Search

In order to study the windage losses caused by the friction between fluid and rotor surface in high speed rotating machines, a series of rundown experiments are performed in a vacuum chamber. By means of an evacuation method, the windage losses are extracted by subtraction operation between specified pressure and near absolute vacuum. The windage losses separated with existing separation models for large gap are compared to the extracted values with evacuation method and the results show big disagreements. For this reason, a modified separation model considering the skin effect and gas state is presented for rotating electrical machines simultaneously including both large and small gap. Using the modified separation model, the results show good agreements with the extracted values. In contrast to the evacuation method, the new model provides a way to quickly assess windage losses in electrical machines, where vacuuming is not obligatory any more.

In this paper, a type of mutual inductance sensor based on the PCB technology is proposed for cryogenic radial displacement measurement. Firstly, the feasibility of the scheme is analyzed from the aspects of the low temperature usability of materials and components, and the temperature sensitivity of the sensor. Then the experiments at low temperature (77 K) and room temperature are carried out with a simple and effective setup. The experimental results show that the sensitivity has no obvious change from room temperature to low temperature, and the linearity remains at a good level. However, the standard deviation and repeatability of the measurement are affected by external factors. Generally speaking, this paper verifies the feasibility of applying this sensor to micro displacement measurement at low temperature, which lays a foundation for the development of more mature displacement sensor for HTS bearing.

HIAF-BRing, the main synchrotron accelerator of the High Intensity Heavy-Ion Accelerator Facility, requires an average pressure lower than 1 × 10−9 Pa and the magnetic field increase rate no less than 12 T/s to fulfill radioactive beam physics and high energy density physics experiments. To reduce the eddy current effect and the gap size of dipoles compared to the thin-wall stainless steel vacuum chamber with reinforced ribs, a new design of ceramic-lined vacuum chamber with wall thickness 0.3 mm has been proposed by IMP. In order to effectively reduce the beam impedance and the desorption rate of ceramic materials, Au coating on ceramic (Yttria stabilized zirconia) by magnetron sputtering has been carried out. The adhesive force of Au film is 28.1 MPa measured by scratch test while the crystalline size of Au particle is in the range of 15.7–21.4 nm by X-ray diffraction (XRD). The longitudinal impedances of four types of round-ring-lined 0.6-m-long straight stainless-steel tubes and the ultimate pressure of the new designed vacuum chamber (uncoated vs Au-coated) have been measured to verify the feasibility of this method.

Cold compressors are the core components needed for the development of a facility for large-capacity refrigeration at superfluid helium temperature. The compressor impeller operates at extremely low temperature and low pressure which involves a performance penalty due to heat transfer from the warm side of the machine to the cold side and thus affects the recycle of the cold exergy downstream. To investigate the heat transfer effect on cold compressor performance, a conjugate heat transfer analysis is performed with commercial CFD solver and is then validated with the experimental data tested at different rotation speed. Then a series of configurations of different thermal boundaries are analyzed to investigate the influence of heat transfer on performance. The simulated results show that the external heat transfer has a negative impact on pressure distribution. The helium gas inside the impeller flow domain is more sensitive to external heat leakage comparing with that inside the diffuser flow. More than that, the mass flow leakage through blade tip clearance is highly affected by the external heat transfer, which counts for the performance degradation.