In 2017, the polarized target systems from Mainz/Dubna and Bonn were combined for data taking in Bonn. After testing the combined system, the experiment with a polarized frozen-spin target and the upgraded Crystal Barrel detector started in winter 2017. First data with a transversal proton target were already taken. In the meantime, the polarized target group at Bonn is building a continuous 4π polarized target. To get a high target polarization and long relaxation times, low temperatures are indispensable. This system will be able to reach temperatures below 30 mK and allows the use of an internal polarization magnet. As an optimizing tool for the construction of
dilution refrigerators and to gain detailed information about the different incoming and outgoing fluid streams, several CFD-simulations were done. Thus, it was possible to calculate the perfor-
mance of the precooling stages. First tests showed, that these simulations can be used to calculate the performance of the different heat exchangers. Nevertheless, some improvements of the model are ongoing.