Study On The Phase Change Plate In Refuge Chambers For Heat Transfer Enhancement And Temperature Control Characteristic

Refuge chambers provide a safe space to survive in the event of the mine disaster.Because of the heat generated by the heat source in the refuge chamber,the temperature of the refuge chamber needs to be controlled.Phase change cooling systems are favoured because of their safety and reliability without the need for electrical power.However,the current phase change cooling systems used in refuge chambers have issues with the low thermal conductivity of the phase change material and the insensitivity of the phase change cooling device to temperature changes.This thesis proposed a novel composite phase change temperature control approach to ensure the chamber temperature remained below 308.15 K for 96 hours.In this thesis,the phase change materials were modified by adding different proportions of nano graphite particles.The thermal and physical properties of the prepared materials were tested and the melting temperature control test was carried out so as to select the composite phase change materials which meet the requirements of the working conditions of the refuge chamber.Numerical simulations were used to compare the enhancement effect of plate fins and pin fins on the cooling performance of the accumulator plate in order to determine the best method of enhancing heat transfer.Finally,this thesis investigated the effect of parameters such as the size and inclination of the accumulator plate and the diameter and spacing of the pin fins on the performance of the accumulator plate.The main conclusions reached are as follows:(1)A comparison of RT25,RT30 and PEG 600 with 0.5%～5% nano-graphite particles shows that the addition of nano-graphite particles significantly increased the thermal conductivity of the phase change material,but also increased the viscosity of the material and reduced the latent heat capacity of the phase change material.The thermal conductivity of the 5% nano-graphite particle reinforced RT25 increased by0.187 W/(m·K),while the kinetic viscosity increased by 0.018 Pa·s.Accumulator plate with graphite nanoparticles alone performed better at controlling temperature in the early stages of melting,while those with pin fins alone performed better in the later stages of melting.Accumulator plate that use both of these enhancements can maintain the lowest plate surface temperatures throughout the melting phase,but with the shortest platform period times.(2)By comparing the pure phase change accumulator plate with the thermally enhanced plate,it was found that the thermally enhanced plate starts melting later and melts faster.Compared with the pure PCM accumulator plate,the initial melting time is delayed by 0.08 h,0.67 h and 0.92 h,and the complete melting time is shortened by2.26 h,9.09 h and 16.67 h respectively,after the addition of nano graphite particles,plate fin and pin fin.The surface temperature of the accumulator plate and the air temperature of the chamber are used to evaluate the temperature control effect of the accumulator plate.The average wall temperature of the pin-fined accumulator plate is298.24 K and the average air temperature for 96 hours is 306.37 K.(3)The average air temperature for the first 96 hours of the accumulator plate decreases with decreasing pin fin spacing,decreases and then increases with increasing pin fin diameter.The average air temperature is lowest at the pin fin diameter of 6 mm.When the pin fin spacing is less than 15 mm,the length of the platform period decreases sharply.The melting process and the change of air temperature in the accumulator plate with different angles were studied.It was found that the melting process of the accumulator plate was basically the same,and the melting speed of the accumulator plate with vertical arrangement was slightly faster.The air temperature is greatly affected by the inclination angle,and the smaller the inclination angle,the higher the air temperature.When the inclination angle is 0° and 30°,the 96 th hour air temperature is 309.12 K and 308.43 K.The average air temperature is greatly affected by height.Compared with the accumulator plate with a height of 400 mm,the average air temperature of the accumulator plate with a height of 700 mm is reduced by 2.77 K,and the platform period is extended by 81.7%.The thickness of energy storage plate has little effect on the average air temperature during the platform period,but mainly affects the duration of the platform period.Compared with the energy storage plate with a thickness of 40 mm,the average air temperature of the energy storage plate with a thickness of 70 mm decreased by 0.33 K,and the plateau time is extended by 73.8%.This thesis has a total of 51 pictures,16 tables and 102 references.