Thermal Management of Automotive Battery Packs – ATS Webinar


Good afternoon and welcome to the latest
webinar presented by Advanced Thermal Solutions Inc. This month’s webinar
is on the thermal management of automotive battery packs and it is
presented by Dr. Kaveh Azar, the CEO and founder of ATS and a
world-renowned expert in the thermal management of electronics. Before I turn
things over to Dr. Azar, I’d like to remind everybody that there will be time
for questions at the end of the webinar so if you have any questions please type
them into the section provided and we will get to as many as we can
at the end. Also we will be continuing our monthly webinar series in November
with a discussion of heat pipes and vapor chambers and their role in heat
transfer. You can register at the same link that you used to sign up for this
webinar which is qats.com/training/webinar With that I
will now turn things over to Dr. Azar Kaveh Azar: Thank You Josh and greetings from ATS to
all attendees thank you for your participation in this webinar. Let me
talk about the electric vehicle battery thermal management review of options and
technologies around the market. So the presentation is going to be at the
understanding the lithium-ion battery working principles and how it compares
to the acid lead batteries and the type of batteries that are deployed in the
automotive industry and then we focus on the battery thermal management from
air and liquid refrigeration PCM and vapor chamber and I will try to bring it
together at the very end with all the stuff that we see. As you’re going to see
this presentation is benefited from the excellent work that’s been done by many
many many researchers across the globe from Asia to North America and I have
benefited from the work that they have done I’ve tried to put it together here
for you to see what is happening and what’s state of the art as far as the
battery thermal management is concerned. So starting with understanding the
working principles of the of the battery. When we work with a lead acid battery it’s a device consisting of 2 or more electrochemical cells that converts
the stored chemical energy into electrical energy. That’s an essential function of a battery
whether it’s a lithium-ion or lead acid battery. In the lead acid battery, current
flows between the positive terminal the cathode and the negative terminal anode,
isolated by a separator obviously the cathode is at a higher energy potential
than the anode. When the battery is connected to external circuit
electrolytes allows iron that’s generated by the chemical reaction to
move between the cathode and anode and as a result it would create the energy
that’s required. With the lithium ion battery working principle the
lithium-ion cell stores energy by inter- collection of the charged lithium ion
in a graphite node and then the cells are released energy transferring these
ions through an organic process and creating the current that we require to
do it. When you look at the performance of the two battery types
you’ll notice that the lithium-ion batteries are much more efficient in
charge and discharge than the lead acid batteries and as a result of it has
got a significantly larger acceptance in the deployment of the electric vehicles
not only electric vehicles but a lot of the other battery requiring
operations across the industry in order to function effectively. So it’s a very
attractive corner piece of the market as far as use and functionality is
concerned with a very broad spectrum, obviously when we get to electric
vehicles that demand on the power is significantly higher and the issues
associated with managing this thermal as we’re gonna see, becomes more prevalent
and significant. So what are the battery types? Two broad spectrum or possibly three is cylindrical it’s a jellyroll or a hard can or is wound or
stacked layers or soft pouches as you can see examples of these that are shown
in these applications you see an example of a soft pouch
or the can that we see that’s very commonly seen in the in the industry.
When we look at the inner structure of it, irrespective of the packaging that we
have whether it’s cylinder prismatic or pouch the inner construction of these
batteries are identical in order for them to function effectively as I showed
you on the first slide we have a negative electrode we have the negative
terminal lead we have the positive electrode and we have a separation or
separator plate in order to make it function and as you can see these
principles or these structure is coming across these battery types in packaging.
So obviously these are packaged for different purposes so they have a
application for as I mentioned a very broad spectrum from automotive all the
way to laptops and so forth that we see they use a similar type of a battery or
technology. When we look at the way the system is packaged in hybrid
electronics and hybrid electric vehicles and so forth we see overall packaging
that looks like like this and from the outside has got some connections and
they’re both for power and cooling depending upon the type of cooling that’s
used. If we sort of break it open you can see that there is a multi-
layers that are composing the overall battery that’s used across the
industry. But I think something is very important to notice in this schematic
that’s shown on the right hand side is the thermal management is encompassing
of the entire system and there is controller as you can see from one
of the researchers what an important role the controller plays but you can
see that the sort of hierarchy of packaging as we go into the
system and there is a heat transfer and heat transport between different layers
that has to be considered so in a given application like this not only we have
to worry about the battery modules we also have to worry about the ancillary electronics that’s going to be functioning properly in order for the
batteries to operate so there is really two prong or two points of concentration
as we go forward in the thermal management of our our system so we can’t
just focus on the battery there is ancillary electronics that’s kind of supporting the battery and battery operation that we
need to know. So when we look at the type and the way it’s composed and
put together, we have in this case is a can and the second case
is a pouch or a plate it’s put into a module from the module into a
pack and eventually into the vehicle and we can see the example for
the Tesla for instance the roadster that the way the battery is packed inside
the rear compartment of the vehicle in order to provide the power that’s
required to go forward and likewise in the bottom when you see on the Nissan
Leaf for instance they have used the cells and then they made a
module the module goes into a larger module that makes it pack and
eventually goes into a vehicle but again it’s packaged differently. So you can see
that the hierarchy of packaging is becoming more and more clear and those
of us who’ve been involved in electronics cooling, traditional
electronics cooling, where we concentrate on the component and in the component we
focus on the junction, here our component is the battery and the junction is the
core temperature inside the battery that we have to be minimizing and making sure
that’s a function here at the level that it’s supposed to in order to
have a fail-safe operation with our electric vehicle. And the technology is
all over the place as very similar to what we see with the traditional
electronics packaging it is very very much system related and the system in
this case is a vehicle that we use as consumers and the designers in these
companies they’re putting the packages differently depending upon how the
ultimate system is put together you can see examples of the Chevy Volt, Nissan
Leaf, Fiat, Tesla, Focus and Nissan Mitsubishi,
I’m sorry under i-MiEV. And you can see the packaging is totally different and
how they utilize the system in order to put it together in order to provide the
energy that’s required for the vehicle to be functional.
