• Journal of the Korean GEO-environmental Society
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• v.15 no.12
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• pp.71-77
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• 2014

Heavy rainfall induces many disasters including slope failure and infrastructure collapse. In this point of view, rainfall-simulated centrifugal model test can be a reasonable tool to evaluate the stability of geotechnical structure. In order to obtain the displacements of a model in centrifugal model test, in general, LVDT and laser displacement sensor are used. However, when the rainfall is simulated, the LVDT has the problem of excessive infiltration into the model ground, and the laser displacement sensor provides the measuring result with inaccuracy due to the dispersion of the laser radiation. Hence, in this study, horizontal displacement sensor for rainfall-simulated centrifugal model test was developed. This sensor produced with a thin elastic steel plate and gave the accurate relationship between the displacement and the strain.

• The KSFM Journal of Fluid Machinery
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• v.2 no.3 s.4
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• pp.45-51
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• 1999

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise due to the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan and to calculate the effects of rotating velocity, flow rate, cut-off distance and the number of blades and its effects on the noise of the fan. We assume that the impeller rotates with a constant angular velocity and the flow field around the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated with the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The cut-off distance is the most important factor effecting the noise generation. Acoustic pressure is proportional to 2.8, which shows the same scaling index as the experimental result. In this paper, the cut-off distance is found to be the dominant parameter offecting the acoustic pressure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.596-604
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• 2011

To improve the total efficiency of centrifugal compressor, it is necessary to reduce the disk friction loss, which is defined as the power loss. In this study, the disk friction loss due to the axial clearance and the surface roughness effect is analyzed and proposed the new empirical equation for the reduction of the disk friction loss. The rotating reference frame technique and the 2-equation k-${\omega}$ SST model using commercial CFD code FLUENT is used for the steady-state analysis of the centrifugal compressor impeller. According to CFD results, the disk friction loss of the impeller is more affected by the surface roughness than the change of the axial clearance. For the minimization of the disk friction loss on the centrifugal compressor impeller, the magnitude of the axial clearance should be designed to the same size compare with theoretical boundary layer thickness and the surface roughness should be minimized.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.209-213
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• 2016

The characteristics of fluidization in a centrifugal fluidized bed with a 184 mm inner diameter, 50 mm width of the gas distributor was observed by photographs and experimental works using Cu-ZSM-5 zeolite catalysts with a mean diameter of $26{\mu}m$ and $32{\mu}m$ as bed materials at a rotor at 400rpm and 600rpm. Under these experimental ranges, the experimental results clearly showed the effects of the number of rotation of the rotor on the behavior of bubbles in the centrifugal fluidized bed. As the number of rotations of the rotor increased, the gas velocity at which bubbles begin to be formed also increased but the diameter of the bubbles decreased. In addition, the size of the bubbles in the centrifugal fluidized bed were relatively smaller than those in the conventional bubbling fluidized bed.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.30-39
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• 2017

In the current study, identifying regimes and behaviors of the various viscous fluids in a typical horizontal single-stage centrifugal pump and improving its performance by enhancing volute throat area have been surveyed numerically and experimentally. Indeed the initial pump had insufficient head at BEP (Best Efficient Point) in relevant applications. In order to solve this problem, the method of increasing the volute throat area on the prototype was used in steps and eventually the increased head values have been achieved. Then modified centrifugal pump, that has been constructed based on the modified control volume from numerical results, has been tested thoroughly. The maximum head and efficiency discrepancy between numerical and experimental results in BEP were 1.4 and 2.6% respectively. The effects of viscous fluids, from 1 cSt to 500 cSt, on the performance curves of centrifugal pump have been investigated as well and results showed that viscous fluids has significant effect on them. Indeed the highest head and efficiency in the same conditions at BEP has been obtained in viscosity 1 cst which was by 19.2% and 44% greater than the viscosity 500 cSt. It is also found that the highest viscous fluid had the highest energy consumption as the absorbed power of highest viscous fluid, 500 cSt, increased up to approximately 55% above the lowest viscous fluid, 1 cSt, values.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.84-91
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• 2002

Temperature distribution in the GTD111 turbine blade used in power plaints is calculated by heat transfer analysis. Linear stress analysis of the turbine blade is also carried out under thermal loads and centrifugal forces. The numerical results of steady state heat transfer analysis slow that high temperature distribution occurs at the leading edge and tip section of the blade. The thermal stress result indicates that the equivalent stress at the tip of the pressure surface is higher than other sections of the blade. Maximum centrifugal stresses without the thermal effect occurs at the front of the fir tree. From the thermal-centrifugal stress analysis, maximum equivalent stress occurs at the fir tree. Stresses applied by the thermal loads and centrifugal forces are less than the yield stress. The GTD111 turbine blade is safe to be used in the power plants.

