Lugano dummy run recalculation compare

This post gives in a table the difference between the published Lugano dummy run data and the recalculation I did.

(I had planned to make this comparison sooner, but fell and now have a concussion.)

The difference can be seen in the following table

--------------------Lugano---------------------------------Recalulation

-----------Radiation-----Convection-----------Radiation------Convection

Rods--------56.16----------74.71-------------------54.70------------63.39

Ribs-------128.56---------101.79-----------------172.35-----------158.50

Caps--------54.76----------31.29-------------------54.79----- -------34.43

Totals -----238.57---------207.79------------------281.84-----------256.32

Total Lugano-------------446.36

Total recalculation-----538.17

I have these comments concerning the differences :

1. Rods

Radiation for the rods is almost the same, however the convection is lower due to the lower value of the stacking correction factor for the convection.

2. Ribs

The radiation of the ribs is much higher in the recalculation then in the Lugano report.

This is due to the increased emissivity because of the reflection berween the fins (infinite refelction method) an dthe larger area (real area times the view factor to the background)

The convection is also significant higher an this is largely due to the difference in area's used in the recalculation and the Lugano report.

In the Lugano report a fin area of 2 x Pi x (Rf^2-Rt^2) is used, Rf being the radius of the top of the fin (12.3 mm) and Rt the tube radius (10 mm) giving a fin area of 3.22E-4 squared meter.

In the recalculation a fin area of 3.81E-4 squared meter was used, based on the real fin area calculated by substracting the area of two cones.

This gives an increase of 19% in area but thsi difference is not enough to explain the increase of almost 50 % in convection for the rib area.

5. Caps

For the end caps the differences are minor.

Conclusion :

Most of the differences between the original Lugano dummy run data and the recalculation can be explained.

However the reason for the large difference in convective heat transfer of the rib area is not known. This may need some further investigation.