And the reality is the mobility industry, not necessarily automotive by itself,
requires a full range of lithium-ion batteries it’s not specific to one
particular type it depends upon the application and the system it’s being
deployed. But I think it’s awarded to pay attention to this to this chart as
well that heat accumulation this cell is equal to the net heat entering or
leaving the cell plus the heat generation and as you can see heat
accumulation in the cell creates additional chemical reaction which is
which is a problem. Heat from the chemical reaction accumulates in the
cell and any kind of a heat accumulation or excess heat that cannot be removed
effectively it could be a causative agent of failures, shortened life and
catastrophic failure that we’ve seen some fires and so forth that’s happening.
So the thermal management it is it is very much system later and it’s very
very broad across the industry. So what about the challenges with a
lithium-ion battery when we look at the issues with electric vehicle the
lithium-ion batteries have the best performance as far as
the battery class is concerned. But they are very temperamental and we
have to be addressing that very accurately when we start to work with
it. Key problems is dealing with heat generated by cell during charge,
discharge and ambient conditions this is the area of the menace we have
that we have to attend to as we go through the design in order to make sure
that it is done properly in order to avoid catastrophic failure. If
our cells get too hot, three high level problems occur – decreased battery life,
decreased performance and risk of fire or explosion. We have seen examples of a
fire happening with lithium-ion batteries a variety of applications
we’ve seen it in the laptops we’ve seen it on the automotive we’ve
seen it in the airplanes depending upon where they were used and whether the
thermal management system worked effectively for them or not. So
when we look at the thermal runaway situation in lithium-ion battery, a large
did a very nice graphic here to to show what exactly happens when we look at the
ion battery we have the anode layer we have the protective layer here we have
the electrolytes and the separator and then the cathode layer. And the first
thing when the heating starts this is area number one then the protective
layer breaks down and electrolyte breaks down into a flammable gas or gases and
then the separator starts melting possibly causing a short circuit and
then cathode breaks down and generating oxygen so we have all the
components for a catastrophic failure if we have this thermal runaway that it’s
not managed effectively in our system and the net result of it is here what
this picture shows I believe this is from 3M, if my memories yes it is 3M,
where they’ve shown a difference between an immersed battery pack into a liquid
versus un-immersed and you can see where the fire occurs and in the 3M Novec
fluid you can see that’s a better containment of the thermal runaway and
the issues could potentially happen with it. By the way, this is practical or not, it
is a question that we’re going to try to address as we go forward but
nevertheless it shows that if we manage the thermal runaway during the charge discharge or possibly extreme ambient conditions we could have
catastrophic failure and there are solutions to address that. So what are
the, let’s start at the thermal management. We know that lithium-ion
batteries could potentially cause fire and sometimes
explosions, but you know we have oxygen and oxygen is an explosive gas so how do
we go about managing this from a thermal step and what are our options what are
the people have done what what are the things that people have done in the
industry in order to be able to address this? I think it would be helpful to just
take a look at and see what are the different options and compare it against
the internal combustion engine vehicles and see what the
changes are as we go from internal combustion engine to electric
vehicle to hybrid systems. You can see the cooling system I apologize if these
pictures are not very large I try to put three of them into one sheet so we can
have an ABC comparison and you can see that the overall structure with
respect to the evaporator and the condenser and some sort of a heat
exchanger here continues to be the same across different industries. Different,
I’m sorry, vehicle design. And obviously as we go to
the hybrid vehicle we can seen in addition to the
battery, we have the engine in here to that we have to also worry about from
the thermal standpoint, not only that but also from the thermal coupling that could
potentially take place between the internal combustion engine and the
battery compartment. So the problem with the hybrid could potentially be twofold
depending upon the packaging that we have. Obviously when we go to the pure
electric vehicle some people call it a plug electric vehicle
you see this PEV or PHEV being used interchangeably they both reference so
however we come to the conclusion. In this particular case there is no engine
internal combustion engine and the vehicle is purely driven by the electric
power that is has to be charged obviously from the electric source. When
we look at this overall thermal management there are some conditions
that we have to address it’s a load profile, current rate, short-circuit and
overvoltage. On the environmental side remember what we saw from the in the
typical electronics packaging we always go from the environment to the
junction temperature we never go from junction to the environment. We have to
address the environment and in electric vehicles it’s no different when it comes
to the battery management we have a system that we have to address and we
have to come all the way down to the core temperature of the battery.
