• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.2
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• pp.150-158
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• 1988

On a refrigeration compressor, damage of a discharge valve is one of the annoying troubles for an engineer. Small size compressors, having ring plate type discharge valve are recently used. Therefore, it is very important for engineers to measure and analyze strains of discharge valve. The purpose of this study is to obtain the basic data of the strain of the flexible ring valve. Measurements were performed by the strain gauge bonded on the surface of the flexible ring valve. Stress and strain of the valve were calculated by the method of uniformly loaded circular plates with a central hole. The results obtained are as follows; (1) the strain of flexible ring discharge valve in refrigeration compressor was influenced by tension and compression strain simultaneously. (2) for a given discharge pressure, the tangential and radial strains was increased with increasing discharge pressure. (3) the valve of radial strain was larger than that of tangential strain.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.12
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• pp.107-112
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• 2010

A gas turbine consists of an upstream compressor and a downstream turbine with a combustion chamber, and also the compressor and the turbine are generally coupled using a single shaft. Large scale gas turbine compressor is designed as multi-stage axial flow and the blade is fan-type which is thick and wide. Recently radial cracking happens occasionally at the compressor blade tip of large scale gas turbine. So, FEM was performed on the compressor blade and vibration modes and dynamic stresses were analyzed. According to the analysis, 9th natural frequency mode of the blade, which is 2 strip mode, is near the vane passing frequency by the vane located at the upstream of the blade.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.533-541
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• 2005

Compared to axial compressors, an analytical model capable of analyzing the flow in centrifugal compressor lacks because of the difficulty in governing equations for radial duct. Therefore, this paper presents a new model to predict flow field in a centrifugal compressor with a sinusoidal asymmetric tip clearance. To predict the 2 dimensional flow in the inlet and exit of the centrifugal compressor, the two flow fields are connected with compressor characteristic based on Moore-Greitzer model. Contrary to axial compressors, the nonuniformity of impeller exit pressure in centrifugal compressor decreases as flow coefficient decreases. In addition, that is sensitive to the slope of pressure rise by eccentricity. The maximum velocity exists right before the maximum tip clearance.

• 유체기계공업학회:학술대회논문집
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• 1998.02a
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• pp.159-163
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• 1998

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.5
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• pp.418-426
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• 2005

Efficiency of the compressor is most important parameter in the domestic refrigerator which runs year around. With developed analytical model about heat transfer analysis in the hermetic compressor, parametric study was performed to know the effect on efficiency by design and material modification of the compressor. Volumetric efficiency of the compressor increased approximately $3\%$ when insulation is increased about $50\%$ in suction component. However, the insulation effect on discharge component was only $1\%$. When the thermal conductivity of the discharge plenum is reduced from 300 to 20 $W/m{\cdot}K$, volumetric efficiency increased about $3.1\%$. There is no attraction in efficiency increment with variation of outside surface area of the compressor and radial heat transfer coefficient of the solid component in the compressor shell.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.199-204
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• 2003

In the present study, the compression process in scroll compressor was simulated in consideration of flow leakage and heat transfer. Tangential and radial leakages of the refrigerant between the scrolls were considered as nozzle flow. The experiment was first conducted with a scroll compressor for automobile air conditioning system and R134a as a refrigerant. Temperature and pressure were measured at the suction and discharge ports of the compressor to determine the thermodynamic states of the refrigerant flow. Temperature distribution of the scroll with the involute angle was also measured by thermocouples that were installed inside the scroll. Measured temperature distribution was compared with the numerical results. From this result, the thermal effect of mechanical contact was found to be important in heat transfer of the compression process.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.29-38
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• 2010

This paper presents a procedure for the design optimization of a centrifugal compressor. The centrifugal compressor consists of a centrifugal impeller, vaneless diffuser and volute. And, optimization techniques based on the radial basis neural network method are used to optimize the impeller of a centrifugal compressor. The Latin-hypercube sampling of design-of-experiments is used to generate the thirty design points within design spaces. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by using finite volume approximations and solved on hexahedral grids to evaluate the objective function of the total-to-total pressure ratio. Four variables defining the impeller hub and shroud contours are selected as design variables in this optimization. The results of optimization show that the total-to-total pressure ratio of the optimized shape at the design flow coefficient is enhanced by 2.46% and the total-to-total pressure ratios at the off-design points are also improved significantly by the design optimization.

• The KSFM Journal of Fluid Machinery
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• v.15 no.6
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• pp.51-57
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• 2012

Performance evaluation of a compressor is conducted to develop 500W class ultra-micro gas turbine (UMGT) for power generation. The performance evaluation is essential to check the performance of the components of UMGT, a radial turbine, a centrifugal compressor, an angular combustor and a shaft, which have been already designed in previous researches. The purpose of this study is to introduce the development process of the performance testing equipments of the UMGT and to present the results of compressor performance test. For the performance evaluation of the compressor, two test equipments are developed and the initial test equipment uses commercial static air bearings with long shaft. In the improved test equipment, static air bearing is improved to increase rotating speed and compressed nitrogen gas is used for utility gas of the static air bearing to supply compressed air in a stable and steady way. To increase rotating speed to 320,000 rpm, 80% speed of design speed, compressed air is provided to the turbine. The performance map of the compressor with the 50%, 60%, 70%, 80% speed of design point is presented. The results of the performance test of compressor show a good agreement with the results of 3D CFD.

• Tribology and Lubricants
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• v.31 no.5
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• pp.221-228
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• 2015

It is possible to prevent a piston from contacting the cylinder by changing the shape of the piston or by applying micro-textures, such as micro-grooves or micro-holes, over the piston surface. Usually, the minimum radial clearance reaches its minimum value at the beginning of the suction stroke because the pressure around the piston is low and almost axisymmetric such that the net pressure force on the piston is not sufficiently high to support the piston from touching the cylinder. In this study, we apply a series of saw-tooth-shaped grooves on the piston surface, and numerically investigate the effects of groove depth, groove angle, and the number of grooves with radial clearance variations using a finite difference method. We conduct a dynamic analysis of the piston for various changes in groove geometries to obtain the minimum radial clearance variation for the entire compression cycle. The minimum radial clearance increases while friction loss decreases when we apply the series of saw-tooth-shaped grooves on the piston. In addition, we analyze the impact of the change in the groove shape variable due to changes in radial clearance. Leakage variations are relevant to radial clearance, but have almost no effect on the groove parameters.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.3
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• pp.132-139
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• 2003

The effects of casing shapes on the performance and the interaction between an impeller and a casing in a small-sized centrifugal compressor are investigated. Especially, numerical analyses are conducted for the centrifugal compressor with both a circular casing and a volute one. The optimum design for each element (i.e., impeller, diffuser and casing) is important to develop an efficient and compact compressor using alternative refrigerant as working fluids. Typical rotating speed of the compressor is in the range of 40,000∼45,000 rpm. The impeller has backswept blades due to tip clearance and a vane diffuser has wedge type. In order to predict the flow pattern inside an entire impeller, vaneless diffuser and casing, calculations with multiple frames of reference method between the rotating and stationery parts of the domain are carried out. For computations of compressible turbulent flow fields, the continuity and time-averaged Navier-Stokes equations are employed. To evaluate the performance of two types of casings, the static pressure recovery and loss coefficients are obtained for various flow rates. Also, static pressure distributions around casings are studied for different casing shapes, which are very important to predict the distribution of radial load. The static pressure around the casing and pressure difference between the inlet and outlet of the compressor are measured for the circular casing.