• Tribology and Lubricants
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• v.39 no.5
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• pp.212-215
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• 2023

Diaphragm compressors play a crucial role in safely compressing large volumes of high-purity hydrogen gas without contamination or leakage, thereby ensuring quality and reliability. Diaphragm compressors use a thin, flat, triple-layered diaphragm plate that is subjected to repetitive piston pressure for compression. They are usually made of metallic materials such as stainless steel or Inconel owing to their high-pressure resistance. However, since they are consumable components, they fail due to fatigue from repetitive pressure and vibration stress. This study aims to evaluate the scratch characteristics of diaphragms in operational environments by conducting tests on three different samples: Inconel 718, AISI 301, and Teflon-coated AISI 301. The Inconel 718 sample underwent a polishing process, the AISI 301 sample used raw material, and the Teflon coating was applied to the AISI 301 substrate at a thickness of 50 ㎛. To assess the scratch resistance, reciprocating motion friction tests were performed using a tribometer, utilizing 220 and 2000 grit sandpapers as the counter materials. The results of the friction tests suggested that the Teflon-coated sample exhibited the lowest initial friction coefficient and consistently maintained the lowest average friction coefficient (0.13 and 0.11 with 220 and 2000 grit, respectively) throughout the test. Moreover, the Teflon-coated diaphragm showed minimal wear patterns, indicating superior scratch resistance than the Inconel 718 and AISI 301 samples. These findings suggest that Teflon coatings may offer an effective solution for enhancing scratch resistance in diaphragms, thereby improving compressor performance in high-pressure hydrogen applications.

• KSTLE International Journal
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• v.1 no.2
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• pp.83-90
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• 2000

The surface roughness between a piston ring pack and a cylinder liner directly affects the fuel economy, the oil consumption, and the emission of the engine so that it is very important to clarify the surface roughness effects on the lubrication characteristics. The friction characteristics of the piston ring during engine operations are known to as mixed lubrication experimentally. In this study to simulate the effects of the surface roughness of the piston ring pack on the lubrication characteristics, the mixed lubrication analysis of piston rings was performed using the simplified average Reynolds equation. From the results the surface roughness was found be considerably affects minimum oil film thickness as well as FMEP(Friction Mean Effective Pressure). Especially, the oil ring was the most sensitive on the surface roughness.

• Applied Science and Convergence Technology
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• v.26 no.4
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• pp.74-78
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• 2017

The discharge characteristics of the radio frequency (RF) surface dielectric barrier discharge have been simulated for the investigation of the ratio of the ion transit time to the RF period. From one-dimensional particle-in-cell (PIC) simulation for a planar dielectric barrier discharge (DBD), it was observed that the high-frequency driving voltage confines the ions in the plasma because of a shorter RF period than the ion transit time. For two-dimensional surface dielectric barrier discharges, a fluid simulation is performed to investigate the characteristics of RF discharges from 1 MHz to 40 MHz. The ratio of the peak density to the average density decreases with the increasing frequency, and the spatiotemporal discharge patterns change abruptly with the change in the ratio of ion transit time to the RF period.

• International Journal of Concrete Structures and Materials
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• v.3 no.1
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• pp.15-23
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• 2009

Over about 30% of problems in construction is related to water-leaking, and the loss from this problem can incur as much as three times the cost of initial construction. Thus, water vapor pressure is known to be the primary cause of defective waterproofing. Accordingly, the theories on the relationship between water pressure and temperature as well as damp-proofing volume of concrete and the change in vapor pressure volume were reviewed and analyzed in this study by making test samples after spraying a dampness remover and applying waterproofing materials to the prepared test specimens. The result of measuring water vapor pressure with the surface temperature of the waterproofing (fluid-applied membrane) layer at the experimental temperature setting of about $10^{\circ}C$, which is the annual average temperature of Seoul, indicated that (1) the temperature of the fluid-applied membrane elevated to about $40^{\circ}C$, and the water vapor pressure generated from the fluid-applied membrane was about 0.03 N/mm 2 when the surface temperature of the waterproofing layer was raised to about $80^{\circ}C$. (2) when the temperature of the fluid-applied membrane of the waterproofing layer was raised from $30^{\circ}C$ to $35^{\circ}C$, water vapor pressure of about 0.01 N/mm 2 was generated, and (3) when a thermal source was applied to the fluid-applied membrane (waterproofing) layer, the temperature increased from $35^{\circ}C$ to $40^{\circ}C$, and approximately $0.005\;N/mm^2$ of water vapor pressure was generated.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.147-150
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• 2006

Of the total defects that have occurred recently in the Korean construction market, over 30% are caused by the construction of defective waterproofing, and the phenomenon of air pockets in the waterproofing layer, which is caused by the concrete vapor pressure, is known to be the primary cause of defective waterproofing. Accordingly, in this study the theory about the relationship between water pressure and temperature as well as the damp-proofing volume of concrete and, then, the change of vapor pressure volume was measured and analyzed by making a test sample after spraying a dampness remover and a waterproofing material to a prepared test body. As a result of measuring the water vapor pressure for the surface temperature of the waterproofing layer with the fluid-applied membrane temperature based on about $10^{\circ}C$, which is the average temperature of Seoul, it was found that first, the fluid-applied membrane elevated up to about $40^{\circ}C$, and the water vapor pressure generated from the fluid-applied membrane was about $0.3kgf/cm^2$ when the surface temperature of the waterproofing layer was raised up to about $80^{\circ}C$. Second, when the fluid-applied membrane temperature of the waterproofing layer was raised from $30^{\circ}C\;to\;35^{\circ}C,\;about\;0.1kgf/cm^2$ of water vapor pressure was generated, and when supplying a thermal source to raise the fluid-applied membrane temperature of the waterproofing layer from $35^{\circ}C\;to\;40^{\circ}C$, approximately $0.05kgf/cm^2$ of water vapor pressure was generated.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.280-288
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• 2000

