Experimental study on the effect of angles and positions of mixing vanes on CHF in a 2 × 2 rod bundle with working fluid R-134a

In this paper, the CHF experiment on the effect of angles and position of mixing vanes was performed in a 2 × 2 rod bundle. The test section had rectangular geometry in which four rod, each with a diameter of 9.5 mm, were inserted. The rod-to-rod gap was 3.15 mm, and the rod-to-wall gap was 1.575 mm. It was vertically installed in the test loop and was uniformly heated by electricity. The heating length was 1.125 m. The working fluid was R-134a. The mass flux ranged from 1000 to 1800 kg/m2. The test pressure ranged from 14.67 to 25.67 bar. CHF data in the 2 × 2 rod bundle without a mixing vane were compared to the Bowring correlation and a CHF look-up table at equivalent hydraulic diameter. For this comparison, Katto's fluid-to-fluid model is applied. The results had a good agreement with error rates of 16 and 20%. In the CHF experiment with the mixing vanes with various angles, the angles of the mixing vanes were 20-40°. The CHF enhancement ratio (CER) was largest at 30°. CHF was enhanced up to 19%. A CHF experiment on the position of the mixing vane was also performed. In the experiment on the position of mixing vane, CER was reduced with increasing distance between grid and CHF location because swirl flow decayed. We also performed the CHF experiment on mixing vane developed by KAIST.