hello i hope ah you have followed the other course ah which i have done which is about

how to make a an enclosure now if you remember contrary to normal engineering analytical

approach to any design the word design in our context means integrating or synthesizing

available knowledge and technology to come out with products

so typically if you were to take a thing like our mobile phone which i keep using right

now this is a clone clone of a well known thing suddenly things have exploded its like

you see at the back can you see front there is nothing now if i touch it at the back it

will go on automatically so there is the sensor here

its not as if this fingerprint sensor is older nobody has invented or anything like that

same thing is about when you want to switch off i just need to touch another thing and

it gets it goes off good known things so you have a user interface and then you have a

sensor and then add it to that in this small size it is between four to six radios antennas

and all of them are nicely packed inside the only disadvantage or ah something which

we is a followed is heat it gets hot so putting any protective case like this seems to beat

all the the whole thing only makes it hotter seen this know these things keep getting hotter

and hotter so suddenly that whole back is hot we do not know that the original designer

wanted it this way with this attached or he wanted it raw this is where the problem of

heating starts so we have here while this is a not a very

critical application we will end up with certain applications like this i think i showed you

this i got ah thanks to another colleague of mine this time i got a new piece which

is no it even works not ah damaged and all that you see this is the temperature measuring

device you have a tip and in case i want to see where it is i just need to touch it and

it shows a number now when we come to more and more understanding

of the physics as well as how to use the knowledge in developing new things we need to be a little

more what you call proficient or professional about these things one of the first things

is it is not as if heat sink and design you know i have not invented the heat sink or

design this in my view is an ok ish something i dont

know what it is its aluminium and it is a nice gray color can also be probably used

as heat something and to start with let me start with a well known ah ah device i strictly

dont know what this devices it has been taken out from i had not know something one of the

first thing you will notice is there are heat generating components i do not know there

are some transistors or linear or ah switching devices or anything i expect that ah there

are so many of them and then we have again one two three four five six relays here

advantage of a relay is it has only two nice states in the open condition there is no current

there is an voltage across it no current in the closed curre condition of the contacts

there is no voltage but current is only passing through as such this is an ideal switch in

contrast with that any of our active devices which see here are not ideal even though you

can have low forward drop something you still have a lower drop means there is a voltage

and similarly there is the current the moment you you know multiply it obviously you get

ah the issue of heat loss and heating up how to get over it a still a lot of what you call

science and engineering and little bit of one because the alternatives you need to generate

the alternatives and one of the things again meant here is you see this whitish thing which

is here i think all of us know we know what it is we loosely call it a heat sink and we

also understand you know it is not an infinite heat sink it is just a heat spreader a heat

exchanger whatever is picked up from here it is passed

on to this block which in turn tries to passed on to any medium in this any fluid medium

in this case we have air it is not a what you call its a common knowledge its just like

a car car has a radiator inside the radiator doesnt radiate it we are in deep soup if it

radiates it doesnt radiate at all what it does is all the time [laughter] it ah tries

to use a convective cooling sometimes natural when the car is moving obviously another thing

which we dont have in the car is a fan built the fan is run not in belt but we all understand

when we mean what a fan built its used for other things for running other things what

it has instead is an electrical fan this electrical fan tries to force air through the heat exchanger

basically its a heat exchanger from a liquid inside typically water mixed with ah probably

propylene glycol with a ambient cold air in some conditions it is needed and generally

when the vehicle is moving at a particular speed often we dont need to have the fan switched

on this is a definitely a jump over the maybe cars made about fifty years sixty years back

where to the crankshaft there used to be yes a fan built which is which connects the what

you call ah dynamo or loosely they use the word dynamo alternate or anything interchangeable

but we know basically it is a generator of some sort it could be ac or dc and then you

also have a water pump and then you have the fan belt and then the fan belt [laughter]

has a fan which throws the air on the radiator so radiator is wrong fan is wrong we still

have that heat exchanger no more fan belt now coming back to this thing now if my friend

can show me the monitor any design if you have already seen this it is been there included

in the other lecture of mine about ah equipment design equipment involves tremendous amount

of various other people which need to work in it together in this case fortunately obviously

it is a social creature and so on so at the thing you have a beautiful what you call ah

i mean beehive these hives are common among the animal kingdom you also have it for ah

