高温熔盐重力热管的关键科学问题研究

Based on the heat transfer fluid and the high temperature thermosyphon this project presents a new type of thermosyphon with molten salt as heat transfer fluid, named as high-temperature molten salt thermosyphon, which can transfer heat efficiently and is low cost and safe in industrial process and environment. Then a selection mechanisms of molten salt for the thermosyphon will be brought forward according to the key thermo-physical properties of moten salt which will be measured. Subsequently influences of some important factors such as heating power, obliquity of the thermosyphon, key thermo-physical properties, molten salt inventory, evaporator length on the startup characteristics of the high-temperature molten salt thermosyphon will be conducted, and then influences of some important factors such as heating power, obliquity of the thermosyphon, key thermo-physical properties on the heat transfer characteristics of the high-temperature molten salt thermosyphon such as isothermal performance, heat transfer limits, heat transfer coefficeint and thermal resistance of the evaporator and the condenser will be performed in detail. Finaly numerical simulation and theory analysis will be carried out to study the heat transfer mechanisms inside the evaporator and the condenser of the high-temperature molten salt thermosyphon. Fhen based on the researh results an optimized design method will be put forward. Final results of the poroject will supply a new way of energy conservation and a new technical support for the high-efficiency utilization of the traditional energy and the renewable energy.

本项目将高效传热工质熔盐与高温热管相结合，开拓一种以熔盐作为传热工质的新型高效传热元件-高温熔盐重力热管，具有高效传热、安全环保、成本低廉等优点。针对熔盐传热工质，研究提出高温热管用熔盐传热工质的优选机制；探索加热功率、倾角、熔盐关键热物性、蒸发段与冷凝段比、充液量等主要因素对高温熔盐重力热管的起动性能影响规律；研究加热功率、倾角、熔盐关键热物性等主要因素对高温熔盐重力热管传热性能如等温性能、传热极限、蒸发段与冷凝段传热系数和热阻等的影响规律，揭示高温熔盐重力热管的传热机理；主要采用数值模拟与理论分析的方法，研究高温熔盐重力热管内蒸发换热与凝结换热的换热机理。在此基础上，提出高温熔盐重力热管的优化设计方法。研究成果将为我国节能减排提供新技术，为我国传统能源和可再生能源的高效利用提供新的技术支撑。

熔盐是一种熔融状态下高效传热工质，广泛应用于传热储热领域。由于其高效传热特性，本课题将其用作高温重力热管的传热工质。本课题通过对单组份硝酸盐、单组份溴化盐、混合硝酸盐、混合溴化盐的高温热物性如密度、熔点、比热、导热系数、粘度、表面张力、饱和蒸汽压、熔化潜热、分解温度等进行实验研究，综合考虑工质传输能力和饱和蒸汽压力，初步选择课题组前期开发的四元混合硝酸盐-低熔点熔盐Hts作为热管传热工质，研制了不同熔盐填充质量的高温熔盐重力热管。在此基础上，通过实验方法研究了熔盐填充质量、热管倾角对热管启动稳定性、启动时间、轴向温度分布等的影响；该熔盐热管在熔盐充装量40g时，热管启动效果最好，在倾角50°时热管传热效果最好。填充40克低熔点熔盐和萘的热管实验对比结果表明，低熔点熔盐热管的响应时间比萘热管的时间短，初步证明了低熔点熔盐作为热管工质的可行性。但由于熔盐在高温下具有较低的饱和蒸汽压及抽真空和真空保持的影响，熔盐在热管内的蒸发速度低，导致热管传热阻力相对较大.熔盐热管还需要进一步研究，优选更适合作为热管传热工质的熔盐。