Thermo-Fluid Analyses For Ucn Cryogenic System

The TUCAN collaboration is now developing the new cryogenic system for ultra-cold neutrons experiments (UCN). This cryogenic system requires superfluid helium (He II) around 0.8 K to 1.15 K because cold neutrons are down-scattered by isopure He II with such temperature range to become UCN. Dynamic heat load applied to He II during UCN production will be as high as approximately 10 W. In order to satisfy such requirements, not only 4 He but also He-3 has to be circulated through the cryogenic system. There are sixteen heat exchangers for He-4 and He-3. In order to design these heat exchangers properly, thermo-fluid simulations are carried out. Some simulations of them are nontrivial because they include film boiling phenomena in superfluid, molecular gas dynamics effect, transition from single phase flow to two phase flow and discrimination of such kinds of the complicated flow behavior. In addition, Time dependent thermo-fluid behaviors of He-II are also simulated using two fluid model and superfluid turbulent model to clarify the He II behavior. In this presentation, the simulation schemes and some results will be discussed.