16 replies to this topic

[TX-2]

I have been reading about PHEs, however I have not come across any methods for calculating the number of plates required in PHEs. Can someone please explain how the number of plates are calculated.

 

In design of STHE, you assume a value of U and perform iterations to see if the assumed value meets/exceeds HT or pressure drop requirements. I have some knowledge about the Bell-Delaware method for STHE calculations by hand and would like to be able to do similar calculations for PHEs.

 

All the calculation methods I have come across involve specifying the number of plates (rating calculations) but I am more interested in designing for a specific plate configuration, say I have a plate and would like to use those to determine the size (number of plates) for the required heat duties.

 

I have access to Aspen EDR (in college) but I don't have a real problem. I just want to be able to understand how the number of plates are calculated. 

 

From Hewwit's Process Heat Transfer

 

Mass flow rate, m = 2*M / N + 1

 

where, M = Total mass flow of the system

 

 

Once I know the number of plates (N) to use here, I should be able to proceed to 

 

S = b*W

 

S = Surface area of passage

b = Channel width

W = Plate width

 

onto velocity v = m /rho * S

 

Re = vD*rho/mu onto Nusselt number and HT coefficients to eventually overall HT coefficient

 

 

 

Any help on this would be greatly appreciated. 

 

[breizh]

From the example attached you should be able to understand the principle of the calculation.

 

http://www.heattrans...Plate_Calc.html

Hope this helps

 

 

Breizh

[TX-2]

Thank you very much Breizh.

 

I had already seen this, unfortunately this is not what I am looking for. In the example calculation, the number of plates is already specified. I am trying to find a way of determining the number of plates required for the heat duty.

 

I really appreciate your help. 

[katmar]

The principles behind sizing plate exchangers and shell & tube units is exactly the same.  From the basic equation (Q = U x A x LMTD) you get the area required.  In an S&T unit you can calculate the number of tubes from the area per tube.  Similarly, you can calculate the number of plates from the area per plate.

 

But the real problem is how to calculate U for a plate exchanger.  The HTC will vary with the type of pattern pressed into the plate, and this information is kept secret by the manufacturers.  In real life no engineer would try to calculate this by themselves - you just ask the plate exchanger supplier to do all the calcs for you and give you a price.

[TX-2]

The principles behind sizing plate exchangers and shell & tube units is exactly the same.  From the basic equation (Q = U x A x LMTD) you get the area required.  In an S&T unit you can calculate the number of tubes from the area per tube.  Similarly, you can calculate the number of plates from the area per plate.

 

But the real problem is how to calculate U for a plate exchanger.  The HTC will vary with the type of pattern pressed into the plate, and this information is kept secret by the manufacturers.  In real life no engineer would try to calculate this by themselves - you just ask the plate exchanger supplier to do all the calcs for you and give you a price.

 

 

Thank you Sir. In Aspen EDR there is an ability to "Design given plate" which means that number of plates can be calculated by hand/software and you don't always have to rely on the manufacturers to do the preliminary calculations. You can also specify the plate geometries yourself instead of using the predefined manufacturer plates so I have the feeling calculation methods exist but they are obviously not easy to find. 

 

I think I would just have to give up on this because I have not had much luck finding calculation methods.  

 

Are there any good books or references materials on PHE design that you can suggest please.

Edited by TX-2, 19 April 2014 - 05:49 PM.

[processengbd]

I previously tried to what you are trying now. Moreover I tried to contact different vendors to share their plate details but none replied.

 

As Mr. katmar said for these heat exchanger design you have to consult with vendors. 

[Art Montemayor]

Katmar stated: "no engineer would try to calculate this by themselves - you just ask the plate exchanger supplier to do all the calcs for you and give you a price".

 

He did not state that "for these heat exchanger design you have to consult with vendors".  I believe that there is nothing to consult about.  The topic is shrouded in proprietary information that is not available.  It is closed architecture - not open architecture.  If you want to find out how this equipment is designed and built, you have only one resource: you buy a unit from experienced manufacturers.

[katmar]

I had a look at the ASPEN EDR web page, and I am confused.  As far as I can see, the user can enter any design parameters they would like to use.  This includes chevron angle, depth, port spacing and so on. I totally fail to see the point of this, and I hope someone who uses the program can explain it to me. 
 
You could design a plate to suit your duty, but the cost of manufacturing it would be very high.  Just to get the tooling done to press the plates would require you making hundreds of units before you could recover the cost.  And where would you get the gaskets made?  I really hope someone can explain this ASPEN feature to me.  They claim to have 35 years of research supporting this feature, so somebody must be getting some value out of it.
 
It could be a useful resource if the major suppliers allowed their plate design to be included in the package.  You could measure up the plates yourself, and then use that information to rate available plate designs - but I don't know how valuable that ability would be.  I have always just got the PHE representative to do the calcs for me.
 
In my opinion, designing your own plate exchanger would be a very similar exercise to designing your own centrifugal pump.  You could probably find a bit more detail in the open literature on things like impeller vane angles and so on than you will find on plate exchanger parameters, but nobody (that I know of) would try to make a custom pump to their own design.  You look in the suppliers' catalogs to see which one suits your duty best.

[TX-2]

Thank you everyone. I think it is best to just rely on Aspen EDR or HTRI. 

Edited by TX-2, 02 May 2014 - 06:04 PM.

[breizh]

TX-2

 

Let you find a copy of Chemical engineering May 2014 you will find some information about PHE .

Hope this helps

Breizh

[TX-2]

Thank you breizh. I appreciate your help. 

[TX-2]

Breizh:

 

 

Are you referring to the Chemical Engineering Journal? I just checked on sciencedirect.com but I do not see any articles on PHEs in May 2014. 

[breizh]

TX-2

YES ! May 2014 issue . Page 52 and followings . You will find a reference (#1) which can help you , on top of advices above.

Hope this helps you out .

 

Breizh

[TX-2]

Thank you Breizh. I have given up on designing a PHE myself, it is best to just rely on Aspen EDR. I didn't find information on PHEs easily (not necessarily a bad thing) but I now know a little more about PHEs. 

[adolfoOR]

I found this ppt on the next link:

 

http://www.engineeri...T EXCHANGER.ppt

 

I made a calculation of the number of plates using the method shown in the ppt, based on the design conditions of a heat exchanger I bought, but I did not get the same number of plates offered by the vendor. I'm going to think why is that difference if it is worth the effort.

Edited by Art Montemayor, 04 June 2014 - 07:12 AM.

[breizh]

adolfoOR

Consider the whole post , in particular answers from Katmar !

 

"the real problem is how to calculate U for a plate exchanger.  The HTC will vary with the type of pattern pressed into the plate, and this information is kept secret by the manufacturers"

 

 

Breizh

[abhaysharma184]

Thanks for all of u sir