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Welcome to module 8 and lecture 2. In this second lecture of this module, we are going
to discuss on evaporation principles and evaporator performance. Actually in the last lecture
that means, the first lecture of this module 8, where we are discussing on evaporation.
In the first lecture, we have discussed that how different types of evaporators are used
for different types of materials. And also we have discussed some important points related
to the what kind of solvent we should use. What is the what should be the proper reserved
the solution that is getting evaporated, and depending on the properties different types
of properties have been the solution what kind of precaution should be taken and all
these we have discussed. Now in this lecture, we are going to discuss on some principles
related to evaporation and also that is performances of the evaporators. That is why we are going
to discuss.
To the start with, we will discuss first evaporator capacity and economy. So, these are two important
two important technologies related to evaporation. What we see first one is the capacity - evaporator
capacity from the name of itself we can see is that vaporization capacity, but it is a
capacity means vaporization capacity, but it has got a very specific definition, it
says that number of kilogram of water is vaporized per hour is the evaporator capacity. Similarly,
there is the terminology is the economy it says that number of kilograms of water of water vaporized, number of a kilograms
of water vaporized from all the effects taken together for each kilogram of steam fed to
the first effect. So, what is the let us try to understand in
the very first cases is that it is it is consider the number of kilogram what will the per hour.
So, from one particular evaporator we are getting how amount of the water vapour evaporated
power, but what about the economy economy it says that number of kilograms of water
vapour from all the effect. So, we can have not only single effective. So, we can have
several effect now what is this effect? Effect means, it the unit where that a solution is
being fed into, and that is heating is being that and the mutual is operated then the thick
licker is drain and the vapour is coming out of. The whole passes which is being happening
in one particular unit that is called an effect. So, this is in case of evaporated is called
then effect single unit which is completed from all expect is called an effect.
So, there can be such effect together that means, there can be series of parallel combination
I will discuss it latter, there will be some effects together this is called fit forward
fit backward fit all these thing we will discuss. So, when you have such effects together total
amount of as vapour which is be realized for feeding one kilogram of steam that is very
important. So, how many affects you have in a system whatever amount of the total is coming
out, and that is coming only for one kilogram of steam. And that steam is feed into the
first effect actually this is the convention to express the the effect to first effect
in which the feed is being the steam is feed into so external steam is feed into that particular
effect is called the first effect. Now what we can understand is that for a single effect.
So, for a single effect we can have the capacity economy to be less than one, as we understand
for if you have single effect the if we put an a steam, then what will happen the amount
of vapour produce will be definitely less than the steam. The reason is there will be
lot of amount of energy that will be wasted during this process. So, this is called we
will discuss in details in a little latter about this what are the factor that is working
on this.
So, this is the reason why it is economy will be less. So, economy for one effect is nearly
0.8. It is less than one definitely it this 18. So, if number of effects is equal to say
0.8 sorry number of effect is equal to is equal to n then total economy will be nearly
equal to 0.8 n. So, this is a this is a very gross estimation of the things now why this
effect why why it is less the reason behind it is that three things as I told you that,
that when the steam is external steam that is heating. So, there will be some heat lost
then at there will be some amount of that enthalpy of vaporization or I should say the
latent heat latent heat of steam at higher temperature is less than that of latent heat
is less than that of steam at lower temperature. So, what is happening in case of evaporator
that steam it put in the say shell side and in the tube side liquid is there. So, the
liquid is being heated so liquid is being boil. So, the boiling temperature of the temperature
of the steam will be definitely higher than the temperature of the boiling liquid in the
tube, this to maintain the heat transfer and therefore, the latent heat is of that steam
which is at the higher temperature has to be that will be definitely of higher pressure.
The latent heat amount will be less for 1 kg of the steam. So, though 1 kg of steam
is being used the amount of heat being supplied to the liquid is boiling is less therefore,
this reduces the automatically this is reduces this value and also another point that there
will be heat lose during this process. Therefore, the amount of vapour generated
will always be less than the than the amount of steam that is being used for that. So therefore,
economy is always less than 1. And then the ratio of capacity to economy is called steam consumption per hour.
Now, the one important aspect related to evaporation is called boiling point elevation. So, I will
I will turn it as BPE we know that boiling point elevation is one definite consequence
in case of in case of evaporator. What happens is that as you are as we know we know what
is the boiling point elevation in a in a solvent. If we put some amount of salutes there will
be an elevation of boiling that is called boiling point elevation though the boiling
point will increase. Now, in case of solution that is to be evaporated; so, what is happening
with time and with more amount of solvent going of a out, and this what is happening
getting constructed higher the concentration the boiling point will go on increase in that
is what is called volume point elevation. And if you see that calculation of the boiling
point elevation. So, in case of evaporation that boiling point elevation is quite substantial
and to boiling point elevation calculation is separated is difficult issue.