So the environment plays an important role, ambient condition,
ambient and coolant temperature, contamination, altitude, climate. Remember these are also the issues that we deal with when we deal with
traditional electronics cooling. And equally as important because of the fact there are
standards in any industry, automotive obviously is very known for it and it’s
no different so existing ecological laws and
safety issues are huge you don’t want to have a passenger car catching on fire
and harming people, So when we go to that the levels that we saw how the system is
packaged it is a cell pack in the system we see the issues that are associated
with that is the chemistry geometry reactions and properties on the pack is
a thermal interface which is huge and you’re going to see examples of how the
interface makes a difference when especially when we come to phase change
material. Coolant medium, coolant flow, where there is liquid force natural
convection what have we, this all happens at the
pack level and then the system. System interfaces between the
packs, optimization amongst packs and then realization of the intelligent
algorithm. And you’re gonna see in examples of this that because of the
fact we’re dealing with a chemically active system we cannot really walk away
from the intelligent algorithm to make sure that the system is being monitored
and controlled and the electronics associated with that and their thermal
management is a huge point of concern that we have to address. So when
we look at the lithium-ion battery this graph on the top clearly shows the
superiority of the lithium-ion battery in comparison to the lead-acid
and other types of batteries that are in there and depending upon the energy
density that we have and the type of vehicle you can see that the power
density changes quite a bit, that depends upon the usage. There are two
other components that we have to pay attention to in addition to the power
density requirements and so forth that is the safe operation of the battery.
There is a point of as a function of temperature notice that
these are all function of temperature as we are talking about it the battery
power and temperature when the temperature ranges between about 20 to
40 degrees C we have a peak performance so if we can
keep our batteries at the at that temperature range we have the best
performance the best return on our investment as far as charging and
discharging is concerned and equally as important is the expected life and there
is a very very much of a temperature range where these devices function that
I had a most optimum so we can get the longest life remember there are
requirements that we have to meet in order to be able to have a product on
the market that’s kind of function effectively otherwise people have to go
with the vehicle to the dealership and change the battery every every every two
months so what is the overall map of the Year thermal management concerns that we
have to address so when we look at this the temperature effects are the
operating limits life cycle and this is the you’re going to see this number
modified by massage by different different researchers and the thermal
runaway which is a huge huge problem and we would like to avoid as a result of
the temperature thermal management and the sources of heat and sinks are
electric heating they have the joules effect that that happens and we have to
manage effectively thermal chemical heating and cooling that takes place and
external thermal effects that always impacts the system as far as the
environment is concerned whether you’re driving in inside Arizona in July and
not July 22nd or you’re in Alaska in Juneau and driving in in in wintertime
so the electric vehicle or hybrid large sized batteries high thermal capacity
high heat dissipation requirements low temperature rise and again the low
temperature rise is important for the functionality of the vehicle as well as
the safety and the longevity of the battery under here hybrid vehicles is a
small smaller size of the of the battery low temperature capacity low heat
dissipation requirements and high temperature rise as a result of it again
high temperature rise is so the temperature-controlled prevent
from overheating heat dissipation at higher rates uniform heat distribution
this is very important at you again those of you who’ve been involved in
electronics cooling when you put the stack of PCBs right next to each other
you see a temperature gradient across that and the batteries are no different
the batteries are effectively for the for the sake of analogy or individual
PCBs that we put right next to each other and we need to make sure that
there’s a very very strong temperature distribution uniformity across these
otherwise we’re gonna have neighbour heating taking place and as a result of
with all kinds of thermal issues so self heating elements external heating a
thermal insulation and so forth is required and also the heat recovery and
some people are using the heat also as an energy source to possibly recreate if
they can but that adds additional payload to the to the to the overall
vehicle so as a result a thermal management is not a singular point that
I can say okay I just I just managed a temperature of the of the EMI and
battery I don’t have to worry about anything else but no it’s an integrated
system we have to address all aspects that would not be aware of it as we go
through the design and make sure that the system is designed properly as I
mentioned there is industry standard that are that are communicated because
of the fact they have a human interface we have a device that interfaces with
human and/or occupies or people occupied this space one of these standards is a
freedom car that is a target about you about 2020 and there are all kinds of
expectations about it but some of the sort of highlights are fifty five
kilowatt for 18 seconds which is a tremendous power surge that we have to
manage and have continuous power of 30 kilowatt and imagine in an in a confined
space this is a tremendous amount of power that we have to maintain manage or
generate and equally as important the daunting task of 15 years of operation
of a lifetime it is 150,000 miles this is not a trivial task those of us who
are a little bit Alzheimer’s we know or when we design
for a long life it’s a very very challenging process and you got to make
sure that all the components that are used in that in that system are meeting
the requirements that are associated with that not going to go through all
these details but just to highlight what the freedom car thermal goal is
dissipate 200 watts per square centimeter and just to get a sense of
what that’s what this means if you look at your sort of pinky finger and look at
your name on your pinky finger that’s effectively if you put 200 watt light
