Tilting pad journal bearing (TPJBs) have been widely used in rotating machinery such as compressors and turbines due to their superior stability compared to that of conventional fixed geometry bearings. As the adoption of TPJBs increases, various failure mechanisms related to TPJBs have been reported and pad wear is a frequently reported one. Pad wear causes geometry changes of the bearing, which can sometimes result in entire system failure. Therefore, it is important to detect the problem in the early stage to prevent unexpected system shut down. The objective of the current research is to investigate the influence of pad wear on the pad temperature, which is one of the widely used condition monitoring methods of TPJBs. For the theoretical investigation, thermohydrodynamic (THD) analysis was conducted by solving the generalized Reynolds equation and 3D energy equation. The developed THD model was validated by comparing the results with test data available in the literature. The results of the analysis showed that the temperature of the loaded pad increases and that of the unloaded pad decreases when wear occurred on loaded pads. In addition, the minimum film thickness also decreases with the wear depth. The validation test conducted with a test rig which mimics axial turbine where a test rotor was supported by two TPJBs. The test bearing consists of five pads with diameter of 60 mm and a resistance temperature detector (RTD) was installed in the pad for temperature monitoring. The test was performed by replacing the two loaded pads with the worn pad. The test result for TPJB with wear depth of 30 μm showed that the temperatures of the loaded pads were 8°C higher and that of the unloaded pad was 2.5°C lower than that of the normal TPJB. Additionally, the predicted pad temperature shows good agreement with the measured pad temperatures.

This paper presents design guidelines for a high-speed permanent magnet synchronous motor (PMSM) for a 110 hp and 12 500 r/min centrifugal pump considering the mechanical and electromagnetic characteristics. We selected the size of the rotor based on the torque per unit rotor volume method. The rotor stress analysis was performed using the analytical method and the finite-element method. Based on these results, appropriate sleeve thickness and material were selected considering mechanical stability and electrical performance. The PMSM design was carried out by using the mechanically stable rotating body, and the model with excellent electromagnetic performance was selected based on the iron loss analysis and the eddy current loss analysis using the finite-element method. In addition, the stability of high-speed operation was confirmed by the critical speed analysis of the finally designed PMSM model. The high-speed PMSM verifies the performance through the manufacturing and test it was confirmed that there is no problem when applied to the actual centrifugal pump systems.

Gas foil bearings (GFBs) have many noticeable advantages over the conventional rigid gas bearings, such as frictional damping of the compliance structure and tolerance to the rotor misalignment, so they have been successfully adopted as the key element that makes possible oil-free turbomachinery. As the adoption of the GFB increases, one of the critical elements for its successful implementation is thermal management. Even though heat generation inside the GFB is small due to the low viscosity of the lubricant, many researchers have reported that the system might fail without an appropriate cooling mechanism. The objective of the current research is to demonstrate the reliability of GFBs installed in the hot section of a micro-gas turbine (MGT). For the cooling of the GFBs, we designed a secondary flow passage and thermohydrodynamic (THD) analysis has been done for temperature prediction. In the analysis, the 3D THD model for the radial GFB extended to include the surrounding structure, such as the plenum, chamber, and the rotor in the solution domain by solving global mass and energy balance equations. In the MGT, the pressurized air discharged from the compressor wheel was used as the cooling air source, and it was injected into the plenum between two radial GFBs. We monitored the pressure and temperature of the cooling air along the secondary flow passage during the MGT operation. No thermal instability occurred up to the maximum operation speed of 43,000 rpm. The test results also showed that the pressure drop between the main reservoir and the plenum increases with an increasing operation speed, which indicated an increased cooling air flow into the plenum. The plenum and bearing sleeve temperature was maintained close to the cooling air source temperature for the entire speed due to a sufficient cooling air flow into the bearing. In addition, the direct injection of the cooling air from the main stream lowered the bearing sleeve temperature by 5–20 °C over the injection through the reservoirs. The predicted plenum and bearing sleeve temperatures with the developed THD model show good agreement with the test data.

A design process for cryogenic expanders that supplies 0.5 TPD of liquefied hydrogen in hydrogen liquefaction plants is introduced. To improve the efficiency of the expander, the optimum design was conducted by adjusting two rotor shape parameters. The designed expander for hydrogen liquefaction has a target rotation speed of 75,000 rpm, and helium is applied as the working fluid. Since the operating temperature of the expander is as low as 49 K, a design that reflects the real gas properties must be considered. For a high-efficiency hydrogen liquefaction plant, increasing the expander efficiency is one of the most critical issues. In this study, the efficiency of the cryogenic expander was optimized using the response surface method (RSM). The hub and shroud meridional contours and blade $\beta$ angle distributions were chosen as the design parameters. As a result, through the optimized design, it was possible to improve the expander efficiency by up to 1.98% compared to the original expander. Flow analysis was conducted to investigate the reason for the efficiency improvement. Through this study, the effect of the blade meridional contour and blade $\beta$ angle on the cryogenic expander efficiency was verified.

This study designed an externally pressurized bearing and analyzed the rotordynamics of a turbo expander for a hydrogen liquefaction plant. The turbo expander, comprising a turbine and compressor wheel assembled to a shaft, lowered the temperature of the helium refrigerant. Its rated speed was 75,000 rpm, and an externally pressurized gas bearing was selected to support the rotor. Pressurized helium was used as the lubricant for the bearing operation. To design the rotor–bearing system, we conducted a bearing performance analysis and rotordynamic characteristic prediction using the developed numerical model. We calculated the bearing stiffness and flow rate of the bearing gas for various feed parameters and selected the appropriate orifice diameter for maximum stiffness. The predicted Campbell diagram showed that the system had a sufficient separation margin with the critical speed, and the predicted critical speed correlated well with the nonlinear orbit simulation. A successful operation was achieved with the manufactured turbo expander within the rated speed. The shaft vibration was monitored during the operation test, and the test results revealed two critical speeds below the rated speed, as predicted by the analytical model. In addition, the shaft vibration was maintained at <3 μm.

The turbomachinery used in the sCO₂ power cycle requires a high stable rotor-bearing system because they are usually designed to operate in extremely high-pressure and temperature conditions. In this paper, we present a pump-drive turbine module applying hydrostatic bearing using liquid CO₂ as the lubricant for a 250 kW supercritical CO₂ power cycle. This design is quite favorable because stable operation is possible due to the high stiffness and damping of the hydrostatic bearing, and the oil purity system is not necessary when using liquid CO₂ as the lubricant. The pump-drive turbine module was designed to operate at 21,000 rpm with the rated power of 143 kW. The high-pressure liquid CO₂ was supplied to the bearing, and the orifice restrictor was used for the flow control device. We selected the orifice diameter providing the maximum bearing stiffness and also conducted a rotordynamic performance prediction based on the designed pump-drive turbine module. The predicted Campbell diagram indicates that a wide range of operation is possible because there is no critical speed below the rated speed. In addition, an operation test was conducted for the manufactured pump-drive turbine module in the supercritical CO₂ cycle test loop. During the operation, the pressurized CO₂ of the 70 bar was supplied to the bearing for the lubrication and the shaft vibration was monitored. The successful operation was possible up to the rated speed and the test results showed that shaft vibration is controlled at the level of 2 μm for the entire speed range.