So, it is very difficult. So, what is used is that duhring’s line is used. Duhring’s
rules used for boiling point elevation calculation; now what is Duhring’s rule? Duhring’s
rule states, but it says that boiling point boiling point of a solution is of a solution
of given concentration is a linear function of boiling point of water. That means, it
is like this that if it is boiling point of water is and boiling point of some solution.
So, we can have so different lines based on concentration of various conservation of solute.
Will have different line and this line are called Duhring’s lines Duhring’s lines.
So, this is a linear. So this is a straight line. So, we can have a relationship for two
points then we can draw straight line. And then, we can go for that interpolation or
extrapolation of the this lines and get information for various concentration terms. So, that
is what the importance of the Rayleigh duhring’s rules is. So, if we say if we except the Duhring’s
rules that it is a linear function. So, if we have for at least two concentrations; so,
two boiling points of water and the corresponding boiling point in the solutes solution if we
know, and then we draw a line. So, this is the boiling point of water and
this boiling point water will change boiling point will change, because of the pressure
of the system, and then the boiling point of the solution is also known. So, then for
two is if it is known then for other concentration we can easily find out. Similarly, for other
pressure we can find out similar for. So, just by knowing that linear it is relationship
by knowing some of the experimental delta, we can find out the other values by using
the Duhring’s rule, but Duhring’s rule is this works good work till moderate range
of pressure.
And it is not satisfactory at higher pressure. Now, this another point is related to the temperature driving force.
In case of evaporation if we see that, for a say long tubes are there. As we have the
seen in the previously that say this is liquid entry, and this is the position and liquid
vapour mixture leaves, and this is distance along tube this is the distance along tube.
So, this is say this is the temperature say boiling point of water T w is the boiling
point of water. This is the boiling point of water T w and so T b this is T b and this
is also I am sorry T b. So, the boiling point of solution; so that means; T b minus T w
is the boiling point alleviation, but and here or you can say that this is the temperature
of saturation temperature. And it is started it is coming with a some higher temperature
and it is coming down. So, this is T s. Now this is vapour and this is liquid. So, this
region for this region is for super-heated vapour and this is for sub cooling. So, what
is happening we have T u and the liquid is entering and then it is boiling and then vapour
liquid mixture is going up and it is a leaving the tube.
So, this is the length of the tube. And this is the boiling water boiling point of water
and this is the boiling point another the pressure conditions. Pressure condition of
the inside the tube and this is boiling point boiling point means, the saturation that it
boils when that it mix up with the saturation temperature. And this T b is the boiling point
of the liquid of the solution at that particular pressure in the tube, but what happens is
actually as it goes along the tube. So, it happens to be like that profile is there is
a profile like this and there is another profile like this. So, this is say for high velocity
and this is the low velocity case. This is a case A and this is case B say. So, what
is happening actually this is the boiling point of the of the liquid, but actual temperature
happens to be like this for low velocity situations. What happens in this case? We can understand
that when a fluid enters into a tube. It it it has got different type of pressures acting
on it. The pressure is that vapour chamber pressure total pressure is equal to vapour
chamber pressure plus, it has got hydrostatic heat plus the frictional heat loss. So, at
any point it has got this much amount of the total pressure. So, based on that it will
boil now what happens is that a fluid, once it enters it does, because the temperature
is high it does not boil at that, because the pressure is high it does not boil is boil
at this point at the end of this when the hydrostatic heat is not there. So, it boils
at this point it does not boil at this point and its temperature rises and then afterwards
it is when it may be that it boils here. And then what is happening that once it starts
boiling then it further reduces the temperature that temperature gets reduces it does not
require any further, because it is going upward. So, hydrostatic is gradually and the boiling
temperature reduces. So initially, the temperature is high, to it is heated of it is not boiling
and once it starts boiling then afterward its temperature reduces. And then boiling
frame starts, because the velocity is low it starts somehow in the middle of the tube,
and in this case when the velocity is high it boils somehow towards the end of the tube
or may not boil even in a tube at all. So, in that situation when it does not boil in
the tube at all, then it is it is allow to flash in the as I told in the last lecture,
it allows to flash in the in the vapour chamber where it will be at a lower pressure. So,
it will be flashing and then using the flash method you can get the vapour out and then
condensate come back. So, it will be condensate means that concentrate come that comes out.
