Experimental study on critical heat flux on a downward-facing stainless steel disk in confined space

Critical heat flux (CHF) is experimentally studied on a relatively large downward-facing surface with a heated stainless steel disk diameter of D = 300 mm in confined space at atmospheric pressure using water as the working fluid. The bulk working fluid is subcooled. The gap size s can be adjusted to 0.9, 2.2, 2.6, 3.0, 3.2, 5.0, 7.0, 10.0, 13.0, 15.6, 19.5, 25.0, 36.0, 51.0 and 77 mm. We found that the average CHF under the present condition is approximately 0.25 MW/m² which is only about 23% of which occurs on an upward-facing surface without confined space in pool boiling. The CHF increases with the increase of the gap size when the gap size is smaller than 7 mm and it is a function of Bond and Jakob numbers when the gap size is larger than 7 mm.