bulbs the one on you on that on that area that’s almost one square centimeter
so you can imagine that the the thermal concentration or the heat density as I
hate to call it is very very severe when it gets to that level and we need to be
able to manage it effectively and coolant temperature of 105 degrees C for
the maximum Junction temperature or device or battery temperature of 1 to 25
degrees C these are these are very very critical numbers that we have to meet
with with a challenge that we have to make sure that it is it is delivered so
what are my cooling options I’m dealing with a potentially significant problem
is the challenging from the thermal coupling standpoint and the packaging is
standpoint and when we look at the options of available in industry that
has been either deployed or accepted or effectively in a broad sense or air
liquid and refrigeration so when we look at the air cooling both cooling and
heating is feasible good performance normally large space needed it’s the
cheapest certainly like any other electronics cooling lowered development
efforts it is needed certainly for these applications liquid is the lowest
temperature gradients and please take your pay attention to this column right
here I will respected liquid on the
refrigerator refrigerator when you look at the air you see a significantly
larger temperature gradient but when we look at the liquid it’s one to three
degrees C now remember what I said a little bit earlier is the uniformity of
temperature from pack to pack or from battery to battery is really really
important so B we don’t get the neighbor effect as severely as we’ve seen in
other applications and refrigeration is a
aggressive cooling due to very low cooler temperatures intelligent thermal
management and a specific design needed to avoid a too aggressive cooling and
condensation of humidity and irrespective of the type of system at
the employed refrigeration the condensation is a huge point of concern
and its management could potentially be very very costly so you can see that
these these products or systems have been deployed or are being contemplated
to be deployed in different electric vehicles and as a result of it we have
options that are better utilized so before we run into the options and
review those with you briefly I’d like to just go over some of the thermal
stuff and see some of the data that you’re gonna see where they have come
from I know we dealing with a chemical process in lithium ion batteries for a
lot of us from mechanical engineers that this could be a sort of a point of
ambiguity that what is it that we’re dealing with up basically we’re coming
out of that out of the battery we try to maintain the core temperature we’re
dealing with the surface temperature and when you put look at the heat transfer
equations that are that are associated with that is very very straight forward
the stuff that we’ve done over and over and over again you can see that there is
a different temperature here in this case I used the example of LGBT but it
could as well be a battery doesn’t really matter it is it is a point of
describing what transpires and what are these inter layers that we have to worry
about whether I put a battery in there or IGBT that there are layers that
interface interface resistances interfaces that we have to manage
effectively so you can see that the for instance the convection losses that we
have Trudy here through the Fenton is H 8 TB minus
T C obviously m dot CP is also a function of the at least to the ant ant
ant in order to be able to take the heat away and the the t heart the silicon or
battery temperature divided by the film temperature which is that highest delta
T that we have is a function of all these resistors
that we have to manage and these are irrespective of what we are putting it
as a cooling system we have these interfaces that we have to account for
and if we don’t take it take it if you don’t pay attention to them they could
come back and adversely impact or design or positively impact your design
depending upon what you miss so the subjectively shows by by us trying to
manipulate these for instance if I if I change the value of H I can
significantly impact it if I change the mass flow rate
I can I can impact a totally damp time transported through this system if I
change the fluid this C sub P I can also again impact the impact the year the
total transfer capability do you remember that m dot is equal to Rho V a
where a is the cross section area that the food is the fluid is being taken
away so if I change the cross sectional area
optimize my heat sink if I change the velocity if I change the fluid tile all
of these is going to impact the total heat that I’m transporting by looking at
these inter facial resistances or material resistor between the source and
the sank I can again further optimize my my thermal transfer capability a smaller
that resistance larger the they kill a tool that I can take the heat transfer
into the to the heat sink and take advantage of it
I see Abraham did a very nice job in it showing the capability of these
packaging as it applies to electric vehicles or in general the cooling of
the IGBTs and this is really done for the
demonstrating the purpose is to show for instance if I if I have a heat source
and heat sink well what is what are the capabilities that I have what if I put
jet impingement meaning the jet the fluid has been impinged in the bottom or
and on the top what do I get what if I put microchannel heat sinks
that have a very very hi thermal transfer capability but at
the same time has a have a very high pressure drop so I have to balance those
together the points in November our target is two hundred two hundred watts
per square centimeter our temperature is about 105 and the hot the coolant
temperature hundred and five then the hottest temperature T sub H that’s
associated with this assembly is that one twenty five anything that falls in
this area is a possible solution for me and the important thing to to look at it
and bring it down to this axis is the effective heat transfer coefficient you
can see that this is from effectively about thirty to about eighty kilowatts
per meter square degree K this is 40,000 watts per meter square degree K all of
us who’ve done some heat transfer work we realize that this number is a
daunting task to to achieve is it achievable absolutely so there is a
solution out there as we go through the design and limitations we have to
understand what it takes for us to be able to get to these temperatures and be
able to deliver this level of cooling system that’s associated with that but
you can see certainly it is it is a plausible and possible the different
applications that you have and as you change the fluid you can decrease your
heat transfer coefficient value as you change develop AA city etcetera subtle
