# Pharma Engineering

For Engineer By Engineer

• ## Thursday, 21 April 2016

Good Day to all, Today i want to make a Demo on Basic Condenser Design Aspects, which involves the calculation of Heat Loads, Utility Loads, Overall Heat Transfer Co-Efficient.

So Before entering the point i want you guys know something basic knowledge which helps you in better understanding of this. The Beginning point is what is Latent Heat and What is Sensible Heat, and what is the Major Difference between these two.

Many of you may confuse over this topic finding the difference but there lies a solid difference between the two of them, starting with,

1. Latent Heat: The Heat energy required for 1 Kg of solvent to transform itself into vapour state without raise in temperature from its boiling point is called Latent Heat., Usually this is the basic Definition that is explained in engineering classrooms, but while coming to exams time many of us will retain only one thing Latent Heat means Phase change, that's it, even if the one who explored it come before also we wont listen, but in addition to the Phase change in definition there lies another one majestic line, WITHOUT RAISE IN TEMPERATURE , which means Latent heat wont depend upon temperature, and also Temperature is directly proportional to pressure, Latent Heat wont depend upon the Pressure also, Please Note this.

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2. Sensible Heat: The Heat energy required for 1 Kg of solvent to raise its temperature without any phase change is Sensible Heat, So if you can clearly observe this, you can find out the difference between Latent Heat and Sensible Heat, So, this is what we call "EK BALL DHO THUKDA",

And the Next basic Thing you need to know is what is the difference between a Heat Exchange and a Condenser??

So, this is a typical question, i can bet that 90% of the Chemical Engineering course relieved students dont know, and even 10% of the working chemical engineers also don't know exactly, because in pharma field everyone will be using these both terms interchangeably,

But there lies a major difference between two of them, in a single line every condenser is a heat exchanger, but every heat exchanger is not a condenser,

The one which exchanges heat can simply called as a Heat Exchanger, just like the reactors, hot water tubs, condensers, distillation columns, etc,

But whereas coming to a Condenser its main duty is Condensation, so whenever the condensers condensers some vapour's then its duty is over.
Condensers were of many types, shell and tube, double pipe, plate and frame, scrapper type, longitudinal extended surfaces, so being frank we can use a Heat Exchanger as a condenser, but we cant guarantee the efficiency, which is basically depends upon the thermal conductivity of the MOC.

Now i think you got some basic knowledge regarding the aspects of heat transfer,
So lets get into point directly,

Let's start our design concept, Once again recollecting, duty of condenser is to take off the latent heat from vapour and condense them, so the load over a condenser will be Latent heat,

Latent Heat, QL = M x Lam

M - Mass FlowRate of vapour,
Lam - Latent Heat of Vapour.

So Basically to define the heat transfer of any heat exchanger we will go with the Overall Heat Transfer Coefficient and the Temperature of the fluids, which are in turn correlated by ,

Q = U x A x LMTD.

Q - Heat Energy, U - Overall Heat Transfer Coefficient, A - Available/Required Heat Transfer Area,
LMTD - Log Mean Temperature Difference.

So whenever we need to decide the Rate of condensation we need to know the Area of Heat Transfer, Luckily we got the Correlation in terms of heat energy.

So for the case of condenser duty,

QL = M x Lam = U x A x LMTD

So, our Required Heat Transfer Area,

A = ( M x Lam ) / ( U x LMTD ),

U value can be considered in between 300 - 450 KCal/Sq.m .hr.°C, this value is not a thumb value, but generated from average of different trials taken while designing the condensers.

That's it, done.

But for sure this Area wont suits your requirement, Because we know that the duty of condenser is to condense the vapours, but the condenser donno this fact and even after condensing the vapours it will still reduce the temperature of the condensate, that means it is doing over duty which involves some change in Sensible heat also, so while equating the QL to Q, we need to add QS to QL and then have to equate it to Q. So, now i'll equate mathematically, Dont worry this equation wont involve that much logical mathematics which makes you fear, but just involves simple ones., So now,

Q = QL + QS  , Q = ( M x Lam ) + ( M x C p x dT ),

To solve this we need to consider same M value for both QL and Qs , and dT should be taken atleast 6°C - 10°C, for getting a better design that suits your requirement.
So our modified equation for Calculating the Heat Transfer Area is as follows,

A = (( M x C p x dT ) + ( M x Lam )) / ( U x LMTD ).

Now Say Cheers, It's perfect now.

For your Convenience i've simulated an excel sheet, use it for accurate values,

Any Queries Please feel free to ask us, We are happy to respond, if you feel great of this then leave some hearty comments here.

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Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.

1. Eludicating process technology n easy aspects..
Cheerz to da tech geek ..
Informative posts.. keep sharing..
Im vry much happie for the passion n sharing wid chem engineer buddies ☺
Lucky to hav yew..keep goin..

1. @JayPrince s, Thanks for the support, keep on visiting for more upcoming posts,

Regards,
Pharma Engineering

2. hi ajay thanks a lot for your valuable info and i just wanted to know that how can we maintain constant condensate flow without reflux with the help of direct heating by control valve to the jacket. we are applying enough heat with the help of a CV but giving a blind value to the CV can u please help me out on amount of heat energy required to the mass in terms of CV to maintain constant condensation.

1. Whats the solvent you are trying to evaporate, and tell me weather the reaction mass is an pure compound or not??

Regards,
Pharma Engineering

2. sorry ajay i didnot see your comment from so long time and My solvent is dichloromethanol(bp=39C) and my reaction mass is composition of product,solvent and water.

3. Very nice it is quite helpful

4. nice work ajay very simply you put a complex things.

raj

1. pharmacalc823@gmail.com / ajaykalva823@gmail.com
You can reach me

6. Dear sir, you have mentioned that latent heat does not depend upon the temperature. But if you look at the steam tables we can clearly see that latent heat changes with the temperature and also of course with pressure.

1. Dear ,

Latent heat is a function of pressure. Temperature is also a function of pressure. Once refer clausius clapeyron equation.

Best Regards,
AJAY K

2. THIS CONTRADICTS YOUR STATEMENT ABOVE THAT LATENT HEAT DOESN'T DEPEND UPON THE TEMP & PRESSURE