.
Aluminium plate on top will be heated to 40 degrees before the beginning of tests. The cooling
liquid will be 10 degrees.
4. Measurements (step by step)
Measurements will be performed by following steps. Each plate will be tested with 6 different
flow rates, and there will be 3 tests per flow rate with each cooling plate. In other words, there
will be 18 tests per one cooling plate. Different flow rates are 3 l/min, 6 l/min, 9 l/min, 12 l/min,
15 l/min and 18 l/min.
Beginning arrangements
1. Building the test system: urethane plate on bottom, cooling plate inside it, aluminum
plate on top. (or horizontally?)
2. Connecting the thermocouples to cooling tubes’ joint parts.
3. Connecting the tubes with the joint parts to the cooling plate.
4. Setting up thermal camera so that the whole aluminium plate can be seen.
5. Warming 3 similar aluminium plates to 40 degrees in a temperature cabinet.
6. Measuring room temperature with a thermocouple left hanging in the air in the cold
chamber.
7. Cooling the liquid (glycol/water) to 10 degrees and adjusting the flow rate with a
frequency converter.
8. Letting the liquid run by opening the taps in the cold chamber.
9. Turning the thermal camera on.
Repeated steps
10. Waiting that cooling plate has reached approximately the temperature of the cooling
liquid and checking it with thermal camera.
11. Taking an 40-degree aluminium plate from the temperature cabinet with mittens and
placing it on top of the cooling plate.
12. Filming the surface area of the aluminium plate with a thermal camera as it cooles.
13. Measuring the temperature of outgoing and ingoing liquid with thermocouples.
14. Waiting until the aluminium plate on top has reached approximately the temperature of
the cooling liquid.
15. Writing down the time it took for the aluminium plate to cool.
16. Waiting for a few minutes to check that the temperature of the plate doesn’t change
anymore.
17. Taking the aluminium plate of the measuring system and putting it back in the
temperature cabinet.
18. Returning to step 10 (and changing the flow rate if necessary), or if one plate has been
measured with all flow rates, moving on to step 19.
19. Shutting the glycol taps and removing the cooling tubes from the cooling plate.
20. Shutting down all measuring devices.
5. Documentation of the results
The measurements data from the thermocouples is recorded by a computer program called
TKK Cold Chamber Recorder. The program draws a graph, and the information can be saved
as an Excel chart. In the chart there is information such as time and temperature.
Thermal cameras can be used to take images from the surface of the hot aluminium plate.
SC660 camera can also be used to take video clips. Images and videos can be transferred to
computer. Images can be analyzed more carefully with a program that comes with the thermal
camera.
We will also have a paper field log, in which we will mark important information of each test,
such as the test date, used cooling plate and who were present during the test. We will also
mark flow rate.
From our test data we will make some calculations. We get the temperature of the aluminium
plate with thermocouples and thermal camera and in addition, we know the specific heat
capacity and mass of the aluminium plate. With this information we can calculate the amount of
heat that is transformed during the test. When we divide the amount of heat with time, we get
cooling power.
Each cooling plate will be tested with six different flow rates, so we can calculate six different
cooling powers for each plate. With this data, we can make graphs that show cooling power as
a function of flow rate. When we have all three cooling plates in the same graph, it’s easy to
compare which is most efficient.
6. Safety analysis
Our tests don’t contain any major safety hazards. However, there are some risks that must be
taken into account. Personal injuries are not likely, but we must still be careful with the glycol so
that it won’t spill over anyone. We must also be careful with the hot aluminium plate in order to
avoid burns.
We must also take care of equipment safety. We must be careful with the expensive thermal
cameras, because they will break if they are dropped to the ground. Thermal cameras must be
handled carefully and placed firmly on the table during tests. It is also important to read
instructions properly before use. In addition, cooling plates must be attached before tests can
begin.
7. Error analysis
There are many possible sources of errors in our tests. Some have already been taken into
account, and some need to be observed during tests and processing the data. One error that
can occur because of the cooling plates is, that FSC plate has smaller cooling channels than
two other plates. In addition, FSC channel won’t probably be in the middle of the plate, and it will
also have a rougher surface. Some of these differences can be influenced by making an optimal
channel route for FSC plate.
Test circumstances should be similar during all tests. For example the temperature of the test
room should be constant. Our cooling plates have different masses, which can affect the cooling
of the plate. That is why we don’t observe the cooling of the cooling plate but the cooling of an
aluminium plate on top of it. We use similar aluminium plates in all tests. The aluminium plate on
top will be pre-heated. We have to be careful that the plate won’t cool before the test can start.
We have to watch out for equipment errors. Some of the thermocouples can show results
incorrectly and they should be calibrated before tests. The calibration can be performed for
example with boiling and ice cold water. There can also be difficulties with the thermal camera.
We also have to watch out for human errors that can occur during tests or with handling the
results. There might be for example errors with the calculations or with reading the pictures from
thermal camera.
Lähteet
Jarrett, A. Kim, I.Y. 2011. Design optimization of electric vehicle battery cooling plates for
thermal performance. Journal of Power Sources. Vol: 196. P. 10359– 10368.
DOI:10.1016/j.jpowsour.2011.06.090.
http://www.sciencedirect.com/science/article/pii/S0378775311013279.
Lampinen, J. Markku. 2010. Termodynamiikan perusteet. ISBN 978-951-672-368-9.
Pizzarelli, M. Nasuti, F. Onofri, M. 2013. Trade-off analysis of high-aspect-ratio-coolingchannels for rocket engines. International Journal of Heat and Fluid Flow. Vol: 44. P. 458–467.
DOI: http://dx.doi.org/10.1016/j.ijheatfluidflow.2013.08.003.
http://www.sciencedirect.com.libproxy.aalto.fi/science/article/pii/S0142727X13001586.
Ferraz, M.F.S. 2012. Friction Stir Channeling Industrial Applications. Prototype Design and
Production. https://fenix.tecnico.ulisboa.pt/downloadFile/2589872816364/Dissertacao_.pdf.