Abstract: Molten salt is a highly efficient heat transfer working fluid. It is widely used in central solar power, nuclear reactor, and heat treatment of metals. The startup process of gravity heat pipe with mixed nitrate as the working fluid was investigated experimentally by analyzing the startup characteristics, stability, and the influence of inclination angle on the startup behavior. The gravity heat pipe was fabricated with 316 L stainless steel, with outer diameter of 22 mm, thickness of 2 mm and total length of 980 mm. In order to explore the heat pipe start-up behavior of mixed nitrates, the experimental result with 40 g mixed nitrate working fluid is compared to that with 40 g naphthalene working fluid. The startup time of heat pipe with mixed nitrates is shorter than that with naphthalene and the heat pipe with mixed nitrates is superior to that with naphthalene in the stability. The boiling point of mixed nitrate is about 250℃. The startup characteristics at inclination angle of 50° are superior to those at 30°, 70° and 90°. The experiment shows that it is feasible for using mixed nitrates as the working fluid of heat pipe.

Key words: mixed nitrates, gravity heat pipe, start up behavior, vaporization, phase change, heat transfer

摘要： 熔盐是一种高效传热工质，广泛应用于太阳能热发电传热、核反应堆传热、金属热处理的工业过程中。以配制的一种混合硝酸熔盐作为热管的传热工质，设计制造了管壳为316L不锈钢、外径Φ22 mm、壁厚2 mm、管壳长度980 mm的硝酸熔盐重力热管，并对硝酸熔盐重力热管的启动性能进行了初步实验研究，分析了混合硝酸盐重力热管的启动特性、稳定性以及倾角对热管启动的影响。然后将采用40 g混合硝酸盐工质的重力热管实验结果与采用40 g萘工质的重力热管的实验结果进行了对比。实验结果表明，混合硝酸盐热管的启动时间比萘热管的时间短，且启动后稳定性高于萘热管；分析认为，该混合硝酸盐的沸点在250℃左右，在倾角为50°时热管启动性能优于在30°、70°、90°时的情况。实验结果初步证明了混合硝酸盐作为热管工质的可行性。

关键词: 混合硝酸盐, 重力热管, 启动特性, 汽化, 相变, 传热