18 replies to this topic

[lohiacp]

Good afternoon,

 

I have to select a plate heat exchanger (PHE) for cooling of a fluid from 130 deg C to 35 deg C using chilled water. The flow rates of both the components are known. How should I proceed? What step-wise approach should I adopt?

Also, will this project, in any way, enhance my knowledge and application?

I am a B.Tech Chemical Engg student.

 

Thank You.

[breizh]

lohiacp,

 

There is a tool which is the search engine (top right) , let you use it and you will get your answer otherwise try Perry's chemical engineering handbook and others ...

 

Probably your text book is a good resource !!!

 

 

 

 

Breizh

Edited by breizh, 23 May 2013 - 12:24 AM.

[Anshul619]

Lohiacp

 

You must be an engineering student in India.  This must be your 4th year project.

 

If you want to start your project, then study the construction of the PHE and its internals.  Then check out the working & principle equation for this.

 

You must also have Xchanger software like HTFS or HTRI.  & most important please have some case report of the rating of the PHE.

[lohiacp]

anshul619:

 

Dear Sir,

 

You are correct in stating my details. However, this is my summer training project. Also, if I dont have the software how can I best proceed? I have studied the construction and the internal working of PHE and now know how it works. I just have to determine the area of PHE required to process a viscous fluid. My calculations were of only 2 pages and gave me a required area of 8.5 m2. I am not quite confident of having got it correct.

One more thing, in another approach to solving this problem, the reynold's no. for the viscous fluid was lesser than 1. I dont know what is the problem.Please help out.

 

Thanking you in anticipation.

[Anshul619]

Lohiacp

 

 

Buddy, first give me the process data from which i can understand what are you doing.If your calculation is correct or not.

 

FIRST PROVIDE PROCESS DATA.

 

And are you also thinking of fabricating the Xchanger??????

 

Also (if you can) send me your calculations.....

Edited by Art Montemayor, 20 June 2013 - 02:07 PM.

[lohiacp]

Anshul619:

 

There is a viscous fluid(in slurry form) of viscosity around 175 cps which is to be cooled from 130 deg C to 35 deg C using chilled water whose temp. rises from 10 deg C to 33 deg C. Flow rate of viscous fluid is 2 m3/hour and its density is nearly same as that of water. I have to find the area of PHE required. I will send you the calculation in about 2 days for you to see it. I have followed the NTU method.

 

And NO, I will not be fabricating it.  I already mentioned that I only have to calculate the area.

[Anshul619]

lohiacp,

 

Give me the heat capacities of both the fluids.

 

Flow rate of chilled water.....

 

Just to confirm,you want to calculate area of what???

a) heat transfer

B)heat xchanger

 

Till Then.....

Edited by Anshul619, 20 June 2013 - 12:47 AM.

[lohiacp]

Dear Sir,

 

Cp of water= 4.187 kJ/kg-degC.

Flow of chilled water can be taken around 10 m3/h.

Area of both is to be calculated.

Pressure drop allowable is 70 kPa.

This is the only information that I have.

 

CALCULATION:

Using heat balance of m(cp)dT, Cp of the hydrocarbon viscous fluid comes out to be 2.524 kJ/kg-degC. LMTD value is 53.1 degC.

NTU based on hot fluid is 1.789, based on cold fluid is 0.433. Using curves of pressure drop vs. h as a function of viscosity, we get:

h(hot) = 350 W/m2-K & h(cold) = 13500 W/m2-K.

Stainless steel plates SS316 has conductivity= 14.9 W/m-K and assumed thickness of the plates is 0.5 mm. Using these, U= 337.294 W/m2-K. Dirt factor of 0.0002 (FPS units) gives Ud= 333.334 W/m2-K.

Therefore, Area= Q/U(LMTD)F, F= 0.96

Area = 7.85 m2.

 

What should I do next? Don't feel it's the full solution.

[Pingue2008]

Dear Hohiacp,

 

The forum always needs enough data to be able to assist. I ran a quick calculation using the data that you provided.

-Like you can see on the attached spreadsheet the duties are not equal. double check the data you provided

-Obviously your area is quite different.

correct my spreadsheet as you see fit and resubmit for further assistance.

If you do not intend to fabricate this HX, why do you bother the manufacturer should be able to provide these info based on you process specs.

 

Thank you

Attached Files

•  PHE Student.xlsx   162.32KB   71 downloads

[lohiacp]

Pingue2008:

 

Dear Sir,

 

 

I am working as an intern (entering into my fourth year of college next month) and have been provided with only this data .  Here, I have to submit a project report and not fabricate an instrument, in which they want to see the estimated area required for a PHE and, also, they want to cross-check whether the existing PHE meets the requirement or not.

Thank you for providing your calculations.  I will check my mistake and get back to you soon.

[lohiacp]

 

Pingue2008:

 

Dear Sir,

 

I saw your calculations and realised that the value of the water flow rate is actually half, i.e. 5 m³/hr.  I am really sorry for my error.  I have modified the calculations in the Excel file.  Your LMTD value needs to be changed since the flow is counter-current.  Now, you can see for yourself that the answer is near to my answer.  Is this procedure correct?

 

Attached Files

•  PHE Student.xlsx   162.23KB   34 downloads

[Pingue2008]

lohiacp,

 

As far as I am concerned, you have everything you need (duty,MOC,U etc...) to compare your new spec HX to the existing HX to see if it can work.

 

 

Good luck

[Anshul619]

lohiacp

 

"Using heat balance of m(cp)dT, Cp of the hydrocarbon viscous fluid comes out to be 2.524 kJ/kg-degC"

 

How are you getting this value???????

 

Because mine is coming 1013.69 J/Kg.K

 

 

 

 

 

PS: 1 kJ/kg.degC = 1000 J/kg.K

[Anshul619]

Also Take a look at this article.

Attached Files

•  Overall Heat Transfer Coefficient.pdf   78.15KB   59 downloads

[breizh]

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

 

This resource should help you , with a detailed calculation.

 

Breizh

[lohiacp]

lohiacp,

 

As far as I am concerned, you have everything you need (duty,MOC,U etc...) to compare your new spec HX to the existing HX to see if it can work.

 

 

Good luck

Dear Sir,

 

I believe that my calculations & result shown to you are correct. Thank You for helping me out.

[lohiacp]

lohiacp

 

"Using heat balance of m(cp)dT, Cp of the hydrocarbon viscous fluid comes out to be 2.524 kJ/kg-degC"

 

How are you getting this value???????

 

Because mine is coming 1013.69 J/Kg.K

 

 

 

 

 

PS: 1 kJ/kg.degC = 1000 J/kg.K

Dear Sir,

 

0.556*Cp*(130-35) = 1.386*4182*(33-10)

 

P.S.: 2 m3/hr = 0.556 kg/s & 5 m3/hr= 1.386 kg/s

Is this calculation wrong????

 

By the way, thanks for the pdf.

[lohiacp]

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

 

This resource should help you , with a detailed calculation.

 

Breizh

Thank you sir, it did help me to calculate by assuming dimensions of the plate and no. of plates.

[Anshul619]

 

Breizh

 

Thanks for the link you provided.

 

 

lohiahcp

 

Yep your calculations are correct.then.