Effective Thermal Conductivity Model Of Foam Aluminum And Effect Of Particles On Foam Structure

Closed-cell foam aluminum has been widely applied in various fields such as automobile ships,electronic communications and aerospace due to its unique mechanical,acoustic,electromagnetic and thermal properties.In the past few decades,although the macroscopic characterization,microstructure and mechanical properties of foam aluminum have been studied extensively,its internal defects have not been well disappeared.The effective thermal conductivity can not only represent the thermal properties of the material as an important physical parameter,but also predict the location of the liquid/solid interface during solidification,and evaluate the internal defects of the aluminum foam.Therefore,it is very important to study the effective thermal conductivity theoretically.At present,cell merging in the aluminum foam production process and the interconnection between the cells is still very common.So the aluminum foam has not widely used.It is known that the addition of particles can improve the cell structure mechanical properties.Therefore,by changing the added particles and analyzing the change of cell structure,the effect of particles on the stability and uniformity of the foam can be obtained,which is very important for improving the production process of the foam aluminum.?.Effective thermal conductivityFirstly,based on the stable hexagonal foam structure,a basic model is established and the mathematical expression of thermal conductivity is deduced.Taking into account the actual structural defects inside foam aluminum-the plateau boundary,the basic model was modified.The theoretical derived formula of calculating the effective thermal conductivity is re-given,the error is reduced greatly.Finally,the formula is simplified,and the mathematical expression of the effective thermal conductivity of aluminum foam with spherical pores is obtained.The value is linear with the relative density.Compared with other classical formulas,the theoretical value obtained in this paper is very closer to the measured values,which proves the feasibility of this theoretical formula to predict the effective thermal conductivity of foam aluminum.In this paper,the numerical simulation method is used to study the heat transfer process of aluminum foam.The following results can be obtained.1.The simulated values coincide with the theoretical values,which illustrate the accuracy of the theoretical formula;2.The thermal conductivity can be used to predicted the defective position of aluminum foam.?.Effect of particles on foam structure.In this paper,water simulation experiment,which replaces the actual production process of aluminum foam,was used to study the effect of the two kinds of particle combinations on the stability and uniformity of the foam structure.The following results can be obtained.1.When the solution does not increase viscosity,the particle size is too small to reduce the foam stability.This is because when the viscosity is low,the solution sinks by gravity and the small size is easily taken away by the solution;2.Excessive particles prone to agglomeration,and is not conducive to the formation of foam.3.The combined effect of the two kinds of particles is superior to any one of the individual particles.The different wettability of the two particles in solution results in different final distribution in the foam.The particles with poor wettability(PTFE)are mainly distributed on the gas/liquid interface and the particles with good wettability(PVC)are more inclined to the inside of the liquid film.The former covers the surface of the bubble,the gas migration process is been suppressed and the stability of the foam increases.The latter particles in the liquid film connected to each other hinder the liquid separation process,and the cell size is more uniform.In the comparative experiment,the foam height and the average size of the cells and their distribution and other factors has been taken into account.PTFE is been determined as content of 2.5%,and PVC is been determined as content of 1.2%for the best combination of content.