キャビテーションを利用した油の脱気法に関する研究

抄録

A hydraulic oil normally contains gas at about 10% in volumetric ratio at atmospheric pressure. When cavitation occurs in an oil flow, diffusion of the dissolved gas is supposed to play a major role in the growth of cavitation bubbles, which can result in unwanted effects such as noise, vibration and response delays in hydraulic oil systems. Consequently if the gas concentration in the working oil can be somehow lowered, it may be possible to suppress cavitation. In the present paper a new method of degassing an oil by positively utilizing cavitation has been developed. To obtain a method which is of practical use at the engineering site, a cylinder having an orifice at the inlet and a piston actuated by hydraulic oil power are used to deaerate the oil. An idea of closing the orifice midway in the suction process proved effective in enlarging cavitation bubbles and accelerating their separation from the oil. Through observation of cavitation initiation in an orifice flow, it is experimentally confirmed that the critical Reynolds number at which cavitation starts increases when the oil is deaerated.