Wall and film temperature

[091123]

Hi Guys, I'm just wondering how experts measure the wall and film temperature of let's say boiler tube. Did they measure it using instruments or theoretical approach? If I arrived at a particular value how would I know If I am close to the actual?

Thanks

 

[athena15]

Hi! With regards to analytical calculations, I believe we always have it as estimates or approximates but then we alwys have factors of safety for allowances of our design. In fact there are a lot of books, particularly heat transfer books to check your calculations such as heat transfer by Incropera, or by Lienhard, J. (Check

http://www.mit.edu/lienhard/www/ahtt.html

for a free downloadable textbook) , or Unit operations by Mc cabe and better yet you can also check this very helpful website

http://www.heaterdesign.com.

Hope I help you.

 

[davefitz]

In the past, the way it was measured was using chordal thermocouples. A Thickwalled waterwall tube ( 3" OD x 0.3" MW) would have installed thin thermocouples in the mid wall section, also on the cold side, in the fin section ,etc. These normally provided and estimate of the variation in heat flux around the furnace perimeter and height. These measurements served to confirm calculation procedures for estimating furnace heat radiation variations and also adequacy of waterwall circulation calcualtions ( prevention of DNB )

The latest laboratory measurents conducted by Siemens KWU ( Erlangen- Prof Keiffer, Kohler, Hein)used single, unfinned tubes heated by induction heating coils and controlled the heat flux- the tubes had installed chordal thermocouples every 3 " along the tube lenght. Teh occurrence of DNB and dryout was deermined, and the correlatios of KonKov and Dorishchuck were confirmed for smooth bore tubes.

For modern large furnaces, numerical modeling of the furnace combuston chanmber's fluid flow and heat transfer is conducted using a Galerkin method ( see Woody Fiveland's papers- B+W) and the expected radiation flux across teh furnace perimeter is estimated. The Siemens KWU correlations are used to confirm adequate water circulation to avoid DNB and dryout does not occur. The metal temperature is calculated over the tube's circumference using standard finited element models.

Currently