as we talked about it before so air cooling is a very nice work that was
done by Tao and that he showed the effectivity the governing equations that
we have in order to be able to simulate and understand what happens in a battery
cooling if I want to do it but by air and then he uses the nusselt number and
the Reynolds number as shown here for a specific battery pack that we have to
use so you can see the SOC is the state of charge and SOC naught is the initial
battery state of charge whatever whatever capacitance says but I like to
point your attend attention to the equations and the kind of information
that we can get out of it as you’ve heard me say in the previous webinars I
call this integral modelling that we can very quickly get a get a
good estimate as to what is happening in our battery system and where is a where
the points of concentration that I have to worry about and they do the
parametric analysis this can easily be done in any of the available tools from
the excel to some like mathcad MATLAB Nemeth it’s available on the market that
we can get and math math deco and so forth and solve the problem so having
these governing equations he did a very nice job in looking at the performance
of the what happens in the system he did something like 3738 different
simulations and changing the variety of parameters i am only showing you three
of those that just to show the capability and the kind of things
happened as a result of the modeling and then the points that we have to pay
attention to and manage this is the system that you have the bunch of
batteries and the air is coming from the outside and leaving leaving the system
so that the adhesive see the battery core temperature is obviously the most
important point this is one that’s shown in the in the red as to what happens to
it this first one shows the back stepping controller that he had he had
deployed as as a parameter shown in these equations that are being
controlled with as as a functional as a function of time and what you can see is
the core temperature is very very stable throughout the process let’s put in the
controller you remember I pointed out to a circuit board in the earlier slide and
said we cannot ignore the the electronics that we have to deploy in
order to be able to solve the problem without this controller this wouldn’t
happen but you can see the surface temperature fluctuations and we can also
see that the coolant temperature air temperature
fluctuating quite quite a bit in this case now when we come to a fixed coding
temperature that means there was no controller involved you can see that the
sort of the onset of the temperature rising very rapidly and going over the
40-degree limit that we had yet the surface temperature and coolant remain
very stable when we go today a linear optimal controller we can see a little
bit of a fluctuation in temperature but the delta T that we see in this is very
small in the order of a 1 1 or 2 degrees but we see a higher level of
fluctuations in the air cooling air temperature and the surface temperature
this may not be attractive in your application but nevertheless very simple
set of equations is enabling us to understand and the dynamics that’s
required in order to manage the system by air cooling and what are the salient
points that we have to worry about and pay attention to you are given an
application for instance this could be perfectly functional as long as you know
that this is gonna stabilize and not go any further
going over 40 degrees C as you saw it is not a very active situation for us to
operate as gonna start impacting the battery performance and life as a result
of higher temperature so the next cooling method is the is a liquid
cooling and again I try to show here what are the our options that we have as
far as the liquid cooling is concerned with different systems that are deployed
in the in the market yes you can see a passive liquid cooling system where we
have the air coming in today here liquid to a heat exchanger here and there’s a
fan that’s exhausting you to bang into the ambient but nevertheless this is
this is the cycle that you have in order to be able to manage the cooling so this
could be an application for a not necessarily electric vehicle or maybe a
light electric vehicle one of these smart cars that are very compact a small
effectively glorified motorcycle so active moderated liquid and heating that
that may be required and again you can see that the presence of a liquid to
liquid heat exchanger and and this goes into the vehicle coolant that comes in
and take advantage of the vehicle coolant so active cooling and heating we
have the air from the evaporator or refrigeration from the from the
condenser comes in we have a heat exchanger place here and the liquid to
our heat exchanger so the problem gets more complex and more components have to
go into the system that we have to address a little bit
reliability we have to address the weight issue we have to address the the
cost issue and also that it’s effective management of the of the battery pack
depending upon what we have to use ultimate objective is to make sure this
battery pack is working properly and it’s giving us the performance that we
want so and you look at the level of packaging that takes place this is an
example from Audi that they’ve done it’s you can see how complex the the process
is you have the you have the cells that are that are shown here and this whole
assembly is put into this structure that has the lower protection cover has the
cooling system as you can see in the middle with the fluid coming in and
going out you have the battery frame that the battery has to be held intact
and housing trade in order to be able to accommodate the batteries and so forth
and the aluminum crash structure in order to make sure that they’re
protected in in the case of possible crash and then you can see how these are
going from here and packed into into this and then eventually into into this
system that the plumbing the all the packaging that’s required in order to
make sure that this one complete unit for transport ability you can see that
as as we talked about it before the serviceability of these batteries are
very very important and you don’t want to have a one battery that you can pull
out and put a new battery in or or be able to uncover this and take it change
the individual similar to that we have stopped functioning properly
and eventually this whole thing goes into a onto a chassis that powers the
vehicle to go forward and and some of the vehicles that we see in the market
right now they have quite a bit of power quite a bit of a range to three to four
hundred depending upon where they’re obviously the weight of the occupants
and what’s inside the vehicle but they can go out at their high speed in long
distances so the battery technology is really transform quite a bit the coulee
