In mobile hydraulic systems such as off-highway vehicles, working fluids are splashed and agitated in the reservoirs. Under these conditions air is entrained from surrounding air in the working fluids. Bubbles in working fluids have much influence on the performance of hydraulic systems and cause some troubles. In conventional hydraulic systems, bubbles in the working fluids are passively eliminated during the resident time of the fluid in the reservoir. However, in view point of environmental compatibility, energy saving, cost saving and safety, one trend in fluid power systems is to be designed in a more compact fashion and requiring less fluid in the reservoir. One of the authors, Mr. R. Suzuki, has developed a new device that utilizes a swirling flow to eliminate actively bubbles in working fluids. In this paper, the performance of the developed bubble elimination device concerning the effect of reducing the oil temperature rise is experimentally investigated. From a view point of energy balance in hydraulic systems, a simple mathematical model is proposed and validity of the model is studied. Numerical Analysis for swirl flow in the bubble elimination device is carried out to investigate the performance of bubble removal in oil flow.
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