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2009_nureth13.pdf

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The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13) N13P1156 Kanazawa City, Ishikawa Prefecture, Japan, September 27-October 2, 2009.

Visualization of Unsteady Behavior of Cavitation in Circular Cylindrical Orifice with Abruptly Expanding Part

Yasuhiro Sugimoto and Keiichi Sato

Kanazawa Institute of Technology

7-1 Oogigaoka, Nonoichi-machi, Ishikawa, Japan y-sugi@neptune.kanazawa-it.ac.jp, ksato@neptune.kanazawa-it.ac.jp

ABSTRACT

Cavitation problems in plant’s piping system have been investigated on the basis of high- speed observation. Cavitation is one of the important factors with potential damage in piping system at nuclear power plant. In a power plant, there is cavitation occurrence to be expected in some local places such as an orifice, a valve and a pressure reducer. We have investigated about unsteady behavior and impact of cavitation in a long orifice with an abruptly expanding pipe. In this study, some detailed cavitation behaviors are observed by varying cavitating condition in the orifice throat and downstream of the orifice. High-speed behaviors of cavitation are observed by means of a high-speed video camera with a laser sheet in order to observe the inside of the circular orifice. Then images are analyzed using a frame difference method. As a result, we observe a series of cavitation developing process with decrease in cavitation number such as I: cavitation inception occurs at the inlet of orifice, II: cavitation develops in the throat of the orifice, III: large-scale cavitation clouds appear downstream of the orifice, IV: liquid jet appears when the pressure downstream of the orifice decrease to about vapor pressure. Cavitation clouds in a circular cylindrical orifice with abruptly expanding part show some unsteadiness even in the steady operating condition. Cavitation clouds also show a large-scale shedding behavior in the transition stage to a liquid jet condition. In addition, we observe that the interface instability of a liquid jet downstream of the orifice depends on the cavitation instability in the orifice throat.

KEYWORDS

Cavitation, Long Orifice, Piping System, Cavitation Instability, Image Processing

1. INTRODUCTION

Cavitation is a high-speed phenomenon and shows an unsteady impulsive behavior. The cavitation unsteady phenomenon was investigated by observation to understand its behavior [1]. Cavitation is an important factor in evaluating the damage potential for the piping systems in nuclear power plants. In a power plant, cavitation can be expected in a few localized places, such as an orifice, a valve, or a pressure reducer. The unsteady behavior of cavitation cloud is observed even in the flow field of a circular cylindrical orifice. Unsteady cloud cavitation can cause large pressure fluctuations or severe impacts in the fluid machinery.

On the other hand, the impact and the vibration caused by cavitation can be used positively. The high impact of cavitation is used to increase the machining ability and shot-less peening of a water jet [2],[3]. Generating cavitation in a nozzle can also enhance atomization [4]. If

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 Supercritical Fluid Extraction 2009_nureth13.pdf Page 001
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