• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.2
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• pp.134-143
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• 2001

This paper presents the characteristics of flank and tip seal leakage in a scroll compressor for air-conditioners with R-22 under actual operating conditions. It is well known that the leakage has significant effect on the performance of the scroll compressor. Experiments were performed by using indirect method for measuring mass flow rate passing through flank and tip seal under actual operating conditions, In addition, an analytical model for tip seal leakage was developed to investigate tangential and radial leakage observed at grooves and contact points of tip seals. For low oil concentration, theoretical results were compared with experimental data to verify the analytical model. As a result, leakages through flank and tip seal parts were evaluated as afunction of pressure ratio, orbiting angle, discharge pressure, tip clearance, and leakage point. It was also found that the tip seal leakage was considerable even though the tip seal provided adequate sealing effect.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1306-1318
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• 2001

This paper presents leakage and performance characteristics of a tip-seal type scroll compressor, The performance of a scroll compressor is strongly dependent on the leak age across the compression pockets. However, literature for leakage characteristics of the tip seal type scroll compressor is very limited due to complex sealing mechanism. In the present study, a simulation study was executed to investigate the tip-seal type scroll compressor by considering leakages passing through flank and tip clearance. As a result, the leakage phenomena of the tip seal type scroll compressor as a function of discharge pressure, tip clearance, dimension of the tip seal were analyzed. Effects of leakage on the performance of the compressor were also clarified.

• Tribology and Lubricants
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• v.30 no.6
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• pp.370-377
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• 2014

The basic elements in a rotary-type scroll compressor are two identical spiral scrolls containing refrigerant gas. The pressure variations in the compression pockets of a scroll compressor change the forces acting on the orbiting scroll, and these forces affect the dynamic behavior of the compression mechanism parts. To achieve high efficiency, using a self-sealing mechanism as a tip seal mechanism is very effective. Tip seals, which are placed on top of the scroll wraps, accomplish thrust sealing. This study calculates the friction force between the tip seal and the side plate of a scroll compressor using the numerical model considered in the Reynolds equation. The calculated friction force is verified by an experiment using a pin-on-disk apparatus. A hydraulic servo valve that controls the pressure of the oil hydraulic cylinder applies the normal load for the test, and a DC servo motor controls the sliding velocity of the disk. The friction force and normal load are measured by the force sensors attached to the supporting parts. The results show that the theoretical and experimental results are similar and that the friction is influenced by the viscosity of the oil and the sliding velocity of the scroll.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.158-162
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• 2000

Secondary flows in gas turbines, especially those associated tip clearance and labyrinth seals, have become a focus of interest for engine manufacturers. In the past, many analytical and experimental studies, which focused solely on the flows in either tip clearances or seals, have been conducted. This paper presents an analytical model that describes the flow response in a single stage turbine induced by a finite sealing gap at the turbine rotor. The flow is assumed to be axisymmetric and the analysis is done in the meridional plane. Upon going through the stage, the radially uniform upstream flow is assumed to split into two streams one associated with the seal and the other which has gone through the blades. The former is referred to as the leakage flow, and the latter is referred the as the passage flow. The passage flow is assumed to be inviscid and incompressible while the flow in the seal can be modeled as either inviscid or viscous. Thus, the model is capable of predicting the kinematic effects of labyrinth seals on the turbine flow field.

• Tribology and Lubricants
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• v.39 no.2
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• pp.61-71
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• 2023

This study proposes a procedure for designing a labyrinth seal that meets both leakage flow rate and rotordynamic performance criteria (effective damping, amplification factor, separation margin, logarithmic decrement, and vibration amplitude). The seal is modeled using a one control volume (1CV) bulk flow approach to predict the leakage flow rate and rotordynamic coefficients. The rotating shaft is modeled with the finite element (FE) method and is assumed to be supported by two linearized bearings. Geometry, material and operating conditions of the rotating shaft, and the supporting characteristics of the bearings were fixed. A single labyrinth seal is placed at the center of the rotor, and the linearized dynamic coefficients predicted by the seal numerical model are inserted as linear springs and dampers at the seal position. Seal designs that satisfy both leakage and rotordynamic performance are searched by modifying five seal design parameters using the multi-grid method. The five design parameters include pre-swirl ratio, number of teeth, tooth pitch, tooth height and tooth tip width. In total, 12500 seal models are examined and the optimal seal design is selected. Finally, normalization was performed to select the optimal labyrinth seal designs that satisfy the system performance requirements.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.307-313
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• 1998