• Journal of the Korean institute of surface engineering
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• v.37 no.5
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• pp.296-300
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• 2004

The defects of partial denture frameworks are mainly shrinkage porosity, inclusions, micro-crack, particles from investment, and dendritic structure. In order to investigate a good casting condition of partial denture frameworks, the three casting alloys and casting methods were used and detected casting defects were analyzed by using electrochemical methods. Three casting alloys (63Co-27Cr-5.5Mo, 63Ni-16Cr, 63Co-30Cr-5Mo) were prepared for fabricating partial denture frameworks with various casting methods; centrifugal casting (Kerr, USA), high frequency induction casting (Jelenko Eagle, USA), vacuum pressure casting (Bego, Germany). The casting temperature was $1,380^{\circ}C$ (63Co-27Cr-5.5Mo and 63Ni-16Cr) and $1,420^{\circ}C$ (63Co-30Cr-5Mo). The casting morphologies were analyzed using FE-SEM and EDX. The corrosion test of the dendritic structure was performed through potentiodynamic method in 0.9% NaCl solutions at $36.5^{\circ}C$ and corrosion surface was observed using SEM. The defects of partial denture frameworks improved in the order of centrifugal casting, high frequency induction casting, and vacuum pressure casting method, especially, pore defects were found at part of clasp in the case of centrifugal casting method. The structure of casting showed dendritic structure for three casting alloys. In the 63Co-27Cr-5.5Mo and 63Co-30Cr-5Mo, $\alpha$-Co and $\varepsilon$-Co phases were identified at matrix and $${\gamma}$-Ni_2$Cr second phase were shown in 63Ni-16Cr. Also, the corrosion resistance of cast structure increased in the order of vacuum pressure casting, high frequency induction casting, and centrifugal casting method.

• Journal of Korea Foundry Society
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• v.42 no.3
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• pp.153-160
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• 2022

The effect of thickness on the microstructure and the mechanical properties of centrifugal cast 625 was investigated. Centrifugal cast 625 with various thickness of 10, 17 and 50mm showed partially columnar grained structure 8, 12.3 and 18.5mm respectively from the outer surface. Secondary dendrite arm spacing in the columnar grains slightly increased with increasing casting thickness. Tensile strength of the columnar region was similar regardless of casting thickness. Solidification behavior of the columnar grained region is similar to that of directional solidification, thus solidification rate in the centrifugal cast tube was extrapolated from the secondary dendrite arm spacing data of the directionally solidified material. The equiax grained region formed interior of the thick castings. The tensile strength of the equiaxed region showed the average value of the columnar region which is presumably originated from the grain structure rather than secondary dendrite arm spacing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.61-69
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• 2024

An ultra-high strength prestressed prismatic beam of 100 MPa in compressive strength was developed by increasing the water-tightness of concrete by utilizing centrifugal molding processes without adding expensive admixtures. The centrifugal prismatic PSC beam developed as the superstructure of the avalanche tunnel was constructed on a rahmen bridge in a small local river. In this study, the centrifugal prismatic beam was compared and analyzed based on the results of measurements made through static load tests and the results of numerical analysis of the target structure. The common load-carrying capacity and safety of the rahmen bridge were evaluated. The static·dynamic load tests and finite element analysis results of this bridge were similar, and it was confirmed that the behavior of the centrifugal prismatic beam was well simulated. All centrifugally formed square beams that make up the composite rahmen bridge were evaluated to secure sufficient load carrying capacity under the design live load, and structural reliability was proven by ensuring safety.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.2
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• pp.97-105
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• 2002

A centrifugal water chiller using alternative refrigerant R134a has been developed. The prototype was designed to have refrigerating capacity of 300RT. Its compressor employs a single high-speed impeller, airfoil diffuser and collector. Newly developed, enhanced tubes were installed in the evaporator and the condenser to reduce the required head for the compressor. Off-design characteristics at various conditions, performance test of the compressor and analysis of the refrigeration cycle were performed. So the probability of use in part load condition was checked and the direction for revision was suggested.