• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.324-331
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• 2010

Cavitation in cryogenic fluids generates substantial thermal effects and strong variations in fluid properties, which in turn alter the cavity characteristics. In order to investigate the cavitation characteristics in cryogenic fluids, numerical simulations are conducted around an axisymmetric ogive in liquid nitrogen and hydrogen respectively. The modified Merkle cavitation model and energy equation which accounts for the influence of cavitation are used, and variable thermal properties of the fluid are updated with software. A good agreement between the numerical results and experimental data are obtained. The results show that vapor production in cavitation extracts the latent heat of evaporation from the surrounding liquid, which decreases the local temperature, and hence the local vapor pressure in the vicinity of cavity becomes lower. The cavitation characteristics in cryogenic fluids are obtained that the cavity seems frothy and the cavitation intense is lower. It is also found that when the fluid is operating close to its critical temperature, thermal effects of cavitation are more obviously in cryogenic fluids. The thermal effect on cavitation in liquid hydrogen is more distinctively compared with that in liquid nitrogen due to the changes of density ratio, vapour pressure gradient and other variable properties of the fluid.

• Advances in Energy Research
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• v.8 no.4
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• pp.233-241
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• 2022

Biodiesel is a non-polluting and non-toxic energy source that can replace conventional diesel. However, the higher production cost and raw material scarcity became challenges that obstruct the commercialization of biodiesel production. In the current investigation, fried cooking oil is used for biodiesel production in a hydrodynamic cavitation reactor, thus enhancing raw material availability and helping better waste oil disposal. However, due to the cavitation effect inside the reactor, the hydrodynamic cavitation reactor can give biodiesel yield above 98%. Thus, the use of orifice plates (having a different number of holes for cavitation) in the reactor shows more than 90% biodiesel yield within 10 mins of a time interval. The effects of rising temperature at different molar ratios are also investigated. The five-hole plate achieves the highest yield for a 4.5:1 molar ratio at 65℃. And the similar result is predicted by the response surface methodology model; however, the optimized yield is obtained at 60℃. The investigation will help understand the effect of hydrodynamic cavitation on biodiesel yield at different molar ratios and elevated temperatures.

• Corrosion Science and Technology
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• v.19 no.4
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• pp.163-173
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• 2020

Cavitation corrosion in many industrial plants has recently become a serious issue. Cavitation corrosion has generally been investigated using a vibratory method based on ASTM G32 standard, and the test can be divided into direct cavitation and indirect cavitation. Cavitation corrosion test uses the vibration frequency of the horn of 20 kHz with constant peak-to-peak displacement amplitude. In this work, the peak-to-peak amplitude was controlled from 15 ㎛ to 85 ㎛, and electrochemical measurements were obtained during indirect cavitation. The relationship between cavitation corrosion rate and electrochemical properties was discussed. Corrosion steps of carbon steel at the initial stage under cavitation condition in 3.5 % NaCl can be proposed. When the cavitation strength is relatively low, corrosion of the steel is more affected by the electrochemical process than by the mechanical process; but when the cavitation strength is relatively high, corrosion of the steel is affected more by the mechanical process than by the electrochemical process. This work confirmed that the critical ultrasonic amplitude of 0.42 %C carbon steel is 53.8 ㎛, and when the amplitude is less than 53.8 ㎛, the corrosion effect during the cavitation corrosion process is higher than the mechanical effect.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.335-346
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• 2021

Since epoxy resin coating shows excellent properties in formability, adhesion, and corrosion resistance, they have been extensively used in many industries. However, various types of damages in the epoxy coated tube within a relative short time have been reported due to cavitation erosion, liquid impingement, variation of temperature and pressure. Nevertheless, there has been little research on the effect of temperature on the cavitation degradation of epoxy coatings. Therefore, this work used an ultrasonic cavitation tester to focus on the effect of solution temperature on the cavitation properties of 3 kinds of epoxy coatings in 3.5% NaCl. The cavitation properties were discussed basis on the material properties and environmental aspects. As the solution temperature increased, even though with large fluctuation, the cavitation degradation rates of A and B coatings were reduced rapidly, but the rate of C coating was decreased gradually. In addition to the cushioning effect, the reason that the cavitation degradation rate reduced with solution temperature was partly related to the brittle fracture and water absorptivity of the epoxy coatings, and the water density, but was little related to the shape and composition of the compound in the coatings or the phase transition of the epoxy coating.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.234-239
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• 2004

In the development of rocket turbo-pump, cavitation at the inducer is one of the major problems. Cryogenic fluids are commonly used for rocket propellant, therefore, thermodynamic effect becomes noticeable compared to conventional water cavitation. In the present study, a numerical simulation method for cryogenic cavitation is proposed, which reveals the difference between cryogenic and water cavitation.

• Corrosion Science and Technology
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• v.14 no.5
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• pp.239-246
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• 2015

Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability, but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment. After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of $30{\mu}m$ and seawater temperature of $25^{\circ}C$, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation.

• Corrosion Science and Technology
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• v.20 no.1
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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.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.229-234
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• 2001

The turbopump inducer cavitation is very important for the success of a Liquid rocket engine. In this study the performance test and cavitation performance test were carried out at various rotational speed with two different diameter inducers. The rotational speed were varied 4000, 6000, 8000 rpm and the variation to the diameter of an inducer were taken as design size and 2 times enlarged size. The major results of the present study were as follows. 1. The hydraulic performance results showed that the similarity was met over the entire test range of the present study. 2. The blade thickness effect was examined and showed that the increased blade thickness resulted in decreased efficiency and worse cavitation performance for large tip clearance. 3. The cavitation performance test results showed that the breakdown NPSH increases as the flow coefficient and does not affected by the rotational speed.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.2
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• pp.105-113
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• 2009

A theoretical study on the pressure fluctuation induced by a propeller was carried out in this study. The main objective of this study is to analyze the source mechanism of the pressure fluctuation induced by propeller sheet cavitation. To analyze the pressure fluctuation induced by propeller sheet cavitation, modern acoustic theory was applied. Governing equation of pressure fluctuation induced by sheet cavitation was derived using Ffowcs Williams proposed time domain acoustic approaches. Several factors affecting pressure fluctuation were analyzed based on the derived governing equation. Pressure fluctuation result was represented by combined results of the far field term and near field term. Finally, the physical mechanism of pressure fluctuation at the blade rate frequency was analyzed using numerically generated cavitation volume variation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.335-341
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• 2001

The bubble cavitation and cloud cavitation are the major sources of cavitation-induced sound and vibration. A numerical method which predicts the trajectory and volume change of a cavity is developed, to predict the cavitation noise of a body. It is shown, by using the numerical method, that the cavitation inception and events rate is strongly dependent on the screening effect caused by the pressure gradient around a body, which is confirmed experimentally. Additionally, the effectiveness of a cavitation control method utilizing air injection is investigated experimentally. It is demonstrated that the noise level of the cloud cavitation can be significantly reduced by the air-injection method.