• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.625-632
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• 2005

This paper describes the shape optimization of a stator blade in a single-stage transonic axial compressor. The blade optimization has been performed using response surface method and three-dimensional Navier-Stokes analysis. Two shape variables of the stator blade, which are used to define a stacking line, are introduced to increase an adiabatic efficiency. Data points for response evaluations have been selected by D-optimal design, and linear programming method has been used for an optimization on a response surface. Throughout the shape optimization of a stator blade, the adiabatic efficiency is increased to 5.8 percent compared to that of the reference shape of the stator. The increase of the efficiency is mainly caused by the pressure enhancement in the stator blade. Flow separation on the blade suction surface of the stator is also improved by optimizing the stator blade. It is noted that the optimization of the stator blade is also useful method to increase the adiabatic efficiency in the axial compressor as well as the optimization of a rotor blade, which is widely used now.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.4
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• pp.27-32
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• 2016

It is estimated that only heating and cooling take about one third of the total energy consumption worldwide. However, the conventional heating and cooling systems have low efficiencies. Also, boilers and electric heaters that are mostly used to generate both domestic and industrial hot water are inefficient and high energy consumers. For this reason, cascade heat pumps which are known to be very energy efficient and have less environmental impact are being promoted to replace conventional heating, cooling and hot water systems. In this study, a newly designed cascade heat pump by two-stage water heating method has been experimentally investigated. By adopting the auxiliary heat exchanger, the performance of the system was increased. The performance enhancement rate of the system could be maximized by adjusting the low stage compressor speed rather than the high stage compressor speed. The performance of the system with the auxiliary heat exchanger was enhanced by 16.5%.

• Journal of Institute of Convergence Technology
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• v.2 no.1
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• pp.38-42
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• 2012

A scroll compressor used in the air conditioning in automobile consists of the fixed scroll and the orbiting scroll. Temperature gradient in the scroll compressor during the operation induces the thermal expansion of two scrolls. Therefore, the gap between scrolls in the initial stage is regarded as an important variable in structural design of the scroll compressor. The coupled thermal-stress analysis was carried out for the scrolls of a scroll compressor. The temperatures of major points of two scrolls in the steady states were referred by the literature of C. Lin. The sequentially coupled thermal-stress analysis is utilized to the heat transfer analysis and the thermal expansion analysis. In the thermal expansion analysis, the contact analysis was considered between the fixed and the orbiting scrolls in order to obtain the penetration distance and the contact pressure between two scrolls. The range of deformation was from 44 to $76{\mu}m$ according to the height of the scroll. The maximum penetration distance of $60{\mu}m$ occurred at the top surface of the fixed scroll in the center of the scroll parts.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.3
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• pp.168-172
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• 2013

A preliminary performance test of a 30RT 2-stage screw heat pump was carried out in order to develop a high performance large-scale unutilized energy source heat pump system, which will be used for district heating and cooling. In this study, two issues of the system operating control were investigated. The first issue is the mode switching control from 1-stage to 2-stage. A stable 2-stage heating operation is guaranteed, only if the load-side water inlet temperature is over a certain value, where the 1-stage heating operation should be done first from a cold start. The second issue is oil level control. An oil shortage problem in the low stage compressor, which depends on the degree of suction superheat, was solved by a proper oil level control scheme.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.11
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• pp.3253-3259
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• 2009

In this study, a computer simulation has been performed for the refrigeration cycle using mixed refrigerants in order to decrease the process stream temperature to $-20^{\circ}C$. Refrigerant supply temperature was assumed to be $-30^{\circ}C$ considering the temperature difference as $10^{\circ}C$ with process stream. Peng-Robinson equation of state model was selected for the computer simulation. A new alpha function proposed by Twu et al was used for an accurate prediction of pure component vapor pressure experimental data. One fluid mixing rules were used for the estimation of mixture vapor-liquid equilibria calculations. A commercial process simulator, PRO/II with PROVISION was utilized for the simulation of the overall refrigeration process. In order to minimize the compressor power consumption, we have optimized the two-stage compression system by varying the first stage compressor outlet pressure. Finally, we could obtain the minimum total power 755.7kW at the first stage compressor outlet pressure, 6 bar.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.182-187
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• 2003

Numerical analysis of three-dimensional vicous flow is used to compute the design speed operating line of a transonic axial-flow compressor. The Navier-Stokes equation was solved by an explicit finite-difference numerical scheme and the Baldwin-Lomax turbulence model was applied. A spatially-varying time-step and an implicit residual smoothing were used to improve convergence. Two-stage axial compressor of a turboshaft engine developed KARI was chosen for the analysis. Numerical results show reasonably good agreements with experimental measurements made by KARI. Numerical solutions indicate that there exist a strong shock-boundary layer interaction and a subsequent large flow separation. It is also observed that the shock is moved ahead of the blade passage at near-stall condition.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.697-703
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• 2003

For a single stage two cylinder rotary compressor, an analytical study has been made on the discharge gas pulsation. Discharge system of the twin rotary compressor consists of lower and upper mufflers and connecting passage holes between them, and cavities on both sides of the motor and passages between them. Acoustic modeling for the discharge system by transfer matrix method gives acoustic impedances at discharge valves so that gas pulsation at the valve sections can be obtained from discharge mass velocity. Since the mass velocity and the pressure pulsation at the valves are affected by each other, iteration should be made for convergence. Gas pulsations at other sections can also be calculated by using transfer matrix.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.501-505
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• 2006

A preliminary performance test of a 30RT 2-stage screw heat pump was carried out in order to develop a high performance large-scale unutilized energy source heat pump, which will be used in district heating and cooling. Two issues on the system control were investigated in this study, A stable 2-stage heating operation is guaranteed only if the load-side water inlet temperature is over a certain value, to where the 1-stage heating operation should be done first from a cold start. An oil shortage problem in low stage compressor, which depends on the degree of suction superheat, was solved by the proper oil level control scheme.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.8
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• pp.2561-2571
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• 1996

The flow in the turbomachinery is very unsteady due to the stator-rotor interaction. It has been indicated that the stator-rotor interaction has three distinct causes of unsteadiness: that is, the viscous vortex shedding, wake rotor interaction and potential stator-rotor interaction. In this paper, the mechanism of unsteady potential interaction and wake interaction in the stator-rotor stage flow is numerically investigated in two-dimensional view point. The numerical technique used is the upwind scheme of Van Leer's Flux Vector Splitting(FVS) and cubic spline interpolation is applied on zonal interface. Then, the flow field of a compressor stage composed of NACA 65410 is analyzed. Flow fields are found to be simulated reasonably by this method and the sensitivity due to back-pressure variation is more stronger than rotor-velocity variation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.77-83
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• 2002

A computational study on the performance prediction of a two-stage axial compressor has been performed. A quasi-steady mixing-plane method is used on the rotor/stator interface to simulate the unsteady interaction phenomena. Detail flow mechanisms, for example, choke, stall, shock/boundary interaction, etc., have been observed and discussed in conjunction with performance characteristics. Calculational data agree reasonably well with the experimental data in terms of the performance characteristics showing the applicability of computational methods to the design validation of multistage axial compressors instead of experimental methods. But it is found that the stall margin of the original compressor was rather small, thus the design modification adopting a simple 1D/2D method has been conducted and its corresponding computations are also carried out. As a result of the redesign process, the stall margin becomes wide enough, but the overall performance is unsatisfactory, therefore, it seems that the redesign of the blades using 3-D methods is needed in the future work.