• Tribology and Lubricants
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• 제9권1호
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• pp.55-61
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• 1993

Recently, due to the erosion damage that were generated increasingly at alloy metals of slide bearing by cavity of lubricating oil with tendency of high speed and high output of reciprocating engine, there is a need to study the process on the formation of cavitation erosion, and the characteristic of cavitation erosion at lubricating oil environments under various condition for marine ship. Therefore, the apparatus of cavitation erosion experiment used 20 KHz, $24 \mu m$ piezoelectric vibrator. The main results obtained through this test method are as follows: 1. The max. erosion rate at lubricating oil environments was related to the change of space, oil film thickness, and shown to tendency of gear oil>system oil>turbine oil>mixed oil environments with different viscosity. 2. The pitted hole by cavitation erosion at high viscosity oil environments became small and deep, and in addition to, they appeared to be wide and shallow at low viscosity.

• 대한기계학회논문집B
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• 제27권5호
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• pp.612-619
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• 2003

This work experimentally studies the fundamental mechanisms by which the ultrasonic vibration enhances convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. It is found that when the liquid temperature is below its boiling point, cavitation takes place due to ultrasonic vibration while cavitation disappears when the liquid reaches the boiling point. Moreover, when the gas dissolved in liquid is removed by pre-degassing, the cavitation arises only locally. Depending on the liquid temperature, heat transfer rates in convection, subcooled boiling and saturated boiling regimes are examined. In convection heat transfer regime, fully agitated cavitation is the most efficient heat transfer enhancement mechanism. Subcooled boiling is most enhanced when tile local cavitation is induced after degassing. In saturated boiling regime, acoustic pressure is shown to be a dominant heat transfer enhancement mechanism.

• 대한조선학회논문집
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• 제37권4호
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• pp.40-47
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• 2000

수중익의 캐비테이션 소음이 캐비테이션 터널에서 측정되었다. 캐비테이션이 초기 발생하면 소음수준이 급격히 증가되며, 기포간에 상호간섭이 나타나지 않는 캐비테이션 수까지 증가된다. 그러나 케비테이션 수가 더욱 감소하여 기포간에 상호간섭이 나타나면, 오히려 소음수준이 감소되는 것으로 나타났다. 기포의 궤적과 체적의 변화는 각각 Lagrangian 추적법 및 Kirkwood-Bethe 가정하에 모형화된 방정식을 사용하여 해석하였다. 기포 체적변화의 수치계산 결과는 실험 결과와 비교적 일치되는 것으로 나타났다.

• Corrosion Science and Technology
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• 제20권1호
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• pp.26-36
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• 2021

Pipes operating in the seawater environment faces cavitation degradation and corrosion of the metallic component, as well as a negative synergistic effect. Cavitation degradation shows the mechanism by which materials deteriorate by causing rapid change of pressure or high-frequency vibration in the solution, and introducing the formation and explosion of bubbles. In order to rate the cavitation resistance of materials, constant conditions have been used. However, while a dynamic cavitation condition can be generated in a real system, there has been little reported on the effect of ultrasonic amplitude on the cavitation resistance and mechanism of composites. In this work, 3 kinds of epoxy coatings were used, and the cavitation resistance of the epoxy coatings was evaluated in 3.5% NaCl at 15 ℃ using an indirect ultrasonic cavitation method. Eleven kinds of mechanical properties were obtained, namely compressive strength, flexural strength and modulus, tensile strength and elongation, Shore D hardness, water absorptivity, impact test, wear test for coating only and pull-off strength for epoxy coating/carbon steel or epoxy coating/rubber/carbon steel. The cavitation erosion mechanism of epoxy coatings was discussed on the basis of the mechanical properties and the effect of ultrasonic amplitude on the degradation of coatings.

• Journal of Advanced Marine Engineering and Technology
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• 제28권2호
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• pp.332-337
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• 2004

The use of gas absorption refrigeration machine has considerably increased because of the shortage of the electric power in the summer and the regulation of freon refrigerant. Gas absorption refrigeration machine consists of a condenser, a heat exchanger. supplying pipes, a radiator etc, This system is likely to be corroded by acid. dissolved oxygen and gases, Cavitation erosion-corrosion by flow velocity of cooling water may happen in absorption refrigeration machine. In these cases. erosion and corrosion occur simultaneously. Then, it makes a serious damage with synergy effect. Therefore, this paper was studied on the cavitation damage of cupronickel(70/30) tube for gas absorption refrigeration machine, In the $30^{\circ}C$ tap water, linear polarization test and anodic polarization test were carried out for copper(C1220T-OL) and cupronickel(70/30) tube. Also, cavitation erosion-corrosion behavior of cupronickel (70/30) tube was considered, The main results are as following: (1) In the linear test, the corrosion current density of cupronickel(70/30) is higher than that of copper. (2) The erosion-corrosion rate of cupronickel(70/30) displayed later tendency than that of copper by vibratory cavitation in cooling water. (3) In cooling water, the progress mechanism of erosion-corrosion rate of copper and cupronickel(70/30) follows a pattern of incubation, acceleration, attenuation and a steady state period.

