• 한국유체기계학회 논문집
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• 제4권1호
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• pp.14-21
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• 2001

In a small centrifugal compressor system, a high-speed motor needs to be developed to drive impellers directly. Heat is generated by both electrical heating due to copper coil resistance and aerodynamic heating in the gap between the rotor and stator in a high-speed motor. Removal of the heat is essential to the design of such motors since most magnetic materials are brittle and can be easily fractured by the heat. In the present study the cooling flow fields and temperature distributions are analyzed by using computational fluid dynamics simulation for a high-speed motor which has air cooling system as well as water cooling system. In the analysis, a conjugate heat transfer problem is solved by considering both convective heat transfer in the cooling system and conduction heat transfer in solid parts. Based on design drawings of a motor, air cooling system and water cooling system are analyzed to obtain temperature field and thus to check the coiling system performance. Also the cooling performance are studied for various flow rates of cooling air and water at the inlets.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.351-358
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• 2000

In a small centrifugal compressor system, a high-speed motor needs to be developed to drive impellers directly. Heat is generated by both electrical heating due to copper coil resistance and aerodynamic heating in the gap between the rotor and stator in a high-speed motor. Removal of the heat is essential to the design of such motors since most magnetic materials are brittle and can be easily fractured by the heat. In the present study the cooling flow fields and temperature distributions were analyzed by using computational fluid dynamics simulation for a high-speed motor which has air cooling system as well as water cooling system. In the analysis a conjugate heat transfer problem is solved by considering both convective heat transfer in the cooling system and conduction heat transfer in solid parts. Based on design drawings of a motor, air cooling system and water cooling system were analyzed to obtain temperature field and thus to check the coiling system performance. Also the cooling performance are studied for various flow rates of cooling air and water at the inlets.

• 한국소음진동공학회논문집
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• 제12권9호
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• pp.717-724
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• 2002

In this study, a numerical analysis for the piston secondary dynamics of small refrigeration reciprocating compressors is performed. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the change in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the hydrodynamic force and moment as functions of crank angle under compressor running conditions. The results explored the effects of the radial clearance, lubricant viscosity, length of the cylinder wall, and pin location on the stability of the piston.

• 설비공학논문집
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• 제17권8호
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• pp.780-788
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• 2005

Two different types of algorithms were developed and applied to detect the partial faults of a multi-type air conditioning system. Partial faults include the compressor valve leakage, the refrigerant pipe partial blockage, the condenser fouling, and the evaporator fouling. The first algorithm was developed by using mathematical models and parity relations, and the second algorithm was developed by using mathematical models and a RBF neural network. Test results showed that the second algorithm was better than the first algorithm in detecting various partial faults of the system. Therefore, the algorithm developed by using mathematical models and a RBF neural network may be used for the detection of partial faults of an air-conditioning system.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.823-827
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• 2008

The effects of blade leading edge sweep on both the aerodynamic performance and the structure stress of a high pressure centrifugal compressor impeller are numerically investigated. Changes in the flow structure occur as a result of the effect of leading edge sweep on the loading distribution in the tip region. The flow separation is avoided by introducing a sweep of the main blade leading edge and the strength of shock is reduced at the same time. Backswept of the leading edge is found to be beneficial to the impeller performance improving. On the other hand, the structural analysis indicated that high rotating speed of the impeller will cause substantial high bending stresses and radial deflections of the blade. Studies have shown that it is possible to control the stress distribution along the tip and root of the blade by slight adjustments to the sweep angle of the leading edge. These adjustments may be used to design the impeller with lower blade root stress distribution without aerodynamics performance penalty.

