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

利用水下空化喷射钻机进行了空化侵蚀试验。试验液可选用自来水、含VG46的合成可生物降解油或含VG32或VG46的矿物油。液体温度保持在40 ~ 65℃。上游压力为10 ~ 18 MPa，空化数为0.02 ~ 0.04。距离从7.5到35mm不等。试件材料为铝合金，直径为15mm。制备了直径为1mm、长度为4mm的尖边长孔喷嘴。测量了试样的质量损失和截面分布，并对侵蚀过程进行了评价。与此同时，用摄像机观察和记录了喷流的空腔云；随后，利用图像处理技术得到云的存在概率分布。自来水的质量损失最大，其次是矿物油（VG32）、矿物油（VG46）和生物降解油。空化数越小，质量损失的差异越明显。随着液体温度的升高，所有液体的损失都越大。温度越低，这种差异就越明显。油品类型对截流距离、上游压力、空化数与质量损失、冲蚀环直径以及质量损失最大的截流距离之间的关系影响较小。云层有一定存在概率的区域与地表受到严重侵蚀的位置重合。空化数越小，空化射流越长，质量损失越大。

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.