• Corrosion Science and Technology
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• 제20권6호
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• pp.466-474
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• 2021

A wet type scrubber for merchant vessel uses super austenitic stainless steels with pitting resistance equivalent number (PREN) of 40 or higher for operation in a harsh corrosive environment. However, it is expensive due to a high nickel content. Thus, electrochemical behavior and cavitation erosion characteristics of UNS S32750 as an alternative material were investigated. Microstructure analysis revealed fractions of ferritic and austenitic phases of 48% and 52%, respectively, confirming the existence of ferritic matrix and austenitic island. Potentiodynamic polarization test revealed damage at the interface of the two phases because of galvanic corrosion due to different chemical compositions of ferritic and austenitic phases. After a cavitation test, a compressive residual stress was formed on the material surface due to impact pressure of cavity. Surface hardness was improved by water cavitation peening effect. Hardness value was the highest at 30 ㎛ amplitude. Scanning electron microscopy revealed wave patterns due to plastic deformation caused by impact pressure of the cavity. The depth of surface damage increased with amplitude. Cavitation test revealed larger damage caused by erosion in the ferritic phase due to brittle fracture derived from different strain rate sensitivity index of FCC and BCC structures.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.376-385
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• 2002

Spray impingement and fuel film formation models with cavitation have been developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process was modeled by considering the effects of surface temperature conditions and fuel film formation. The behavior of fuel droplets after impingement was divided into rebound, spread and splash using the Weber number and parameter K(equation omitted). The spray impingement model accounts for mass conservation, energy conservation, and heat transfer to the impinging droplets. The fuel film formation model was developed by integrating the continuity, momentum, and energy equations along the direction of fuel film thickness. Zero dimensional cavitation model was adopted in order to consider the cavitation phenomena and to give reasonable initial conditions for spray injection. Numerical simulations of spray tip penetration, spray impingement patterns, and the mass of film-state fuel matched well with the experimental data. The spray impingement and fuel film formation models have been applied to study spray/wall impingement in high-speed direct injection diesel engines.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.456-461
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• 2004

In this study, the characteristics of the cavitation behavior around hydrofoil are investigated with the commercial CFD code CFX-5. Calculations are performed for NACA 64108 hydrofoil by solving the time-averaged turbulent Navier-Stokes equations and discretized by finite volume method. We classify the different cavitating regimes in which appear at the hydrofoil according to the values of cavitation number, surface roughness and angle of attack. Special attention is paid to the following topics: cavity length, void fraction and lift breakdown.

• 대한조선학회논문집
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• 제41권2호
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• pp.33-46
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• 2004

The cavitating noise of underwater propeller is considered numerically in this study. The main purpose of this research is to analyze these noise sources from marine propeller. The approach for investigation is a potential based panel method coupled with acoustic analogy. To predict propeller sheet cavitation noise, the blade surface cavity is considered as a single valued pulsating volume of vapor attached to the blade surface. The time dependent cavity volume data are used for noise prediction. Furthermore, we analyze hydrofoil cavitation bubble behavior and noise using Eulerian/Lagrangian approach. Through this study, we can analyze dominant noise source of marine propeller and provide a basis for proper noise control strategies.

• Journal of Advanced Marine Engineering and Technology
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• 제38권7호
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• pp.883-889
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• 2014

고속유체 환경에서 압력차에 의한 국부적 비등으로 캐비테이션 침식 손상이 발생한다. 캐비테이션은 유체의 압력, 속도, 온도, pH, 그리고 매질 등의 다양한 환경에 영향을 받는다. 특히 해수 용액에서 캐비테이션 환경에 노출될 경우 염소이온에 의한 부식이 캐비티에 의한 침식 손상을 가속화 시킨다. 따라서 본 연구는 마르텐사이트계 스테인리스강에 대해 천연 해수 용액에서 적용 전류밀도와 캐비테이션 시간에 따른 시편 손상 경향을 규명하였다. 정전류 실험 결과 캐비테이션 조건에서 정적인 조건에 비해 비교적 적은 손상 경향이 나타났다. 또한 캐비테이션 실험 결과 3시간부터 급격하게 무게 감소량, 캐비테이션 손상률, 손상깊이가 증가하였다.