# Pharma Engineering

For Engineer By Engineer

• ## Friday, 15 April 2016

Some of the engineers who were working in technical services will be well aware of the theoretical calculations that were performed to get an brief idea before taking some trials,while coming to the process engineers those who will be focusing on the product launches or technology transfer activities ,need some sound knowledge regarding the heat load calculations, Steam consumption,  pump and its sizing's that are used while going for equipment mapping,and many of us will be going as per thumb rule,which will support upto some extent, and we can take this thumb and apply to every case, Lets say that,

"If somebody is asked a question about what is your condenser capacity needed for a 10KL distillation reactor,I bet within 5Secs,20 sq.m will hit my ears.And Usually while selecting a condenser the major required parameters were the Amount of vapours to be condensed,Nature of vapours to be condensed and the temperature of the vapours to be condensed,Without these all I'l be getting an answer"

So, here my intension is only one thing,and that,it is to mention you guys that Thumb rules are tolerate only upto some extent,it can't be applied to every case,so learn the theoretical one's perfectly,If you want to take heating trial for any heat exchanger then we should be aware of the range of the Temperature in which it lies,so for that we should the mechanical and thermal properties of heat exchanger on which the rate of heat transfer depends, and along with sometimes fouling/scaling factors, Dirt resistance.

Usually the Heat transfer rate strongly depends on the material of construction[MOC] and the thermal conductivity of Material[MOC], Area available for Heat transfer.

The Rate of Cooling/Heating depends on the Utility that we are providing for the operation and the Heat transfer rate.

And whenever we need to calculate the Time-Cycle of heating or Cooling of a mixture, we will have two choices,

1) Calculation based on MOC physical/Thermal properties,
2) Calculation based on the Utility we are using,

So here, you may get a doubt, How can we calculate based on thermal properties, Actually this is a simple way of determining the Time-Cycle, and i'll explain it later in a Separate post.

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Coming straight away to the point, Calculating Time-Cycle based on the Utility that we are using:

For this we should be knowing the following data:

1) Temperature of Utility ( Hot water/Hot oil/ Brine/Chilled water/Steam/Liquid Nitrogen ) [T],

2) Initial temperature and Final temperature and Volume of the mixture ( t1, t2, V ),

3) Specific heat capacity of the mixture to be heated ( C p ),

4) Average Overall Heat Transfer Co-efficient of the system ( U ),

5) Heat Transfer Area of the System ( A ).

[How To] Calculate the Heat Transfer Area of a Reactor?

So, Initially we need to calculate the load over the Utility, Whether its a cooling load or heating load,
That Can be calculated by our traditional formula,

Q= M x C p x dT
M  - Mass flowrate - Volumetric Flowrate x Density,
C p - Specific Heat Capacity,
dT  - Temperature difference of the Mixture
( t2-t1) for Heating, ( t1-t2 ) for Cooling.

Now the Heat Load based on the vessel Overall Heat transfer co-efficient to be calculated,

Q= U x A x (dT)ln

U  - Overall Heat Transfer Co-efficient,
A  - Heat Transfer Area,
(dT)ln - Log Mean Temperature Difference - (( T - t1) - ( T - t2 ))/Log[( T - t1 )/( T- t2 )],

M x C p x dT  =  U x A x ( dT )ln  =  U x A x (( T - t1)-( T - t2 ))/Log[( T - t1 )/( T- t2 )],

Time Required for Heating/Cooling = [ M x C p x Log(( T - t1 )/( T- t2 )) ] / ( U x A ).

That's it......... Cheers,
Any Clarifications required, drop a comment, we will be happy to hear from you.......!!!

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

Pharma Engineering

1. dt is temp boss..............not time

1. Thats what i mentioned boss, have a clear look

2. Ajay I didn't got at final step. Can you explain me clearly.

1. Dear Sai,

Can you please spot it out clearly, so that i can explain you what i mean over there.

Regards,
AJAY K

3. Dear Ajay,
How to predict particle size distribution during crystallisation operation???

1. Dear Mahesh,

There wont be any predictions, just only calculations / thumb rules. And i donno any of them.

As per my knowledge, PSD will vary based on Agitator, Agitator's RPM and geometry of the vessel, Temperature parameters and all of their combinations.

Regards,
AJAY K

4. Dear ajay,
How u got this equation, couldn't understand .
Time Required for Heating/Cooling = [ M x C p x Log(( T - t1 )/( T- t2 )) ] / ( U x A ).

1. Dear ,

It is derived from ( M / t ) x Cp x dT = U x A x LMTD.

Making t as subject.

Regards,
AJAY K

2. Sir what is M/t in this equation...

3. Dear ,

M/t is mass flow rate.

Next time pl comment with your good name.

Regards,
AJAY K

5. how cooling water network design for new plant?

1. Dear ,

Where you got problem ?

Regards,
AJAY K

2. Mr. Ajay,

Whether the value of U vary with ageing of the reactor

Thanks
Anbu

7. Dear Mr. Ajay,

Its good. 1. The Time Cycle arrived is theoretical. However, what is the acceptable time cycle taking the factors like fouling, scaling, dirt resistance etc and beyond which the system has to be taken up for descaling
2. How frequently we can descale the GLR jacket and method of cleaning
3. Whether the Over all heat transfer coefficient will vary with respect to time like aging etc
Regards
Anbu

8. Mr. Ajay,

Whether the U Value vary with the ageing of the equipment

Thanks
Anbu

1. Dear Anbu,

The above calculation is pure theoretical and i've used the fourier's law of heat conduction for calculating the time of heating. With aging usually the heat transfer efficiency will reduce due to the above mentioned factors, also apart from those the wear and tear will have some impact on the hat transfer.
Usually the reactor jacket shall be descaled for every 3 years and sometimes based on requirement only.
Usually 15% Sodium hypochlorite solution is used for descaling purpose. But if the Scaling is quite high, then we need to opt for Sulphamic acid solution.

Best Regards,
AJAY K

9. Dear sir,
I've a doubt that is in your Excel sheet you have taken "A" into account which is the H.Tr.area..how u got that value??Is that the total H.Tr.Area of the reactor or only the area available for the rxn mass??(usually for heat transfer we would consider area available for rxn mass to transfer heat right!!)

Another doubt is that, consider I've a mass volume of 2m³ in a 4m³ capacity reactor how to find the area available for it??

1. Hiii dear,

We need to consider effective heat transfer area only i.e., where the reaction mass will be in contact.

For calculating the heat transfer area of reactor, pl refer below link:

https://www.pharmacalculations.com/2016/03/how-to-find-reactor-heat-transfer-area.html

Regards,
AJAY K