ISSN Online: 2377-424X
ISBN Print: 0-89116-909-1
International Heat Transfer Conference 9
LOCAL VOID FRACTION MEASUREMENTS IN FINNED TUBE BUNDLES
Sinopsis
A fiber optical probe is used to measure the local void fraction under pool boiling conditions in a bundle of 18 low-finned tubes (26 fpi, Gewa K-type) with a pitch of s/d = 1.3 and 1.15. Refrigerant Rll at the saturation state of 1 bar is used as working fluid. The heat flux is varied from 30 kW/m2 to 3 kW/m2. Void-fraction profiles are obtained within the bundles and above them using an optical probe. Within the tube bundle bubbly flow was observed. For 3 kW/m2 the local void fraction increased slightly to 5 % or 10 % between the top row tubes with a pitch of s/d = 1.3 or 1.15. The respective increase for 30 kw/m2 is 50 % and 80 %. A statistical analysis of the local void fraction exhibits in the two bottom rows an even production of many small bubbles with uniform size. Behind the second row and throughout the other 4 rows, the size and frequency of bubbles follows a Gaussian distribution.