• International Journal of Air-Conditioning and Refrigeration
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• 제11권3호
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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.

• 한국결정성장학회지
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• 제7권4호
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• pp.536-547
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• 1997

축방향으로 균일한 자장이 가하여진 Czochralski 도가니에서 도가니와 성장결정이 다양한 각속도로 회전하는 경우에 대하여 유동장, 온도장 및 산소의 농도장이 수치적으로 연구되었다. 도가니 벽의 가열에 의한 부력의 효과와 자유표면에서 온도차이에 의한 열모세관효과로 인한 용융물질의 유동은 도가니와. 성장결정의 회전에 따른 원심력에 의하여 차등적으로 억제될 수 있다. 이 원심력에 가장 큰 영향을 주는 인자는 도가니의 회전속도이며 이것이 초크랄스키 결정성장과정에서 속도장, 온도장, 농도장에 큰 영향을 주고 있다. 도가니의 회전속도가 작을 때에는 성장결정의 회전이 원심력을 효과적으로 발생시킨다.

• 한국유체기계학회 논문집
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• 제19권5호
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• pp.5-11
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• 2016

The purpose of this study is to design the transonic centrifugal compressor impeller with splitter blades and analyze the flow fields with respect to various splitter blades. Seven impellers with different splitter chord length or pitchwise location were tested by using CFD method. To investigate aerodynamic performance, Mach number distribution and entropy distribution were confirmed. As a result, it is found that the size of transonic region and shock wave location are related to the splitter chord length and pitchwise location. Also the impeller with long chord length of splitter shows higher total pressure ratio but lower efficiency than those of the impeller with short chord length of splitter. In terms of pitchwise location, the impeller with the splitter located in mid-pitch of main blades shows the best performance with respect to pressure ratio and efficiency.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.122-128
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• 2000

Aerodynamic optimization of an automotive air-conditioning blower is a hard task because of the highly complex flow phenomena related to three-dimensional flow separations and the unsteady nature caused by the interaction between primary and secondary air flows throughout the fan. In this paper, an aerodynamic study on a forward-curved centrifugal fan has been carried out Firstly we obtained the fan performance curves versus flow rates showing its unstable nature in the surging operation range. Secondly aerodynamic characterizations were carried out by investigating the velocity and pressure fields in the casing flow passage using a 5-hole pilot probe, at different operating conditions. Surface flow pattern near the cut-off area exhibits similar flow behavior above the best efficiency operating point, although the pressure level increases substantially with the Increase of flow rate. Vorticity in the casing passage flow occurs in all (low rates, downstream from the r-Z plane $\theta$=120 deg., where the position of its core changes with the circumferential location. Although complex, the general flow behavior were common, giving insight in its main aerodynamic features.

• Design & Manufacturing
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• 제16권1호
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• pp.43-49
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• 2022

As technologies in various industrial fields develop, high-quality parts are required. In the past, precision parts were produced by the contact machining method, but the contact machining method has clear limitations. In order to solve this problem, research on a non-contact processing method has been conducted, and laser processing and electric discharge processing are representative. However, the non-contact method has a problem in that productivity is insufficient, and there is a problem that it takes a lot of time to continuously process microholes. Researchers have developed an electron beam drilling equipment for continuous processing of fine holes, and a vaporization amplification sheet to increase the processing efficiency of the equipment. In this study, a cylindrical vaporization amplification sheet using room temperature curing type silicon was fabricated, and the metal distribution and thickness uniformity of the produced sheet were analyzed. In order to manufacture a cylindrical vaporization amplification sheet, an equipment capable of using centrifugal force was developed, and a sample in which metal powder was evenly distributed and a constant thickness was produced.

