| With the rapid development of science and technology, energy storage technology is more and more widely applied in the field of energy, aerospace, electronics, etc. In the field of energy, energy storage technology is an important method to guarantee the stable application of renewable energy sources, such as solar energy, wind energy, etc. And the energy storage technology is also an effective measure for energy conservation and emissions reduction in energy systems such as building energy management and cooling system. In the field of aerospace and electronics, the electronic devices and other devices may have the risk of working failure as a result of the existence of cyclically, pulse type heat source. The energy storage technology can effectively alleviate the effect to ensure the normal operation of the system. Therefore, it is an effective method for thermal control. The solid-liquid phase change material (PCM) can absorb or release a large amount of latent heat in a very small temperature range during the phase transition. So energy storage with PCM has the advantage of high energy storage density, stable working property and low cost, etc. Therefore, the solid-liquid phase change energy storage receives considerable attention and is widely used in the field of energy, thermal control and so on. However, the existing phase change energy storage technology has certain limitations, such as the difficulties in encapsulation and leakage caused by the change of material density and the liquidity of the liquid after the phase transition from solid state to liquid state. The low thermal conductivity of the conventional PCM is also a limiting factor in the application. Meanwhile, many key issues haven’t been solved effectively yet because of the complexity of the phase change process. Based on the above issues, this paper carry out a systematic theoretical and experimental study on the key problems, such as heat transfer characteristics and influencing factors in the phase change heat transfer, preparation and properties of the novel phase change energy storage material and so on.Firstly, a kind of high porosity honeycomb structure composite PCM is proposed, and the heat transfer characteristics and influencing factors in the phase change process are studied through the method of combining the theory and experiment. The sensible heat capacity method is adopted to establish the theoretical model. To increase the calculation efficiency and accuracy, the equivalent heat capacity changing with temperature in the phase change range follows a Gaussian function to smooth the phase transition progress. The accuracy of the theoretical model is proved by compared with the experimental results. The results show that the thermal conductivity of high porosity honeycomb composite PCM is anisotropic. And the longitudinal thermal conductivity is enhanced substantially compared with the conventional PCM, resulting in a significantly improvement to lower the temperature of the heating surface in the process of energy storage or thermal control. Besides, the effective thermal control cycle is inversely proportional with the heat flow.Based on the above research results,a thermal control device composed of high thermal conduction carbon-carbon honeycomb (HTC-CCH) and n-tetradecane is proposed and studied. The thermal control device is used in the spacecraft thermal control in a periodic load and external heat flow conditions. The results show that the addition of HTC-CCH can improve the effective thermal conductivity of the thermal control device, so as to make the highest temperature of the system in thermal control cycle does not exceed the scope of security. The thermal control system can reach a steady state when the heat load matches the cooling time. In addition, contact thermal resistance between the cellular wall and PCM. contact thermal resistance between honeycomb material and shell, contact thermal resistance between phase change devices installed base and the deck are studied to analyze the overall thermal control effect. The results show that contact thermal resistance has small effects on thermal control system when the contact heat transfer coefficient is over 1000 W/(m2·K).The effects of thermal conductivity on the heat transfer characteristics and energy storage characteristics are further studied through the building energy storage under-floor heating system and long duration measurement of MV-level high heat flux. And a new method to measure MV-level high heat flux of long duration is proposed. The results of under-floor heating system show that the improvement of the thermal conductivity can make a more uniform temperature distribution in the PCM and increase the energy storage utilization efficiency of PCM, improve the heat transfer to the indoor environment and decrease the heat leakage though the insulation material. The theoretical results show that the heat will be reduced by about 40%with the thermal conductivity increasing from 0.15 W/(m·K) to 1.0 W/(m K), which is conducive to building energy conservation.However, the effect of improving thermal conductivity on the heat leakage will be not obvious when the thermal conductivity is over 1.0 W/(m·K). The results of high heat flux measurement study show that enhancing the thermal conductivity of PCM is a necessary condition for long duration measurement, larger phase change latent heat can help to control weight of heat flow meter, and the phase change temperature is better to be lower but must be higher than the environment temperature. And a new method to measure high heat flux of long duration is proposed based on the above study. In the measurement condition of heat flow of 1 MW/m2 and measurement time of 2000s, the designed heat sink structure can make the heat flow meter work in a safe temperature range with the weight of only 0.82 kg.In order to further improve the performance of PCM, a new kind of composite material composed of high porosity honeycomb and shape stabilized PCM (SSPCM) is proposed. And the thermal stability, thermal properties, mechanical properties and thermal control features of the composite material are studied. The SSPCM is used to solve the encapsulation problem, and the high porosity honeycomb is used to enhance the thermal conductivity and the mechanical properties. The results show that the thermal conductivity of the prepared high porosity aluminum honeycomb/SSPCM composite material is enhanced to 2.08W/(m K). And the stress tolerance limit is 4.77MPa, which is increased by 25.2% compared with that without the aluminum honeycomb. The thermal control features of the aluminum honeycomb/SSPCM composite material are theoretically and experimentally studied, and the results show that the addition of the aluminum honeycomb can make the highest temperature of the PCM in a storage period below the tolerance temperature limit of the support structure, especially when the heat load is high, thus making the materials and system work in a safe temperature range.A method of using the flexible phase change materials (FPCM) to solve the installation problem in the progress of phase change energy storage or thermal control is proposed in this paper. And the FPCM is prepared and studied. The results show that the FPCM presents a good structure flexibility and shape recoverability. The FPCM presents a good encapsulation performance, for there is no PCM leakage phenomenon occurrence in the experiment. The latent heat of the FPCM is 110.6J/g, the thermal conductivity of the FPCM is 0.93W/(m·K),therefore, the thermal properties of the FPCM can meet the demand of phase change energy storage and thermal control.At last, in order to make it easier to analyze the relationship between the thermal parameters in the process of phase change energy storage and thermal control, the dimensionless correlations study is conducted in this paper. The dimensionless correlations study will provide a simple and convenient analysis method to the application of phase change energy storage and thermal control. The study aims at the second category boundary condition, i.e. constant heat flux boundary condition. The phase change heat transfer characteristics and large amount of calculation results are analyzed to study the dimensionless criterion. The key dimensionless parameters, such as dimensionless time, dimensionless temperature, dimensionless heat flux, dimensionless initial temperature, were analyzed to acquire the dimensionless criterion. And the calculation error of the dimensionless criterion is within 5%. |
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