This paper presents the experimental results of the friction characteristics of double lip-type oil seals which show an improvement in sealing performance over single lip-type oil seals. The major differences between two oil seals are the number of contact lip and seal materials; Nitrile Butadine Rubber(NBR) and urethane rubber. The measured results show that the friction torque of double lip seals shows 12-17% increases compared with those of single lip-type seals. But the sealing performance and service life of double tip oil seals have been increased and stabilized due to an optimized design of the seal lip and material properties.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.442-447
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• 2007

A very abnormal vibration was occurred at the LP(low pressure) turbine continuously during the pre-operation for a 550MW class USC(ultra super critical) steam turbine. This vibration was initiated at the rotating speed of about 3,450rpm and then the vibration amplitude was highly increased the number by $2{\sim}3$ times with the increase of the rotating speed to the rated speed(3,600rpm). In this paper, this abnormal vibration named spike vibration. This spike vibration was caused by the rubbing between the rotating bucket tip seal and the Lower Half of spill strip. Also, this paper presents the mechanism of the spike vibration and the proper method to eliminate this abnormal vibration problem. This result would be good practice to find the solution of similar high vibration in the USC steam turbines for power plant as well as industrial rotating machineries.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1238-1245
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• 2007

A very abnormal vibration was occurred at the LP(low pressure) turbine continuously during the pre-operation for a 550MW class USC(ultra super critical) steam turbine. This vibration was initiated at the rotating speed of about 3,450 rpm and then the vibration amplitude was highly increased the number by $2{\sim}3$ times with the increase of the rotating speed to the rated speed (3,600 rpm). In this paper, this abnormal vibration named spike vibration. This spike vibration was caused by the rubbing between the rotating bucket tip seal and the lower half of spill strip. Also, this paper presents the mechanism of the spike vibration and the proper method to eliminate this abnormal vibration problem. This result would be good practice to find the solution of similar high vibration in the USC steam turbines for power plant as well as industrial rotating machineries.

• Restorative Dentistry and Endodontics
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• v.18 no.1
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• pp.187-196
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• 1993

The purpose of this study was to evaluate the microleakage of retrofilled teeth with various materials [non-zinc Amalgam, IRM, Ketac-silver, CGP(cold-burnished, ultrafil)[and instruments for cavity preparation. Root apex were resected 2mm from apex horizontally and class I cavities were prepared in 2mm denpth, 1.5mm width and were filled with above mentioned materials. Root apex were resected 2mm from apex horizontally and class I cavities were prepared in 2mm depth, 1. 5mm width and were filled with above mentioned materials. 2% methylene blue dye solution was used for 4 days immersion and the linear leakage was measured with calipers and the volumetric leakage was determined with a spectrophotometer. The results were as follows : 1. Amalgam group showed the greatest amount of leakage and Ketac-silver group showed the least value. 2. By linear leakage test, the group retrofilled with Ketac-silver, or CGP showed better seal than the group of Amalgam or IRM. This was shown in both retrograde tip and Conventional method. 3. By volumetric leakage test, the group retrofilled with Ketac-silver showed significantly better seal than the group with IRM in retrograde tip method. 4. By volumetric leakage test, the group retrofilled with Ketac-silver showed significantly better seal than the group with Amalgam in the Conventional method.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1715-1720
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• 2004

This paper presents the characteristics of internal clearances for the interstage of blades and shaft gland seals on the steam turbine which are installed in tandem compound. Internal clearances was changed when the rotor turned in the cylindrical sleeve bearing due to the generation of oil film wedge. This presented concern is very useful to prevent the rubbing damage of seal edge between the fixed and moving parts in steam turbine due to the misalignment at the rotating and stationary parts. This method is applied for the unbalanced clearances distribution to the left and right sides in the turbine casing. A considerable amount of unbalanced clearances distribution trend is determined according to the rotating speed of rotor, size and type of proceeding bearing, oil viscosity, surface roughness of bearing and shaft, oil temperature, oil pressure and bearing load.