Cavitation Erosion Characteristics of Biodegradable Fluids--In Comparison with Tap Water and Mineral Oils

利用淹没空化射流试验台进行了空化冲蚀试验。自来水、含VG 46的合成可生物降解油或含VG 32或VG 46的矿物液压油可替代地用作测试液体。液体温度保持在40 - 65℃。上游压力规定为10至18 MPa，空化数为0.02至0.04。间隔距离从7.5 mm到35 mm不等。标本由铝合金制成，直径为15 mm。制备了直径为1 mm、长为4 mm的锐边长孔喷嘴。测量了试样的质量损失和横截面轮廓，并评估了侵蚀的演变。同时，用摄像机对射流的空泡云进行了观测和记录，并通过图像处理技术得到了空泡云的存在概率分布，发现自来水的质量损失最大，其次是矿物油VG 32，VG 46和生物可降解油。随着空化数的减小，质量损失的差异显著。液体温度越高，所有液体的损失越大。随着温度的降低，这种差异是显著的。油的种类对空蚀距、上游压力和空蚀数与质量损失和冲蚀环直径之间的关系以及质量损失最大时的空蚀距影响较小。云的存在概率区域与地表侵蚀严重的位置相吻合。随着空化数的减小，空化射流长度增加，质量损失增大.

By utilizing submerged cavitating jet rigs, the experiment of cavitation erosion was conducted. Tap water, synthetic biodegradable oil with VG46 or mineral hydraulic oils with VG32 or VG46 was alternatively used as the test liquid. The liquid temperature was kept at 40 to 65℃. The upstream pressures were specified as 10 to 18 MPa and the cavitation numbers were 0.02 to 0.04. The stand-off distance was varied from 7.5 to 35mm. Specimens were made of aluminum alloy and the diameter was 15mm. A sharp-edged long orifice nozzle with the diameter of 1mm and the length of 4mm was prepared. The mass loss and cross-sectional profiles of the specimens were measured and the tune evolution of erosion was evaluated. In parallel, the cavity-clouds of the jets were observed and recorded with video cameras ; subsequently, the existence-probability distributions of the clouds were obtained by picture processing techniques.The mass loss by tap water was largest, followed by the mineral oil with VG32, the oil with VG46 and the biodegradable oil. The difference in the mass loss was marked as the cavitation number became smaller. As the liquid temperature was higher, the loss was larger for all liquids. The discrepancy was notable as the temperature became lower. The types of oils less influenced essentially the relation between the stand-off distance, the upstream pressure and the cavitation numbers and the mass loss and the erosion-ring diameter as well as the stand-off distance where the mass loss maximized. The region of a certain existence-probability of the clouds and the location where the surface was eroded severely coincided. The cavitatingjets lengthened and the mass loss increased as the cavitation number became smaller.