CONDENSATION HEAT TRANSFER ON THE THREE-DIMENSIONAL EXTENDED SURFACE TUBE ATTACHED BY A POROUS DRAINAGE STRIP

An experimental study was carried out for the condensation heat transfer on the three dimensional extended surface tube attached by a porous drainage strip. The results show that the combination of the three dimensional extended surface and the porous drainage strip is the effective method enhancing condensation heat tiansfer on the horizontal tube. The change of the shape arid depth of the axial grooves results in a 10% vaitation of condensation heal transfer coei ficienls. In the range of the experiments, for aocohol as the working fluid, the enhancement is up to 152%, and for water, 185% as compared with the horizontal low-finned tube.     

农用柴油机活塞环组机油消耗和窜气的灰色关联分析与预测

活塞环组的润滑和密封性能直接影响柴油机的动力性、经济性和排放特性，机油消耗量（lube oil consumption,LOC）和窜气量（crankcase blow-by,CB）是评估活塞环组润滑和密封性能优劣的主要指标。为探究影响农用柴油机活塞环组LOC和CB的影响因素及LOC和CB对影响因素的敏感程度，该研究提出农用柴油机活塞环组LOC和CB的多影响因素系统分析及预测方法。以YNF40农用柴油机为对象，首先搭建柴油机LOC和CB测试台架，建立活塞环组运动学与动力学仿真模型并验证模型的精确度和可靠度，然后采用灰色关联分析（grey relation analysis,GRA）得到不同影响因素的灰色关联度（grey relational grade,GRG），并基于此进行影响因素敏感性分析，最后基于BP神经网络建立不同转速工况下LOC和CB瞬态变化的时间序列预测模型。多因素GRG分析结果表明：对活塞环组LOC和CB影响最敏感和最不敏感的因素分别是活塞第一环槽下边缘倒角和活塞第三环槽背隙，其对应的GRG分别为0.892 79和0.583 61，得到目标与影响因素敏感程度的降序排列为：第...