Phase Change Material Based Thermal Management For Electronic Devices On Nuclear Rescue Robot

There are a plenty of radiation in the scene of the nuclear accident. Besides, high ambient temperature, high humidity, dust and boracic acid would also accompany with the disaster. The nuclear rescue robot is the only choice to replace the human being for entering the scene of the accident to execute disaster relief missions. Therefore, the robot should not only have a high radiation resistance, but also own a good heat-resistant quality. The inner space of the robot is generally compact for reducing body weight. The thermal problems, which were caused by high temperature environment and radiant heat effect of the metal, would lead to premature failure of electronic devices on nuclear rescue robot. Therefore, developing a reliable thermal protection system is the prerequisite of the normal operation of robot. In view of the special temperature condition in the nuclear accident environment, a thermal control design for electronics on nuclear rescue robot was proposed based on passive energy storage. The parameters of the thermal control system such as types of PCM, size of the heat sink, input power levels were studied. The effect of nanoparticle doping on the thermophysical property of the PCM was researched. Investigation and evaluation on the thermal management scheme were conducted in the cases of room temperature and elevated temperature environment. The main research contents and achieved results are stated as follows:(1) Design, experiments and numerical simulation for the thermal control system of double drivers in room temperatureFor the purpose of safe working, a thermal management system, which was composed of metal support and PCM based heat sink, was put forward. The system was packaged with a chute-form.44# PCM was selected as the PCM used in experiments after investigating parameters like phase change temperature, latent heat and radiation resistance. It was found that, lower temperature would be acquired by PCM based heat sink without fins compared with the PCM based heat sink with fins, which resulted in extending the safe working time by 12 times. The operating time of electronics increased linearly with the growth of PCM weight, and was a linear decreasing function of input power. The melting process of the PCM system was investigated using thermal resistance model analysis combined with numerical simulation. It was found that the existence of the air layer in the system delayed the melting of the PCM and hindered the heat absorption. The enhancement of thermal conductivity could make up the defects of the air layer.(2) Study on the effect of thermal conductivity enhancement on thermal controlThree kinds of copper metal foams with similar porosity and different pore density of 5 PPI,10 PPI and 20PPI were adopted to enhance the thermal conductivity of the PCM based heat sink. It can be concluded that better heat conduction would be obtained when a bigger pore density was chosen. However, good heat conduction in the heat sink resulted in a bad thermal protective effect. The metal foam system with copper metal foam of 5 PPI got a slightly better performance than the system used PCM only. The effect of the multi-walled carbon nanotubes (CNTs) doped composite PCMs (mass fraction of 0%,0.08%,2% and 0.08%) on the thermal control system was also studied. The thermal control system with 2% CNTs doped PCM got the best results, and made the drivers safely work for 97 min, which was 30 min longer than the system without CNTs. Because the CNTs are much lighter and smaller than the metal foams, it was a better solution for the thermal control system of double drivers to employ CNTs in the thermal management system.(3) System design and experimental study for the thermal control system in high temperature environmentAccording to the idea of double insulation and heat absorption, a thermal management system was designed for high temperature application. The temperature uniformity, heating power and the ambient temperature were studied for an overall understand of the system. Results showed that the temperature difference among each driver could be controlled within 1 ℃. The best working hours and phase transition time both got a downward trend with the increase of input power. Compared with the support frame of aluminium alloy, filling PCM in the fame could prolong operating time by 34 min for double drivers, and make six drivers safely work for 164.3 min in experimental environment of 100 ℃. When the environment temperature was lower than 50 ℃, the drivers were able to operate more than 180 min. According to the heat calculation of system, it can be seen that PCM absorbed 56% of total heat, and played an indispensable role in thermal control. Enhancing the heat-shielding performance is supposed to further improve the thermal control ability of the airtight thermal controller.(4) Performance study of multiwall CNTs doped composite PCMsMultiwall CNTs doped composite PCMs with different mass fraction (0.1%、0.2%、0.5%、 1%、2%、5%) were prepared by two-step method. The thermal stability and dispersion of the composite PCMs were evaluated by sedimentation test, DSC measurement and temperature-time curve test. The amount of carbon nanotubes doped in 44# PCM had little influence on the phase change temperature of the composite materials. The latent heat value decreased linearly with the mass fraction increasing of carbon nanotubes. A latent heat enhancement phenomenon was found at the mass fraction of 0.1%. The heat conductivity coefficient of composite PCMs grew up gradually with the increase of doping amount. It increased by 61.7% when CNTs occupied 5% in composite PCMs. The thermal conductivity of liquid composite PCM was lower than the solid state. Higher heat conductivity coefficient appeared at 35 ℃ and 45 ℃, which increased by 104.8% and 49.0% relative to the solid thermal conductivity.(5) The application evaluation of passive thermal protection systemThe application evaluation was conducted for high temperature thermal protection system of multiple drivers. The thermal insulation material was important to the system. Hence, the principles of material selection were stated from the points of heat conductivity coefficient, operating temperature and radiation resistance. In consideration of irradiation heating effect caused by heavy metal shielding layer, the insulation needs to install inside the heavy metal shielding box. The overall unit thermal protection scheme was put forward after a temperature test of the robot. Weight and price assessments were also conducted for a hexapod robot, which showed that the suggested scheme owed advantages of light weight and low cost. In order to meet the task requirements of longer operating time, a restorative solution and an adaptive environmental solution were proposed to enhance the work efficiency of the passive thermal protection system.A thermal management scheme for electronics on nuclear rescue robot was proposed with the idea of combining heat insulation with heat absorption structure. It realized the thermal protection for multiple drivers in high temperature (100 ℃) environment. The designed system could implement its thermal control function in multi - field coupling environment with nuclear and high temperature conditions. In addition to the nuclear disaster relief applications, the scheme can also protect the electronics on nuclear power plant maintenance robot, welding robot and fire - fighting robot. The achievement can be the theoretical basis and solutions to thermal management of electronics working in harsh environment.