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

• Journal of Technologic Dentistry
• /
• v.34 no.4
• /
• pp.361-368
• /
• 2012

Purpose: The aim of this study was to analysis the composition on the centrifugal casting and the oxide on the casting temperature. Methods: The nickel based alloy were used in this study. Wax pattern specimens (10*10*2) were invested with phosphate-bonded investment in metal rings, the liquid/powder ratio and overall burn-out schedules for these investments were followed in accordance with the manufacturer's instructions. After casting, the alloy specimens were evaluated as regards composition(EPMA). The casting temperatures were as follows: $1400^{\circ}C$ and $1700^{\circ}C$. The quantitative analysis of oxides were scanning electron microscope(SEM), energy dispersive spectroscopy(EDS) and line scanning. Results: Nearer the injection lines showed that there is a large amount of nickel. Quantitative of oxides of Ni-Cr alloy cast from $1400^{\circ}C$ is lager than Ni-Cr alloy cast from $1700^{\circ}C$. Conclusion: Casting when using a centrifugal casting machine centrifugal force affects the composition of the alloy. The higher the temperature, the amount of oxide that is generated many.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.3
• /
• pp.952-957
• /
• 2015

Recently, the interior permanent magnet (IPM) motors for electric vehicle (EV) traction motor are being extensively researched because of its high energy density and high efficiency. The traction motor for EV requires high power and high efficiency at the wide driving region. Therefore, it is essential to fully consider the characteristics of the motor from low speed to high-speed driving regions. Especially, when the motor is driven at high speed, a significant centrifugal force is applied to the rotor. Thus, the rotor must be stably structured and be fully endured at the critical speed. In this paper, aims to examine the characteristics of the IPM motor by adjusting the width of air-barrier according to the permanent magnet position which is critical in designing an IPM motor for EV traction motors and to conduct a centrifugal force analysis for grasping mechanical safety.

• Journal of computational fluids engineering
• /
• v.20 no.4
• /
• pp.1-6
• /
• 2015

Centrifugal pumps consume considerable amount of energy in various industrial applications. Therefore, improvement of the efficiency of these machines has become a major challenge. Cavitation is a phenomenon which decreases the pump efficiency and even causes structural demage. Hence, the goal of this paper is to investigate the cavitation problem in the single-stage and double-stage centrifugal pumps. The Volume of Fraction (VOF) method has been used for the numerical simulations together with Rayliegh-Plesset model for the gas-liquid two-phase flow inside the pump. In order to capture the turbulent phenomena, the standard k-${\varepsilon}$ turbulence model has been adopted, and the simulations have been done as unsteady cases. In addition, the motion of the rotating parts has been simulated using Multi Reference Frame(MRF) method. The results are presented and compared in terms of hydraulic head and NPSH for both the single-stage and double-stage pumps. The H-Q curves show the effects of cavitation on decreasing the pumps performances.

• Journal of computational fluids engineering
• /
• v.18 no.1
• /
• pp.7-12
• /
• 2013

This paper presents a numerical investigation of the influences of various non-uniform tip clearances on the performance and flow field in a centrifugal compressor. Numerical simulations were conducted for three centrifugal compressor impellers in which the tip clearance height varied linearly from the leading edge to the trailing edge. The numerical result was compared with the experimental data for validation. Although the performance improved for low tip clearances, a smaller tip clearance at the trailing edge reduced the overall tip leakage flow more effectively than a smaller tip clearance at the leading edge. Therefore, a smaller tip clearance at the trailing edge lowered the mixing loss caused by interactions between the tip leakage flow and the main passage flow.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.10
• /
• pp.1445-1450
• /
• 2001

Stall inception in a high-speed centrifugal compressor has been examined. The main objective was to find stall precursor and to develop a reliable stall warning method. For stall warning, a method which uses the spectrum at impeller frequency is suggested. The use of the spectrum at impeller frequency as a stall warning method showed a warning time of about two hundreds impeller revolutions. This method uses only one sensor that it has made the stall warning method more useful. And the well-known traveling wave energy method proved to be a good method for stall warning also in a high-speed centrifugal compressor. The warning time was about one hundred impeller revolutions at lower speeds, and about one thousand impeller revolutions at higher speeds. The stall warning methods used here were found to be robust and reliable. Therefore, it seems to be promising to set up a reliable stall avoidance control based on this analysis.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.12
• /
• pp.1730-1738
• /
• 2001

This paper presents an overview of testing and analyzing field performance of a centrifugal chiller which has a rated capacity of 200 RT(703 kW). Field data of a chiller installed in the cleanroom research building of KIST has been collected far performance analysis. The operating data included start-up, shut-down, and quasi-static state where cooling capacity and compressor power consumption varied cyclically. It was found that the steady-state thermodynamic model could be applied to relate the cooling capacity and COP under quasi-static conditions. The results led to finding the required cooling load pattern and a possible energy saving method. This study provides a method of evaluating performance of a large capacity centrifugal chiller in which field test is necessary.

• The KSFM Journal of Fluid Machinery
• /
• v.15 no.6
• /
• pp.46-50
• /
• 2012

A high-speed centrifugal pump requires more attention to the control of its axial thrust due to the high discharge pressure than a conventional industrial pump. Vanes employed toward the rear cavity of the impeller can be an effective device to control the axial thrust of the pump. The vanes disturb circumferential flow of the cavity and it can modify the axial force acting on the impeller. In this paper, three types of vanes are installed in the high-speed centrifugal pump for liquid rocket engines and the thrust of the pump is measured with an additional thrust measurement unit. According to the results, shapes of cavity vanes have effects on the axial thrust of the pump. As the height of vanes increases, the outlet pressure of the rear floating ring seal decreases which results in a decrease of the thrust. On the other hand, head of the pump is almost same regardless of cavity vanes. Also, the pressure drop of the bypass pipeline increases when vanes are removed.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.2
• /
• pp.136-148
• /
• 1997

The present study has been carried out to develop a computational procedure for the analysis of the off-design performance in centrifugal compressors with vaneless diffusers by integrating empirical loss models and analytical equations. Losses in centrifugal compressors stem from a number of sources and their exact calculation is not yet possible. This study investigates several modeling schemes and shows that a fairly good prediction can be achieved by a proper selection of the most important flow parameters resulting form a meanline one-dimensional analysis. The performance maps for compressors are calculated and compared with measured performance maps. The off-design performance characteristics in terms of the pressure ratio vs. mass flow produced have generally correct forms. However, no universal means have been found to predict accurately the onset of surge. The prediction method developed through this study can serve as a tool to ensure good matching between parts and it can assist the understanding of the operational characteristics of general purpose centrifugal compressors.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.4
• /
• pp.428-435
• /
• 2016

In this paper, high-performance and low-noise centrifugal fan used to circulate cold air inside a household refrigerator is developed by reducing the vortex flow observed near the tip of fan hub. First, the performance of the existing centrifugal fan is investigated through the experiment using a fan tester and the characteristics of detailed flow field obtained from the CFD simulation are closely examined. The strong vortex flow is observed in the vicinity of the tip of fan hub. Based on this result, new design is devised to reduce this vortex flow. As a result, it is numerically and experimentaly found that the volume flow rate of the new fan increases and the radiated noise decreases in comparison with the existing fan at the same rotation speed.