Study On Coupling Model Of Space Droplet Radiation Heat Transfer And Heat Transfer Characteristics Of Liquid Droplet Radiator

As a new type of space waste heat removal system for high power space nuclear reactor power,liquid droplet radiator(LDR)has the advantages of small system mass,high heat transfer power per unit mass,easy deployment and assembly,high safety and long operation life compared with the traditional space radiation heat sink,which has become the most promising space radiation heat sink.The droplet layer between the droplet generator and the collector in the heat exchanger is the key part of space radiation heat transfer.The study of the radiation heat transfer characteristics of the droplet layer is of great significance for the optimal design of LDR system and the design matching with nuclear power system.At present,the commonly used way to calculate the droplet layer is to regard its temperature as a two-dimensional continuous distribution,while the angular coefficient matrix theory used in this paper regards the droplets in the droplet layer as a three-dimensional discrete distribution,and the calculation results are more in line with the actual radiation heat transfer process of droplets.Starting from the radiation heat transfer of discrete droplets firstly,this paper studies the radiation heat transfer coupling model and heat transfer characteristics of single droplet,two droplets and multiple droplets.Based on the method of Monte Carlo emitting random rays,the variation law of the angular coefficient of droplets with different droplet number and size is obtained.According to the general angular coefficient matrix theory,the calculation model of droplet layer radiation heat transfer in LDR system is established,and the preliminary calculation and analysis of droplet layer radiation heat transfer is completed.By comparing the coupling heat transfer characteristics of radiation heat transfer of different numbers of droplets,it is concluded that the more the number of interaction around droplets under the same conditions,the more obvious the inhibition of radiation heat transfer of droplets.Then,by using the typical LDR droplet layer model,the heat transfer characteristics of space droplet radiation heat exchanger are analyzed based on the working fluid properties of droplets,the structure of droplet layer and the initial parameters of droplets.It is concluded that the array type of droplets in the droplet layer can not affect the radiation heat transfer of the droplet layer.,and the smaller the droplet spacing is,the larger the radiation heat transfer angle coefficient matrix is,and the higher the end temperature of the droplet layer is.Reducing the droplet radius,emission velocity and increasing the initial temperature of the droplet can greatly increase the radiation heat transfer performance of the droplet layer.Finally,based on the megawatt space nuclear reactor system model,the reactor system analysis program is developed.According to the requirements that the radiator should be arranged in the shadow shielding range and the operation life should be more than 10 years,three optimal design schemes of LDR system suitable for the reactor system are proposed,which is more than 60% smaller than that of traditional heat pipe radiation heat exchanger,and the weight is more than 68% lighter.Based on the system analysis program,the transient operation characteristics of the system under the conditions of projectile rod accident and radiator flow change are analyzed.It is concluded that both rod ejection accident and LDR damage accident can lead to the rise of droplet temperature and radiation power in LDR system.In general,the change caused by rod ejection of intermediate control rod is greater than that caused by rod ejection of peripheral rod.When less than or equal to two LDR systems are damaged,the system can still operate below the rated power due to the good self-stability and self-regulation ability of the Brayton cycle reactor system.