Research On Heat Transfer And Impact Mechanical Properties Of Energy-saving Plate With Honeycomb Core And Cement-based Skins

Currently,there is a large amount of cement consumption in the construction industry,and materials such as rockwool that have high energy consumption and are a source of pollution are predominantly used in the heat insulation layers of enclosures.According to the straw and other renewable resources have the characteristics of good thermal insulation property and poor mechanical properties,if they can be used as the core filling material of lightweight and high strength sandwich plate,the complementary advantages can be obtained.In view of this,the paper honeycomb plates and the energy-saving honeycomb plates(EHPs)filled with straw and other thermal insulation materials are taken as the core materials,and then the energy-saving plate with honeycomb core and cement-based skins(ECHP)with cement-based plates on its two surfaces are taken as the research object,the research is carried out through such two aspects as their heat transfer and impact mechanical properties,laying a foundation for the research and development of energy-saving plate with honeycomb core and cement-based with heat insulation and structural integration.For the research on the heat transfer performance of ECHP,considering that the thermal resistance of cement-based plate is far less than that of the core layer,and the heat transfer property of ECHP mainly depends on EHP,HP and EHP were taken as the research object.Firstly,by measuring the equivalent thermal conductivity?_E of EHP,the heat transfer performance and its influence mechanism of horizontal two types of plates under external hot/internal cold conditions were qualitatively investigated.On this basis,it was theoretically confirmed that the radiation heat transfer in HP was much greater than the heat conduction,and other equiqualitative conclusions.Then,The?_E values of HP and EHP were measured and calculated for the external cold/internal hot and left cold/right hot conditions,which included the convective heat transfer,respectively,the influence mechanism of honeycomb element geometric parameters and filling materials such as straw as straw on heat transfer performance of HP was discussed.The conclusions of the study are as follows:(1)Under hot external/internal cold conditions in summer,although the thermal conductivity of the filling material was higher than that of air,the?_Evalues of the EHP was significantly lower than that of the HP,and the?_Evalues of all the EHP met or approached the requirements of the high-efficiency heat insulation materials for envelope structure.A simple model for spatial distribution of slender materials and spherical granular materials with the clear spatial distribution characteristics was presented.The radiative heat transfer,considering whose radiation space was reduced from the cell honeycomb to the cavity and the fine void,was defined as divisional local radiative heat transfer(DLR).Whether there was DLR in the core structure can fundamentally determine the?_E values of the above HP and EHP.The thermal characteristics of EHP were also determined by the joint action of DLR,thermal conductivity and shape of the filling material.(2)Under the normal temperature condition,the radiation heat transfer was usually neglected,but the theoretical calculation results showed that it accounts for 50%?70%of the total heat transfer of HP under external hot/internal cold conditions,which,in theory,proved that the DLR given in the previous experiments is the fundamental cause of the?_E values of HP and EHP.When the plate thickness h>15-20 mm,local convection occured in HPs due to weak disturbance.On this ground,a technical approach to improve the thermal insulation performance of HP was proposed.Simple models of cavity size and DLR of two kinds of filling systems in EHP was presented.The results showed that the filling materials could effectively prevent radiation heat transfer and local convection heat transfer by drastically reducing the cavity in the honeycomb,while the bottleneck of particle solid heat conduction lied in the contact surface(point)between particle and particle,and the influence on the?_E values of EHP was limited.(3)Under the condition of simulating internal hot/external cold in winter,the thermal insulation performance of HPs with different cell wall lengths varied with the thickness of the plates.This study not only provided indirect experimental evidence for the phenomenon of honeycomb circulation reported in the literatures,but also first put forward the concept of matched honeycomb structure and matched convection.Hereby,the plates could be selected and optimized reasonably according to the results of the study and the engineering needs.It was proposed that the radiation and convection heat transfer effects of BEPs were not superior to those of HPs and other four heat transfer characteristics,and the heat insulation effect of BEPs was not weaker than that of HPs when the experimental results of HPs with the same plate thickness and structure unit size were used as BEPs.The effects of the temperature distribution of upper and lower plants and the three-dimensional size of the honeycomb structure on matched honeycomb structure and matched convection and their internal influence mechanism were investigated.(4)Under the left cold/right hot conditions,HPs which was vertically placed,presented a series of characters:the natural convection heat transfer was dominant,radiation heat transfer was secondary.With the increase of plate thickness,the flow pattern of HPs changed.The boundary layer of HPs,the unit side length of which was 8 mm,under the more active flow pattern was obviously limited by the honeycomb wall,thus affecting the convective heat transfer effect.It was revealed that the main modes of heat transfer were the heat transfer between the wall and the filler,radiation heat transfer between the filler and solid heat conduction in filler.The heat transfer mechanism and performance of EHPs was not affected by ways of their placement,but the temperature affected the heat transfer performance of EHP.For the impact mechanical properties of composite plate with honeycomb core and cement-based skins(CHP)and ECHP,the dynamic mechanical response parameters such as contact force,impact displacement,rupture damage and impact velocity under the slight damage and serious damage impact were mainly investigated.The impact response characteristics of sandwich plate and influence mechanism of honeycomb core layer and fillers such as straw on the impact resistance of the whole structure were explored.(1)The changing pattern of the contact force of the four plates varing with time under the slight damage impact was represented,which in general presented a changing process from fast lifting to longer platform segments.Influenced by air recovery,organic horizontal support and contact between the walls,under dynamic impact,the paper core layer showed a greater stiffness,and the support ingress on the upper panel was obvious,effectively alleviating the impact damage suffered by the upper panel.Increasing the frictional resistance between particles could effectively improve the overall impact strength of ECHP,and the filling material could improve the impact stability of ECHP by effectively alleviating the shaking of the honeycomb wall.(2)Under the serious damage impact,the core layer and the filling material with greater dynamic stiffness provided the upperpanel with honeycomb wall support,air recovery,extrusion deformation space.The upperpanel and the core layer complement each other and provided good protection against impact damage for the lowerpanel,thus improving the overall safety performance of the structure.The filling materials such as straw not only effectively hindered the horizontal shear expansion of impact waves in the panel,but also greatly alleviated the hammer impact when crossing the core layer,further improving the impact-resistant performance of CHP.In engineering practice,a lower-strength upperpanel could be used to effectively reduce the damage to the lower panel by taking greater impact damage.(3)By the synthetically comparison of two damage conditions,it was found that the peak contact force of CHP increased as the impact energy increases.The peak duration of each laminate was shortened with the increase of impact energy.With the increase of the impact speed of the drop hammer,the impedance capacity of the core layer plate was gradually reduced.The impact mechanical properties of the whole sandwich panel were significantly affected by the breakdown of the upperpanel or not.