Abstract:

In order to study the cavitation characteristics of the working fluid in the confined space and high shear state, a visualization experiment platform for the cavitation evolution law of the micro-gap working fluid was designed and built. The cavitation characteristics of R134a in micro clearance were tested at different working conditions, including inlet and outlet pressure differences, subcooling degrees and inflow velocity. The evolution of the cavitation area was emphatically analyzed. The visualization experiment results show that the cavitation form is determined by the inlet flow velocity and cavitation number. According to the difference of the cavitation form, the process of cavitation in micro clearance can be divided into single-bubble cavitation pattern, multi-bubble cavitation pattern, gas-liquid mixing cavitation pattern and fog-core zone cavitation pattern. The single-bubble pattern and multi-bubble pattern appear randomly, which are related to the cavitation vapor nucleus in the medium during the experiment. The two patterns both occur in the case of low flow rate. The bubble area increases approximately exponentially in the single-bubble pattern. Gas-liquid mixing cavitation pattern and fog-core zone cavitation pattern mostly occur at higher flow rates and lower cavitation numbers, while the evolution of cavitation area follows a near-linear growth law. In each pattern, the generation of cavitation is promoted by the reduction of subcooling. In the multi-bubble mode, multiple independent tiny bubbles appear in the initial stage of cavitation. With the development of cavitation, the bubbles increase and interfere with each other. There is a phenomenon of fusion between the bubbles.

Key words: cavitation, micro clearance, visualization research, multiphase flow, phase change, fluid mechanics

摘要：

为了研究在受限空间和高剪切状态下工质空化特性，设计并搭建了微间隙工质空化演变规律可视化实验台。对不同进出口压差、过冷度及来流速度下R134a在微间隙下空化特征进行实验研究，着重分析了不同空化特征下空化面积演变规律。实验结果表明：工质入口流速和空化数决定了工质在微间隙内空化形态。按此空化形态差异可将空化过程分为单气泡空化模式、多气泡空化模式、气液掺混空化模式及雾态核心区空化模式。单气泡模式与多气泡模式出现有一定随机性，与实验时工质内空化汽核相关，两者多发生于低流速情况下。单气泡模式下气泡面积近似指数增长，气液掺混空化模式及雾态核心区空化模式多发生在较高流速和较低空化数下，此时空化面积演变遵循近线性增长规律。各模式下，过冷度的减小都会促进空化产生。多气泡模式下，工质空化初生时表现为多个相对独立微小气泡。随着空化发展，气泡体积增大，彼此相互干扰，存在气泡间的融合现象。

关键词: 空化, 微间隙, 可视化研究, 多相流, 相变, 流体力学