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JohnMiddleton1-Visitor
1-Visitor
April 21, 2011
Solved

Heat transfer between pipeline and aluminium anode sub-sea

  • April 21, 2011
  • 22 replies
  • 40580 views

I am struggling to find where I am going wrong in the attached mathcad sheet. I have a pipeline with an internal fluid of 82.2c and then a thin coating then a 50mm thick aluminium anode is clamped around the pipeline (details on sheet). The sea temp is 5C but I keeep getting the external aluminium surface at the same temp as the sea water.

Before there is no hair left on my head where am I going wrong?

John

Best answer by ValeryOchkov

John Middleton wrote:

Hi Lou,

OK I see what you are saying but how do insert a thermal resistance between the aluminium and sea-water?

Many thanks,

John

Sorry comments is in Russian

http://twtmas.mpei.ac.ru/mas/worksheets/therm/Heat_Flow_4.mcd

but see the picture in the WebSheet

>how do insert a thermal resistance between the aluminium and sea-water

You can use ) know alpha2 (heat transfer coefficient - W/(m^2 K)

22 replies

ValeryOchkov24-Ruby IV
24-Ruby IV
April 21, 2011

John Middleton wrote:

I am struggling to find where I am going wrong in the attached mathcad sheet. I have a pipeline with an internal fluid of 82.2c and then a thin coating then a 50mm thick aluminium anode is clamped around the pipeline (details on sheet). The sea temp is 5C but I keeep getting the external aluminium surface at the same temp as the sea water.

Before there is no hair left on my head where am I going wrong?

John

1) It will be good to have a picture of your pipe - as here for example

2) May be this help you

3) See the attach too

JohnMiddleton1-VisitorAuthor
1-Visitor
April 21, 2011

Hi,

Thanks very much for replying. I am struggling a bit to follow it as my Russian is not that great. Can you explain a little more if possible in English for me?

Thanks in Advance

John

ValeryOchkov24-Ruby IV
24-Ruby IV
April 21, 2011

John Middleton wrote:

Hi,

Thanks very much for replying. I am struggling a bit to follow it as my Russian is not that great. Can you explain a little more if possible in English for me?

Thanks in Advance

John

Sorry, I try use both languages on my Mathcad Serve.

It is one page from the Web Reference Book Power & Heat engineering:

ThemCond-r1r2r3.png

RichardJ19-Tanzanite
19-Tanzanite
April 21, 2011

The unit C is a Coulomb. Temperature units in Mathcad have to be handled in a special way. See "Help", "Tutorials", "Features in Depth", ""Temperature and User Defined Units".

ValeryOchkov24-Ruby IV
24-Ruby IV
April 21, 2011

Richard Jackson wrote:

The unit C is a Coulomb. Temperature units in Mathcad have to be handled in a special way. See "Help", "Tutorials", "Features in Depth", ""Temperature and User Defined Units".

Sorry, with units all is Ok!

RichardJ19-Tanzanite
19-Tanzanite
April 21, 2011

Sorry, with units all is Ok!

Interesting. And a little worrying. I looked, and it was just "C". Then about 3 minutes later my computer blue-screened on me! Now it shows the correct temperature units!

Time to back everything up!

LouP12-Amethyst
12-Amethyst
April 21, 2011

Why would you expect something else? Not withstanding Richard's comments on units, you have set up the problem as a heat flow calc between two defined temperatures, t1 and t5, with three intervening thermal resistances in series. The assumptions of the calc are that the inside temp is t1 and the outer anode temp = sea temp= t5; the basis of your calc. Getting Tanode at exterior = Tsea=t5 is just validating the assumptions of your calc. Is there some other resistance you expect that is not in the model?

Lou

JohnMiddleton1-VisitorAuthor
1-Visitor
April 21, 2011

Hi Lou,

T5 is the sea water temp and T4 is the anode surface temp. The anode outer temp (T4) isn't assumed to be the same as the seawater temp. Does that give it a bit more clarity?

Thanks

John

ValeryOchkov24-Ruby IV
24-Ruby IV
April 21, 2011

John Middleton wrote:

Hi Lou,

T5 is the sea water temp and T4 is the anode surface temp. The anode outer temp (T4) isn't assumed to be the same as the seawater temp. Does that give it a bit more clarity?

Thanks

John

John!

Please create the picture with r1, r2... T1, T2... using a template in my attached file!

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