发动机缸盖模拟冷却通道内过冷沸腾传热特性

Experiment on Heat Transfer Characteristics of Subcooled Flow Boiling in a Water Jacket Simulated Channel of Diesel Engines

搭建一套试验台架用来模拟发动机鼻梁区冷却通道内的传热状况,采用与发动机缸盖相同的铸铁材料作为加热块,并且安装3块石英玻璃用来观察沸腾发生时气泡运动状态.对不同流速、不同入口温度和不同系统压力状况下的沸腾传热特性做了相应的研究,为真实发动机冷却水腔内沸腾传热预测提供较为全面的试验数据.结果表明:沸腾起始点位置与通道流动参数有着直接关系,表现为速度越高、入口温度越低,沸腾起始壁面过热度越高;提高通道速度和降低冷却入口温度可以强化壁面对流换热程度,但对充分发展沸腾下的传热特性影响很小;增加系统压力,沸腾起始壁面温度越高,其增加幅度与饱和温度增幅大致相同.此外,控制系统压力是抑制沸腾过度发展的重要手段.

An experimental facility was designed using cast iron as heater block and three transparent windows to observe the boiling process and simulate the coolant subcooled flow boiling within the cooling passages. Boiling process was recorded using high-speed visualization technique,and heat transfer characteristics of subcooled water flow boiling water flow at different pressures,flow velocities and liquid subcooling were investigated. A wide range of experimental data was obtained,which is important for the prediction of wall heat flux of subcooled flow boiling in the diesel engine's cylinder head regions. Results show that the influence of flow velocity on wall heat transfer is significant which indicates that heat flux rate depends strongly on the velocity in the single-phase convective region and the partially developed boiling region,whereas the low- and high-velocity curves merge in the fully developed boiling region. With the increase of system pressure,the onset of nucleate boiling is delayed,and then maintains the same developing pattern in the nucleate boiling region. System pressure is an important parameter in the control of subcooled boiling.