本文提出了一种管束直径在0.4∼1.0 mm 范围内逐渐变化的无翅片微管换热器结构。采用CFD 模拟的方法，对管径渐变的微管换热器的空气侧流动和传热性能进行了研究分析。同时，利用已提出的相关经验公式结合NSGA-II 算法对流动摩擦因子f 和传热性能因子j 进行了多目标优化，确定了管径渐变微管换热器的最优结构参数，当纵向管壁间距为0.214 mm，横向间距为1.127 mm，管束直径从外到内依次为0.876 mm、0.746 mm、0.697 mm、0.550 mm 时，传热性能因子j 达到最大值0.04169，流动摩擦因子f 达到最小值0.01270。与等径无翅片微管换热器相比，新型结构不仅降低了压降、提高了换热效率，还节省了金属制造材料和制冷剂充注量。

In this paper, a finless micro-bare-tube heat exchanger with tube bundle diameter varying gradually in the range of 0.4 ∼ 1.0 mm is proposed. The air-side friction and heat transfer performance of micro-bare-tube heat exchangers with bundle diameters varying gradually were studied by CFD simulation. By using the relevant empirical formula and NSGA-II algorithm, the multiobjective optimization of the dynamic friction factor f and heat transfer performance factor j was carried out, and the optimal structural parameters of the micro-bare-tube heat exchanger with varied pipe diameter were determined. When the longitudinal tube wall spacing is 0.214 mm, the transverse tube wall spacing is 1.127 mm, and the tube bundle diameter is 0.876 mm, 0.746 mm, 0.697 mm and 0.550 mm from outside to inside, the heat transfer performance factor j reaches the maximum value of 0.04169, and the flow friction factor f reaches the minimum value of 0.01270. Compared with the equal-diameter finless micro-bare-tube heat exchanger, the new structure not only reduces the pressure drop, improves the heat transfer efficiency, but also saves the amount of metal manufacturing materials and refrigerant charge.