Study On The Insulation Mechanism Of Tree Cavities

The Pteromys volans is the northernmost gliding mammal in China.Due to the impact of the logging,the population of P.volans is reduced and the IUCN listed P.volans as VN.In the northern of Greater Hingan Mt's,the winter average temperature-30 ?(an)The species does not hibernate,using membrane gliding in forest as the bigger the ratio of surface area to volume,heat dissipation area is bigger than with the same weight of other species,characteristics of insulation wintering preferences using the tree cavities.What kind of structural characteristics of the tree cavities can be used by P.volans to insulation remains unknown.2015,the Greater Hingan Mt's formally ceased commercial logging,instead of tending and cutting operations will aim:dying,decaying woods,snags,and tree cavity most often appear in such logs.In order to conservate the wintering P.volans,it is necessary to reserve the tree with the characteristics of its winter demand.For this purpose,this study investigates the tree cavities used by P.volans.My results show that compared with the available cavities in territory,P,volans preference with bigger DBH,small diameter with entrance,more deep,more internal diameter,hole depth and the wall thickness of tree,the 50%of cavity-bearing trees is dead trees.In this study,a tree cavity geometry model with mean characteristics is obtained by means of "A method of 3D tree hole merging",which has the characteristics of eccentricity.The geometrical model of the P.volans was obtained by using the MIMICS software and the CT scanning in vivo and the MIMICS software modeling,which proved the feasibility of establishing the geometric model of living animals and tree cavities.This research use the digital thermometer for tree cavity inside temperature and environmental temperature,found the tree cavity temperature changes xwith ambient temperature changes,the tree cavity to thermal environment volatility has obvious reduction effect,the peak temperature have significant delay.At the same time,this study obtained a sample from 489 trees in the lumber yard.The study found that there was a positive correlation between the internal diameter and the external diameter of the tree cavity.It is found that the specific heat capacity,density and thermal conductivity coefficient of tree cavities form the thermal inertia of tree cavities.The density and thermal conductivity of the nest material have good effects on the insulation of the tree cavities.Based on heat transfer of thennal resistance superposition principle,this research in the three conservation equations of fluid mechanics is used to establish "Ambient-Tree cavity-P.volan"heat transfer model,under the framework of squirrels in metabolic heat production through a squirrels geometric model of the surface of the heat flux density of 398 W/m2 as the critical value of thernal equilibrium,CFD numerical simulation by using the tree cavity under variable factors at different levels of change of the surface of the fur is average cavity surface heat flow density and average temperature.The results showed that in the "Ventilation Heat Loss",when the forced convection wind speed of the directly blowing cavity reached 15m/s,the thermal equilibrium of the P.volans was broken.In "Structural Heat Loss",with the increase of wall thickness,cavity depth and nest material thickness,the better the insulation effect of tree cavity is.As the diameter of the cavity entrance increases,the insulation effect of the cavity becomes worse,but the orientations of the cavity have no significant influence on the thermal environment of the cavity under the influence of eccentricity structure.This research adopts the "Experimental-Model-Simulation"system,the method of using the CFD technology research proved tlhat the method of continuous thermal system and technology in the study of small animals in the tree cavity insulation has certain feasibility.In view of the above results,this study proposes the following:the tree cavities with more than 13 per hectare are retained,and the entrance features of the preserved cavities are more than 34mm in diameter.The cavities height is greater than 2.6m;The diameter of the tree cavities is greater than 22cm.In this study,Numerical Simulation was used to explain the mechanism of constructing the thermal environment of the tree cavity,and reasonable suggestions were put forward for the management of the tree cavities during tending and cutting.