Number of Transfer Unit NTU Heat Exchanger HMT Tutorial- 27, Heat and Mass Transfer, GATE Video Lecture | Topper Handwritten Notes & Videos for GATE ME - Mechanical Engineering

okay my dear so this is Elka Marcin and
in this video taught well I'm going to
share with you about NTU well you know I
hope you know about NTU well the full
form of NTU is number of transfer units
so as you know NTU is one of the most
important topic if you are preparing for
gate examination because they have
already s quotient in gate 2009 for two
months directly they have s quotient oil
well little bit related to heat
exchanger because this the topic inside
the heat exchanger so what we are
exactly going to do in this video
tutorial I am going to share with you
what is exactly NTU first and second an
example with you I am going to share
with your example that's why you can do
much better you can understand it how to
solve numerical problem if in any
examination may be complete examination
mainly university examination you will
give such question you can quite easily
solve the problem okay I hope you are
getting me right so you are getting my
know that because it's been long time I
have been making videos and there are
thousands of your students and we have
in over hell melt from your as forms
thank you very much for watching our
videos while my videos have covers okay
so let's go for it
so basically what is NTU NTV's number of
transfer unit n2 is equal to PU a by MC
P and here one thing I am just notifying
that is minimum U is overall heat
transfer coefficient a is area M dash
mass flow rate KZ per second and CP is
specific heat but here what is the
meaning of minimum that is important
because without knowing this concept we
cannot solve problem quite easily and
accurately because will be in confusion
while solving problems if any portion
ask related to NTU so first of all we
need to
and it's basic concept what is MCP so
MCP is also known as heat capacity okay
so let's go for it
suppose that we are having a heat
exchanger okay that is a parallel flow
heat exchanger suppose that we are
having a heat exchanger parallel fluid
exchanger so in case of parallel flow
heat exchanger I would hit X ends like
this suppose that this is th one this is
TS 2 this is TC 1 and this is TC 2 okay
so as you know this is a they're
definitely mass flow rate something the
temple a CP the definitely some values
will have for this hot fluid and for
this cold fluid the same there should be
some values of immunise there should be
some mass flow rate and that few must
have some specific heat at constant
pressure okay so this is about it I mean
here what we have to do we have to find
out total value of M CP for cold fluid
and total value of M CP for hot fluid
then we have to compare we have to
compare which one is minimum and that
one we have to use here for finding out
you that is heat transfer overall heat
transfer coefficient I must say that
okay so this is about it now if if we
don't have given the value of U then how
we can find out that so we know that
formula there is a formula Q is equal to
UA theta M this theta M is known as LMT
logarithmic mean temperature difference
okay now we had we can find out we can
find out this you this you from here we
can find out this you from here so we
don't need to have penny for that we can
easily find out okay that thing okay so
I hope you understand about it all right
so let's go for it now now most
important what is the unit of Q that is
Joule per second
or what first second what is the unit of
LM LM TD maybe
centigrade or Kelvin okay now what is
the unit of area meter square and you
what per meter square Kelvin or
centigrade okay so this is about it this
is about the old data all things we can
use here to find out n tu now if you
will say what is el MTD well I have
already shared with you what is LM today
and how we can find out logarithmic mean
temperature difference sir we easily we
can easily solve problem related to eat
for parallel flow as well as counter
flow heat exchanger well in this part of
video we have I have shared with you
what is NT and how we can relate these
things with this one and this one so
only knowing the formula and you cannot
help you in the in good complete
examination you have to know its root
basic concept okay so this is this is
about all this about you know this is
about NTU and other other things I have
shared with you now suppose that we are
having a numerical we have given a
numerical problem okay suppose that we
have given a numerical problem because I
know what there are many I mean around
70% of my students are preparing for
gate so they are watching this video
this videos only we call of gate so I am
focusing to help them to get basic
concept as well as some important tricks
to solve problems with accuracy with
maintaining accuracy because without a
Gracie what's the use of solving problem
so suppose that we are we have given a
numerical problem okay so in this
problem what's up we just need to
consider I am just going to consider
this they have said that there is a
parallel flow Bella flow heat exchanger
and hot food master old is it is to KZ
per second and CPE suppose that mmm 4
kilo joule per kg Kelvin and here mass
flow rate is suppose at 4 kg per second
and CPE suppose that 3
kilo Joule per kg Kelvin I hope this is
visible that's why I means I am using
different different colored marker so
that's about it so suppose that we are
here we have given these two values okay
for any parallel flow heat exchanger
they said hot fluid is flowing like this
and cold flavor flowing like this their
values this and their value is this okay
so this is CP this is CP this is a mass
flow rate then this is mass flow rate
that's why I have been oh dear M - M -
means mass flow rate means kz per second
okay if we are considering KC but gram
per second we can also happen okay so
this is about now suppose that they say
to find out NTU find out and do for this
parallel flow heat exchanger if they
have given these values now they said
area of the heat exchanger
suppose that five meter square and
overall heat transfer coefficient
they said around what I say - kilo watt
per meter square Kelvin right so here we
can easily we easily write that n2 is
equal to you a m CP and CP is required
minimum value we required minimum value
so we need to consider also that thing
now we have in bed we are going to make
me stay you will just write to you don't
write only to this side 2 into 10 to the
power 3 because kilo is their first
second we have to write area area is 5
now third we easy understand which one
is minimum that is 8 into 3 sorry for
into the for multiple 3 12 to multiple
sorry to multiple for 8 so yeah
8 is minimum okay so that's it that's
about it now we can easily use Kelsey
was by the way can we use this Kelsey
engage probably get a good examination
so 10 to the power 3 into 5 so I to
multiple 10 to the power 3 into 5
divided by 8
okay so this is 1250 now do you have any
idea what is the unit of this can give
what is the unit of and tu if you don't
know or maybe you know I don't know
about you okay so can you guess what is
the unit of NP you know
okay okay let me share with you how you
can find out unit event you well it is
actually dimensionless but how you can
how can be so Co that unit of NTU is
dimensionless so you know that you the
unit of you is what I have already
shared with you what per meter square
Kelvin area meter square mass KZ into
second
okay now CP CP CP in kilo Joule kilo
joule per kg KZ into Kelvin okay now now
what is meter square meter square cancel
Kelvin Kelvin cancel and KZ okay there
is something missing a KZ is there kilo
joules are there so what I caught a
second Kelvin in the end this is what
what means Joule per second so second
second cancel but depending key Luke is
Joule and Kelvin cancel can be in cancel
so what we got June only so Joule means
Newton meter Newton means mass into
acceleration KZ meter square per second
second second would be cancel their
right and meter is also there so after
calculation we go out here dimensionless
will be not get any dimension of this
that's why that's why this NTU is
dimensionless I hope you are getting my
point right so this is all about NTU and
it's all important things about it okay
so I hope you understand what I mean I
wanted to share with you and thanks for
watching see you soon in my next video
bye bye