• 한국결정성장학회지
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• 제3권1호
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• pp.18-30
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• 1993

균일한 자장과 비균일한 자장이 도가니에 가하여졌을 때의 Czochralski유동장이 수치적으로 해석되었다. 여기에서 부력의 효과, thermocapillarity 효과, 원심력의 효과, 자장의 효과등이 Czochralski유동장을 지배하고 있다. 자오면에서의 속도성분과 회전방향의 속도성분이 구하여졌으며 온도, 전류의 흐름 등이 해석되었다. 균일한 자장의 경우에 세기가 증가하면 모든 속도성분이 작아지고 있으며 결정표면 아래에서 회전방향으로의 전류의 세기가 증가한다. 불균일한 자장의 경우에는 자장의 불균일성이 증가하면 자오면에서의 평면유동은 억제되는 반면 회전방향의 속도성분은 더 증가하게 된다. 이와 같은 여러 형태의 자장의 영향아래에서의 Czochralski 유동장에 대한 이해는 도가니(Crucible)안의 용질 및 불순물의 농도에 관한 거동을 연구할 수 있는 기초를 제공하고 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.819-824
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• 2001

Mean velocity and Reynolds stress components of the developing turbulent flows in a rotating 90 degree bend with square cross-section were measured by a hot-wire anemometer. Effects of the centrifugal and Coriolis forces generated by the curvature and rotation of bend on the mean motion and turbulence structures are investigated experimentally. Results show that the Coriolis force associated with the rotation of the bend may act both through the mean motion and turbulent structures, thereby changing the pressure fields, mean and turbulent velocities distributions.

• 대한기계학회논문집B
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• 제20권11호
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• pp.3639-3648
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• 1996

The effect of 15% pinched diffuser in a centrifugal air compressor with a cascade airfoil diffuser on the aerodynamic performance is investigated using a numerical approach. The commercial CFD code for three-dimensional, turbulent, compressible flow fields is executed for various mass flow rates at a design speed which can be obtained as long as the calculation succeeds. The pinched diffuser is found to help improve the instability of flow within vaneless diffuser space, especially the reverse flow near shroud, and to change both stall/surge line and choking line to increase the surge margin. It is also found to generate more favorable increase of static pressure in diffuser region, and to increase the resulting pressure ratio and efficiency.

• Journal of Biosystems Engineering
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• 제40권2호
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• pp.102-109
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• 2015

Purpose: Slow manual harvesting of rain-fed chickpeas cultivated in fallow fields in developing countries have encouraged the design of a mechanical harvester. Methods: A tractor-pulled harvester was built, in which a modified stripper header detached pods from an anchored plant and a chain conveyor transferred material. The stripper harvester was redesigned to use: 1) the maneuverability of tractor-mounted frames, 2) the adaptability of floating headers, and 3) the flexibility of pneumatic conveyors. Results: A mobile vacuum conveyor, which was an innovator open system, was designed for the dilute phase transferring mode for both grain and material other than grain. A centrifugal fan transferred harvested material to a cyclone separator that settled harvested material in a grain tank 1 m high. The machine at the spot work rate of $0.42ha{\cdot}h^{-1}$ harvested chickpea pods equal to the output of 16.6 farm laborers. Conclusion: The low cost and reasonable projected purchase price are the advantages of the concept. Additionally, the shattering loss reduction confirms the feasibility of the prototype chickpea harvester for commercialization.

• 대한기계학회논문집B
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• 제39권4호
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• pp.293-299
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• 2015

여러 산업분야에서 다양한 원심압축기가 사용되고 있다. 따라서 사용자의 요구에 맞는 원심압축기의 설계가 복잡해졌고, 최적화된 설계점을 찾는 것은 더욱 어려워졌다. 전통적으로 효율은 최적화의 중요한 요소이다. 본 연구에서는 효율 외에도 압축기의 무게를 고려하여 설계하였다. 본 연구의 목적은 압축기의 효율과 무게를 고려할 때에 그 고려하는 가중치의 변화에 따라 설계의 경향성이 나타남을 확인하는 것에 있다. 또한, 이를 바탕으로 초기 설계 단계에서 객관적인 설계점을 선택할 수 있음을 보여주는데 있다. 본 연구에서는 베인이 없는 디퓨저를 한정하여 연구하였다. 최적화를 위해서 크리깅을 사용하였고, 1차원 설계 프로그램의 표본을 적절히 이용하였다. 설계공간을 적절히 가정하였고, 설계공간 내에서 최적설계점을 계산하였다.