The Study Of Performance Regulation And Heat Transfer Mechanism Of Ammonium Alginate/cellulose Based Aerogel Insulation Material

Alginate and cellulose aerogels have attracted more and more attention because of their special properties such as reproducibility,low cost,good environmental benefit and good design.However,their applications are limited because these two aerogels have disadvantages such as low mechanical strength,poor hydrophobic properties,and inability to be produced on a large scale.Through composition optimization and modification,the microstructure and properties of aerogels can be adjusted to improve their mechanical strength,hydrophobic performance,thermal insulation effect,etc.,so as to achieve more functions.Green oil absorption,thermal insulation aerogels with mass production,high strength and hydrophobicity can be prepared.Aiming to solve the above problems,aerogels with good mechanical properties were prepared by using ammonium alginate or cellulose as substrates.Ammonium alginate and cellulose are considered as an almost inexhaustible source of raw material with renewable,low cost and good environmental benefits.Based on this,hydrophobic modified aerogels and aerogel-based phase change composites materials were prepared.The properties and applications of aerogel and its phase change composites materials were studied by multiple experimental characterization and numerical simulation of the experimental samples,and their thermal insulation effects were analyzed.The aerogel can not only realize the thermal insulation of the oil pipeline,but also absorb the oil in time when the oil pipeline breaks,so as to avoid the pollution to the environment.The combination of aerogel and phase change composites materials can further improve the thermal insulation effect.Therefore,the composite material has important significance for energy conservation and environmental protection.The main contents and conclusions of this thesis are as follows:(1)The ammonium alginate-based aerogels with ammonium alginate and different inorganic nanoparticles were prepared by easy-to-realize and low-cost solution blending method and vacuum freeze-drying method.The cross-linking reaction of aerogels can promote the formation of three-dimensional porous network structure,and its mechanical properties were obviously improved.In order to enable the aerogel to be used in the field of flexible thermal insulation under high humidity environment,the aerogel was hydrophobically modified by the chemical vapor deposition method.The modified aerogel with a high water contact angle of 116.6° had a good oil absorption effect,which greatly expanded the application range of aerogel materials.In order to further improve the short-term thermal insulation performance of aerogels,aerogel-based phase change composites were prepared by vacuum impregnation method,which was based on the higher latent heat and excellent thermal stability of polyethylene glycol(PEG).Aerogels had good compatibility with PEG.The three-dimensional framework network structure of aerogels was conducive to its heat transfer and coating effect in the formalized phase change materials.The aerogel-based phase change composite material showed a large range of mass loss between350? and 450?,and the decomposition rate was faster.The aerogel-based phase change composite material had high thermal stability.(2)Cellulose-based aerogel was prepared using arboxylated cellulose nanocellulose and ammonium alginate as raw material in the mass fraction ratio of 9:1,7:3,5:5,3:7 and 1:9.With the increase of ammonium alginate content,the mechanical properties of cellulose-based aerogels increased.When the mass ratio was 5:5,cellulose-based aerogels had the better mechanical properties.The increase of ammonium alginate content also made the aerogel exhibit different microstructure,and the three-dimensional structure was more compact and stable.The material had up to 500? of thermal oxidation stability,making it a more suitable candidate for thermal insulation than ordinary polymers.After hydrophobic modification,the water contact angle of aerogel reached 103°.The aerogel was a kind of thermal insulation material with good hydrophobic properties.The cellulosic aerogel phase change material had higher phase change temperature and phase change enthalpy.The thermal conductivity of cellulosic aerogel phase change material reached 0.26,which met the requirements as an energy storage material.(3)The heat transfer model of porous media using aerogel as prototypes was established by using COMSOL software.The heat transfer process of the porous media was numerically simulated.The heat transfer results of aerogels were predicted by numerical simulation method.The heat transfer mechanism was analyzed,which provided theoretical basis for their application in the field of petroleum pipeline insulation.