hornets nest ah you also have it for ah various other thing the common purpose we know is

to probably make store food and also know use it for ah various other thing and then

probably a little bit of socializing i will not talk about it i am just going to talk

about the allegorical representation about this thing

contrary to what we think it is not pigeonhole the activity is not pigeon holed everything

is to work together probably the next slide will try to explain what is a times trying

to do about it all these are needed so in this cor corner you know we have only this

what you call thermal heat technology slightly related to is the interconnection

so if you remember i have ah mentioned this earlier saying in our case normally as far

as possible with right only work about the enclosure and then how to treat heat with

this i have mentioned it in passing earlier that ah we have this dotted line you know

probably represents the external enclosure and then we have this thermal aspects by which

inside the device how do you bring the heat out what we have here is a breadboard ok its

made with a on a what you call i think you would have seen these things [laughter] ok

ah board which has a lot of things and all that and then we have this aluminium plate

here and aluminium plate here they have tried a circuit and in this case it is easy nicely

you know things it here and there is no problem this is a starting point

but eventually when you end up with a complicated thing like this this is a full ip sixty seven

sealed drive from a commercial ah manufacturer its a dc motor controller the voltage you

know is thirty six volts in the current is hundred and fifty amps thats a lot of current

so even if we assume ninety percent ah what you call ah efficiency it means ten percent

loss and its ten percent loss this ah one sixty amps comes to sixteen amps into thirty

six thats a lot of power is it not sixteen into thirty six something like ah i think

ah five hundred watts five hundred watts of losses are associated with it but the magic

is it is not continuous not continuous neither is the current continues obviously you know

it goes in peak side the back the manufacturer has taken care to give us a flat plate in

fact all drives you know like this unless you ask the manufacturer to fit the heat spreader

on the trend give they all come with its now they give all the specifications here

saying it works with an ambient up to sixty five degrees centigrade provided you can maintain

this at something its fashionable to use the word twenty five degrees centigrade but impossible

to maintain anywhere like this so typically if we can maintain this around ah fifty degree

centigrade and the ambient is around twenty five we still have twenty five degrees to

play so we need to dev make a device or ah make

a method know by which that ah twenty five degree centigrade for a given wattage of these

five hundred watts will give you the thermal resistance of it so you have seen that we

ended up with the beautiful twenty five by five hundred which will come to a very small

number typically all power heat sinks are all designed with these numbers like that

so if you take normally fifty by what you call five hundred it will come to a point

one if you take twenty five by five hundred it will come to a point zero five so if you

have something which can be made at point zero five centigrade per watt it can be used

safely in continuous running conditions alternatively you need to deride the drive which is typically

what is done where are early full one sixty amperes passes

and then three sixty thing is there because one sixty and three sixty sixty comes to five

kilowatt this is not intended for a motor like that you know typically this is used

in wheelchairs it is used in a little type of you know high power ah electrical mobility

devices and the peak currents are never used this is only for ah this thing so typically

they use it for ah motors up to around you know two hundred three hundred watts so if

i take it i get only thirty watts so thirty watts i can design the heat sink for it

you will notice that most of the thing inside is how sensitive are the components this is

where you know electronics has been improving and in fact if you can look up the internet

you will discover things like high temperature ah what you call electronics there are electronic

device which will work it ah i believe two hundred degrees centigrade i will show you

the link afterwards another is how will you make a layout and

then important thing is heat bridges how do you bring the heat from inside to the outside

so typically the plate i have shown you had something make sure that everything is brought

and the plate uniformly has to be at a very high temperature its a very very interesting

thing if you have a heat sink when you put your hand on it if it feels cold something

must be wrong either its really working very efficiently with zero this thing and or inside

the devices already failed or its not switched on and all and a heat sink which is at the

ambient temperature or a heat spread at ambient temperature it can really not take any this

thing across you seen this show you it cannot really take anything across

so we have the problems about it my lecture is going to be a little about basics of thermal

aspects and then little bit of how to select a little heat sink and all it and then ah

how to manage this ah what you call what are the heat transfer mechanisms if any of you

recollect this this about sums up all that is there in modern ah thing including face

change you will see you know we have this beautiful face change devices and even see

here its not as if its everything is you know cut and dry you have you have a heat pipe