Now this is what is called the true violin temperature true temperature defines is variable
one. The temperature the temperature of the liquid inside the tube, and this is the temperature
of the jacket that is steam jacket it is the outside the tube.
So, this T s minus this temperature should be the true temperature difference, T s minus
this temperature should be is the temperature true temperature in case of in case of any
flow, but actual this were true or actual temperature, but what is being is taken is
the boiling temperature and the total conditions is taken as the temperature difference on
a average. This is what one important phenomenon that one should understand critically. Now,
second point is this is about that boiling point temperature driving force and boiling
point alleviation with this liquids and then we go to that single and multiple effective
evaporators evaporator.
Now, so we have understood that one thing that evaporator means, that there will be
liquid solution and which will be heated up by heating media which could be normally a
condense steam are used. And and and and what happens in that case is that it is evaporated
and that thick liquor come out. The when everything happens it is called single effect. Now many
times it may not be a single effect there can be a multiple effect. So, before I just
tell about that one thing I should say here, that here that super-heated vapour comes into
this little bit super-heated it is not exactly saturated heated, because if there is some
heat loss. So, then it will be condensed previously itself. So, it is not allowed some of the
super heat is needed, and why is going out of the this heat exchanger, then it is little
bit of sub cooling is possible. Now, coming to this in case of multiple heat
evaporated is needed as we as we have seen, that economy is less economy is we have seen
that less than one that 0.8 around reasons already I have told there are two reasons
could be one is called is the lantern tend evaporation that is that is high that value
is low at higher temperature of this steam, and the heat loss in the evaporator from the
evaporator to the m v n that is these are the two things. In addition to this there
could be another point that for which the economy could be less is that the feed entering
that feed entering it may not be at saturated temperature, the feed entering would be may
be a cold feed. So, feed may be at temperature below boiling point. So then, we need to put
sensible heat. So, this is a different thing all together we need to put some sensible
heat for that. So, it depending upon the type of or amount of heating need needed sensible
heat needed for this for this liquid we that economy will be gradually changing for that.
Now therefore, that we say there is the population to have multiple effects. So, multiple effects
means, that it depends upon the this definition has come or the variation has come based on
the mode of feed supply. As I already told that it is customary or it is engineered view
that the evaporator in which the externals steam is feed is called the first effect.
Now mode depending on the mode of the feed supply; so one is the steam supply external
steam supply another is the feed supply. So, depending on the mode of the feed supply it
can be divided into four types, one is called forward feed, then backward feed, then mixed
feed, and then we have parallel feed. We have the four different types of feeding arrangements
of possible. Now, we know that for this kind of situations that usually the if there are
single effect in place of single effect, if there are two effects there can be three effects,
there can be more than three effects. So, what we have discussed is that that with
the help of the three effects, we try to show that what is the forward feed what is the
backward feed; what is the mix feed. And what is the parallel feed and what are the situations
and what are the positive and negative points that they should be used and advantages and
disadvantages one would get.
So, if we try to see that for this is the example, of the forward feed. Now, you see
so this is steam is given here. So, this is how you called the first effect, this is second
effect, and this is the third effect, that is the very important thing. And then second
point is that feed is coming this feed is coming from this region. It is the first time
it is coming and then it is coming like this so there is some amount of recirculation.
So, it is a basically recirculation it is a example of a typical recirculation evaporator
and the thing. So, this feed is coming going down and then feed is coming and then here.
So, what is happening is that and also you can see that this the vapour chamber and vapour
is coming again this vapour is again in the form of steam. So, if it is a water solution
the vapour is nothing but the steam again. So, this is coming as heating medium again
it is coming as heating medium and this. So, and this is called this is the separator where
we are getting the condensate out and that vapour goes and so this is a natural condensation
that takes place and here the thick licker is taken out. So, that is what that means,
it in case of forward feed triple effect, this is the triple effect see effects are
there forward feed what we can see here is that vapour goes from this to this to this
that means, what is happening that temp pressure in the first effect, second effect, if the
pressure this effect has to be lower than this pressure of this effect has to be lower
than this therefore, it will move to this region. So, that should be maintenance of
smaller pressure in the subsequent effect that is very important that is for the not
only the smooth movement of the of the vapour. So, what is advantages is here is that the
steam were putting only once, but in the multiple evaporator. So, this vapour which is coming
out again there energy used for this evaporation again that for the economy get increased therefore,
the economy get increase, but point over here over here is, that which is that one were
putting the feed over here, that as pressure is high the volume point is high, but here
the liquid is at a dilute liquid. And once it is a it is high. So, it is concern
getting concentrated and go through the other one. So, it is getting concentrated go through
the other one once it is getting concentrated means boiling point increases. As we have
seen boiling point alleviation. So, if the boiling point alleviation is there. So, and
what we want that pressure to be reduced. So, it works in the in the favoring direction.
