Liquid Injected Seal to Reduce Leakage Flow in a Refrigerant Compressor

The leakage flow through a traditional labyrinth seal reduces the compressor capacity of an oil-free magnetic bearing centrifugal compressor. Also, the super-heated leakage flow pollutes the downstream coolant flow, affecting motor cooling. A novel design is introduced to utilize the pressure loss across the seal by injecting liquid refrigerant near the seal inlet. The liquid-injected seal also functions as an expansion valve, producing low-temperature wet vapor at the seal exit. The wet vapor is projected to be utilized for motor cooling. A multiphase numerical simulation is performed to quantify the compressor performance of the liquid-injected seal and traditional seal under adiabatic conditions. The numerical simulation utilizes a Eulerian-Eulerian approach with an equilibrium phase change model. This study evaluates the compressor performance at three-speed lines: N1, N2, and N3. The base case results are validated with the experimental findings, with a maximum error of 3% in compressor efficiency. The local distribution of vapor mass fraction, pressure, and temperature are analyzed. The numerical results show that the leakage flow in the liquid-injected seal is reduced by 95%, and the compressor capacity is increased by 2.9%.