Steady state boiling crisis in a helium vertically heated natural circulation loop – Part 1: Critical heat flux, boiling crisis onset and hysteresis

摘要: Abstract Experiments were conducted on a 2-m high two-phase helium natural circulation loop operating at 4.2 K and 1 atm. The same was used in two experiments with different heated section internal diameter (10 6 mm). power applied the wall controlled increasing decreasing sequences, temperature along section, mass flow rate pressure drop evolutions recorded. values of critical heat flux (CHF) found positions test post-CHF regime studied. predictions CHF by existing correlations good downstream portion however anomalies have been observed near entrance, low quality region. In resonance this, re-wetting surface has distinct hysteresis behavior each regions. Furthermore, hydraulics effects crisis, namely friction, studied (Part 2). This research is starting point to future works addressing transients conducing boiling crisis loops.