So, boiling point is increased. So, what we have to do is we have to reduce the pressure
in any case to get into the boiling point situation to get it is boil. So, that reduction
in pressure in this effect will not only make this thick licker to boil at a lower temperature,
but also allow the vapour to come to this and similarly, this thing happens. So similarly,
so gradual maintenance so gradual decrease in the pressure feed is in the forward direction
moving in the that means, concentration getting concentrated more and more in forward direction,
vapour is also going in the forward direction this is what is called the forward feed.
Now, what is there is that important point over here that. So, using forward feed economy
is increased. And it would be as could as three times of the economy of the first one.
And the next part is that
second part is that this is called backward feed. What is the difference here? In this
case what is being given is that feed is starting from here so feed has started from here. So,
this is the circulation and then it is going to the previous one and this equal to this,
but the vapour is moving in the as whatever is direction is given in the vapour is moving
in the forward direction but the feed is moving in the backward direction that is why. So,
mode of heat supply that is what is being classified as. So, what happens in this case
that; that means, in the last effect in the last effect that temperature is less, because
steam pressure is less temperature is less, but first effect the steam pressure temperature
is high. And in case of backward direction in the last
effect, what happens is that concentration of the feed is also concentration of the feed
is also high. That means, a thick licker it treated at the higher temperature. So, a thick
licker is treated is is is heated at the higher temperature. So, the only problem in this
case is that possibility of having the damage. So, it is a heat sensitivity material then
there it is a possibility of having a damage. If I see in case of further treat that is
economy is increase and we see that there is no intermediated pump piece needed. So,
there is no pump requirement. So, flow through natural ways in a gradual decreasing pressure.
And that more concentrated liquid is evaporated at lower temperature and lower pressure. So,
we can say that it is suitable for heat sensitivity material. So, this is for forward feed, but
in case of backward whatever we have seen that we need to have the pumps.
So, what I will say here, now in case of backward feed we need to have pump. So, this will increase
the cost capital cost, but what happens is that it is a good for highly viscous material.
And not only that it is good for high heat transfer coefficient can be obtain in the
later in the subsequent stages. As we understand, because it is, because increased flow ability
if we see again that as we have here, in this in this effect, it is the thickest material
in the last in the effect one, is the thickest material is vaporized at highest temperature
thickest material highest temperature in effect one in case of backward. So, thickest liquor
at highest steam temperature. So, because of this reason because of this reason what
happens is that thick liquor it is app thick liquor means high viscosity. So, it is flow
ability will be reduced. So, it is heat transfer coefficient will be
reduced. So, if we done at a higher temperature; so then it will be good heat transfer would
be possible, but only thing is that in this case in this case, that heat sensitivity materials
cannot be used, because the thick liquor at high temperature may get damaged.
Now, the next part of this is that when feed is when the feed is cold. So, when the feed
is cold it is if it is if admitted in the fast effect of the backward case. So, if we
have that cold feed, and if it is if it is admitted here in the back backward case. Then
what will happen some amount of this steam will be used to use as as as a sensible heat
to raise the to raise the temperature of this, and then the boiling point here, in this point
is boiling point is less. And so, requirement of sensible heat is will be low. As what I
was trying to say is that in case of backward feed, suppose the feed is cold. So, in case
of forward feed the feed would be placed over here. In case of backward feed the feed is
placed over here. And if the feed is cold, and we know that to have a boiling in this,
because it is a lower temperature; so boiling will be at a lower temperature. So that means,
I have to give less amount of energy for the sensitivity as in the form of sensible heat
for this heat to this to this boiling point, whereas in this case if the feed was here.
