• The KSFM Journal of Fluid Machinery
• /
• v.7 no.6 s.27
• /
• pp.38-44
• /
• 2004

In this study, the overall performance and the effect of the tip leakage flow of the centrifugal compressor with a refrigerant HFC-l34a were numerically studied using CFX-TASCflow. To study the effect of the tip leakage flow, the numerical study of the overall performance of HFC-l34a centrifugal compressor with a cascade diffuser was preceded and compared with the experimental result. Six different tip clearances were used to consider the influence of the tip clearance on the performance. The tip leakage flow was illustrated for qualitative discussion. The results obtained in this study can be applied to the determination of the cold clearance.

• 유체기계공업학회:학술대회논문집
• /
• 2003.12a
• /
• pp.451-456
• /
• 2003

In this study, the overall performance and the effect of the tip leakage flow of the centrifugal compressor with the refrigerant HFC-l34a were numerically studied using CFX-TASCflow. To study the effect of a tip leakage flow, the numerical study of the overall performance of HFC-l34a centrifugal compressor with a cascade diffuser was preceded and compared with experimental result. Six different tip clearances were used to consider the influence of a tip clearance on performance. The tip leakage flow was illustrated for qualitative discussion. The results obtained in this study can be applied to the determination of the cold clearance.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.1
• /
• pp.89-95
• /
• 2015

A surge phenomenon cause noise and pulsations in a turbo compressor, which is an unstable operating regime. Because surge protection ensures a safe compressor operation, it is important to understand the physics of the surge phenomenon. In this study, the surge characteristics of a 250-hp class turbo-compressor were evaluated experimentally. The experimental parameters were the rotational speed, opening angles of the inlet guide vane and exit valve, and inlet pipe diameter and flow rates of the inlet gases. The results showed that the compressor surge was very sensitive to the gas flow rates, exit pressure, rotational speed, and bypass flow rates.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2823-2828
• /
• 2007

Numerical simulation on the two-stage centrifugal compressor with Low Solidity Vaned Diffuser LSVD) for HFC-134a Turbo-chiller was performed using a commercial code. The comparative study with experimental results from other compressor was also investigated to testify the simulation schemes. The numerical analysis was separately simulated for each stage of the compressor and the effect of impeller-diffuser flow interaction was considered. Setting angle of the diffuser vane changed in the range of 15 deg. and the effects on its variation were discussed in detail including the flow analysis in the passage of the compressor. The vane setting angle obtained from the preliminary design was slightly adjusted to the optimal value by the performance enhancement in terms of pressure recovery and flow characteristics.

• 유체기계공업학회:학술대회논문집
• /
• 2006.08a
• /
• pp.157-160
• /
• 2006

A turbo-expander is developed for the regeneration in the expansion process. The turbo-expander operates in the partial admission and supersonic flow, and an axial-type single stage turbine is applied to the turbo-expander. Its outer diameter is 82mm and the operating gas is R134a. A 15kW reciprocating compressor is applied in this experiment and the turbo-expander is installed in the expansion process instead of the commonly using expansion valve. Two supersonic nozzles are applied for the expansion process. The high speed of R 134a after passing the supersonic nozzles gives the impulse force to the turbo-expander and some powers are generated on this process. A generator is installed at the end of the turbo-expander shaft. The generating output power from the turbo-expander is controlled by the power controller. Pressures and temperatures are measured on the lines for the performance investigation. More than 600W/(kg/sec) are generated in this experiment.

• Journal of Mechanical Science and Technology
• /
• v.18 no.6
• /
• pp.979-989
• /
• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• The KSFM Journal of Fluid Machinery
• /
• v.13 no.3
• /
• pp.43-48
• /
• 2010

In this study rotordynamic characteristics of an air turbo-compressor (ATC) used in oxygen plant are analyzed and its operating-speed balancing is performed to solve the vibration trouble caused by rotor unbalance. Three dimensional model of the ATC rotor is completed and then analytical FE (finite element) model, which is verified by experimental modal testing, is developed. A rotordynamic analysis includes the critical map, Campbell diagram, and unbalance response, especially considering the pedestal housings supporting tilting pad bearings. A test run of operating-speed, using tilting-pad bearing of actual use, showed that the vibration level increased very sharply as approaching the rated speed. The operating-speed balancing specified by API 684 was carried out by using influence coefficient method. The results showed that the vibrations at the bearing pedestal housings represented good levels of 0.1 mm/s. From the test run and operating-speed balancing, the analytical results, that is, critical speeds are in good agreement with the test results and unbalance responses introducing the correction masses are similar to the as-is test responses in its aspect.

• Journal of KSNVE
• /
• v.10 no.6
• /
• pp.963-970
• /
• 2000

The turbo chiller uses centrifugal compressor, which operates at about 14,500 rpm. Due to the high rpm of the impeller, the noise of chiller males one of the serious problems. The possibility of the sound reduction by using absorbing material is studied in this paper. The generated sound propagates through the duct and then radiates to the outer field. So, the use of sound absorption material inside the duct is one of the effective methods. To study the effect of location of the material, we use Boundary Element Method to analyze the sound field inside the duct system. Numerical study shows the highest sound pressure region is near the elbow of curved duct. From the numerical study, it is also shown that appropriate use of sound absorbing material at this region makes 8dB reduction of the highest noise level.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.6 no.3
• /
• pp.103-110
• /
• 2003

The present work was conducted to achieve the better understanding of the performance analysis technique for the expander type air turbo ramjet engine. For this purpose, the performance analysis was carried out using a small engine(8.0kN thrust) with two types of fuels. From this analysis, at the same input condition, the thrust of methane-fueled engine was 25% lower than that of hydrogen. In addition, the case of methane shows the inapplicable engine performance cycle.(i.e., The compressor work exceeds the turbine output power) These results come mainly from the different heating value of each fuel and specific heat. This analysis also shows that, to build a same performance cycle as the hydrogen case, the methane-fueled engine requires increased air and fuel flow rates, increased turbine expansion ratio, and decreased compressor pressure ratio.

• The KSFM Journal of Fluid Machinery
• /
• v.7 no.2 s.23
• /
• pp.14-20
• /
• 2004

In this study, the overall performance and the local flow field of the centrifugal compressor with the refrigerant HFC-l34a were numerically studied using CFX-TASCflow. The thermodynamic and transport properties of the refrigerant gas were modeled by REFPROP which is NIST refrigerant properties database. The impacts of a grid qualify, discretization scheme, turbulent model and interaction between a impeller and a cascade diffuser were analyzed comparatively. The results were compared with experimental data and 1-D design results using COMPAL and agreed well with others. The numerical method and data obtained in this study can be applied to the design and modification of centrifugal compressors with real gases