| In the era of rapid economic development,the demand for energy in all walks of life is increasing day by day,and the excessive use of energy has created a shortage of energy.In order to reduce energy consumption in all walks of life,vacuum insulation panels(VIP),as a high performance insulation material,has attracted more and more attention.At present,VIP is widely used in all walks of life,and in terms of energy conservation,it also presents the superiority of VIP.However,the cost of VIP core material is relatively high,so it is urgent to develop a low cost and super efficient insulation material.This study was to investigate the feasibility of using wood powder as core materials for the production of VIP.The focus of this research work was on the understanding of basic characteristics of various wood powders in order to identify the most suitable raw materials for wood powder VIP production,the processing of the core materials to be in line with the requirements of conventional VIP processes and the investigation of the core structure in relation with the thermal conductivity.Therefore,the study firstly analyzed the micro-structure,chemical composition and particle geometry of various wood powders,and their possible effect on the formulation and thermal conductivity of the core material of VIP.The study then developed processing technology in order to formulate the powder based VIP core(i.e.hanging strength),that is,the effect of pressing temperature,time and pressure on the flexural strength of the core material by single factor experiment and orthogonal test.The optimum pressing parameters were finally used to prepare the wood powder core of VIP,and the fractal dimension theory was used to analyze the influence of different structures of core materials on thermal conductivity and establish their relationship.To further enhance the thermal conductivity of VIP,activated carbon and expanded perlite as additives have been included in the formulation of VIP core to investigate thermal performance of wood powder VIP.Specific results of the research can be summarized as follows:(1)Compared with Masson Pine,Chinese fir had more spits,less obturator structure and lower bulk density,and hence its thermal conductivity is lower even without vacuum.Therefore,Chinese fir could be a better core material for the production of wood powder VIP.(2)To meet the requirements of forming wood powder based VIP core material,the optimum parameters were the pressing temperature of 160℃,pressure of 3MPa and time of 20min.The mechanical properties of powder VIP core increased with the increase of density,at the core material of 200 kg/m3 and the thickness of 10mm,MOR of the core material met the requirements of EN 1608,which is the European standard for the insulation materials for construction application.(3)With the increase of wood powder mesh when the size of particles is below 300 mesh,the average pore size of wood powder VIP core decreased,the smaller the fractal dimension of solid particles,the lower the thermal conductivity is.At the density of the core material of 300 kg/m3 and the particle size of wood powder of 100～300 mesh,the thermal conductivity of wood powder VIP core was the lowest,its value was 0.0159 W/(m·K).(4)With the increase of the density of wood powder VIP core,the solid particles per unit volume increased,the average pore size and the porosity of core material decreased,and the fractal dimension of the solid particles increased.The larger the fractal dimension of solid particles,the higher the thermal conductivity is.At the particle size of wood powder of 100～300 mesh and the density of the core material of 200 kg/m3,the thermal conductivity of wood powder VIP was the lowest,its value was 0.0102 W/(m·K).(5)Addition of both porous additives resulted in further reduction in the thermal conductivity of wood powder VIP core.The addition of activated carbon gave lower thermal conductivity than that of perlite.With the addition of activated carbon of 60～100 mesh and additives of 10%,the thermal conductivity of wood powder VIP core was the lowest,0.0081 W/(m·K).Although the thermal conductivity of wood powder VIP was different from that of VIP with different core materials,its preparation cost was low and it had certain advantages. |