technology in this case liquid has also transferred quite a bit in order to be
transformed quite a bit in order to be able to support that level of function
that so when we look at the liquid in this
example you can see the schematic we have the battery cells here and then we
have the cooling plates that are in gray if you can see it on your screen and
this is one one embodiment of if you will one design and eventually these are
coming to the to the connections to be able to circulate the liquid and take it
out this is a design the one in the bottom that was done by Tesla well you
can see that there is a tube that is being drawn right through the battery
pack but there is a connection between the the the battery pack here and the
the plate and again this is a patented technology by by Tesla so you can see
the different embodiment different improvement implications that are done
in order to be able to cool the battery the objective is to make sure the
batteries are maintained properly and I’d like to draw your attention to the
number of batteries that are being used in this particular application for for
Tesla eighteen thousand batteries are used in this application for the Model S
battery and again more deployment of the liquid cooling and I locked you again to
draw your complexity draw your attention to the complexity and how designers have
gone about to to design this very effectively what you see here is an
example of a volt by boy I believe by Chevy where you have the battery you
have the thin plate and you have the cooling plate and then and this this
area is attached to the Year coolant that’s been circulated within the
battery pack all of these are put into these plastic frames and and packed
together into a structure and eventually is packed into this but when you can see
as you can see here there is there is Inlet and outlet for the for the glycol
material to fluid to circulate inside the inside the system to to provide the
cooling that’s required it’s a very very effective system as was designed by
Chevy or GM but you can see the complexity that they have to go through
in order to be make sure that that the connection is made notice that every
single one of these effectively is a fluid connection joint that has to be
effectively sealed and make sure that’s functioning properly with the expected
life that we talked about we are talking about the seal that’s most last 15 years
in elevated temperatures with shock and vibration and extreme temperatures and
be able to function effectively and not provide a leak the next concept for a
coolie that’s been explored by some manufacturers is the old concept is
called the immersion cooling in the old traditional immersion cooling
you just dropped your electronics into the into the bath and there was a heat
exchanger on the top where as the fluid vaporizes it condenses and comes back so
there is a full cycle taking place in them this concept found its way I think
initially was designed in the vacuum tube era and then in the 60s and 70s
mainframe computers like IBM and others started exploring this possibility and
was never really successfully deployed they kept on coming back to a less
cost-effective less costly I should say systems for cooling and and deployed it
accordingly and now you can see it’s been be possibly contemplating the
battery cooling where you can put yourselves inside a container and you
have the liquid cooled heat exchanger on the top where the fluid turns you to
from vapor to liquid and the cycle is repeated over and over again
the biggest challenge obviously we see is in the packaging and serviceability
repair of these parts as you go forward here is a concept that stone by I think
zinc modular battery systems in out of China that they’re they’re putting the
whole system into a into a immersion bath and this is what the system looked
like and you always have to have a liquid to air heat exchanger in order to
be able to take the heat out if you don’t have that heat exchanger on the
top but irrespective you have to have that another heat exchanger further back
to take that heat that you generate by the battery
in order to make sure they’re working properly
3m Novak that as Novak that we talked about before they obviously claim that
this is a very effective cooling system and that they have highlighted the
benefits of these as a direct cell contact helps improve heat transfer
performance help to improve his pack temperature uniformity I mentioned that
this is very important and certainly cooling or immersion cooling can help
health help helps protect against cell to cell a thermal runaway which is the
neighbor effect that we talked about potentially enables a higher charge and
discharge rate depending it because of the fact the whole system is at a lower
temperature if you remember the chart that I showed you that said for the
liquid cooling the temperature gradients between one to three degrees C so the
success of this now requires an liquid to our heat exchanger or on active
cooling system in order to make sure that we can to move the heat and create
this recirculation that’s required and we have a change of the phase change
take simple takes place from vapor to liquid so we never have a dry out if
your liquid to our heat exchanger fails you’re gonna have a dry out all the
liquid II so the emergent system is going to vaporize and as a result of it
may have all kinds of catastrophic failures certainly heat pipes have been
used in a variety of applications and automotive air battery cooling is no
different we all know that the heat pipe is a transport mechanism that takes the
heat from point A to point B and they come in a round and flat shape and
they’ve been certainly deployed or considered in the battery coating note
no different than any other applications where you have the heat source and you
bring it out to an area that you have a better airflow and and you put the fins
on it excuse me in order to be able to cool the batteries and take the either
way so in order for this to function effectively with or without the heat
pipe is you have to have an effective heat sink at this end of it otherwise
your system is not going to function effectively this time your ploys excuse
me for one second the same applies for the cells of the
cancers and so for if you put it in it’s inside the container and if the
container is filled with some sort of a transfer fluid or medium you can take
that take the heat away and use the flat heat pipe to dissipated elsewhere the
heat pipes do two things number one they they transport the heat very effectively
from point A to point B number two is it allows you to spread the heat more
uniformly over over your entire surface in the back of your heat sink if you
have heat pipes you can get a better distribution and so I can use your heat