flatten such that the what you call actually evaporation of the working flow it takes place

from there and then it comes and ah circulates and then in this case you know probably by

definition heat pipes do not have a internal circulator and then we have a heat spreader

one thing have you noticed the color [laughter] heat spreader is not black

ah some reason we have all been told heat sinks better be black have a look at this

is actually inside an equipment and its coated black does it make sense to make it black

in due course so you will you know you can probably take a call on that saying whether

you agree with me or not and just look around any of the new equipment

you know instantly they have discovered that if you coated with black contrary to whatever

theory you have been taught they tend to fail because black absorbs heat as much as it can

radiate heat so to say i mean in one of the lectures i heard know there three modes of

thing and then one of them is conduction another is ah you know convection third is radiation

and they take equal thing maybe that equal is only a simplified way of explaining to

a common man they never take an equal thing in fact in the normal thing wherever you see

its unlikely that ah radiation you know ever is used to lose heat

again like all rules i have give an exception if we take a break toaster it best works with

radiation and if you ever wondered about it we have a beautiful toaster inside you can

see the hot coils but outside ah even its a plastic it doesnt melt and then you dont

have any what you call insulator like a polyurethane foam and all that you instead have a simple

heat shield which is a what you call ah um polished aluminum foil which will reflect

away all the heat that can come inside plus there is a small air gap air gap plus this

reflective shield is sufficient to make the walls warm ah not hot otherwise the plastic

will melt now i will coming back ah to this again you

see here you see this beautiful what you call ah if we drive for the electric ah vehicle

which is typically characteristic of most of these ah things here dont ask me sir then

why is it painted black pass pass the question it has been made for a replacement ah mechanism

hence it is even big and that was made for a i think twenty kilowatts or something probably

its much smaller than this you dont need to make and then this environmentally and all

i have shown so i will now skip go back demonstrations

today i have shown you this this is a drive we make our best interest to see that we put

a heat spreader to make sure that this is maintained around fifty degrees centigrade

only when around fifty or sixty degree centigrade we can take away the heat to the spreader

so typically this heat spreaders will be like this no problem about it i have here a small

experiment you know that one ah you show me this i have an experiment which i wanted to

zoom it out ok which i wanted to conduct to see how do things reach a steady state know

this is a thermocol box ah which was you know actually it has come from some biological

thing at the bottom inside what you have is a plate and this plate uses a a heating element

a ptc what you call thermistor element mounted on a some one type of an aluminum sheet with

spacers and all that this is the same thing which is used in our

mosquito coils you have that small mosquito pad there its written seven watts and then

i am sure you would have seen it also if we take a that mosquito pad and put it on that

it feels a little hot but then by using a insulating mechanism in this case it is a

an expanded ah po form i am sorry ps from polystyrene expanded polystyrene form otherwise

ah we know it is thermocol and then insulating it and leaving it here after around one or

two hours you will notice that it gets hot really really hot you cant touch its seventy

or eighty degrees so i will get back to you later when the time comes and then part of

this is this small instrumentation this information typically is something which we will show

you the temperature at a contact point if the word subjective makes some sense probably

they should this is a huge thermal mass there by the time i touch something already the

temperature would have changed which i am sure in your physics and or anything if you

are the curious you would have found out how come a block of steel feels cold and a block

of wood doesnt feel cold we are at the same temperature that both the steel and ah the

wood also feels ah its ambient lets say the ambient has a reduced to fifteen degree centigrade

and our body is normally skin temperature around thirty five degrees inside is thirty

seven this thing a fifteen degree steel block feels cold and a fifteen degree wood block

no looks ok not cold or anything i am sure you like guess the answer it is a lot to do

heat about the very very local heat the moment you touch the what you call wood thing it

is already attained the temperature of pure thing on the surface it will be thirty five

only and if you touch the steel thing steel continues

to be at fifteen and if you touch it this strip becomes maybe twenty or twenty five

degrees your thing there is a small error which is exactly why instead of just depending

on this usually in very critical applications they build the sensors also in to be other

things now as we go on this let me show you this

device which we have made ok i am sure somebody would i went right to play with it this uses

the now suddenly you know once in a while suddenly people discover that we have a peltier

cooler like that it has a peltier cooler something which they forget or ah i am sorry something

which needs a due attention is peltier cooler is not an absolute cooler [laughter] it just