In this study, flow factors are evaluated in terms of kurtosis using random rough surface generated numerically. As h/$\sigma$become large øx, øy, øfp approach to 1 and øs, øfs to 0 asymptotically regardless of kurtosis. øx, øy, øfp increase with increasing kurtosis in the mixed lubrication regime. øs, øfs is associated with an additional flow transport due to the combined effect of sliding and roughness. As h/$\sigma$ decreases øs, øfs increase up to a certain point, and then decrease toward zero. This behavior can be attributed to the increasing number of contacts in the mixed lubrication regime. øx in the presence of elastic deformation on the surface is larger than øx in the absence of it because local film thickness( h$\_$T/) increases by elastic deformation.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.4
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• pp.44-51
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• 2005

In this paper, a new polishing head with the variable pressure structure was studied to improve the planarization uniformity of the conventional template-metal head. Metal surface waviness and slurry distribution on the pad have been known to affect the polishing uniformity even in the synchronized quill and platen velocities. A polishing head with silicon rubber sheet was used to get a curved pressure distribution. In the experiment, the vertical deflection behavior on the pad was characterized with back pressure in the air chamber. Quill force increased linearly with backpressure. However, backpressure under a quill force made the upward movements of the quill. In the wafer polishing experiments, polishing rate and polishing thickness distribution were severely changed with backpressure. The best uniformity was observed with the standard deviation off.5％ level of average polishing removal 215nm at backpressure 12.1kPa.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1649-1657
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• 2010

We have investigated the unexpected phenomena on the surface of molded GFRP composites. The major cause of the unevenness, as a result of which the surface becomes rough, is a shrinking of the matrix in the process of holding pressure and cooling temperature. The higher holding pressure load in a molding process and the lower demolding temperature in an annealing experiment, the better GFRP composites moldings improved its appearance. In addition, by taking the holding pressure and demolding temperature into consideration, we evaluate the process that causes the surface unevenness and the variation in the fiber projection height.

• Wind and Structures
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• v.33 no.6
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• pp.463-470
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• 2021

This study investigates the aerodynamic characteristics of NACA series airfoil by altering the trailing edge in the form of extended and serrated sections. This contemporary advent examined NACA 0020 airfoil experimentally at the angle of attack ranging from 0° to 45° and for the Reynolds number of 2.46 × 105. To figure out the flow behaviour, the standard average pressure distribution over the airfoil surface is estimated with 50 pressure taps. The time series surface pressure is recorded for 700 Hz of sampling frequency. The extended trailing edge of 0.1 c, 0.2 c and 0.3 c are attached to the base airfoil. Further, the triangular serration is introduced with the base length of 2 cm, 4 cm and 6 cm. Each base length with three different amplitudes of 0.1 c, 0.2 c and 0.3 c were designed and equipped with the baseline case at the trailing edge and tested. The aerodynamic force coefficient, as well as pressure coefficient are presented. The obtained data advises that modification in the trailing edge will reflect the aerodynamic characteristics and the flow behaviour over the section of a wing. Resultantly, the extended trailing edge as a thin elongated surface attached to a base airfoil without revising the main airfoil favors good lift increment. The serrated trailing edge acts as a flow control device by altering the flow pattern results to delay the stall phenomenon. Besides it, improves lift co-efficient with less amount of additional drag. This extended and serrated trailing edge approach can support for designing the future smart airfoil.

• Journal of Biosystems Engineering
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• v.28 no.5
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• pp.411-420
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• 2003

Physical and cultural properties were investigated on the rice-seed pellets made by the pelleting machine(Yu, 2003) as the changes with mixing ratios of soil to rice seed of 6 : 1, 7 : 1, and 8 : I, and rotating speeds of forming rolls of 7, 10, and 13 rpm. Average weight, average diameter, and average sphericity of the pellets were 1.70 g, 12.0 ㎜, and 99.1 ％, respectively. Average number of seeds per pellet was more than 3, and almost all pellets had more than 3 seeds in the cases of mixing ratios of 6 : 1, and 7 : 1 at the forming rolls' speed of 7 rpm. Gradual drying was needed because rapid drying caused cracks on surface of the pellets. Compression strength of the pellets dried in shady room was in the range of 132 ∼ 152 N, which was enough for handling. Comparing with the previous pellets(Park, 2002), average number of seeds per pellet, ratio of pellets including more than 3 seeds, and compression strength increased due to the effects of pressure feed of pellet materials, and improvements of the forming rolls. Emergence ratio of the pellets made at the mixing ratio of 6 : 1 and the forming rolls' speed of 7 rpm, was 100 % on dry paddy and was 97 % on flooded paddy surface. Good growth characteristics, and yield except number of seedling stand and ratio of missing plant were shown in planting of the pellets made at the mixing ratio of 7 : 1 and the forming rolls' speed of 7 rpm on flooded paddy surface field. Considering the cultural results, the mixing ratio of 6 : 1, and the forming rolls' speed of 7 rpm seems to be optimum operating condition for the improved pelleting machine.