微纳复合表面HFE-7100/水的BRT现象及沸腾传热特性

Boiling refrigerant transition and heat transfer characteristics of HFE-7100/water on the hierarchical structured surfaces

HFE-7100/水作为非共沸不互溶工质可以拓宽核状沸腾传热的有效温区,目前关于其在微纳复合表面的沸腾传热特性和气泡运动机理尚不明晰。利用气泡模板电沉积法在铜基表面上制备了具有微纳孔洞的复合结构,测试了HFE-7100/水的沸腾传热特性,并通过可视化探究了沸腾工质转换(BRT)过程中两相工质在表面的润湿状态和气泡运动现象。结果表明,微纳复合表面上HFE-7100/水的BRT过程中,气泡先后经历小气泡聚并、气膜膨胀、轻工质接触壁面核化三个过程。在BRT过程中,HFE-7100与水对热壁面的润湿性存在竞争关系,随着过热度增加,薄的HFE-7100液层难以维持稳定的重工质沸腾,上层水工质可以穿过HFE-7100层对热壁面实现完全润湿,完成BRT过程。与单一工质相比,常压下HFE-7100/水混合工质体系可以在343~423 K下实现高效的核状沸腾传热。该研究揭示了HFE-7100/水在微纳复合表面的沸腾传热特性,为沸腾强化表面设计提供了思路。

HFE-7100/water as a non-azeotropic and immiscible working medium can broaden the effective temperature range of nucleate boiling heat transfer.At present,it is not clear about its boiling heat transfer characteristics and bubble movement mechanism on the micro-nano composite surface.In this paper,a hierarchical micro/nano structured surface composed of nano-particles and micro-holes was fabricated by the bubble-templateassisted electro-deposition method.Surface wettability and bubble dynamics during the boiling refrigerant transition(BRT)were investigated to clarify the heat transfer characteristics of HFE-7100/water boiling on the hierarchical micro/nano structured surface.The results show that the bubbles experience the small bubbles coalescence,gas film expansion and water nucleates on the heated surface at the BRT of HFE-7100/water.During the BRT process,there is a competition of liquid wetting between HFE-7100 and water on the surface.With the increase of superheat,stable nucleate boiling of thin HFE-7100 layer is broken and the upper water fluid can pass through the HFE-7100 layer to wet the heated surface,completing the BRT process.Compared with single liquid boiling,the HFE-7100/water boiling widens the effective temperature range of 343—423 K.This work clarifies the boiling heat transfer characteristics of HFE-7100/water on the hierarchical micro/nano structured surface and provides guidelines for structure design of enhanced heat transfer surfaces.