Effect Mechanism Of Dry And Wet Alternating Aging On Wood Combustion And Spread Behavior

The fire safety protection of ancient wooden structure buildings has always been paid attention by the country and all sectors of society.However,due to the characteristics of wood aging,diverse wood structure design and complex spatial layout,it is difficult to make early prediction and accurate warning of the fire and fire spread of ancient wooden structure ancient buildings.In recent years,there have been many fire accidents of ancient wooden structure buildings,causing major loss of cultural relics and social impact.Therefore,according to the characteristics of dry and wet aging damage of ancient wood structure buildings,in view of the key scientific problems such as the burning and fire spread behavior of aging wood materials.Using the combination of dry and wet aging,combustion experiment and theoretical analysis,the combustion and fire spreading behavior of dry and wet aging wood are carried out to master the combustion and spreading characteristics of aging wood.It is of certain scientific value and practical significance to provide data reference and theoretical support for the precise fire prevention and rescue of ancient wooden buildings.The main innovative achievements were made are as follows:(1)According to the characteristics of long-term aging damage of wood,the method of artificial accelerated dry and wet alternating aging is determined.Taking the common wood types of ancient buildings as the research object,the wood with different dry and wet aging degrees was obtained,and the basic physical characteristics of artificial accelerated dry and wet aging were tested and analyzed.The study shows that,affected by the plastic deformation of the cell wall in the process of alternating dry and wet aging,the local structure of the wood collapses to different degrees,the surface tear degree increases,and the small cracks increase.Due to the joint influence of elastic stress and mechanical adsorbed creep stress in the process of desorption cycle,the pore deformation of wood shows periodicity and damping with the aging degree,that the thermoproperty parameters of wood were both sinusoidal damping characteristic with the deepening of aging degree.(2)The wood heat flow evolution process was analyzed before and after dry and wet aging,and the stage migration law of wood heat release before and after dry and wet aging is mastered.The evolution characteristic of wood combustion heat release process with dry and wet aging degree was explained.The dynamics of the heat release process in dry and wet aging wood was analyzed,the mechanism of the influence of the dry and wet alternating aging process on the heat reaction process was revealed.The study shows that the main heat release stage of dry and wet aging on wood combustion process was volatilization analysis stage.Due to the enhancement of the alternating aging process of the heat transport capacity of wood,the temperature range required in the volatile analysis stage was greatly reduced,the heat release in the volatile combustion stage was enhanced,and the carbon combustion stage was shortened.The apparent activation energy analysis shown that the dry and wet aging effect reduces the energy barrier of wood in the initial stage of accelerated heat release,and the effects of alternating dry and wet aging on the energy demand of wood in different exothermic stages exist in stages during the dry and wet aging.In the stage of accelerated exothermic,the initial dry and wet alternating aging process(10-30 times)leads to the opposite trend of apparent activation energy.The effect of alternating dry and wet aging on the energy demand of oxidation reaction at the end of the rapid exotherphase gradually decreases with the deepening of aging.(3)Using a cone calorimeter,combined with the heat release characteristics of wood under the action of dry and wet aging,the combustion characteristics of wood were studied.The variation law of key combustion parameters such as ignition time,mass loss,heat release and flue gas yield under dry and wet aging and thickness was analyzed,and the evolution law of wood combustion process under dry and wet aging and thickness coupling was revealed.The results show that with the deepening of dry and wet aging,the performance of wood in maintaining the original size and shape was gradually weakened.The continuous alternating dry and wet aging leads to the increase of precipitation peak and exothermic peak strength of volatiles during wood surface combustion.After dry and wet aging,the occurrence time of carbon combustion peak and exothermic peak in the central carbon combustion stage of wood gradually advances with the deepening of dry and wet aging degree,but the strength of mass loss peak and exothermic peak was reduced.The larger the wood thickness,the wider the aging degree of the peak strength of the surface volatile precipitate changes and stabilizes,and the less the influence of dry and wet aging.Under the same degree of aging,the degree of aging and thickness were negatively correlated by the influence of central volatile transport and heat transfer.When the thickness of the aging wood was less than the thermal penetration thickness,the characteristic peaks of the combustion process show periodic and damped changes with the degree of aging.(4)The experiment of dry and wet aging wood under horizontal and inclination conditions,analyzed the influence law of dry and wet alternating aging on wood fire spread behavior,established the aging wood fire spread model under horizontal conditions,and revealed the evolution mechanism of wood fire spread behavior affected by dry and wet aging.Under the horizontal condition,due to the periodic and damped evolution of wood heat transport capacity caused by the aging,the flame parameters such as flame height,flame width,flame area and fire spread rate all shown the change law of sinusoidal damping along with the deepening of dry and wet aging degree.When the tilt Angle was small,the dry and wet alternating aging process has a great influence on the spread behavior of wood fire.Because the aging process causes the increase of wood combustion volatile analysis strength,the critical tilt angle of wood fire spread rate becomes smaller.