Experimental Investigation of Critical Heat Flux on Different Surfaces at Low Pressure and Low Flow

Abstract

Steady state flow boiling experiments were carried out on several heated tubes with outer diameter 9.14 mm at outlet pressures 120, 200 and 300 kPa, inlet temperatures 64, 78 and 91 °C and approximately 400, 500, 600 and 800 kg/(m2·s) mass flux entering the vertically aligned test annulus until critical heat flux (CHF) was reached. The tubes were made of Inconel 625 with a length of 400 mm. The Inconel tubes were tested in three different modifications as smooth, abraded with 150 grit sandpaper and bead blasted. Multiple experiments were repeated on the same specimen to investigate the effect of surface characteristic changes (i.e., wettability, roughness and oxide layer morphology) on the occurrence of CHF. Despite the changes in initial wettability, the CHF dependency was not clearly observed, however, the changes in roughness led to an increase in CHF. The total number of 115 experimental runs were collected and the results were also compared with other literature experimental data.

Experimental Investigation of Critical Heat Flux in Annulus at Low Pressure and Low Flow Parameters

“…Presented data should serve as a reference for comparison with other materials including accident tolerant fuel [26]. The facility should be improved for ionex filters preventing the corrosive particles from depositing on test tubes and therefore extend the operation time with a clean surface as it was discussed in [21]. To obtain better flow stability and less oscillations, the inlet section will be slightly modified together with the change of the measuring probe.…”

“…The flow boiling experiments were performed on the Mobile Research Critical Heat Flux Apparatus (MR-CHA) which was constructed and operated by the University of Technology in Brno at Faculty of Electrical Engineering and Communication and its thorough description can be found in the article [21].…”

“…According to [21] the power is calculated by the multiplication of electric current and voltage. The heat flux is then estimated by dividing the power by the heated surface which is equal to π • d i • L, where d i is the inner diameter of the annulus and L is the heated length.…”

“…Except the literature comparison, Haas [20], [6] also presented his experimental data from the COSMOS-L experimental loop. This was the main inspiration for the author's research team to develop a test facility of similar design [21]. Haas pointed out that flow boiling experiments could be strongly affected by instability, which could lead to pulsating flow and therefore these oscillations could cause a premature CHF at much lower heat fluxes.…”