sink more effectively so you won’t have hot spots on your heat sinks as a result
of it less effective coating that takes place in there so phase change is
another thing that has been socializers are contemplated for a variety of
applications what a face you change material is it’s like a paraffin or some
sort of a wax that changes phase from one state to another from from solid to
liquid from from liquid to vapor and as long as the cycle is repeated we are we
are all set you can see here that there is a storage temperature as well as the
capacity to retain heat and the increase of the internal resistance which is
another something very attractive that we want to see and we can see the
temperature dependency temperature dependency affects both parameters that
are very very important in the face George Wein had done a very nice study
to show what happens to these to these the devices as we go forward so he uses
a PCM that was pure paraffin then he changed it to the expanded graphite and
paraffin some mixture of 20 80 percent and then he chose the the third one that
was expanding graphite/epoxy and paraffin and as you’re gonna see
epoxy has has other advantages that that provides some some consideration so this
is the setup that Bank looked at and you got to look at the also functionality of
the year of the of the piece TMS or materials that you need to have active
could in order to be able to return today to to original state so the first
one that the blue dots show the pure paraffin the red dots or red markers
show the 80/20 combination and the black ones show the third combination but is
the epoxy paraffin and expanded graphics and I think as you can see obviously the
lower the temperature better off we are but equally as important pay please pay
attention to the cycle at the time that is changing as a result of it when we
when we changed the mixture and the combination so it’s a highly transient
problem the combination of the mixtures that we have depending upon the
discharge at three different levels that’s discharge one discharge three and
discharge far right and this shows that the discharge rate as and also the
temperature difference and the green one shows no no cooling if I if I had just a
standard cooling process and you can see that the composition and the mixture
that we have plays a significant role in the effect about PCM so let me not go
through these details you saw that the numbers that you see so with respect to
what the temperature fluctuations are and what they gain a benefit sort of to
upwards of twenty thirty percent when we change the mixture but important things
let me just do these observations battery thermal management using PCM
shows excellent performance in limiting peak temperature at short period so when
I read when I say that conclusion that the thing that comes to my mind is PCMs
are certainly good as a sort of a safety valve I have a cooling system in place
I’m gonna put a dilution of PCM in there in order to make sure that if I have a
thermal runaway at least I have a secondary system to suppress the peaks
and manage it effectively the battery using PC and without convective cooling
methods may not be practical at all we have to have a cooling system in order
to be able to bring it back to normal temperature
the use of the PCM in those applications enables us to use a smaller air cooling
application I bring it to reality and lesser the weight more effective our
devices and vehicle designs will need to wait the potential increase in mass and
and cost associated PCM against the anticipated benefits we had eight years
I’ve done the use of the vapor chambers to be able to effectively cool these
batteries what we’ve developed is a an array of aluminum and titanium vapor
chambers vapor chamber for those of you who may not be familiar with it is
effectively a flattened heat pipe effectively and what we’ve done very
successfully it’s been able to oops sorry been able to I’d lost my
pointer here somehow to make it out of aluminium and titanium but in very large
sizes unable to put a copper plate and or heat sink on top of it whether this
is an individual system or connected to the bigger system doesn’t make any
difference the point is its ability to have a very large platform they can rest
against the batteries you still have the thermal interface materials but what the
vapor chamber does a uniform eise’s temperature gradients across multiple
batteries and then you have the dedicated cooling system to be able to
take it away you take the heat away and or put it into a bigger system so if you
can see there is a broad deployment of batteries in variety of applications
across the industry so whether we have done automotive or whatever that that is
that’s a point of concern you see that the batteries are being deployed and the
point that we have to pay attention to as we go through it like other
electronics that we’ve dealt with over the years the phone I mean this is very
much system-specific we cannot take the system that’s done for company a and
just plant it into a company B because of the fact that it is very much
designed for the final application that we have to go through so in summary
temperature needs an effective management play key role in deployment
of battery system in any application including electric vehicles
two major problems caused by temperature can be found on when it comes to battery
cooling one is the year the temperature exceeds permissible level during the
charge and discharge and uneven temperature distribution attributes to
localized deterioration of the of the battery and potentially catastrophic
failure temperature effects heats heat source and heatsink electric hybrid
vehicles and batteries in smoke or the temperature control should be considered
before designing the battery thermal management system it is it is very
important that we have the that information in front of us before we go
on design something that’s not going to fit effectively either law for – less
than 15 degrees C or higher temperature greater than 50 degree C will adversely
reduce the battery cycle life and that’s very effective remember the batteries
that beers that it’s expected to be designed by the freedom car supposed to
operate for 15 years or hundred fifty thousand miles
research suggests that lithium ion batteries the desired operating
temperature to achieve required safety and performance is between fifteen to
thirty five degrees C with five degree C temperature variation from module to
module a daunting task it’s not an easy easy thing to attain if we especially
don’t have the proper resources in order to make sure that we can design the
cooling system that’s going to fit the application the address and his team
provides the following temperature bands at different operations level battery
capacity and pulse performance from zero to ten degrees c optimal range twenty
