7 replies to this topic

[leyva_luis]

Hi, I'm sizing aircooler. Propane at conditions 138°F and 208.6 psig is desuperheating and condensing.Propane rate is 9166 lb/h. Propane is saturated liquid(113°F) at outlet conditions. Propano is in tube side. Air inlet at conditions 77°F and 14.7 psia. Air outlet 105°F.

I selected tubes OD 1in, BWG16, 2 3/8triangular spacing, fin high 3/8in, fin width 0.035in, density 8fins/in, fin material aluminium. I assumed duct size lengh 24ft,width 12ft.

I did calculations with Donald Kern's book (process of heat transfer). But Overall Coeficient(desuperheating) calculated was 6 BTU/h.ft2.°F and Overall coeficient(condensing) calculated was 65 BTU/h.ft2.°F. #tubes/row =60tubes, #row=3. I considered 1 pass for side tubes, and 2 fans.

The values of overall coeficient are good?
How can I determine power of fans?

Thanks in advance

[Zauberberg]

The condensing coefficient seems to be a bit high but we don't know whether it is expressed on a bare tube surface area basis, or did you use extended (total) surface area? Attached are some guidelines from the GPSA Databook for your reference. The same resource gives the procedure for calculating fan power as well, and also to check if the thermal design has been done correctly.

Additionaly, there is a software from Hudson which you can use for cross-checking your results. It is not meant to be a final design tool but it can certainly tell you whether you are in the same ball park.

http://www.hudsonpro.../ACHE2Setup.exe
http://www.hudsonpro...eV5.7 setup.exe

Attached Files

•  ACHE.pdf   65.4KB   524 downloads

[leyva_luis]

Zauberberg,

I attached the spreadsheet for aircooler.
Checking and comments.

Thanks in advance

Attached Files

•  Sizing Aircooler.xlsx   592.59KB   773 downloads

[Zauberberg]

You have calculated 8.8 BTU/hr.ft2.°F as the air film coefficient, and 240 BTU/hr.ft2.°F as the Propane film coefficient, and then you come up with 65 BTU/hr.ft2.°F being the overall heat transfer coefficient which is not possible.

The way it should be calculated (without taking into account fouling resistance - which should be accounted for, by the way - otherwise you will end up with an undersized air cooler), is:

1/U = 1/ho + 1/hi = 0.1176, therefore U = 8.5 BTU/hr.ft2.°F

If you add the fouling contingency factor, you'll probably end up with a U-value closer to 5.5 - 6.0 BTU/hr.ft2.°F which is a guideline figure from the GPSA Databook table attached in my previous post.

Best regards,

[ankur2061]

levya_luis,

One downloadable software for air cooled heat exchangers is available at:

http://www.hudsonpro...m/download.html

Another online calculator for ACHE's by GEA-Rainey is available at:

http://www.gearainey...Calculator.html

The Hudson Products Corporation software also provides "overall heat transfer coefficient" based on a selction of applications.

Hope this helps.

Regards,
Ankur.

[UNMESH BISWAS]

Dear Zauberberg:

Can you please provide the spreadsheet in .xls format. I have Excel 2003 loaded, and this updated type (i.e. xslx) does not open in my 2003 version.

Thanks in advance

Unmesh Biswas

[Zauberberg]

There is a Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint File Formats which allows you to open MS Office 2007 files through previous MS Office versions, available for free download from:

http://www.microsoft...&displaylang=en

Download, install, and run.

[srfish]

I am supprised at the fin configeration used. Normal is 5/8 inch high fins and 10 fins/inch. For fan HP, you can also contact Moore fans and they have free software to calculate the HP.