Abstract: In order to study the sensitivity of factors affecting the coagulation efficiency of fine particles，a compo- site coagulation model suitable for different coagulation approaches was established，coupling the particle goup po- pulation balance model with the Euler's multiphase flow model and using the user-defined function to simultaneously introduce the Brownian-turbulent-acoustic composite coagulation kernel function and the condensation growth rate function． The numerical simulation of fine particle composite coagulation process was performed by using orthogonal design，and the primary and secondary relations of the effect of initial steam supersaturation，residence time， sound pressure level and sound frequency on the coagulation process were analyzed based on the simulation results． The simulation results show that the model can effectively characterize the coagulation efficiency of PM_2.5 particles． Through orthogonal simulation tests of coagulation efficiency of PM₁₀ and PM_2.5 ，it is further concluded that the in- fluence degree of each parameter under composite coagulation is: sound pressure level ＞ residence time ＞ initial steam saturation ＞ sound frequency． The increase of sound pressure level，residence time and initial steam satu- ration is conducive to the improvement of coagulation efficiency，while there is an optimal value of sound frequency to maximize the coagulation efficiency，and the optimal frequency of PM_2.5 coagulation efficiency is higher than that of PM₁₀ ． The establishment of the model is significant to the research on the influence degree of correlation parame- ters for fine particle composite coagulation．

Key words: fine particle, composite coagulation, population balance model, orthogonal design