That means, in case of order feed I would have used more amount of sensible heat for
raising the temperature of heat to the boiling point. Therefore, for cold feed that backward
mode is always preferred. So for when a feed is cold backward mode is
preferred, but backward mode there is a problem that is the palms are requires and this palms
will add extra to the cost and the geometry will be little bit complicated flow geometry
will be little bit complicated. And then an another point that I should say that when
the on the other hand when the feed is hot, so going to the similar logic though forward
mode is preferred, because we are not getting these advantages of the forward feed, when
the feed is when the feed is hot. And another we may sacrifice some amount of vapour, because
when the feed is hot then there would be once if you put over here the feed and it this
at lower pressure there can be automatic there can be some flash in this region. So, all
the vapour may not be used up for the vaporization purpose. So, there be that that kind of situation
may exist so in that case would be losing. So, if the feed is hot we should use if the
feed is hot we should use further mode of heat transfer. Now coming to the next part
which is called to the mix feed evaporator. So, mix feed case means that feed is it is
it is becoming very easy, because we have taken triple effect if there are multiple
effect more than three also, we can understand the concept concept it that feed is given
somewhere in the intermediate. And then it is going to the forward direction like a forward
feed. And then from the last effect it goes to the first effect again as a backward mode.
So, if we have more than three if we have more than three, then this mixed feed arrangement
can be there are many possibilities or any combination can be used, but in case of triple
effect on only one particular combination that is it is given in the second secondary
effect, and then it is going forward and then coming back to the first one. So, first in
the middle and then forward effect, and then comes backs. So, what is the reason behind
this? This is a kind of thing that is happening like a it is becoming like a intermediate
kind of thing and what it does? It reduces it compromise it compromises between the positive
and the negative of both forward and backward feed heat operator. For example, less pump
requirement, less complicacy, less complex is the typing. And so, with and so that these
are the these are the positive things. And also we can use we can get that high heat
transfer rate as we get for backward mode higher heat transfer rate compare to forward
mode, but less than the backward mode. So, this is what is important and then another
method is there, that we will see this called the parallel feed. And this parallel feeding
we can see from here that yes the feed is given just feed is divided and given to the
all the effects at the same time. So, it is a parallel supply of the feed to this steam,
to the effects, evaporators, and that liquor also, the product is also collected parallel,
say parallely from different effects it is collected. So, there is almost they are independent
of each other except the vapour. So that means, heating arrangement heating arrangement is
a interdependent things. And therefore, we are increasing the economy that these heating
arrangements increase the economy that is what is the idea, but other things are almost
independent.
And what happens is this is particularly parallel feed this particularly used for crystallization
for this case it is used. Now, so this is about the different type of supply.
Then, if you see say this is typical summary of the things the advantages and the different
disadvantages of the forward feed and the backward feed cases. And if you see that feed
is based on the supply mode for forward feed it is the simple operation. That is what is
important simple operation, less expensive, no pump requirement more concentrated liquor
is vaporized at low temperature, and thus good for heat sensitive material as I was
telling is good for heat sensitive material, but backward feed is lower viscosity and higher
heat transfer rate in the first effect, and it is lower heat transfer rate in case of
in subsequent effect and steam economy is low in subsequent effect is the lower heat
transfer rate, but in backward inter effect pump and inter effect pump is require and
more folic. So, fouling possibility is more in backward
and damage of viscous material due to high temperature that is what was told. And for
mix flow cases mix feed supply that takes in account of simplicity forward and economy
of backward feed and good for highly viscous and number of pump reduced with respect to
backward feed. And complex piping and instrumentation more expensive complicated to handle. This
is also there to pipe complexity is there like your backward feed condition, but parallel
feed is the suitable for the pressurizes, and it is a it has got a better control over
the system. And complex arrangements pump for each effect. So, it is very important
that we have to drain out this liquid and then we may have to put pump for each effect,
because this pump for means, because it is being placed to the next another unit, which
is called the crystallization unit that is to be placed it is this material it is a that
means, it is a evaporation is the what should I say that it is the prior unit operation
after in unit operation for crystallization. So, with the help of the pump the material
is thick material or thick liquor is being placed or put forward to the crystallizer.
Now, there are two important issue that we should say one is heat transfer coefficient.
Now, if we say from heat transfer coefficient that in case of evaporator the how the heat
transfer is happening, if we just try to see that there are two things here, one is that
tube fluid is getting heated and shell side there is steam there is the steam in the shell
side which is mostly condensing steam, and tube side fluid is heated. So, what happens
is the condensing steam has got a very high heat transfer coefficient high heat transfer coefficient. Then another
point over here is for condensing steam almost no scale formation, because there is no solute
over there apart from corrosion, there is no scale formation over here, but tube fluid
large possibility of scaling. So, that is very important that we should see that scaling
or you can say fouling. So, that is the large possibility of scaling or fouling, we should
we should reduce as much as possible the scaling or fouling.