maintains attempts to maintain a temperature between two surfaces

in this case we have an aluminum heat spreader and here we have a contact block it was made

specifically for a biomedical application in this we keep two what you call ah ampules

of ah some sample and we need to maintain the sample like various ah temperatures it

was part of some what you call ah sensor instrumentation for biomedical applications typically ah the

effect of ah various types of biological ah things typically antibiotics on curing some

sample so the sample is kept there it is collected from a human body some scientifically urine

sample which when it comes out as i said know it may be some thirty six degrees centigrade

quickly it is shield and kept back in a temperature we want to see the rate of activity and then

afterwards it is again incubated back at thirty seven degrees and then one is a control thing

the other is not a control the actual thing we add ah the concentration of medicine in

it and then we are able to find out the action specifically

if i have a urinary tract infection and if i give a sample and if you can ah put it in

that you can easily find out what is the ideal concentration and what is the frequency where

i need slow releaser what you say dosage and all that which is there which instantly saves

lives the focus of it is the peltier cooler peltier cooler has advantage the we can heat

it as well as cool it and rapidly but everything depends on the rate of heating

and secondly which most of us will tend to forget this surface here is expected to be

cooled this surface here is expected to be warm and you cannot afford to have a short

circuit the moment you have a short circuit any amount of ah you know putting your current

here will not help at all so this whole thing has been made so should it as a cap which

we close the cap or in critical applications we also use ah polyurethane forming arrangement

the movement you cool it and then we have a small opening and then if you put our sample

and this mass has been calculated critically saying quickly within given mass of the what

you call ah liquid typically which has specific it a one and ah we have this aluminium block

and all that the moment you keep all this you know we know the rate at which we can

heat or cool the device the issue is you need to insulate it it works only when it is insulated

these are all well known things as to how to mount something and how to you know attach

it to this and all that which will which is used for temperature things

so what starts as a reasonably simple ah what you call ah calculation we need to again remember

two or three things one is physical process have not changed we do not know creation or

ah what you call by evolution it exists natures vacuum exists natures ah rules exists we have

absolute zero then we have ah five thousand six thousand degree something and then we

have flux all these that natural things our understanding of it you know seems to be moving

a little up and down and all the more that is why when i point out you know i suggest

you check i am sure ah several people say may call heat sinks black first of all its

not a heat sink secondly making it black wont make any difference

and in fact the issue is that epsilon or heat transfer coefficient in radiation that does

not depend on the color especially in the case of aluminum whether you use ah what you

call white or gold or black it is typically around point eight eight you know changing

over it now we can go and check on the internet what is the epsilon for ah various types of

materials very very carefully they have tried to formulate certain materials slightly but

its not a ordinary application you need to what you call it is a surface make everything

and then slightly you know you can improve another thing

but whether a naturally anodized and you know sealed gray color aluminum material or if

you anodize it black color of the paint which is to the human eye does not make any difference

this understanding is new new means maybe lasts around fifty years back

so we have physical process ah just allow me to go here and you know do a little bit

of ah let me take it here we have several commercial ah you know these heat sinks and

ah things nonstop you will see something very peculiar about it you see the device which

is on the left side this is a two six three zero one this is supposed to be a diode heat

sink one of the two things you will notice is at the base where is attached a thick so

does the mass help or not yes it does help here in the case to the best way this heat

spreader works is if the fins all the surfaces are maintained at the highest possible temperature

which depends a lot on how well the heat is conducted to this and how well the heat is

taken away from this if you are to take this right side one mounted

small device here you will see that towards the end in the end they already it it has

become very cold and then if we go to the fin tip you will notice that ah a not much

of temperature differential exists between the tip and the ambient as such it will not

be able to maintain the heat transfer rate which we are looking for

typically things like this are meant for one type of thing where one side you have a device

to be mounted like the drive what i have shown you it comes in long lengths and this time

this thing is slightly different these two limbs are used for mounting and this is cooled

by natural convection on both the directions you have seen that know

we slowly get into this ah idea of how to calculate or how to work on a gross thermal

resistance which we need to have so right now ah my suggestion is right now i will take

a small break here so far we have started please go to the go to your ah what you call

ah if you have a browser and if you have a reasonably ah first connection i am not saying