thirty degrees c faster self discharge we had 30 to 40 degrees c
irreversible reaction.add short circuit they filled forty to sixty degree c and
there are three primary cooling approaches that are considered for the
battery thermal management at this junction air liquid and refrigeration
and every single one of them have branches that are associated with that
air cooling could have a TCM heat pipe liquid cooling could have a
PCM and some sort of a system level cooling refrigeration etc so design of
the cooling system is a strong function of the final product that that will be
resilient of the ownership is very very important
a lot of us have will have it we don’t pay attention to it as we going through
the design it is not just the cost of the battery it’s the service life access
to parts operating expense and all the way to the disposal and every other
thing that’s in between among other parameter is our important consideration
once considering it design of the couny system so it’s not a if you don’t want
to design your vacuum we want to understand what’s going to happen at the
end and the users we’re going to use it in order to make sure that we have it we
have designed an effective system for it similar to any other electronics coding
problems there must be a technical or marketing reason to go to a higher
capacity cooling always to start with air cooling and travel up the cooling
ladder to make sure that you have exhausted our options that are
associated with the cheaper less less complicated systems like air cooling
before we go to liquid and as we go from from liquid to refrigeration it gets
that much more complicated one thing that’s really important to know is that
the market is rich to saturate that with design including options for battery
thermal management we need this we need to see that use and don’ts because there
are a lot of stuff that’s been done this trim there’s so many article of so many
presentations and so many conference and so forth dedicated to this concept
people are doing all kinds of work across the globe before you jump into a
design please take the time to understand and what has been happening
and what’s the best thing that you can do what we can learn from what’s been
done but the do’s our review and understand the problems and the boundary
conditions that are that the solutions or the solution was developed for
understand the approach that the engineer took to solve the problem at
hand not not just the final system the don’ts are do not assume that the
solution is an end-all meaning since it work for their product it will work for
your design do not copy what they did solutions published a very problem is
specific and they speak to the possibilities not the exact solution we
can learn a lot from more colleagues who’ve done and when you come up with a
nice design if your company allows you to to publish it please share it with
the community I think it’s always very valuable my people published
and as long as no proprietary and and get the get the technology communicated
but what’s something that ever advocated all the time to solution approaches
whether a numerical analytical experimental are fundamental to the
Soviet vtm issues there are no different than any other thermal problems or
engineer problem that you solve you have to have two solutions and accurate
estimation of the battery core temperature like the a6 Junction
temperature is the court focused for developing an effective cooling
temperature the cooling solution there is no difference between the John
temperature and the core temperature that we’ve done with the batteries these
are these are all the same we have a temperature that we have to maintain and
you saw the important the important the important role the junction temperature
or the core temperature of the battery plays in its expected life and their
performance so with that I thank you 80s has been around for almost 30 years
we provide mechanical and thermal design services cooling solutions air liquide
an active and passive is Temptation Airmen tunnels manufacturing services
training programs and QP dia so with that I thank you for your attention and
I’d be more than happy to answer any questions that is that is coming the
question is what are the major advantages and challenges associated
with two phase immersion cool the biggest challenge with the two phase
immersion cooling is the same thing that we’ve seen in the in the our computing
industry or the vacuum tubes which is very way back before that the issue is
the issue of packaging issue of the thermal runaway making sure that the
cooling system that is that exterior that are short on the top let me see
well I can go back to what I had so I can I can point to it effectively right
here if its core is not working effectively it’s this this combination
all the liquid is gonna turn into vapor and you’re gonna have a dry out so
you’re gonna have you’re gonna be dissipating all that power
and you have no effective coding that takes place inside the system so the
challenge is the packaging it’s a control it is it is serviceability what
what do you have to do if you want to change the batteries in here
how you gonna fill that system how you gonna change this change the fluid which
is the fluid now as a result of the functionality you are mentally safe
disposal of the fluid so all of those things every system has its own
challenges but from the thermal standpoint making sure that your your
heat exchanger is working effectively and the condensation is taking place
that’s that’s the biggest thing so whatever is residing at the end of end
of this system to take this heat away this has to function perfectly at all
time you have to have a shutoff system meaning if this failed the controls that
we talked about this system is shut down so it doesn’t work anymore so those are
from the thermal standpoint that other part of it is deployment when you deploy
it I’d love to see how this is going to be changed or done in the service area
if you go after you have to go back and fill this cavity or this path stop with
fluid again and how you’re gonna be doing it very effective very very
difficult very expensive thank you for everyone who’s joined us this afternoon
if you do have any other questions you can feel free to try to come in just a
reminder that the our monthly webinar series will continue next month in
November I believe it’s November 29th it is the exact date and that will be on
key pipes and in the vapor chambers and their role in heat transfer and you can
sign up and register for that webinar add the same link that you had
registered for this webinar as well I’m not seeing any other question so I just
want to say thank you to everyone who joined us and thank you dr. azar for the
presentation hopefully you’ll join us again next month thank you