• Tribology and Lubricants
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• 제35권1호
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• pp.44-51
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• 2019

The paper presents the rotordynamic performance measurements and model predictions of a fuel cell electric vehicle (FCEV) air compressor supported on gas foil bearings (GFBs). The rotor has an impeller on one end and a thrust runner on the other end. The front (impeller side) and rear (thrust side) gas foil journal bearings (GFJBs) are located between the impeller and thrust runner to support the radial loads, and a pair of gas foil thrust bearings are located on both sides of the thrust runner to support the axial loads. The test GFJBs have a partial arc shim foil installed between the top foil and bump strip layers to enhance hydrodynamic pressure generation. During the rotordynamic performance tests, two sets of orthogonally installed eddy-current displacement sensors measure the rotor radial motions at the rotor impeller and thrust ends. A series of speed-up and coast-down tests to 100k rpm demonstrates the dominant synchronous (1X) rotor responses to imbalance masses without noticeable subsynchronous motions, which indicates a rotordynamically stable rotor-GFB system. Finite element analysis of the rotor determines the rotor free-free (bending) natural modes and frequencies well beyond the maximum rotating frequency. The predicted damped natural frequencies and damping ratios of the rotor-GFB system reveal rotordynamic stability over the speeds of interest. The imbalance response predictions show that the predicted critical speeds and rotor amplitudes strongly agree with the test measurements, thus validating the developed rotordynamic model.

• 한국산학기술학회논문지
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• 제16권6호
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• pp.3722-3730
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• 2015

하수 처리용으로 사용되는 소형 원심 압축기의 베인 없는 디퓨져와 볼류트 케이싱의 성능 개선을 수행하였다. 기존의 두 모델은 임펠러가 동일하나, 베인 없는 디퓨져의 폭과 길이 및 볼류트 케이싱의 형상은 서로 다르다. 기존 모델에 대한 실험과 유동해석 결과를 바탕으로 베인 없는 디퓨져와 볼류트 케이싱의 설계를 변경하였다. 세 모델에 대한 연구 결과로부터, 볼류트 케이싱의 단면적 및 입구 반경 길이는 볼류트 혀와 베인 없는 디퓨져 및 임펠러와의 상호작용 강도에 영향을 주었고, 시스템 손실량에 변화를 나타내었다. 베인 없는 디퓨져 폭이 감소하면 임펠러의 효율은 증가했지만 디퓨져에서의 손실도 증가하였다. 결과적으로 개선된 모델의 효율이 설계 점에서 기존 대비 약 2.88%p 향상된 것이 유동해석 결과로 확인되었다.

• Tribology and Lubricants
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• 제34권1호
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• pp.9-15
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• 2018

Modern high-performance automotive turbochargers (TCs) implement ceramic hybrid angular contact ball bearings in series with squeeze film dampers (SFDs) to enhance transient responses, thereby reducing the overall emission levels. The current study predicts the rotordynamic responses of the commercial automotive TCs (compressor wheel diameter = ~53 mm, turbine wheel diameter = ~43 mm, and shaft diameter at the bearing locations = ~7 mm) supported on ball bearings and SFDs for various design parameters of SFDs, including radial clearance, axial length, lubricant viscosity, and rotor imbalance conditions (i.e., amplitudes and phase angles) while increasing rotor speed up to 150 krpm. This study validates the predictive rotor finite element model against measurements of mass, polar and transverse moments of inertia, and free-free mode natural frequencies and mode shapes. A nonlinear rotordynamic model integrates nonlinear force coefficients of SFDs to calculate the transient responses of the TC rotor-bearing system. The predicted results show that SFD radial clearances, as well as phase angles of rotor imbalances, have the paramount effect on the dynamic responses of TC shaft motions.

• Tribology and Lubricants
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• 제18권4호
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• pp.291-298
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• 2002

In this study, a numerical analysis f3r the piston secondary dynamics and lubrication characteristics of small refrigeration reciprocating compressors is presented. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the change in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the hydrodynamic forces and moments as functions of crank angle under compressor running conditions. The results explored the effects of the radial clearance, lubricant viscosity, and pin location on the stability of the piston, the oil leakage, and friction losses.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.314-319
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• 2002

Performance analysis and test of a 50kW micro gas turbine is carried out. The present study was initiated in 1996 by KIMM researchers to develope a 50kW class turbogenerator gas turbine engine for hybrid vehicle propulsion system. but with its low emission and compactness, it seemed that it can also be applied as a source of distributed power generation. In this study, general description of the KIMM's efforts to acquire performance test skills of the self-made 50kW micro gas turbine engine. At present, non-load performance test up to 615000 rpm was accomplished and is expected to make through 80,000 rpm by the end of year. Several revisions in design and manufacture were made during the course of experiments. The resulting outputs is thought to be valuable for the further refinement of the system for eventual commercialization of the product.