小管径垂直管水下排气完全携带点实验及分析

船用柴油机采用水下排气方式具有降低排气噪声、改善舱外空气质量等优点，在大型豪华游轮等特殊船舶中具有广泛应用前景。为防止海水由排气管倒灌入柴油机造成事故，需弄清水下排气管内水倒流发生的条件。对大管径垂直管防止水倒灌临界条件即完全携带点的已有认识较为统一，而对小管径垂直管仍未有清晰的认识。在管径25~100 mm范围对垂直管的完全携带点进行了实验，探究了小管径垂直管的完全携带点预报方法。实验结果表明在小管径范围，垂直管完全携带点对应的临界表观气速随管径增大而升高，但气相Wallis数随管径增大而减小，说明Wallis数过度关联了管径对临界表观气速的影响。基于气相Kutateladze数和无量纲气相黏性，对小管径垂直管提出了新的完全携带点预报模型和相应实验关联式。

Experiment and Analysis of Zero Liquid Penetration Point of Vertical Underwater Exhaust Pipes in Small Diameter

Using the underwater exhaust method can benefit marine diesel engines with a reduced exhaust noise and an improved air quality outside the cabin. It shows a competitive application prospects in some special ships such as cruise ships. In order to prevent the diesel engine from a damage caused by the seawater pouring back into the diesel from the exhaust pipe, it is necessary to clarify the occurrence condition of water backflow in exhaust pipes. There have been an unified understanding on the zero liquid penetration (ZLP) point of vertical pipes in large diameter, whereas the understanding on that of vertical pipes in small diameter is not yet clear. In this study, the ZLP points of vertical exhaust pipes were tested in the diameter range of 25-100 mm with an underwater exhaust experimental system and the prediction models for zero liquid penetration points of vertical exhaust pipes was analyzed. Results show that, in this diameter range, the critical superficial gas velocity corresponded to the ZLP point increases with the increase of diameters, while the gas phase Wallis number tends to decrease with the increase of diameters. This indicates that, for the vertical pipe in small diameter, Wallis number presents an excessively correlation to the effect of diameter change on the critical superficial gas velocity. A new prediction model that is a combination of Kutateladze number and dimensionless viscosity, as well as a corresponding correlation, were proposed for the ZLP point of the vertical pipe in small diameter based on the experimental results.