Soot particulate matter deposition on the tubes of exhaust gas recirculation (EGR) coolers would form an insulating deposit layer, which deteriorates the thermal efficiency of the cooler and increases the pressure drop substantially. The objective of this research is to examine the influence of using helical tubes instead of straight horizontal tubes on the development of deposit layer. An experimental setup has been designed and constructed to examine the thermal performance of different types of EGR coolers under both clean and fouling conditions. Two sets of experiments have been performed, i.e. with and without soot particles, and in each set three types of EGR coolers have been examined, namely straight tube cooler, and two helical tube coolers of 5 and 10 windings. The effectiveness of the helical tube cooler is highest in case of 10 windings and lowest in case of a straight tube cooler which is due to the increase in the heat transfer surface area. The thermal resistance of the fouling layer in case of a straight tube cooler and 10 windings cooler has stabilized, however the thermal resistance in case of 5 windings is not stable and it is increasing with time. It has been concluded that there is a cleaning action during the fouling experiment in case of the helical tube coolers, and that is due to the secondary flow, and the efficiency of cleaning is a function of the intensity of the secondary flow. The thermal performance of the 5 windings cooler is not stable due to the development of the fouling layers, while in case of the 10 windings is stable, and that means there is a critical number of windings for the helical tube EGR coolers above which fouling diminishes. This critical number of windings is a function of the gas speed, particles size, tube diameter, radius of curvature and the winding pitch. The secondary flow in helical tubes agitates the boundary layer and decreases the pressure drop, such that it is advised to use helical tube coolers with more windings from a thermal and a fluid mechanics point of view.

中文翻译：

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二次流对废气再循环（EGR）冷却器热性能的影响


烟尘颗粒物沉积在废气再循环（EGR）冷却器的管上会形成绝缘沉积层，这会降低冷却器的热效率并大幅增加压降。本研究的目的是检验使用螺旋管代替直水平管对沉积层发育的影响。设计并建造了一个实验装置，用于检查不同类型 EGR 冷却器在清洁和污垢条件下的热性能。进行了两组实验，即有和没有烟灰颗粒，并且在每组中检查了三种类型的 EGR 冷却器，即直管冷却器以及 5 和 10 绕组的两种螺旋管冷却器。螺旋管冷却器的效率在 10 个绕组的情况下最高，在直管冷却器的情况下最低，这是由于传热表面积的增加。直管冷却器和10绕组冷却器的污垢层热阻已经稳定，但5绕组的热阻不稳定，并且随着时间的推移而增加。得出的结论是，在螺旋管冷却器的结垢实验过程中，由于二次流的作用，存在清洗作用，并且清洗效率是二次流强度的函数。由于污垢层的形成，5 绕组冷却器的热性能不稳定，而 10 绕组冷却器的热性能稳定，这意味着螺旋管 EGR 冷却器存在临界数量的绕组，超过该数量污垢就会减少。 该临界缠绕数是气体速度、颗粒尺寸、管直径、曲率半径和缠绕节距的函数。螺旋管中的二次流搅动边界层并降低压降，因此从热力学和流体力学的角度来看，建议使用具有更多绕组的螺旋管冷却器。