Study On High Temperature Molten Salt Paddle Heat Exchanger

Paddle heat exchanger is a kind of indirect agitated heat exchange equipment, composed of shell, cover, hot shaft, hollow paddle and rotary joint etc. The heating medium is hot water, steam or heat conduction oil commonly. Working temperature is from room temperature to 300 degrees. High temperature molten salt is a kind of excellent heat transfer and heat storage medium. Especially the nitrate molten salt is with low melting point, low corrosion, big heat capacity and good thermal stability for an advantage. The author developed a paddle heat exchanger using high temperature molten salt as heating medium. The working temperature of paddle heat exchanger can be widened from 300 to 600 degrees. At the same time, the basic data of researching the flow and heat transfer characteristics that high temperature molten salt flows through paddle heat exchanger are lack. As the key component, the rotary joint normally works at 300 degrees below. High temperature molten salt rotary joint working from 300 to 600 degrees needs further study.In this paper, firstly by adopting numerical simulation method, the flow and heat transfer characteristics of high temperature molten salt internal flowing through hot shaft were studied. The basic flow and heat transfer data were acquired. The simulation results show that the pressure drop of hot shaft principally is generated by high temperature molten salt flowing through the circulation hole and the hollow paddle. The heat transfer of the hollow paddle accounts for around 75% of the total heat transfer.Secondly, a high temperature molten salt rotary joint was designed. The static high temperature molten salt rotary joint experimental device was built. The temperature characteristic and sealing property of high temperature molten salt rotary joint were studied under stationary state. Through the experiment, the melting and heating processes of solid molten salt were observed, and the steady state and dynamic temperature characteristics of rotary joint were obtained. The rotary joint’s leakage situation was qualitatively observed under stationary state. Under high temperature molten salt from 450 to 500 degrees, the rotary joint worked about 150 hours without leakage.Finally, under the condition of high temperature molten salt flowing, rotary joint’s thermal characteristic numerical model was established. The temperature distribution of rotary joint, especially the temperature distribution of seal structure was simulated. The rotary joint’s high temperature thermal strain was calculated. The external cooling and the internal heat insulating theory schemes were proposed for the rotary joint’s performance improvement, and numerical analysis was performed. The numerical results show that the temperature of seal structure can be effectively reduced by adopting the combination of external cooling and internal heat insulating.