So, time to time clearing cleaning is needed. Cleaning is necessary this very important
the fouling part is very important, because it is a it is a solute and solution is there
so solute will deposit the solute scale formation and salting out effect all this point are
there already we have discussed. Now many a situations what happens is that that liquid
in the tube is not allowed to boil liquid in a tube is not allow to boil, it flashes
in the vapour chamber. So, and there it gets it separated into thick liqour and a vapour
its temperature is raise. So, under that situation we can use correlation like, h i d by k 0.0278
Reynolds to the power 0.8 it is a like sedadata equation like that sedadata kind of correlation
is not exactly sedadata relation and this is the tube diameter tube in a diameter tube
Id. So, this situation when correlation is used when no boiling. And when there is a
boiling, then we have discussed already in convex heat transfer that there will be some
correlation used when boiling boiling correlations can be used.
And one thing as I said that the fouling is important. And so, fouling changes the overall
heat transfer coefficient and there is the relationship one by U naught square is equal to one by U c square plus
beta into theta. So, this is after fouling this is clean beta is equal to your constant
for a particular fluid, and theta is equal to time of operation. Theta is equal to time
of operation. And typical U D values sorry U o values for STV short tube vertical evaporator
this 750-2,500 this value unit is kilo calorie per hour per meter square per degree centigrade,
for LTV long tube vertical and for circulation these value is roughly 2,000 to 10,000 unit
is same kilo calorie per hour per meter square degree centigrade, LTV then for natural circulation
for forced circulation. The value is very high it would be around for natural circulation
it is less 1,000 to 3,000 provably same unit. Agitated film such plate type they have values
something around 1,500 to 2,700 kilo calorie per hour per meter square per degree centigrade.
These are typical ranges of the over heat transfer coefficient values.
And then, another thing what I was interested to tell is that enthalpy of solution it is
very important. So, enthalpy of solution is very much needed enthalpy of solution is very
much needed for calculation in this is relay required for heat exchanger sorry here. In
this case evaporator calculation and this can be enthalpy of solution can be determined
by calorimetry or can be calculated from integral heat of solution. So, integral heat of solution
is it is it is the change in enthalpy of a solution when one mole of solute is dissolved in the
say in n 1 moles of solvent at 25 degree centigrade and 1 atmosphere pressure.
So, the enthalpy of a solution at temperature T relative to the pure solvent and solute
at temperature T naught is H s; H enthalpy of this solution at temperature t is equal
to n 1 H 1 plush n 2 H 2 plush n 2 into delta H s 2; this n 2 is the n 1 is number of moles
of 1 stands for solvent moles, 2 stands for solute. So, number of moles of solute n 1
and n 2 is equal to number of moles of moles of solvent and solute and H 1, H 2 are enthalpies.
Molar enthalpies of solvent and solute and delta H s 2 is called integral heat of solution
of solute at temperature say T. And then H s also can be written as n 2 delta H s 2 naught
plush n 1 plush n 2 into s into T minus T naught.
Here delta H s 2 naught is called integral heat of solution of solute at temperature
T naught, temperature is equal to T naught is equal to 25 degree centigrade and s is
called molar specific heat of solution molar specific heat of solution. So thus, this is
just to have an idea to get the values of enthalpy of solution from integral enthalpy
of heat of solution we can find out the enthalpy solution, but actual all we can find out the
from the supplied data or available data in the literature. We can find out the enthalpy
of the solution so this is one important except regarding the evaporator calculations may
be in the next lecture will be discussing on the calculation of the evaporators. So
here, I will ask you two questions based on by first two lecture, the what kind of evaporators
we should use for case one highly heat sentential material, but moderate varicosity material.
So, the answer should be four circulations vertical four circulate vertical or falling
film or climbing film evaporator. Second case, highly heat sensitive with large varicosity
heat sensitive but large in that case, the answer would be agitated film or plate type
evaporators. So, the third question is third part is that for foaming liquid, but not heat
sensitive. So, naturally the choice should be natural circulation and long tube vertical
that is should be used for foaming liquid we should use long tube vertical. So, this
is about the some idea about the different type types of evaporation that should use.
Now this is all about for today’s lecture. And in the next lecture, I will be discussing
and there will be the final lecture for the evaporation. I will be discussing on the evaporation
calculations for the design and we will see the calculation for single effect as well
as multi effect evaporators. And will illustrate with some specific problems on this thank
you very much.