you need the type of connection we have here which is three hundred or four hundred mbps

even we have something around two mbps and just give a search go to youtube give a search

on heat and mass transfer and see whether i can get a youtube heat and mass transfer

first of all i need to check whether i have youtube yeah i have they have not disconnected

it yeah it even works ok then i go here and say

npte l heat transfer have you noticed it gives thousand seven hundred and thirty results

so i am not the first one even on our courses several of them there i feel you should go

back and at your leisure try to see which one of them is likely to make sense to you

so it your leisure kindly go through any one of these things which you know they you fancy

and whatever i wanted to talk as i said this is not the first time that has been done it

has been done done and again and again like this the only difference being their analytical

methods and then there are tools for you given a configuration very much possible for us

to estimate actually in a very very complicated case like this we have a small conviction

here we have a mass and then this is likely to lose heat so on this you know we have a

a cap which is so probably made with polyurethane foam

the other side we have this heat spreader which it goes to the heat spreader again you

know this the surface is you know hot without it being heat the hot it cant it transfer

anything and then we expect the surface to be cold [laughter] ok so this whole thing

it is possible for us to very much to model it as if this complication is not sufficient

here for good effect we have added a fan also here so ah first cooling ah then we have you

know something which people dread at the renaults number and i am sure renaults friends like

ah you know prandtl and all that you know four of them nusselt and all the people also

joined and you have more numbers then what you want to deal with

so you see a complex model like this we have heat ah what you call a mass transfer on top

of it then we have a heat spreader in which you see these fins are thin by definition

they are not ideally suited for this site of mass transferred like thing how does it

matter yes in this case it make sense because its cheap this is available for nothing if

you want to make an optimized thing you dont ah you know you cant do it with it its used

in the case of space and all that you know this big heavy thing probably if you optimize

it probably can be made in ah my guesses one third to one sixth of the weight for the given

flux here for the given flux even this is over designed all you need is probably a small

tube like thing and a small really really tiny fan and this is where all the theory

helps alert which goes on here so you see here that if you go here you have

seen this i will be probably repeating if you have these things here but at your leisure

know he suggest you kindly also no read up these things upfront and come back and then

you will not be disappointed about it you see here nice beautiful very threatening

equations are there however the radiation constrained epsilon is only one of the ah

things here you see here a surfaces the shape factors because it is concave then we have

all this you know beautiful what you call a non threatening i am sure where ah the people

are there you know and a small area in the parallel circular disk right from various

things like this are have all been dealt already so i am not the first and one thing have you

noticed here everything has been simplified such that the very complicated problem can

be made into a smaller problem in spite of the best software that you have and all these

things still every instance is a unique instance so i have shown you that ah what you call

ah covered thing which i wanted to do kindly go through ah these links and see what best

will help you i have seen that very very critical things

have been put l by k and q and all are constant that is about the same there is no variation

at all and then the thermal gradient also is constant there is no problem about it at

all the problem is our if you take a gross problem how do you simplify it such that in

case you have a surface which is generating heat in case a surface does not generate heat

these are all this symbol then have you seen in the small thing this is one hc coefficient

in conduction or in that case you know in the ah thing

how well let you deal with it and then you also have a transfer coefficient in convection

how do you deal with these things this is where ah mix of ah both theory and then a

mix of ah ah practical ah things and then finally a gross ah combined thermal resistance

we usually use the word thetas so when you buy a commercial heat sink

directly that ah the sales person gives you or the manufacturer know they already give

you given these conditions the ambient to the heat sink the what you call ah heat transfer

coefficient is typically in this case you know it may be around twenty degree centigrade

per watt small heat sink total mass is small small area is available and then you need

to decide now you take a device and then you mount it how well it works here

this is invariably you know the starting point of most design so you have a physical model

which you need to do and then you can use simple instrumentation like this and then

we want to further improve on this you know maybe you can put a sleeve and all that touch

it wherever you want i have done this right now its a little bit dirty but i can even

take the sublingual temperature with this its initially very accurate and generally

they have made sufficient accuracy such that this tip know can take ah i mean there is

in fact a a dam like thing inside it dammed ensures that this heat is not transferred

to the tip and the tip is really really accurate i think at this point i will take a break

and then so that the whole lecture you know can be condensed into a manageable thing so

thank you